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  • Author or Editor: Ellis Caniglia x
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Two hundred sixty-six Citrullus lanatus (Thumb.) Matsum. & Nakai accessions (Plant Introductions and named cultivars) were tested against a race 2 Sphaerotheca fuliginea (Schlechtend.: Fr.) Pollacci isolate to evaluate for resistance to powdery mildew disease. Growth room-grown seedlings were artificially inoculated with conidia from watermelon host leaves at 2-day intervals from the appearance of the first true leaf until test results data were taken, when the second true leaf was fully expanded. Plants were evaluated on a 1 to 9 scale of increasing disease severity. Disease indices (DIs) were calculated as weighted averages for each entry. All genotypes with resistant plants (powdery mildew rating 1 to 3) were reevaluated in a replicated test of 3 replications of 10 plants each. Disease indices were again calculated. Twenty-two plant introductions (PIs) and one named variety displayed intermediate resistance to powdery mildew in the replicated test with DIs ranging from 5.0 to 6.0.

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Broccoli (Brassica oleracea L. Italica Group) breeders routinely use anther or microspore culture to produce doubled-haploid (DH), homozygous lines. In addition to DH (diploid) regenerants, haploid, triploid, tetraploid, octaploid, and aneuploid regenerants may also result from anther culture. Thus, regenerated populations must be screened to identify the diploids, which are the only regenerants likely to set seed and serve as inbred lines. DNA flow cytometry is a useful procedure to determine ploidy of anther-derived regenerants. This study was undertaken to evaluate the effect of plant stage and sampling procedures on ploidy determination by flow cytometry. Anther-derived plants were analyzed at both seedling and mature plant stages. In separate tests, leaves were sampled on a given date, and stability of flow cytometry preparations were evaluated at 1, 2, 4, and 7 days after preparation. In addition, the stability of ploidy readings of excised leaves stored at 4 °C was examined over a 7-day period. In 139 out of 140 comparative assays there was no effect of plant stage on ploidy determination. Flow cytometry preparations stored at 4 °C gave consistent ploidy determinations up to 2 days after they were made, but some instability was observed by 4 and 7 days. Refrigerated leaves were more stable than nuclei preparations, and ploidy determinations did not differ from the first sampling through storage for 7 days. Results indicate that broccoli breeders could make flow cytometry preparations on site and send them offsite for flow cytometry analysis as long as analysis was completed within 1 or 2 days of sample preparation. More consistent results would be obtained by refrigerating leaves and sending them offsite for preparation and analysis at the offsite location.

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Broccoli (Brassica oleracea L. Italica group) breeders routinely use anther or microspore culture to produce dihaploid (diploid), homozygous lines. During the culture process, polyploidization occurs and diploid regenerants can result. However, polyploidization may not occur at all, or it may involve a tripling or quadrupling of the chromosome complement. Thus, regenerated populations must be screened to identify the diploids that are the regenerants most likely to set seed and serve as inbred lines. DNA flow cytometry has proven a useful procedure for determining ploidy of anther derived regenerants. This study was undertaken to evaluate the effect of leaf age and sampling procedures on ploidy determination via flow cytometry. Anther-derived plants were analyzed at a four- to five-leaf stage (transplant stage) and at time of heading (mature plant stage). In addition, leaves were sampled on a given date and stability of the flow cytometry preparations was evaluated over 7 days. Lastly, the stability of ploidy readings of leaves stored at 4°C was examined over a 7-day period. In only one case out of 123 comparative assays did leaf age affect ploidy determination. For that exception, a haploid at transplant stage was a diploid at the mature plant stage. Flow cytometry preparations and also leaves stored at 4°C gave consistent ploidy determinations up to four days after preparations were made or tissue was refrigerated, respectively. These results indicate that broccoli breeders can make flow cytometry preparations on site and send them offsite for flow cytometry analysis. Alternatively, leaves could be refrigerated, sent offsite, and then prepared and analyzed at another location.

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