Abstract
Phytobiocides are a good alternative to chemicals in managing bacterial diseases including bacterial wilt of tomato caused by Ralstonia solanacearum. In the present research study, finely ground dried powders of seven widely available medicinal plants/weeds species viz., Peganum harmala (esfand or wild rue), Calotropis procera (sodom apple), Melia azedarach (white cedar), Allium sativum (garlic), Adhatoda vasica (malabar nut), Tagetes patula (marigold) and Nerium oleander (oleander) were assessed for their anti-microbial activity, both in-vitro (10% w/v) and in-vivo (10, 20, 30, and 40 g/kg of potted soil) against R. solanacearum. Aqueous extracts (prepared as 10% w/v, soaking for 48-72 h and filtering) of C. procera, A. vasica, and T. patula inhibited the in-vitro growth of the bacterial pathogen over 60% of that produced by the standard antibiotic streptomycin. A. sativum, N. oleander and P. harmala aqueous extracts were less effective while M. azedarach showed no effect against R. solanacearum. The higher dose (40 g/kg of soil) of C. procera, A. vasica and T. patula decreased disease severity quite effectively and increased yield and plant growth characters as much as the standard antibiotic did. No phytotoxicity of medicinal plants powder was observed on tomato plants. Alkaloids, flavonoids, tannins, saponins and terpenoids were detected in the aqueous extracts of T. patula and A. vasica whereas C. procera was found to have only alkaloids, flavonoids, tannins and saponins. Our data suggest that dried powders of T. patula, C. procera and A. vasica (40 g/kg of soil) could be used as an effective component in the integrated disease management programs against bacterial wilt of tomato.
Highlights
Tomato (Solanum lycopersicum L.), is an important vegetable crop throughout the world
Phytobiocides are a good alternative to chemicals in managing bacterial diseases including bacterial wilt of tomato caused by Ralstonia solanacearum
Aqueous extracts of C. procera, A. vasica, and T. patula inhibited the in-vitro growth of the bacterial pathogen over 60% of that produced by the standard antibiotic streptomycin
Summary
Tomato (Solanum lycopersicum L.), is an important vegetable crop throughout the world. In Pakistan, tomato is cultivated on 52,000 hectares with an annual production of 529,600 tons (Anonymous, 2011). Cultivar, climate, soil type, cropping pattern and the particular strain of the bacterium, R. solanacearum has been reported to cause direct yield losses of 0-91% in tomato, 33-90% in potato, 10-30% in tobacco, 80-100% in banana, and 0-20% in groundnuts (Elphinstone, 2005). The incidence of the disease was found to be 21.9% on sweet peppers, 16.6% on hot peppers, 13.3% on tomatoes, 10.5% on potatoes and 5.5% on brinjals. Over 80% of R. solanacearum strains present in Pakistan belong to biovar 3 (Begum et al, 2012; Shahbaz et al, 2015)
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