Disorders of the Pistillate Flower on Blooming In-season and Pre-season Crops of “E-Daw” and “Puangthong” Longan (Dimocarpus longan Lour.)

Abstract

Longan (Dimocarpus longan Lour.) is an important economic crop of Thailand. Nowadays farmers use potassium chlorate for flower induction in both in- and off-season crops. Off-season cropping helps stabilize the farmers’ income as the prices of longan are less fluctuate than the  in-season crops.  However, there have found that the yields of pre-season (a part of off-season) cropping in the North were lower than the in-season yields. This phenomenon might probably relate with the malformation of the flowers during the low air temperature of the cool season, consequently, results in a lower fruit set. The objective of this study was to identify any malformation of the flowers, especially pistillate flowers, those are subjected to cool temperature. The study was carried out on “E-Daw” and “Puangthong” cultivars of the longan trees in the orchard of Pomology Division, Maejo University,               Chiang Mai.  Potassium chlorate was applied for flower induction of pre-season and in-season cropping on October15 and November 12, 2020, respectively. It was found that “Puangthong” (in-season) had low flowering at 51%, while “Puangthong” (pre-seasons) and “E-Daw” (in- and pre-seasons) had 84-97% flowering. Inflorescences showed leafless and leafy types had not significantly difference. Diameter of pistillate flowers and stigma was found the higher values in “E-Daw” (in-season) than in the other treatments with 6.07 mm and 2.60 mm of width of stigma and 5.60 mm of style length. However, in “Puangthong” (off-season) and “E-Daw” (pre-season) disorders were found with the shortened style length. Especially the open of “E-Daw” the stigma were 1.08 mm and 1.10 mm of “Puangthong”. The sex ratio of longan flower between pistillate and staminate flowers were 1:5.39-15.68. With respect to fruit set, it was found that both of longan cultivars had a higher percentage of fruit set in on-season than in pre-season. As a conclusion, it is recommended to flower induction period before winter by potassium chlorate, which will have a positive effect on pistillate, stigma and style, and consequently a positive effect on fruit set as well.