Evaluation of Alternaria alternata causing leaf spot of barnyardgrass grown in rice fields

Barnyardgrass (Echinochloa spp.) is considered one of the world worst weeds. Fungal pathogens can be exploited as biological agents for the management of agricultural weeds. In this research, Alternaria alternata was isolated from Echinochloa spp. and studied as a biocontrol agent against this weed in paddy fields. Pathogenicity test of isolates was done in desiccators, and revealed the pathogenicity of this fungus and its ability to cause leaf blight on Echinochloa spp. Inoculation was done using a spore suspension consisting of 105spore/ml distilled water and 1% Tween-20 at the 2-3 leaf stage. Also, seeds germination inhibition test was done. The results indicated that A. alternata was able to infectEchinochloa spp. in a higher rate compared with rice cultivar. Moreover, the results showed that seed germination of Echinochloa spp. was significantly affected by A. alternata in comparison with controls. Cluster analysis using unweighted pair group method with arithmetic mean (UPGMA) method gave two groups. The different isolates of A. alternatashowed different reactions in seeds germination test and pathogenicity test. Hence, A. alternata can be considered as a probable bioherbicide for the control of Echinochloa spp. at early stages of growth of weed.   Key words: Echinochloa spp., Alternaria alternata, fungi, biological control.