Exploiting novel genes to improve resource use efficiency in wheat

Resource use efficiency can be improved by either maintaining yield with lower crop inputs or increasing yield with the same, or reduced, inputs. Increasing yield is likely to be the most sustainable approach given the need to ensure global food security and the limited scope for expanding the cropped area without further degrading the environment. Achieving greater yields without increasing crop inputs will improve the use efficiency of land area, sunlight, nutrients and other crop inputs, as well as reducing greenhouse gas (GHG) emissions per unit of crop production.  UK farm wheat yields increased rapidly after the 1970s, but the rate of yield improvement had slowed markedly by the late 1990s and has hovered at around 8 t/ha since the turn of the century. Making progress towards higher yield potentials will require the development of new varieties and changes to crop management to ensure that high genetic yield potential of new varieties are realised.

This project aimed to increase resource use efficiency by developing reliable genetic markers and a physiological understanding for Quantitative Trait Loci (QTL) that increase yield and lodging resistance without increasing the crop’s requirement for inputs. This was achieved through the following objectives; i) Identify reliable genetic markers for genes that improve resource use efficiency, increase yield and affect height; ii) Understand the physiological mechanisms by which the genes increase resource use efficiency and yield; iii) Investigate which yield and height genes are in current varieties and the scope for combining them to increase yield without increasing lodging risk; iv) Quantify the responsiveness of the different height genes to Plant Growth Regulators (PGR) active ingredients.

Across 21 field experiments, this project has demonstrated that three QTL for yield on chromosomes 3A, 6A and 7D each increased yield by 0.25 to 0.49 t/ha, with the potential for a combined yield improvement of about 1 t/ha. Some QTL are not commonly present in elite germplasm and it is very unlikely that any elite varieties have all three yield enhancing QTL, which demonstrates there is scope to continue to increase wheat yield. Nitrogen (N) fertiliser treatments showed no evidence that the yield effects would necessitate more N fertiliser, but they would require action to reduce a greater lodging risk since some yield QTL also increased height. The yield QTL were often associated with increases in total crop biomass, more grains or both more and larger grains, with most growth improvements occurring after flowering.

One of the drawbacks of combining the QTL for greater yield using existing genetic markers is that this will increase crop height by several centimetres. To investigate whether the increase in height could be mitigated a specific breeding population was made to stack the three yield QTL within a double-dwarf background (Rht1 and Rht2; NB current elite varieties possess one of these dwarfing genes, but not both). The resulting genetic lines were 60 to 80 cm tall, therefore showing that the yield QTL could be combined into one variety without causing a high lodging risk. 

Near inbred lines (NILs) are pairs of lines differing only for the region of the chromosome containing the yield or height QTL of interest. This project focussed on NILs for three yield QTL and three height QTL. The project developed new NILs for the yield QTL on chromosome 7D and further refined and multiplied up existing NILs which will provide valuable pre-breeding materials. This project has developed new and more reliable genetic markers for yield and height that are amenable for high throughput use in commercial breeding programmes. Gene candidates have been proposed for some QTLs which will help to find even more reliable genetic markers which are necessary to understand whether yield/height effects can be uncoupled.

Varieties were shown to undergo significantly different amounts of shortening (up to 2-fold) in response to PGRs. However PGR effects commonly interacted strongly with the environment which made it difficult to identify consistent varietal differences. There was no consistent evidence that varietal differences in PGR sensitivity were related to crop height, the presence of specific height genes, or differences in leaf waxiness. If a variety was sensitive to a PGR then it tended to be sensitive to a wide range of PGR active substances.