Isolation of local Bacillus spp. from Afghanistan soils and their potential in suppressing the root-knot nematodes on tomato

抄録

One hundred twenty antibiosis-positive and 34 antibiosis-negative heat-resistant bacteria (Bacillus spp.) were isolated from the surface-sterilized roots and the rhizosphere soils of tomato seedlings grown in Afghanistan soils and evaluated for their biocontrol potential against the root-knot nematode Meloidogyne incognita. Firstly, antibiosis properties of the isolates were tested using the tomato Fusarium-wilt pathogen. Then, effects of culture-filtrates of the selected isolates on the second stage juveniles (J2) mortality and egg-hatch were evaluated. Among antibiosis-positive isolates, 12 showed significantly higher J2 mortality (83.6 ± 1.5%) and lower egg-hatch (14.2 ± 2.3%) and were selected for further experiments using tomato plants. Antibiosis-negative isolates showed relatively lower J2 mortality (30.9 ± 7.6%). The antibiosis-positive isolates Kh2-27, Kh2-30, B7-2, and B1-6 decreased the nematode damages to tomato plant by 57.7%, 55.8%, 57.7% and 61.5%, respectively. The other eight isolates also significantly decreased damage to tomato plant. The antibiosis-negative isolates Kh2-5 and B7-12 also decreased the root-knot disease to a similar degree to those of the antibiosis-positive isolates, suggesting that antibiosis was not the main factor for the root-knot disease suppression. Phylogenetic analysis based on the 16S rDNA sequences and the physiological properties indicated that the antibiosis-positive isolates are closely related to B. subtilis and B. tequilensis. The two antibiosis-negative isolates were closely related to B. megaterium species. These results indicate the capability of heat-resistant bacteria as a biocontrol tool for the management of the root-knot nematode under local environmental conditions in Afghanistan.