# Heterotic parameterizations of crosses between tropical and temperate lines of popcorn.

Introduction

Popcorn is quite popular in Brazil, and the crop area required for its growth has been expanding mainly due to the increased consumption of this product and of industrialized derivatives (CATAPATTI et al., 2008; FREITAS JUNIOR et al., 2009; RANGEL et al. 2008; RINALDI et al., 2007; SCAPIM et al., 2002). However, production can be considered low with respect to the vast market potential of this crop (ARNHOLD et al., 2009).

One of the limiting factors for increasing the yield of this crop is that there are very few cultivars that have both favorable agronomic traits and high popping expansion (FREITAS JUNIOR et al., 2009; MIRANDA et al., 2003; RINALDI et al., 2007). Currently, only four hybrids (IAC 112, IAC 125, Zelia and Jade) and three varieties (BRS ANGELA, RS 20 and UFVM2-Barao de Vicosa) are recommended and/or registered by the National System for Protection of Cultivars of the Ministry of Agriculture, Livestock and Supply (PACHECO et al., 2000; RANGEL et al., 2008; SAWAZAKI, 2001; SCAPIM et al., 2002, 2010; TRINDADE et al., 2010; VIEIRA et al., 2009).

Though rare, diallel studies of popcorn in Brazil have been nearly exclusively done with crosses between varieties (ANDRADE et al., 2002; FREITAS JUNIOR et al., 2006; MIRANDA et al., 2008; RANGEL et al., 2008; SCAPIM et al., 2002, 2006; ZANETTE, 1989). Miranda et al. (2008), working with five genitors in a diallel cross with advanced generations of hybrids (IAC 112 and Zelia) and three varieties (RS 20, Branco and SAM), concluded the following: a) there is sufficient variability in Brazilian lines to allow for exploration of the non-additive effects for grain production, and b) there is little possibility of obtaining commercial varieties directly from local varieties because local varieties have poor popping expansion. Consequently, developing popcorn line hybrids can be considered a relevant strategy for crop improvement programs (MIRANDA et al., 2008; RANGEL et al., 2008; SILVA et al., 2010; VIEIRA et al., 2009).

To date, popcorn hybrids have not been evaluated in Brazil by diallel cross analysis. For hybrid production, the few existing published studies have been based on testcrosses to infer the combining capacity of lines at generations [S.sub.3], [S.sub.5] and/or [S.sub.6] (SAWAZAKI et al., 2000; SEIFERT et al., 2006; VIANA et al., 2007). For this reason, we decided to determine the heterotic parameterizations of diallel crosses between 10 inbred lines of popcorn derived from tropical, subtropical and temperate zone genotypes. Experiments were conducted in two different environments, examining five agronomic characteristics in total.

Material and methods

Ten pre-selected lines, originating from tropical, temperate and subtropical genotypes (Table 1), were crossed in a complete diallel scheme resulting in 45 [F.sub.1] hybrids. In March 2007, seeds of the inbred lines were planted with a spacing of 0.9 m between rows and 0.4 m between plants in the row to obtain the hybrids. Pollen grains for the crosses between lines were collected in brown paper bags during flowering.

In November 2007, two trials were run in the following environments: i) in the experimental fields of the Colegio Estadual 'Antonio Sarlo', in the municipality of Campos dos Goytacazes, in the northern region of Rio de Janeiro State (21[degrees] 45' south latitude, 41[degrees] 20' W longitude and 11 m altitude), and ii) in the experimental fields of PESAGRO-RIO, in the municipality of Itaocara, in the northeastern region of the state of Rio de Janeiro (21[degrees] 39' 12" south latitude, 42[degrees] 04' 36" W longitude and 60 m altitude), 120 km away from Campos dos Goytacazes.

In both fields, the trials were carry out in a complete block experimental design with three replications. The treatments were the 45 F1 hybrids and the 10 genitor lines. Randomization of the treatments was done separately for the group of inbred lines and for the group of hybrids so that the hybrids and inbred lines were not in neighboring plots, avoiding competition effects. The experimental plots consisted of planted rows 10.0 m long with 0.90 m spacing between rows and 0.20 m spacing between plants.

Several agronomic traits were evaluated, including the following: i) grain yield (GY), for which ears were harvested by hand in each parcel, and the production values were corrected to a standardized humidity of 15% and transformed into kg [ha.sup.-1], ii) mean plant height (PH), in m, of the point of insertion of the flag leaf in six competitive plants within the parcel, iii) ear height (EH), in m, in the same six plants per parcel, and iv) days to silking (FL). Popping expansion (PE), in mL [g.sup.-1], was also evaluated and estimated for a sample of 30.0 g of grains that were popped in a microwave oven (Panasonic, model NN-S65B) at 1000 W for 3 min. Six replications were conducted per treatment. The grains submitted to the popping test were taken from the central-basal part of the corn ears. These samples, and the 1.0 kg standard sample, were maintained in a cool, dry storage chamber. The expansion capacity estimate was made when the standard sample reached 14% humidity.

