Application timings of antagonists against Dematophora necatrix – the incitant of white root rot of apple

The white root rot of apple is one of the most prevalent disease in all the apple-growing regions of Himachal Pradesh. It causes serious losses both in nursery as well as in orchard conditions. The disease incidence of white root rot varied between 12 to 27 per cent in Shimla district of the state. The present studies were designed to evaluate three methods of application (pre, post and simultaneous inoculation) of fungal antagonists (Trichoderma viride or Trichoderma harzianum) against Dematophora necatrix in soil under pot conditions to ascertain the best time of application of antagonist to control the pathogen. Pre inoculation of T. harzianum 15 days before pathogen inoculum was highly effective and recorded long incubation period (25 days), maximum per cent disease control (73.33 per cent), maximum average root parameters (root area, root length, root tip number, number of forks, root diameter, root volume), minimum cfu/g root weight of D. necatrix (7.67×10⁴), minimum per cent root infection (36.06 per cent), and maximum soil enzymes activities [urease (10.45 µg (NH₄)⁺/ g soil / hr), dehydrogenase (10.48µg TPF/ g soil/ 24 hr) and phosphatase activity (67.36 µg PNP/ g soil/ hr).In simultaneous inoculation of antagonist and pathogen, antagonists prevented the appearance of disease, however, post inoculation of these was less effective.