To understand the genetics that control pod Ca concentration in snap beans, two snap bean (Phaseolus vulgaris L.) populations consisting of 60 genotypes, plus 4 commercial cultivars used as checks, were evaluated during Summers 1995 and 1996 at Hancock, Wis. These populations were CA2 (`Evergreen' × `Top Crop') and CA3 (`Evergreen' × `Slimgreen'). The experimental design was an 8×8 double lattice repeated each year. No Ca was added to the plants grown in a sandy loam soil with 1% organic matter and an average of 540 ppm Ca. To ensure proper comparison for pod Ca concentration among cultivars, only commercial sieve size no. 4 pods (a premium grade, 8.3 to 9.5 mm in diameter) were sampled and used for Ca extractions. After Ca was extracted, readings for Ca concentration were done via atomic absorption spectrophotometry. In both populations, genotypes and years differed for pod Ca concentration (P = 0.001). Several snap bean genotypes showed pod Ca concentrations higher than the best of the checks. Overall mean pod Ca concentration ranged from a low of 3.82 to a high of 6.80 mg·g-1 dry weight. No differences were detected between the populations. Significant year×genotype interaction was observed in CA2 (P = 0.1), but was not present in CA3. Population variances proved to be homogeneous. Heritability for pod Ca concentration ranged from 0.48 (CA2) to 0.50 (CA3). Evidently enhancement of pod Ca concentration in beans can successfully be accomplished through plant breeding.
Tassel date, silk date, plant height, ear height, shank length, husk extension, tip blanking, row number, ear length, and first ear weight were studied in a diallel involving 7 inbred sweet corn parents. Both general combining ability (GCA) and specific combining ability (SCA) were involved in the inheritance of all 10 characters. This was consistent for F1 crosses in 2 years and for F2 families. SCA variance (VSCA) was larger than GCA variance (VGCA) for ear length and first ear weight in the F1 and ratios of VSCA/VGCA for these characters were slightly larger than 1.0. VGCA was larger than VSCA all other characters in the F1. Ratios of VSCA/VGCA ranged from .05 for row no. to .57 for plant height.
Variance ratios for most characters decreased in the F2. The failure of some ratios to decrease in the F2 was attributed to either differential interactions of GCA and SCA with environment or inadequate sampling of F2 families. Genotype × year interactions influenced the expression of most characters. A greater portion of the genotype × year interaction was contained in estimates of SCA than in estimates of GCA. Heritability estimates from parent-progeny regression were generally larger than those from variance components, although these estimates were generally in close agreement.
The effectiveness of directional phenotypic selection to improve tomato (Lycopersicon esculentum Mill.) seed germination under salt-stress was investigated. Seed of F2 and F3 progeny of F1 hybrids between a salt-tolerant (PI174263) and a salt-sensitive (UCT5) tomato cultivar were evaluated for germination response at three stress levels of 100 (low), 150 (intermediate), and 200 mm (high) synthetic sea salt (SSS). At each salt-stress level, the most tolerant individuals, as determined by the germination speed, were selected. Selected individuals (F2s or F3s) were grown to maturity and self-pollinated to produce F3 and F4 progeny families. The selected progeny from each experiment were evaluated for germination at four treatment levels of 0 (nonstress), 100, 150, and 200 mm SSS and were compared with unselected populations. The results indicated that selections were equally effective at all three salt-stress levels and in F2 and F3 generations and significantly improved seed germination of progeny under salt-stress and nonstress treatments. Estimates of realized heritability for rapid germination under the various salt-stress levels ranged from 0.67 to 0.76. Analysis of response and correlated response to selection indicated a genetic correspondence of up to 100% between germination at different salt-stress levels. Genotypic family correlations between germination at the low, intermediate, and high salt-stress levels ranged from 0.67 to 0.89, and those between nonstress and salt-stress conditions ranged from 0.25 (between 0 and 200 mm) to 0.71 (between 0 and 100 mm salt). The results indicated that similar or identical genes with additive genetic effects contributed to rapid germination response of tomato seeds at different salt-stress levels. Thus, selection at one stress level resulted in progeny with improved germination at diverse salt-stress levels. The results also indicated that to improve tomato seed germination, selection can be based on individual seed performance and early segregating generations.
Resistance to wilt caused by Verticillium dahliae Kreb. was evaluated for 41 strawberry genotypes from the Univ. of California breeding program and 1000 offspring from crosses among 23 of these genotypes. Runner plants from these genotypes and seedlings were inoculated with a conidial suspension containing a mixture of five isolates of V. dahliae from strawberry. Symptoms were scored as the number of dead or seriously stunted plants per plot, or based on a subjective phenotypic resistance score assigned to each plot on five dates during the spring after planting. Most of the California germplasm is highly susceptible to V. dahliae, with an average resistance score of 2.1 (±0.10) and 84.1% (±2.1) plants stunted or dead compared with a score of 3.2 (±0.24) and 57.4% (±4.9) of plants stunted or dead for a control set of six non-California genotypes identified previously as resistant. However, a broad range of intermediate resistance was detected, and 4 of the 41 California genotypes evaluated had resistance scores superior to the mean score for the non-California resistant checks. Plot-mean heritabilities for resistance and stunting scores estimated using genotypic, full-sib family, and offspring-parent analyses ranged from 0.44 to 0.88. Comparison of different estimates of variance components suggests that half or more of the genotypic variance for resistance traits detected is due to the additive effects of genes. There appears to be sufficient variation within the California population to proceed with an effective selection program, despite the absence of directional selection for resistance during the past 3 decades. However, developing cultivars with adequate resistance will ultimately depend on the recovery of transgressive segregants from superior parents, as even the most resistant genotypes from all sources showed some disease symptoms.
