Bacillus subtilis IIHR BS-2 enriched vermicompost controls root knot nematode and soft rot disease complex in carrot

Abstract

Root knot nematode (Meloidogyne incognita) and soft rot bacterium Pectobacterium carotovorum subsp. carotovorum are major pathogens of carrot (Daucus carota) throughout the world, reducing both quality and quantity of marketable yield. Bacillus subtilis IIHR BS-2, a potential biocontrol agent, was evaluated against the nematode-bacterium disease complex in carrot under in vitro and field conditions. Under in vitro, culture filtrates of B. subtilis not only exhibited strong nematicidal activity by inhibiting the hatching of M. incognita eggs (94.65%) and causing juvenile mortality (91.26%), but also inhibited the growth of P. carotovorum (60.6%). Liquid formulation of B. subtilis IIHR BS-2 (CFU −1 × 108 per ml) was tested under field conditions as seed treatment (10 ml kg−1 seeds) and soil application (after enrichment in vermicompost), individually and in combination, and compared with application of chemicals (carbofuran and streptocycline) and untreated control. Among all the treatments, seed treatment together with soil application of B. subtilis (5 l ha−1) enriched vermicompost (2 tons ha −1) recorded the maximum increase in carrot yield (28.8%) and decrease in nematode population (69.3%) and disease incidence (70.2%). This was followed by treatment with chemicals (carbofuran 1 kg a.i. ha−1 + streptocycline- 0.02%) which recorded 62.2% and 68.15% decrease in disease incidence and nematode population, respectively. This study proves the bioefficacy of B. subtilis IIHR BS-2 and demonstrates its appropriate delivery mechanism through enrichment in vermicompost for managing nematode disease complex and reaping maximum yield in carrot under field conditions.