5.2.40
PSEUDOMONAS FLUORESCENS B29 FOR BIOCONTROL OF XANTHOMONAS AXONOPODIS PV. GLYCINES IN PLANTA

A SUWANTO1 and B TJAHJONO2

1Department of Biology, Faculty of Science and Mathematics, Bogor Agricultural University, Bogor 16144, Indonesia; 2Department of Plant Protection, Faculty of Agriculture, Bogor Agricultural University, Bogor 16144, Indonesia

Background and objectives
Diseases have been one of the important factors that contribute to low productivity in agricultural crops. Under certain circumstances, diseases often cause total failure in agriculture system. A large portion of agricultural systems in Indonesia, which are significantly influenced by hot and humid tropical climate, is susceptible to bacterial diseases. Our research group is attempting to understand the ecology and pathogenesis of bacterial pustule disease in soybean that is caused by Xanthomonas axonopodis pv. glycines (Xag). In this study we present our screening, isolation and characterization of phyllosphere bacteria for biocontrol of Xag in planta.

Materials and methods Xag isolates and Pseudomonas fluorescens B29 (PfB29) were isolated from soybean plantations in Java. E. coli DH5a(pJL1703) [1] was employed to introduce ice nucleation gene (inaZ) into PfB29 employing triparental mating [2]. Ice nucleation activity was conducted using both in test tube and droplet assay.

Results and conclusions
PfB29 by itself did not express ice nucleation activity. Introduction of ice nucleation gene (inaZ) from Pseudomonas syringae into PfB29 generated a recombinant strain B29 (ice+). This strain expressed ice nucleation activity as high as 106 ice nucleus per cell at -5C. The greenhouse experiment demonstrated that B29 (ice+) was able to survive on soybean leaves and prevent the growth of Xag isolates from several soybean plantation in Java. After five days of incubation in planta, population of B29 (ice+) increased up to 2x106 cells per gram fresh weight of leaves. The inhibitory effect of B29 (ice+) toward the growth of Xag isolates was reproducible and therefore it could be applied to the growth of all Xag isolates used in this study.

References 1. Lindow SE, 1991. J. Adv. Molec. Gen. Plant Microbe Interact 1, 457-464. 2. Suwanto A, Kapian S, 1992. J. Bacteriology 174, 1135-1145.