| The vegetable of pumpkin had a long history of cultivation and was distributed all over the world. Pumpkin had been considered as a yellow and green vegetable and beneficial for health care. So it had increasingly attracted more and more people's attentions in recent years. Furthermore, inside seeds and outside flesh of pumpkin all have of great value of nutrition. If exploited more deeply, they would create much more economic situation. However, with the increasing spread of area of salinity and alkali soil, it is quite necessary to study on the salt resistance mechanism and select salinity tolerance breed of pumpkin as a nonhalophyte. Salt tolerance under NaCl, Na2SO4 and Na2CO3 stresses and salt stress characteristics under Ca(NO3)2 stress of the pumpkin, used "Duanwanmiguan" pumpkin and "Mibenwang" pumpkin as materials, were studied in order to investigate the difference between salinity and alkali stress and provide soil improvement and the select of salt tolerance pumpkin breed with theoretical basis.1 .The "Duanwanmiguan" pumpkin and "Mibenwang" pumpkin seedlings had been treated with different concentrations of Na+ (120,240 and 480 mmol/L) of NaCl,Na2SO4 and Na2CO3 for 6 days, and the stress degree of pumpkin seedlings under three different sodium salts were compared. The results indicated that the stress effect of Na2SO4 on dry weight of pumpkins was greater than NaCl stress. However, the variation trend of the other entire indexes demonstrated that the stress effect of NaCl salt stress was higher than Na2SO4 salt stress. But, under the Na2CO3 stress, the dry weight, content of chlorophyll in the leaves of pumpkin and root activity were decreased;the content of free proline and MDA in leaves of pumpkin seedling were increased sharply. The results prove that the salt stress in pumpkin seedling is the most serious under Na2CO3 stress and the least serious under Na2SO4.2.Two pumpkin varieties ("Duanwanmiguan" and "Mibenwang") were treated with Ca(NO3)2 solution with the concentration of 80, 120, 160, 240 and 320 mmol/L. The results showed that pumpkin seedlings being under 240 and 320 mmol/L Ca(NO3)2 solution, the salinity resulted in the deterioration of growth and leaf area, the decrease of shoot relative water content and root activity, the increase of MDA content and cell membrane permeability, and the sharply rise of proline content and soluble sugar. The SOD and POD activity of both pumpkins under 160 and 240 mmol/L Ca(NO3)2 solutionwere all more than those under control treatment. With increase of Ca(NC>3)2 concentration, the content of nitrate had a clearly rise and was no obviously relationship with the activity of nitrate reductase (NR). According to synthesis comparison of results above, it was seriously harmful to pumpkins seedling under 240 and 320 mmol/L Ca(NO3)2 solution.3. Salt tolerance of 10 pumpkin varieties such as "Qingli", "Taiwanjinfu", "Ribenmeiyu", "Jingounangua", "Baizi", "Lvbaoshi", "Ribennangua", "Nenyu", "Wuwanyihao" and "Tianmiannangua" under 200 mmol/L Ca(NO3)2 was studied. With prolonging the Ca(NC>3)2 stress time , for two pumpkin varieties ("Wuwanyihao" and "Tianmiannangua"), the leaf area of seedlings gradually enhanced. Moreover, the decrease of the root activity and increase of content of MDA and soluble sugar were all not markedly. On the contrary, for other two pumpkin varieties such as "Nenyu" and "Lvbaoshi", the leaf area and root activity had evidently fallen and the content of MDA, proline and soluble sugar rose obviously. It is clear that salt tolerance of "Wuwanyihao" and "Tianmiannangua" pumpkins were stronger than other pumpkin varieties.4.The experiment firstly has studied the physiology response to different sodium salts and calcium salt in pumpkin seedlings. At first, it proved that high pH value of alkaline salt destroyed seriously the root functions of pumpkin seedling and was the most direct and important factor which caused marked salt injury symptom, in addition to Na+ effect and osmotic stress which were the mutual factors together with natural salts. So it was very important to enhance study on the plant root under salt stress further and improve the salt tolerance of plant by graft. At the same time, it made sure that calcium stress effected more than sodium stress under higher concentration and the C.pepo L. which grown slowly were more sensitive than the C.moschata D. and the C.maxima D. under calcium stress, providing theoretical basis of selection and breeding of greenhouse pumpkin varieties. |
