Inheritance of resistance to tomato anthracnose caused by Colletotrichum coccodes (Wallr.) S.J. Hughes was evaluated in parental, F1, F2, and backcross populations developed from crosses between adapted resistant (88B147) and susceptible (90L24) tomato (Lycopersicon esculentum Mill.) breeding lines. Resistance was evaluated via measurement of lesion diameters in fruit collected from field-grown plants and puncture inoculated in a shaded greenhouse. Backcross and F2 populations exhibited continuous distributions suggesting multigenic control of anthracnose resistance. Anthracnose resistance was partially dominant to susceptibility. Using generation means analysis, gene action in these populations was best explained by an additive-dominance model with additive × additive epistatic effects. A broad-sense heritability (H) of 0.42 and narrow-sense heritability (h2) of 0.004 was estimated for resistance to C. coccodes. One gene or linkage group was estimated to control segregation for anthracnose resistance in the cross of 90L24 × 88B147.
John R. Stommel and Kathleen G. Haynes
Carol A. Lemke and Martha A. Mutschler
The absence or presence of type IV trichomes seemed to be simply inherited in crosses of the tomato, Lycopersicon esculentum Mill, and Lycopersicon pennellii Correll. F2 and BC1 data showed a good fit to a 15 : 1 and 3 : 1 ratio, respectively, suggesting that the presence of type IV trichomes is controlled by 2 unlinked genes. Broad sense heritability estimates of type IV trichome density were high. Generation means analysis of type IV trichome density indicated that genic interaction was important in the 3 crosses. All plants examined possessed type VI trichomes. Density of type VI trichomes seemed to be under large environmental influences. Broad sense heritability estimates for the density of type VI trichomes were low to moderate. Correlation coefficients comparing adaxial and abaxial trichome density measurements of both types of trichomes were significant for most of the populations studied. Correlation coefficients comparing type IV and type VI trichomes were not significant in most of the populations studied.
F. A. Bliss
The precision of a 9-plant hill-plot design in which plants were sown 15 cm apart in a 3 × 3 arrangement compared favorably to that of 3-m-row plots containing approximately 75 plants for the estimation of pod yield of snap beans Phaseolus vulgaris L. Quality traits and sieve size distribution based on pod diameter in both plot designs were similar. Using the square design, the entire 9-plant plot can be taken as the unit of selection, or single plant selection can be practiced when the test plant is grown in the center hill surrounded by 8 uniform guard plants. Single plant selection using this design has been used effectively to modify traits of beans having moderate to high heritability. Selection based on family means should be used for traits with low heritability. Efficiency of the hill-plot design is realized in terms of smaller plot size, fewer required seeds per plot and reduced harvest time.
R. A. Werner, D. C. Sanders, and W. R. Henderson
The inheritance of tolerance to rhizoctonia fruit rot incited by Rhizoctonia solani Kuhn differed depending upon the source of the plant material of tomato (Lycopersicon esculentum Mill.). The tolerance in USDA 75B 846-1-1 was controlled by 1 major gene without dominance. The tolerance in USDA 75B 610-3 was polygenic with 4 major genes. Tolerance in USDA 75B 846-1-1 had a narrow-sense heritability of 71% while in USDA 75B 610-3 heritability was 30%. Fruit rot tolerance and resistance to puncture pressure were highly correlated in both families. Fruit shape and fruit rot tolerance were also highly correlated in the family with USDA75B 846-1-1.
Douglas V. Shaw and Kirk D. Larson
The genetic opportunity for selection of early fruiting strawberry cultivars was evaluated using seedling populations from the Univ. of California (UC) breeding program in three years. Narrow-sense heritabilities for early season yield and for the proportion of an individual's total yield expressed early were moderate (h2 = 0.24-0.53) and broad-sense heritabilities were slightly larger (H2 = 0.31-0.70), suggesting the presence of some nonadditive genetic variance for these traits. These two traits were genetically correlated with each other (rg = 0.78-0.98), but only early yield was consistently genetically correlated with seasonal yield (rg = 0.52-0.82). Selection was performed for each trait using an index on full-sib family means and individual phenotypic values in two of the three years, and predicted response was compared with that obtained using vegetatively propagated runner plants from selected genotypes in the subsequent fruiting season. Statistically significant (P < 0.05) selection response was obtained in one of two years for each trait, and combined analysis demonstrated highly significant (P < 0.01) response for both traits. However, realized response over all traits and years was just 27.3% of that predicted based on the estimated heritabilities and applied selection intensities. These results suggest that selection for early yield should be based at least in part on runner plant evaluations rather than exclusively on seedling performance.
