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P. Healey, T.J Ng, and F.A. Hammerschlag

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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Timothy J Ng, Anita N. Miller, and T.H. Barksdale

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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W.A. Mackay, T.J Ng, and F.A. Hammerschlag

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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W.A. Mackay, T.J Ng, and F.A. Hammerschlag

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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W.A. Mackay, T.J Ng, and F.A. Hammerschlag

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.