Biocontrollers in the management of yam dry rot nematodes

Abstract

One of the main diseases affecting yam crops (Dioscorea spp.) in Brazil is the dry rot caused by Scutellonema bradys, Pratylenchus brachyurus and P. coffeae nematodes. The use of biological control agents is an auspicious procedure which has been tested in order to reduce losses by pathogens. The objective of this work was to evaluate the nematicidal activity in vitro and in vivo of commercial biological products on yam dry rot nematodes. Products based on Trichoderma harzianum (2.0 x 109 conidia mL-1) at dosages of 1.5 and 2.0 L 200 L-1 of water; Bacillus subtilis 20% - 1.0 x 1011 cfu g-1 + B. licheniformis 20% - 1.0 x 1011 cfu g-1 at 100 and 150 g 100 L-1; B. subtilis 200 g kg-1 + B. licheniformis 200 g kg-1 at 130 and 200 g 100 L-1; combination of rhizobacteria including Bacillus spp. and organic carbon at 5L and 7L 100 L-1; and the control (distilled water), were tested in in vitro assays on S. bradys or Pratylenchus sp. In experiments performed under greenhouse conditions, healthy seed tubers were planted in sterilized soil and thirty days later the soil was infested with a suspension of 1,000 specimens of a mixed population of S. bradys and P. coffeae. Then, after 30 days products based on B. subtilis 20% + B. licheniformis 20% - 150 g 100 L-1; T. harzianum 2 L 200 L-1 and rhizobacteria + organic carbon 7 L 100 L-1, at 100 mL per pot, were applied to the soil. Three months after planting, the percentage of sprouting of the seed tubers was evaluated and in the fifth month, the nematode population densities were determined. The sprouting of seed tubers was of 100% in all treatments. Bacillus subtilis 20% + B. licheniformis 20% and T. harzianum caused 89% and 61% mortality in S. bradys respectively, at the highest concentrations. In specimens of Pratylenchus sp., rhizobacteria + organic carbon exhibited 51% and 45% mortality at higher and lower concentrations, respectively. Under greenhouse conditions, B. subtilis 20% + B. licheniformis 20% and rhizobacteria + organic carbon were more effective in reducing nematode population densities, compared to the control.
 KEYWORDS: Dioscorea spp.; Scutellonema bradys; Pratylenchus sp.