Biological control of bacterial stem rot caused by Erwinia chrysanthemi on tomato

Abstract

Possibilities of biological control were investigated by the use of some antagonists for controlling Erwinia chrysanthemi, the causal agent of soft rot on tomato. Seventy-one candidate antagonists were isolated from tomato rhizosphere in Adana and Mersin sites in Turkey and the remaining seven isolates were obtained from Plant Protection Department in Israel. In petri dishes studies, 14 isolates inhibited E. chrysanthemi's growth. Laboratory assays for suppression of soft rot development on potato slices were carried out using all candidate antagonists and 16 isolates prevented development of symptoms of soft rot caused by E. chrysanthemi. Thirteen out of 16 antagonist isolates, which prevented the development of the pathogen on potato slices, were chosen for further tests. Their abilities to prevent the disease development were investigated on young tomato seedlings in climate room conditions. Eight out of 13 selected isolates reduced the disease development between 89% and 33%. Greenhouse experiments were carried out using five selected antagonists on tomato plants. One of the antagonists provided a good level (74% protection) on tomato plants against E. chrysanthemi in the greenhouse experiments. The present study is the first report on the efficiency of potential biocontrol agents against tomato bacterial pathogens in Turkey.

Introduction

Although many plant pathogenic bacteria produce pectolytic and macerating enzymes, most bacteria causing soft rot on many crops belong to certain Erwinia species. The species causing soft rot on many plants are Erwinia carotovora subsp. atroceptica (Van Hall, 1902) Dye, 1969, Erwinia carotovora subsp. carotovora (Jones, 1901) Bergey et al. (1923) and Erwinia chrysanthemi Burkholder et al. (1953). They affect storage organs and succulent leaves of vegetables (potato, tomato, onion, crucifers), field crops (corn, rice, sugar beet), and ornamental plants (begonia, dieffenbachia, dahlia, philodendron). Erwinia chrysanthemi is known as a greenhouse pathogen in mild climate regions (Perombelon and Kelman, 1980). In recent years, stem rot caused by E. chrysanthemi on tomato in greenhouses has been first reported in Turkey, at Mersin by Cinar and Aysan (1995). The pathogen induces wilt throughout the whole plant, finally causing collapse of the whole plant. To our knowledge, the disease firstly, appeared on the roots of some plants, probably by seed borne or soil borne infection, and then spread to the other plants by cultural practices (Aysan, 2001). If the conditions of the greenhouses are favorable for the disease, then symptoms develop quickly. It is known that tomato cultivation in several greenhouses in Mersin have been destroyed by stem rot and the prevalence of this disease has steadily increased since 1995 (Aysan and Cinar, 2001).

Because the pathogen invades the inner parts of the plants, the conventional chemical products such as copper may not provide adequate control for the disease. To solve this problem, many scientists have focused on alternative solutions such as biological control in conventional and ecological (organic) agriculture. Several research groups have used plant growth-promoting rhizobacteria (Kloepper, 1983), fluorescent Pseudomonas strains (Geels and Schippers, 1983; Colyer and Mound, 1984; Altin and Bora, 2001), gram-negative and positive antagonistic bacteria isolated from potato rhizosphere (Tani et al., 1990; Chard et al., 1991) as biological control options for soft rot pathogens. The results of biological control studies are promising but there is no applicable biocontrol agent for suppressing the soft rot up to this moment.

The purpose of this study is to develop biocontrol agents for controlling stem rot caused by E. chrysanthemi on tomato in greenhouse conditions for conventional and ecological agriculture.