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Regina Fernandes, Irvin Widders and Mark Uebersax

Sand culture experiments were conducted in controlled environments to determine the effects of endogenous fruit Ca concentration on tissue firmness and the rates of softening following fresh-pack processing of pickling cucumbers. Fruit Ca status was modified by exposing the cucumber plants to 0.01, 0.1, 10, and 20 mM Ca in the nutrient solutions from fruit set to harvest. Ca concentrations were measured in pericarp and endocarp tissue. Spears were 4.5 cm diam. fruit were fresh-pack processed in 0, 5 or 20 mM CaCl2 solutions. Tissue texture during incubation at 46°C was measured at 0, 5 and 20 days using a shear press (TMS-90, Food Tech. Corp.). Pericarp tissue Ca concentrations were positively correlated with tissue firmness immediately following fresh-pack processing. High endogenous Ca levels, however, were correlated with high rates of pericarp softening during accelerated aging. Refrigeration extended the Ca effect on texture for 3 weeks following processing.

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George L. Hosfield, James D. Kelly and Mark A. Uebersax

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Kimberly J. Walters, George L. Hosfield, Mark A. Uebersax and James D. Kelly

Three populations of navy bean (Phaseolus vulgaris L.), consisting of recombinant inbred lines, were grown at two locations for 2 years and were used to study canning quality. The traits measured included visual appeal (VIS), texture (TXT), and washed drained mass (WDM). Genotype mean squares were significant for all three traits across populations, although location and year mean squares were higher. We found a positive correlation (r = 0.19 to 0.66) between VIS and TXT and a negative correlation (r = -0.26 to -0.66) between VIS and WDM and between TXT and WDM (r = -0.53 to -0.83) in all three populations. Heritability estimates were calculated for VIS, TXT, and WDM, and these values were moderate to high (0.48 to 0.78). Random amplified polymorphic DNA markers associated with quantitative trait loci (QTL) for the same canning quality traits were identified and studied in each population. Marker-QTL associations were established using the general linear models procedure with significance set at P=0.05. Location and population specificity was common among the marker-QTL associations identified. Coefficient of determination (R2) values for groups of markers used in multiple regression analyses ranged from 0.2 to 0.52 for VIS, 0.11 to 0.38 for TXT, and 0.25 to 0.38 for WDM. Markers were identified that were associated with multiple traits and those associations supported correlations between phenotypic traits. MAS would offer no advantage over phenotypic selection for the improvement of negatively associated traits.

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Frank M. Elia, George L. Hosfield, James D. Kelly and Mark A. Uebersax

A knowledge of the relative proportion of additive and nonadditive genetic variances for complex traits in a population forms a basis for studying trait inheritance and can be used as a tool in plant breeding. A North Carolina Design II mating scheme was used to determine the inheritance of cooking time, protein and tannin content, and water absorption among 16 genotypes of dry bean (Phaseolus vulgaris L.) representative of the Andean Center of Domestication. Heritability and the degree of dominance for the traits were also calculated to provide guidelines for adopting breeding strategies for cultivar development. Thirty-two progeny resulted from the matings and these were assigned to two sets of 16 progeny each. Variances due to general combining ability (GCA) and specific combining ability (SCA) were significant for the traits. The GCA was larger in all cases. Narrow-sense heritability for protein, tannin, water absorption, and cooking time averaged 0.88, 0.91, 0.77, and 0.90, respectively. Degree of dominance estimates indicted that the traits were governed by genes with partial dominance except, in one case, tannin had a degree of dominance value of zero, indicating no dominance. The phenotypic correlation (-0.82) between water absorption and cooking time justifies using the water absorption trait as an indirect selection method for cooking time. With regard to parent selection in crosses, significant differences between GCA females and GCA males suggested cytoplasmic influences on trait expression. Hence, the way a parent is used in a cross (i.e., as female or male) will offset trait segregation. Using fast-cooking bean cultivars in conjunction with fuel-efficient cooking methods may be the best strategy to conserve fuelwood and help reduce the rate of deforestation in East and Central Africa.

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Maria-Carmela T. Posa-Macalincag, George L. Hosfield, Kenneth F. Grafton, Mark A. Uebersax and James D. Kelly

Canning quality of dry bean (Phaseolus vulgaris L.), of which the degree of splitting (SPLT) and overall appearance (APP) of canned beans are major components, is a complex trait that exhibits quantitative inheritance. The objectives of this study were to identify major genes that affect APP and SPLT in kidney bean, and map the location of these loci to the integrated core map of common bean. The analysis was performed using random amplified polymorphic DNA (RAPD) markers and two populations of kidney bean, consisting of 75 and 73 recombinant inbred lines (RILs), respectively. The two populations—`Montcalm' × `California Dark Red Kidney 82' and `Montcalm' × `California Early Light Red Kidney'—were planted in six year-location combinations in Michigan, Minnesota and North Dakota from 1996 to 1999. Correlations between APP and SPLT were high (0.91 to 0.97). Heritability estimates for APP and SPLT ranged from 0.83 to 0.85 in the two populations. Major genes for these traits were identified on two linkage groups. The first QTL, associated with seven RAPD markers, was putatively mapped to the B8 linkage group of the core bean linkage map. Desirable canning quality appeared to be derived from Montcalm at this locus. The second QTL, associated with four markers, appeared to be derived from the California parents. The second linkage group was not assigned to a linkage group in the core map. Population and environment-specificity were observed for the markers identified.