Effects of fluorescent pseudomonads on the control of Verticillium wilt (Verticillium dahliae Kleb.) and plant growth of cotton

The study was undertaken to determine the effects of fluorescent pseudomonadswhich were isolated from the rhizosphere of cotton plants and weeds in the cottongrowing areas of Aydın province, on the control Verticillium wilt and plant growthof two cotton varieties (Sayar 314 and Acala Maxa) between 2004 and 2006. A totalof 59 antagonistic bacteria consisting of 41 from weeds and 18 from cotton plantswere selected and 32 Verticillium dahliae isolates were collected from infectedcotton plants. 30 out of 59 isolates inhibited mycelial growth of V. dahliae in-vitro.Fifteen isolates selected were screened for the effects of planth growth andVerticillium wilt on potted cotton plants. In 2005 and 2006, randomized block designfield trials with four replicates were conducted by seed bacterization with fourfluorescent pseudomonads isolates (FP 22, FP 23, FP 30 and FP 35) includingSerratia plymuthica (strain HRO-C48). The data for disease intensity on leaves andthe incidence in each plot were evaluated during the stage of 5-10 %, 50-60 % and 75% cotton boll opening and after harvest in both years. Field trials indicated that seedbacterization with antagonistic bacteria induced a significant reduction of the diseaseincidence and severity of Verticillium wilt compared to untreated control. Based onobservation of foliar symptoms, the percentage of effectiveness of seed bacterizationaveragely ranged from 33 % to 45 % in 2005 and 22 % to 25 % in 2006. Seedbacterization also caused significant increase on seed cotton yield (12 %-17 %) in2005 but there was no significant difference in yield in 2006. Significant negativecorrelations were also found between Verticillium wilt and Nodes above whiteflower (NAWF), seed cotton yield, kernel weight, fiber strength and Speeningcontent index (SCI).Key words Pseudomonas, biological control, seed cotton yield, Aydın