Determining the Tolerance of Selected Cassava (Manihot esculenta Crantz) Genotypes to Drought and Salinity using Chlorophyll, Phenol and Yield as Screening Tools

Abstract

Aims: To ascertain and compare the tolerance of the selected cassava (Manihot esculenta) genotypes to drought and salinity using chlorophyll, total phenolic acid content and yield attributes as the screening parameters. Study design: The design was factorial consisting of ten cassava genotypes, three treatments (and control) with six replications laid out in a randomized complete block design (RCBD). Place and duration of study: Department of Botany, University of Ibadan, between January and July, 2019. Methodology: There were a total of 240 experimental units, 60 units in each group. It was semi-field as the plants were potted, treatments controlled while still exposed to natural environmental factors such as direct sunlight, air etc. All plants were watered for 6 weeks before exposing them to the physiological stresses of drought (D), salinity (S) and their interaction (D×S). The designated plants were subjected to S by applying 100mM of NaCl solution, D by with-holding water for 2wks interval, (D×S) by combining the two stresses and the first block (the first 60 units) serve as control. Results: With respect to total chlorophyll content (TCC) at the final stage, the highest TCC was synthesized by TMEB419 (42.84 mg/g) under drought (D), IBA120008 (48.23 mg/g) and (39.80 mg/g ) under salinity (S) and under drought and salinity (D×S) respectively while the least TCC was recorded in genotypes I070593 (4.37 mg/g) under D, I920326 (21.86 mg/g) under S and I098510 (15.65 mg/g) under D×S. With respect to total phenolic acid content (TPC), the most tolerant genotype was the salt-stressed I070593 (4.201 mg/g) among all the stressed genotypes and their controls while the least tolerant was combined stressed I980581 (1.89 mg/g). With respect to tuber yield (fresh weight), cassava genotype I980581 is the most tolerant in all the stresses (174g under D, 350g under S and 224g under D×S) while the least tolerant were TMEB693 (23.97g) under D, IBA120008 (39.53g) under S and I010040 (16.80g) under D×S. Conclusion:  In conclusion, genotype I980581 is the most tolerant under all the stresses while the least tolerant were TMEB693 under D, IBA120008 under S and I010040 (D×S).