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Identification, mapping, and economic evaluation of QTLs encoding root maggot resistance in Brassica.

IN WESTERN CANADA, infestations of root maggots are responsible for substantial economic losses in the production of canola (Liu and Butts, 1982; Griffiths, 1986, 1991; Dosdall, 1998). Primary plant damage occurs when larvae feed on root tissue, which can be exacerbated when feeding channels are subsequently invaded by root rot fungi, leading to even greater loss of root function (Griffiths, 1986, 1991). Both the incidence and severity of root maggot infestations in canola have increased dramatically from 1983 to 1997 (Dosdall, 1998). Although the degree of crop damage from root maggots varies depending on several biotic and abiotic factors (Dosdall, 1998; Dosdall et al., 2003), decreased yields from these pests can reach 52% for Brassica rapa and 20% for Brassica napus in Alberta (Griffiths, 1991).

Several cultural strategies have been identified for reducing losses due to root maggot infestations in canola (e.g., Dosdall et al., 1994, 1996a, 1996b, 1998). Implementation of these strategies can reduce the economic impact of root maggots, but substantial losses can still occur in canola. Consequently, our research has focused on developing canola resistant to root maggot infestations as a method for providing sustainable, long-term control of these pests (Dosdall et al., 2000).

It has been widely reported that wild and undomesticated crop relatives possess valuable insect resistance that may be transferable to crop species (reviewed in Yencho et al., 2000). The process of introgression of desirable traits can be time consuming and laborious: however, the availability of molecular markers for use in genome analysis and tracking of specific traits can be invaluable in reducing the time and efficiency for achieving this goal. Many insect-resistant genes have been successfully identified and mapped using molecular markers (e.g., Mohan et al., 1994; Dweikat et al., 1997; Ma et al., 1998: Huang et al., 2001), and we have adapted this approach to introgress and tag genes for insect resistance in canola.

In previous research, we screened a number of genotypes of Brassicaceae for resistance to root maggot infestations and identified Sinapis alba L. as one of the most resistant (Dosdall et al., 1994, 2000). Several intergeneric hybrids derived from crosses between S. alba and B. napus were also resistant (Dosdall et al., 2000) and have been developed further with the aim of genetically mapping the root maggot resistance in these lines from the S. alba parent.

In this paper, we report the mapping of QTLs introgressed from S. alba that confer resistance to root maggots in B. napus. We reassessed and confirmed that resistance levels were maintained between years and between generations of host plants. Further, we compared levels of root damage and yield loss associated with root maggot infestations between B. napus, S. alba/ B. napus intergeneric hybrids, and S. alba. In Canada alone, we estimate that the introgression of these QTLs into commercial canola varieties could save the canola industry more than $75 million per year.

MATERIALS AND METHODS

Plant Material

All plant materials used in this study were obtained from the University of Alberta germplasm collection, except the intergeneric hybrids. Intergeneric hybrids designated with the prefix BNH were obtained from the germplasm collection of Dr. L. Kott (University of Guelph, ON, Canada) and were described in Ripley and Arnison (1990).

Susceptibilities of Intergeneric Hybrids to Root Maggot Infestation

Field studies to evaluate resistance and susceptibilities of hybrid accessions (Table 1) were conducted in plots at the Alberta Research Council in Vegreville, AB, Canada (112[degrees]06' W: 53030' N). The soil type was black chernozemic, and was fertilized before seeding according to the soil test recommendations for canola production. The seed used was treated before sowing with carboxin (1,4-Oxathiin-3-carboxanilide, 22.5 mL per kg containing carbathiin-thiram (N,N-tetramethylthiuram disulfide)--lindane (gamma- 1,2,3,4,5,6-Hexachlorocyclohexane) at 1:2:15 g a.i.) to reduce seedling mortality from phytopathogens and herbivory by flea beetles.

