Biological control of root knot nematodes (meloidogyne spp.) using bacterial and fungal antagonists.
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Date
2014
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Abstract
Root-knot nematodes are an important pest of many crops worldwide. Chemical nematicides are the main control methods used to reduce damage caused by nematode pests on crops. However, there are aims of reducing the use of chemical nematicides, resulting in a shift towards the use of biological control, which is an environmentally friendly and safer method of control. Potential antagonists of Meloidogyne javanica were isolated from grazing pastures of livestock, and the rhizosphere of tomato plants grown under glasshouse conditions. A total of 94 bacterial and 22 fungal isolates were screened in vitro by means of microwell bioassays. Twenty bacterial and eight fungal isolates showed nematicidal activity, causing root-knot nematode second-stage juvenile (J2) mortalities of between 47.0% and 65.4%, and 33.0% and 66.3%, respectively. Five bacterial and three fungal isolates caused J2 mortalities of more than 60%. In vitro studies were conducted to evaluate the efficacy of these isolates (Bacillus spp., Hypocrea lixii-the teleomorph of Trichoderma harzianum) and Trichoderma spirale, together with two previously isolated biocontrol agents, Hypocrea lixii Strain Eco-T® and Clonostachys rosea, on the root-knot nematode M. javanica. All the bacterial isolates and fungal treatments caused significant levels of J2 mortality of M. javanica of between 59.0% to 94.0% after 12, 24 and 48 h. Bacillus thuringiensis (Isolate BG25) and H. lixii (Isolate Cr5) caused the highest mortality of J2. B. thuringiensis (Isolate BG25) and H. lixii (Isolate Cr5), when applied as a seed dressing or as a soil drench significantly (P<0.001) reduced penetration of M. javanica J2into the roots of tomato plants. The two isolates also reduced disease severity and significantly (P<0.001) reduced formation of galls, production of egg masses and the number of eggs per root. Growth parameters in terms of shoot length, shoot weight and dry shoot weight were significantly (P<0.001) increased by seed dressing and soil drench treatments of all bacterial and fungal isolates. B. thuringiensis (BG25) and H. lixii (Cr5) caused the greatest effect on growth parameters measured on tomato plants under greenhouse conditions.
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Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.