Indian Phytopath. 51 (2) : 111-120 (1998) Molecular biology of pathogenesis and induced systemic resistance*

It is a great privilege for me for having been invited to deliver Jeersanidhi lecture before the august gathering of eminent Plant Pathologists of our coun-try. In my lecture, I would like to highlight recent advances in molecular plant pathology which pave way for development of innovative techniques to man-age crop diseases. Defense genes Crop plants are endowed with numerous defense genes which encode various proteins responsible f?r synthesis and accumulation of defense arsenals III plants. The defense genes are involved in production of antimicrobial compounds like phenolics, phytoalex-ins, pathogenesis-related (PR) proteins and active ox-ygen species or involved in reinforcement of cell wall by accumulating hydroxyproline- rich glycoproteins, callose, lignin and wall-bound phenolics (Vidhyasekaran, 1997). Many of the defense gene encoded proteins are enzymes. Several other proteins without known enzyme actions have also been detect-ed (Table 1; Vidhyasekaran, 1997). Some of them show antifungal action, some show elicitor-releasing activity; some increase mechanical strength of host cell wall; and some others are involved in release of second messengers and systemic signal molecules (for review, see Vidhyasekaran, 1997) (Table 1). How many defense genes may a plant have? The list in Table 1 indicates the presence of large number of defense genes. Most of the defense genes belong to multigene family. Twelve peroxidase isozymes have been detected in tobacco cell walls (Ye et al., 1990). PAL is encoded in bean by a family of divergent class-es of genes (Mavandad et aI., 1990). Seven CHS genes have been detected in bean genome (Ryder et aI., 1987). Several enzymes of 4CL have been reported in soy