Each genotype was seeded in a 6- by 1-m plot comprising four rows spaced 20 cm apart at a plant density of approximately 300 per row. Seeding was performed with a double disc press drill. In 1999, eight intergeneric hybrid accessions were evaluated, comprising accessions BNH-006, BNH-014, BNH-015, BNH-106, BNH-293, BNH-533, BNH-555, and BNH-574: in 2000, three hybrid accessions were reevaluated: BNH-014, BNH-015, and BNH-106 (Table 1). The plots were interspersed with B. napus cv. Quantum, a cultivar of B. napus known to be susceptible to root maggot attack (Dosdall, 1996, unpublished data). At the end of the season when the plants were mature and root maggot larvae had completed their development, taproots of 75 randomly selected plants of each accession were excavated, washed, and evaluated for degree of root injury according to the rating scale of Dosdall et al. (1994).

Root Maggot Damage and Yield Losses in B. napus, Selected S. alba/B, napus Intergeneric Hybrids, and S. alba

A paired treatment experimental design was used with four replications in a field trial conducted at Vegreville, AB, in 2000. Seeding of each of the following genotypes was performed over an area of 24 [m.sup.2] on 10 May with a double-disc press drill at a rate of 5 kg [ha.sup.-1] and row spacing of 20 cm: B. napus cv. Delta and cv. Quantum, intergeneric Hybrid Accessions BNH-014 and BNH-015, and S. alba. Two weeks after seeding, eight 1-[m.sup.2] plots of each genotype were established so that each plot was separated from the corresponding plot of its pair by a distance of 1 m. Counts were made to ensure that each 1-[m.sup.2]: plot contained exactly 100 seedlings: extra seedlings were pulled. Weeds were removed by hand as necessary throughout the season.

At the rosette stage of development (Growth Stage 2.5 of Harper and Berkenkamp, 1975), root maggot eggs were abundant on or near the basal stems of plants in the experimental plots. Once per week for 6 wk an insecticidal drench was applied to all plants in one plot of each pair, for each genotype. The plots receiving the insecticide treatments were selected randomly at the beginning of the season and the same plots received insecticide in subsequent weeks. Applications of diazinon (diethyl 2-isopropyl-4-methyl-6-pyrimidyl thionophosphate) were made at the rate registered for use against cabbage root maggot in vegetable crops (1.40 g a.i. [ha.sup.-1]). Plants in the companion plot of each pair were treated with an equivalent volume of water. Insecticide and water applications were made with a watering can, with care taken to ensure uniform distribution across each plot.

At the end of the season, 50 plants from each replicate plot were selected randomly, cut at the base, bagged, labeled, and all seed was threshed, cleaned, and weighed to determine seed yields per plot. Roots from these plants were also dug out, washed, and scored for degree of root maggot damage using the semiquantitative scale of Dosdall et al. (1994). Significance of differences in mean seed yields and mean root maggot damage ratings among the different genotypes was determined with a paired t test analysis (SAS Institute, 1999).

Susceptibilities to Root Maggots of Accessions from the Gene Mapping Population

The [P.sub.1] parent was intergeneric hybrid accession BNH-014, determined as relatively root maggot resistant in previous research (Dosdall et al., 2000): the [P.sub.2] parent was B. napus cv. Delta, determined previously as root maggot susceptible (Dosdall et al., 1994). The mapping population was a doubled haploid (DH) population derived from a single [F.sub.1] plant derived from the cross between [P.sub.1] and [P.sub.2]. Sixteen genotypes of the gene mapping population were evaluated for susceptibilities to attack by root maggots in 2000, and 89 were assessed in 2001. Single-row plots of each accession were established in mid-May of 2000 and 2001. Each genotype was seeded in a 6- by 1-m plot with a double-disc press drill, at a rate estimated to produce a plant density of 300 plants per row. At the end of the season, taproots of 75 randomly selected plants of each accession were rated for root maggot damage according to the method stated previously. In 2001, basal stem diameters of taproots were measured with a caliper.

