Genetic hybridization among genotypes of Taro (Colocasia esculanta) and recurrent selection for leaf blight resistance

Abstract

Twenty six genotypes selected from the progeny of cycle-3 recurrent selection on the basis of having 10 suckers or more were screened for taro leaf blight (TLB) resistance using in vitro leaf-disc method which detected six genotypes with durable resistance. Field evaluation of the 26 genotypes, compared to the local control cultivar "Numkowec", on the bases of TLB horizontal resistance, high comparable yield (dry matter, corm and cormel weight etc.) and good eating quality identified three superior genotypes, C3-10, C3-12 and C3-22. The three genotypes showed durable resistance to TLB and Coefficient of Infection (CI) = 20, 50 and 80 compared to CI=240 for the local control cultivar "Numkowec". In a different study, the adaptability of the three genotypes were assessed in a range of agro-ecological locations and recommended for release. The breeding program was further advanced to generate cycle-4 population by performing 85 selective partial diallel crosses among the 26 genotypes. Crosses amongst the 26 genotypes were limited to those which flowered naturally or under the effect of gibberillic acid (GA). Various degrees of natural flowering occurred in 58% of the population; however, flowering was enhanced to 82% following the application of 0.5 gl-1 GA. Crosses among the remaining 23 genotypes were carried out by other workers following the same procedure. A total of 6000 vigorous seedlings generated from bulked progeny seeds of all crosses involving the 49 genotypes, were identified out of more than 10,000 seedlings, and transplanted to the field, constituting cycle-4 progeny population. A preliminary field evaluation of the population's flowering ability, resistance to TLB and agro-morphological characteristics was carried out. A total of 237 genotypes with large size and non-deformed corms with no or little hair were initially chosen for further selection in a range of agro-ecological locations and release of elite lines, which will constitute the parental lines for cycle-5 recurrent selection population.