Abstract
The aim of this study is to assess the effect of extracts of Nerium oleander, Eucalyptus chamadulonsis and Citrullus colocynthis against bacterial spot disease of tomato and to investigate the induction of resistance by tomato (Solanum lycopersicum) in order to promote a sustainable management system. The antibacterial activity of aqueous and ethanol plant extracts was tested against Xanthomonas axonopodis pv. vesicatoria, isolate PHYXV3, in vitro and in vivo. The highest antibacterial activity in vitro was obtained with C. colocynthis, N. oleander and E. chamadulonsis, respectively. In vivo, ethanol extracts of N. oleander and E. chamadulonsis were more effective than aqueous extracts in reducing pathogen populations on tomato leaves. Under greenhouse conditions, application of the plant extracts at 15% (v/v) to tomato plants significantly reduced disease severity and increased the shoot weight of ‘Super Marmande’ tomato. In most cases, plant extracts significantly increased total phenol and salicylic acid content of tomato plants compared to either healthy or infected ones. In addition, C. colocynthis and E. chamadulonsis extracts significantly increased peroxidase activity while only E. chamadulonsis increased polyphenol oxidase after infection with the causal agent. The results indicated that the plant extracts showed promising antibacterial activity and could be considered an effective tool in integrated management programs for a sustainable system of tomato bacterial spot control.
Highlights
Worldwide tomato (Solanum lycopersicum) production is 182,256,458 MT with a harvested area around 4762,457 ha [1]
The greatest reduction was obtained with both extracts of C. colocynthis at 15% (ethanol (0.81 mm) and water
(0.65)) followed by the ethanol extract of N. oleander (ethanol (0.59 mm) and water (0.50)), while the least reduction was obtained from E. chamadulonsis (ethanol (0.44 mm) and water (0.51))
Summary
Worldwide tomato (Solanum lycopersicum) production is 182,256,458 MT with a harvested area around 4762,457 ha [1]. Tomato crops are facing many bacterial diseases including bacterial spot caused by Xanthomonas axonopodis pv. Vesicatoria [2,3]. The application of copper bactericides, alone or in combination with other pesticides and antibiotics (especially streptomycin), is the primary tool to control such bacterial diseases [4]. Several limitations have restricted their use including bactericide resistance, market demands related to residues and worries of human health [5]. Safe alternative control methods need to be tested and developed [6,7,8].
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