Research On Physiological Mechanism Of Resistance To Cucurbita Ficifolia Bouche Under Fusarium Wilt Stress

Cucurbita ficifolia Bouche is a valuable melon vegetable resource,Which has many excellent resistance genes.Cucurbita ficifolia Bouche has a strong resistance to low temperature,drought,poor soil and other adversities,especially high resistance to melon Fusarium wilt.Cucurbita ficifolia Bouche as a grafted rootstock has been effective in controlling the occurrence and harm of cucumber Fusarium wilt.In order to screen the high resistance materials of Cucurbita ficifolia Bouche and reveal the mechanism of resistance of Cucurbita ficifolia Bouche under Fusarium stress.In this study,three kinds of Cucurbita ficifolia Bouche which are ‘White peel',‘Green peel',‘Green peel with White',was infected by Fusarium wilt.And Changes of gas exchange parameters,chlorophyll a fluorescence parameters,antioxidant enzyme activity and oxidative damage substances and NBS type resistance gene analogs HQRGA2 expression were measured in different stages of Fusarium wilt stress.The main results are as follows:(1)In this study,we used the method of root injury and root irrigation,1×108/ml concentration of spore suspension was inoculated to Cucurbita ficifolia Bouche.Plants showed obvious symptoms of the disease.Disease index statistics found:‘White peel' disease index was 52.6,‘Green peel with White' disease index was 45.5,‘Green peel' disease index was 42.6.Indicating that ‘Green peel with White' and ‘Green peel' resistance is greater than ‘White peel',but no significant difference.(2)In this study,the changes of gas exchange parameters,chlorophyll a fluorescence parameters,oxidative damage substances and antioxidant enzymes were measured under the stress of Fusarium wilt.It was found that the Gs and Tr were reduced after the infection of Fusarium wilt and the corresponding Pn was also lower.Indicating that the stomatal conductance of ‘White peel' and ‘Green peel with White' was easily destroyed by Fusarium wilt,and its transpiration rate was reduced,which affected the photosynthetic rate.Gs and Tr did not change much after infection,while Pn is significantly decreased of ‘Green peel'.This indicates that Fusarium wilt is affected by the destruction of photosynthetic rate of ‘Green peel',rather than destroying stomatal conductance.It was found that the heat dissipation mechanism of ‘Green peel with White' was strong in the early stage.The use of heat dissipation mechanism to protect their own photosynthetic capacity of ‘White peel' and ‘Green peel' is low.In the antioxidant enzyme system,‘Green peel' and ‘Green peel with White' through a strong antioxidant enzyme activity to protect their own cell membrane lipid peroxidation damage.The results showed that the resistance of the ‘White peel' to Fusarium oxysporum was the weakest,while the ‘Green peel' had the best resistance.(3)The expression of NBS resistance gene in Cucurbita ficifolia Bouche showed that there were different resistance mechanisms of three kinds of Cucurbita ficifolia Bouche.In this study,real-time fluorescence quantitative PCR was used to analyze the expression of NBS type resistance gene analogs HQRGA2 in different periods of ‘White peel',‘Green peel',‘Green peel with White'.Found that there were differences in gene expression at differents times in the same meterial.This indicates that HQRGA2 gene is involved in the mechanism of disease resistance of Cucurbita ficifolia Bouche.The response of genes in different material was different.The expression of HQRGA2 in the ‘White peel' showed increased and reduced compared with the control.The ‘Green peel with White' showed a reduced and increased change.‘Green peel' showed a continuously increasing and reduced change.The results showed that the expression of disease resistance gene of ‘Green peel' was the most rapid and sustained.Based on the above research results,‘White peel' resistance is the worst,‘Green peel' resistance is best.The resistance mechanism of Cucurbita ficifolia Bouche is not only physical resistance,but also is closely related to multiple physiological and biochemical reactions,and the related disease resistance genes are involved in the response process.Different types of Cucurbita ficifolia showed higher resistance to Fusarium wilt,and the difference was the speed of response.