| Sunflower broomrape(Orobanche cumana Wallr.)is a pernicious weed that parasitizes on the roots of sunflower.The occurrence and damage caused by sunflower broomrape have been increasing annually due to the large-scale continuous farming and sloppy management of sunflower,which has caused serious impact on the sunflower industry.During sample collection of some sunflower broomrape,we found dark brown long striped disease symptoms on the stalks of the broomrape,which could cause the whole broomrape to die in severe cases.In this study,29 disease samples of sunflower broomrape were collected from 11 regions in Inner Mongolia,Hebei,and Xinjiang.The pathogens were isolated and identified using Koch’s postulate,and their biological characteristics and pathogenicity differentiation studied.The results of the research are as follows:1.After isolation and identification,five isolates were obtained from the diseased sunflower broomrape.Using morphological and molecular identification,the isolates were identified as five different species of the fungi Fusarium(Fusarium spp),namely F.oxysporum,F.solani,F.equiseti,F.verticillioides and F.proliferatum.It was confirmed that all five fungus could cause disease after pathogenicity test.2.The results on the growth rate measurement of the five isolated pathogens showed that F.oxysporum had the fastest growth rate and the average colony diameter was 7.98 cm after 6 days of incubation,while the growth of F.solani was the slowest with an average colony diameter of 6.38 cm.In terms of spore production,the largest spore production strain was F.proliferatum XGD-1 with 2.78×107 conidia/m L,while the strains with the smallest spore production were F.oxysporum 183 1-1 and WYKBY-5 with 2.50×105/m L.In terms of growth temperature,with the exception of two strains,F.oxysporum 183 2-4and XHZ 1-2,whose optimum growth temperature was 30℃～35℃,all the test strains were25℃～30℃.The growth of the strains were affected when the temperature was lower than10℃ or higher than 35℃.All test strains could grow in a p H range of 4 to 11.There were significant differences in the secretion of crude toxin among the five Fusarium isolates,with the highest being 2.135mg/m L for F.equiseti YL-1 and the lowest being 0.422 mg/m L F.oxysporum XGD3-10,had significantly different crude toxin secretion among the isolated strains of Fusarium.3.The pathogenic differentiation studies data showed that all the isolated strains were able to infect sunflower and broomrape,however,there were certain differences in their pathogenicity;mainly stronger exhibition of pathogenicity on isolated hosts than that of other host.Based on the results of the pathogenicity differentiation,three strains of F.oxysporum GHC 1-2,XXZ-9 and HD 1-1 had weak pathogenicity on sunflower but strong pathogenicity on broomrape. |
