Morphological characterisation of Australian ex situ wild rice accessions and potential for identifying novel sources of tolerance to phosphorus deficiency

Australian wild rice (Oryza sp.) diverged in isolation from the progenitors of cultivated rice millions of years ago and is likely to harbour novel alleles of value to rice breeding programs. Since the separation from Gondwana 100 MYA, Australia has been characterised as a primarily dry continent with nutrient-impoverished soils. This has led to speculation that alleles conferring tolerance to nutritional deficiency and other abiotic stresses such as drought or heat may be present within Australian wild rice germplasm. Previous genetic studies suggested that representative ex situaccessions of O. meridionalis and O. rufipogon are distinct from Asian wild rice but the variation in morphological or nutrient stress traits within the Australian wild rice germplasm collections has not been investigated. We therefore characterised 14 key morphological traits at flowering and maturity in five O. meridionalis ex situ genetic resource accessions in comparison with representatives of O. rufipogon, O. australiensis, O. officinalis and the O. sativa mega-variety IR64. The results were consistent with genetic analyses that indicate O. meridionalis and O. rufipogon are closely related. Variation in tolerance to phosphorus deficiency, a major nutritional constraint to global rice production, was identified among Australian wild rice accessions, although at the phenotypic level this did not appear to exceed levels of tolerance present in the O. sativa mega-variety IR64. More detailed genetic analysis may establish whether this has been achieved through convergence of distinct loci and alleles or whether recombination between the distinct lineages may generate novel transgressive levels of tolerance. We conclude that subsequent collections of Australian wild rice should be guided by underlying geological, topographical and other long-term environmental features which indicate locations known to be P deficient or exert selection pressure for adaptations to other abiotic stresses including salinity or drought stress.