the Symposium on Wheats for More Tropical Environments - cimmyt

78Practice has showed that <strong>the</strong> followingmeasures would be effective inresolving <strong>the</strong> above problems:• Establish systems for rapid drainage,so that <strong>the</strong> ground-water level islowered and soil moisture contentdecreased. With <strong>the</strong> consequentincrease in soil aeration, injuriesfrom excessive soil moisture wouldbe avoided or alleviated:• Improve tillage practices in order tomake <strong>the</strong> soil more suitable for <strong>the</strong>growth of wheat;• Utilize proper rotation systems ofrice, wheat. rape seeds and greenmanure crops so that soil fertility isincreased, and• Eliminate damage from disease andinsect pests. Scab. rusts (stem, leafand stripe). powdery mildew, sheathblight, armyworm and aphids aremajor problems in <strong>the</strong> region.Bavistin spray at <strong>the</strong> flowering stageis an effective deterrant. Powderymildew and rusts can be controlledwith Bayleton; Validamycin isrecommended for sheath blight.Research PrIorities in <strong>the</strong>Sou<strong>the</strong>rn Winter Wheat RegionWheat production in this region hasbeen greatly increased in <strong>the</strong> last 30years. Without doubt, this has beenclosely related to varietal improvement.research on <strong>the</strong> rice-wheat rotation and<strong>the</strong> improvement of farm capitalinvestment. Research must now resolve<strong>the</strong> problems of instabll1ty while fur<strong>the</strong>rincreasing production and averageyield. The wheat research programswill focus on variety improvement, withspecial attention on disease resistance,early maturity and increased yieldpotential.Disease resistanceDiseases are one of <strong>the</strong> main productionconstraints to increasing wheat yieldsin <strong>the</strong> region. Wheat scab, rusts,powdery mildew and sheath blight areall present, but head scab causes <strong>the</strong>greatest damage. Breeding for scabresistantvarieties has been carried onin Jiangsu province since 1975.Screening for scab-resistantgermplasm-Although no germplasmhas been found with completeimmunity to scab, <strong>the</strong> response ofvarieties to scab are different. Somehave fairly good resistance to scab,while o<strong>the</strong>rs are badly damaged. Forinstance, Wangshuibai is an oldindigenous variety with good scabresistance. Scab-resistant germplasm isbeing used in <strong>the</strong> crossing program. Afew advanced lines have beendeveloped with high resistance to scaband o<strong>the</strong>r diseases, combined withbetter yield potential and earlymaturity.Identiflcatton ofscab-resistantstrains-Artificial inoculation in <strong>the</strong>laboratory or in <strong>the</strong> field by soil-surfaceinfection is being conducted in Nanjing.Multilocation tests are also beingconducted on 30 sites in <strong>the</strong> mid-lowerYangtze Valley and Fujian province toidentify materials with enhanced scabresistance.Early maturityEarly-maturing varieties with high yieldpotential could meet <strong>the</strong> needs of adouble or triple cropping system andescape destructive diseases andpremature senescence caused by hightemperatures and excessive moistureinjury.Increased yield potentialIn <strong>the</strong> better production areas.semidwarf varieties that have largespikes and that are responsive to inputsand resistant to lodging are requiredand must be developed.