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J.R. Baggett, D. Kean, and N.S. Mansour

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James R. Baggett and R.O. Hampton

The inheritance of tolerance to infection by bean leaf roll luteovirus (BLRV) in Pisum sativum L. was studied in the cross of cv. Parlay (sensitive to BLRV infection) × cv. Oregon Sugarpod II (BLRV tolerant). The parents, reciprocal F1, back-crosses, F2, and 234 random F3 families were screened in 1986 and 1987 in the field at Twin Falls, Idaho, under natural BLRV inoculation by aphids. Overall disease index scores for the F1, F2, and F3 were about intermediate between indices of the parents, with the F1 usually slightly higher than midparent values. Backcross disease indices were intermediate between the F1 and the respective parent involved. Distribution of individual F3 family indices was continuous and semi-normal. BLRV-sensitivity ranges within parents and selected cultivars, as well as segregating populations showed continuous variation and differed between the 2 years, suggesting that expression of a major gene was significantly influenced by natural variation in BLRV inoculation pressure and timing. An apparent “additive gene action” was probably an artifact of nonuniform timing and levels of infection within plant populations. Chi-square analyses of segregating populations indicated that a major recessive gene, called lrv, conferred BLR disease tolerance.

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Paul W. Bosland, Jaime Iglesias, and Max M. Gonzalez

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Randolph G. Gardner

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Paul C. St. Amand and Todd C. Wehner

Heritability of resistance to gummy stem blight (Didymella bryoniae (Auersw.) Rehm.) was measured in two diverse cucumber (Cucumis sativus L.) populations [North Carolina elite slicer 1 (NCES1) and North Carolina wide base pickle (NCWBP)]. Heritability was estimated using parent-offspring regression and half-sib family analysis in North Carolina field tests during 1991 and 1992. NCES1 is a slicing cucumber population with a narrow genetic base, and NCWBP is a pickling cucumber population with a wide genetic base. Heritability estimates were low to moderate ranging from 0.12 to 0.49 for the gummy stem blight leaf rating and from -0.03 to 0.12 for stem rating. Estimates of gain from selection were at least two times larger for selection based on half-sib families than for mass selection for all traits in both populations. Approximately three to five cycles of selection would be required to improve the NCES1 population mean for gummy stem blight leaf resistance by one rating scale unit, and three to four cycles of selection would be required to improve the NCWBP population mean for gummy stem blight leaf resistance by one rating scale unit, based on half-sib family selection. One rating scale unit decrease is equivalent to an 11% reduction in susceptibility. Gain would be slower if selecting for stem, or leaf and stem resistance. A moderate amount of additive genetic variation exists in both populations for gummy stem blight leaf resistance, but estimates for additive genetic variation for stem resistance indicate little to no additive genetic variation. Development of populations specifically for greater initial resistance and greater additive variance than found in these populations should aid in selection for resistance.

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Marisa Wall and Joe Corgan

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V.I. Shattuck and B. Brolley

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Timothy J Ng, Anita N. Miller, and T.H. Barksdale

A tomato (Lycopersicon esculentum Mill.) breeding line (81B416) with' resistance to anthracnose caused by Colletotrichum dematium was crossed to three susceptible genotypes. Parental, F1, F2, and backcross populations were analyzed in the cross with `US28', while parental, F1, and F2 populations were tested in crosses of 81B416 with `US141' and 81B9. Inheritance of resistance was primarily additive, but 3- and 6-factor scaling tests indicated the presence of dominance and epistatic effects. The average broad-sense heritability estimate was 0.57; narrow-sense heritability was estimated at 0.42.

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James R. Baggett, Deborah Kean, Brian Yorgey, Diane Barrett, and G.W. Varseveld