Pale green lethal seedlings of apple (Malus spp.) are characterized by yellowish green color, poor growth of lateral roots, of epicotyl and of leaves, early cessation of apical meristematic activity, and death of the whole plant in about 1 month. Lethal seedlings occur in about 25% of the progeny of 2 heterozygous diploid parents. By this test we determined the homozygosity of 107 diploids (LL) and the heterozygosity of 97 diploids (LI). Among tetraploids 12 were quadriplex (LLLL) and 8 were probably duplex (LLll) or triplex (LLLl), but the expected ratios were not obtained.
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.
Ozone sensitivity was compared in F1 and F2 populations from crosses between 2 ozone-sensitive bean cultivars, ‘Spurt’ and ‘Blue Lake Stringless’, and 2 ozone-resistant cultivars, ‘Black Turtle Soup’ and ‘French’s Horticultural’, under controlled environmental conditions. F1 plants were as sensitive as the sensitive parent. About 10% of the F2 progeny obtained by selfing F1 plants appeared to be as resistant as the resistant parent and 90% of the progeny could be divided equally between a group as sensitive as the sensitive parent and a group intermediate in sensitivity between the parent plants. However, precise separation of F2 progeny was not possible because of the variability in injury expression. The average injury on the F2 plants was greater than the parental midpoint value and the variance in injury on the F2 plants was about 3.5x greater than that for the parents. The heritability of resistance to ozone was estimated to be 0.83. It was concluded that ozone resistance is recessive in P. vulgaris and appears to be regulated by a few major genes.
Inheritance of resistance to tomato anthracnose caused by Colletotrichum coccodes (Wallr.) S.J. Hughes was evaluated in parental, F1, F2, and backcross populations developed from crosses between adapted resistant (88B147) and susceptible (90L24) tomato (Lycopersicon esculentum Mill.) breeding lines. Resistance was evaluated via measurement of lesion diameters in fruit collected from field-grown plants and puncture inoculated in a shaded greenhouse. Backcross and F2 populations exhibited continuous distributions suggesting multigenic control of anthracnose resistance. Anthracnose resistance was partially dominant to susceptibility. Using generation means analysis, gene action in these populations was best explained by an additive-dominance model with additive × additive epistatic effects. A broad-sense heritability (H) of 0.42 and narrow-sense heritability (h2) of 0.004 was estimated for resistance to C. coccodes. One gene or linkage group was estimated to control segregation for anthracnose resistance in the cross of 90L24 × 88B147.
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.