Analysis of the diallel was done using model II of Gardner and Eberhart (1966), with adaptations proposed by Morais et al. (1991) for analyses in various environments according to the statistical model.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

"Where: [Y.sub.ijj'] is the mean of the inbred lines if j = j' and of the cross if j [not equal to] j', in the ith environment; [e.sub.i] is the environmental effect; [ev.sub.ij] and [ev.sub.ij'] are the effects of the interaction environment x inbred lines, and h is the mean heterosis effect; hi is the effect of the environment x mean heterosis; [h.sub.j] and [h.sub.j'] are the heterosis effects of the inbred lines; [eh.sub.ij] and [eh.sub.ij'] are the effects of the interaction environment x inbred lines heterosis; [s.sub.ij'] is the effect of specific heterosis; and [es.sub.ijj'] is the effect of the interaction environment x specific heterosis. The parameters of the model are defined by analogy to the model of Gardner and Eberhart (1966), in which for j = j', we have [theta] = 0 and for j [not equal to] j', [theta] = 1. The statistical analyses were done with the program GENES (CRUZ, 2006).

Results and discussion

The sources of variation genotype, inbred lines and heterosis had significant effects for all traits based on the F test (Table 2). With regard to the source of variation inbred lines, significant mean squares indicated that the lines did not constitute a uniform group, differing in the general combining capacity. The significant effect of heterosis demonstrates that heterosis affects the general combining capacity.

Separation of source of variation of heterosis revealed significant mean heterosis values for all of the traits, indicating that there is sufficient genetic divergence among the inbred lines that were evaluated to allow for genetic improvement. Inbred lines heterosis did not significantly affect PE, indicating that the lines were not significantly different for this trait. Among the other traits, the finding of most significance demonstrated that at least some of the genitors were different from each other in terms of mean genetic frequencies or in the degree of dispersion of these frequencies.

When specific heterosis was evaluated, it was found that only PE did not differ significantly, which demonstrates that these heterotic effects are not favorable for the synthesis of superior hybrids. This conclusion is similar to that of former studies that demonstrated the superiority of additivity for PE (DOFING et al., 1991; FREITAS JUNIOR et al., 2006; LARISH; BREWBAKER, 1999; LYERLY, 1942; PACHECO et al., 1998; PEREIRA; AMARAL JUNIOR, 2001; RANGEL et al., 2008; SCAPIM et al., 2006; SIMON et al., 2004; VIANA; MATTA, 2003).

However, it is important to understand that the lack of importance of heterosis for PE does not impede the ability to obtain superior hybrid combinations because if one has lines with elevated CE, due to successive expression of additivity in a series of selfings, this same additivity will help the hybrid express the mean of the estimates of PE in the genitor inbred lines.

Analysis of the sources of environmental variation, including genotype x environment, inbred lines and heterosis x environment interactions gave significant values for all traits but PE (Table 2). Alexander and Creech (1977) indicated that inheritance of PE is polygenic with little environmental influence. When heterosis was partition in mean heterosis x environments, inbred lines heterosis x environments and specific heterosis x environments, the following results were found: i) in mean heterosis x environments, only GY was significantly affected, and ii) in inbred lines heterosis x environments and specific heterosis x environments, only PE was not significantly affected.

For grain yield, the inbred lines [P.sub.3], [P.sub.5], [P.sub.2] and [P.sub.4] were the most promising per se for use due to the high values expressed for the [V.sub.i] estimate (Table 3). Despite the reduced values, the characteristics PH and EH had higher magnitudes of [V.sub.i] for the inbred lines [P.sub.4] and [P.sub.5], indicating that these lines contributed to increases in the value of this trait. On the other hand, considering the interest in the reduction of plant size and height of the first ear because of the high winds that are common in Campos dos Goytacazes and Itaocara, the line with the best performance per se was [P.sub.1]. Although [P.sub.7] also resulted in negative values for both traits, they were of low magnitude (Table 3).

Inbred Lines [P.sub.4] and [P.sub.9] stood out as being exceptional for the FL trait because they gave high negative values for the estimate [V.sub.i], which revealed potential for reducing the number of days to flowering in intrapopulational breeding programs. Six Inbred lines gave negative estimates of [V.sub.i] for PE, including the following: [P.sub.1], [P.sub.3], [P.sub.4], [P.sub.5], [P.sub.6], and [P.sub.7]. Based on these results, a direct relation between [g.sub.i] and [V.sub.i] was made clear, especially for traits that were little influenced by the effects of dominance, such as PE, in which dominance contributed only 10% towards total inherent heterosis of the sum of squares of the genotypes.

We can affirm that inbred lines P2, P3, P4 and P5 were the most promising for the greatest number of traits, especially for grain yield. Nevertheless, these inbred lines did not have good values for PE, demonstrating that the best genitors for production are not the best for grain quality.

In terms of the amplitude of variation in the effects of genitors and between genitors, it can be concluded that the genitors differ when the amplitude of variation is greater than twice the standard deviation; that is, there is genetic variability between the inbred lines (SINGH; CHAUDHARY, 1985). The characteristics PH, EH and PE had differences greater than two. Characteristic GY gave the lowest value (0.0202). This leads to the idea that allelic complementations contributed more than differences between the inbred lines for heterotic expression of these characteristics.

The characteristic GY gave high positive values for mean heterosis, demonstrating the expected hybrid vigor. FL gave negative heterosis values, demonstrating the possibility of selecting for precocity (Table 4). On the other hand, the mean negative heterosis for PE indicated that genetic improvement through heterosis of these inbred lines will not be viable. Consequently, it is necessary to follow the premise of Scapim et al. (2006), who indicated that when there is a low level of heterosis predictions about the hybrid should be made based on a mean of the genitors.

