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Disease caused by Fusarium solani f.sp. phaseoli in mung bean grown in hydroponic solutions was influenced by temperature and hydrogen ion concentration but not by ambient humidity or light quality. Differences in fresh weights between inoculated and noninoculated plants were greatest at 20 °C; they decreased as temperature increased to 28 °C and they were not significant at 30–36 °C. At 20 °C, 52–97% of inoculated plants wilted by 14 days after inoculation and plant fresh weights were reduced an average of 60–75% compared with noninoculated plants. Disease was similar among inoculated plants maintained at 20 °C and pH 4, 5, 6, and 7. However, when plants were maintained at 25 °C, fresh weights of inoculated and noninoculated plants were different at pH 5, 6, and 7, but they were not different at pH 4. Mature conidiophores and macroconidia were produced between 10 and 14 days after inoculation at 20 °C and by 14 days at 24 and 28 °C when the pH of the nutrient solution was maintained at 5–7. However, when plants were maintained at 20 °C and pH 4, mature conidiophores and macroconidia of F. solani f.sp. phaseoli were not observed; sporodochia and branched monophialides were disorganized and poorly developed. Results of bioassays, based on root lengths of germinating seedlings of Lactuca sativa, did not support the hypothesis that plant growth-inhibiting or growth-promoting compounds accumulated in hydroponic solutions. Key words: controlled ecological life support systems, NASA, space agriculture. |
