Physiological basis of yield gains in wheat associated with the LR19 translocation from Agropyron elongatum

The physiological and genetic basis of yield improvement in wheat is only p artially understood. Nonetheless, a significant increase in yield and bioma ss has been observed in several backgrounds when alien chromatin associated with Lr19 was introgressed from Agropyron elongatum. Theoretically, higher yield and biomass may be achieved through (i) greater interception of inci dent radiation, (ii) increased radiation use efficiency, (iii) a more optim al source-sink balance permitting higher sink demand and/or a higher partit ioning of assimilates to yield. The objectives of the current study were to evaluate the performance of near isogenic lines differing in Lr19 to obser ve the physiological basis of superior performance. Lr19 was associated wit h increases in yield (average 13%), final biomass (10%) and grain number (1 5%) in all backgrounds studied. Differences were not associated with improv ed light interception based on measurements of biomass shortly after canopy closure, nor with improved radiation use efficiency (RUE) prior to grain f illing based on biomass accumulation rate and direct measurement of flag-le af photosynthetic rate prior to anthesis. Lr19 was associated with an incre ased partitioning of biomass to spike growth at anthesis (13%), a higher gr ain number per spike, and higher RUE and flag-leaf photosynthetic rate duri ng grain filling. The mechanism causing increased partitioning of assimilat es to spikes relative to the rest of the plant in Lr19 isolines was apparen tly not related to phenology or assimilation capacity.