Susceptibilities of selected accessions from the root maggot mapping population were reassessed in the 2003 field season to ensure that resistance levels were maintained between generations of host plants, and to gain insight into the mechanism of resistance to root maggot attack. Twelve accessions comprised of nine genotypes presumed to be resistant in previous field trials based on consistent low root maggot ratings and three susceptible genotypes were tested in a randomized complete block design in field plots at Edmonton, Alberta (113[degrees]28' W: 53[degrees]33' N). Selections of accessions to be tested were made on the basis of availability of sufficient quantities of seed. Each accession was seeded in a 6- by 1-m plot comprising four rows, and plots were replicated four times. Seeding was performed with a double disc press drill at a rate of 5 kg [ha.sup.-1] and rows were spaced 20 cm apart. Susceptibilities of the accessions to infestation by Delia spp. were assessed by counting eggs deposited on or near individual plants, and by evaluating root injury at the end of the growing season. Eggs were counted visually in situ according to the method of Dosdall et al. (1994) once per week for 3 wk from mid-June to early July 2003. Root maggot damage assessments were performed at the end of the season according to the method specified previously from 50 plants per plot collected randomly from the middle two rows of the treatment plots. Significance of differences among root maggot egg numbers for accessions in the gene mapping population were determined using ANOVA and Tukey's studentized range test (SAS Institute, 1999).

DNA Extraction, Southern Hybridization, and Clones

DNA extraction, restriction enzyme digestion, gel electrophoresis, and alkaline transfer were performed as described by Sharpe et al. (1995). The RFLP clones (names starting with ec, wg, tg) were provided by T.C. Osborn, University of Wisconsin, Madison, WI, USA. All other RFLP probes used in this study were Arabidopsis ESTs described by Sillito et al. (2000). One-hundred and twenty-three RFLP and R-EST clones were screened for informative polymorphisms using EcoRI digested DNA of parental lines (BNH-014 and B.napus cv. Delta) used to generate the mapping population.

Linkage and Quantitative Trait Loci Analysis

Linkage analysis was performed using Mapmaker version 3.0 (Lander et al., 1987). A logarithm of odds (LOD) score of 4 and a distance of 25 cM were used to form the initial linkage groups. Order, Sequence, Compare, and Try commands were used to construct marker positions of individual groups. Wherever necessary, LOD score and distance were then reduced to 3 and 40 cM, respectively, to bridge the large gaps between markers. Double crossovers, especially in short intervals, were double-checked. The Kosambi mapping function (Kosambi, 1944) was used to convert recombination frequencies into map distances.

The QTL mapping and analysis were performed using MapQTL (version 3.0) (Van Ooijen and Maliepaard, 1996) using the MQM (multiple QTL model) approach developed by Jansen and Stam, 1994. The first step in this approach involves the use of interval mapping to find putative QTLs set at a specified LOD value. The second step involves the selection of markers close to the putative QTLs as cofactors, thus leading to a multiple QTL model. The LOD threshold of 2.0 was chosen in this study as the minimum to declare the presence of a QTL in a given genomic region.

RESULTS

Susceptibilities of Intergeneric Hybrids to Root Maggot Infestations

In general, for all the field seasons, moisture conditions were excellent, prompting development of comparatively high root maggot populations. In 1999, mean root maggot damage ratings of the S. alba x B. napus hybrid accessions evaluated ranged from 1.37 (BNH-015) to 2.11 (BNH-106); all hybrids except BNH-015 had higher root damage values than the check line, B. napus cv. Quantum (Table 1). In 2000, mean root maggot damage ratings of the intergeneric hybrids evaluated ranged from 0.20 (BNH-106) to 1.10 (BNH-015); all intergeneric hybrids had mean root maggot damage values lower than those of the check line. The low mean root damage value observed in 2000 for BNH-106 may not be a true indication of its susceptibility to infestation. Germination of BNH-106 plants was poor in 2000, and plants that did germinate had a spindly growth form with small basal stems.

Insecticide Effects on Root Damage and Yield

Mean root maggot damage ratings were significantly lower for plants of all genotypes of B. napus, intergeneric hybrid accessions, and S. alba subjected to applications of insecticide compared with damage to control plants treated only with water (P < 0.05) (Table 2). Mean seed yields for plots of B. napus treated with insecticide significantly exceeded yields from the control plots for both B. napus cv. Delta and cv. Quantum (P < 0.05) (Table 2). Yield improvements resulting from the insecticide application were 25 and 14% for Delta and Quantum, respectively. Yields for plots of intergeneric hybrids BNH-014 and BNH-015 that were treated with insecticide did not differ significantly from the untreated plots (P > 0.05). Yields of S. alba plots were similar and not significantly different for those treated with insecticide compared with the untreated controls (P > 0.05) (Table 2).

