Water Relations of Seed Development and Germination in Muskmelon (Cucumis meloL.)

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Abstract
Seed priming (imbibition in water or osmotic solutions followed by redrying) generally accelerates germination rates upon subsequent re-imbibition, but the response to priming treatments can vary both within and among seed lots. Seed maturity could influence responsiveness to priming, perhaps explaining variable priming effects among developmentally heterogeneous seed lots. In the current study, muskmelon (Cucumis melo L.) seeds at two stages of development, maturing (40 d after anthesis (DAA)) and fully mature (60 DAA), were primed in 0·3 M KNO3 for 48 h at 30 °C, dried, and imbibed in polyethylene glycol 8000 solutions of 0 to −1·2 MPa at 15, 20, 25, and 30 °C. Germination sensitivities to temperature and water potential (ψ) were quantified as indicators of the influence of seed maturity and priming on seed vigour. Germination percentages of 40 and 60 DAA control seeds were similar in water at 30 °C, but the mean germination rate (inverse of time to germination) of 40 DAA seeds was 50% less than that of 60 DAA seeds. Germination percentages and rates of both 40 and 60 DAA seeds decreased at temperatures below 25 °C. Reductions in ψ also delayed and inhibited germination, with the 40 DAA seeds being more sensitive to low ψ than the 60 DAA seeds. Priming significantly improved the performance of 40 DAA seeds at low temperatures and reduced ψ, but had less effect on 60 DAA seeds. Priming lowered both the minimum temperature (Tb) and the minimum ψ (ψb) at which germination occurred. Overall, priming of 40 DAA seeds improved their germination performance under stress conditions to equal or exceed that of control 60 DAA seeds, while 60 DAA seeds exhibited only modest improvements due to priming. As the osmotic environment inside mature fruits approximates that of a priming solution, muskmelon seeds may be ‘primed’ in situ during the late stage of development after maximum dry weight accumulation.

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