Variability of early bulking and related characters in sweetpotato (Ipomoea batatas (L.) Lam)

Storage root bulking in sweetpotato varied among the 15 genotypes evaluated in all environments (location-season combination) at every harvest date. All of them exhibited high yield increment from 60 to 90 DAP. In BSU [Benguet State Univ., La Trinidad, Benguet, Philippines] bulking was early and fast dduring the wet season but became slower during the dry season probably due to lower temperature and insufficient amount of water available to the plant during this period. In UPLB, faster and early root bulking was detected during the dry season because of higher temperatures and longer exposure of the plant to solar radiation than the wet season. Significant regression coefficients for almost all genotypes evaluated indicate linear response of storage root yield to dates of harvest. Higher total root yield during the wet season than the dry season was produced in BSU while the reverse was observed in UPLB. The same trend was noted for marketable root yield, number of roots per plant and average root weight. The root dry matter and starch contents increased with root maturity which varied among genotypes. Total free sugar was comparable among genotypes in all environments except during the wet season in UPLB. Considering all the characters investigated in this study, crosses involving some parent clones or parent clones themselves such as Binicol, NPSP 48 and UPLSP 1 showed outstanding performance suggesting that they can be used as parents in producing early and high yielding sweetpotato genotypes. Highly significant variation among genoytpes (i.e. among parents and among crosses) was detected for almost all characters considered in this study which indicated significant genetic effects. Combined analysis of variances over four environments showed that genotype x environment interactions were present and significant for average root weight and harvest index throughout all harvest periods except at 60 and 150 DAP for average root weight. This indicates that sweetpotato genotypes performed differently in different environments, however, a stable genotype in terms of average root weight can be found in sweetpotato at 60 and 150 DAP. Sweetpotato performed significantly better in UPLB during the dry season planting than in all other three test environments