the Symposium on Wheats for More Tropical Environments - cimmyt

120Efficiency in phosphorus useThe soils in <strong>the</strong> main wheat-producingregion of Rio Grande do Sul arecharacterized by a low level ofphosphorus aVailability. The interactionof plant response and aluminum andphosphorus absorption is well known.Ben and Rosa (3), working withcultivars tolerant to crestamento.identified <strong>the</strong> cultivars Toropi and PG1(a selection of Polissu) as haVing betterdevelopment in soils with lowphosphorus aVailability. These cultivarshave a better (more efficient) utilizationof phosphorus (natural or applied),indicating <strong>the</strong> possibility ofencountering genetic variability for thischaracter.Koehler (4), working at WashingtonState University, USA, carried outexperiments involVing 1600 springwheat accessions, with <strong>the</strong> objective ofidentifying accessions tolerant tophosphorus stress and learned how toselect for this characteristic. His resultsidentified various cultivars with goodadaptation to soils with low phosphoruslevels.Attempts are being made at <strong>the</strong>National Wheat Research Center totransfer such phosphorus-use efficiencyto o<strong>the</strong>r cultivars with better yieldpotential. The segregating generationsare grown in soils with low phosphorusavailability (around 3 ppm) and withtoxic aluminum. It is expected that, by1985, lines with better phosphorusutilization will be available for finalevaluation.ConclusioDSEcological conditions in Rio Grande doSul vary greatly, as compared to thoseof <strong>the</strong> wheat-producing regions ofArgentina or Mexico. Never<strong>the</strong>less,using <strong>the</strong> technology available atpresent, good farmers in <strong>the</strong> regionhave obtained average yields of 2.068kglha over <strong>the</strong> last five crop years. Theyutilize a production system involVing<strong>the</strong> use of <strong>the</strong> best cultivars. croprotations to control root diseases andfungicide application to complementgenetic resistance.New cultivars developed jointly byEMBRAPA and CIMMYT will be madeavailable to farmers in Rio Grande doSuI in 1985 (new lines of <strong>the</strong> crossIAS631Alondra''S"IIGabotol LagoaVermelha (PF79765, PF79767.PF79780 and PF79782)). It is expectedthat. with this material, <strong>the</strong>se samefarmers will be able to raise <strong>the</strong>ir yieldsto 3 t/ha within <strong>the</strong> next five years.