Effect of Combination between Bioagents and Antioxidants on Management of Tomato Powdery Mildew

Abstract

Isolation of microorganisms occurring on the phyllopane of tomato leaves yielded many Basillus and Trichoderma strains. The isolated Bacillus spp. were purified and identified as B. chitinosporus, B. megaterium, B. pumilus, B. subtilis and B. thuringiensis and the isolated Trichoderma spp. were, T. album, T. hamatum, T. koningii, T. harzianum and T.veredi. All the tested Bacillus and Trichoderma strains caused significant inhibition to the germinated conidia of Leveillula taurica (imperfect stage = Oidiopsis taurica) the causal of tomato powdery mildew compared with control treatment. In addition, B. thuringiensis B. subtilis and B. chitinosporus were the most efficient bacteria in this regard and T. harzianum and T. veredi were the most efficient fungi. The inducer resistance chemicals (IRCs) bion, chitosan, humic acid, salicylic acid and zinc sulphate resulted in significant reduction to the germinated conidia of the causal fungus compared with control treatment. This reduction was gradually increased by increasing the tested concentration. In plastic house experiments, spraying tomato plants with the tested bioagents B. thuringiensis and T. harzianum and the IRC salicylic acid resulted in significant reduction to powdery mildew severity during 2012/2013 and 2013/ 2014 growing seasons. Spraying of the bioagents B.thuringiensis and T. harzianum and the IRC salicylic acid, each alone or in different combinations, resulted in significant reduction to the severity of the disease with significant increase to the produced fruit yield. Furthermore, spraying any of these compounds alone was of less effect in this regard compared with spraying their combinations. However, the fungicide Sumi-8 was the superior in this regard, being 3.7 % disease severity and fruit yield 16.2 k g. / plant followed by the mixture of the three treatments, being 4.6% disease severity and fruit yield 13.7 kg. / plant. The three oxidative-reductive enzymes, i.e. PAL, PO and PPO were greatly increased in the leaves of all sprayed treatments compared with control treatment. In addition, plants sprayed with salicylic acid recorded the highest activity of the three enzymes followed by that sprayed with B. thuringiensis then T. harzianum. Meanwhile, untreated leaves (control) recorded the lowest activity followed by that sprayed with Sumi-8.