Abstract
Heat at any growth stage can damage green beans (Phaseolus vulgaris L.), but plants are most susceptible at or near bloom. The effect of heat during the bloom period resulted in reduction of a yield in proportion to the duration of the heat period. The most critical growth stage was found to be 2 to 3 days before anthesis, rather than at anthesis itself. By subjecting F1 plants to heat during the bloom period, genetic selection for heat tolerance was moderately effective. The heritability for heat tolerance was quite low. Broad-sense heritability was 19% to 79% and narrow-sense heritability 0% to 14%. These values are probably conservative, since during the genetic study the heat period was initiated on the first day of bloom, which resulted in some escapes and excess variability.
Abstract
A wide-base pickling cucumber (Cucumis sativus L.) population was formed by intercrossing all available cucumber lines (1063) and selecting for short fruit length. After intercrossing twice, 112 S0 plants and their half-sib progeny were evaluated for Rhizoctonia fruit rot resistance using a detached-fruit test. Parent-offspring regression indicated a narrow-sense heritability of 0.24, considered low to moderate. Gain from selection was calculated for 2 recurrent selection systems. Based on the heritability estimate, selection using replicated progeny rows was recommended for improving resistance to this trait.
Experiments were conducted to estimate the relative importance of additive and dominance genetic variances and non-allelic interactions in the inheritance of resistance to Colletotrichum spp. in strawberry (Fragaria × ananassa Duch.). Progeny of 40 parents crossed in a Comstock and Robinson Design II Mating scheme were inoculated with three isolates of C. fragariae and one isolate of C. acutatum. Disease development on each plant was rated visually. Variance components were estimated and converted to genetic variances. Estimates of were six to 10 times higher than those for Within-family variance not accounted for by equaled 35% and 38% of the total genetic variance in females and males, respectively, indicating probable epistatic effects. The frequency distribution of disease severity ratings was bimodal in both experiments, suggesting major gene action. Narrow-sense heritability estimates were 0.37 and 0.26, and broad-sense heritability estimates were 0.87 and 0.85 for females and males, respectively. Narrow-sense heritability estimates are probably sufficient to produce gains from recurrent selection. Gains from selection of clonal value should be possible because of the high broad sense heritability estimates. It appears feasible to establish a broad genetic-based population resistant to Colletotrichum spp. from which selections could be evaluated per se and/or recombined to produce improved populations.
heritability estimates. Family diversity. Cultivated sweetpotato (2n = 6x = 90) is widely recognized as a diverse species and the 25 full-sib families, of 20–25 progeny each, generated in this experiment demonstrated extensive diversity for storage root shape
Abstract
Genetic variance components, narrow-sense heritabilities, and general combining ability (GCA) effects were estimated for plant growth habit traits from a partial diallel cross among 17 blueberry (Vactinium corymbosum L., V. angustifolium Ait., and V. corymbosum x V. angustifolium hybrids) parents. Plant height, plant diameter, and a subjective stature rating were recorded for parent and progeny plants in 1984 after 9 growing seasons at Becker, Minn. General and specific (SCA) combining ability variances were significant for all traits. GCA variance components were larger than SCA components for height and stature rating, and heritabilities (family-mean basis) were 0.68 and 0.64, respectively, indicating the relative importance of additive genetic variance for these traits. Desired stature or height in this population should be recoverable through recurrent phenotypic selection. SCA variance components were much larger than GCA components for plant diameter measures, and heritability was low. Vaccinium angustifolium parents had very negative GCA effects for plant height and stature ratings, while parents with largely V. corymbosum ancestry had positive effects. Coefficients of determination between parental phenotype and GCA effects indicated that progeny performance should be predicted by parental phenotype for stature or height but not for diameter.
Abstract
Procedures for forced field infestation of maize with European corn borer egg masses, placed to simulate possible natural ovipositional sites and to emphasize damage to the ear, were compared. A growth chamber procedure using excised ears and a free-choice (preference) infestation procedure were also used. Forced infestation in the field permitted infestation at a uniform relative maturity and uniform development of borers from time of infestation to evaluation. An ear-and-leaf infestation procedure appeared to be the most appropriate for simultaneous evaluation of kernel damage and stalk tunneling. Estimated heritabilities, using this procedure on 2 segregating populations, were 0.71 and 0.84 for kernel damage and 0.39 and 0.79 for stalk tunneling. Phenotypic correlations among 3 ear damage criteria were noted (r = 0.42 to 0.46). Evaluation based on kernel damage alone, excluding cob tunneling and number of surviving larvae, was considered sufficient. There was no evidence that kernel damage was influenced by level of stalk tunneling.
