the Symposium on Wheats for More Tropical Environments - cimmyt

184immature, field-grown pods of sixsoybean cultivars. The soybean isolateswere able to produce typical take-allsymptoms on wheat roots and stems.This could have a significant effect ontake-all disease in that area (9).In regard to nematodes, examples ofpossible pathogens might be <strong>the</strong> rootknot nematodes, Melotdogyne spp., and<strong>the</strong> cyst nematodes, Heterodera spp.,both of which occur on cereals,including rice. in warmer climates(3, 10). Once again, <strong>the</strong> introduction ofwheat into an area may provide anappropriate host for <strong>the</strong>se or o<strong>the</strong>rnematodes.These are only a few examples of <strong>the</strong>possible disease syndromes that couldoccur. However. many gr.oups of soilfungi might become relatively moreimportant in warmer climates as. forexample. <strong>the</strong> fusaria and <strong>the</strong> watermolds.Possible Avenues of ControlAs better understanding of <strong>the</strong>epidemiology and genetics of foot rotorganisms is achieved, resistance andtolerance will become more useful toolsfor breeders. When dealing with moretropical conditions, obtaining adequateresistance or tolerance becomes evenmore elusive due to <strong>the</strong> predispositionof <strong>the</strong> host in those climates. It isprobable that, for a long time to come.an integration of resistance ortolerance, appropriate husbandrypractices and chemical or biologicalcontrol will be critical to procuringadequate. economical control measuresof foot rot organisms. Breeders andpathologists should be aware that, insome warmer areas, it may beimpossible to obtain high levels ofdisease control. due to <strong>the</strong> nature of <strong>the</strong>environment and <strong>the</strong> condition of <strong>the</strong>host.However, <strong>the</strong>re is no need forpessimism ei<strong>the</strong>r; a possible scenariofor attaining adequate control ofS. rolfstt can be used as an example. Todate, some progress has been made insou<strong>the</strong>rn India with chemical seedtreatments, such as Carboxin, PCNBand Guatazine, for controlling S. rolfsttthrough <strong>the</strong> seedling stage (6). Theseseed treatments have a dual advantagesince <strong>the</strong>y also control loose smut andcommon bunt. The next step might beto find some level of resistance ortolerance in wheat that would increase<strong>the</strong> level of control. Mechanicalresistance has been found inLycoperstcon pimptnellifolium where.after six weeks, phellem developmentprevents penetration of S. rolfsii (2).Perhaps analogous types of resistancecould be found in wheat or relatedgenera. Finally, a multipronged attackmight include planting rotation cropsthat reduce sclerotial formation, orPCNB might be applied to <strong>the</strong> soil toreduce inoculum potential. The point tokeep in mind is that no single controlmeasure may be adequate. To have <strong>the</strong>best chance of success. pathology andbreeding will have to be fullyintegrated.Although <strong>the</strong> literature is meagerrelating to foot rots. some examples offoot rot organisms have been presentedthat are problems at this time, as wellas o<strong>the</strong>rs that could become problems,with <strong>the</strong> hope of making breeders andpathologists aware of <strong>the</strong> greatercomplexity of controlling facultativeparasites in tropical areas as comparedto temperate zones. Controlmethodologies may also have to bemore complex. and levels of controlmay never approach immunity.