The intervals, in days, between 10%, 50%, and 90% ripened fruit, as well as crop load, were estimated over 2 years in progenies from a partial diallel cross among 17 blueberry (Vaccinium corymbosum L., V. angustifolium Ait., and V. corymbosum × V. angustifolium hybrids) parents. General combining ability (GCA) mean squares were highly significant for all ripening intervals and for crop load, while specific combining ability mean squares were nonsignificant, indicating a large proportion of additive genetic variance. Narrow-sense heritability estimates were about 0.50 for the three ripening intervals (10–50%, 50–90%, and 10–90%). Several parents had large positive GCA effects, indicating their contribution to a long ripening interval. Most progenies with large crop loads required >15 days between 10% and 90% ripened fruit. Despite the consistently positive relationship between ripening interval length and crop load, variation among families and the potential for within-family segregation suggest the possibility of obtaining genotypes with high yield potential and improved uniform ripening.
Progenies from crosses among 17 highbush (Vaccinium corymbosum L.), lowbush (V. angustifolium Ait.), and V. corymbosum/V. angustiforium hybrid parents were evaluated in 1983 and 1984 of dates for 50% bloom and 50% ripe fruit, length of the fruit development interval, and berry weight. Additive genetic variance was more important than nonadditive genetic variance, based on general combining ability (GCA) variance components. Heritability estimates were moderately high (0.44-0.78) for all traits. GCA effects were largely dependent on the parents’ ancestry. A long fruit development interval was not necessarily associated with large fruit size. Selection for large fruit size, late bloom period, early ripening, and short fruit development interval in this population should be successful. Parental phenotype should be indicative of relative progeny performance.
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.
The large number of horticultural crops represents a great genetic diversity. This diversity is important in numerous ways such as in pollination control, product use, and environmental requirements for the production and handling of seeds, propagules, and the commercial product, to name only a few. The diversity is reflected further in the business structure of horticulture and, most relevant to our discussion, to relationships at the interface between the public and the private sectors in crop improvement.
Breeders of horticultural food crops are usually concerned with multiple traits related to yield and quality as well as other traits such as biotic and abiotic stresses. Yield in these crops is not solely tonnage of biomass produced in the field. Rather, it is the proportion of the crop that can be harvested and brought to market in a condition and at a price acceptable to the consumer. Quality may include flavor, color, shape, size, degree of damage, nutrient levels, and traits that permit greater perceived food safety or environmental sustainability. Some traits may exhibit phenotypic associations. Traits with unfavorable associations will be of concern to the breeder if the cause is unfavorably correlated genetic effects, especially those resulting from pleiotropy. Several multiple trait selection schemes have been developed, including independent culling levels, tandem selection, and index selection. These schemes can result in improvement even for traits with unfavorable associations. However, the breeder must have a strong rationale for each trait addressed in a breeding program because each additional trait necessitates larger breeding populations and more resources. Thus, the breeder's first challenge for each crop is to determine which traits are most important and which issues are most amenable to a breeding solution.
Progenies from a partial diallel mating scheme using 17 highbush (Vaccinium corymbosum L.), lowbush (V. angustifolium Ait.), and half-high (V. corymbosum/V. angustfolium hybrid) parents were subjectively evaluated for fruit color, picking scar, and firmness in two seasons. General combining ability (GCA) mean squares were significant (P ≤ 0.01 for all traits), but specific combining ability was significant for no traits (P > 0.05). However, the correlation coefficients between the GCA effects and the parental phenotype scores were low, indicating that selection of parents within this material based on their phenotype may not be indicative of progeny performance. GCA effects depended to some extent on the species ancestry. Vaccinium angustifolium parents produced progeny with relatively dark, soft fruit with large scars. Lowbush parents having light-blue fruit produced segregating progenies that were heavily skewed toward dark fruit, regardless of the color or species ancestry of the other parent. When the highbush and half-high parents were crossed with one another, segregation patterns were typical of predominately additive gene action.
The genes that determine cyclic flowering in all commercially grown cultivars of strawberry (Fragaria ×ananassa Duch.) were derived from a single source of F. virginiana ssp. glauca from the Wasatch Mountains in Utah. To broaden the germplasm base of cyclic flowering cultivars, we evaluated the reproductive characteristics of 5 to 10 colonies of F. virginiana ssp. glauca from each of 32 Rocky Mountain sites ranging in elevation from 700 to 2900 m. Populations at high and low elevations had high percentages of putative day neutrals with cyclic flowering (43% to 100%) and hermaphrodites (20% to 80%), although most hermaphrodites were only partially fertile. There was also little association between elevation and crown numbers or flower number per cycle, but the total number of flowers per plant was negatively correlated with elevation. Fruit size was not significantly correlated with fruit number. When the data were subjected to a principal component analysis, two distinct groups were identified: one from the Black Hills of South Dakota and the other from low-elevation sites in Idaho and northwestern Montana. These patterns mirrored previously described patterns based on leaf traits.
Root sections of cranberry (Vaccinium macrocarpon Ait. cv. Searles) were microscopically examined to document the typical anatomy of cranberry roots and changes in root anatomy in response to N-form and solution pH. Cranberry cuttings were rooted, then established in hydroponic conditions with three N and two pH regimes. The three N regimes with equal N levels were 1) NH4-N alone, 2) NH4/NO3-N in combination, or 3) NO3-N alone. pH was maintained at 4.5 or 6.5. Root apical regions were examined using phase contrast, bright field, and epifluorescence microscopy. The cranberry root tip develops with a closed apical organization with the tetrarchal vascular cylinder, cortex, and root cap traceable to independent meristem cell layers. The most obvious treatment difference was an accumulation of unidentified “granules” in the subepidermal layer, readily visible with epifluorescence microscopy with NO3-N alone. Roots produced at pH 4.5 branched less than those at 6.5 and had more “quiescent” root initials; at pH 6.5, these developed more frequently into branch roots.