Lytic enzymes induced by Pseudomonas fluorescens and other biocontrol organisms mediate defence against the anthracnose pathogen in mango R. Vivekananthan*, M. Ravi, A. Ramanathan and R. Samiyappan Centre for Plant Protection Studies, Department of Plant Pathology, Tamil Nadu Agricultural University, Coimbatore 641 003, India *Author for correspondence: Tel.: +91-0422-2442438, E-mail: patvivek@rediffmail.com Received 22 May 2003; accepted 2 October 2003 Keywords: Bacillus subtilis, biocontrol, carbendazim, chitinase, Colletotrichum gloeosporioides, b-1,3-glucanase, mango, Pseudomonas fluorescens, Saccharomyces cerevisiae Summary Talc-based bioformulations containing cells of Pseudomonas fluorescens, Bacillus subtilis and Saccharomyces cerevisiae were evaluated for their potential to attack the mango (Mangifera indica L.) anthracnose pathogen Colletotrichum gloeosporioides Penz. under endemic conditions. The preharvest aerial spray was given at fortnightly and monthly intervals. The plant growth-promoting rhizobacteria Pseudomonas fluorescens (FP7) amended with chitin sprayed at fortnightly intervals gave the maximum induction of flowering, a yield attribute in the preharvest stage, consequently reduced latent symptoms were recorded at the postharvest stage. An enormous induction of the defence-mediating lytic enzymes chitinase and b-1,3-glucanase was recorded in colorimetric assay and the expression of discrete bands in native PAGE analysis after FP7+ chitin treatment. The enhanced expression of defence-mediating enzymes may collectively contribute to suppress the anthracnose pathogen, leading to improved yield attributes. Introduction Mango (Mangifera indica L.) is an important fruit crop in several countries. In India, it occupies a wider cultivatable area in conjunction with wild forests of Assam but suffers from a number of biotic and abiotic constraints. Among them, anthracnose is a condition which is incited by the fungus Colletotrichum gloeospo- rioides Penz. This can render the tree completely unproductive (up to 100%), as it destroys the developing or developed fruits both in field and storage conditions. It causes leaf, blossom blight and tree die-back in the orchard and can subsequently give rise to rotted fruits during storage and thus poses several problems. In the past, indiscriminate use of chemical fungicides to control this pathogen has created undesirable toxicity and pollution effects. The application of biological control is now gaining importance, due to the enhanced production of defence-mediating enzymes to suppress the pathogen called ‘induced systemic resistance’ (Vi- swanathan & Samiyappan 1999; Ramamoorthy & Samiyappan 2001; Ramamoorthy et al. 2001; Viswana- than & Samiyappan 2001). ISR is associated with accumulation of PR proteins (Viswanathan & Samiyap- pan 1999) and synthesis of phenolics (Chen et al. 2000). PR proteins are soluble host-coded proteins including defence-related lytic enzymes viz., chitinase (PR-3) and b-1,3-glucanase (PR-2) which hydrolyse the chitin and b-1,3-glucan, respectively, which are major components of fungal pathogen cell wall. The enzymes are quiescent in all the plants and allied with a multigene family. During pathogen access the plants release signals and these signals are mandatory to activate defence genes (Vidhyasekaran 1996). These signals have also been detected in bacteria (He et al. 1993), fungi (Schaffrath et al. 1995) and viruses (Culver & Dawson 1991). Recently, plant growth-promoting rhizobacteria (PGPR) strains have been developed commercially as a talc-based formulation (Vidhyasekaran & Muthamilan 1995) and tested against several crop diseases (Rabin- dran & Vidhyasekaran 1996; Samiyappan et al. 1998). Based on the above facts, present investigation was undertaken to determine whether PGPR bioformula- tions induce the accumulation of defence-mediating lytic enzymes in relation to anthracnose resistance, conse- quently enhancing the fruit yields and quality in mango. Materials and methods Isolation of biocontrol microorganisms Various strains of fluorescent pseudomonads, Bacillus subtilis and Saccharomyces cerevisiae were collected World Journal of Microbiology & Biotechnology 20: 235–244, 2004. 235 Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands.