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Agronomic traits affecting resistance to white mold in common bean. (Crop Breeding, Genetics & Cytology).

WHITE MOLD IS A destructive yield-limiting fungal disease that seriously affects common bean production in temperate regions (Steadman, 1983; Purdy, 1979). White mold infections in bean are typically initiated during flowering, coinciding with the closure of the plant canopy and the development of apothecia from soil-borne sclerotial bodies (Boland and Hall, 1987). Ascospores disperse from the apothecia into the plant canopy and require a nutrient source, such as senescent flowers, for germination and subsequent mycelial infection (Abawi and Grogan, 1975; Hunter et al., 1978). Symptoms of white mold on bean plants include wilting, lesions, bleached stems, the presence of sclerotial bodies in infected tissue, and plant death. Resistance to white mold in bean is quantitatively inherited (Fuller et al., 1984a; Miklas and Grafton, 1992) consisting of physiological resistance and avoidance (Miklas et al., 2001). Previous studies have indicated that heritability estimates were low to moderate for partial physiological resistance, and moderate to high for field resistance (Miklas and Grafton, 1992). Resistance to white mold has been described in several navy bean cultivars, such as Bunsi (also known as Ex Rico 23) and C-20, (Schwartz et al., 1987; Miklas and Grafton, 1992; Tu and Beversdorf, 1982; Kelly et al., 1984).

Plant avoidance of white mold can be due to plant architectural traits or agronomic management practices. A decrease in plant row width, resulting in higher plant density was shown to increase the level of white mold in bean (Park, 1993; Steadman et al., 1973). Elevating the canopy of a prostrate highly susceptible indeterminate great northern bean in a semiarid climate reduced white mold infection and increased yield (Fuller et al., 1984b). In comparison to determinate navy bean types, upright indeterminate navy bean cultivars escape white mold infection or spread because of a narrower canopy (Park, 1993). Reduced levels of white mold in the field have been associated with the open porous canopy of the indeterminate navy bean cultivar Bunsi (Tu and Beversdorf, 1982; Park, 1993). An open, porous canopy of larger seeded determinate beans was also identified as an architectural avoidance mechanism (Coyne et al., 1974; Weiss et al., 1980; Schwartz et al., 1987). Dense canopies in bean generally resulted in higher white mold severity than porous canopies because of the development of a favorable microclimate within the canopy (Blad et al., 1978; Coyne, 1980). Fewer apothecia were produced underneath the open canopy of the determinate dark red kidney bean cultivar Charlevoix and the upright canopy of the indeterminate small white bean cultivar Aurora compared with the dense canopy of several prostrate indeterminate great northern bean cultivars (Schwartz and Steadman, 1978). Plant height was found to be associated with lower field white mold levels in an A55/G122 recombinant inbred line (RIL) population (Miklas et al., 2001) and a PC-50/XAN159 RIL population (Park et al., 2001). In soybean [Glycine max (L.) Merr], however, increased plant height was associated with increased white mold levels in the field. Other agronomic traits in soybean, such as an increase in days to R1, lodging, and maturity date, were also found to be associated positively with white mold levels in the field (Kim and Diers, 2000).

Progress in breeding for white mold resistance in bean is hindered by environmental conditions and morphological factors that confound the expression and detection of physiological resistance mechanisms. Combining physiological resistance with agronomically desirable avoidance mechanisms may offer a stable approach to the long-term improvement of resistance to white mold in bean. The identification of agronomically desirable avoidance mechanisms in advanced or elite lines and segregating populations is essential. The objectives of this study were to identify agronomic avoidance traits that contribute to resistance to white mold in the field, determine the heritabilities of agronomic traits and resistance to white mold in the field, and investigate the resulting effect of the agronomic avoidance traits on resistance to white mold and yield levels.

MATERIALS AND METHODS

Plant Materials

A group of elite lines and two segregating navy bean populations were used to study relationships among agronomic traits and field resistance to white mold. The elite lines were tested in three field trials and consisted of 30 (Test 1) and 36 (Tests 2 and 3) genotypes; including cultivars and breeding lines from seven commercial bean classes, new sources of improved resistance, and genotypes entered for testing in the National Sclerotinia Bean Nursery. Twenty-seven genotypes were common across all three tests. The elite lines were typically high-yielding cultivars or advanced breeding lines selected for useful agronomic attributes and previously evaluated in three corresponding greenhouse tests for resistance to oxalate (Kolkman and Kelly, 2000).

The Bunsi/Newport (BN) population consisted of 98 [F.sub.3]-derived lines developed from a biparental cross between Bunsi, an indeterminate (Type II; Singh, 1982) resistant cultivar with an open porous canopy, and Newport, a determinate (Type I) susceptible cultivar (Kelly et al., 1995; Kolkman and Kelly, 2000). Bunsi has physiological resistance to white mold, resistance to oxalate, and exhibits plant avoidance through an open, porous canopy (Tu and Beversdorf, 1982; Schwartz et al., 1978; Miklas and Grafton, 1992; Tu, 1985; Kolkman and Kelly, 2000). The 98 [F.sub.2] individuals were advanced in the greenhouse to the [F.sub.3] generation by single seed descent. Seed from individual [F.sub.3] plants was bulked and advanced in the greenhouse. Seed harvested from three [F.sub.3:4] plants was bulked and [F.sub.3:5] plants were increased in a winter nursery in Puerto Rico.

