Preliminary Study On Resistance Mechanism Of Pumpkin To Powdery Mildew

Pumpkin,with quality value and economic value,has a rich nutrition and wide range of using and is an important vegetable on behalf of the food.Not only these,but also pumpkin distributes a wide area,healthy growth and strong adaptability.However,powdery mildew makes pumpkin commercial value decrease,which impedes the maximum value of the pumpkin gain.In this paper,we selected different varieties of pumpkin for studying resistance mechanism to powdery mildew.In addition to toxicity determination of six germicides on the pumpkin powdery mildew,the contents of chlorophyll,protein,superoxide dismutase'(SOD)and polyphenol oxidase(PPO)were determined by inoculating of powdery mildew on the different resistance of pumpkin included in resistant cultivars(Samsung and Award)and susceptible cultivars(Tianran and Guangban).The results were as follows:1).The total chlorophyll content of the resistant and susceptible cultivars was not significantly different from those of the inoculated ones.And the total chlorophyll content increased and reached the peak at the third day after inoculation.The content of chlorophyll a was higher than that of chlorophyll b,and the content of carotenoid was increasing gradually.2).The protein content of resistant cultivars(Award and Samsung)increased firstly and then decreased after inoculation,while the susceptible cultivars(Tianran and Guangban)just the opposite.3).The activity of SOD of resistant and susceptible cultivars has no significant difference before inoculation.There is a certain degree increased after inoculation,but which was similar with the control basically.The activity of SOD reached a basic approach level between the resistant and susceptible varieties after inoculation 7d.4).PPO activity reached rapidly the peak after 1d of inoculation,resistant cultivars(Award,Samsung)were higher 0.03633(U/g· FW)and 0.07333(U/g· FW)than the controls,while susceptible cultivars(Tianran and Guangban)were higher 0.0145(U/g· FW)and 0.0045(U/g· FW).The activity of PPO of resistant cultivars had dropped slightly after inoculation 3d,while the susceptible cultivar(Tianran)had no effect.5).The indoor potted spray method was taken in this research to study the control effects and inhibitory effects of six germicides on the main pathogen fungus-Erysiphe.cucurbitacearum,with aim to provide theoretical basis for preventing and controlling powdery mildew.The results show that six kinds of germicides do have certain inhibition effects for powdery mildew,inside of which Difenoconazole shows the greatest inhibition to powdery mildew.EC50 values is up to 1.4244 ug/ml while Azole ether polyram and Kresoxim-methyl are in the second place,and the inhibition effect of Carbendazim is poorest,which EC50 values comes 2.4577 ug/ml.Therefore,the use of Difenoconazole is worthy of promoting and can serve as the effective chemical control for the disease of pumpkin powdery mildew.