Leaf retention and cassava productivity.

摘要

Increased longevity of leaves, or improved leaf retention, has been suggested as a possible means to increase productivity of cassava (Manihot esculenta Crantz). This study evaluated variation in leaf retention and its relation to cassava productivity under irrigated and stressed conditions. In the first trial 1350 clones were evaluated on the North Coast of Colombia with a 5-month dry period towards the end of the growth cycle. Clones with the leaf retention trait produced more total fresh biomass and yielded 33% more root dry matter than plants without the trait. In the irrigated trial 110 clones were evaluated on the CIAT farm at about 1000 mamsl. Leaf retention was quantified using a 1-5 visual score with five corresponding to excellent leaf retention. Genetic correlations between leaf retention and fresh foliage production (0.49), root dry matter yield (0.46), fresh root production (0.43) and root dry matter content (0.25) were obtained. Increased root yield under stressed and unstressed conditions was associated with increased total biomass production and increased harvest index. These finding concur with the results of cassava growth models that include leaf longevity as a variable. The lack of any negative genetic correlations between leaf retention and useful agronomic traits coupled with the relatively high genetic correlation for root yield and the high heritability (0.55) for leaf retention indicate that it should be relatively easy and advantageous to incorporate this characteristic in breeding and selection programs directed to increasing root yield under both water stressed and unstressed conditions..