the Symposium on Wheats for More Tropical Environments - cimmyt

125Screening Wheats for QualityA. Amaya, Industrial Quality Laboratory, Wheat Program,CIMMYT, MezlcoAbstractScreening tests are simple methods that are used to eliminate undesirablematerialsfrom <strong>the</strong> breeding program; <strong>the</strong>y can be made rapidly, using smallsamples of individual plants in early generations. In <strong>the</strong> case ofquality, <strong>the</strong>sepreliminary screening tests help breeders to select materials with <strong>the</strong> type ofgluten that is deSirablefor <strong>the</strong> preparation ofvarious products. Seed-typeselection is used in segregating materialfor eliminating all lines with poorkernel characteristics. After seed selection, o<strong>the</strong>r preliminary screening tests areperformed, among <strong>the</strong>m, <strong>the</strong> Pelshenke test which is used to separate breadwheats according to gluten strength. The microsedimentation or Zeleny test and<strong>the</strong> sodium dodecyl sulfate (SDS)/lactic acid sedimentation tests are o<strong>the</strong>r rapidmethodsfor estimating gluten strength in bread and durum wheats.Good milling and baking characteristicscan be selected for in <strong>the</strong> developmentof higher-yielding varieties. InCIMMYT's wheat program,improvements are being made indeveloping higher-yielding, broadlyadapted varieties with improved diseaseresistance and improved milling andbaking quality. Everyone working inwheat research, production, utilizationand industrialization should beconcerned with <strong>the</strong> quality reqUired for<strong>the</strong> preparation of local products; itmust be kept in mind that quality is arelative concept, depending on who isconsidering it.For <strong>the</strong> grower, good quality meanshigh yield potential; for <strong>the</strong> mlller,quality means high flour yields, whichpartly depends on high test weight anduniform kernel size and shape. For <strong>the</strong>consumer, wheat quality means a goodend-product. Therefore, for <strong>the</strong>preparation of sandwich bread. wheatwith strong, balanced gluten is needed;for cookies. <strong>the</strong> best quality wheat hasextensible weak gluten. White wheatswith strong or medium-strong glutenare preferred by <strong>the</strong> whole wheatconsuming countries. such as India andPakistan. for <strong>the</strong> preparation ofchapatis.To have all <strong>the</strong>se qualities available. <strong>the</strong>use of preliminary screening tests isvery important. Screening tests shouldbe simple. reprodUcible tests that canbe made rapidly. and in large numbers.on grain samples from individualplants. in order to eliminate undesirablematerials from <strong>the</strong> breeding program;<strong>the</strong>y are not tests which would be usedfor choosing lines to be released as newcommercial varieties. These tests have<strong>the</strong> advantage that <strong>the</strong>y can be carriedout beginning with <strong>the</strong> F3 generation.allOWing many inferior lines to beeliminated early in <strong>the</strong> program. Ingeneral, at CIMMYT. all screening testsare performed after segregatingmaterials have been selected for seedtype.Selection forDesirable Grain TypesEmphasis is given to grain classificationin all wheat breeding programs atCIMMYT; all lines that have poor kernelcharacteristics, and thus are likely toresult in low grain test weight. areeliminated. In grain tests. samples areevaluated for grain size. plumpness.texture and color.