Susceptibility of the Gene Mapping Population to Root Maggots and Genetic Mapping of Resistance

In 2000, mean root maggot damage ratings for the accessions from the root maggot gene mapping population ranged from 0 to 3.25 (Fig. 1). For the purposes of this research, genotypes were separated arbitrarily as resistant or susceptible, based on mean root maggot damage rating: genotypes with ratings < 1.0 were considered resistant, and accessions with mean ratings [greater than or equal] 1.0 were considered susceptible. Even though yield loss would be negligible or zero at damage ratings between 1.0 and 2.0 (Dosdall, 1998), our strategy was to be deliberately conservative in assessments of resistance to ensure validity of germplasm classified as resistant. Twelve of 16 accessions were considered resistant, and four accessions were susceptible. Eight of 12 accessions showed a high level of resistance, with mean damage ratings [less than or equal to] 0.20 (Fig. 1).

[FIGURE 1 OMITTED]

In 2001, 69 of 89 genotypes evaluated from the root maggot mapping population were considered resistant, and 20 were scored as susceptible (Fig. 1). Segregation for root maggot damage in the population ranged from highly resistant (mean damage rating = 0) to very susceptible (mean damage = 2.76). The mean root maggot damage for the parents was 0.68 for BHN-014 and 1.20 for B. napus cv. Delta. There were transgressive segregants observed with lower mean root damage than the BHN-014 parent (55% of DH population) (Fig. 1). There were also transgressive segregants with mean root damage that exceeded the B. napus cv. Delta parent (15% of the DH population) (Fig. 1). Twenty-seven accessions showed a high level of resistance, with mean damage ratings [less than or equal to] 0.20. In 2003, 10 of the 12 accessions evaluated were found to express the same phenotype (resistant or susceptible) that was observed in the 2001 assessment (Fig. 2). The susceptible (B. napus cv. Delta) and resistant (BNH-014) parents had similar levels of resistance between years, and B. napus cv. Q2 was rated as susceptible in both 2001 and 2003.

[FIGURE 2 OMITTED]

Significantly more root maggot eggs were deposited per plant on Delta and Q2 than on plants of BNH-014 (P < 0.05: Fig. 2). More root maggot eggs tended to be deposited on plants expressing the susceptible phenotype compared with the resistant phenotype. For example, Accessions 2, 30, and 288 were considered susceptible in the 2001 field evaluation based on high root damage ratings, and in 2003 these genotypes had mean egg numbers ranging from 0.10 to 0.11 per plant. Eggs on genotypes classed as resistant based on the 2001 evaluation had, on average, 50% fewer mean eggs deposited, ranging from 0.03 to 0.07 per plant (Fig. 2). Mean eggs per plant of the three susceptible genotypes differed significantly from those deposited on all resistant genotypes except Accession 108 (P < 0.05: Fig. 2).

Mean basal stem diameter in the mapping population ranged from 2.57 mm ([+ or -] 0.16) to 6.81 mm ([+ or -] 0.50) (Fig. 3). The mean basal stem diameter for the parents was 3.99 mm ([+ or -] 0.31) for BNH-014 and 5.44 mm ([+ or -] 0.32) for B. napus cv. Delta. There was also transgressive segregation observed for either greater or smaller mean basal diameter than the parents. Sixty-seven percent of the population had smaller mean basal diameters than the BNH-014 parent, while only 2% of the population had mean basal diameters greater than the susceptible parent, B. napus cv. Delta (Fig. 3).

[FIGURE 3 OMITTED]

Of the 123 RFLP and R-EST clones screened, 75 detected 135 loci distributed on 18 linkage groups, three pairs, and 27 unlinked markers (Fig. 4). Mapped loci covered a total map distance of approximately 1660 cM. These markers have been used previously to generate genetic maps of B. napus (Sillito et al., 2000) and B. juncea (Mahmood et al., 2003).

