Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

___________________________________________________________________________________________Disease EcologyDirect transmission through:• Seed: pathogens can be carried on or inside a plant seed. Examples are early blight (Alternariasolani) and bacterial wilt (Ralstonia solanacearum).• Vegetative plant parts: infected transplants may carry diseases from nursery to the main field;similarly diseases can be transmitted by infected tubers, cuttings, runners, grafts, etc.Indirect transmission through:• Growth of the pathogen: pathogens can spread over short distances by growth of the mycelium. Forexample wood rotting fungi can spread through the soil from one tree or trunk to the next by activegrowth.• Wind: fungi which produce spores on the surface of plants can be disseminated by wind. An exampleis early blight (Alternaria solani) of eggplant. There are examples of spores such as grain rust(Puccinia graminis) that have been found over 4000 m above an infected field! Often wind blows thespores over certain distances and rain may deposit the spores down. Some bacteria can also bedispersed by wind.• Water: flood or irrigation water may carry pathogens or spores, especially those in or near soil. Thesplashing of water during rain or heavy dews can spread spores and bacteria to plant parts near thesoil or to different parts of the same plant or to neighboring plants. Bacterial wilt of eggplant, forexample, can be spread by surface water. Water however is not as important as wind for longdistance dissemination.• Soil: soil can contain infected plant left-overs and it contains spores of fungi such as damping-off (e.g.Pythium sp.), Verticillium and Fusarium wilt fungi, and bacteria such as Ralstonia solanacearum,causing bacterial wilt. Soil can be a reservoir of diseases which are spread when soil particles aretransported, for example attached to seedling roots or attached to tools or shoes of people.Survival and spread of soil-borne pathogensSoil-borne pathogens can survive on or in a host plant (including weeds), some survive on dead hostplant tissue or on dead organic material, some form resting spores or latent stages (such as thickwalledbacteria or fungus spores to survive in adverse conditions). Root nematodes survive as eggs(egg cysts) or as adults.Soil-borne pathogens can be spread by wind, water, vectors or humans and carried with soilparticles. An example: Pythium sp. causes damping-off disease in seedlings. Dying seedlingscontain the spore-carrying structures of the fungus. The spores can drop to the soil (and attackseeds or young seedling roots), or be carried by wind or spread by surface water or irrigation waterto another location. Pythium can be transported attached with soil to the seedling roots duringtransplanting. And Pythium can form thick-walled spores (called oospores) that can survive duringadverse conditions and persist for several years in the soil.• Insects, mites, nematodes: dissemination of pathogens can occur incidentally when e.g. spores stickto the body of an insect or mite going from one plant to another. More important is in case of insectswhen an insect becomes a vector and carries and transmits a pathogen (for example jassids carryingthe mycoplasma causing little leaf in eggplant) from one host plant to another. Most vectors aresucking insects such as aphids, whiteflies and leafhoppers.Nematodes can also be transmitters of pathogens. Incase of vegetables, it is also likely that nematodescreate entry points for bacteria and fungi by makingwounds in roots.• Humans, animals: spread of pathogens occurs in twoways: through the person, tools or animals andthrough the objects that are transported. Persons andDiseases can be spread by people120Eggplant Ecological Guide