Effect of whitefly/sooty mold infestation on leaf pigments and ros quenching metabolites in selected cassava (Manihot esculenta Crantz) varieties grown in Uganda

Abstract

Cassava (Manihot esculenta Crantz) is the primary host plant of the whitefly (Bemisia tabaci),which transmits viruses to it. The cassava crop is subjected to direct and indirect whitefly/sootymold-mediated damage through its feeding mode. As a result, there is a co-occurrence of reactiveoxygen species and leaf-associated oxidative internal damage. The oxidative condition, thus force, jeopardizes metabolism and, as a result, the crop's significant yield losses. Nonetheless, in response to survival strategies, crop plants such as cassava use ROS-scavenging enzymes as well as non-enzyme-scavenging antioxidants to maintain a balanced metabolism and efficient growth. The purpose of this study was to identify ROS-scavenging enzymes and non-enzyme scavenging antioxidant production patterns in response to ROS products, as well as chlorophyll a, b, and carotenoids as cassava efficient growth bio markers. A complete randomized design (CRD) field experiment was set up. Cassava varieties MKUMBA, NASE 13, NASE 14, NAROCASS 1, NAROCASS 2, and NASE 3 were assigned to 18 subplots in triplicate and then infested with whiteflies/sooty mold. A control plot was also established 10 meters away from the experimental plot, with whiteflies screened off with a 0.06mm pore diameter net. After six months, leaves with visible sooty mold coverage on a scale of 3 were evaluated in the Bio-analytical and Nutrition laboratory at NaCRRI using UV-vis spectrophotometric technology and standard operating protocols for target variable characterisation. The study found that whitefly/sooty mold infestation reduced cassava leaf chlorophylls and total carotenoid contents in all tested cassava varieties when compared to non-infested (Tukey's test, p˂0.05). Furthermore, MKUMBA and NASE 3 were found to be superior to NASE 13 and NASE 14 in terms of photosynthetic pigment stability, low ROS product concentrations, and an enhanced phenolic defensive mechanism. Similarly, the higher stability of MKUMBA and NASE 3 could be attributed to significantly lower pigment loss than any other variety, photoprotection mediated by higher carotenoid content, and a balanced metabolism. MKUMBA and NASE 3 may be able to maintain higher photosynthetic efficiency and production under whitefly/sooty mold oxidative stress than NASE 13 and 14 varieties. Chlorophyll fluorescence, molecular, and biochemical research aimed at unraveling chlorophyll pigment production and degradation, carotenogenesis, and photoprotection processes should be conducted to guide breeding efforts, particularly in the varieties MKUMBA, NASE 3, NAROCASS 1, and NAROCASS 2.