Agglutination potential of Pseudomonas fluorescens in relation to energy stress and colonization of Macrophomina phaseolina

Agglutination potential of 172 isolates of Pseudomonas fluorescens, isolated from the rhizosphere soil of chickpea plants, was evaluated in crude agglutinin (CA) of Macrophomina phaseolina and on sclerotia and hyphae surfaces. Eighteen such isolates varied significantly in their agglutination potential (10-73%). Isolates 12 (Agg(+)) and 30 (Agg(1)) showed maximum (73%) and minimum (10%) agglutination, respectively. Total loss of endogenous C reserve did not differ significantly (P = 0.05) from sclerotia incubated with Agg(+), Agg(1) or Agg(-) (a non-agglutinable Tn5 mutant of wild type 12). Most of the C lost from stressed sclerotia was evolved as (14)CO(2) (40%), whereas 5% C was lost in the form of sclerotial exudate (residual C). The total C loss was in the order: Agg(+) > Agg(1) > Agg(-) > unsterilized soil. Germination of sclerotia incubated with Agg(+), Agg(1), Agg(-) cells or in soil was suppressed both in the presence or absence of C source and such sclerotia retained a greater portion of their viability even after 60 d. Loss of C from the sclerotia incubated with isolates of P. fluorescens was directly correlated with germination repression (r = -0.89 to - 0.96; P = 0.05). Greater colonization of sclerotia by Agg(+) was observed compared to Agg(1) or Agg(-) isolates. Our findings clearly demonstrate the existence of a great diversity of P. fluorescens isolates in natural soils in respect to their agglutination potential on M. phaseolina sclerotia. Irrespective of the agglutination potential of isolates, they can invariably impose energy stress on sclerotia resulting in accelerated loss of C and also elevating the nutrient requirement for sclerotia germination. (C) 2000 Elsevier Science Ltd. All rights reserved.