ABSTRACT
Several metabolites are linked to cassava resistance to whitefly. There is limited information however, on the mode of gene action of the metabolites associated with cassava resistance to whitefly (Bemisia tabaci). The objective of the study was to determine the combining abilities and mode of gene action of salicylic acid, antioxidative capacity, total phenolic content, flavonoid, tannin, peroxidase and protein of selected cassava genotypes. Ten genotypes were crossed in half diallel and the parental and 45 S1 progenies evaluated for nymph count, whitefly count, leaf damage and sooty mold at Namulonge in season two of 2016. In season one and two of 2017, the parental genotypes and their corresponding forty-five S1 progenies were evaluated in randomized complete blocks with two replications for Bemisia tabaci population and leaf damage and leaf metabolite content assayed. The results indicated highly significant (P<.001) differences among genotypes for general combining ability (GCA) to antioxidative capacity; (P<.05) for total phenolic content, peroxidase and protein and (P<.01) for salicylic acid, tannin and flavonoid. The specific combining ability (SCA)showed significant (P<.001) differences for salicylic acid; (P<.01) for antioxidative capacity and total phenolic content. The additive variance was significant (P< .05) for flavonoid, protein; (P<.01) for antioxidative capacity, total phenolic content, tannin and peroxidase. The dominance variance had high significance (P<.001) for salicylic acid; (P<.05) for flavonoid and (P<.01) for antioxidative capacity and total phenolic content. Although additive gene action was higher than non-additive, both were influencing most metabolites indicating complexity of inheritance. A critical evaluation is necessary when exploiting metabolite related traits in breeding for resistance to Bemisia tabaci.
ABSTRACT
Aims: A procedure was developed for embryogenesis from embryo explants derived from mature seeds of freshly harvested Serenut 4T, Serenut 1R and Acholi-white groundnut cultivars representing the three broad groundnut botanical classifications. Methodology: This study explored the use of mature embryo axes as explants for somatic embryogenesis, and determined the factors that affect regeneration of three Ugandan groundnut cultivars. Freshly harvested mature seeds of the three groundnut cultivars were collected and the embryo explants were initiated on 3 media namely; Murashige and Skoog (MS) basal media with varying concentrations of the growth regulator 2,4-Dichlorophenoxy acetic acid (2,4-D); Chu N6 basal medium with vitamins (N6); and Callus Induction Medium (CIM). The shoot formation and elongation medium contained MS basal medium supplemented with indolebutyric acid (IBA) and 6- Benzylamminopurine (BAP) in isolation, and BAP in combination with a-naphthaleneacetic acid (NAA) and indoleacetic acid (IAA). For root induction, elongated shoots were transferred to MS medium supplemented with various combinations of NAA with IBA, BAP and a combination of IBA and Kinetin. Results and Conclusion: Different concentrations of 2,4-D elicited different callogenesis responses in the cultivars with Acholi white (Valencia botanical) and Serenut 4T (Spanish botanical) giving the optimal response at 5mg/l whereas Serenut 1R (Virginia botanical) showed best response at a concentration of 30 mg/l. N6 and CIM supported callogenesis in Acholi white (AW) and Serenut 4T only. In all cultivars, maximum root production was gained when using MS medium supplemented with NAA- 1 mg/l and IBA -2.0 mg/l. On the other hand, for Serenut 1R and Serenut 4T, BAP 2.5 mg/l; NAA 0.5 mg/l combination yielded higher shoot regeneration percentage whereas for AW BAP 3 mg/l; NAA 0.5 mg/l supported maximum shoot production.This is the first ever report of successful regeneration of the three groundnuts botanicals in Uganda. These results are likely to facilitate genetic transformation of three preferred Ugandan groundnut varieties.