Diversidade de isolados de Alternaria brassicicola (Schwn.) Wilt. de cultivos convencionais e orgânicos de brássicas de Pernambuco

Abstract

The Alternaria black spot is considered one of the most common and destructive diseases of brassica, and although it may be caused by several species, Alternaria brassicicola is the predominant pathogen in both conventional and organic brassica crops in State of Pernambuco, Brazil. To assess the pathogenic variability of 120 isolates of A. brassicicola, was analyzed the virulence to brassica species, physiology aspects of the pathogen and sensitivity to fungicides. The isolates obtained from conventional and organic crops were inoculated under greenhouse conditions in 40 days old plants of broccoli, cabbage, cauliflower and Chinese cabbage and disease severity was assessed 10 days after the inoculation. Under laboratory conditions the following parameters were evaluated for all isolates: rate of growth mycelial, sporulation, and sensitivity to fungicides iprodione and tebuconazole. Based on the variables analyzed, it was found variability among isolates of A. brassicicola, but there were no significant (P>0.05) correlation among the analyzed variables, regardless of the cultivation system and the original host of each isolate. The variables were useful in distinguishing individual groups of isolated with similarity in virulence to the host, physiological characteristics and sensitivity to fungicides. The cross inoculations and the development of symptoms in brassica highlighted the absence of host specificity. All isolates weresensitive to the fungicides iprodione and tebuconazole. Based on the components of variance analysis, there was no significant effect of the cultivation system on the variables, except for disease severity on Chinese cabbage (P = 0.0391). Most of the variance results from the difference among isolates of A. brassicicola within the cropping systems and the host of origin. In the context multivariate, no effect was found regarding the host of origin of the isolates (P = 0.4993), however, there was great variability (P <0.0001) among isolates within the cropping systems and the host of origin.