Effects of priming and stage of development on vigor and longevity of muskmelon (Cucumis melo L.) seeds

Muskmelon seeds were harvested at eight stages of development to determine the optimal harvest time for best seed quality and long-term storage. Several types of osmotic and matric priming treatments were investigated to determine the optimal treatment for maximal seed vigor and to test the effects of priming on seed storage life. The most effective priming treatments for improved germination of muskmelon seeds occurred at water potentials (Ψ) between -1.5 and -1.8 MPa and at priming durations of 4 to 7 days. Osmotic priming in KNO₃ and PEG 8000 solutions was more effective than matric priming with calcium silicate, vermiculite, and Hayter loam soil. Priming increased the storage life of newly matured 40 and 45-days after anthesis (DAA) stored seeds but decreased the storage life of 55 DAA seeds. Fifty, 55, and 60-DAA seeds showed the greatest tolerance to adverse storage conditions and water stress and had the greatest seedling vigor. The highest quality seeds were attained 50 to 60 DAA from fruit harvested after edible maturity but before the onset of severe decomposition. After 6 years of storage, seeds washed in water at harvest were more vigorous and resistant to accelerated aging than unwashed seeds at most stages of development. Primed seeds retained some beneficial effects after 9 years of storage at optimal conditions but lost viability, vigor, and uniformity of germination more rapidly than non primed seeds following controlled deterioration. Instron analysis showed that priming weakened the perisperm envelope tissue prior to radicle emergence. Less force was required to puncture primed seed pieces than non primed. The penetration force and energy required to puncture the perisperm envelope tissue decreased gradually during imbibition, increased steadily during seed development and dry storage, and was negatively correlated with seed vigor. Priming accelerates enzymatic breakdown of perisperm envelope during germination. Endo-β-mannanase-like activity declined steadily during imbibition and was higher in non primed seeds than primed seeds, indicating that enzymatic activity in the perisperm peaked during priming. Flow cytometry revealed that the beneficial effects of priming and seed maturity do not correlate with DNA replication activity in muskmelon seeds. This study has shown that seed maturation inside the fruit until just after edible maturity is necessary for highest muskmelon seed vigor. Priming treatments should be performed as close to the planting date as possible, because primed seeds exhibit reduced storage life compared to non primed seeds.