The Huron/Newport (HN) population consisted of 28 [F.sub.5:6] RILs, developed by single seed descent from a biparental cross between the resistant indeterminate (Type II) cultivar, Huron (Kelly et al., 1994), and the susceptible determinate (Type I) cultivar, Newport. Huron has both physiological resistance to while mold, as determined through resistance to oxalate and resistance to white mold in the field (Kolkman and Kelly, 2000). The HN population was advanced by single seed descent and bulked in the [F.sub.5] generation for seed increase. No intentional selection was made for agronomic traits during the development of either population.

The elite lines and two segregating populations were evaluated for resistance to white mold in the field in three individual experiments. The elite lines were grown in field trials at the Montcalm Research Farm (MRF), Entrican, MI, in 1996 (MRF96; Test 1), 1997 (MRF97; Test 2), and 1998 (MRF98; Test 3). The BN [F.sub.3:6] population was grown in MRF97, and at the Sanilac Cooperator Farm (SCF97) location, Palms, MI, in 1997, and the [F.sub.3:7] lines were grown in MRF98. Only 88 of the 98 [F.sub.3:6] lines in the BN population were grown in SCF97, due to limited seed availability. The HN population was grown in MRF96 ([F.sub.5:6]), MRF97([F.sub.5:7]), SCF97 ([F.sub.5:7]), and MRF98 ([F.sub.5:8]). Planting was delayed to the second week in June in all field experiments to favor disease development. Plot rows were 6 m in length, with a 0.5-m-row spacing in the MRF experiments, whereas all plots at the SCF97 location had a 3-m-row length and 0.76-m-row width. The two center rows of each four row plot were planted with the experimental line, while the two outer border rows were planted with a highly white mold susceptible cultivar, Midland. Standard agronomic practices for tillage, fertilization, and herbicide were applied to ensure good crop growth and development at both field sites. To promote uniform disease pressure across the field at MRF, plots were overhead irrigated five times in 1996, three times in 1997, and six times in 1998 during the flowering period with approximately 13 mm of water each irrigation. The field site at SCF97 was selected on the basis of past history of heavy white mold infection in previous years.

Traits

Plots were rated for DSI and disease incidence (DI; Kolkman and Kelly, 2000; Steadman, 1997; Steadman et al., 1998) by means of a "quarter scale" (Hall and Phillips, 1996) shortly before harvest, when the plants had reached physiological maturity. Thirty plants per plot were rated from 0 to 4, where 0 = no disease present, 1 = 1 to 25% of the plant with white mold symptoms, 2 = 26 to 50% of the plant with white mold symptoms, 3 = 51 to 75% of the plant with white mold symptoms, and 4 = 76 to 100% of the plant with white mold symptoms. DSI was calculated for each plot on a percentage basis by the following formula:

DSI = [SIGMA] (rating of each plant)/4 x (number of plants rated) x 100

DI was calculated as the number of plants out of the 30 individuals with white mold infection on a percentage basis.

The elite lines and segregating populations were evaluated for the following agronomic traits: growth habit, days to flower, mid-season canopy height, mid-season canopy width, branching pattern, days to maturity, lodging, seed size, and yield. Growth habit was determined during the growing season as either indeterminate (Type II) or determinate (Type I). Days to flower were recorded as the number of days following planting, when 50% of the plants in a plot had at least one open flower. At midseason (post-main flower flush) canopy height and width measurements were averaged on each individual plot, from six measurements per plot (three measurements per row) in all experiments except for the MRF96 trials, where 10 measurements per plot were taken. Plots were evaluated for branching pattern on the basis of a 1 to 5 scale, where 1 = acute upright branching, and 5 = obtuse prostrate branching. Days to maturity were recorded as the number of days following planting, until 90% of the pods were physiologically mature and drying down. Lodging was determined at maturity, on the basis of a 1 to 5 scale, where 1 = no lodging, and 5 = excessive lodging. All plots were harvested at maturity after the disease ratings were taken. Seed yield and seed size (the weight of 100 seeds) were adjusted to 18% moisture content by weight.

Statistical Analysis

In the elite lines, the MRF96 experiment was analyzed as a rectangular lattice and the MRF97 and MRF98 field experiments were each analyzed as a partially balanced triple lattice by means of PROC LATTICE (SAS, 1995). The 27 common elite genotypes were analyzed across all three field seasons as a RCBD, by means of PROC GLM, with environments considered as a random effect and genotypes as a fixed effect. The BN and HN populations were evaluated in individual field environments as RCBDs by means of PROC GLM. Both segregating populations were analyzed across the three years as a RCBD, by means of PROC GLM, with both genotypes and environments considered as random effects. Estimates of heritability for all traits were calculated on an entry-mean basis, where [h.sup.2] = ([[sigma].sup.2.sub.g])/[[[sigma].sup.2]/(re) + [[sigma].sup.2.sub.ge]/e + [[sigma].sup.2.sub.g]] (Hallauer and Miranda, 1988). The 90% confidence intervals for the heritability estimates were determined on the basis of Knapp et al. (1985). A chi-square goodness-of-fit test was used to test growth habit for a normal determinate to indeterminate segregation ratio in the segregating populations. Pearson correlation coefficients (r) were calculated by PROC CORR, and multiple stepwise regression of significant agronomic traits (P < 0.15) on DSI and yield (excluding seed size) and [R.sup.2] values were determined by PROC REG (SAS, 1995).

