The Botanical Diversity, Genotypic Difference And Mechanisms Of Genotypes In Resistance To Phosphorus Deficiency In Cucurbita

Cucurbita is one of the major vegetable crops in Cucurbit family. Cucurbita had been considered as a green vegetable and beneficial for health care. So it has been increasingly attracting more and more people's attentions in recent years. The deficiency of P is one of the main problems that hinder the productivity of Cucurbita. Soil improvement and fertilizer is one of effective way to overcome P deficiency, with the limited factor of production cost increased and environmental pollution aggravation. It's effective to work out these problems by breeding of P deficiency resistant varieties which can be used in the production. In this study, nutrient solution experiments were conducted in greenhouse, and the morphological characters, physiological and biochemical properties of Cucurbita ficifolia Bouche. and Cucurbita pepo L. cv. Luoren were determined under P deficiency, to discuss the mechanism for P deficiency tolerance in seedling stage. The research will provide the reliable guidance for index selection in gene mapping and variety improvement pertinently. The main results of this study were summarized as follows:The botanical diversity of 20 accessions of Cucurbita germplasm resources was analyzed firstly to discuss the botanical differences and screen seed-used Cucurbita. There were genetic diversity in seed traits, crop growth and fruit characters of Cucurbita germplasm. Shell weight,1000-seed weight, shoot dry weight, main stem length and number of seed per fruit were representative for seed-used Cucurbita botanical character evaluation. Optimal P concentration and related indicators for seedling screening were proposed firstly by multi P concentration gradient test. The study showed that the concentration of 0.013mmol·L-1 is suitable for low P treatment and 0.67mmol·L-1 is a proper for normal P treatment in the seedling screening in nutrient solution. The synthesized index for seedling screening was reliable and comprehensive. There were genotypic differences in P nutrition quality in Cucurbita. Correlation analysis showed that H2, D1 and H3 were the only varieties which were tolerant to low P, and Z2, N1,S1 lower P sensitive species. Anthocyanins, flavonoids and total phenolic content were increased in low P treatment which would be an adaptive response of Cucurbita.Under P deficiency, C. ficifolia, a Cucurbita variety tolerant to low P, had larger root system, its root lengths, root surface, root tips, root/shoot ratio, root dry weight and TTC deoxidizing ability were higher than C. pepo cv. Luoren, a Cucurbita variety sensitive to low P. There were no significant difference in Chlorophyll content between C. ficifolia and C. pepo cv. Luoren under P deficiency. The efficiency of P uptake was the main contributor to low P tolerance at seedling stage. C. ficifolia had higher P absorb ability and larger P distribution coefficient than C. pepo cv. Luoren. The research found that there was a positive correlation between citrate secretion and the ability of low P tolerance. C. ficifolia and C. pepo cv. Luoren secreted more citrate under P deficiency than normal P treatment, and citrate secreted by C. ficifolia was 2.1 times than that of C. pepo cv. Luoren.PEPCase activity of C. ficifolia was significant higher than that of C. pepo cv. Luoren. PEPCase activity was positively correlation with citrate secreted, and PEPCase activity played an important role in citrate secreted. Under P deficiency, C. ficifolia had higher NAD-MDH activity than C. pepo cv. Luoren, but NAD-MDH activity of Cucurbita root had no significant correlation with citrate secreted.Under P deficiency, root exudates of C. ficifolia and C. pepo cv. Luoren were more than those of normal P status. Compared with normal P treatment, alkanes content in the root exudates of C. ficifolia increased, and Phenol, aromatic, ester, amine, olefin content decreased, however, C. pepo cv. Luoren showed a contrary tendency. Ester and amine in the root exudates of C. ficifolia was lower than those of C. pepo cv. Luoren. Both C. ficifolia and C. pepo cv. Luoren had autotoxicosis, and the autotoxicosis increased under P deficiency.In summary, there were genotypic differences in P nutrition quality in Cucurbita. Under P deficiency, Cucurbita variety tolerant to low P had higher TTC deoxidizing ability, P distribution coefficient and PEPCase activity, and more citrate, less Ester and amine were exudated to make pH decreased and effectiveness of hardly soluble P increased, then root morphology changed to make P absorb ability increased. Some researches have shown that under long selection stress of low P, some plants would form the genetic properties of P nutrition that could exploit the hardly soluble P in the soil. Consequently, root morphology changes, root/shoot ratio, root exudates, TTC deoxidizing ability and PEPCase activity increased were all response mechanism in Cucurbita variety tolerant to low P.