G.H. Mohamedali and A.H. Nourai
Jack E. Staub, Isabelle Y. Delannay, and Jin-Feng Chen
Don R. La Bonte, Christopher A. Clark, Tara P. Smith, Arthur Q. Villordon, and C. Scott Stoddard
Robert G. Fjellstrom and Paul H. Williams
Thirty-seven Brassica rapa L. and B. juncea L. lines from nine subspecies were tested for their reaction to two pathotypes of Fusarium yellows (Fusarium oxysporum Schlecht. f. sp. conglutinans (Wr.) Snyd. & Hans. race 1 and F.o. f. sp. raphani Kend. & Snyd. A subset of 16 lines from these same vegetable types were tested for their reaction to four strains of turnip mosaic virus (TuMV-C1, C2, C3, and C4). Resistance to both Fusarium pathotypes was widespread in these Brassica subspecies, whereas resistance to any strain of TuMV was uncommon. The broad availability of resistance to Fusarium yellows and scarcity of resistance to TuMV necessitate different approaches to obtain disease-resistant cultivars.
S. Alan Walters, Nischit V. Shetty, and Todd C. Wehner
Gene linkage was investigated in 11 families using 18 genes in cucumber (Cucumis sativus L.). The genes studied were B (black spine), B-3 (Black spine-3), B-4 (Black spine-4), bi (bitterfree cotyledons), Bt (bitter fruit), Bt-2 (bitter fruit-2), D (dull fruit skin), df (delayed flowering), de (determinate habit), F (female sex expression), gl (glabrous foliage), lh (long hypocotyl), ns (numerous spines), pm-h [powdery mildew (Sphaerotheca fuliginea Schlecht.:Fr.) resistance expressed on the hypocotyl], ss (small spines), Tu (tuberculate fruit), u (uniform immature fruit color), and w (white immature fruit color). A major objective of this study was to measure linkages of genes for fruit bitterness (Bt and Bt-2), and spine color (B-3 and B-4) relative to previously studied loci: B, bi, D, de, df, F, gl, lh, ns, pm-h, ss, Tu, u, and w. The F2 progeny of LJ 90430 × PI 173889 segregated 13 bitter fruit: 3 nonbitter fruit, indicating that different genes are controlling fruit bitterness in these lines. Bt-2 is proposed as the gene controlling bitterness of fruit in LJ 90430. It is a separate locus from Bt, that causes bitter fruit in PI 173889. Several new gene linkages were found: bi—Bt, (Bt-2)—de, D—(Bt-2), D—ns, gl—F, ss—(Bt-2), Tu—(Bt-2), and u—(Bt-2). The Bt gene appears to be linked to bi and may be located on linkage group I. Bt-2 appears to be linked with several genes that could connect linkage groups I and IV. Bt-2 was linked to u, Tu, D, and ss, that are all on linkage group IV. Bt-2 was also found to be linked loosely to de, that is on linkage group I. No linkages were found between B-3 and B-4 and the genes evaluated in this study. Weak linkages (>25 cM) between several gene combinations [(Bt-2)-de, de—ns, de—ss, de—Tu, de—u, ns—F, and ss—F] provided more evidence that linkage group I and IV may be linked. Due to the weak linkages, more information needs to be obtained using larger populations and more markers to confirm these findings.
James R. Baggett, N.S. Mansour, and Deborah Kean
Rejah Muhyi and Paul W. Bosland
A reliable screening method to detect Rhizoctonia solani Kuhn resistance in chiles (Capsicum annuum L.) was developed using infested corn (Zea mays Bonaf.) kernels as inoculum. The most aggressive New Mexican isolate of R. solani (PWB-25) was used to screen 74 Capsicum accessions for resistance to root rot caused by the fungus. The accessions differed in resistance, with disease ratings ranging from 2.9 to 8.6 on a 0 (no disease) to 9 (seedling dead) scale. The percentage of resistant plants, those in the interaction phenotype index class 0, 1, 2, and 3, ranged from 2.4% to 77.1%. Nineteen accessions representing four species had ≥50% resistant individuals and would be useful in breeding programs.
Elzbieta U. Kozik and Todd C. Wehner
An experiment was conducted to determine the genetics of chilling resistance in cucumber (Cucumis sativus L.) inbred NC-76 that was developed from PI 246930, an accession from the U.S. Department of Agriculture germplasm collection. NC-76 was crossed with ‘Chipper’ and breeding line Gy 14 to produce F1, F1 reciprocal, F2, and BC1 generations for evaluation. Cucumber seedlings at the first true leaf stage were placed in growth chambers set at 4 °C for 7 h and a photosynthetic photon flux of 500 μmol·m−2·s−1. Segregation in the F2 fit a 3 : 1 inheritance pattern, with resistance being dominant. The backcross of the F1 to the susceptible parent produced a 1 : 1 ratio, confirming that chilling resistance was from a single gene. The single dominant gene controlling chilling resistance in NC-76 was given the symbol Ch.