Growth of Near-isogenic Wheat Lines Differing in Development--Plants in a Simulated Canopy

An understanding of the principal factors regulating the growthof temperate cereals will identify opportunities to manipulatecrop growth. In an accompanying paper (Gomez-Macpherson, Richardsand Masle,Annals of Botany82: 315–322, 1998), growth aroundthe start of floral initiation was studied in isogenic wheat(Triticum aestivumL.) lines grown as spaced plants. In thispaper, two of the same near-isogenic wheat lines were grownas mini-canopies in a growth chamber. The objective was to determinewhether results obtained using spaced plants also apply to plantsgrown in a simulated canopy as a first step to emulate fieldconditions. Biomass of plant organs, leaf area and leaf andtiller appearance were determined from sowing to ear emergenceof the early developing line. Contrary to results obtained usingspaced plants, lines differed in their above-ground biomassaccumulation, although total plant biomass accumulation wassimilar. 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 resultedin a lower root:shoot ratio in the early flowering line thanin the late line which remained vegetative. Tiller senescencealso began after TS in the early line whereas no tiller senescencewas observed in the late line during the experiment. Furthermore,after TS, net assimilation rate was greater and leaf area ratiowas lower in the early line. It is suggested that, after reachingTS, plants grown in a canopy become source limited comparedto widely spaced plants, or compared to plants that have notreached TS, and this results in less root growth.Copyright 1998Annals of Botany Company Development, growth, partitioning,Triticum aestivumL., wheat.     

Growth of Near-isogenic Wheat Lines Differing in Development--Spaced Plants

The relationship between phenological development in wheat (TriticumaestivumL.) and growth was studied to determine if the switchfrom a vegetative to a reproductive apex increases plant growthrate. Plant partitioning and relative growth rates during vegetativeand pre-flowering reproductive periods were determined in twosets of near-isogenic lines differing in phenological development.Spaced plants were grown in two photoperiods (15 and 10 h) toincrease the range of development rates. Lines within each isogenicset and photoperiod treatment did not differ in whole plantgrowth rate despite large differences in developmental rate.In addition, the partitioning of biomass between roots and shootswas also similar. The transition of the apex from vegetativeto reproductive mostly affected the partitioning of shoot biomassinto leaf (blades) and stems (rest of the shoot). A longer timeto reach floral initiation was associated with the productionof more, and larger, leaves as well as more tillers. This resultedin large differences in leaf area between isolines. However,at the whole plant level, all lines accumulated biomass at thesame rate with time. The early flowering lines compensated fortheir reduced leaf area by having a higher net assimilationrate and were thereby able to maintain the same relative growthrate as their later flowering counterparts.Copyright 1998 Annalsof Botany Company Development, growth, partitioning,Triticum aestivumL., wheat, isolines.