the Symposium on Wheats for More Tropical Environments - cimmyt

126After seed selection. some of <strong>the</strong>preliminary screening tests areperformed on segregating materials in<strong>the</strong> breeding programs. In <strong>the</strong> case ofbread wheats. <strong>the</strong> segregating materialsare evaluated for gluten strength. ThePelshenke test. which separates wheatswith weak gluten from wheats withstrong gluten. gives an indication of <strong>the</strong>ability of <strong>the</strong> gluten to retain carbondioxide gas which is formed duringfermentation.In this test. a 3-gram sample of grainfrom each plant is ground into wholemeal. mixed with a standard yeastsuspension and formed into a doughball. The ball is immediately placed in abeaker of distilled water at 30°C. and<strong>the</strong> time in minutes until <strong>the</strong> doughball disintegrates is a measure of glutenstrength; this is called <strong>the</strong> Pelshenkevalue. Wheats with strong gluten havePelshenke values of more than 100. minutes; ones with weak gluten havePelshenke values of less than 60minutes. Even though this test hassome weaknesses, it is very useful insome breeding programs.Microsedimentation or <strong>the</strong> Zeleny test isano<strong>the</strong>r method for estimating <strong>the</strong>strength of wheat gluten. Like <strong>the</strong>Pelshenke test. it takes only 3 grams ofwheat from each plant to produce <strong>the</strong>.64 grams of flour needed to perform<strong>the</strong> test. The flour is suspended inwater in a graduated cylinder andtreated with lactic acid. The volume ofsediment. consisting principally ofswollen gluten and occluded starch.which is measured after standing forfive minutes, is <strong>the</strong> sedimentationvalue.The sodium dodecyl sulphate (SDS)­tactic acid sedimentation test is ano<strong>the</strong>rrapid method for estimating glutenstrength in both bread and durumwheats. The test is simple and rapid.allOWing for <strong>the</strong> evaluation of severalhundred samples in one day; it alsorequires only 3 grams of wheat. Theground sample is mixed with <strong>the</strong> SDSlacticacid solution in a graduatedcylinder for a short period of time and.after a rest period of ten minutes. <strong>the</strong>volume of <strong>the</strong> sediment is recorded. asin <strong>the</strong> Zeleny test. Wheats with stronggluten have large sedimentation values•while those with weak gluten havesmall values.There are o<strong>the</strong>r tests that can be usedfor <strong>the</strong> screening of segregatingmaterials. but <strong>the</strong> ones mentioned herehave been very important at CIMMYTfor creating <strong>the</strong> quality Variabilityrequired for <strong>the</strong> various countrieswhere genetic materials from <strong>the</strong>CIMMYT wheat program are utilized.