Melon (Cucumis melo L. group) plants of two resistant lines and one susceptible line to viviparous sprouting were grown with three different concentrations (2.4, 4.2, and 6.0 me・L ) of potassium to investigate the relationship between viviparous sprouting and endogenous abscisic acid (ABA). Seed yield per fruit was considerably decreased with decreasing potassium application in the susceptible line. In the resistant line, however, no influence on seed yield was observed. Potassium concentrations both in the petiole and in the juice around the placenta were higher in the resistant line than in the susceptible lines. Vivipary increased with decreasing concentration of potassium applied to the susceptible lines. No viviparous sprouting was observed in any potassium treatments for the resistant line. ABA content in the fruit juice decreased with decreasing potassium concentration. A germination test was carried out with different concentrations of ABA, and resulted in sharp decline of seed germination with increasing ABA concentrations in the resistant line. These results suggest that lower potassium application may cause a decreased ABA content in fruit juice, may cause a increase of viviparous sprouting in the fruit, and that the resistant line showed an inhibitory effect of ABA on sprouting at a lower threshold value of ABA concentration.

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The present experiments were undertaken in order to clarify the effects of a high potassium fertilization level on the occurrence of viviparous sprouting in melon fruit. Melon (Cucumis melo L. group) plants of two susceptible lines and one resistant line to viviparous sprouting were used at two different potassium concentrations. A high potassium fertilization level (12.0 mmol·L) resulted in a marked decrease of the occurrence of viviparous sprouting in the susceptible lines, and in the increase of the endogenous ABA content. No significant differences were observed in the seed number per fruit, the seed weight, and the percentage of seed germination at a high level of potassium fertilization. Further experiments were conducted in order to analyze the effects of exogenous ABA treatment at a low potassium fertilization level (1.5 mmol·L −1 ) on the occurrence of viviparous sprouting in melon fruit. At 25 days after pollination, ABA solution at different concentrations was sprayed on the fruits of the susceptible melon line grown at two different potassium fertilization levels. Even at a low potassium fertilization level, exogenous ABA application inhibited the occurrence of viviparous sprouting and increased ABA contents both in juice samples around the placenta and in the seeds. ABA treatment, however, led to a significant decrease in the seed number per fruit and in the percentage of seed germination, as a result of a marked increase in the ABA content and potassium absorption.

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