Exploiting resource use efficiency and resilience traits in ancient wheat species (PhD)

Globally, 590 million metric tonnes of wheat are produced each year, however by 2025, the estimated requirement is projected to be 840 million tonnes (Murchie et al., 2009). Over the course of the 20^th century, wheat yields notably increased due to improved cultivars from breeding schemes. However, these plants are often reliant upon the established environmental conditions in which they were bred (Calderini & Slafer, 1998; Frederick & Bauer, 1999). Further genetic enhancements in modern wheat are thought to be somewhat limited, since it has been hypothesised that early domestication and focussed breeding schemes have reduced the allelic variance within the modern wheat gene pool (Peleg et al., 2005). This makes it increasingly difficult to select for novel plant types that are able to resist biotic and abiotic stresses (Sparkes, 2010), consequently reducing overall productivity through drought, salinity, temperature and nutrient imbalances (Trethowan and Mujeeb-Kazi, 2008). It is therefore imperative that the modern bread wheat (MBW) gene pool is supplemented with more variance, and it is thought that this will most likely derive from external sources (Trethowan & Mujeeb-Kazi, 2008).

Ancient wheat species form a conduit between wild ancient wheat and cultivated Triticum species, and may harbour the genetic variation to supplement the modern bread wheat gene pool. The current work investigated a range of morphological and physiological aspects of several ancient wheat species including several representatives of spelt, emmer and einkorn. These were compared to modern bread wheat in the two field and three glasshouse experiments with the aim to investigate their resource use efficiency, where radiation use and water use formed the crux. The main components of the current work relate to 1) canopy interception characteristics 2) leaf photosynthetic capabilities and 3) water use. There was variation for a number of traits across the cultivars assessed and all species displayed favourable characteristics with respect to resource acquisition of radiation and water. Spelt genotypes demonstrated increased WUE and green area longevity compared with modern bread wheat. Emmer displayed increased WUE, assessed on three scales using instantaneous transpiration efficiency (ITE), biomass to water uptake ratios, and carbon isotope discrimination (Δ¹³C). In addition, the mechanisms whereby emmer, einkorn and spelt maintained ITE differed. Emmer was observed to increase photosynthetic rates, whereas spelt maintained low transpiration as a result of low stomatal conductance. Einkorn however, maintained ITE through an intermediate of both of these mechanisms. This was further supported by species differences for maximum photosynthetic rates (Asat) which, for emmer and einkorn, were comparable with modern bread wheat. Investigation of WUE through Δ¹³C and biomass production to water uptake ratios ranked species similarly, showing emmer and spelt to have superior WUE during grain filling. Additionally, spelt was observed to produce biomass comparable to modern bread wheat, thought to be due to enhanced RUE (observed in one field trial) or increased green area longevity rather than increased assimilation capability. In field experiments, biomass production and light interception was relatively high for einkorn species, however this was believed to derive from excessive tiller production due to poor emergence. Overall, ancient species did partition a larger proportion of assimilates toward tillers. Modern bread wheat produced fewer tillers, but directed more biomass towards the ear, and therefore had greater harvest indices (HI) compared to all ancient species.

Despite this broad analysis, further investigation of the mechanisms responsible for these traits is required. The current work however does suggest that stability, survival and duration may be prioritised over productivity in the ancient wheat growth cycle, and that there is sufficient variation for these traits with some genotypes indicating increased RUE, WUE and leaf longevity; these genotypes therefore warrant further exploration. With further investigation, resource capture and utilisation efficiency, and the morphological traits that confer these advantages in these genotypes, genetic markers could be identified with the aim to introduce valuable traits for the production of novel modern bread wheat varieties. The differences observed highlight potential successful adaptations conferring resource use efficiency between these ancient wheat species and modern bread wheat which could provide an opportunity through which modern wheat gene pools may be supplemented to improve yield productivity and stability, particularly in sub-optimal environmental conditions, thus increasing biomass production per unit resource, thereby enhancing the productivity and the efficiency of crop systems.