| Bottle gourd is considered to be the most suitable rootstock species for watermelon grafting. However, the germination of bottle gourd seed is undesirable, slow, and irregular, because of its thick seed coat and hard absorbing of water. Thus, improving the germination rate and germination energy is very important for the productivity of grafted watermelon. To evaluate the method that would promote the germination of bottle gourd seed and the physiological mechanism of seed priming, the effects of seed priming with four kinds of methods on seed germination and plant growth were investigated. In addition, we also investigated the physiological mechanism of seed priming with substrate on improving the germination of bottle gourd seed.1. The effects of seed priming with substrate No.1, gibberellic acid, polyethylene glycol, and substrate No.2 on the seed germination and plant growth of two bottle gourd plants (cv. "Nabizhen" and "Jiangjun") were investigated. The results showed that the germination of "Nabizhen" was better than that of "Jiangjun" independent of priming or not, whereas the germination energy of "Jiangjun" seed was lower. The germination of bottle gourd seeds could be improved by either of the four methods in priming. Among of them, seed priming with substrate No.2 exhibited the best results, and the following is priming with substrate No.1. The germination energy, rate of germination and emergence of "Jiangjun" increased by 64.1%,24.8%, and 31.4%, respectively, after seed priming with substrate No.l. After the priming with substrate No.2, the germination energy of "Jiangjun"increased to 98.6%, which was higher than other priming treatments. This result indicated that seed priming with substrate No.2 was the best priming methods, and the priming with substrate No.2 containing 60% water for 48 hours was the optimal method of priming to bottle gourd seeds.2. The effects of priming temperature, drying temperature, and weight ratio between substrate and seed on the seed germination were investigated, which used substrate No.2 as the priming substrate. The results showed that the emergence rate of plants enhanced significantly by priming with 25℃temperature, and the germination energy increased by 52.0% compared to the control. Compared to the control and non-drying away treatment, the germination energy, vigor index, and emergence rate with 20℃drying temperature exhibited the highest level. The germination energy and germination rate were increased by 39.8% and 37.7%, respectively, when weight ratio between substrate and seed was 1:3. The results of orthogonal test among water content, priming time, and priming temperature showed that the optimal priming was using substrate No.2 containing 60% of water content for 48 hours at 25 "C temperature.3. The effects of seed priming on physiological characteristics of plant seeds with substrate No.2 used as priming substrate were investigated. The results showed that with the increasing time of seed germination, seed priming increased the soluble protein and soluble sugar contents, the activities of amylase, protease, and dehydrogenase gradually, and exhibited significant higher than the control. The results implied that seed priming could promote the metabolism in the seed. In addition, seed priming decreased the conductivity of seed soak solution and MDA content, but increased the activities of CAT, SOD, and POD, implying that seed priming could protect the structure and function of cell membrane. |
