High temperature injuries in tomato. III.

In the previous papers, it was reported that the effect of high temperature on fruit setting and yield differed by the growth stages of seedlings, and it was also suggested that this result was due to the difference in susceptibility of flower buds and flowers of different stages of development on the seedlings to high temperature.Experiments reported here were conducted to determine the effect of high temperature on the flower buds and flowers of different stages of development, the stages of buds being accurately defined by measuring their length. As high correlation was found between the length of flower buds and the duration of time to their anthesis, the stages of flower buds were expressed in terms of days to anthesis.Seedlings of two groups (in one group, the first flower of first cluster just opened; and in another group, all the flowers in first cluster opened) were exposed to 40°C for three hours daily, twice.Percentage of setting of flower buds treated 11 days before anthesis was 100%, 9-5 days before 10-20%, 3 days before 70%, and one day before 100%. Percentage of setting of flowers 1-3 days after anthesis was 20%, and 8 days after anthesis 100%. Thus it was revealed that flower buds of 9-5 days before anthesis and flowers of 1-3 days after anthesis were highly susceptible to high temperature.Hand pollination with normal pollen increased the setting percentage of flowers which had been treated 7-5 days before anthesis to 60%, but failed to increase the set of flower buds treated at other stages. This result shows that the high temperature treatment affected both pistill and stamen in the flower buds of 9 days before anthesis, while it affected mainly stamen in the buds of 7-5 days before anthesis.p-chlorophenoxyacetic acid (CPA) spray improved setting of flowers treated with high temperature after anthesis, but did not increase the setting of flowers treated at their bud stages.Considerable number of small fruits appeared from the flowers treated with high temperature after anthesis. CPA spray on these flowers after high temperature treatment did not alter this tendency.Percentage of puffy fruits, though degree of puffiness was very slight, was increased by the high temperature treatment. CPA spray increased green gelatinous fruits, and the high temperature had a synergistic effect on the incidence of these fruits.Highly positive correlation was found between the number of seeds per fruit and fruit weight. Fruit weight per seed was 0.36g in the control, 0.34g in the plot treated with CPA, and 0.49g in the plot treated with high temperature.