Inheritance of agronomic and quality characteristics in sweet potato (Ipomoea batatas (L.) Lam.)

English: 1. The study was undertaken to estimate genetic parameters like variance components, general and specific combining ability effects, phenotypic and genetic correlation coefficients, heritability coefficients, heterosis, genotype by environment interaction and genotypic stability for various characteristics of sweet potato. 2. Four male parents (Kenia, Brondal, Impala and Mafutha) were crossed in a factorial fashion with three female parents (Bosbok, Koedoe and Ribbok). The offspring and their parents were planted in three different environments at Roodeplaat, near Pretoria. One trial was planted under irrigation in 1998. The other two were planted in 1999 under irrigation and rainfed conditions, respectively. Twenty-five different agronomic and quality characteristics were measured. The computer program AGROBASE (1997) was used to perform the different analyses of variance such as the Line x Tester and additive main effects and multiplicative interaction, and correlations. 3. Significant differences were found among the averages of the parents and their offspring for nearly all characteristics except NMRW. The G x E interactions were significant for TRW, MRN, TSS, Hl, Pl, VC, lO, llT and Nl. Kenia and Mafutha were outstanding with regard to their high dry matter content. 4. The male parent Mafutha had the largest GCA effect for TRN (0.65), RFC (0.46), OMC (0.01) and HI (0.04). Impala had the largest GCA effect for TRN (0.75), Bosbok for RSC (1.55) and Kenia for OMC (0.02). No significant SCA effects were found between the crosses for economic important characteristics. 5. GCA: SCA ratios across environments for all root yield characteristics of economic importance were close to unity except for TRN with a ratio of 8.6. Extremely high GCA: SCA ratios were found for LLT (81.65), VC (61.56), La (54.12), PL (44.72) and VIL (39.25). 6. The VAIVG ratios were relatively high for most of the characteristics except for MRW (0.59) and TRW (0.68). 7. Larger heritability coefficients were found from the female parents for RSC, RO, LVP and PP. Combined narrow and broad-sense heritabilities estimated over both parents (h2 M+F) were negative for most economic important characteristics. Relatively high narrow-sense heritabilities were found for RFC (0.47), VL (0.46), VIL (0.46), LVP (0.45), La (0.48) and LLT (0.49). Narrow-sense heritability estimates by the parent-offspring regression method ranged from negative for NMRW and TRW, to 1.44 for PL. Among the characteristics of economic importance, OMC had the highest estimate (0.66) followed by RSC (0.57) and TRN (0.54). 8. Highly significant phenotypic correlation coefficients were found between OMC and TSS (0.75), TRN and MRN (0.86), VIL and VL (0.90), LLT and LO (0.84), NL and LO (0.83), NL and LLT (0.78), MRN and TRN (0.79), Hl and FW (-0.93) and HI and VL (-0.77). Extremely high and significant genetic correlations were found between TRW and MRW (0.92), LVP and NMRW (0.94), TRN and NMRN (0.88), Hl and TSS (0.94), TSS and VIL (0.91), TSS and NL (0.96), OMC and Hl (0.91), OMC and PP (0.93), OMC and LLT (0.97), FW and Hl (-0.91), Hl and LL (-0.95), VL and VIL (0.94), PL and FW (0.91), TRW and LL (0.91), VC and PP (0.93), LO and LLT (0.92) and between FW and LL (0.93). 9. Correlated response to selection indicates that selection for high HI is likely to increase MRW (0.02) and MRN (0.07 - 0.08). Furthermore, selection for long vines is likely to increase TSS (0.12 - 0.22), MRW (0.06), MRN (0.11), and TRW (0.08). 10.When combined across parents and environments, mid-parent heterosis was negative for all root yield and quality characteristics of economic importance except RO, which showed a positive heterosis of 12.9%. However, positive heterosis was found for individual crosses at some of the environments. 11.The AMMI stability value (ASV) showed that the parents were less stable than their crosses. The cross Koedoe x Impala was ranked first for MRN, Ribbok x Brondal for TRN, Ribbok x Kenia for MRW and Ribbok x Impala for TRW. The cross Koedoe x Impala showed significant levels of mid-parent heterosis for stability for MRN (-98.3%), Ribbok x Brondal (-89.5%) for TRN, Ribbok x Impala (-89.4%) for MRW and Ribbok x Impala (-95.4%) for TRW.