floral longevity. In this study, 259 commercial inbred lines of impatiens were evaluated for floral longevity. A set of 12 inbreds was selected for diallel crossing to estimate GCA and SCA for floral longevity. These estimates can be used to determine how
complete diallel mating design. The diallel is a useful tool to estimate the combining abilities of inbreds and heterosis ( Griffing, 1956 ). The general combining ability (GCA) of an inbred is a measure of the average performance of hybrids from crosses
combining of dominant disease resistance genes, allow gene complementation, and have numerous other advantages ( Scott and Angell, 1998 ). Because hybrids are widely grown in Florida and elsewhere, a diallel analysis seemed appropriate to develop useful
To investigate the genetic control of rain check (cuticle cracking) in tomato (Lycopersicon esculentum), a full diallel cross including five parents ranging from very resistant to very susceptible was grown in late spring 1994. A randomized complete-block design with four replications was used and the proportion of fruit showing check was measured on all mature fruit from eight plants per replication at three harvests. Analysis of variance indicated significant (P < 0.0001) variation for line, harvest, and line by harvest interaction. The proportion of fruit affected increased with each successive harvest. Reciprocal differences were tested on a by-harvest basis and found to be nonsignificant. Reciprocals were combined and a Hayman's analysis was performed on a by-harvest basis on the means. Additive effects on variance were significant (P < 0.05) for all harvests. Under high environmental stress (harvest 3), dominance effects were negative and significant (P < 0.05). Narrow-sense heritability ranged from 0.54 to 0.67 and increased with increasing environmental stress. General combining ability was significant for all harvests, whereas specific combining ability was significant only for harvest 3 (P < 0.05).
are involved. Two specific experimental designs using field hand crosses (pairwise touching-neighbor and a 5 × 5 diallel) were performed and coupled with genetic similarity calculations from EST-PCR markers of breeding partners to better understand the
A 6-parent diallel was used to study combining ability and type of gene action contributing to resistance in tomato (Lycopersicon esculentum Mill.) to anthracnose caused by Colletotrichum dematium (Pers. ex Fr.). The 6 parents, one set of F1, hybrids, and 5 selected reciprocal crosses were grown at 2 locations. Ripe fruit were harvested, puncture-inoculated with the pathogen, and subsequently evaluated for resultant lesion diameter. No reciprocal effects were found at either location for the 5 crosses studied. The analysis of variance for parent and F1 hybrid performance revealed a genotype × location interaction. Combining ability analysis based on the F1 hybrids alone indicated a significant general combining ability (GCA) effect. The specific combining ability (SCA) and GCA × location interaction mean squares were smaller than the GCA value but were still significant. Differential performance over locations of the hybrids of one line was primarily responsible for the GCA × location interaction. Analysis of variance and covariance of parental arrays indicated partial dominance in the direction of susceptibility. Narrow sense heritability for the trait was 70% over both locations.
Five inbred lines of papaya (Carica papaya L.) ranging from susceptible to resistant to phytophthora root rot (Phytophthora palmivora Butl.) were crossed in a diallel, and inbred parents and F, progenies were inoculated with P. palmivora isolate P170. The diallel analysis of mortality from phytophthora infection indicated significant general combining ability and specific combining ability; the GCA: SC A mean square ratio of 15.7 indicated GCA to be more important than SCA. Parental means correlated well with hybrid array means (r=0.89).
Three orange-mesocarp derivatives of the xishuangbannan cucumber (Cucumis sativus L. var. xishuangbannanesis Qi et Yuan), P100, P101, and P104; and NPI (P105), an unrelated cucumber (Cucumis sativus L.) reported to have orange flesh, were selected as parents for a diallel experiment to evaluate inheritance of orange cucumber mesocarp pigment over 3 years. Visual color intensity and carotenoid content were closely related. A preponderance of additive genetic effects for cucumber mesocarp pigmentation was observed in grade size 2 fruit (immature fruit used for pickling). Both additive and nonadditive genetic effects were important in grade size 4 fruit (mature). Years and yea× genotype interactions were highly significant for pigmentation of size 2 fruit, indicating the importance of environment on the expression of pigmentation in this size class. In contrast, color development was stable among years for size 4 fruit. P104 exhibited high general combining ability (GCA) estimates for size 4 fruit pigmentation across years, while P101 had high GCA estimates for size 2 fruit. The diallel analysis illustrated high fruit carotene content of parents per se. However, most hybrid combinations of the diallel reduced carotenoid content relative to parents, indicating both dominance for low carotenoid content for both fruit sizes and lack of genetic complementation among parents to enhance fruit color. Genetic control of pigmentation in size 2 fruit appeared to be independent of that for size 4 fruit.
Genetic control of cuticle cracking (CC) in tomatoes (Lycopersicon esculentum Mill.) was studied using half-diallel analyses and reciprocal hybrid comparisons of five parents and reciprocal F1 hybrids over 3 years in Bradenton, Fla. Maternal effects were usually not significant, but in general, CC incidence in hybrids with a resistant cultigen as the female parent was lower than if the resistant cultigen was the male parent. General combining ability (GCA) was significant at all harvests, with specific combining ability (SCA) becoming significant under high environmental stress. Narrow-sense and broad-sense heritabilities for CC incidence ranged from 0.45 to 0.69 and 0.62 to 0.89, respectively, increasing directly with environmental stress.
Diverse carrot (Daucus carota L.) inbreds were evaluated as young plants in the greenhouse and mature plants in the field for resistance to the pathogen Alternaria dauci (Kühn) Groves and Skolko. Persistence of leaves after infection was the criterion used to estimate disease damage by the pathogen. Partial resistance was identified. A five-parent diallel evaluated for resistance indicated a preponderance of additive variation with some dominant gene action for resistance. Reciprocal cross differences were significant for certain crosses. Responses of most inbreds were useful in predicting resistance in their hybrids, but exceptions to this trend did occur. Field resistance ratings generally correlated well with resistance ratings obtained in greenhouse, even in grower fields where fungicides were applied.