In vitro fungicidal effect of chitosan with different molecular weights on fungicide-resistant Phytophthora fruit rot on durian from the export market

Abstract

Fruit rots of durian were collected from the export market in Chumphon province, Thailand. The causal organism, Phytophthora spp. was isolated on PAR(PH)-V8 selective medium by tissue transplanting technique. Resistance to dimethomorph, fosetyl-Al, metalaxyl and mancozeb was detected from the mycelial growth on V8 agar amended with fungicide. Multiple fungicide resistant (Mu-FHR) and sensitive (Mu-FS) isolates are used to study the fungicidal effect of chitosan with different molecular weights. The low, medium and high molecular weight chitosan at 0 (control), 500, 1,000 and 2,000 ppm were evaluated for the development of Mu-FHR and Mu-FS isolates on mycelial growth by poisoned food technique and on sporangium production and zoospores release by culture disc technique. The results indicated that the fungicidal effect of three types of chitosan strengthened as the concentration of chitosan increased for mycelial and sporangium inhibition. However, all chitosan treatments were not significant in zoospores release.