Foliar diseases are a major constraint to cultivated tepary bean (Phaseolus acutifolius A. Gray var. latifolius Freeman) production in some environments. The reactions of 12 cultivated teparies to eight individual races (41, 47, 49, 51, 53, 58, 67, and 73) of the bean rust fungus Uromyces appendiculatus (Pers.) Unger var. appendiculatus maintained at Beltsville, Md., were examined under greenhouse conditions. These diverse races, used together, overcome all of the major rust-resistance genes present within the 19 host differential cultivars of common bean (Phaseolus vulgaris L.). Seven lines (GN-605-s, GN-610-s, PI 321638-s, PI 502217-s, Neb-T-6-s, Neb-T-8a-s, and Neb-T-15-s) exhibited similarly high levels of resistance (immunity or necrotic spots without sporulation) to all eight races. Inheritance of resistance was examined across five susceptible × resistant (S × R) and three resistant × resistant (R × R) populations. The rust reactions in the F1, F2, and F3 generations derived from S × R crosses revealed that the immune or necrotic resistance response was conditioned by a single locus exhibiting incomplete dominance. The rust resistance of four lines tested for allelism in R × R crosses was found to be derived from the same gene. This apparent lack of variability for rust resistance suggests that a single introgression event may realize the full potential for cultivated tepary bean to contribute rust resistance to common bean through interspecific hybridization. In addition, the limited variability for resistance to the highly variable rust pathogen in cultivated tepary bean supports the occurrence of a “bottleneck effect” during domestication of this species, as observed in germplasm diversity studies.
Phillip N. Miklas and J. Rennie Stavely
Pecan [Carya illinoinensis (Wangenh.) K. Koch] fruit presents a considerable weight for the tree to support during the growing season. A major part of this weight is due to the pecan shuck that surrounds the developing nut and kernel. Pecan clones vary considerably for the amount of shuck per nut, and little is known as to the value of this weight in determining final nut quality. Six cultivars differing in basic nut shapes and sizes were studied and found to vary greatly for shuck thickness, and weight of shuck per unit final nut weight and volume. Shuck thickness was shown to be a favorable genetic characteristic since fruit with thicker shucks had slightly greater nut fresh and dry weight, nut volume, nut density, kernel weight and content, and shuck weight per nut volume. `Sioux' had the thickest shucks (4.70 mm), while `Pawnee' had the thinnest shucks (3.72 mm). Fresh weight per fruit varied from 21.25 g for `Podsednik' to 10.18 g for Osage. Weight of fruit per tree was extrapolated using average shuck and nut weights, and it was determined that the fruit on each tree would weigh about 104 kg. This is a considerable weight, and adds substantially to limb breakage. However, thicker shucks contribute to final nut quality.
Tommy E. Thompson and L.J. Grauke
Tommy E. Thompson, L. J. Grauke, and Leonardo Lombardini
In controlled tests, 110 cultivars (77.5%) of common bean (Phaseolus vulgaris L.) responded to broad bean wilt virus (BBWV) with a localized infection (resistant), while 32 cultivars (22.5%) reacted with local and systemic infection (susceptible). The majority of susceptible cultivars were of the yellow-podded (wax bean) and red kidney types. In F1, F2, and backcross populations of the BBWV-resistant cultivar Sanilac with the BBWV-susceptible ‘California Light Red Kidney’ (‘CLRK’) resistance to systemic infection was conferred by a single dominant gene, to which the symbol Bbw is assigned. BBWV was not transmitted in 471 ‘CLRK’ seeds derived from severely infected plants.
M. H. Dickson and R. Petzoldt
Narrow sense heritabilities were 28%, 56%, 45%, and 74%, respectively, imbibition at 5°C and, at 16°, for seedling vigor, plant vigor, and days to bloom in a cross of NY 590 × BBL 92. Cold tolerance at these stages was inherited independently. Pod set at 16° behaved as a recessive, compared to only setting at warmer temperatures. Selections made under 16° generally did very well in an unusually cool season in New York. Double setting was absent in lines that showed set at 16°, and present in many cultivars.
A single plant selection of the cucumber (Cucumis sativus L.) cultivar Taichung Mou Gua (TMG-1) from China was the source of resistance to zucchini yellow mosaic virus (ZYMV) in crosses with the domestic cultivars Marketer and Marketmore 76. In F1, F2, and reciprocal backcross populations, resistance to ZYMV-CT (Connecticut strain) was demonstrated to be conferred by a single recessive gene to which the symbol zym was assigned.
Shawn A. Mehlenbacher and Ralph Scorza
Inheritance of growth habit was studied in F1, F2, and backcross progenies of peach [Prunus persica (L.) Batsch ‘Com-Pact Redhaven’]. Segregation ratios indicate that compact growth habit is conditioned by a single dominant allele, for which ‘Compact Redhaven’ is heterozygous. The symbol Ct is proposed for this locus.
T. E. Thompson, E. F. Young Jr., W. O. McIlrath, H. D. Petersen, and G. S. Sibbett
Results are presented for performance of pecan [Carya illinoinensis (Wangenh.) C. Koch] clones at six established National Pecan Advanced Clone Testing System (NPACTS) sites for 16 nut quality factors from 1980 through 1985. Total nut weight and percent kernel were significantly greater at Tulare, Calif. than at any other location, with ≈80% of the clones averaging 6.5 g/nut or more and ≈90% averaging at least 54.5% kernel. Nut weight was smallest at El Paso, Texas. Daily mean temperatures during nut expansion may be a major factor determining nut weight response. Low nut density was characteristic of more clones at Baton Rouge, La. than at any other location. Kernel color was lightest at El Paso and darkest at Baton Rouge, with darker color appearing to be related to high field moisture conditions before harvest. Nut weight was not related to kernel percentage, color, or percent kernel covered with fuzz (packing material); thus, large nuts are not necessarily of lower quality and can be selected in an effective breeding program. Amount of nut “packing material” retained in the sutures of kernel halves after shelling was generally not related to other traits, except that material retained in ventral grooves increased with nut and kernel weight. Depth and width of dorsal grooves were not related to retention of packing material and can be disregarded in future pecan nut evaluation systems. Many other expected character relationships were verified and the overall NPACTS nut evaluation system will be revised based on these results.