[FIGURE 4 OMITTED]

One major QTL, RM-G8, was detected for mean root damage resistance in this cross (Table 3). This QTL, linked to RFLP marker wg1 g6 was present on linkage group G8 and explained 35.9% of the variation (Table 3). Another putative QTL RM-G4 affecting this trait was also detected, however its LOD value was slightly below the threshold of 2 (Table 3). The significance of this putative QTL was confirmed by single factor ANOVA (P = 0.0069)and explained 18.7% of the variation. The BNH-014 alleles at the RM-G8 QTL reduced mean root damage giving resistance against the root maggot attack. At the RM-G4 QTL however, BNH-14 alleles increased mean root damage (Table 3). Interestingly, both RM-G8 and RM-G4 are linked to the same RFLP marker, wg1 g6, located on linkage groups G8 and G4, respectively. The proportion of the total phenotypic variation collectively explained by the two QTLs was 54.6%.

Two QTLs were detected and found to significantly affect the trait of basal stem diameter. The QTLs SD-G8 and SD-G21 together explained 38.9% of the phenotypic variation for mean basal stem diameter. Individually they explained 22.9 and 16% of the variation, respectively (Table 3). BNH-014 alleles at both QTLs contributed to reduce the mean basal shoot diameter.

DISCUSSION

Root maggot infestations had an adverse effect on seed yield of untreated control plants of B. napus. Yields of B. napus plots treated with insecticide were significantly greater by an average of 20% over those of plots treated only with water. No significant yield differences were observed between treated and untreated plots of the BNH intergeneric accessions or S. alba. Dosdall (1998) determined that mean root maggot damage values must exceed levels attained by the BNH intergeneric accessions and S. alba plants before a negative yield effect occurs.

Results of this study indicate that BNH-014 and BNH-015 possess resistance to infestation by root maggots. Although the level of resistance was not as high as that of S. alba, resistance in the intergeneric hybrid accessions was approximately equivalent to that attained in B. napus following application of diazinon. In general, good correspondence occurred from both the oviposition and root damage indices used to evaluate the gene mapping population in 2003. Accessions with low root maggot damage to taproots also had fewest eggs. These data suggest that the mechanism of resistance to Delia spp. was not strongly related to differential larval establishment and survival, but rather appears to involve nonpreference or antixenosis resistance according to Painter (1951) and Kogan and Ortman (1978). Jyoti et al. (2001) reported that S. alba, the source of genetic resistance in our studies, possessed both antibiotic and antixenotic effects on D. radicum. A combination of resistance mechanisms involving both antibiosis and antixenosis may also be involved in our intergeneric germplasm, but further study is needed to validate this aspect.

Two QTLs, RM-G8 and RM-G4, were detected and found to affect root maggot resistance by decreasing the amount of damage sustained by the roots during root maggot infestation. Together, these two QTLs explained 54.6% of the phenotypic variation for this trait. The relatively low LOD score for the RM-G4 QTL in the mapping population may be due to the small population size or scoring anomalies. Interestingly, the RM-G8 and RM-G4 QTLs are linked to the same RFLP marker, wg1 g6, on different linkage groups. The A and C genomes were not differentiated in this study, but it is worth speculating that these QTLs may lie on homeologous segments on the different linkage groups. A QTL, SD-G8, significantly affecting mean basal stem diameter, was detected at the exact location as the RM-G8 QTL for root damage resistance. The strong positive correlation between mean root damage and mean basal stem diameter (r = 0.74) suggests that having smaller stem diameters may confer a selective advantage against root damage caused by root maggots. Dosdall et al. (1996a, 1996b) found that increases in basal stem diameter corresponded with increases in Delia spp. oviposition and damage to taproots, suggesting that females select larger plants for egg deposition, and these plants subsequently suffer more root damage.