Heritability of resistance to early blight disease in potatoes (Solarium tuberosum L.) incited by Alternaria solani (En. & Martin) Ser. was estimated in tetraploid × diploid crosses. Susceptible tetraploid cultivars and breeding lines were the female parents. Diploids that produced a high proportion of first-division restitution (FDR) gametes and possessed different levels of early blight resistance were the male parents. Tubers from seedlings that resulted from the tetraploid × diploid crosses were planted in a field and artificially inoculated with spores of Alternaria solani. Resistance was measured as the slope (r) of the regression of the logit of the percent defoliation of each plant vs. time. Higher r values indicated lower resistance. Mean r values ranged from 0.123 to 0.157 for the tetraploid parents, and from 0.054 to 0.116 for the diploid parents. Mean r values for the tetraploid × diploid crosses were intermediate, ranging from 0.077 to 0.143. Narrow-sense heritability (h2) was 0.815. The partial correlation coefficient between r and mean maturity values was – 0.2086.
Thirteen peach [Prunus persica (L.) Batsch] fruit characteristics were investigated for 3 years, 1993, 1994, and 1995, in College Station, Texas, to determine heritability, genetic and phenotypic correlations, and predicted response to selection. Seedlings of 108 families resulting from crosses among 42 peach cultivars and selections were used in the evaluations. A mixed linear model, with years treated as fixed and additive genotypes as random factors, was employed to analyze the data. Best linear unbiased prediction (BLUP) was used to estimate fixed effects. Restricted maximum likelihood (REML) was used to estimate variance components, and a multiple trait model was used to estimate genetic and phenotypic covariances between traits. Genetic and phenotypic correlations ≥0.65 and <0.30 were considered strong or very strong and weak, respectively. Date of ripening, fruit development period (FDP) and date of full bloom had the highest heritability (h2) estimates, 0.94, 0.91, and 0.78, respectively. Fruit cheek diameter and titratable acidity (h2 = 0.31) were the traits with the lowest estimates. Fruit development period, fruit blush, and date of ripening had the highest predicted selection responses, whereas fruit suture, fruit cheek, L/W12 (ratio fruit length to average fruit diameters), and fruit tip had the lowest values. Most genetic correlations were ≥0.30 and were, in general, much higher than the corresponding phenotypic correlations. All four measures of fruit size were genetically and phenotypically very strongly correlated. Important genetic correlation estimates were also observed for date of ripening with FDP (ra = 0.93), date of ripening and FDP with fruit blush (ra = -0.77, ra = -0.72), SS (percent soluble solids) (ra = 0.63, ra = 0.62) and TA (ra = 0.55, ra = 0.64), and SS with TA (ra = -0.56). Direct selection practiced solely for early ripening and short FDP is expected to have a greater effect on correlated traits than direct selection for early bloom and large fruit mass.
Pistachio (Pistacia vera L.) progeny were evaluated at two locations in California for resistance to alternaria late blight caused by Alternaria alternata (Fries) Keissler in 1995 and 1997. Large differences in alternaria late blight infection among seedlings were observed. Narrow sense heritabilities based on half-sib analysis of 20 open pollinated families were 0.48 and 0.11 at Kearney Agricultural Center in 1995 and 1997, respectively, and 0.56 and 0.54 at the Wolfskill Experimental Orchard near Davis in 1995 and 1997, respectively. Differences among families to alternaria late blight infection were highly significant and associated with the female parents. Fifty-eight highly resistant seedlings were identified for future cultivar selection efforts.
A knowledge of the relative proportion of additive and nonadditive genetic variances for complex traits in a population forms a basis for studying trait inheritance and can be used as a tool in plant breeding. A North Carolina Design II mating scheme was used to determine the inheritance of cooking time, protein and tannin content, and water absorption among 16 genotypes of dry bean (Phaseolus vulgaris L.) representative of the Andean Center of Domestication. Heritability and the degree of dominance for the traits were also calculated to provide guidelines for adopting breeding strategies for cultivar development. Thirty-two progeny resulted from the matings and these were assigned to two sets of 16 progeny each. Variances due to general combining ability (GCA) and specific combining ability (SCA) were significant for the traits. The GCA was larger in all cases. Narrow-sense heritability for protein, tannin, water absorption, and cooking time averaged 0.88, 0.91, 0.77, and 0.90, respectively. Degree of dominance estimates indicted that the traits were governed by genes with partial dominance except, in one case, tannin had a degree of dominance value of zero, indicating no dominance. The phenotypic correlation (-0.82) between water absorption and cooking time justifies using the water absorption trait as an indirect selection method for cooking time. With regard to parent selection in crosses, significant differences between GCA females and GCA males suggested cytoplasmic influences on trait expression. Hence, the way a parent is used in a cross (i.e., as female or male) will offset trait segregation. Using fast-cooking bean cultivars in conjunction with fuel-efficient cooking methods may be the best strategy to conserve fuelwood and help reduce the rate of deforestation in East and Central Africa.