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C.S. Kousik, D.C. Sanders, and D.F. Ritchie

The impact of a single hail storm injury in combination with bacterial spot caused by Xanthomonas campestris pv. vesicatoria was assessed on three commercial pepper (Capsicum annuum) cultivars—King Arthur, Jupiter, and Rebell. In addition, the effectiveness of copper plus maneb sprays on hail-damaged plants to suppress bacterial spot was evaluated. A hail storm of ≈5-min duration severely damaged and defoliated the pepper plants. Severe bacterial spot was observed 10 days later on all plants. Disease ratings taken 2 weeks after the hail storm were significantly greater than ratings before the storm. Unsprayed plots of all three cultivars had the greatest disease and the least yield. Plots sprayed weekly (7-day schedule) had a significantly greater yield and less disease compared to unsprayed and biweekly sprayed (14-day schedule) plots for all three cultivars. The combination of hail damage and bacterial spot resulted in a 6-fold reduction in yield in the absence of copper plus maneb sprays and a 2-fold reduction with weekly sprays when compared to the previous season with no hail injury, but similar levels of bacterial spot disease. Disease ratings were less and yields were greater for `King Arthur', than for `Jupiter' and `Rebell'. A judicious copper plus maneb spray program can suppress bacterial spot and help recovery of a young pepper crop when hail damage occurs.

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Howard F. Harrison Jr, Amnon Levi, and C.S. Kousik

Watermelon [Citrullus lanatus v. lanatus (Thunb.) Matsum & Nakai] seed exudates are inhibitory to germination and seedling growth of other plant species. A miniature bioassay experiment that measured proso millet (Panicum miliaceum L.) radicle growth was used to assess the inhibition caused by seed exudates of 125 genotypes of watermelon and related Citrullus species. Exudates of most genotypes were not inhibitory; however, exudates of 53 accessions reduced radicle growth in comparison with the control. In subsequent proso millet radicle growth experiments, genotypes were found to vary in inhibitory potential, and concentration response curves generated using filtered, pasteurized exudates were different among genotypes. Filter-sterilized seed exudates of Citrullus accessions also varied in the level of inhibition in a bioassay that measured their effect on sporangia formation by the watermelon pathogen, Phytophthora capsici. These observations suggest that constituents in Citrullus seed exudates affect organisms in the spermosphere and that the inhibitory potential of seed exudates varies among genotypes. Differences in concentration response curves in the millet bioassay and differences in the relative inhibition of genotypes in the millet and fungus bioassays indicate that the inhibitory constituents in seed exudates vary among genotypes.