ABSTRACT
In the last three decades, the yield of economically important crops has been substantially increased through plant breeding and optimization of growing conditions. The improvement of yield was made possible through some increase in dry-matter production in the leaves, but more importantly, through improvement in the accumulation of dry matter by harvestable organs (Austin et al., 1987; Gifford et al., 1984). For instance, in modern cultivars of potato (Solanum tuberosum), tuber dry weight, as a proportion of plant weight (i.e. harvest index), has been increased to 81% as compared to only 7% in the wild species, Solanum demissum (Inoue and Tanaka, 1978).
