Genotypic variations in activities of phosphoenolpyruvate carboxylase and correlations with leaf photosynthetic characteristics and crop productivity of cassava grown in low-land seasonally-dry tropics

Field trials with a large group of cassava germplasm were conducted at the seasonally-dry and hot environments in southwest Colombia to investigate photosynthetic characteristics and production under drought conditions. Measurement of net photosynthetic rate (P-N), photosynthetic nitrogen use efficiency (PNUE), mesophyll conductance to CO2 diffusion (g(m)), and phosphoenolpyruvate carboxylase (PEPC) activity of upper canopy leaves were made in the field. All photosynthetic characteristics were significantly correlated with final dry root yield (Yield). Correlations among the photosynthetic traits were also significant. PEPC activity was highly significantly correlated with P-N and PNUE, indicating the importance of the enzyme in cassava photosynthesis and productivity. Among a small selected group from the preliminary trial for yield performance, the second year Yield was highly significantly correlated with P-N measured on the first year crop. Thus variations in the measured photosynthetic traits are genetically controlled and underpin variations in yield. One short-stemmed cultivar M Col 2215 was selected for high root dry matter content, high harvest index, and tolerance to drought. It was tested under the semi-arid conditions of the west coast of Ecuador; participating farmers evaluated cultivar performance. This cultivar was adopted by farmers and officially released in 1992 under the name Portoviejo 650.