Inoculating method for Alternaria alternata in seedling stage of tobacco.

Under greenhouse and potted condition,inoculating the strong pathogenic isolate GY-31 of Alternaria alternata on tobacco seedlings of the tested varieties,Hongda and K326 at 7-leaf stage was conducted by applying mycelium block inoculation,spore spraying inoculation,spore suspension tampon inoculation,spore hanging drop inoculation,mycelium hanging drop inoculation,respectively,to select and develop a suitable method for inoculation of the brown spot pathogen in seedling stage of tobacco.The results show that both spore suspension tampon method and mycelium block inoculation can cause brown spot on the two varieties of tobacco,suggesting that the two methods are suitable to the inoculation of A.alternata in seedling phase.However,spore spraying inoculation and spore hanging drop method had a low success rate,and mycelium hanging drop inoculation wilted the leaves of Hongda and didn't cause any lesion on K326,with a worse repeatability,suggesting that the these methods are not suitable to the inoculation of the pathogenic fungus.Further,the influence of conidial suspension concentration and moisture on the inoculation results of tobacco brown spot by spore suspension tampon method was investigated by two-factor randomized block design,and the results indicate that the incidence of diseased leaves caused by inoculation increased with the conidial suspension concentration.The incidence of diseased leaves was less than 35% when the conidial suspension concentration was below 104 CFU·mL-1,while the incidence of diseased leaves was between 70% and 92% when the conidial suspension concentration ranged from 105 to 107 CFU·mL-1.The results also suggest that moisturizing may improve the incidence of diseased leaves caused by inoculation.