Pest Management Science Pest Manag Sci 63:714–721 (2007) Pseudomonas-induced defence molecules in rice plants against leaffolder (Cnaphalocrocis medinalis) pest Duraisamy Saravanakumar, 1∗ Kannappan Muthumeena, 2 Nallathambi Lavanya, 1 Seetharaman Suresh, 2 Lingan Rajendran, 1 Thiruvengadam Raguchander 1 and Ramasamy Samiyappan 1 1 Department of Plant Pathology, Centre for Plant Protection Studies, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India 2 Department of Agricultural Entomology, Centre for Plant Protection Studies, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India Abstract: Fluorescent pseudomonad strains Pf1, TDK1 and PY15 individually and in combination were evaluated against leaffolder, Cnaphalocrocis medinalis Guen., in rice under in vitro, glasshouse and field conditions. Among the various treatments used, a combination of Pf1, TDK1 and PY15 strains effectively reduced the incidence of leaffolder pest in rice plants to an extent comparable with chlorpyrifos-methyl. In addition, morphogenesis of the insect pest in all stages, larval, pupal and adult, was greatly affected by a combination of Pseudomonas Pf1, TDK1 and PY15 strains. Further, the induction of defence-related molecules was demonstrated. An increased accumulation of defence molecules such as chitinase and proteinase inhibitors was observed with a combined Pf1, TDK1 and PY15 treatment compared with all other treatments. Western blot analysis of chitinase revealed the extra induction of 18, 28 and 35 kDa isoforms in rice plants treated with a mixture of Pf1, TDK1 and PY15 strains against leaffolder pest. The study revealed that a combination of fluorescent pseudomonad strains affects the development of leaffolder pest by inducing defence molecules in rice plants which in turn enhance resistance to leaffolder attack.  2007 Society of Chemical Industry Keywords: bioformulation; Cnaphalocrocis medinalis; defence molecules; fluorescent pseudomonads; proteinase inhibitors 1 INTRODUCTION Rice (Oryza sativa L.) is an important food crop worldwide, 1 the productivity of which is threatened by a number of insect pests attacking the crop from nursery to harvest, causing enormous yield loss. Of these, the leaffolder insect (Cnaphalocrocis medinalis Guen.) has gained major importance because of its ability to defoliate the plant, leading to considerable reduction in yield. 2 The symptoms of leaffolder damage are characterized by the presence of a large number of leaf folds. The larvae, prior to feeding, fold the leaves longitudinally and fasten the leaf margins with stitches of silk thread. The larvae feed by scraping the green mesophyll tissue from all over the inside of the folded leaves. 3 The vigour and photosynthetic ability of an infested rice plant is greatly reduced 4 and yield loss is high when the flag leaf is damaged. 5 It has been observed that a 10% increase in damage to the leaves reduces the yield by 0.15 g per tiller. Leaffolder outbreaks have been reported from various countries including Bangladesh, China, Fiji, India, Japan, Korea, Malaysia, Nepal, the Philippines, Sri Lanka and Vietnam. 6 The management of rice leaffolder pest has been almost exclusively based on the application of chemical pesticides. Many effective pesticides have been recommended against this pest but not considered as a long-term solution because of concerns about exposure risks, health and environmental hazards, expense, residue persistence, pest resurgence and elimination of natural enemies. The non-availability of breeding varieties resistant to this pest has aggravated this problem. Therefore, the need for alternative methods of control of leaffolder has become vital. Unfortunately there is no ecofriendly viable practice currently available for this purpose. The utilization of a plant’s own defence mecha- nisms is an attractive area of research practised all over the world to manage plant pests and diseases. Plants treated with plant growth promoting rhizobac- teria (PGPR) have latent defence mechanisms against pests and pathogens that can be systemically acti- vated upon exposure of plants to stress or infection by pathogens. 7 This phenomenon is called induced systemic resistance (ISR). 8 The mechanism operates through the activation of multiple defence compounds ∗ Correspondence to: Duraisamy Saravanakumar, Department of Plant Pathology, Centre for Plant Protection Studies, Tamil Nadu Agricultural University, Coimbatore 641 003, Tamil Nadu, India E-mail: agrisara@rediffmail.com (Received 1 June 2006; revised version received 5 October 2006; accepted 19 December 2006) Published online 8 May 2007; DOI: 10.1002/ps.1381  2007 Society of Chemical Industry. Pest Manag Sci 1526–498X/2007/$30.00