the Symposium on Wheats for More Tropical Environments - cimmyt

22and many of our cooperators around<strong>the</strong> world are attempting to identifywheats that can be grown successfullyin <strong>the</strong> warmer areas of <strong>the</strong> world wherewheat is not a traditional crop.Tropical wheat environments includemost of <strong>the</strong> areas lying between <strong>the</strong>Tropic of Cancer (23 0 north) and <strong>the</strong>Tropic of Capricorn (23 0 south), plusadjacent areas with tropical orsubtropical conditions. Within this areaof <strong>the</strong> world, <strong>the</strong>re appear to be twobasic types of environments in whichwheat can be grown. One ischaracterized by warm temperatures,generally sunny days and low relativehumidity compared to <strong>the</strong> norm for <strong>the</strong>tropics. Under <strong>the</strong>se conditions, diseaseresistance will not be a majorconsideration, but varieties with heattolerance and adapted to a ra<strong>the</strong>r shortgrowing season will be necessary. Theo<strong>the</strong>r major wheat environment istypified by warm temperatures andhigher relative humidity. A number ofwheat diseases, many of which are notcommon to traditional, temperate,wheat-growing areas, will be prevalentunder <strong>the</strong>se conditions. For wheat to besuccessfully grown, better resistance to<strong>the</strong>se diseases must be incorporated.CIMMYT's Interest inTropical WheatsICIMMYT's research mandate calls for<strong>the</strong> rapid and continuous developmentof improved germplasm, primarily foruse in <strong>the</strong> developing world.Approximately one billion people live in<strong>the</strong> tropical countries of <strong>the</strong> developingworld and, while wheat is currently aminor crop in <strong>the</strong> tropics, itsconsumption is increasing rapidly,especially in <strong>the</strong> urban areas. As ofmid-1983, about 85% of <strong>the</strong> wheatconsumed in tropical nations was beingimported, and <strong>the</strong>se countriesaccounted for about 20% of <strong>the</strong> totalworld wheat trade.Rapidly expanding consumption ofwheat in <strong>the</strong> countries of <strong>the</strong> tropics isresulting in an increasing dependanceon imports. In many instances, <strong>the</strong>seimports represent a large drain onforeign exchange. Many governmentsnow believe it would be better toconduct <strong>the</strong> research necessary todevelop wheats for <strong>the</strong>ir specificconditions, in order to be able to growat least a portion of <strong>the</strong>ir wheatrequirements.The development of wheats adapted to<strong>the</strong> short, cool season in <strong>the</strong>se moretropical countries would also allow forcrop intensification. Rice is currently<strong>the</strong> predominant crop, and is generallygrown during <strong>the</strong> summer monsoon. Asecond crop is seldom grown in <strong>the</strong>winter season, except in those areaswhere irrigation is available. With itslower moisture requirements comparedto rice, and with its adaptation to coolertemperatures, wheat has potential as analternate crop for <strong>the</strong> winter season. Inmany instances, a crop of wheat couldbe grown on residual moisture or withlimited irrigation, and recent researchhas indicated that reasonable yields canbe achieved under <strong>the</strong>se conditions. Byintroducing a second crop into <strong>the</strong>cropping cycle, <strong>the</strong> total domesticproduction of food grains could besignificantly increased.General Production ConstraintsThere are many production constraintsthat must be resolved before wheat canbe introduced successfully into <strong>the</strong>seenvironments. ResolVing <strong>the</strong>seproblems would benefit more than <strong>the</strong>tropical countries alone; wheatproduction in many of <strong>the</strong> traditionalwheat-growing areas would also beenhanced. Among <strong>the</strong> areas requiringresearch are <strong>the</strong> follOWing:Heat toleranceGermplasm with better tolerance tohigher temperatures is absolutelynecessary for many areas. Greater heattolerance during <strong>the</strong> juvenile growthstage and also during <strong>the</strong> flowering and