Alternaria leaf spot is one the most important fungal disease of Crusiferous palnts, that affect the quality and quantity of these plants every year.This disease is caused by three seedborne pathogenic fungi named A. brassicae , A. brassicicola and A. raphani in most area of the world. Infection caused by Alternaria . is an important in the decrease of the seed germination. A. brassicae is known as disease agent of canola leaf spot in Canada , America , India and most Euroupian countries, and in Iran this species was isolated from canola fields of Golestan, Khozestan and western Azarbayejan. A. brassicae produce some phytotoxins in infected tissue and followed by the colonization of infected tissues, A. brassicae produce some phytotoxins in host tissue. Destruxin B is the major phytotoxin produced by this fungus in vitro and in plant. Synthesis and secreting of this toxin is related to NRPS-ABC traorter gene cluster in the genom of thes fungus.Mor gene analysis of this cluster my show the role of NRPS-ABC traorter gene cluster and phytotoxins synthesis by them in pathogenicity, ecology and physiology. Therfore, this research focused on the study of disease mechanism in six isolates of A. brassicae by molecular, chemical and biological methods to increase our knowledge of disease mechanism. In this research, from 65 isolates of Alternaria . isolated from leaf, pod and stem of canola,was obtained four species A. alternate , A. arborescense , A. infectoria and A. raphani , six isolates of A. brassicae was taken from Tarbiat Modarres of Tehran. A. brassicae isolates confirmed by the use of specific primers. For detection of present or absence of AbrePsy1 and AbreAtr1 genes in the studied isolates, PCR assay was done. The amount of transcription in the mentioned genes correspondenced to pathogenicity NRPS-ABC traorter gene was studied by Real time PCR method. In determining the ability of toxin production, produced toxin was extracted and relatively purified. The role of phytotoxins produced by each isolate was investigated on canola plants in vitro .On the other hand, severity of pathogenicity of each isolate was measured in the greenhouse. For assessment of AbrePsy 1 and AbreAtr 1 expression and the Keywords : canola , A. brassicae , Phytotoxin, NRPS, ABC traorter.
