Studies on the seed production of onion. I

Abstract

It has been reported that the pollen of onion is susceptible to rain or high relative humidity. It is doubtful, however, whether rainfall or high humidity induces direct injury to seed production of the onion. So experiments were carried out to investigate how various factors affect the fruit setting under the natural and artificial conditions. 1. Fruit setting under the natural and artificial conditions (a) Under the natural condition The influence of weather before and after the flowering of a floret on its fruit setting was investigated. When rain continued for one or two days after the flowering, it inflicted little injury on the fruit setting. However, the rainfall which continued for two days from the next day of the flowering did much injury, and the most severe injury occured when the rain continued for three days from the next day of the flowering or for four days after the flowering. While, the clear weather for five to six hours interrupting the continous rain reduced the injury exceedingly. (b) Under the artificially maintained continuous wet conditions A floret was kept under the artificial rain for one to five days after the flowering or for four days from one to four days after the flowering. In these experiments the results similar to those mentioned above were obtained. (c) Under the artificial alternate wet and dry conditions, four plots were provided as follows; 1) wet every night, 2) wet every forenoon, 3) wet every other day, and 4) dry throughout the period (check). Little injury was inflicted on the fruit setting by the raining treatment, and fertility of the treated plants was about the same as the check. 2. The dehiscence of anther as influenced by temperature and relative humidity (a) Temperature: At 35-40°C, six to ten hours was required from the flowering of a floret to the dehiscence of its innerwhorl of stamens, and thir-teen to twenty hours to that of the outer whorl of stamens. The time was prolonged by three to eight hours at 30°C. At 25°C, the dehiscence of the anther required twice as many hours, and at 20°C, four times as many hours after the flowering as at 35°C. (b) Relative humidity: The relative humidity was controlled at 50, 60, 70, 80, 90, and 100per cent. No difference in the time of the dehiscence of the anther was found among fifty to seventy per cent relative humidity. At eighty per cent relative humidity, the dehiscence of the anther required some more time than at fifty per cent relative humidity. At ninety per cent relative humidity, it required twice to three times as many hours as at fifty per cent relative humidity, and no anther dehisced in saturated humidity. 3. The seed production of various plants under the artificial raining Ten kinds of plants were used to compare their resistance to rain with that of the onion. They were kept under the artificial raining for four days. With snap beans and gardenia, the flowers of which are formed as the anthers are not exposed to the rain, fruit setting was little injured by the. raining treatment. With carrot, Cancalis scabra MAKINO and Onion, the pistils of which retain its fertilizing capacity for three to four days after flowering, fruit setting was injured only when the raining was continued more than three to four days. The fruit setting of the other plants (Veronica persica POIR., Oxalis corniculata L., Polygonum-aviculare L., Polygonum capathifolum L., Polygonum senticasum FRANCH et SAV. and egg plant) was severely injured by the raining and seeds were-not produced. After the raining treatment was stopped, however, the plants produced seeds again. 4. The germination of pollens as influenced by relative humidity The materials used were the same as mentioned. above. Some kinds of plants were found to have pollens very resistant to high relative humidity. The pollens of snap beans, gardenia, lily, etc.