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

Agglutination potential of 172 isolates of Pseudomonas fluorescens, isolate d from the rhizosphere soil of chickpea plants, was evaluated in crude aggl utinin (CA) of Macrophomina phaseolina and on sclerotia and hyphae surfaces . Eighteen such isolates varied significantly in their agglutination potent ial (10-73%). Isolates 12 (Agg(+)) and 30 (Agg(1)) showed maximum (73%) and minimum (10%) agglutination, respectively. Total loss of endogenous C rese rve did not differ significantly (P = 0.05) from sclerotia incubated with A gg(+), Agg(1) or Agg(-) (a non-agglutinable Tn5 mutant of wild type 12). Mo st of the C lost from stressed sclerotia was evolved as (CO2)-C-14 (40%), w hereas 5% C was lost in the form of sclerotial exudate (residual C). The to tal 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 sc lerotia retained a greater portion of their viability even after 60 d. Loss of C from the sclerotia incubated with isolates of P. fluorescens was dire ctly 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 t heir agglutination potential on M. phaseolina sclerotia. Irrespective of th e agglutination potential of isolates, they can invariably impose energy st ress 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.