Little progresshasbeenmadeindeterminingthecombiningabilityandgeneactioncontrollingearly
storage rootyield(SRY)anddiseaseresistancetraitsintheUgandancassavagermplasm.Suchinformation
is importantintheselectionofparentsandbreedingstrategiesforaneffectivebreedingprogramme.The
objective ofthisstudywastoestimatethegeneralcombiningability(GCA)ofninecassavaparentsand
their specificcombiningability(SCA)forearlySRYanddiseaseresistancetraits,aswellastodeterminethe
gene actioncontrollingthesetraits.Thirty-sixfull-sibcassavafamiliesweregeneratedfroma9×9 half-
diallel matingdesignandwereevaluatedintwodistinctenvironmentsinUgandausinga3×12 rowby
column design.Family,GCAandSCAeffectsandtheirinteractionswithenvironmentsweresignificantly
different formosttraits,indicating,respectivelysignificantdifferencesinthemeanperformancesof
the families,additiveandnon-additivegeneactionintheexpressionofthetraits,andthenon-additive
influence oftheenvironments.Therelativeimportanceofadditiveandnon-additivegeneactionvaried
between traits,indicatingtheneedforspecificbreedingstrategiesforeachtrait.Parentswithdesirable
GCA effectsformosttraitsweredevelopedfromcassavaintroductionsfromSouthAmerica,highlighting
their importanceandpossibilityofwideninggeneticvariabilityofAfricancassavagermplasm.TheGCA
effects fortheparentsdidnotalwayscorrelatewiththeir per se performance, implyingthatselectionof
parents basedontheir per se performance maynotnecessarilyleadtodevelopmentofsuperiorhybrids.