In the case of GY, for which there were environmental effects both for the inbred lines and for heterosis and its components, an indication of genitors for producing hybrids based on the performance of inbred lines heterosis is a fragile strategy, especially when the participation of this effect in total heterosis is markedly inferior. This became clear when the sum of squares of the inbred lines heterosis contributed only 2.03% to the sum of squares of total heterosis. Consequently, the logical strategy for this characteristic is to choose genitors for crosses based on estimates of [V.sub.i] because it is clear that genetic divergence strongly contributes to the expression of hybrid vigor.

For PH and EH, the positive values for the estimates of mean heterosis can be explained by the higher percentage of the contribution of the sum of the genotypes to the sum of squares of total heterosis. Examining the environments together, 70.90 and 62.05%, respectively, of the sum of the squares effects of total heterosis of PH and EH contributed to the sum of squares of the genotypes. This degree of heterotic expression makes it difficult to produce hybrids with reduced ear insertion height. When we examined the number of days to flowering, the inbred lines with negative values for the estimate [h.sub.i], including: [P.sub.2], [P.sub.3], [P.sub.4], [P.sub.6] and [P.sub.9], tended to promote precocity in the resulting hybrids.

For grain yield, the expectations for the best hybrids were based on the most highly positive estimates of [S.sub.ij], which were found in the following: [P.sub.1] x [P.sub.9], [P.sub.2] x [P.sub.9], [P.sub.3] x [P.sub.7], [P.sub.5] x [P.sub.9], and [P.sub.6] x [P.sub.7] (Table 5).

By associating the characteristics PH and EH, it was found that the most promising combinations were [P.sub.6] x [P.sub.9], [P.sub.2] x [P.sub.8], [P.sub.1] x [P.sub.7] and [P.sub.2] x [P.sub.4] because they gave high negative values for the estimate [S.sub.ij]. For the characteristic FL, the combinations that gave the highest negative values for the estimate [S.sub.ij], were the following: [P.sub.6] x [P.sub.9], [P.sub.1] x [P.sub.4], [P.sub.1] x [P.sub.8] and [P.sub.7] x [P.sub.8].

Conclusion

The inbred lines did not have good values "per se" for popping expansion, demonstrating that the best genitors for production are not the best for grain yield. The hybrids [P.sub.1] x [P.sub.3] and [P.sub.2] x [P.sub.4] had the best responses for the grain yield and popping expansion.

DOI: 10.4025/actasciagron.v33i2.9607

Acknowledgements

We thank UENF for supplying a scholarship, and Faperj and CNPq for financial support for the field studies and laboratory analyses.

References

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Received on March 11, 2010.

Accepted on May 13, 2010.

Vanessa Quitete Ribeiro da Silva (1), Antonio Teixeira do Amaral JUnior (1) *, Leandro Simoes Azeredo Goncalves (1), Silverio de Paiva Freitas JUnior (1) and Rodrigo Moreira Ribeiro (1)

(1) Centro de Ciencias e Tecnologias Agropecuarias, Universidade Estadual do Norte Fluminense "Darcy Ribeiro", Rua Alberto Lamego , 2000, 28013-620, Campos dos Goytacazes, Rio de Janeiro, Brazil. * Author for correspondence. E-mail: amaraljr@uenf.br

Popcorn is quite popular in Brazil, and the crop area required for its growth has been expanding mainly due to the increased consumption of this product and of industrialized derivatives (CATAPATTI et al., 2008; FREITAS JUNIOR et al., 2009; RANGEL et al. 2008; RINALDI et al., 2007; SCAPIM et al., 2002). However, production can be considered low with respect to the vast market potential of this crop (ARNHOLD et al., 2009).

One of the limiting factors for increasing the yield of this crop is that there are very few cultivars that have both favorable agronomic traits and high popping expansion (FREITAS JUNIOR et al., 2009; MIRANDA et al., 2003; RINALDI et al., 2007). Currently, only four hybrids (IAC 112, IAC 125, Zelia and Jade) and three varieties (BRS ANGELA, RS 20 and UFVM2-Barao de Vicosa) are recommended and/or registered by the National System for Protection of Cultivars of the Ministry of Agriculture, Livestock and Supply (PACHECO et al., 2000; RANGEL et al., 2008; SAWAZAKI, 2001; SCAPIM et al., 2002, 2010; TRINDADE et al., 2010; VIEIRA et al., 2009).

Though rare, diallel studies of popcorn in Brazil have been nearly exclusively done with crosses between varieties (ANDRADE et al., 2002; FREITAS JUNIOR et al., 2006; MIRANDA et al., 2008; RANGEL et al., 2008; SCAPIM et al., 2002, 2006; ZANETTE, 1989). Miranda et al. (2008), working with five genitors in a diallel cross with advanced generations of hybrids (IAC 112 and Zelia) and three varieties (RS 20, Branco and SAM), concluded the following: a) there is sufficient variability in Brazilian lines to allow for exploration of the non-additive effects for grain production, and b) there is little possibility of obtaining commercial varieties directly from local varieties because local varieties have poor popping expansion. Consequently, developing popcorn line hybrids can be considered a relevant strategy for crop improvement programs (MIRANDA et al., 2008; RANGEL et al., 2008; SILVA et al., 2010; VIEIRA et al., 2009).