RESULTS AND DISCUSSION

Significant genotypic variance among the elite lines and within the BN and HN populations was observed for DSI, DI, and all agronomic traits measured (Table 1). Genotypic expression for all traits was influenced by environment, as indicated by significant genotype x environment interactions, except for DSI, DI and days to maturity in the HN population. Mean DSI and DI values indicated that adequate disease pressure was attained in each environment (Table 2). In both the BN and HN populations, parental genotypes varied for disease reaction and for all agronomic traits, except lodging (Table 3). The DSI and DI means for the elite lines were reported previously (Kolkman and Kelly, 2000) and the agronomic trait means for the elite lines are available upon request. Lodging scores between parents were identical, yet the progeny segregated for lodging in both populations. Determinate and indeterminate growth habit segregated as expected in the BN ([chi square] = 1.98; P = 0.16) and HN ([chi square] = 0.57; P = 0.47) populations.

Variation between environments affected the disease pressure and agronomic characteristics. Abundant rainfall and exceptional growing conditions at the SCF97 location were ideal for excessive plant growth, resulting in broader branching pattern and increased canopy width, lodging, seed size, and yield. The SCF97 environment was favorable for heavy white mold pressure, resulting in high DSI and DI scores (Table 2), with ranges in DI from 2.2% to 100% (BN population) and 21.1% to 96.7% (HN population). Genotypes in the SCF97 environment produced both the highest yield (4704 kg [ha.sup.-1]; BN population), and the lowest yield (1348 kg [ha.sup.-1]; BN population) compared with other environments. In contrast, the MRF98 location was irrigated during flowering, while the latter part of the season was uncharacteristically hot and dry, resulting in narrower plant canopies, earlier maturity, and subsequently lower DSI and DI. As a result, the lowest means for DSI were identified in the MRF98 environment. The correlation between DSI and DI was highly significant for the elite lines, and BN and HN populations across environments (r = 0.97, P < 0.0001; r = 0.97, P < 0.0001; and r = 0.95, P < 0.0001, respectively) as well as within environments. As a result, only DSI will be discussed further.

Heritability estimates for resistance to white mold ranged from 0.47 for DSI in the BN population to 0.82 in the HN population (Table 3). Previous estimates of heritability for resistance to white mold in the field have been moderate to high in a Bunsi-derived population ([h.sup.2] = 0.70), and in two snap pod bean populations ([h.sup.2] = 0.77; [h.sup.2] = 0.58), suggesting that progress in breeding for resistance is possible (Miklas and Grafton, 1992). Heritability estimates of agronomic traits in the BN population were generally high, ranging from [h.sup.2] = 0.65 for canopy width, to [h.sup.2] = 0.90 for days to flower. In the HN population, heritability estimates for agronomic traits were generally moderate to high, ranging from [h.sup.2] = 0.58 for canopy width to [h.sup.2] = 0.95 for days to maturity. The estimates of heritability for yield under white mold pressure were moderate in both populations. The strong influence of DSI on yield (Table 4) under white mold pressure most likely accounted for a clear separation in yield among segregating progeny, resulting in the atypically moderate to high heritability values for yield (Table 3).

The comparison of the single regression of agronomic traits to DSI depicts the complexity of avoidance mechanisms associated with white mold between the various locations and years (Table 4). In general, more agronomic traits were correlated to DSI and the level of the correlations were higher in the SCF97 and MRF97 tests with heavier white mold pressure, suggestive of a key role in disease avoidance mechanisms. The location with the lowest disease pressure, MRF98, had the least number of traits associated with DSI, and therefore fewer, yet significant avoidance mechanisms affecting DSI. Interestingly, there were also major differences between the composition and number of agronomic traits associated with DSI in the elite lines and the two segregating populations. Overall, the BN population had the most agronomic traits associated with DSI, particularly in the MRF97 and SCF97 locations. The elite lines had fewer agronomic traits associated with DSI, probably due to less variability among these selected lines. Most consistently, increased days to maturity was generally associated with decreased DSI in all three of the elite line locations due to the wide range in maturity between genotypes. In contrast, an increase in days to maturity was associated with an increase in DSI in the SCF97 location in the BN and HN populations, possibly due to more vegetative growth in later maturing genotypes. The HN population had the fewest number of agronomic traits associated with DSI. The two parents in the HN population shared the greater similarity in branching pattern, which resulted in fewer agronomic traits affecting DSI. Despite the recognition that growing conditions favorable for high yield similarly favor disease development, reduced DSI was associated with an increase in yield at almost all sites, particularly for the elite lines and BN population. Increased yield under white mold pressure may be an inherent result of larger seed weight in plants with lower disease severity (Kerr et al., 1978).

Multiple regression analysis of agronomic traits on DSI and yield also depicted the complexity of resistance to white mold in bean (Table 5). Desirable avoidance mechanisms are recognized as those traits that reduce DSI and either increase yield or have no negative effect on yield under white mold pressure. In contrast to the single regression analysis (Table 4) growth habit was one of the most important desirable avoidance mechanisms identified in the elite lines and segregating populations, contributing to both DSI and yield (Tables 5 and 6). The indeterminate growth habit was associated with a decrease in disease pressure in the BN and HN populations, except for the SCF97 location. Indeterminate growth habit was also generally associated with an increase in yield, accounting for up to 34.4% of the yield in the BN population in MRF97, and up to 51.6% of the yield in the HN population in MRF96. Yield stability associated with indeterminate navy bean genotypes has been previously demonstrated in the absence of white mold (Kelly et al., 1987). Indeterminate growth habit as a desirable avoidance phenotype in navy bean is reversed in large-seeded bush bean, where the determinate growth habit is an avoidance phenotype (Miklas et al., 2001; Park et al., 2001; Schwartz and Steadman, 1978).

