Screening Of Rootstocks And Effects On The Grafted Watermelon Tolerance To Salt Stress

Watermelon(Citrulluslanatus M.) is a major global vegetable, and it is also one of the main economic fruit crops in C hina, which has a large of planting area. Recently, the increasing serious secondary salinization of protected cultivation soil has become the most importantly limited factor of watermelon’s production. It has been proved that grafting could improve the adaptability of plants to adverse conditions. However, different types of rootstocks showed different tolerant to salt stress. In this study, ‘Jingxin 2’ was used as experimental scions to investigate the different affinity, symbiosis and salt-tolerance of different rootstocks. The main results were as follows:1. ‘Jingxin 2’ watermelon was used as scion, Pumpkin root stocks including ‘Quanneng Tiejia’, ‘Tie Mu Zhen’, ‘Xiu Zhen’, ‘388’, ‘Qingyan 1’, ‘Qingzhou 1’, ‘Guangdian 1’and ‘Kaijia 1’ and gourd root stock ‘Hanzhen 3’ were used experimental stocks, and ‘Quanneng Tiejia’ was used as control stock. The results showed that the dry weight, survival rate, seedling index and strengthen seedling rate of both ‘Kaijia 1’ and ‘Hanzhen 3’ graftlings were significantly increased compared with control, and among those ‘Kaijia 1’ was the best with increasing by 20.1%, 0.14%, 9.7%, respectively. 6.3%, 8% higher survival rates were observed when ‘Kaijia 1’ and ‘Hanzhen 3’were used. All indexes of ‘Guangdian 1’ and ‘Quanneng Tiejia’ graftlings had no significant difference, and the others were declined compared with control. In conclusion, affinity and symbiosis of ‘Kaijia 1’ graftling were the best, ‘Hanzhen 3’ graftling following behind.2. Using nutrient solution for culture and through daily incremental 25 mmol·L-1Na Cl, we investigated the highest salt-tolerance concentrations of ‘Kaijia 1’, ‘Hanzhen 3’, ‘Guangdian 1’, ‘Quanneng Tiejia’ and ‘Jingxin 2’ seedlings. They were 325 mmol·L-1, 350 mmol·L-1, 275 mmol·L-1, 275 mmol·L-1, 225 mmol·L-1, respectively. The results showed that the gourd rootstock ‘Hanzhen 3’ seedling had the highest concentration, with ‘Jingxin 2’ seedling lowestly.3. Using ‘Hanzhen 3’, ‘Kaijia 1’, ‘Guangdian 1’, ‘Quanneng Tiejia’ and ‘Jingxin 2’ as materials, we determined the malondialdehyde(MDA), chlorophyll content and relative electrical conductance in leaves and root activity under different saline stress. The resulted indicated that all seedlings under saline stresses had various damage degrees. Compared with rootstock seedlings, watermelon seedling ‘Jingxin 2’ showed lower salt-tolerance under the same saline stress. Under low concentration(≤100 mmol·L-1) saline stresses, the MDA content, relative electrical conductance and root activity of all rootstock seedlings had no significant effect comparing with control, and so did all rootstock seedlings themselves. However, under high concentration(150, 200 mmol·L-1) saline stresses, the salt-resistance between all rootstock seedlings had dramatic difference. Under 200 mmol·L-1Na Cl, the above indicators’ variation scope of ‘Hanzhen 3’ and ‘Kaijia 1’ seedlings were similar, significantly less than that of ‘Guangdian 1’ and ‘Q uanneng Tiejia’ seedlings, which showed higher salttolerance. This study chose the limiting concentration of ‘Jingxin 2’(200 mmol·L-1) after 10 d treatment with Na C l as the further experimental concentration.4. Using ‘Hanzhen 3’, ‘Kaijia 1’, ‘Quanneng Tiejia’ as rootstocks and ‘Jingxin 2’ as scion for grafting, it was found that, compared with the self-rooted watermelon, grafting remarkably increased the photosynthetic capacity and dry matter accumulation of watermelon plants under saline stress, and ‘Kaijia 1’ rootstock showed the most significantly mitigating effect. Under saline stress, the O2.- productive rate, H2O2 content and membrane’s relative permeability of self- rooted and grafted watermelon was dramatically increased, but the increasing extent of graftlings was lower than self-root seedlings of ‘jingxin 1’, and among those three grafted watermelon ‘Kaijia 1’ graftling had the lowest oxidative damage. Furthermore, grafting remarkably increased the activities of antioxid ant enzymes in watermelon leaves. Among those, the increasing extent of SOD and APX activities in Jingxin/Hanzhen grafting was the biggest and the increasing extent of CAT and POD activities in Jingxin/Kaijia grafting was the biggest. Compared with the self-rooted seedlings, grafting significantly decreased the Na+ content of shoot and increased the K+ content of root under saline stress, and ‘Jingxin/Kaijia’ had the highest K+/Na+ in the shoot. This was in good accordant with the plant growth, and explained that the increasing salt-tolerance of grafted watermelon was closely related to the regulation of Na-K homeostasis.