Other reports have shown that genetic resistance against insect damage exists in the wild relatives of cultivated Brassicaceae such as B. fruticulosa (Jensen et al., 2002; Pink et al., 2003), B. incana, B. spinescens (Ellis et al., 1999), and S. alba (Dosdall et al., 2000). This report however, is the first one to associate molecular markers with resistance to damage caused by insect infestation in Brassicaceae.

Research results generated in our studies represent significant progress toward producing cultivars of B. napus with resistance to infestation by root maggots. Furthermore, since root maggots are pests of several brassicaceous vegetable crops (e.g., Coaker and Finch, 1971; Ellis, 1988), it should also be possible to introgress these genes for resistance to other species of Brassica. This approach, when completed, would represent a significant enhancement of environmental and economical sustainability because of reduced insecticide use.
Table 1. Mean root maggot damage ratings ([+ or -] SE) of Sinapis
alba x Brassica napus hybrid accessions evaluated from 1996 to 2000
and compared with B. napus cv. Quantum.

                              Mean root maggot damage
                                rating [+ or -] SE

Accession No.           1996 ([dagger])      1997 ([dagger])

BNH-006                        --                   --
BNH-014                0.10 [+ or -] 0.07   1.13 [+ or -] 0.12
BNH-015                0.90 [+ or -] 0.05   1.00 [+ or -] 0.09
BNH-106                0.20 [+ or -] 0.04   0.78 [+ or -] 0.07
BNH-293                        --                   --
BNH-533                        --                   --
BNH-555                        --                   --
BNH-574                        --                   --
B. napus cv. Quantum           --                   --

                               Mean root maggot damage
                                 rating [+ or -] SE

                          1998, Site 1         1998, Site 2
Accession No.              ([dagger])           ([dagger])

BNH-006                1.90 [+ or -] 0.16   0.79 [+ or -] 0.09
BNH-014                1.16 [+ or -] 0.14   1.11 [+ or -] 0.11
BNH-015                1.48 [+ or -] 0.14   0.56 [+ or -] 0.08
BNH-106                1.45 [+ or -] 0.17   1.91 [+ or -] 0.34
BNH-293                        --                   --
BNH-533                2.52 [+ or -] 0.12   1.23 [+ or -] 0.13
BNH-555                1.29 [+ or -] 0.15   0.72 [+ or -] 0.10
BNH-574                        --                   --
B. napus cv. Quantum           --                   --

                               Mean root maggot damage
                                 rating [+ or -] SE

Accession No.                 1999                 2000

BNH-006                1.74 [+ or -] 0.15           --
BNH-014                1.82 [+ or -] 0.13   0.56 [+ or -] 0.17
BNH-015                1.37 [+ or -] 0.14   1.10 [+ or -] 0.28
BNH-106                2.11 [+ or -] 0.15   0.20 [+ or -] 0.13
BNH-293                1.73 [+ or -] 0.13           --
BNH-533                1.88 [+ or -] 0.13           --
BNH-555                1.76 [+ or -] 0.15           --
BNH-574                1.79 [+ or -] 0.41           --
B. napus cv. Quantum   1.45 [+ or -] 0.14   1.68 [+ or -] 0.13

([dagger]) Data reported previously by Dosdall et al. (2000).

Table 2. Mean root maggot damage ratings and seed yields ([+ or -] SE)
for plants of Brassica napus, Sinapis alba, and Sinapis alba x Brassica
napus hybrid accessions subjected to application of either insecticide
or water during the peak period of root maggot activity.

           Accession or                  Mean root maggot
Species      cultivar      Treatment    damage [+ or -] SE

B. napus     'Delta'      water         1.41 [+ or -] 0.07a
                                          ([dagger])
                          insecticide   0.48 [+ or -] 0.08b
            'Quantum'     water         1.69 [+ or -] 0.09a
                          insecticide   0.69 [+ or -] 0.09b
Hybrid       BNH-014      water         0.88 [+ or -] 0.07a
                          insecticide   0.40 [+ or -] 0.03b
             BNH-015      water         1.01 [+ or -] 0.07a
                          insecticide   0.32 [+ or -] 0.08b
Sinapis                   water         0.32 [+ or -] 0.02a
  alba                    insecticide   0.00 [+ or -] 0.00b