The effect of days to flower on DSI differed greatly between environments (Tables 5 and 6). Fewer days to flower in the BN population at SCF97 was associated with a decrease of up to 50.2% in DSI. Alternatively, in the BN population at MRF98, an increase in days to flower resulted in a 4.0% decrease in DSI. The contradictory results for these two locations is supported by the significant genotype x environment interaction (Table 1), and highlights the differential expression of avoidance mechanisms under high (SCF97), and low (MRF98) levels of white mold pressure. Both SCF97 and MRF98 represent extreme environments, and the corresponding effect of days to flower may be a result of the timing of disease initiation and the subsequent infection potential throughout the entire season. An increase in days to flower was associated with decreased yields for most environments. Although earlier flowering genotypes showed a yield increase under heavy white mold pressure, fewer days to flower must be regarded generally as an undesirable avoidance mechanism because there is strong environmental variability and during years of reduced white mold levels, that trait adds severe restrictions on selection for increased yield potential.

Increased canopy height was associated with an increase in DSI and yield in the elite lines and the BN and HN populations, except for the elite lines tested at MRF98, where an increase in height was associated with a decrease in DSI (Tables 5 and 6). An increase in plant height has been associated previously with reduced disease levels (Miklas et al., 2001; Park et al., 2001). The contrasting results may be due to the extreme differences in resistance phenotypes evaluated and environments tested. Most significantly, in the HN population, an increase in canopy height resulted in a 19% increase in DSI at MRF96, and a 26.2% increase in yield at SCF97. Interestingly, the susceptible parent had a greater canopy height than either resistant parent. For the two segregating populations, reduced plant height would be considered an undesirable avoidance mechanism since it also reduced yield potential.

An increase in canopy width was a desirable avoidance mechanism in the elite lines, since it reduced DSI levels while increasing yield. Larger-seeded genotypes that may have had wider but more porous canopies that those of the segregating populations may have contributed to this result (Tables 5 and 6). In general, greater canopy width allows for more rapid canopy closure, which could result in higher white mold pressure and less avoidance. Although decreased canopy width was associated with a decrease in DSI in the segregating populations, it is still an undesirable trait because of the negative impact on yield.

Branching pattern, lodging, and days to maturity also had variable impacts on DSI and yield in each environment and between the elite lines and segregating populations (Tables 5 and 6). The parental genotype Bunsi has a more open, wider branching pattern than the susceptible parent and the wider branching pattern resulted in a decrease in DSI for the BN population. In contrast, Huron has a narrower upright branching pattern than does Newport and branching pattern was not a factor for DSI in this population. For the elite lines, an increase in branching pattern was attributable to an increase in yield at MRF97 and a decrease in yield at MRF98. An increase in lodging in the BN population at MRF97 and MRF98 was associated with an increase in DSI and a decrease in yield. The microclimate within a lodged canopy is more conducive to heavy white mold infection and spread of disease. For the elite lines, an increase in lodging also contributed to an increase in DSI (13.4%) and a decrease in yield (6.1%) in the MRF97 environment. Generally, more days to maturity resulted in less disease and higher yield in the multifactor analysis except at the MRF98 location, where more days to maturity reduced yield. The function of maturity on DSI as a desirable or undesirable avoidance mechanism is highly variable and dependent upon specific environmental conditions, genotypes evaluated, and the desired yield potential.

The DSI score in each trial had a major impact on seed size and yield. Heavy white mold pressure typically reduces seed size and subsequently yield (Kerr et al., 1978). In this study, as DSI increased, seed size decreased for BN at all three locations and in the HN population at MRF97 and MRF98 (Table 4). Similarly, as DSI increased, yield decreased in most environments for the elite lines and BN and HN populations. Although genotypes and environments that produce high yield potential are also conducive to heavy white mold levels, realized yield was severely curtailed since high DSI negatively affected yield across most environments in the elite lines and segregating populations.

The complexity of the relationship between agronomic traits and white mold in the field in contrasting environments and differing tests or populations underlies the difficulties bean breeders face when trying to select for resistance to white mold. Agronomic avoidance mechanisms played a major role in the final disease development in the segregating populations. Of the traits measured, growth habit was the most important avoidance mechanism affecting resistance to white mold. The indeterminate growth habit of the Bunsi and Huron cultivars was associated with reduced DSI and increased yield. Many of the other agronomic traits varied in their avoidance characteristics to white mold between the elite lines and segregating populations, as well as between environments. Specifically, such traits as days to flower and canopy height must be considered individually in relation to the environment and population tested, and the potential direct effect on yield.

The choice of the resistant parent is an important factor in dictating how much variability in DSI is attributable to agronomic avoidance traits versus physiological resistance. The resistant parents, Bunsi and Huron, possess a similar growth habit, yet differ in branching pattern. The variation in correlations between agronomic and disease-related traits indicates that the overall architecture of the resistant parent is very important in determining potential avoidance mechanisms in a segregating population. Early generation selection against highly heritable, undesirable agronomic avoidance traits such as the determinate growth habit in navy bean, may be a useful approach in minimizing the selection of less desirable genotypes.

