Evaluation of potential increase in photosynthetic efficiency of cassava (Manihot esculenta Crantz) plants exposed to elevated carbon dioxide.

Cassava (Manihot esculenta Crantz), an important tropical crop, is affected by extreme climatic events, including rising CO2 levels. We evaluated the short-term effect of elevated CO2 concentration (ECO2 ) (600, 800 and 1000ppm) on the photosynthetic efficiency of 14 cassava genotypes. ECO2 significantly altered gaseous exchange parameters (net photosynthetic rate (P n ), stomatal conductance (g s ), intercellular CO2 (C i ) and transpiration (E )) in cassava leaves. There were significant but varying interactive effects between ECO2 and varieties on these physiological characteristics. ECO2 at 600 and 800ppm increased the P n rate in the range of 13-24% in comparison to 400ppm (ambient CO2 ), followed by acclimation at the highest concentration of 1000ppm. A similar trend was observed in g s and E . Conversely, C i increased significantly and linearly across increasing CO2 concentration. Along with C i , a steady increase in water use efficiency [WUEintrinsic (P n /g s ) and WUEinstantaneous (P n /E )] across various CO2 concentrations corresponded with the central role of restricted stomatal activity, a common response under ECO2 . Furthermore, P n had a significant quadratic relationship with the ECO2 (R 2 =0.489) and a significant and linear relationship with C i (R 2 =0.227). Relative humidity and vapour pressure deficit during the time of measurements remained at 70-85% and ~0.9-1.31kPa, respectively, at 26±2°C leaf temperature. Notably, not a single variety exhibited constant performance for any of the parameters across CO2 concentrations. Our results indicate that the potential photosynthesis can be increased up to 800ppm cassava varieties with high sink capacity can be cultivated under protected cultivation to attain higher productivity.

Pre evaluation of cassava (Manihot esculenta Crantz) germplasm for genotypic variation in the identification of K efficient genotypes through different statistical tools.

Among the tropical tuber crops, cassava (Manihot esculenta Crantz) deserves special attention as regards to its higher biological efficiency in terms of dry matter production which incidentally implies to the higher amount of nutrient extraction from the soil resulting in better response to the application of manures and fertilizers. Among the major nutrients, Potassium (K) is considered as the key nutrient for cassava owing to its influence both in tuber yield and tuber quality. The above facts as well as the availability of sufficient cassava genotypes in the germplasm collection of ICAR-CTCRI made us to initiate research work to screen cassava germplasm including the pre breeding lines. The objective being to identify K efficient genotypes which can yield well under limited availability of K so that the external application of K can be reduced. This paper describes the wide variation noticed during the pre evaluation of 83 elite genotypes which was done as a prelude in the screening and identification of K efficient genotypes. The characters studied were tuber yield, tuber characters, plant dry matter percentage, plant K content, tuber quality (starch, cyanogenic glucosides) attributes, physiological efficiency and plant biometric characters. The variation among the genotypes for the above traits was assessed by making some yardstick for classification which in turn helped in determining the percent distribution of genotypes in each category. The variation among the genotypes were further affirmed through principal component analysis, wherein the first five components explained more than 77% of variability and the cluster analysis performed grouped these genotypes into five clusters. The biplot showed the traits which are closely linked to the genotypes. The dendrogram constructed indicated similar genotypes to that of the clusters to the extent of more than 50% revealing the association of members with similar traits in clusters and dendrograms. The study helped in establishing the drastic variation among the genotypes along with identification of six genotypes viz., Aniyoor, 7 Sahya (2), 7 III E3-5, W-19, CR 43-8, 6-6 for further detailed experimentation to identify K efficient genotypes.