BACTERIAL WILT OF LIMA BEAN (PHASEOLUS LUNATUS) CAUSED BY CURTOBACTERIUM FLACCUMFACIENS PV. FLACCUMFACIENS, A NEW DISEASE IN IRAN

Abstract

In the summer of 2013, during surveys in lima bean (Phaseolus lunatus) (cv. Christmas Pole) fields of East Azerbaijan, Northwest Iran, interveinal necrotic lesions and marginal chlorosis were observed on the leaves. The isolation of bacterial was done on Yeast Peptone Glucose Agar (YPGA) medium (EPPO, 2011). Yellow-colored colonies 1-2 mm in diameter were present on YPGA plates after incubation at 25°C for 48 h. All isolates were Gram-positive, of oxidative but not fermentative metabolism, and had the ability to grow at 37°C. All hydrolyzed aesculin, casein, and gelatin, produced acid from inositol, mannose and maltose but not from mannitol and erythritol, were of positive catalase and oxidase, but of negative urease and indole production (EPPO, 2011). Bacterial strains were identified as Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) based on biochemical test results. The pathovar-specific primer pair CffFOR2 and CffREV4 amplified a 306 bp fragment of the isolates and confirmed them as Cff (Tegli et al., 2002). The strains were deposited in the University of Tehran Microorganisms Collection (Accession No. Cffcb123). Pathogenicity test was conducted on 20 day old lima bean (cv. Christmas Pole) plants. The Cff suspensions (1×108 CFU/ml) were prepared from 48 h old culture on YPGA. Node infiltration method was conducted for the inoculation of plants (Hsieh et al., 2003). Disease symptoms appeared 10-15 days after inoculation. First trifoliate leaves of the inoculated plants exhibited symptoms of marginal necrosis and interveinal yellowing. Cff was consistently re-isolated from artificially infected lima bean tissues on YPGA and re-identified using CffFOR2 and CffREV4 primer pairs. This is the first report of Cff causing bacterial wilt in lima bean in Iran.