Given the complexity of interactions between agronomic traits on white mold development and yield in bean, we would propose that the small-seeded resistant ideotype for the Midwest should possess physiological resistance to white mold and be indeterminate, with a Type II growth habit, resistant to lodging, medium canopy width and branching pattern, and medium height, days to flower and maturity, to ensure adequate vegetative growth and yield potential without creating a favorable microclimate within the plant canopy for disease development. Choosing among the types of variability present for different agronomic traits in populations segregating for resistance needs to be conducted in different environments if critical progress is to be made in breeding for resistance to white mold in common bean.

Abbreviations: BN, Bunsi/Newport; BP, branching pattern; DI, disease incidence; DSI, disease severity index; DTF, days to flower; DTM, days to maturity; GH, growth habit; HN, Huron/Newport; HT, canopy height; LDG, lodging; MRF, Montcalm Research Farm; RIL, recombinant inbred line; SCF, Sanilac Cooperator Farm; WD, canopy width.
Table 1. Analysis of variance for resistance to white mold and
agronomic traits in 27 elite bean lines common across evaluation sites
at Montcalm Research Farm in 1996, 1997, and 1998, a Bunsi/Newport
population evaluated at the Montcalm Research Farm in 1997, 1998 and
at the Sanilac Cooperator Farm in 1997, and a Huron/Newport population
evaluated at the Montcalm Research Farm in 1996, 1997, 1998, and at
the Sanilac Cooperator Farm in 1997.

                               Mean Squares

                                                     Days to
Source           df   DSI ([dagger])  DI ([dagger])   flower

Elite lines ([double dagger])

Genotype (G)      26     1 512.9 **     2 566.2 **    86.1 **
Environment (E)    2     8 817.5 **     5 426.0 **   519.7 **
G x E             52       418.7 **       734.4 **     2.5 **

Bunsi/Newport Population ([double dagger])

Genotype (G)      97     1 580.5 **     2 069.5 **    47.5 **
Environment (E)    2    12 803.7 **    37 766.5 **     8.9ns
G x E            184       838.1 **     1 196.5 **     4.6 **

Huron/Newport Populations ([double dagger])

Genotype (G)      27     1 362.8 **     2 128.2 **    58.3 **
Environment (E)    3    16 878.7 **    47 810.3ns    641.5 **
G x E             81        24.7ns        510.7ns      3.6 **

                               Mean Squares

                   Canopy       Canopy     Branching
Source             height        width      pattern    Lodging

Elite lines ([double dagger])

Genotype (G)         87.7 **      57.1 **     8.0 **   7.4 **
Environment (E)  10 387.8 **   1 536.7 **     0.2ns   15.3 *
G x E                25.4 **      20.2 **     0.5 **   0.8 **

Bunsi/Newport Population ([double dagger])

Genotype (G)        135.1 **      85.4 **     1.0 **   3.5 **
Environment (E)     260.8ns   21 774.7 **     8.4 **  16.2ns
G x E                15.0 **      30.2 **     0.3 **   0.8 **

Huron/Newport Populations ([double dagger])

Genotype (G)         62.6 **      64.0 **     2.7 **   2.5 **
Environment (E)   7 492.7 **   5 717.1 **    11.9 **  23.6 **
G x E                21.3 **      27.2 **     0.5 **   0.7 *

                               Means Squares

                   Days to
Source            maturity    Seed size     Yield

Elite lines ([double dagger])

Genotype (G)         98.3 **   1 070.9 **     76.8 **
Environment (E)  12 992.2 **      39.5ns     156.8ns
G x E                25.1 **      18.9 **     27.1 **

Bunsi/Newport Popniation ([double dagger])

Genotype (G)         89.2 **      33.8 **    107.8 **
Environment (E)  56 614.3 **     399.1 **  3 728.7 **
G x E                22.8 *        3.3 **     44.5 **

Huron/Newport Populations

Genotype (G)        166.3 **      57.3 **     76.0 **
Environment (E)   6 900.7 **     217.3 **  1 396.7 **
G x E                 8.1ns        3.6 **     36.3 **

* Indicates significance at P < 0.05.

** Indicates significance at P < 0.01.

([dagger]) DSI = disease severity index; DI = disease incidence.

([double dagger]) Elite lines consisted of 27 common genotypes;
Bunsi/Newport population (98 genotypes); Huron/Newport population
(28 genotypes).
Table 2. Means values for resistance to white mold and agronomic
traits for the common bean elite lines, Bunsi/Newport, and Huron/
Newport populations tested across locations at the Montcalm Research
Farm in 1996, 1997 and 1998, and at the Sanilac Cooperator
Farm in 1997.

