Physiological and genotypic analyses of the African leafy vegetable, Amaranthus dubius, in response to environmental stresses and cryopreservation.

Abstract

Africa’s population is predicted to double by 2050. However, the current population’s dietary demand exceeds the agricultural output capacity of arable land and irrigable water. This issue is further exacerbated by the climate crisis, causing unpredictable rainfall and weather patterns and influencing soil quality and water supply. Identifying under-utilised crops that are resistant to water-deficit, soil salinity, and high temperatures can therefore mitigate some of these challenges to secure a sustainable food supply. Furthermore, long-term preservation of identified resilient genotypes is necessary to safeguard germplasm for future research and use. It is, therefore, also necessary to investigate post-storage plant growth and development to determine viability retention and true-totype genetic fidelity.

Amaranthus dubius, an under-utilised African leafy vegetable, thrives in southern Africa and is a nutritious food source containing many essential vitamins, minerals, and nutrients. This annual shrub can also tolerate environmental stresses and remains resilient on marginal lands. However, phenotypic variations observed in wild-type populations, including altered growth rates and biomass partitioning, result in reduced nutrient concentrations and yield, unpredictable quality, and overall agricultural inefficiency, hindering propagation and cultivation. Furthermore, the underlying genetic regulation of these stress responses has not been investigated, representing a missing step towards improving crop resilience, resource-use efficiency, and developing propagation strategies. This study aimed to elucidate the growth, physiological and genetic responses of A. dubius to waterdeficit, soil salinity, high-temperature, and preservation stresses, thereby identifying superior, resilient genotypes. Phenotypic responses were quantified by individually exposing A. dubius seedlings to each stress and measuring various growth and physiological parameters. Genetic expression was measured by quantifying mRNA transcripts of stress-responsive genes. This data was used to identify and clonally propagate superior genotypes, through cuttings and in vitro propagation, to conserve desired traits and increase scalability for greater agricultural capacity.

Multiple stress-tolerant specimens of A. dubius were identified by measuring biomass, shoot height, leaf area, water pressure potential, electrical conductivity, and contents of total chlorophyll, proline, and protein. Proteins were characterised in water-deficit and heat stress tolerant genotypes. The expression of putative Na+/H+ antiporter transcripts was quantified using degenerately-primed realtime qPCR, revealing a mechanism of ionic stress tolerance whereby toxic solutes were increasingly compartmentalised in roots rather than foliar tissues under salinity stress. Quantification of waterdeficit, high-temperature and cryopreservation-responsive transcripts requires further optimisation. Nevertheless, this research produced water-deficit, salinity, high-temperature and preservationtolerant clonal genotypes of A. dubius, aiding the struggle for food security in southern Africa. This work culminated in the expansion of indigenous knowledge and facilitates future studies regarding gene identification, sequencing, and the possible development of transgenic crops to withstand achanging climate.