Identification Of Pathogen Causing Pumpkin Leaf Blight And Variety Resistance

1.Pumpkin leaf blight occurred in Wuwei district ,Gansu province.The pathogen was identified as Alternaria cucumerina through isolation culture, test of pathogenicity and retro-isolation, etc. The host range test showed that the pathogen could infect all Cucurbitaceae plants, The most susceptible gourds crops are Cucurbita moschata,Cucurbita pepo and Cucurbita melo; While Luffa cylindrical and Momordica charantia were light infected;This pathogen could attack Brassica pekinensis Rupr and Phaseolus vulgaris L. The optimum temperature for the pathogen infection was 25～30℃, the incubation period was only 2～3 d. Different moisture time significantly influenced the infection of Alternaria cucumerina,when the moisture time was longer (60h), the percentage of infected leaves was reached 88%,but when the moisture time was 6h , the percentage of infected leaves was only 8%.2.The results of the biological characteristics of the pathogen of pumpkin leaf blight showed that temperature ,pH and light time affected the mycelium growth and sporulation of the fungus.The optimum growth temperature was 28℃.The suitable pH was 8.The best temperature for sporulation was 25℃under dark condition .Both carbon sources and nitrogen source had an effect on the mycelium growth and sporulation.The growth of mycelia was the quickest with mannitol ,and the number of sporulation was the largest with sorbitol .So did the nitrogen sources.Beef extract was the most suitable for the growth of mycelia and sporulation while ammonium sulfateis the poorest. Alternaria cucumerina grew faster on OA, the number of sporulation was the largest on PDA;The lethal temperature of Alternaria cucumerina was 50℃,10min.3. The different pumpkin varieties showed different resistance to the pathogen. The high resistance varieties were Tianran, Erxing, number1-guangban, Wuke(lijianming) and Jinwuke;while the most susceptible varieties were Lisaijin, Zhengfenguangban, Jindadi and Sixing. The difference of the pumpkin chlorophyll content was quite obvious between various varieties, and the high resistant varieties and disease-resistant varieties contain high chlorophyll, but the chlorophyll content of high susceptible varieties and susceptible varieties was low; The number of stomata on different pumpkin varieties was remarkable.It was most on the Disease-resistant variety Sanxin and high anti-variety Number1-Guangban, respectively reacheed70.7 and 70.1 each field of vision; It was least on the high sensitivity Lisaijin and anti-variety Wuke(lijianming) ,respectively was 23.2 and 21.0 each field of vision; The number of pumpkin stomata and the pumpkin anti-leaf blight did not have the relevance.4 .The result indicated that 0.1~10mmol. L-1 salicylic acid (SA) had no direct inhibition over the growth of Alternaria cucumerina by using plate growth rate method. The best induction of disease resistance could only be obtained with 5 mmol SA 3 days prior to inoculation of the pathogen,and hold the best effective during 11day.The activity of PAL, POD and PPO was rapidly enhanced after inducted by SA, The activity PAL and PPO reached most after 3days, with 1 times and 2.6 times higher ,respectively,compared to the comparison, afterwards starts to drop slowly; But POD activeness was biggest after 5days, was 2.3 times of comparison .SA also may induce the pumpkin to have the system disease resistance.