THE FIRST REPORT OF STENOTROPHOMONAS SP. ASSOCIATED WITH CANKER AND LEAF SPOT DISEASE OF STONE FRUITS IN IRAN

In September of 2012 some bacterial strains were isolated from peach (Prunuspersica),apricot (Prunusarmeniaca)and sour cheery (Prunuscerasus)trees with leaf spot, canker and dieback symptoms on twig and stem in Alborz province. The symptoms were similar to those caused by Pseudomonas syringaepv. syringae (Pss) and Xanthomonasarboricolapv. pruniwhich have been previously reported in north of Iran (Aldaghi, et al., 2010.;Mahmoudiet al., 2012). The smooth, pale yellow and round, mucoid colonies were recovered from symptomatic tissues on sucrose nutrient agar (NAS). For pathogenicity tests, ten detached young leaves of peach,apricot and cherry (Prunus sp.)were separately placed on 1% agar plate and sprayed with strains isolated from infected tissues in Iran and three type strains of X. a. pv. pruni(ICMP17186), Pss(ATCC19310) and Erwiniaamylovora(ICMP1540) at 1×108 CFU/ml. Bacteria were identified on the basis of the biochemical and molecular characteristic (Palleroni, & Bradbury., 1993; Schaadet al., 2001).Ice nucleation activity measured by the droplet freezing method.Based on biochemical tests, none of isolated bacteria were identified as Pss or X. a.pv. pruni. All strains induced a hypersensitive response in tobacco. Representative strains were gram-negative, oxidative negativeand also negative for formation of levan and casein, hydrolysis of starch and tyrosine, the reaction of isolates forindole production, reducing substance from sucrose, production of urease, oxidase, lecithinase, arginine dehydrolase, reduction of nitrate, growth on 5% on NaCl and acid production from, maltose, lactose and trehalose were negative. The isolates were positive for, production of H2S from cysteine and peptone, protease, hydrolysis of gelatin and growth at 37°C. Induction of fast hypersensitive reaction on tobacco and geranium may be considered as the potential of the isolates in causing disease in one or more plant species. The leaves inoculated with isolates developed leaf spots similar to those observed in the field. The same bacteria were reisolated from symptomatic leaves and identification was confirmed. The 16S rDNAwas amplified by PCR using primer pairs 63f and 1384r (Marchesiet al., 1998). PCR products were sequenced and sequences were aligned and compared with those deposited in GenBank. 1100 nucleotides of sequences of the strain number 106 (accession No.KF752591) and 81 (accession No.KF7440537) showed 99% identity with those of Stenotrophomonas isolates. All of isolates were positive for ice nucleation. Mostof ice nucleation active bacteria are epiphytic and exist almostin all plants. The ability of bacteria to form ice nucleus is very important. Ice nucleation active bacteria can catalyze ice formation at temperatures as high as -2°C and have significant role in freezing injuries ofcold sensitive plants. The association of two species of this genus, including S. maltipholia and S. rhizophila with citrus blast havepreviously been reported from northern Iran, and their icenucleation activity of demonstrated (Alimiet al., 2012).In that study the possibility of pathogenicity of collected strains has not been evaluated.This is the first report on, association of Stenotrophomonas sp.with canker and leaf spot disease of stone fruits tress in alborz province of Iran.