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  • Author or Editor: Timothy J Ng x
  • Journal of the American Society for Horticultural Science x
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Abstract

Five parental cultivars of muskmelon (Cucumis melo L.) and 16 F1 hybrids, including six reciprocals, were evaluated in a diallel design for reaction to inoculations with Myrothecium roridum and its phytotoxic metabolite roridin E using a detached leaf screening test. Analyses of variance revealed genetic variability for tolerance to the fungus and to the toxin; the correlation coefficient between inoculations with the pathogen and the toxin was 0.94. Disease and toxin tolerance were associated with highly significant general combining ability (GCA) effects, but specific combining ability were significant only for inoculations involving the pathogen. The GCA component accounted for 95.8% of the genotypic variation for pathogen tolerance and 99.3% for toxin tolerance. Reciprocal effects were not present in either set of inoculations.

Open Access

Abstract

Changes in respiration, ethylene production, firmness, pectolytic enzyme activity and carotenoid accumulation during ripening were monitored in fruit of a segregating population of the non-ripening (nor) mutant of tomato (Lycopersicon esculentum Mill.). In fruit from mutant (nor/nor) plants, no respiratory or ethylene climacteric was observed, firmness declined very slowly with only trace levels of polygalacturonase present in mature fruit and phytoene, β-carotene and neurosporene were the major carotenes. In very old fruit (120 days’ post-anthesis), lycopene and β-carotene were the predominant carotenoids, however lycopene content was less than 10% of normal.

Ripening of fruit from heterozygous (nor+/nor) plants was delayed and occurred more slowly than for normal (nor+/nor+ ) fruit. The respiratory climacteric was partially suppressed, peak ethylene production was one-sixth of normal, fruit softening was retarded, and polygalacturonase activity was lower at comparable maturity stages. Fruit from heterozygous (nor+nor) plants accumulated lycopene, gamma-carotene, phytofluene, and phytoene at a slower rate, but β-carotene accumulation was similar to normal. A mechanism for action of nor in control of ripening is proposed.

Open Access

Abstract

The inheritance of low temperature seed sprouting ability in tomato (Lycopersicon esculentum Mill.) was found to be polygenic with dominance for inability to germinate at suboptimal temperatures. A minimum of 3 genes is suggested from F2 data and a minimum of 5 genes from backcross results. Broad sense heritability was estimated at 97%; narrow sense heritability, at 66%.

Genes controlling determinate, brachytic, and dwarf habits of growth had no significant effect upon subsequent low temperature sprouting response in the F2 generation. Significant differences in ability to germinate at low temperatures were found among reciprocal F1’s.

Open Access

Studies examining exposure methods and callus type were conducted to develop an in vitro selection system using roridin E as a selection agent. Vacuum infiltration of callus with the toxin solution was the only successful selection method at the concentrations tested. Primary callus (callus originating directly from the explant) was not sensitive to roridin A or E at the concentrations used. Secondary callus (callus produced from primary callus) exhibited a differential response to roridins A and E similar to that of detached-leaf assays. Electrolyte leakage studies of callus were not conclusive in establishing the membrane as the site of toxin action or useful for screening tolerance in vitro. A small percentage of callus from tolerant and susceptible cultivars survived repeated exposure to roridin E at 50 μg·ml-1.

Free access

Abstract

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.

Open Access

Abstract

Six inbred tomato (Lycopersicon esculentum Mill.) genotypes and 13 hybrids among them were evaluated at two locations for resistance to early blight (Altemaria solani). The breeding lines 71B2, C1943, and NC EBR-1 were the most resistant, while ‘Castlejay’ was consistently the most susceptible. Hybrid means for area under the disease progress curve (AUDPC) generally were intermediate to their parental values, indicating quantitative genetic control. Five of the parents were included in a diallel mating design to obtain estimates of general combining ability (GCA) and specific combining ability (SGA) for the resistance trait. Both GCA and SCA were highly significant; the GCA component accounted for 88.2% of the genotypic variation.

Open Access

Abstract

Data from 2 experiments, each involving a set of 6 muskmelon cultivars grown over a period of 4 years, were subjected to joint regression analysis to characterize performance across environments. ‘Burpee’ and ‘Gold Star’ were common to both experiments. A majority of the cultivars exhibited linear response for yield but not for fruit characteristics. There were also significant differences in regression coefficients among cultivars in each experiment. ‘Burpee’ and ‘Gold Star’ each had similar joint regression coefficients in both experiments for total weight of fruit per plant, but not for total number of fruit.

Open Access