To date, popcorn hybrids have not been evaluated in Brazil by diallel cross analysis. For hybrid production, the few existing published studies have been based on testcrosses to infer the combining capacity of lines at generations [S.sub.3], [S.sub.5] and/or [S.sub.6] (SAWAZAKI et al., 2000; SEIFERT et al., 2006; VIANA et al., 2007). For this reason, we decided to determine the heterotic parameterizations of diallel crosses between 10 inbred lines of popcorn derived from tropical, subtropical and temperate zone genotypes. Experiments were conducted in two different environments, examining five agronomic characteristics in total.

Material and methods

Ten pre-selected lines, originating from tropical, temperate and subtropical genotypes (Table 1), were crossed in a complete diallel scheme resulting in 45 [F.sub.1] hybrids. In March 2007, seeds of the inbred lines were planted with a spacing of 0.9 m between rows and 0.4 m between plants in the row to obtain the hybrids. Pollen grains for the crosses between lines were collected in brown paper bags during flowering.

In November 2007, two trials were run in the following environments: i) in the experimental fields of the Colegio Estadual 'Antonio Sarlo', in the municipality of Campos dos Goytacazes, in the northern region of Rio de Janeiro State (21[degrees] 45' south latitude, 41[degrees] 20' W longitude and 11 m altitude), and ii) in the experimental fields of PESAGRO-RIO, in the municipality of Itaocara, in the northeastern region of the state of Rio de Janeiro (21[degrees] 39' 12" south latitude, 42[degrees] 04' 36" W longitude and 60 m altitude), 120 km away from Campos dos Goytacazes.

In both fields, the trials were carry out in a complete block experimental design with three replications. The treatments were the 45 F1 hybrids and the 10 genitor lines. Randomization of the treatments was done separately for the group of inbred lines and for the group of hybrids so that the hybrids and inbred lines were not in neighboring plots, avoiding competition effects. The experimental plots consisted of planted rows 10.0 m long with 0.90 m spacing between rows and 0.20 m spacing between plants.

Several agronomic traits were evaluated, including the following: i) grain yield (GY), for which ears were harvested by hand in each parcel, and the production values were corrected to a standardized humidity of 15% and transformed into kg [ha.sup.-1], ii) mean plant height (PH), in m, of the point of insertion of the flag leaf in six competitive plants within the parcel, iii) ear height (EH), in m, in the same six plants per parcel, and iv) days to silking (FL). Popping expansion (PE), in mL [g.sup.-1], was also evaluated and estimated for a sample of 30.0 g of grains that were popped in a microwave oven (Panasonic, model NN-S65B) at 1000 W for 3 min. Six replications were conducted per treatment. The grains submitted to the popping test were taken from the central-basal part of the corn ears. These samples, and the 1.0 kg standard sample, were maintained in a cool, dry storage chamber. The expansion capacity estimate was made when the standard sample reached 14% humidity.

Analysis of the diallel was done using model II of Gardner and Eberhart (1966), with adaptations proposed by Morais et al. (1991) for analyses in various environments according to the statistical model.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

"Where: [Y.sub.ijj'] is the mean of the inbred lines if j = j' and of the cross if j [not equal to] j', in the ith environment; [e.sub.i] is the environmental effect; [ev.sub.ij] and [ev.sub.ij'] are the effects of the interaction environment x inbred lines, and h is the mean heterosis effect; hi is the effect of the environment x mean heterosis; [h.sub.j] and [h.sub.j'] are the heterosis effects of the inbred lines; [eh.sub.ij] and [eh.sub.ij'] are the effects of the interaction environment x inbred lines heterosis; [s.sub.ij'] is the effect of specific heterosis; and [es.sub.ijj'] is the effect of the interaction environment x specific heterosis. The parameters of the model are defined by analogy to the model of Gardner and Eberhart (1966), in which for j = j', we have [theta] = 0 and for j [not equal to] j', [theta] = 1. The statistical analyses were done with the program GENES (CRUZ, 2006).

Results and discussion

The sources of variation genotype, inbred lines and heterosis had significant effects for all traits based on the F test (Table 2). With regard to the source of variation inbred lines, significant mean squares indicated that the lines did not constitute a uniform group, differing in the general combining capacity. The significant effect of heterosis demonstrates that heterosis affects the general combining capacity.

Separation of source of variation of heterosis revealed significant mean heterosis values for all of the traits, indicating that there is sufficient genetic divergence among the inbred lines that were evaluated to allow for genetic improvement. Inbred lines heterosis did not significantly affect PE, indicating that the lines were not significantly different for this trait. Among the other traits, the finding of most significance demonstrated that at least some of the genitors were different from each other in terms of mean genetic frequencies or in the degree of dispersion of these frequencies.

When specific heterosis was evaluated, it was found that only PE did not differ significantly, which demonstrates that these heterotic effects are not favorable for the synthesis of superior hybrids. This conclusion is similar to that of former studies that demonstrated the superiority of additivity for PE (DOFING et al., 1991; FREITAS JUNIOR et al., 2006; LARISH; BREWBAKER, 1999; LYERLY, 1942; PACHECO et al., 1998; PEREIRA; AMARAL JUNIOR, 2001; RANGEL et al., 2008; SCAPIM et al., 2006; SIMON et al., 2004; VIANA; MATTA, 2003).

