Identification Of The Pathogen Causing Root Rot Of Sand Pear And Screening Of Fungicides In Laboratory

In recent years,the root rot disease of sand pear in three pear producing areas in three provinces including Hubei,Fujian,and Sichuan of China has occurred seriously,resulting in pear tree dying,however the pathogenic species causing the disease are still unclear.In this study,the field investigation for the disease was carried out,and the disease root samples were collected for pathogen isolation and identification to clarify the pathogen species and dominant pathogen species.The strains from dominant pathogenic species were used for screening of fungicides in laboratory to control root rot of sand pear.The following main results were obtained:1.Identification for the pathogen species causing root rot in three sand pear producing areas in China and the comparison on culture characteristics of the pathogens.The occurrence and damage of pear root rot were investigated and the symptoms were observed in three pear producing areas in Hubei,Fujian,and Sichuan province.The diseased roots showing typical symptoms of pear root rot were collected for pathogen isolation and purification.A total of 31 strains of Fusarium spp.were obtained according to the morphological characteristics of the colonies.The representative strains were carried out morphological observation and phylogenetic analysis with ITS,EF-1α and RPB2 genes.The results showed that the strains of Fusarium belonged to four species including F.fujikuroi,F.commune,F.solani and F.falciforme,respectively,the root rot caused by F.falciforme,F.commune and F.fujikuroi on pear trees was first discovered.The results of pathogenicity test showed that these four Fusarium species were pathogens causing root rot of sand pear in China.Among them,the isolation ratio of F.solani was the highest,reaching 54.8%(17/31),which was the dominant pathogen causing root rot of sand pear in China.There were differences between pathogenicities of strains from different species,different regions and pear varieties,which of the strains from F.solani had the strongest pathogenicity.The results by adding different compounds showed that there were also significant differences between the culture characteristics of different Fusarium species causing root rot of sand pear.Among them,F.fujikuroi had most tolerant to NaCl and Sorbitol,and most sensitive to CR,SDS and H2O2.2.The screening of fungicides in laboratory to control pear root rot and determining of sensitivity to the dominant pathogen.The FJ7 strain of F.solani,the dominant pathogen causing pear root rot in three sand pear producing areas in China,was selected for fungicide screening in laboratory.The results showed that 50%carbendazim WP,43%tebuconazole SC and 25%tebuconazole·imazalil EW had better inhibitory effects on mycelial growth,and their EC50 values were 0.2225 μg/mL,0.4757 μg/mL and 0.4794 μg/mL,respectively.50%carbendazim WP had the best inhibitory effect on sporulation,and its EC50 value was 1.5958 μg/mL.The results of sensitivity test showed that these three fungicides had good inhibitory effects on strains from different regions,and the average EC50 values were 0.4755 μg/mL,0.8491 μg/mL and 1.0410 μg/mL,respectively.The above results showed that 50%carbendazim WP,43%tebuconazole SC and 25%tebuconazole·imazalil EW could be used to control root rot of sand pear.In this study,the pathogenic species and dominant pathogens causing pear root rot in China were identified,and the fungicides with good inhibitory effect on the dominant pathogens were determined,which providing theoretical basis and technical support for the prevention and control of pear root rot.