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  • Author or Editor: G. Morris Southward x
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Allium cepa L., A. fistulosum L., A. galanthum L., and A. cepa × A. fistulosum reciprocal interspecific hybrids were grown in vitro as calluses, shoots, and plantlets, and exposed to the filtrate of the pink root disease-causing fungus, Pyrenochaeta terrestris (Hansen) Gorenz, Walker, and Larson. Tissue culture reponses to the filtrate were assessed by visible damage ratings and fresh weights. Calluses exposed to the filtrate incorporated into the culture medium reflected the degree of whole plant susceptibility among the tester lines. However, in vitro shoot and plantlet culture responses did not reflect this correlation. Filtrate action appeared to be localized in meristematic cells. This in vitro approach may prove useful in screening or selection for onion pink root disease resistance.

Open Access

Color loss of Chile pods (Capsicum annuum L.) weathered on and off the plant was compared to that of refrigerated powder of comparable pods. Pods were harvested at 4-week intervals, dried at 65C, and ground and analyzed for color. Powder from these fruit was stored at 2C and analyzed at 4-week intervals. Pods that were weathered on or off the plant lost redness at a rate about one-half of that for refrigerated powder during 84 days of storage or weathering.

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Callus cultures were established from intraspecific lines of Allium cepa L., interspecific F1 progeny of A. cepa crossed to A. fistulosum L. and to A. galanthum L., advanced generations of A. fistulosum x A. cepa backcrossed to A. cepa, and lines of A. fistulosum and A. galanthum. These genotypes had been identified as susceptible, resistant, or partially resistant tester lines based on prior seedling and field nursery screenings using the pink-root pathogen Pyrenochaeta terrestris (Hansen) Gorenz, Walker and Larson. Tester line calli were challenged in vitro with culture filtrates of the fungal pathogen and were assessed by visible damage ratings expressed as the percentage of pigmentation in response to the filtrate. The degrees of callus sensitivity to the filtrate observed in vitro corresponded well with the in vivo tester line classifications. These results eliminated the possible confounding influence of using various species of Allium for in vitro screening. Our results indicated the suitability of the in vitro screening approach for the possible identification of useful segregants or somaclonal variants possessing pink-root resistance. However, in vivo pathogenicity may involve mechanisms in addition to sensitivity to the putative toxins present in the filtrate.

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