Abstract
Cassava resistance to Bemisia tabaci is a result of many plant processes which involve plant biochemical constituents, shown to be affected by genotype and environment. The objective of this study was to assess the effect of genotype × environment interactions on concentrations of tannin, flavonoid, total phenolic content, antioxidative capacity and B. tabaci resistance. Fifteen cassava genotypes were evaluated monthly for tannin, flavonoid, total phenolic content and antioxidative capacity in three locations over two seasons with varying temperatures and rainfall. In addition, data were collected on B. tabaci population density and damage. The data collected was subjected to analysis of variance and additive main effects and multiplicative interactions (AMMI) analyses. Flavonoid, total phenolic content and antioxidative capacity varied significantly (P < 0.001) across seasons with higher concentrations in season one than season two, attributed to different temperature and rainfall readings. Total phenolic content was significantly (P < 0.001) associated to antioxidative capacity (r = 0.83) and temperature (r = 0.91). Leaf damage due to adult whitefly and nymphs was significantly (P < 0.001) negatively correlated (r = -0.67) to antioxidative capacity. Genotypes UG 120257, UG 120291 and UG 120124 were shown to have high antioxidative capacity and more stable performance across environments. Temperature and B. tabaci feeding influenced concentrations of the phenolic content and antioxidative activity, as a result affected cassava resistance.
Highlights
Cassava (Manihot esculenta Crantz), one of the most important food root crops in Uganda is cultivated over an area of 852,000 ha but has relatively low average productivity (FAO, 2017)
Fifteen cassava genotypes previously screened for resistance to whitefly, of which nine were resistant and six susceptible, were obtained from National Crop Resources Research Institute (NaCRRI) under the cassava breeding program in Uganda
4.1 Genotype by Environment Effect on Nymph Count, Whitefly Count, Leaf Damage, Sooty Mold, Tannin, Flavonoid, Total Phenolic Content and Antioxidative Capacity The genotypes varied significantly (P < 0.001) for all traits measured in different environments, relating to the significant genotype by location, genotype by season and genotype by location by season interactions (Table 2)
Summary
Cassava (Manihot esculenta Crantz), one of the most important food root crops in Uganda is cultivated over an area of 852,000 ha but has relatively low average productivity (FAO, 2017). Insect pests and environmental factors are major contributors to low cassava production (Nweke, 2009). Insect species for instance Bemisia tabaci, cause direct damage (Bellotti & Arias, 2001), act as vectors of African cassava mosaic disease (ACMD) (CIAT, 2005) and have been reported to adversely affect cassava yields by 79% (CIAT, 2011). The combinations of insects and environmental factors in natural environments, severely affect plants such as cassava (Kloth, Thoen, Bouwmeester, Jongsma, & Dicke, 2012). The processes lead to alteration in metabolite pool of affected plants (Ncube, Finnie, & Van Staden, 2012) sometimes causing a negative impact on plant insect interactions (Jamieson et al, 2017), lower plant fitness (Huber et al, 2016) and affect total cassava starch yields of up to 100% (Nuwamanya et al, 2014). Some studies have reported the complexity of plant responses to combinations of attacks making it impossible to directly infer from pairwise plant-insect interactions (Barah & Bones, 2017)
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