Identification of pathogen causing heart rot of pitaya(Hylocereus polyrhizus)and studies on its initial infection point
Heart rot is a newly identified pitaya disease,which affects the yield and commercial value of the fruit,with an incidence rate of 10%in autumn and winter seasons.In order to effectively prevent and control heart rot in pitaya fruit,we used strains isolated from diseased fruit in the field as materials.We con-ducted ITS gene sequence analysis,as well as in vivo inoculation methods in both indoor and field set-tings,to identify the pathogen and determine the initial point of infestation and its biological properties.The results showed that the the symptoms of pitaya heart rot disease in the field include yellowing and dropping of some young fruits,premature reddening of young fruit skin,and brown rot of the fruit flesh.The patho-genic strain was identified as Gilbertella persicaria.The initial infection point of the pathogen is the stigma of the pistil,and the sporangiospores can colonize the stigmas of female either directly or indirectly through pollen,resulting in heart rot during pollination,fertilization and fruit development.The optimal growth tem-perature and pH value for G.persicaria were 30℃and pH 5,respectively,while light exposure could in-hibit the sporulation of the fungus.These results indicate that G.persicaria could cause pitaya heart rot by in-fecting the stigmas of female.To mitigate the damage of G.persicaria to pitaya fruits,it is recommended to promptly remove petals after pollination or apply fungicide treatments,thus decreasing the initial inoculum load.
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