--Dondo Gosic, S, Drinic Mladenovic, S, Konstantinov, K
Diseases caused by phytopathogenic fungi are a serious problem in
maize production, as they can result in premature ripeness of maize. Infected
plants produce ears of poorer quality, and lodged plants are not suitable
for mechanised harvest, etc. Control by the application of chemicals is
limited due to resistance of fungi and destruction of antagonistic soil
mycoflora.
The biological control of disease affecting plants has gained much attention in the past two decades as a way of reducing the use of chemical products. The existence and active metabolism of endophytic bacteria within plant tissue make them potential candidates for biological control of plant resistance to phytopathogenic fungi. The effects of endophytic bacteria isolated from maize and sunflower on growth of phytopathogenic fungi B. zeicola, E. turcicum, F. oxysporum, Ph. zeae, M. bolleyi, N. oryzae were observed in the present study under in vitro and in vivo conditions.
Two bacterial strains were selected for these investigations: Bacillus licheniformis, isolated from maize embryo, and Seratia liquefaciens, isolated from sunflower. The bacterial strains were determined by the application of API and Microlog 1 system. The slightly modified method of Gutterson et al. (Journal of Bacteriology, vol.165, No.3, 696-703, 1986) was applied to monitor fungi/bacterial interaction. The effects of bacteria on fungal development and growth were evaluated in dual cultures on media optimal for growth of bacteria (LB) and fungi (PDA) in the course of 3 and 7 days.
According to the results obtained, it can be concluded that effects of both bacteria on all fungi were antagonistic. Inhibition of fungal growth occurred without physical contact between the bacterium and the fungus. The typical appearance of dual culture growth on both mediums is shown in Figure 1.
Fig. 1. Separate and dual cultures of Bacillus licheniformis and Seratia liquefaciens on PDA and LB medium.
The growth rate of fungi is expressed as the colony diameter of dual or separated cultures through seven days. The greatest antagonistic effect was obtained in dual cultures with B. zeicola and Ph. zeae. A greater effect on fungal growth was achieved on the LB medium. Results of fungal growth in dual cultures in relation to the control are presented in Figure 2.
Endophytic bacteria release components in the medium that reduce fungal growth. Proteins were isolated from bacteria grown as single cultures, as well as from bacteria interacting with fungi, and were separated on polyacrylamide gels. A greater number of new polypeptide fractions in relation to the control were determined in the interactions with observed fungi. The studies on the molecular basis of this antagonism are in progress.
Two fungi B. zeicola and F. oxysporum, i.e. M. bolleyi and N. oryzae, were selected for investigation of antagonistic effects of B. licheniformis and S. liquefaciens, respectively, under in vivo conditions. Untreated seed and seed treated only with fungi were used as the control. The length of the shoots and roots of treated and control maize plants were measured and results are presented in Figure 3.
Fig. 3. The length of shoots (a, c) and roots (b, d) of plants treated with bacteria and fungi as well as plants treated only with fungi and control plants.
Greater lengths of roots and shoots were detected in plants treated with both bacteria and fungi than in plants treated only with fungi.
The results obtained point out that endophytic bacteria isolated from
maize and sunflower can be used in biological control of observed phytopathogenic
fungi of maize.
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