Exogenous glucose preserves the quality of watermelon (Citrullus lanatus) plug seedlings for low-temperature storage

Plug seedlings are usually stored for a short-term period before transplanting in large-scale production operations, and a decrease in carbohydrates is thought to be a major factor limiting seedling survival and regrowth capacity. In this study, we investigated whether sugar supply can preserve the quality of seedlings during low-temperature storage in darkness and promote regrowth after transplanting. We sprayed 0, 3, or 6% glucose (Glc) solution onto watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plantlets. Plugs were then stored in dark growth chambers for 6 days at 15 degrees C before being transplanted and allowed to recover in a greenhouse. Comparisons between Glc-treated and control plants (0% Glc) showed that the seedlings treated with Glc effectively maintained their dry mass and showed an improved regrowth rate after transplanting. Plants treated with Glc showed higher contents of endogenous soluble sugar and starch, lower electrolyte leakage, and lower levels of malondialdehyde compared with those of control plants during 6 days of storage. These differences became greater with increasing storage time and with greater concentrations of Glc in the spray solution. After transplanting, the net photosynthetic rate and maximum quantum efficiency of photosystem II were significantly higher in leaves of Glc-treated plants than in those of control seedlings. These results suggested that Glc pretreatment may delay carbohydrate starvation, retain membrane integrity, and suppress senescence during low-temperature storage, thus ensuring the transplant quality of seedlings after removal from darkness. (c) 2012 Elsevier B.V. All rights reserved.