Yield improvement associated with Lr19 translocation in wheat: which plant attributes are modified?

Abstract

Resistance to three rust pathogens (leaf rust, stripe rust and stem rust) is related to different resistance genes. Leaf-rust resistance gene Lr19, transferred to hexaploid wheat from Agropyron elongatum, appears to be a promising gene not only through the resistance to rust conferred by this gene, also because of yield increases produced in different backgrounds when alien chromatin carrying Lr19 is introgressed in wheat. It was reported that Lr19 was associated with increases in grain yield. Aerial biomass was also increased when Lr19 was introgressed, although differences were not associated with improved light interception (indirectly measured) or radiation use efficiency (RUE). The physiological basis of the increased biomass and the mechanisms causing increased number of grains per spike, in terms of dynamic of floret development, are not completely understood. The objective of this study was to determine the performance of a near-isogenic line (cv. Bourlaug) differing in Lr19 in relation to: (i) the differences in grains per spike, by analysing the dynamics of floret primordia; and (ii) the dynamics of biomass partitioning between the spike and the rest of the vegetative organs pre- and post-anthesis. Two field experiments were carried out during the 2001 and 2003 growing seasons; one nearisogenic line (cv. Bourlaug) was grown under potential conditions (i.e., without water and nutritional limitations). Also a check without Lr19 was grown. The results showed that Lr19 was associated with increases in yield and a higher number of grains per unit area than the check. An increase in biomass was only observed in the 2003 growing season. Nonsignificant differences were observed in cumulative radiation intercepted between lines. Although RUE differed between growing seasons (i.e., 1.53 and 2.07 g MJ–1), there was no significant difference between the Lr19 and check genotype. In both years Lr19 allocated more assimilates and nitrogen to the spike (14% and 50% more biomass and nitrogen, respectively), and this phenomenon was associated with more fertile florets per spike. Summarizing the data, it can be concluded that the Lr19 gene promotes the partitioning of assimilates to the reproductive organs and the nitrogen partitioning to the spike. This resulted in an increased number of fertile florets per spike and number of grains per unit area, without effecting number of spikes per unit area and crop development. Increases in biomass were not always evident