However, it is important to understand that the lack of importance of heterosis for PE does not impede the ability to obtain superior hybrid combinations because if one has lines with elevated CE, due to successive expression of additivity in a series of selfings, this same additivity will help the hybrid express the mean of the estimates of PE in the genitor inbred lines.

Analysis of the sources of environmental variation, including genotype x environment, inbred lines and heterosis x environment interactions gave significant values for all traits but PE (Table 2). Alexander and Creech (1977) indicated that inheritance of PE is polygenic with little environmental influence. When heterosis was partition in mean heterosis x environments, inbred lines heterosis x environments and specific heterosis x environments, the following results were found: i) in mean heterosis x environments, only GY was significantly affected, and ii) in inbred lines heterosis x environments and specific heterosis x environments, only PE was not significantly affected.

For grain yield, the inbred lines [P.sub.3], [P.sub.5], [P.sub.2] and [P.sub.4] were the most promising per se for use due to the high values expressed for the [V.sub.i] estimate (Table 3). Despite the reduced values, the characteristics PH and EH had higher magnitudes of [V.sub.i] for the inbred lines [P.sub.4] and [P.sub.5], indicating that these lines contributed to increases in the value of this trait. On the other hand, considering the interest in the reduction of plant size and height of the first ear because of the high winds that are common in Campos dos Goytacazes and Itaocara, the line with the best performance per se was [P.sub.1]. Although [P.sub.7] also resulted in negative values for both traits, they were of low magnitude (Table 3).

Inbred Lines [P.sub.4] and [P.sub.9] stood out as being exceptional for the FL trait because they gave high negative values for the estimate [V.sub.i], which revealed potential for reducing the number of days to flowering in intrapopulational breeding programs. Six Inbred lines gave negative estimates of [V.sub.i] for PE, including the following: [P.sub.1], [P.sub.3], [P.sub.4], [P.sub.5], [P.sub.6], and [P.sub.7]. Based on these results, a direct relation between [g.sub.i] and [V.sub.i] was made clear, especially for traits that were little influenced by the effects of dominance, such as PE, in which dominance contributed only 10% towards total inherent heterosis of the sum of squares of the genotypes.

We can affirm that inbred lines P2, P3, P4 and P5 were the most promising for the greatest number of traits, especially for grain yield. Nevertheless, these inbred lines did not have good values for PE, demonstrating that the best genitors for production are not the best for grain quality.

In terms of the amplitude of variation in the effects of genitors and between genitors, it can be concluded that the genitors differ when the amplitude of variation is greater than twice the standard deviation; that is, there is genetic variability between the inbred lines (SINGH; CHAUDHARY, 1985). The characteristics PH, EH and PE had differences greater than two. Characteristic GY gave the lowest value (0.0202). This leads to the idea that allelic complementations contributed more than differences between the inbred lines for heterotic expression of these characteristics.

The characteristic GY gave high positive values for mean heterosis, demonstrating the expected hybrid vigor. FL gave negative heterosis values, demonstrating the possibility of selecting for precocity (Table 4). On the other hand, the mean negative heterosis for PE indicated that genetic improvement through heterosis of these inbred lines will not be viable. Consequently, it is necessary to follow the premise of Scapim et al. (2006), who indicated that when there is a low level of heterosis predictions about the hybrid should be made based on a mean of the genitors.

In the case of GY, for which there were environmental effects both for the inbred lines and for heterosis and its components, an indication of genitors for producing hybrids based on the performance of inbred lines heterosis is a fragile strategy, especially when the participation of this effect in total heterosis is markedly inferior. This became clear when the sum of squares of the inbred lines heterosis contributed only 2.03% to the sum of squares of total heterosis. Consequently, the logical strategy for this characteristic is to choose genitors for crosses based on estimates of [V.sub.i] because it is clear that genetic divergence strongly contributes to the expression of hybrid vigor.

For PH and EH, the positive values for the estimates of mean heterosis can be explained by the higher percentage of the contribution of the sum of the genotypes to the sum of squares of total heterosis. Examining the environments together, 70.90 and 62.05%, respectively, of the sum of the squares effects of total heterosis of PH and EH contributed to the sum of squares of the genotypes. This degree of heterotic expression makes it difficult to produce hybrids with reduced ear insertion height. When we examined the number of days to flowering, the inbred lines with negative values for the estimate [h.sub.i], including: [P.sub.2], [P.sub.3], [P.sub.4], [P.sub.6] and [P.sub.9], tended to promote precocity in the resulting hybrids.

For grain yield, the expectations for the best hybrids were based on the most highly positive estimates of [S.sub.ij], which were found in the following: [P.sub.1] x [P.sub.9], [P.sub.2] x [P.sub.9], [P.sub.3] x [P.sub.7], [P.sub.5] x [P.sub.9], and [P.sub.6] x [P.sub.7] (Table 5).

