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Spore Germination of Diplodia gossypina in the Presence of Carbohydrates and Phenolic Compounds in Relation to Boll Rot of Cotton. Sy-ying C. Wang, Formerly Postdoctoral Fellow, Louisiana Agricultural Experiment Station, Baton Rouge 70803, Present address of senior author: Sugar Experiment Station, Tainan, Taiwan; J. A. Pinckard, Professor, Louisiana Agricultural Experiment Station, Baton Rouge 70803. Phytopathology 63:1181-1185. Accepted for publication 22 March 1973. DOI: 10.1094/Phyto-63-1181.

Black boll rot of cotton (Gossypium hirsutum) caused by Diplodia gossypina is transmitted by spores extruded from pycnidia, the ostioles of which protrude through the epidermis of the carpel walls. The emerging spores are hyaline and nonseptate. These spores became dark colored and 1-septate about 6 hr after discharge. Maximum spore production occurred on bolls over 40 days of age (from anthesis) but before sutural dehiscence. Young, nonseptate, hyaline spores germinated more rapidly and with higher percentage than older 1-septate spores. Optimal conditions for germination occurred with approximately week-old spores at 30 C and at pH 6.5 to 7.0 in 1.0 × 103 M citrate-phosphate buffer. Germination was stimulated by boll surface washings and leachates of dewaxed bolls but inhibited by extracts of cuticular fractions. Spore germination was stimulated by 12 of 14 carbohydrates tested and inhibited by all of the 11 phenolic compounds tested. Polygalacturonase was released during spore germination in the presence of Na-polypectate, polygalacturonic acid, pectin, xylan, CM-cellulose, araban, and boll leachates.