Selection of effective antagonistic bacteria for control of tomato wilt caused by Fusarium oxysporum f.sp. lycopersici and root-knot nematode Meloidogyne incognita
1997
Photchana Trakunsukharat
Screening of antagonistic bacteria was conducted from 115 soil samples collected from 8 provinces in the North-east part of Thailand with dilution-plate method. Altogether, 803 bacterial isolates were determined. They were tested on PDA medium for isolates which could inhibit growth of wilt fungus, Fusaruim oxysporum f.sp. lycopersici. Seventy-seven isolates of bacteria produced inhibition zone between fungus colonies. They were again tested on PDA and CAM media when they were 24, 36 and 48 hours old. Only 35 isolates remained effective. Average inhibition zone on PDA (0.46 centimeters) was higher than on CAM (0.37 centimeters). Bacteria cultured for 48 hours gave the maximum inhibition rate (0.50 centimeters). The next was 24 hours (0.38 centimeters) and 36 hours (0.36 centimeters), respectively. Most of selected bacteria were gram-positive. They had 2 colony characters. One was white colony, ungreasy surface and unsmooth colony margin. The other was creamy white colony, greasy with unsmooth colony margin. They formed endospores, UV negative and could stand 55 C temperature, similar to the bacteria Bacillus subtilis which was used as a control. In greenhouse experiment, the treatment with soil drenching with bacterial suspension before transplanting gave higher average height of tomato (46.16 centimeters). It gave less average gall number (46.46), gall index (2.0) and percent nematode infection index (49.87 percent) than 20-hour night soaking seedling root in bacterial suspension treatment (45.86 centimeters, 51.64, 2.03 and 50.90 percent, respectively). Fusarium wilt symptom was found slightly and could not determine with disease rating. The interesting bacterial isolates were SKTB 1' 55-03 and UBM 1' 55-06. They gave moderate average height (49.50 and 43.94 centimeters), produced few galls (39.4 and 37.8) and less gall-forming rate (2.0 and 1.9), respectively.
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