6.76
AGGLUTINATION RESPONSE OF PSEUDOMONAS FLUORESCENS IN RELATION TO C LOSS, GERMINATION AND COLONIZATION OF MACROPHOMINA PHASEOLINA
AGGLUTINATION RESPONSE OF PSEUDOMONAS FLUORESCENS IN RELATION TO C LOSS, GERMINATION AND COLONIZATION OF MACROPHOMINA PHASEOLINA DK ARORA and TK JANA Department of Botany, Banaras Hindu University, Varanasi 221 005, India Background and objectives Recognition of microorganisms to appropriate host surface is a specialized form of cell adhesion. Several agglutination assays have been done between animal host cells and a variety of bacteria or plant root surface and microorganisms or fungal host-fungal antagonist or nematode and fungi to understand the process of interaction mechanism of cellular recognition [1]. Agglutination of antagonistic microorganisms to fungal host or pathogen surface or to one another is commonly observed during antagonistic interactions [2]. From biocontrol point of view, agglutination of antagonists on fungal host appears to be important phenomena because it might enable retention of antagonists on pathogenic fungal propaguies. Though antagonistic potential of fluorescent pseudomonads has already been established against scierotial pathogens, no detailed study has been done to elucidate the mechanism of agglutination between fungal pathogens and bacterial antagonists, i.e. fungai-bacterial system in general, and M. phaseolina and P. fluorescensin particular. Therefore, the purpose of this research was: (i) to isolate different strains of P. fluorescensfrom chickpea rhizosphere, and to evaluate their potential for agglutination on scierotialhyphae surface and agglutinin produced from different isolates of M. phaseolina, (ii) to asses the ability of aggiutinable (Agg+12-94), less agglutinable (Aggi30-94) and non agglutinable Agg(Tn5mutant generated from wild type Agg+ 12-94) for imposition of energy (nutrient) stress on M. phaseolinascierotia, and its subsequent effect on germinability and viability, (iii) to evaluate the agglutination response of P. fluorescens on the stressed scierotia surface and in agglutinin produced by stressed scierotia, and (iv) to assess the role of agglutination potential in colonization of scierotia by Agg+, Aggi and Agg- Tn5 mutant. Resuits and conclusions Agglutination potential of 172 isolates of P. fluorescens, that were isolated from the rhizosphere soil of chickpea plants, was evaluated in crude agglutinin (CA) of M. phaseolina and on scierotialhyphae surface. Eighteen isolates showed different degree of variation in agglutination potential (10-73%). Most of the C loss from stressed scierotia occurred as evolved carbon di-oxide (40%), whereas 5% C was lost in the form of scierotial exudate. Germination of scierotia incubated with Agg +, Agg I, Agg - cells or in soil for 1-60 days, was suppressed both in the presence or absence of C source. Loss of C from the scierotia incubated with Agg +. Aggi or Agg - was directly correlated (r= 0.89-0.96) with germination repression. Significant greater colonization of scierotia by Agg+ was observed as compared to Agg l or Agg - isolates. Agglutination potential of Agg + or Agg i isolates did not change significantly on scierotia surface, and in CA produced from previously colonized scierotia. Agglutinin from M. phaseolina also agglutinated to erythrocytes of human blood group B suggesting involvement of lectins in M. phaseolina-P. fluorescens agglutination reaction. Overall, our findings demonstrate that soil contains a large number of Agg +, Agg i and Agg - isolates of P. fluorescens that can parasitize M. phaseolina. The ability to impose energy stress on scierotia by these isolates is not related to the potential of agglutination. Agglutinable isolate plays a significant role in colonization of M. phaseolina scierotia, and could be important as potential biocontrol agents for charcoal rot disease of chickpea caused by M. phaseolina. References 1. Manocha MS, Sahai AS, 1993. Canadian Journal of Microbiology 39, 269-274. 2. lnbar J, Chet I, 1994. Microbiology 140, 651-657.