Biochemical and secondary metabolites changes under moisture and temperature stress in cassava (Manihot esculenta Crantz)

Abstract

Cassava's (Manihot esculenta Crantz) importance as a food security crop in Sub Saharan Africa is enhanced by its special traits such as tolerance to drought and high yields under drought stress. However, full understanding of tolerance mechanisms under hydrothermal stress in cassava is a key in developing highly tolerant varieties with increased yield. In our study, the effects of low soil moisture and increased temperature on cassava physiology were investigated. Twenty (20) cassava varieties were evaluated in a Randomized Complete Block Design in western Uganda. Hydrothermal stress was described as a period of no rainfall for a period of eight weeks leading to low soil moisture (contents between 28 to 35%) and average daily temperatures of ≥35°C. The average daily relative humidity during this period was considerably low (≤40%) further complementing already enhanced stress conditions. As such, the contents of important biochemicals and secondary metabolites in the plants were altered in a bid to counteract the effects of stress. Significant differences occurred in accumulation of main biochemicals such as soluble proteins (P<0.05), free reducing sugars (P<0.05) and bound reducing sugars (P<0.05) while reductions in the total starch yield by 70 to 100% of the original composition before stress were observed in all the test varieties. Changes in pigment properties were also observed with a decrease in the total carotenoid content (~65%) and chlorophyll a (Chla) (~40%) but no significant changes were observed for chlorophyll b (Chlb). Secondary metabolites such as phenolics and tannins too depicted varied but non-significant changes and they existed in low quantities. There were also significant changes in the phenotype (foliar portion of the plant) with at least two mechanisms of tolerance identified. The study showed the importance of carbohydrate and nitrogen cycle related metabolites in mediating tolerance in cassava by affecting their phenotypic expression in the plant.

Water Stress Revealed Physiological and Biochemical Variations in Taro [Colocasia esculenta (L.) Schott] Varieties/Genotypes

“…The total chlorophyll reduction in drought conditions is a consequence of the reduction in relative water content (Makbul et al, 2011). Results are in agreement with Nuwamanya et al, (2014) in cassava, Sakya et al, (2018) in tomato and Ghodke et al, (2018) in onion.…”

Morphological And Ecogeographic Study Of The Diversity Of Cassava (<em>Manihot esculenta</em> Crantz) In Ecuador

“…Our study identified that the rainfall in the cultivation sites, during the hottest quarter was a minimum of 193 mm and a maximum of 1615 mm, which would imply that there are materials resistant to drought. Drought is one of the most important adaptation characteristics of the crop [59,60], and it can be evaluated [61]. On the other hand, the annual mean temperature range of the collection ranges from 18.4° C to 26° C, which also indicates an important range of adaptation.…”

Genotype by Environment Interaction Unravels Influence on Secondary Metabolite Quality in Cassava Infested by Bemisia tabaci

“…Bemisia tabaci infestation (War et al, 2012), temperature and moisture stress (Pandey, Irulappan, Bagavathiannan, & Senthil-Kumar, 2017) result in biochemical and physiological plant defensive mechanisms (Kant et al, 2015). 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 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).…”

“…Changes in phenolic concentrations (Zobayed, Afreen, Goto, & Kozai, 2006;Nuwamanya et al, 2014), modify lipid packing order and reduce fluidity of plant membranes (Sharma, Jha, Dubey, & Pessarakli, 2012). The changes in phenolic content result in increased antioxidative power (Fürstenberg-hägg et al, 2013) via protein denaturation (Ncube et al, 2012) and lead to decreased nutrient availability (Stevens, Waller, & Lindroth, 2007).…”

“…Biotic stresses (including Bemisia tabaci feeding) (War et al, 2012) and abiotic factors specifically varying temperature and moisture trigger multiple biochemical products; protein (Kimmins et al, 2005), phenolics (Fürstenberg-hägg, Zagrobelny, & Bak, 2013), antioxidants (Fürstenberg-hägg et al, 2013), jasmonic acid/ethylene and peroxidase (Nuwamanya et al, 2014;Pandey et al, 2017), based on various pathways. This is due to plants incorporating a variety of environmental signals into their developmental pathways that provide for their wide range of adaptive capacities over time (Fürstenberg-hägg et al, 2013).…”