Study On The Resistance Of Litchi Cultivars To Litchi Downy Blight Caused By Peronophythora Litchii

Litchi is an important fruit grown in tropical and subtropical regions.Litchi downy blight caused by Peronophythora litchii is one of the most important litchi diseases worldwide.The use of resistant litchi cultivars is the safest and most effective method for the disease control.There is a large number of different litchi cultivars in China.But the resistance of most of the cultivars to litchi downy blight is unkown.In this study,a set of criteria for disease classification was set up and the virulence of 31 different isolates of P.litchi was tested by “Feizixiao” fruit.Then,15GDCHr1 isolate was choosed to test the resistance of 140 cultivars.A set of methods for measuring the resistance of litchi cultivars leaves to litchi downy blight was establosed and the leaf resistance of 11 cultivarswith different development ages against litchi downy blight was tested meanwhile the the correlation between the fruit resistance and the leaf resistance was analysied.The resultswill provide scientific basis for the screen of resistant cultivars against to litchi downy blight in the future.The main results were as follows:1.Optimized the grading standard of litchi downy blight.Using litchi cultivars fruit "Feizixiao",31 isolates of P.litchii as materials,A set of disease classification standards suitable for the determination of litchi downy blight was selected.2.The virulence of 31 isolates of P.litchii was tested by spot inoculation.The results showed that there were 7 high virulent isolates,15 moderate virulent isolates,and 9 low virulent isolates.The isolates with moderate pathogenicity are the dominant isolates.3.Choose representativeness isolate of 15GDCHr1.140 different cultivars litchi fruits were inoculated respectively with sporangia suspension,and the time to investigate the disease incidence and disease index was 96 h after inoculation.On the basis of evaluation of disease incidence and evaluation of disease index,comprehensive evaluation of their resistance.The results indicated that there were 3 immunity cultivars ie,“ Yiqiaomili ”,“ Edanli ”,and “ Jiayuanmili ”;14 high resistant cultivars,16 moderate resistance cultivars;18 low resistant cultivars.Among the 140 litchi cultivars tested,the resistance of 117 cultivars was measured for the first time.4.Determine the leaf development stage.Establish a method for measuring litchi downy blight of litchi cultivars.Choose representativeness isolate of 15GDCHr1 tested 11 different cultivars litchi leaves of 6 to 10 leaf ages were inoculated with sporangia suspension,and the time to investigate the morbidity and condition index was 96 h after vaccination.On the basis of evaluation of disease incidence and evaluation of disease index,comprehensive evaluation of their resistance.The result show: With the development of leaf age,the resistance of litchi leaves to litchi downy blight gradually increased,the measurement results of 7～leaf leaves were selected for resistance evaluation of each cultivar.Screen out 4 middle～resistance cultivars;2 low～resistant cultivars;2middle～resistant cultivars;3 middle～resistant cultivars.5.The correlation between fruits and leaves of litchi varieties was analyzed.The leaf disease resistance of the 11 litchi cultivars tested had no correlation with the fruit disease resistance.