James Luby and Anne Fennell
Marvin Pritts and James Luby
James J. Luby, James F. Hancock Jr. and James R. Ballington
Matthew Clark, Peter Hemstad and James Luby
James J. Luby and Douglas V. Shaw
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.
James J. Luby and Douglas V. Shaw
Chad E. Finn and James J. Luby
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.
Steven J. McKay, James M. Bradeen and James J. Luby
The commercially successful apple (Malus pumila Mill.) cultivar Honeycrisp is known for its high degrees of crispness and juiciness. This cultivar has been incorporated into numerous breeding programs in an effort to duplicate its desirable texture traits in conjunction with such other traits as reduced postharvest disorders, disease resistance, and improved tree vigor. This study characterizes variability and estimates heritability for several apple fruit texture traits within a large breeding population over several years. Five full-sib families, all sharing ‘Honeycrisp’ as a common parent, were assayed with respect to crispness, firmness, and juiciness using sensory evaluation panels and total work required to fracture tissue using instrumental methods. The incomplete block design of the sensory panels, coupled with best linear unbiased prediction, facilitated the evaluation of a large number of genotypes with small numbers of fruit per genotype while accounting for individual sensory panelist effects. Broad-sense heritability estimates exceeded 0.70 for all four traits. Principal component analysis, applied to the phenotypic data, characterized ‘Honeycrisp’ as having average crispness and low firmness (53rd percentile relative to its offspring) but also as being a relatively extreme example of high juiciness and low work to fracture (first percentile). The improved characterization of desired fruit texture phenotypes and the high levels of broad-sense heritability provide valuable tools for the further development of new, high-quality apple cultivars.
James J. Luby, David K. Wildung and Gene J. Galletta
David A. Munter, James J. Luby and Neil O. Anderson
Zanthoxylum americanum is a common understory species in the northern forests of Minnesota and surrounding regions. It has potential economic importance for its citrus fragrance, pharmacological or insecticidal properties, and produces peppercorns similar to those of the related Zanthoxylum species. Zanthoxylum americanum is a dioecious species but has been reported to have aberrant flowers with autonomous apomixis instead of other potential reproductive barriers. The reproductive biology of Zanthoxylum americanum was investigated in two native Minnesota populations. Determinations of male fertility, whether autonomous apomixis was the predominant floral reproductive mechanism, the presence of seedless fruit (parthenocarpy/stenospermocarpy), and the occurrence of hermaphrodism were made over 2 years. Sex ratios (female:male plants) within each population differed. The mean pollen stainability was 95.8% ± 0.3% (fresh) and 78.6% ± 1.1% (stored 18 months). Parthenocarpy did not occur in either population. Autonomous apomixis was not the primary floral reproductive mechanism. Stenospermocarpy (seedlessness) occurred in 13% of the female fruit clusters. Although commonly described as being dioecious, two additional reproductive strategies were identified: 1) plants with functional protandrous flowers with rudimentary pistils and 2) hermaphroditic flowers with fully functional pistils (protogynous) and anthers. As many as 10% to 30% of the male plants bore at least one fruit/plant each year. One clonal stand had both hermaphroditic and functionally staminate flowers on the same plant. Two evolutionary pathways to dioecy in Z. americanum are proposed.