By associating the characteristics PH and EH, it was found that the most promising combinations were [P.sub.6] x [P.sub.9], [P.sub.2] x [P.sub.8], [P.sub.1] x [P.sub.7] and [P.sub.2] x [P.sub.4] because they gave high negative values for the estimate [S.sub.ij]. For the characteristic FL, the combinations that gave the highest negative values for the estimate [S.sub.ij], were the following: [P.sub.6] x [P.sub.9], [P.sub.1] x [P.sub.4], [P.sub.1] x [P.sub.8] and [P.sub.7] x [P.sub.8].

Conclusion

The inbred lines did not have good values "per se" for popping expansion, demonstrating that the best genitors for production are not the best for grain yield. The hybrids [P.sub.1] x [P.sub.3] and [P.sub.2] x [P.sub.4] had the best responses for the grain yield and popping expansion.

DOI: 10.4025/actasciagron.v33i2.9607

Acknowledgements

We thank UENF for supplying a scholarship, and Faperj and CNPq for financial support for the field studies and laboratory analyses.

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Received on March 11, 2010.

Accepted on May 13, 2010.

Vanessa Quitete Ribeiro da Silva (1), Antonio Teixeira do Amaral JUnior (1) *, Leandro Simoes Azeredo Goncalves (1), Silverio de Paiva Freitas JUnior (1) and Rodrigo Moreira Ribeiro (1)

(1) Centro de Ciencias e Tecnologias Agropecuarias, Universidade Estadual do Norte Fluminense "Darcy Ribeiro", Rua Alberto Lamego , 2000, 28013-620, Campos dos Goytacazes, Rio de Janeiro, Brazil. * Author for correspondence. E-mail: amaraljr@uenf.br

