Drought-resistance physiological characteristics during the seed germination period of thick-skinned melon in Xinjiang

【Objective】Evaluated the drought tolerance differences in seed germination period among thick-skinned melon varietiesplanted in Xinjiang, and explored the drought-resistant mechanism of melon varieties during seed germination, to provide technique support for optimizing melon breeding and planting.【Method】Five thick-skinned melon varieties planted in Xinjiang were used as test materials(Huangmengcui, Huangpi 9818, Xizhou Honey 17, Nasimi and Flavor 5) and evaluated their drought resistance during seed germination by treating each variety with different concentrations of PEG-60000%(CK), 5%, 10%, 15%, 20%, 25%. The contents of malondialdehyde(MDA) and proline(Pro), the activities of superoxide dismutase(SOD), peroxidase(POD) and catalase(CAT) and the contents of endogenous hormones of melon seeds with different drought resistance were compared under drought stress.【Result】With the increase of PEG-6000 concentration, the germination potential, germination rate, relative germination potential, relative germination rate, embryonic axis length, radicle length and fresh weight of each melon variety decreased. The membership function analysis showed that the order of drought resistance was Nasimi>Huangmengcui> Huangpi 9818 >Flavor 5>Xizhou Honey 17. Drought stress significantly(P<0.05, the same below) or extremely significantly(P<0.01, the same below) promoted the accumulation of MDA and Pro contents, and enhanced the activities of SOD, POD and CAT in the most drought-resistant melon Nasimi seed and the most drought-sensitive melon Xizhou Honey 17 seed. Nasimi had a lower increase in MDA but a higher increase in Pro content, SOD and POD activities. In addition, under drought stress, abscisic acid(ABA) content significantly increased in Nasimi and Xizhou Honey 17 seeds while jasmonic acid(JA) content significantly decreased. Auxin(IAA) content extremely significant decreased in Xizhou Honey 17 seeds, salicylic acid(SA) content extremely significant decreased in Nasimi seeds. Compared to Xizhou Honey 17, Nasimi variety exhibited a 20% higher rate of IAA/ABA and 55% and 68% higher contents of JA and SA respectively. The results of exogenous hormone treatment showed that, under drought stress, exogenous ABA treatment reduced the germination rate of melon seed at different time points. Low concentration SA(0.25 mmol/L) increased seed germination rates by 23% and 27% at 12and 24 h respectively, while co-treatment with low concentration MeJA(0.025 μmol/L) further increased seed germination rates. Moreover, appropriate concentration of MeJA alleviated the inhibitory effect of high concentration of SA on seed germination.【Conclusion】Nasimi has the strongest drought resistance during the seed germination period, while Xizhou Honey 17 has the weakest drought resistance. Under drought stress, Nasimi has higher antioxidant enzyme activity than Xizhou Honey 17, and its drought resistance is related to IAA, ABA, SA and JA levels.