D. V. Shaw, R. S. Bringhurst, and V. Voth
Strawberry (Fragaria × ananassa) seedlings were evaluated for yield, fruit weight, and commercial appearance in two field trials established in 1985 and 1986. Genetic analyses for unbalanced diallels were performed to quantify genetic, environmental, and interaction variance for each trial separately, and for crosses common to two locations in a single year. When data from crosses common to two test locations were analyzed simultaneously, narrow-sense heritabilities (h2) averaged 0.35 (±0.11), 0.21 (±0.07), and 0.08 (±0.06) for yield, fruit weight, and appearance score. Broad-sense heritabilities (H2) were 0.35 (±0.11), 0.27 (±0.12), and 0.21 (±0.11) for the same traits, respectively. These estimates do not differ significantly from heritabilities estimated from the ancestral breeding population 20 years ago. Estimates of H2 for single-location analyses were biased upwards by dominance × location interactions for all traits. Additive × location interactions were detected for appearance score and contributed a small bias to single-location estimates of h2. Use of biased estimates in predicting genetic gain could lead to errors in choice of appropriate selection strategy.
Ahmed A. Hassan, Robert E. Wilkinson, and Donald H. Wallace
Resistance to T. basicola was found in Phaseolus vulgaris lines P.I.203958 (N203) and 2114-12. To determine the inheritance of resistance, these 2 lines were crossed with each other and with the susceptible cv. Redkote. Greenhouse tests were conducted on parental, F1, F2, and backcross progenies of each of the 3 crosses, and on F3 progenies of crosses ‘Redkote’ × 2114-12 and ‘Redkote’ × N203. The data indicate that N203 and 2114-12 possess the same genes for resistance, that resistance is partially recessive, and that resistance is controlled by approximately 3 genes. Broad sense heritability was estimated as 59% and the additive variance as 39%.
Allan F. Nash and Randolph G. Gardner
Early blight resistance was estimated in field plots for parents and F1, F2, and backcross progenies of crosses with NC EBR-1, a line derived from Lycopersicon hirsutum P.I. 126445. Areas under the disease progress curve (AUDPC) showed that resistance from NC EBR-1 was heritable and quantitative in nature. generation means in two families were intermediate to those of NC EBR-1 and susceptible parents. The distribution of AUDPC means for the different generations in both families indicated the presence of epistasis or gene linkage. Lack of fitness tests for curve-linearity confirmed this in one family. A, B, and C scaling tests showed similar results. A joint three-factor model and subsequently a six-factor model displayed the presence of epistasis in both families. Ignoring epistatic effects, narrow-sense heritability (h2) was 0.49 in one family and 0.40 in the other. By regressing F3 progeny AUDPC means on selected F2 plant values, h2 was 0.25 and 0.17, respectively.
Peter M. Hanson, Jen-tzu Chen, and George Kuo
High-temperature fruit set (heat tolerance) is a critical trait of tomato (Lycopersicon esculentum Mill.) cultivars targeted for lowland wet season production in the tropics and subtropics. Heat-tolerant Asian Vegetable Research and Development Center (AVRDC) tomato line CL5915-93D4-1-0-3 (CL5915) is a valuable source of heat-tolerance genes for tomato genetic improvement. The gene action of heat tolerance in CL5915 was determined by evaluating the F1, F2, BCP1, and BCP2 of a cross between CL5915 and heat-sensitive line UC204A for fruit set traits in two wet-season trials at AVRDC. Parent-offspring regression of F2-derived F3 (F2:3) family means on the F2 plants from CL5915 × UC204A was used to estimate the heritability of F2 single plant selection for heat tolerance. Mean percentage of fruit set and fruit number per cluster of the F1 and BCP1 exceeded midparent values and were not significantly different from those of CL5915, indicating complete dominance for heat tolerance. Generation means analyses indicated that a model including simple additive and dominance effects adequately explained the inheritance of mean fruit number per cluster both years. For mean percentage of fruit set, a model including simple additive-dominance effects produced an adequately fitting model in the 1996 season but the best-fitting model included an epistatic component in the 1997 season. Heritabilities estimated for fruit set traits in 1996 and 1997, respectively, were: 0.31 and 0.21 for percentage of fruit set; 0.28 and 0.14 for mean fruit number per cluster; and 0.53 and 0.15 for flower number per cluster. The low heritabilities for percentage of fruit set and mean fruit number per cluster under high temperatures imply that single plant selection in the F2 for heat tolerance from crosses involving CL5915 is not effective and that selection should be based on replicated family testing in the F3 and later generations.
M. H. Dickson and C. J. Eckenrode
Resistance to Trichoplusia ni (Hubner), Pieris rapae (L.), and Plutella xylostella (L.) in cabbage [Brassica oleracea L. (Capitata group)] and cauliflower (B. oleracea, Botrytis group) was studied using a 5-parent diallel. Resistance was quantitatively inherited without undesirable linkages. When Plant Introduction (PI) 234599 (a glossy-leaved cauliflower) was used as a parent, narrow sense heritabilities of 22-47% were obtained for resistance. This resistance was maintained irrespective of plant age or presence or absence of alternate oviposition hosts. Plants with moderate tolerance only express it at maturity. The highest levels of resistance were transferred with difficulty into desirable type cauliflower and cabbage with slight bloom.