The influence of cryogenic pollen storage on fruit set and seed production in tomato (Lycopersicon esculentum Mill.) was investigated. Flowers pollinated with pollen samples stored for 5 weeks at –80C, with or without 20 h precooling at 4C, had similar fruit set and number of viable seed per fruit as those pollinated with fresh pollen. Pollen samples, which were repeatedly cooled (–80C) and warmed (to 22 to 24C) for up to six cycles, continuously maintained the same viability as the fresh pollen. When cryogenically stored pollen of L. esculentum 2-837, LA359, LA3198, and LA3199 were used to pollinate LA359, the number of viable seed formed per fruit differed significantly. Results of this study suggest that pollen cryopreservation can be used successfully for tomato breeding and germplasm storage.
Erik J. Sacks and Dina A. St. Clair
Erik J. Sacks and Douglas V. Shaw
Color change in fresh, ripe strawberry (Fragaria ×ananassa Duch.) fruit stored at 0C for up to 7 days was recorded using the Commission Internationale de l' Éclairage color space (L*, a*, and b*). External (skin) fruit color became darker and less chromatic but did not change hue. Internal (flesh) fruit color became darker and more chromatic. Regression coefficients calculated for individual genotypes were homogeneous for each of the color traits except internal hue. Depending on genotype, the red fruit flesh either became a bluer red or did not change hue. In all cases, rates of change were small. Color change for fresh strawberry fruit during several days of storage at 0C likely is not an appreciable source of error in plant breeding experiments.
Erik J. Sacks and David M. Francis
The genetic and environmental variation for flesh color of tomato (Lycopersicon esculentum Mill.) fruit was quantified using 41 red-fruited breeding lines, open-pollinated cultivars, and hybrids that are representative of the diversity of tomatoes grown for whole-peel processing in the midwestern and eastern United States and Ontario, Canada. Objective color measurements were made for 2 years from replicated experiments with 2 to 4 blocks per year. Genotypes differed significantly in lightness value (L*), saturation (chroma), and hue angle. Variation within fruit and among fruit in plots accounted for more than 75% of the environmental variation for the color traits. The crimson locus (ogc) accounted for less than one-third of the variation in fruit color among genotypic means, and explained 18% to 27% of the genotypic variation for L*, chroma, and hue. Estimates of variance components were used to develop sampling strategies for improving selection efficiency. Genotypes were identified that may be useful for studying genetic differences that lead to quantitative variation for fruit color in red-fruited populations of tomato.
Erik J. Sacks and Douglas V. Shaw
To determine the best sampling strategies, components of variance were estimated for 10 color traits of strawberry (Fragaria × ananassa) fruit. Over three dates in one growing season, 2000+ fruit from 47 genotypes were observed. Within-fruit, among-fruit within genotypes, and harvest date variances were compared. Variances for harvest dates were non-significant or small (0-8% of the total variance). Genotype × date variances were highly significant but small (≤ 6% of the total) for all color traits except internal hue (14% of the total). For external color traits, the within-fruit variance was greater than the among-fruit variance (16-64% and 0-14% of the total, respectively). For internal color traits, the among-fruit variance was greater than the within-fruit variance (20-37% and 9-19% of the total, respectively). Obtaining two observations per fruit for multiple fruit on one harvest date is an efficient strategy for determining a genotype's fruit color. With two observations per fruit, 7 to 22 fruit are needed to estimate a genotype's value within 2 units (CIELAB or degrees) with 95% confidence.
Erik J. Sacks and Douglas V. Shaw
Components of variance were estimated for 10 strawberry (Fragaria ×ananassa) color traits to determine their relative importance and to design optimal sampling strategies. The color attributes of >2000 fruit from 47 genotypes from the Univ. of California Strawberry Improvement Program were evaluated over three harvest dates (HDs) in one growing season. Measurements were obtained for a moderate number of fruit from each genotype on each date, and two measurements were obtained for each trait on all fruit. Variances for HDs were nonsignificant or small (0% to 8% of the total variance). Genotype × date variances were highly significant but small (≤6% of the total) for all color traits except internal hue (14% of the total). For external color traits, the within-fruit variance was greater than the among-fruit variance (16% to 64% and 0% to 14% of the total, respectively). For internal color traits, the among-fruit variance was greater than the within-fruit variance (20% to 37% and 9% to 19% of the total, respectively). Obtaining two measurements per fruit for several fruit on one HD is an efficient strategy for characterizing a genotype's fruit color; seven to 22 fruit are needed to estimate a genotype's fruit color within 2 units (Commission Internationale de L'Eclairage L*a*b* or degrees) with 95% confidence.
Douglas V. Shaw and Erik J. Sacks
Four sets of selected strawberry (Fragaria ×ananassa Duch.) genotypes were generated from within a single breeding population to evaluate the correspondence between predicted and realized selection response for fresh fruit color traits. Genotypes were selected for extreme phenotypes, dark or light, of either internal or external color value (CIELAB L*). Genotypic selection response was evaluated empirically by scoring fruit from the clonal derivatives of these selected genotypes, and response for breeding value was estimated by scoring the offspring of crosses performed among a subset of the genotypes within each selected set. Realized selection response was slightly larger than predicted for internal and external L* when calculated for selected genotypes. Also, more than half of the selected genotypes had genotypic values for L* outside the range of the original parents, providing evidence for transgressive segregation. Realized selection response for breeding value in exterior and interior color was slightly less than predicted. Compared in a different way, genotypic selection response for external color was significantly greater than selection response for breeding value, whereas genotypic and breeding value responses did not differ for internal color. These observations suggest the presence of some nonadditive genetic variance for external color but support the conclusion that the heritabilities predicted previously were reasonably accurate. Estimates of variance components within each of the offspring populations demonstrated that genetic variances were modified substantially by one generation of selection. Selection for dark fruit color reduced genetic variance to nonsignificant levels, with internal color more affected than external color. The total genetic variances within both of the offspring populations from parents selected for light color were changed little by one generation of selection, but substantial dominance variance was detected that had not been found in the original population. The rapid response to selection and large changes in the distribution of genetic variances may indicate the presence of a few genes with comparatively large effect in strawberry color expression. Additional divergent selection response can be expected, but primarily in the direction of light fruit color.