                                      Elite lines ([dagger])

                                 MRF96 ([double
Traits                            dagger])        MRF97    MRF98

DSI ([section]) (%)                   24.3         32.4     12.2
DI ([section]) (%)                    36.7         47.1     30.7
Days to flower                        40.3         44.9     42.9
Canopy height (cm)                    34.1         55.6     51.9
Canopy width (cm)                     35.1         42.7     42.1
Branching pattern ([paragraph])        2.7          2.6      2.6
Lodging (#)                            2.2          2.9      2.3
Days to maturity                      98.9        112.1     86.9
Seed size (g 100 [seed.sup.-1])       25.7         27.4     25.1
Yield (kg [ha.sup.-1])              3122         3380     3099

                                 Bunsi/Newport Population

Traits                             MRF97   SCF97   MRF98

DSI ([section]) (%)                 35.5    46.5    32.4
DI ([section]) (%)                  47.6    71.1    52.0
Days to flower                      42.7    42.7    42.4
Canopy height (cm)                  49.2    50.9    49.2
Canopy width (cm)                   43.4    59.0    42.9
Branching pattern ([paragraph])      2.7     2.9     2.5
Lodging (#)                          2.7     3.3     3.0
Days to maturity                   111.6   110.9    86.8
Seed size (g 100 [seed.sup.-1])     20.9    22.9    20.7
Yield (kg [ha.sup.-1])            2740    3481    2785

                                        Huron/Newport Population

Traits                             MRF96     MRF97     SCF97    MRF98

DSI ([section]) (%)                23.0      20.4      48.4     17.6
DI ([section]) (%)                 36.1      32.7      82.2     34.8
Days to flower                     37.2      43.4      42.7     41.2
Canopy height (cm)                 32.4      52.9      52.1     46.8
Canopy width (cm)                  32.5      40.9      52.0     37.7
Branching pattern ([paragraph])     2.6       2.5       2.8      1.9
Lodging (#)                         2.1       2.7       3.3      2.3
Days to maturity                   95.8     104.0     106.6     86.5
Seed size (g 100 [seed.sup.-1])    20.6      20.8      24.0     22.3
Yield (kg [ha.sup.-1])           2852      2869      3706     2684

([dagger]) Mean values for 30 genotypes in MRF96, 36 genotypes in
MRF97 and MRF98.

([double dagger]) MRF96 = Montcalm Research Farm, 1996,
MRF97 = Montcalm Research Farm, 1997; MRF98 = Montcalm Research
Farm, 1998; SCF97 = Sanilac Cooperator Farm, 1997.

([section]) DSI = disease severity index; DI = disease incidence.

([paragraph]) Branching pattern based on a 1-to-5 scale, where
1 = acute upright and 5 = obtuse prostrate.

(#) Lodging based on a 1-to-5 scale, where 1 = no lodging and
5 = excessive lodging.
Table 3. Parental and progeny means, progeny ranges, and estimates of
heritability ([h.sup.2]) for resistance to white mold and agronomic
traits in common bean in the Bunsi/Newport population evaluated in
combined environments at the Montcalm Research Farm in 1997, 1998
and at the Sanilac Cooperator Farm in 1997, and the Huron/Newport
population evaluated in combined environments at the Montcalm Research
Farm in 1996, 1997, 1998, and at the Sanilac Cooperator Farm in 1997.

                              Bunsi/Newport Population

                 Parental means      Progeny

Traits           Bunsi  Newport    Mean (range)     [h.sup.2] (90% CI)
                                                        ([dagger])

DSI ([double
 dagger]) (%)     28.7     68.7   37.8 (4.4-68.6)     0.47 (0.28-0.60)
DI ([double
 dagger]) (%)     35.3     80.2   56.4 (8.5-88.5)     0.42 (0.22-0.57)
Days to flower    41.6     43.1   42.6 (37.7-48.4)    0.90 (0.87-0.93)
Canopy
 height (cm)      48.0     52.5   49.7 (35.7-57.8)    0.89 (0.85-0.92)
Canopy
 width (cm)       49.0     43.5   48.0 (37.0-55.1)    0.65 (0.52-0.73)
Branching
 pattern
 ([section])       3.0      2.6    2.7 (1.5-3.3)      0.73 (0.63-0.79)
Lodging
 ([paragraph])     2.9      2.9    3.0 (1.3-4.4)      0.78 (0.70-0.83)
Days to
 maturity        105      100    102.7 (91.0-110.6)   0.74 (0.65-0.81)
Seed size
 (g 100 [seed.
 sup.-l])         22.9     19.2   21.5 (17.5-26.9)    0.90 (0.87-0.93)
Yield (kg
 [ha.sup.-1])   3531     2288     2987 (1988-3818)    0.59 (0.44-0.69)

                               Huron/Newport Population

                 Parental means       Progeny

Traits           Huron   Newport    Mean (range)    [h.sup.2] (90% CI)
                                                        ([dagger])

DSI ([double
 dagger]) (%)     19.8     50.7   27.3 (5.6-50.1)    0.82 (0.69-0.89)
DI ([double
 dagger]) (%)     35.3     72.9   46.4 (12.2-73.9)   0.76 (0.58-0.85)
Days to flower    40.5     41.3   41.1 (35.7-47.3)   0.94 (0.89-0.96)
Canopy
 height (cm)      46.0     47.4   46.1 (38.2-50.1)   0.66 (0.40-0.79)
Canopy
 width (cm)       39.6     39.3   40.8 (36.2-45.3)   0.58 (0.25-0.74)
Branching
 pattern
 ([section])       1.9      2.7    2.4 (1.4-3.1)     0.82 (0.69-0.89)
Lodging
 ([paragraph])     2.7      2.7    2.6 (1.7-3.7)     0.71 (0.49-0.82)
Days to
 maturity         98       97     98.2 (90.8-107.7)  0.95 (0.91-0.97)
Seed size
 (g 100 [seed.
 sup.-l])         23.8     19.1   21.9 (18.0-25.8)   0.94 (0.89-0.96)
Yield (kg
 [ha.sup.-1])   3256     2268     3028 (2542-3488)   0.52 (0.16-0.71)

([dagger]) 90% Confidence intervals calculated using procedures
based upon Knapp et al., 1985.

