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 partially understood. Nonetheless, a significant increase in yield and biomass 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 incident radiation, (ii) increased radiation use efficiency, (iii) a more optimal source-sink balance permitting higher sink demand and/or a higher partitioning of assimilates to yield. The objectives of the current study were to evaluate the performance of near isogenic lines differing in Lr19 to observe the physiological basis of superior performance. Lr19 was associated with increases in yield (average 13%), final biomass (10%) and grain number (15%) in all backgrounds studied. Differences were not associated with improved light interception based on measurements of biomass shortly after canopy closure, nor with improved radiation use efficiency (RUE) prior to grain filling based on biomass accumulation rate and direct measurement of flag-leaf photosynthetic rate prior to anthesis. Lr19 was associated with an increased partitioning of biomass to spike growth at anthesis (13%), a higher grain number per spike, and higher RUE and flag-leaf photosynthetic rate during grain filling. The mechanism causing increased partitioning of assimilates to spikes relative to the rest of the plant in Lr19 isolines was apparently not related to phenology or assimilation capacity.