Phenotypic and genotypic variation in Australian native Sorghum species along aridity clines

Abstract

Context Wild sorghum taxa (Sorghum Moench) cover much of the northern Australian landscape and harbour potentially useful traits for crop improvement. Specialised metabolites such as phenolics, silicon and cyanogenic glucosides (which are toxic to grazing animals) are present in Sorghum and have been associated with drought tolerance. However, these taxa remain poorly studied, especially regarding intraspecific variation. Aims To investigate the intraspecific diversity of wild sorghums growing along aridity clines, including morphology, biochemistry and genotype. We hypothesised that genotypic and phenotypic diversity would co-vary with niche diversity. Methods Multiple accessions of Sorghum plumosum, S. stipoideum and S. timorense were grown under common conditions for 10 weeks. Concentrations of cyanogenic glucosides, phenolics and silicon were measured alongside five morphological traits. Accessions were genotyped using single-nucleotide polymorphisms. Key results Several traits varied significantly within species, but no trait consistently co-varied with aridity across species. In S. timorense, there appeared to be genotypic differentiation among accessions, but this was not translated into phenotypic differences, which was likely to be due to similarities in climate. Conclusions Our results challenge assumptions that phenotypic and genotypic diversity correlate with niche diversity and support the hypothesis that mature Australian wild sorghums store most of their cyanogenic glucosides in their roots. Implications Wild sorghums harbour advantageous traits for crop improvement, such as niche diversity and low toxicity. Future wild sorghum research must acknowledge intraspecific diversity, and as many populations as possible should be conserved, because genetic diversity is not necessarily discernible from phenotype or provenance alone.