Relationship between growth/yield of green papaya and meteorological parameters: An example of field cultivation in a hilly and mountainous area in Yamanashi, Japan

The green papaya (Carica papaya L.) is now being cultivated from Okinawa to Kanto regions in Japan. Because of its low susceptibility to damages by birds and animals, it has started to be cultivated in hilly suburban areas where abandoned farmlands are increasing. In order to evaluate possibility of adaptation of green papaya into these areas of Japan, field experiments were conducted for 3 years from 2017 at an upland field on the slope facing Kofu basin. As growth indicators for papaya, plant height, stem diameter, leaf number and number of buds, flowers and fruits were measured. As meteorological parameters, average daily temperature, daily solar radiation and daily rainfall were used to consider with the growth indicators. The growth indicators were fitted into logistic function to convert them into daily basis. The daily changes of each growth indicator showed high multiple correlations with cumulative changes of the three meteorological parameters. Fruit weight harvested from a plant in 2017 also showed statistically significant multiple correlation with four growth indicators. The fruit yields for 22 years from 1998 were estimated from those multiple regression equations and meteorological data of each year. The predicted yields fell into a range from 1.4 to 12.0 kg plant-1 with an average of 8.2 kg plant-1 and coefficient of variation of 0.39. In the mountainous regions within the Kofu Basin, one of Japanʼs hottest areas, it was anticipated that situations such as low yields or complete crop failure, similar to what was observed in 2018, would occur at a frequency of about once every five years. This is suggested to be related to the inhibition of pollen germination due to high temperatures during the flowering period. When introducing green papaya cultivation in these mountainous areas, it is essential to acknowledge the associated risks and explore technical solutions to address them.