Search Results

Abstract

Forty-five plants of sweet potato (Ipomoea batatas (L.) Lam.) taken randomly from the second cycle of a mass-selection population, and 25 open-pollinated progeny from each were used to estimate heritabilities (h²) of 7 root traits: root weight, 0.25 ± 0.13; intercellular space (IS), 0.70 ± 0.14; percent of dry matter (DM), 0.65 ± 0.12; sprouting, 0.39 ± 0.14; flesh oxidation, 0.24 ± 0.13; flesh color, 0.53 ± 0.14; and cortex thickness, 0.25 ± 0.13. IS was distributed normally with mean and mode of about 7%. DM had a bimodal distribution with mean 28.8 and modes of 27 and 31%. At least 2 genetic systems were apparently involved in expression of DM; one was associated with orange flesh and the other, with white flesh. This is the first report of the h² for IS, DM, and sprouting.

Abstract

Variance component estimates were obtained in a North Carolina Design I experiment for several traits in pickling cucumber (Cucumis sativus L.) for a simulated once-over mechanical harvest. The reference population was random-mating and derived from 18 inbred lines obtained from several U.S. breeding programs. Environments sampled were the spring and fall of a single year. Data indicated most of the genetic variance was additive for all traits except fruit color. Evidence for relatively large genotype by environment interaction variances were found for number of fruit, length to diameter (L/D) ratio, and fruit firmness. Heritabilities, based on full-sib families grown in 2 replications in each of 2 seasons, for dollar value and number of fruit, were .19 and .17 respectively. Genotypic and phenotypic correlations for number of fruit and dollar value were high indicating selection for increased number of fruit would be effective in increasing crop value.

Abstract

Cultivar emergence base (CEB) temperatures were calculated for the tomato (Lycopersicon esculentum Mill.) cvs. G-18824 and H2134 and their hybrid progenies. Each population required a mean accumulation of 160 daily heat units above their CEB. The early emerging parent had a low CEB of 42.6°F, the late emerging parent had a high CEB of 46.1°F, and their progenies were intermediate. The CEB of each cultivar and progeny was the same at different temperatures. Inheritance was found to be quantitative and an estimated 24 gene pairs differentiated the parents for CEB. There was strong evidence for additive gene action. Dominance and epastasis were not ruled out. Broad sense and narrow sense heritability estimates were 25-40% and 25% respectively. The same gene system appears to control emergence at both low and high temperatures. Selection for emergence at low temperature could be achieved at high temperatures on the basis of CEB.

Improving melon root systems by traditional breeding is one component of the program to develop multiple-stress-resistant melons at the Texas Agricultural Experiment Station, Weslaco. Ten diverse melon lines representing four horticultural groups were intercrossed utilizing a Design II mating scheme. The male parents were: `PI 403994,' `Perlita,' `Doublon,' `Caravelle', and `PI 525106.' The female parents were: `Créme de Menthe,' `Magnum 45,' `BSK,' `PI 124111 × TDI', and `Deltex.' F₁ progeny were grown in pasteurized sand in the greenhouse using a randomized complete-block design with four reps. After 4 weeks, root systems from all plants were carefully washed to remove the sand. Each root system was then placed onto a glass, plated, and scanned into the computer software Rhizo Pro 3.8 (Regent Instruments, Quebec). This software calculated root lengths of various diameter classes, root area, and root tip number. All data was input into Agrobase software for calculation of genetic variances based on Design II analysis. Significant differences of contributions by male parents to progeny variation were few. Only length of roots with 1.0- to 1.5-mm-diameter and vine length were significantly different. Differences in contributions by female parents to all traits except root tip number were highly significant. No significant interaction effects were observed for any trait. Narrow-sense heritability estimates were moderate to high for all traits. The range was from 0.56 for root tip number by males to 0.81 for both length of 0.5- to 1.0-mm-diameter roots and vine length for females. Estimates for total root length (0.76) and root surface area (0.77) were high. The lack of male by female interaction suggests very low dominance genetic variation and contributed to high heritability estimates, which represent predominantly additive gene action. Additive genetic variation allows more-efficient progress by selection, making the potential for root system improvement favorable.

Abstract

The heritability of efficiency in phosphorus utilization under deficiency stress was investigated using 6 bean families derived from crosses between selected efficient, moderately inefficient, and inefficient lines. Total plant dry weight (DW) was used as an index of efficiency. Epistasis, notably additive by additive and dominance by dominance gene effects, made imyor contributions to the efficiency in P utilization. Additive and dominance gene effects also made significant contributions. Estimates of broad sense heritability for total plant DW showed that efficiency in P utilization was a highly heritable trait. Narrow sense heritability estimates for total plant DW were high in all families studied.

Seventy-seven trees representing 41 hazelnut (Corylus avellana L.) genotypes were to evaluate variance components and broad-sense heritability for 10 nut and kernel traits from 1994 to 1996. All effects in the models were assumed to be random. All traits had extremely high heritability. This indicated that nearly all of the phenotypic variation had a genetic basis. Knowledge of variance components may help us efficiently allocate resources. Broad-sense heritability estimates were larger than those in narrow sense, suggesting the presence of nonadditive genetic variation in the population.