TREES SURVIVAL EXPOSED TO DIEBACK DISEASE IMPLIES EVOLUTIONARY MODULATION RESISTANCE IN SHISHAM (DALBERGIA SISSOO ROXB .) IN VARIOUS AGRO ECOLOGICAL ZONES OF PUNJAB (PAKISTAN)

Abstract

Plant pathogens cause mortality of species, effect on host population and composition of natural plant communities. Current study was conducted to evaluate ecological reason of possible survival of Dalbergia sissoo Roxb. (shisham) plantations after massive damage by dieback disease in various zones of Punjab, Pakistan. A broad base survey was conducted in 2005 and 2009 to assess morality percentage in five ecological zones of Punjab. Among selected zones, shisham dieback incidence was high in Barani (V) and Northern irrigated plains (IV) zones as compared to sandy deserts (IIIA & IIIB) and Sulaman piedmont (X) in 2005. The difference in dieback disease incidence revealed that variations in the physical environment have played a significant role in the development and spread of shisham dieback in agro ecological zones of the Punjab. It seemed that temperature and moisture influenced both pathogen virulence and host plant resistance responses. Current study concludes that thinning of shisham plantations is evident of high mortality in last decade; however the variation in shisham biotypes apparently is the major reason of shisham survival from high disease epidemic during 1998 to 2005. It seems those so called resistant biotypes have been evolved due to new genetic recombination and are the progeny of susceptible varieties that have almost vanished. At present stage, selection of improved gemplasm is crucial for success of plantation programme, in Punjab, Pakistan.