([double dagger]) DSI = disease severity index; DI = disease incidence.

([section]) Branching pattern based on a 1-to-5 scale, where 1 = fully
upright and 5 = prostrate.

([paragraph]) Lodging based on a 1-to-5 scale, where 1 = no lodging
and 5 = excessive lodging.
Table 4. Pearson correlation coefficient (r) between Disease Severity
Index and nine agronomic traits for individual environments in the
elite lines, Bunsi/Newport and Huron/Newport populations evaluated at
the Montcalm Research Farm in 1996, 1997, 1998, and at the Sanilac
Cooperator Farm in 1997.

                             Disease severity index

                                  Elite lines

Agronomic traits   MRF96 ([double    MRF97         MRF98
                      dagger])

Growth habit       -0.05             -0.05     -0.34 *
Days to flower     -0.10              0.04     -0.26
Canopy height       0.18              0.44 **   0.07
Canopy width        0.35 ([dagger])  -0.17     -0.41 *
Branching pattern   0.12              0.26     -0.01
Lodging             0.24              0.62 **   0.05
Days to maturity   -0.39 *           -0.65 **  -0.29 ([dagger])
Seed size          -0.02              0.04      0.06
Yield              -0.52 **          -0.36 *   -0.31 ([dagger])

                             Disease severity index

                                                  Huron/Newport
                     Bunsi/Newport Population       Population

Agronomic traits    MRF97     SCF97     MRF98         MRF96

Growth habit       -0.29 **  -0.02     -0.08     -0.14
Days to flower      0.41 **   0.71 **  -0.03      0.10
Canopy height       0.30 **   0.33 **   0.14      0.44 *
Canopy width        0.33 **   0.24 *    0.10      0.35 ([dagger])
Branching pattern   0.49 **   0.66 **   0.40 **   0.06
Lodging             0.39 **   0.23 *    0.32 **   0.06
Days to maturity   -0.02      0.58 **  -0.05     -0.08
Seed size          -0.41 **  -0.49 **  -0.31 **  -0.22
Yield              -0.42 **  -0.70 **  -0.51 **  -0.36 ([dagger])

                             Disease severity index

                               Huron/Newport Population

Agronomic traits        MRF97             SCF97             MRF98

Growth habit       -0.24              0.12             -0.29
Days to flower      0.31              0.46              0.07
Canopy height       0.26              0.42 *            0.00
Canopy width        0.34 ([dagger])   0.32 ([dagger])  -0.02
Branching pattern   0.19              0.22              0.27
Lodging             0.37              0.22             -0.02
Days to maturity    0.06              0.46 *           -0.25
Seed size          -0.36 ([dagger])  -0.25             -0.62 **
Yield              -0.07             -0.34 ([dagger])  -0.35 ([dagger])

* Indicates significance at P < 0.05.

** Indicates significance at P < 0.01.

([dagger]) Significant at P < 0.10.

([double dagger]) MRF96 = Montcalm Research Farm, 1996;
MRF97 = Montcalm Research Farm 1997; SCF97 = Sanilac Cooperator
Farm, 1997; MRF98 = Montcalm Research Farm, 1998.
Table 5. Multiple regression models of agronomic traits on Disease
Severity Index and yield of common bean under white mold pressure
in elite lines, a Bunsi/Newport population, and a Huron/Newport
population evaluated at the Montcalm Research Farm in 1996,
1997, and 1998, and at the Sanilac Cooperator Farm in 1997.

                          Model ([double dagger])

Environment
([dagger])     Disease severity index              Yield

                                Elite lines

MRF96          y = 87.6+2.0(HT)-1.3(DTM)    y = -4426-6(DSI)+85(WD)
                                            -161(LDG)+51(DTM)

MRF97          y = 294.9-1.3(WD)            y = -3470+687(GH)+63(WD)
               +10.2(LDG)-2.1(DTM)          +175(BP)-310(LDG)+29(DTM)

MRF98          y = 47.2-0.7(HT)             y = 8268-19(DSI)+247(GH)
                                            -68(DTF)+26(WD)-151(BP)
                                            -37(DTM)

Across
 environments  y = 222.6-2.0(DTM)           y = 1086-9(DSI)+705(GH)
                                            -39(DTF)+27(DTM)

                           Bunsi/Newport Population

MRF97          y = -29.9-12.3(GH)+1.7(HT)   y = 1934-10(DSI)+335(GH)
               +1.9(WD)+5.6(LDG)-0.8(DTM)   -64(DTF)+45(HT)+32(WD)
                                            -97(LDG)

SCF97          y = -184.1+3.2(DTF)+1.6(WD)  y = 6004-16(DSI)-229(GH)
                                            -91(DTF)+49(HT)

MRF98          y = 42.2-9.1(GH)-2.7(DTF)    y = 6643-12(DSI)+291(GH)
               +3.0(WD)-9.7(BP)+5.7(LDG)    -64(DTF)+45(WD)-94(LDG)
                                            -34(DTM)
Across
 environments  y = -27.1-6.5(GH)+1.7(DTF)   y = 5837-12(DSI)+130(GH)
               +0.6(HT)+2.0(WD)-1.2(DTM)    -82(DTF)+36(HT)+45(WD)
                                            -108(LDG)-27(DTM)