Table 1. Origin of the popcorn inbred lines. Parental inbreds Description of the population which the inbred were obtained [P.sub.1] (PR 023) from the three-way hybrid 'Zelia', which belongs to Pioneer Seeds, and consists of temperate and tropical inbreds [P.sub.2] (PR 024) from the composite of yellow grains 'CMS- 42', which belongs to Embrapa-Maize and Sorghum, and consists of tropical inbreds [P.sub.3] (PR 036) from the composite of white grains 'CMS-42', which belongs to Embrapa-Maize and Sorghum, and consists of tropical inbreds [P.sub.4] (UEM J1) from South American races of tropical regions [P.sub.5] (PR 045-1) from the three-way hybrid 'Zaeli', [P.sub.6] (PR 045-2) which consists of [P.sub.7] (PR 045-3) temperate inbreds [P.sub.8] (PR 087-1) from the modified one-way hybrid 'IAC112', adapted [P.sub.9] (PR 087-2) to tropical regions, and which consists of inbreds [P.sub.10] (PR 087-3) from the open pollinated variety 'South Americam Mushroom' with inbreds from the South American interparietal hybrid 'Guarani' x 'Amarela' Table 2. Combined analysis of variance of the five traits, using the methodology of Gardner and Eberhart (1966), in a diallel cross between 10 popcorn inbred lines. Campos dos Goytacazes and Itaocara, Rio de Janeiro State. Source of variation df Mean square of traits (1) GY Genotypes (G) 54 3294181.2991 ** Inbred Lines (L) 9 8013436.3216 ** Heterosis (H) 45 2350330.2946 ** Mean Heterosis (M) 1 55323786.1878 ** Inbred Lines Heterosis (IL) 9 2383559.1237 ** Specific Heterosis (S) 35 828258.4273 ** Environment (E) 1 7015589.8315 ** G x E 54 457732.9609 ** L x E 9 608958.3015 ** H x E 45 427487.8927 ** M. Heterosis x E 1 3825176.2117 ** IL. Heterosis x E 9 212041.4128 ** S. Heterosis x E 35 385811.6070 ** Error 216 83668.8350 Source of variation Mean square of traits (1) PH EH Genotypes (G) 0.2715 ** 0.1159 ** Inbred Lines (L) 0.4740 ** 0.2637 ** Heterosis (H) 0.2310 ** 0.0863 ** Mean Heterosis (M) 0.9500 ** 0.6530 ** Inbred Lines Heterosis (IL) 0.1430 ** 0.0370 ** Specific Heterosis (S) 0.2331 ** 0.0829 ** Environment (E) 14.8952 ** 2.1749 ** G x E 0.1765 ** 0.0597 ** L x E 0.1407 ** 0.0499 ** H x E 0.1837 ** 0.0616 ** M. Heterosis x E 0.0015n.(n.s.) 0.0233 (n.s.) IL. Heterosis x E 0.0914 ** 0.0390 ** S. Heterosis x E 0.2126 ** 0.0685 ** Error 0.0250 0.0080 Source of variation Mean square of traits (1) FL PE Genotypes (G) 136.5277 ** 5.9008 ** Inbred Lines (L) 57.9929 ** 31.7997 ** Heterosis (H) 152.2347 ** 0.7211 ** Mean Heterosis (M) 2413.6706 ** 12.7574 ** Inbred Lines Heterosis (IL) 28.5926 ** 0.3991 (n.s) Specific Heterosis (S) 119.4159 ** 0.4599 (n.s) Environment (E) 84.5830 ** 0.0318 (n.s) G x E 112.8340 ** 0.0941 (n.s) L x E 121.8820 ** 0.0700 (n.s) H x E 111.0244 ** 0.0989 (n.s) M. Heterosis x E 8.4162 (n.s.) 0.8849 (n.s) IL. Heterosis x E 51.5329 ** 0.1884 (n.s) S. Heterosis x E 129.2539 ** 0.0535 (n.s) Error 4.5100 0.3514 (1) GY = Grain Yield; PH = Plant Height; EH = Ear Height; FL = Days to silking; and PE = popping expansion. (ns) = not significant (p > 0.05); ** = significant at p < 0.01; * = significant at p [less than or equal to] 0.05. Table 3. Estimates of the means of the inbred lines effects ([V.sub.1]) and the corresponding standard deviations (SD), using the methodology of Gardner and Eberhart (1966), for five traits evaluated in 10 popcorn inbred lines. Campos dos Goytacazes and Itaocara, Rio de Janeiro State. Inbred Lines Traits (2) effects ([V.sub.1]) (1) GY PH EH FL P1 -786.7490 -0.5400 -0.3460 1.4325 P2 318.2510 0.1420 0.0240 -0.0675 P3 339.9160 -0.0900 0.0340 -0.2325 P4 267.4160 0.1620 0.1240 -0.5675 P5 324.0810 0.1670 0.1190 -0.0675 P6 -14.2540 -0.0400 0.0090 1.1025 P7 -350.9140 -0.0900 -0.1160 -0.3975 P8 159.0860 0.1570 0.0990 -0.4025 P9 -212.5840 0.1070 0.0590 -0.5675 P10 -44.2490 0.0420 -0.0060 -0.2325 Mean 1475.0840 1.8930 1.0910 60.0675 SD (Mean) 2788.9611 0.0008 0.0003 0.1503 SD ([V.sub.1]) 25100.6505 0.0075 0.0024 1.3530 sd([V.sub.1]-[V.sub.j]) 55779.2233 0.0166 0.0053 3.0060 Inbred Lines Traits (2) effects ([V.sub.1]) (1) PE P1 -0.7280 P2 1.1453 P3 -1.0880 P4 -0.8113 P5 -1.3113 P6 -1.1213 P7 -1.3213 P8 2.4120 P9 1.3287 P10 1.4953 Mean 33.1710 SD (Mean) 0.0117 SD ([V.sub.1]) 0.1054 sd([V.sub.1]-[V.sub.j]) 0.2342 (1) [P.sub.1] = PR 023; [P.sub.2] = PR 024; [P.sub.3] = PR 036; [P.sub.4] = UEM J1; [P.sub.5] = PR 045-1; [P.sub.6] = PR 045-2; [P.sub.7] = PR 045-3; [P.sub.8] = PR 087-1; [P.sub.9] = PR 087-2; [P.sub.10] = PR 087-3. (2) GY = Grain Yield; PH = Plant Height; EH = Ear Height; FL = Days to silking; and PE = popping expansion. Table 4. Estimates of mean heterosis ([bar.h]), and inbred lines ([[??].sub.i]) effects, and the corresponding standard deviations (SD), using the methodology of Gardner and Eberhart (1966), for five traits evaluated in 10 popcorn inbred lines. Campos dos Goytacazes and Itaocara, Rio de Janeiro State. Effects Traits (2) GY PH EH FL Mean Heterosis ([bar.h]) 1061.5866 0.1391 0.1153 -7.0119 SD ([bar.h]) 3408.7300 0.0010 0.0003 0.1837 Inbred lines Heterosis ([[bar.h].sub.I]) (1) P1 265.6626 0.1966 0.0728 0.8675 P2 369.2026 0.0573 0.0459 -0.257 P3 515.3720 0.0441 0.0084 -0.446 P4 525.8713 0.0529 0.0515 -0.153 P5 -441.316 -0.0965 -0.0635 1.7630 P6 -492.148 -0.1033 -0.0547 -2.57 P7 -86.1942 0.0123 0.0103 0.7400 P8 -171.421 -0.0321 -0.0103 1.3470 P9 -254.857 -0.1102 -0.0585 -1.67 P10 -230.17 -0.0208 -0.0016 0.3862 SD ([V.sub.i]) 9412.7439 0.0028 0.0009 0.5073 SD (V.sub.i]--V.sub.j]) 20917.2080 0.0062 0.0020 1.1270 Effects Traits (2) PE Mean Heterosis ([bar.h]) -0.5098 SD ([bar.h]) 0.0143 Inbred lines Heterosis ([[bar.h].sub.I]) (1) P1 -- P2 -- P3 -- P4 -- P5 -- P6 -- P7 -- P8 -- P9 -- P10 -- SD ([V.sub.i]) -- SD (V.sub.i]--V.sub.j]) -- (1) [P.sub.1] = PR 023; [P.sub.2] = PR 024; [P.sub.3] = PR 036; [P.sub.4] = UEM J1; [P.sub.5] = PR 045-1; [P.sub.6] = PR 045-2; [P.sub.7] = PR 045-3; [P.sub.8] = PR 087-1; [P.sub.9] = PR 087-2; Pw = PR 087-3. (2) GY = Crop Yield; PH = Plant Height; EH = Ear Height; FL = Days to silking; and PE = popping expansion. Table 5. Estimates of the effects of specific heterosis ([S.sub.ij]) and corresponding standard deviation (SD), using the methodology of Gardner and Eberhart (1966), for four characteristics evaluated in 45 [F.sub.1] hybrids. Campos dos Goytacazes and Itaocara, Rio de Janeiro State. Genotypes (1) Traits (2) RG AP AE P1 x P2 -148.9510 0.0395 -0.0080 P1 x P3 222.3763 0.0526 0.0435 P1 x P4 -171.8730 -0.1110 -0.0640 P1 x P5 243.6519 0.0257 -0.0020 P1 x P6 60.3169 0.0926 0.0491 P1 x P7 -590.6420 -0.1170 -0.0780 P1 x P8 -155.4090 0.0563 0.0000 P1 x P9 498.8606 0.1245 0.0879 P1 x P10 41.6713 -0.1620 -0.0260 P2 x P3 -481.9980 -0.0500 -0.0640 P2 x P4 -57.9130 -0.0890 -0.1070 P2 x P5 -98.2230 0.0176 -0.0150 P2 x P6 49.2769 0.1195 0.0510 P2 x P7 50.8176 -0.0510 -0.0460 P2 x P8 -151.4540 -0.2210 -0.0280 P2 x P9 701.1506 0.2013 0.1597 P2 x P10 137.2963 0.0345 0.0604 P3 x P4 -593.2440 -0.0560 -0.0550 P3 x P5 -129.3890 -0.0140 -0.0170 P3 x P6 295.6100 0.0976 0.0735 P3 x P7 702.3206 -0.0470 0.0010 P3 x P8 -88.4518 0.0063 -0.0350 P3 x P9 124.1488 0.0495 0.0373 P3 x P10 -51.3705 -0.0370 0.0179 P4 x P5 33.8607 -0.1620 0.0492 P4 x P6 263.0256 0.2088 0.0754 P4 x P7 168.7313 0.0482 0.0329 P4 x P8 82.2988 0.0776 0.0110 P4 x P9 244.0694 0.1557 0.1242 P4 x P10 31.0451 -0.0710 -0.0652 P5 x P6 -628.9540 -0.0640 -0.0720 P5 x P7 -137.4130 -0.0340 -0.0045 P5 x P8 146.1488 -0.0900 -0.0664 P5 x P9 428.7544 0.1876 0.0717 P5 x P10 141.5650 0.1357 0.0573 P6 x P7 402.5863 0.0870 0.0967 P6 x P8 271.1488 0.2213 0.1898 P6 x P9 -826.2455 -0.9200 -0.5370 P6 x P10 113.2351 0.1576 0.0735 P7 x P8 -16.4756 -0.0140 -0.0377 P7 x P9 -553.8699 0.0888 0.0554 P7 x P10 -26.0543 0.0420 -0.0189 P8 x P9 -158.6424 0.0882 0.0335 P8 x P10 70.8382 -0.1230 -0.0658 P9 x P10 -458.2261 0.0245 -0.0327 SD ([S.sub.ij]) 21691.9201 0.0064 0.0021 SD ([S.sub.ij]-[S.sub.IK]) 48806.8204 0.0145 0.0047 SD ([S.sub.ij]-[S.sub.KL]) 41834.4175 0.0125 0.0040 Genotypes (1) Traits (2) FLOR P1 x P2 0.3169 P1 x P3 -0.5760 P1 x P4 -5.5300 P1 x P5 0.7963 P1 x P6 5.2160 P1 x P7 1.3190 P1 x P8 -2.2800 P1 x P9 2.1540 P1 x P10 -1.4000 P2 x P3 0.4638 P2 x P4 1.0070 P2 x P5 -1.6000 P2 x P6 -0.5700 P2 x P7 -0.9700 P2 x P8 -1.9000 P2 x P9 3.3500 P2 x P10 -0.0300 P3 x P4 0.1090 P3 x P5 -1.2000 P3 x P6 3.1900 P3 x P7 -1.0000 P3 x P8 -1.6000 P3 x P9 1.4600 P3 x P10 -0.7600 P4 x P5 -0.5100 P4 x P6 -1.0000 P4 x P7 -0.6500 P4 x P8 2.2300 P4 x P9 4.8400 P4 x P10 -0.3800 P5 x P6 3.9000 P5 x P7 -0.3200 P5 x P8 -0.5900 P5 x P9 -0.3200 P5 x P10 -0.0500 P6 x P7 0.9230 P6 x P8 5.6500 P6 x P9 -21.0000 P6 x P10 3.8600 P7 x P8 -2.5000 P7 x P9 5.0200 P7 x P10 -1.7000 P8 x P9 2.5900 P8 x P10 -1.4000 P9 x P10 1.9600 SD ([S.sub.ij]) 1.1600 SD ([S.sub.ij]-[S.sub.IK]) 2.6300 SD ([S.sub.ij]-[S.sub.KL]) 2.2550 (1) [P.sub.1] = PR 023; [P.sub.2] = PR 024; [P.sub.3] = PR 036; [P.sub.4] = UEM J1; [P.sub.5] = PR 045-1; [P.sub.6] = PR 045-2; [P.sub.7] = PR 045-3; [P.sub.8] = PR 087-1; [P.sub.9] = PR 087-2; [P.sub.10] = PR 087-3. (2) GY = Crop Yield; PH = Plant Height; EH = Ear Height; FL = Days to silking; and PE = popping expansion.