                                                              Yield
                                                             change
           Accession or                    Mean yield         with
Species      cultivar      Treatment      [+ or -] SE      insecticide

                                               g                %

B. napus     'Delta'      water         215 [+ or -] 14a
                          insecticide   286 [+ or -] 28b   +24.8
            'Quantum'     water         369 [+ or -] 42a
                          insecticide   429 [+ or -] 55b   +14.0
Hybrid       BNH-014      water         216 [+ or -] 30a
                          insecticide   234 [+ or -] 18a    +7.7
             BNH-015      water         288 [+ or -] 22a
                          insecticide   302 [+ or -] 31a    +4.6
Sinapis                   water         158 [+ or -] 12a
  alba                    insecticide   144 [+ or -] 14a    -9.7

([dagger]) Means within a genotype followed by the same letter
indicate no significant differences using a paired t test analysis.

Table 3. Genetics of QTLs for root damage and basal stem diameter
in a segregating DH population for root maggot resistance.

               QTL
Trait        ([double    Distance                          LODI
([dagger])   dagger])   ([section])   Flanking loci    ([paragraph])

RM           RM-G8          0.0        wg1g6a-wg2b7        4.54
             RM-G4         20.0       z30800b-wg1g6b       1.85
SD           SD-G8          0.0        wg1g6a-wg2b7        2.60
             SD-G21         0.0       ec3d3a-wg6f12c       2.23

                                      Total
               QTL       [sigma]    [sigma]p
Trait        ([double   [p.sup.2]   ([dagger]   Add ([double dagger]
([dagger])   dagger])      (#)      [dagger])     [double dagger])

RM           RM-G8        35.9        54.6           -0.280588
             RM-G4        18.7                        0.209257
SD           SD-G8        22.9        38.9           -0.332981
             SD-G21       16.0                       -0.272472

([dagger]) RM, root damage resistance; SD, basal stem diameter.

([double dagger]) First part of the name of a QTL refers to the trait
(e.g., RM, SD), and the second part (alpha-numeric) to the linkage
group of the genome.

([section]) Distance to QTL from first flanking marker.

([paragraph]) Logarithm of odds.

(#) Phenotypic variance explained by QTL.

([dagger][dagger]) Total phenotypic variance explained by all QTLs.

([double dagger][double dagger]) Additive effect. Negative additive
effect means that BHN-014 alleles reduced damage and increased
resistance; positive additive effect means that the BHN-014 alleles
increased damage at a certain QTL.


Abbreviations: DH, doubled haploid; LOD, logarithm of odds; QTL, quantitative trait locus: RFLP, restriction fragment length polymorphism.

ACKNOWLEDGMENTS

Sincere appreciation is extended to Dr. M. Cohen for critical review of the manuscript. We gratefully acknowledge the assistance of Dr. M. Thiagarajah in generating the DH mapping population, and both P. Conway and N. Cowle for technical assistance in the project.

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U. U. Ekuere, * L. M. Dosdall, M. Hills, A. B. Keddie, L. Kott, and A. Good

U.U. Ekuere, M. Hills, A.B. Keddie, and A. Good, Dep. of Biological Sciences, Univ. of Alberta, Edmonton, AB, Canada T6G 2E9; L.M. Dosdall, Dep. of Agricultural, Food and Nutritional Science, Univ. of Alberta, Edmonton, AB, Canada T6G 2P5; L. Kott, Crop Science Dep., Univ. of Guelph, Guelph, ON, Canada NIG 2W1. The Alberta Agricultural Research Institute, the Natural Sciences and Engineering Research Council of Canada, Alberta Agriculture, Food and Rural Development, and the University of Alberta funded this research. Received 24 Feb. 2004. * Corresponding author (uekuere@ualberta.ca).
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Title Annotation:Genomics, Molecular Genetics & Biotechnology
Author:Ekuere, U.U.; Dosdall, L.M.; Hills, M.; Keddie, A.B.; Kott, L.; Good, A.
Publication:Crop Science
Geographic Code:1CANA
Date:Jan 1, 2005
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