Growth of near-isogenic wheat lines differing in development - Plants in a simulated canopy

An understanding of the principal factors regulating the growth of temperate cereals will identify opportunities to manipulate crop growth. In an accompanying paper (Gomez-Macpherson, Richards and Masle, Annals of Botany 82 : 315-322, 1998), growth around the start of floral initiation was studied in isogenic wheat (Triticum aestivum L.) lines grown as spaced plants. In this paper, two of the same near-isogenic wheat lines were grown as mini-canopies in a growth chamber. The objective was to determine whether results obtained using spaced plants also apply to plants grown in a simulated canopy as a first step to emulate field conditions. Biomass of plant organs, leaf area and leaf and tiller appearance were determined from sowing to ear emergence of the early developing line. Contrary to results obtained using spaced plants, lines differed in their above-ground biomass accumulation, although total plant biomass accumulation was similar. After the early line reached terminal spikelet stage (TS), biomass partitioning to the roots and leaves decreased, whereas partitioning to the stem and ear increased. This resulted in a lower root:shoot ratio in the early flowering line than in the late line which remained vegetative. Tiller senescence also began after TS in the early line whereas no tiller senescence was observed in the late line during the experiment. Furthermore, after TS, net assimilation rate was greater and leaf area ratio was lower in the early line. It is suggested that, after reaching TS, plants grown in a canopy become source limited compared to widely spaced plants, or compared to plants that have not reached TS, and this results in less root growth. (C) 1998 Annals of Botany Company.