Horticultural Science and Technology 원예과학기술지 ISSN:1226-8763(Print) 2465-8588(Online)

This study examined the contribution of leaves on the secondary-lateral branches to sucrose concentration in the fruit of watermelon (Citrullus lanatus ) ‘Sambok-kkul’. Plants were trained to two primary-lateral branches after topping the main stem, and treated with either removal of the entire secondary-lateral branch (treatment 2C), or removal of the secondary-lateral branch below the fruit set node (treatment 2C-1). On average, 2C-1 plants had 30% smaller leaves at the 5th node above fruit set on the primary-lateral branches (EL) at 3 weeks after pollination compared to the 2C plants. Total leaf area of 2C-1 plants was 26% higher, on average, however, due to the leaves on the remaining portion of the secondary-lateral branch. At 2 weeks after pollination, both the leaves on the primary-lateral branches of the EL of the 2C treatment plants and leaves on the secondary lateral branches (SL) of the 2C-1 treatment showed significantly higher photosynthetic activity than other leaves. However, at 4 weeks after pollination, the highest photosynthesis activity and lowest water potential were observed in the leaves on the secondary lateral branch SL of the 2C-1 treatment plants. The leaf sucrose content of the 2C-1 treatment plants started increasing much more steeply from 4 weeks after pollination, while there was no significant increase in the sucrose content under the 2C treatment at the same period. In particular, the sucrose content in the SL of the 2C-1 leaves became greater than that of the EL of the 2C leaves starting 3 weeks after pollination. There was a 3.9-fold increase in sucrose content of the 2C-1 fruit for 4 to 5 weeks after pollination, while there was only a 1.4- fold increase in the 2C fruit. Micrographs of harvested fruit flesh showed higher cellulose in the 2C fruit flesh than in 2C-1. These results suggest that a transition from sink to source of carbon in younger and older leaves may influence the availability of carbohydrates for fruit development and quality.