Evaluation of antagonists and natural plant extracts in controlling collar rot of groundnut caused byAspergillus niger

摘要

Forty five isolates of Trichoderma spp. were isolated from soil samples collected from groundnut growing fields of north-coastal zone of Andhra Pradesh and of them10 morphologically different isolates were identified. The native isolates of Trichoderma spp. significantly inhibited the growth of Aspergillus niger over control. The isolates T,, T2， TJg, T21and recorded more inhibition than others in dual culture and seeded agar methods. The extent of inhibition was more pronounced in seeded agar method than in dual culture method. The results revealed that all the ten bioagents tested in vitro applying dual culture technique against A. niger significantly inhibited the mycelial growth of the test pathogen over untreated control. However, Trichodermaisolate T21 recorded minimum colony diameter (2.07 cm) and highest inhibition (75.44%) of mycelial growth ofんniger over untreated control followed by the T, and T40 which recorded mean colony diameter of 2.50 cm, 2.53 cm and mean mycelial inhibition of70.34 %， 69.99%, respectively. Where as in seeded agar methods maximum inhibition was recorded in T, (85.00%) followed by T2 (81.93%) and T21(81.11%). The native isolates of Trichoderma spp. showed a clear cut superiority over commercial formulations. But the commercial formulation of bacterial antagonist Bacillus subtilis showed significantly more antagonistic effect on the growth of A. niger than native isolates. Evaluation of different botanicals by poisoned food technique showed that all plant extracts tested in vitro were found significantly effective in reducing the percentage mycelial growth of Aspergillus niger over untreated control. However, plant extract (@ 5,10 and15% of garlic, recorded lowest mean colony diameter (1.57 cm) and highest mean mycelial growth inhibition (81.51%) followed by Pofyalthia longifolia, Annona squamosa and Pongamia glabra which recorded the mycelial growth of 3.38 cm, 3.75 cm, 3.87 cm and the mean mycelial growth inhibition of 60.18%, 55.87%, 54.44% respectively.Among the concentrations and plant extracts, A. sativum (@10 and 15%) was most effective in reducing the growth of A. niger (100%) followed by Pofyalthia longifolia @15% {11.1 Wo), Annona squamosa @15% (74.61%) and Pongamia glabra @15% (70.33%). When plant extracts compared with the isolates of Trichoderma spp., E fluorescens and B. subtilis showed inhibition of growth of the A. niger which ranged from 62.95 to 100.00 per cent. A. sativum showed the highest inhibition of growth of A. niger (100.0%) followed by B. subtilis and Trichoderma T， isolate, which caused 84.52 and 84.49 per cent growth reduction of A, niger, respectively.