Narrow sense heritabilities (h2) for reducing sugar concentration of pickling cucumbers (Cucumis sativus L.) were estimated for a population of half-sib families from 501 plant introductions and cultivars. Reducing sugar concentration averaged 22.3 mg/g fresh weight, and ranged from 10.4 to 51.9 mg/g. Half-sib family heritability of reducing sugar concentration was 0.30, and after correction for estimated genotype × environment interaction was 0.051. Parent-offspring heritability was 0.042. Expected gains per cycle of half-sib progeny testing and half-sib testing, corrected for genotype × environment interaction bias, were 0.42 and 0.21 mg reducing sugar/g, respectively. Expected gain per cycle of mass selection was 0.38 mg/g.
Thirty-six cultivars and 948 seedlings from 15 controlled crosses in the U.S. Dept. of Agriculture-Agricultural Research Service pecan [Carya illinoinensis (Wangenh.) K. Koch] breeding program at Brownwood, Texas, were rated for susceptibility to nut scab [Cladosporium caryigenum (Ell. et Lang.) Gottwald] to determine heritability of this trait. Differences between parents and progenies, and within progenies, were highly significant. Within most families, a complete range of resistance reactions were evident, from fully susceptible to fully resistant. Heritability of resistance was determined by regressing individual progeny values on female, male, and midparent values, with the midparent heritability estimate being the highest (0.54). This moderate level of additive gene action and the identification of superior parents in this study will contribute to the efficiency of breeding resistant cultivars.
Genetic variation for percent soluble solids, percent titratable acidity, and fruit firmness was analyzed for representative progenies from the California strawberry breeding population. Fruit samples were harvested from individual seedlings from 28 biparental crosses, organized in two factorial mating sets. Individual narrow-sense heritabilities were estimated as 0.07, 0.48, and 0.38 for solids, acids, and firmness, respectively. Broad-sense heritabilities were estimated as 0.35, 0.78, and 0.38 for the same traits, suggesting the presence of dominance variance for soluble solids and acidity, but not for firmness. Opportunities for genetic manipulation of traits with different additive-dominance genetic variation profiles are discussed.
The heritability of shortened fruit maturation (SFM) period in Cornell 871213-1, an inbred cherry tomato [Lycopersicon esculentum var. cerasiforme (Dunal.) A. Gray] line, was estimated from a greenhouse experiment. Cornell 871213-1 was crossed with the cherry tomato line NC 21C-1. Mean fruit maturation period (FMP) (days from anthesis to the breaker stage of fruit color) was 40.8 days for NC 21C-1 and 32.0 days for Cornell 871213-1. Parental, F1, F2, and backcross generations all differed in mean FMP and yielded, estimates of broad- and narrow-sense SFM heritabilities of 72% and 40%, respectively, on a single-plant basis. A test for midparent heterosis showed significance. Genetic control of SFM was quantitative in nature and highly dominant. A field study of an F2 population developed from the cross Cornell 871213-1 × NC 84173, the latter a large-fruited tomato line (Lycopersicon esculentum Mill.), gave a mean FMP of 48.4 and 31.2 days for NC 84173 and Cornell 871213-1, respectively. The F1 and F2 generations had FMP of 33.1 and 34.7 days, respectively. The parents, F1, and F2 generations all differed in FMP. Parental, F1, and F2 generations yielded an estimate of broad-sense SFM heritability of 64% on a single-plant basis. F3 progenies from selected F2 s were grown in a greenhouse, and F3-F2 regression analysis gave a narrow-sense SFM heritability of 39%. Parental means differed from each other and from the F1 and F2 means for period from sowing to anthesis, fruit weight, and locule number. F1 and F2 means did not differ for any trait and were far below the midparent values, approaching Cornell 871213-1 for each trait except for the number of days from sowing to anthesis. Significant correlations existed in the F2 generation between FMP and fruit weight (0.61) and between fruit weight and locule number (0.69). Significant correlations existed between selected F2s and their F3 progeny for FMP (0.53), fruit weight (0.78), and days from sowing to anthesis (0.78). In the F3 generation, a significant correlation occurred between FMP and fruit weight (0.48). F3-F2 regression and realized heritabilities were used as two estimates of narrow-sense heritability (29% and 31%, respectively) for days from sowing to anthesis.
Additive genetic components of variance and narrow-sense heritabilities were estimated for flowering time and cut-flower yield for generations 8-13 of the Davis population of gerbera, using the least squares (LS) and restricted maximum likelihood (REML)
methods. Estimates of heritability for flowering time were 0.54 and 0.50 using REML and LS, respectively, indicating a close agreement between the two methods. However, estimates of heritability for cut-flower yield were 0.30 and 0.46 from REML and LS. This may result from the fact that cut-flower yield was selected in each generation; flowering time was not. Realized heritability for cut-flower yield was estimated to be 0.26 which agreeded more closely with the heritability estimated from REML. The advantages of REML, and its applications in the estimation of components of genetic variance and heritability of plant populations are discussed.
the F 1 hybrid exceeded that of the high seed parent in this cross and reduced seed count progeny were over-represented in the F 2 generation. In related Solanaceous crops, production of seedless parthenocarpic fruit is heritable but does not fit a