                            Huron/Newport Population

MRF96          y = -122.7+32.1(GH)+1.9      y = -3318-10(DSI)+415(GH)
               (DTF)+4.9(HT)-13.1(BP)       -62(DTF)+56(WD)+65(DTM)

MRF97          y = -113.5-11.2(GH)+3.2      y = -3997+413(GH)+44(HT)
               (DTF)+5.3(LDG)               +37(DTM)

SCF97          y = -165.4+1.3(HT)+1.4(DTM)  y = 4879-9(DSI)-146(DTF)
                                            +106(HT)

MRF98          y = -7.9-13.3(GH)+1.0(HT)    y = 3138+384(GH)-63(DTF)
                                            +40(WD)
Across
 environments  y = -95.2-14.2(GH)+3.1(HT)   y = 2634+506(GH)-57(DTF)
                                            +42(HT)

([dagger]) MRF96 = Montcalm Research Farm, 1996, MRF97 = Montcalm
Research Farm, 1997; MRF98 = Montcalm Research Farm, 1998;
SCF97 = Sanilac Cooperator Farm, 1997.

([double dagger]) DSI = disease severity index; GH = growth habit;
DTF = days to flower; HT = canopy height; WD = canopy width;
BP = branching pattern; LDG = lodging; DTM = days to maturity.
Table 6. [R.sup.2] (%) values for the full model in multiple
regression, for significant (P < 0.15) agronomic traits on Disease
Severity Index and yield in common bean in the elite lines, Bunsi/
Newport, and Huron/Newport population evaluated at the Montcalm
Research Farm in 1996, 1997, and 1998, and the Sanilac Cooperator
Farm in 1997.

                                      Elite lines

                                                          Across
Traits                 MRF96 ([dagger])  MRF97  MRF98  Environments

                                  Disease severity index

Growth habit                 -            -      -         -
Days to flower               -            -      -         -
Canopy height                7.2          -     16.5       -
Canopy width                 -            4.3    -         -
Branching pattern            -            -      -         -
Lodging                      -           13.4    -         -
Days to maturity            15.3         42.8    -        26.3
Total                       22.5         60.5   16.5      26.3

                                          Yield

DSI ([double dagger])        6.4          9.1    7.6      39.5
Growth habit                 -           19.9   20.6      17.3
Days to flower               -            -     23.7       6.3
Canopy height                -            -      -         -
Canopy width                 7.0         11.2    2.7       -
Branching pattern            -            3.9    9.2       -
Lodging                      7.6          6.1    -         -
Days to maturity            52.3          4.6    4.5       4.5
Total                       73.2         54.8   68.3      67.6

                            Bunsi/Newport Population

                                               Across
Traits                 MRF97  SCF97  MRF98  Environments

                          Disease severity index

Growth habit           10.9    -      3.3       8.9
Days to flower          -     50.2    4.0       4.1
Canopy height           4.6    -      -         1.7
Canopy width           23.7   16.3   16.2      27.1
Branching pattern       -      -      1.9       -
Lodging                 3.4    -      3.6       -
Days to maturity        1.7    -      -         3.0
Total                  44.3   66.5   29.0      44.9

                                   Yield

DSI ([double dagger])   3.3   49.5   25.6       7.2
Growth habit           34.4    1.8   13.6       1.3
Days to flower          4.9    5.7    3.7      26.8
Canopy height           6.7    4.8    -        18.0
Canopy width            1.0    -      5.8       5.1
Branching pattern       -      -      -         -
Lodging                 7.8    -      3.0       1.7
Days to maturity        -      -     10.2       1.5
Total                  58.0   61.8   61.8      61.6

                          Huron/Newport Population

                                                      Across
Traits                 MRF96  MRF97  SCF97  MRF98  Environments

                              Disease severity index

Growth habit            7.5   10.5    -      8.7       23.5
Days to flower          5.2    8.7    -      -          -
Canopy height          19.0    -      6.9    8.2       16.1
Canopy width            -      -      -      -          -
Branching pattern      16.9    -      -      -          -
Lodging                 -     13.6    -      -          -
Days to maturity        -      -     21.3    -          -
Total                  48.6   32.8   28.2   16.8       39.7

                                     Yield

DSI ([double dagger])   3.1    -      4.1    -          -
Growth habit           51.6    6.0    -     27.7       48.6
Days to flower          9.7    -     46.8    6.0        7.1
Canopy height           -      7.8   26.2    -          7.5
Canopy width            4.2    -      -      5.3        -
Branching pattern       -      -      -      7.7        -
Lodging                 -      -      -      -          -
Days to maturity        9.8   65.0    -      -          -
Total                  78.4   78.8   77.1   46.6       63.2

([dagger]) MRF96 = Montcalm Research Farm, 1996, MRF97 = Montcalm
Research Farm, 1997; MRF98 = Montcalm Research Farm, 1998;
SCF97 = Sanilac Cooperator Farm, 1997.

([double dagger]) DSI = disease severity index.


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Judith M. Kolkman and James D. Kelly *

J.M. Kolkman, Dep. of Crop and Soil Sciences, Oregon State Univ., Corvallis, OR, 97331; J.D. Kelly, Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI, 48824. Received 22 Feb. 2001. * Corresponding author (kellyj@msu.edu).
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