Ability of Moderately Halophilic Bacteria to Control Grey Mould Disease on Tomato Fruits

Abstract

Tomato is one of the leading crops in Tunisia in terms of weight consumed (20 kg⁄per person⁄year). Preserving the quality of the fruit from field to consumer is essential to successful marketing. Grey mould rot induced by Botrytis cinerea is an important cause of postharvest loss depending on season and handling practices. We describe here the ability of halotolerant to moderately halophilic bacteria isolated from different Tunisian Sebkhas (hypersaline soils) to protect freshmarket tomato fruits from B. cinerea. The tomatoes tested were at two different stages of ripening, (i) mature-green and (ii) red. Six strains significantly reduced growth of the pathogens from 67% to 87%. The effectiveness of these antagonists was also confirmed on green tomatoes; in which the fruit rot protection rate ranged from 74% to 100%. The antagonists were characterized by morphological, biochemical and physiological tests as well as 16S rDNA sequencing. The halotolerant effective isolates were identified as belonging to one of the species Bacillus subtilis (M1-20, J9) or B. licheniformis (J24). One effective moderately halophilic isolate (M2-26) was identified as Planococcus rifietoensis. These strains are a source of hydrolytic enzymes such as chitinases, proteases, laminarinases, amylases, lipases and cellulases. For comparison, 12 halotolerant or moderately halophilic strains obtained from DSM culture collection were also evaluated for their antifungal activity against B. cinerea on tomato fruits. The most effective strains were Halomonas subglaciescola, Halobacillus litoralis, Marinococcus halophilus, Salinococcus roseus, Halovibrio variabilis and Halobacillus halophilus with a percentage of grey mould rot reduction ranging from 71% to 97%. Inoculation of mature-green tomatoes by the bacterial antagonist of Halobacillus trueperi resulted in no disease development. Our results indicate that the use of halotolerant to halophilic microorganisms should be helpful in reducing grey mould disease of stored tomatoes.

Characterization of a novel chitinase from a moderately halophilic bacterium, Virgibacillus marismortui strain M3-23

“…Thus, agricultural industries need in novel biofungicide formulations (Gohel et al 2007). Chitinolytic enzymes, which are key players in the lysis of cell walls of higher fungi, are produced by several microorganisms including bacteria (Sadfi-Zouaoui et al 2008;Essghaier et al 2009). Recently, a number of commercial biocontrol products have been developed from rhizobacteria, and many plant disease biocontrol products that contain Bacillus spp.…”

“…Previous research also aimed to identify the mode of action of the most successful isolates as this information may help optimize their biocontrol efficiency in the field. Understanding the mechanisms involved in biological control may enable efficacy to be enhanced (Sadfi-Zouaoui et al 2008;Essghaier et al 2009). We reported previously the efficiency of the moderately halophilic Virgibacillus marismortui strain M3-23 in biological control, and its high production of chitinase.…”

“…However, our laboratory was the first to take an interest in the study of antifungal chitinase from moderately halophilic bacteria such as Virgibacillus marismortui, Terribacillus halophilus and Planococcus rifitoensis. These moderately halophilic bacteria were isolated previously from shallow salt lakes in Tunisia and selected as strong antagonists of Botrytis cinerea-the causal agent of grey mold disease on strawberries and tomatoes under the commercial standard conditions applied in Tunisia (Essghaier et al 2009;Sadfi-Zouaoui et al 2008).…”

In vivo and in vitro evaluation of antifungal activities from a halotolerant Bacillus subtilis strain J9

“…Our previous laboratory studies showed the efficiency of halotolerant Bacillus isolates in the control of potato dry rot under storage conditions (Sadfi et al, 2001(Sadfi et al, , 2002. Recently, we described the ability of moderately halophilic bacteria isolated from shallow salt lakes in Tunisia to protect fresh-market tomatoes and strawberry fruits from B. cinerea under commercial standard conditions (Sadfi-Zouaoui et al, 2008a;Essghaier et al, 2009). To our knowledge, we were the pioneer to evaluate the ability of halophilic bacteria to protect plant diseases from pathogenic fungi.…”

“…Finding a broad antifungal enzyme able to function under such environmental conditions is relevant for biocontrol purposes. Previously, we have reported the efficiency of the halotolerant B. subtilis strain J9 in biological control under postharvest conditions on strawberries and tomatoes (Sadfi-Zouaoui et al, 2008a;Essghaier et al, 2009) and on tomato stems under greenhouse conditions (Sadfi-Zouaoui et al, 2008b). The main objective of this work was to evaluate the biological activity of the halotolerant B. subtilis strain J9 on strawberry plants under field conditions.…”