The Influence of Soil Temperature on the Expression of Abnormal Overgrowth of Plants caused by Gibberella Fujikuroi

Abstract

A study was was made on the influence of so il temperature upon the expression of abnormal overgrowth of Bakanae disease of the rice plant caused by Gibberella Fujikuroi (SAW.) WR.Besides the rice plant, corn and wheat plants were also used in the present study for comparative purpose. Inoculated seedlings of these plants were prepared by germinating seeds over the agar culture of the fungus, and were carefully transplanted to pots maintained at the constant temperatures of 22, 25, 28, 31, 34, 37, and 40°C. A diagram showing the construction of one of the pots is given in figure 1.Preliminary experiments without regard to the soil temperature showed that there exist various degrees of abnormal overgrowth as expressed by the different strains of Cjbbereiia Fujikuroi (figs. 2 and 3).The results of the soil temperature experiments uping the three jifferent strains of the fungus showed, that in rice, corn, and wheat the greatest abnormal overgrowth occurred at thepoil temperatures of respectively 31, 31, and 28°C (figs. 4 to 6).These temperatures were also the optimum soil temperatures for the respective uninoculated plants. The occurrence of the greatest abnormal overgrowth at the soil temperatures which were optimums for the re pective plant suggests that the effect of the soil temperature as promoting the normal growth of the plants, by far, overshadowp the other possible factors such as the variation in the amount of toxin formed or their selective action by temperature on the plants. And as long as a certain amount of the toxin is produced by the fungus, this amount will most likely satisfy the requirement for that plant in making its maximum growth at the specifjed tempersture.