Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________________________Major Diseases of Eggplant8.1 Root rot and root deformation8.1.1 Damping-off (Fusarium, Rhizoctonia, Pythium and Phytophthora sp.)See photo 18 (page 177).Causal organism: fungi - Fusarium, Rhizoctonia, Pythium and Phytophthora sp.These soil-dwelling fungi infect vegetables, especially legumes, crucifers and solanaceous crops.Species of Pythium are more common than the others. If the infection occurs either before (preemergence)or just after emergence (post-emergence), and development of a spot (lesion) at the soil lineresults in collapse and shriveling of the plant, the disease is called ‘damping-off’.Signs and symptomsInfection occurs just around the soil line in young seedlings. Damping-off fungi rarely attack transplants inthe field or established seedlings.The symptoms of this disease are brown, water-soaked areas around the lesion that shrivel and pinchthe seedling off at the base. The dry rot is usually limited to the outer part of the stem and infected plantsmay fall down or may remain more or less upright. Infected plants remain under-developed and usuallydie.pre-emergence stem rot post-emergencedamping-offdamping-off(from: Kerruish et al, 1994)Source and spreadThe fungi are natural soil inhabitants but when circumstances are favorable and when susceptible hostplants are present, the population can increase to damaging levels. It is difficult to predict when that willoccur: it depends on temperature and humidity but also on the population of micro-organisms in the soil.Sometimes, there are micro-organisms (antagonists) that serve as natural enemies of the pathogens:they can keep the population of the pathogen under control. This can occur especially when the soilcontains a lot of organic material such as compost.Infection occurs through wounds or natural openings but Pythium can also actively penetrate the tendertissue near root tips.In case of Pythium infection, dying seedlings contain the spore-carrying structures of the fungus. Thespores can drop to the soil (and attack seed or young seedling roots), or be carried by wind or spread toanother location by surface water or irrigation water. Pythium can be transported in soil attached toseedling roots during transplanting. And Pythium can form thick-walled spores (called oospores) that cansurvive during adverse conditions and persist for several years in the soil.Role of environmental factorsDamping-off occurs in areas with poor drainage or areas with a previous history of the disease.Damping-off is often associated with high humidity and high temperature. The temperature range inwhich these fungi can live is quite broad, from about 12 to 35 o C with an optimum (the temperature atwhich damping-off develops fastest) of 32 o C. That is why you can find damping-off disease both inhighlands with a temperate climate and in (sub)tropical lowlands.131Eggplant Ecological Guide