PHOTOSYNTHESIS OF CASSAVA AND ITS RELATION TO CROP PRODUCTIVITY

Irrespective of the original habitat of cassava (Manihot esculenta Crantz) cultivars, net photosynthetic rate (P(N)) was substantially reduced in leaves developed in a cool climate as compared with warm-climate leaves. Cool-climate leaves partially recovered their photosynthetic capacity after 7 d acclimation in warm climate. The hot-climate cultivar showed a broad optimum temperature from 30 to 40-degrees-C, while the cool-climate cultivar showed an upward shift in optimum temperature in the acclimated and warm-climate leaves. In field-grown cassava, maximum P(N) of upper canopy leaves was greater than 40 mumol(CO2) m-2 s-1 when measured in high rainfall season and the rates did not show saturation by radiant energy up to 1800 mumol m-2 s-1 PAR. The seasonal average P(N) of upper canopy leaves was significantly correlated with both root yield and harvestable biomass. The selection for high P(N) in parental materials may lead to high yields when combined with other yield determinants.