the Symposium on Wheats for More Tropical Environments - cimmyt

122Breeding and Disease ProblemsConfronting <strong>the</strong> Successful Cultivationof Wheat in <strong>the</strong> Cerrados of BrazilA.R. da SUva, lUnlaterio de Agricultura, Provaraeas Nacional,BrasWa, D.F., BrazUAbetractThere are three systems ofwheat production in <strong>the</strong> Cerrados. rainfed. irrigatedupland and irrigated lowland. Important breeding points and <strong>the</strong> main diseasesare discussedfor each of<strong>the</strong> systems in <strong>the</strong> Cerrados area ofBrazil. as well asinformation on climate and soils in relation to each of <strong>the</strong>m. Wheat yields onfarmers' fields and a comparison with o<strong>the</strong>r poSSible crops are presented.Climate andSOU. of <strong>the</strong> CerradosBrasilia will be considered here asrepresentative of <strong>the</strong> <strong>the</strong> Cerradosregion of central Brazil. It has twoseasons. a rainy season and a dry one.The rainy season lasts from October toApril. and <strong>the</strong> dry season from May toSeptember. During <strong>the</strong> rainy season.<strong>the</strong> average monthly rainfall is 215mm; dUring <strong>the</strong> dry season it is only 14mm. From January to April. <strong>the</strong> totalrainfall is 780 mm. During <strong>the</strong> rainyseason. dry periods (veranicos) arefrequent and can influence <strong>the</strong> wheatcrop in two ways. by reducing plantgrowth and by favoring a serious pest.Elasmopalpus lignosellus Zeller.The temperature in Brasilia Isrepresentative of that of <strong>the</strong> highplateau (1.000 meters); it is lower thanthat of <strong>the</strong> low-altitude Cerradosregions. The average temperature in<strong>the</strong> rainy season is 21.3°C and. in <strong>the</strong>dry season. 19.3°C; if <strong>the</strong> temperatureofSeptember (wheat harvest month) isnot considered. <strong>the</strong> dry season averagedrops to 18.6°C. The relative moistureof <strong>the</strong> air is high during <strong>the</strong> rainyseason and low in <strong>the</strong> dry season. Dewis frequent until 9:00 or 10:00 a.m. inMay and June; <strong>the</strong>re is little dew inJuly. August and September.The Cerrados soils are acid. with highsoluble aluminum content. They arevery low in calcium and magnesium aswell as in phosphorus; <strong>the</strong>re is a strongfixation when phosphorus is applied asfertilizer. There is also a deficiency inmicronutrtents. mainly zinc and boron.Boron application at a rate of 1 kglha isneeded to prevent male ster1l1ty. alimiting factor in wheat production thatis also conditioned by climate. Thephysical properties of <strong>the</strong> soils are goodfor root development of <strong>the</strong> plants. but<strong>the</strong>ir water retention is poor. Soils in<strong>the</strong> paddy fields in <strong>the</strong> lowlands vary agreat deal but. in general. have poordrainage which leads to waterlogging;<strong>the</strong>y are more appropriate for riceproduction and flood 1rr1gation than<strong>the</strong>y are for wheat cultivation.Systems of Wheat ProductionThere are three systems of wheatproduction used by farmers in <strong>the</strong>Cerrados region. as a ratnfed crop.sown in <strong>the</strong> middle of <strong>the</strong> rainy season(February) and harvested in <strong>the</strong> dryseason (With total rainfall of 700 mmdUring <strong>the</strong> crop season). as an irrigatedcrop in <strong>the</strong> uplands and as an 1rr1gatedcrop in <strong>the</strong> paddy fields. In <strong>the</strong> last twosystems. <strong>the</strong> crop season is <strong>the</strong> dryseason. May to September. with 273