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  • Author or Editor: T. J Ng x
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An Impatiens germplasm collection consisting of accessions (from Africa, New Guinea [NG[, Sri Lanka, and Java/Celebes, a NG breeding population, and selected interspecific hybrids was characterized for 32 morphological traits and two ensyme systems, peroxidase (PER) and aspartate amino transferase (AAT). Thirteen PER and three AAT isozymes were identified, and both enzyme systems appeared to be co-dominatly inherited. There were unique zymograms for the accessions and the interspecific hybrids, but not the NG breeding population.

A Generalized Fisher Exact Test indicated that qualitative characters of the accessions were independent of each other, of isozyme traits and of geographical origin of the accession; this was not true for isozymes. Principal component analysis combining both morphological and isozyme traits uniquely separated the accessions while also indicating clusters of similarity. Extensive genetic diversity was indicated for all traits in the accessions and for quantitative traits in the NG breeding population.

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Abstract

The reactions of 50 cultivars and breeding lines of muskmelon (Cucumis melo L.) to inoculation with a pathogenic strain of Myrothecium roridum Tode ex Fries were evaluated using detached leaf tissues from greenhouse plants and immature fruits from field-grown plants. Leaf susceptibility was characterized by chlorosis, necrosis, and extensive fungus sporulation, whereas fruit susceptibility was evidenced by host tissue decay and fungus sporulation. Differences in reactions among muskmelon cultigens using detached leaves were consistent among tests and correlated well with susceptibility of young, immature fruits. Tolerance appeared to decrease with increasing physiological age of the immature fruits. ‘Hales Best’ exhibited the greatest tolerance, whereas ‘Summet’ was very susceptible.

Open Access

A tomato (Lycopersicon esculentum Mill.) breeding line (81B416) with' resistance to anthracnose caused by Colletotrichum dematium was crossed to three susceptible genotypes. Parental, F1, F2, and backcross populations were analyzed in the cross with `US28', while parental, F1, and F2 populations were tested in crosses of 81B416 with `US141' and 81B9. Inheritance of resistance was primarily additive, but 3- and 6-factor scaling tests indicated the presence of dominance and epistatic effects. The average broad-sense heritability estimate was 0.57; narrow-sense heritability was estimated at 0.42.

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Mesophyll cells are desirable targets for studying responses to pathogens or pathogen-induced toxins. Based on host-pathogen or host-toxin interaction studies at the cellular level it can be determined whether a toxin can be used as a selective agent. Suspension cells are suitable selection units for in vitro selection of potentially useful somaclonal variants. Protocols for the isolation of muskmelon mesophyll and suspension cells were developed in order to study the effects of roridin E, a toxin produced by Myrothecium roridum, on leaf spot tolerant and sensitive muskmelon cultivars. Viable mesophyll cells were obtained by exposing leaf tissue to 1% cellulysin and 5% macerase in B5 medium with 0.4M sucrose for one hour. Viable suspension cells were maintained a medium consisting of MS salts, 3% sucrose, 3 (μM thiamine·HCl, 555 μM myo-Inositol, 28 μM kinetin and 9 μM IAA. Fluorescein diacetate was used to determine viability over time. Membrane stability was monitored by measuring changes in the fluorescence of cells stained with Merocyanine 540 (MC 540), an optical probe for changes in transmembrane electrical potential (PD).

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Cucumis melo L. (muskmelon) is susceptible to Myrothecium roridum at all stages of growth with no known source of resistance. Screening of regenerants from long-term cotyledonary-derived callus cultures of muskmelon cv. Hales Best (tolerant), Iroquois (susceptible), and Perlita (intermediate) was carried out to determine if novel plants with increased levels of resistance could be obtained. A detached-leaf bioassay was used to screen greenhouse-grown regenerants and seedlings of the three cultivars. Resistance was determined by measuring necrotic lesion diameter and chlorotic plus necrotic lesion diameter. No change in the level of resistance to M. roridum has thus far been observed. Thus, screening for somaclonal variation may not be aviable approach to recover resistance in muskmelon to M. roridum.

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Genetics of the host-pathogen interaction between Cucumis melo L. (muskmelon) and Myrothecium roridum were investigated by evaluating six populations: the parents, F1, F2, BCP1 and BCP2 of crosses between `Hales Best' (tolerant), `Perlita' (intermediate) and `Iroquois' (susceptible). A spore inoculation bioassay with detached-leaves was used to determine levels of resistance. Resistance was determined by measuring necrotic lesion diameter, chlorotic plus necrotic lesion diameter, and a subjective rating score. Parents and F1s had consistent performance while the segregating generations were inconsistent. Factors contributing to the response will be discussed.

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Genetics of the host-pathogen interaction between Cucumis melo L. (muskmelon) and Myrothecium roridum were investigated by evaluating six populations: the parents, F1, F2, BCP1 and BCP2 of crosses between `Hales Best' (tolerant), `Perlita' (intermediate) and `Iroquois' (susceptible). A spore inoculation bioassay with detached-leaves was used to determine levels of resistance. Resistance was determined by measuring necrotic lesion diameter, chlorotic plus necrotic lesion diameter, and a subjective rating score. Parents and F1s had consistent performance while the segregating generations were inconsistent. Factors contributing to the response will be discussed.

Free access

Abstract

Most progenies from intercrossed or outcrossed inbred selections of strawberry (Fragaria × ananassa Duch.), germinated as well or better than a control outcross between 2 vigorous noninbred clones. Germination of an S3 progeny was lower than the control. In general, inbreeding reduced seedling vigor while intercrossing or outcrossing of inbreds restored vigor. Germination total and rate as expressed by an index were unrelated to subsequent seedling growth.

Open Access