Drought is one of the critical abiotic stresses that significantly affect agricultural production, and current models predict an increase in its severity and intensity in the future. Generally, polyploidy has been found to improve the resistance of plants to abiotic stress. Understanding the role of ploidy in resistance to drought was achieved by comparing the response between diploids and their respective induced autotetraploids of Westerwolths ryegrass (Lolium multiflorum ssp. multiflorum). Field trials were carried out in the 2017 and 2018 growing seasons, and mild drought simulation experiments in controlled conditions were carried out to validate the effect of chromosome duplication. Results obtained from morphological traits in the field experiment revealed that the induced tetraploids were significantly (p < 0.05) taller, had longer inflorescences and larger flag leaf area than their diploid counterparts, especially in the year 2018 characterized by the prolonged drought. This study also revealed that the induced tetraploids produced more dry matter yield than their diploid progenitors, especially in drought periods. The induced tetraploids had significantly higher antiradical activity and phenolic content than the diploid progenitors in response to mild drought, and this significantly correlated with the plant performance in 2018 field trials, indicating that increased ploidy level plays an important role in conferring resistance to drought in Westerwolths ryegrass. Furthermore, the antiradical activity and total phenolic content proved to be a good tool to evaluate drought tolerance at the vegetative stage in Westerwolths ryegrass.

Soil salinity is a global challenge emanating from climatic changes, depletion of fresh water reserves and extensive irrigation practices among other factors. Soil salinization still remains a huge concern in the realization of sustainable agricultural production. While emphasis has been placed on the food crops, forage production, which is an important component of the food chain, is affected as well. The aim of this study was to evaluate the morphological and physiological response to salinity stress in diploid cultivars and auto-induced tetraploid lines of annual ryegrass (Lolium multiflorum spp. multiflorum). Diploid seeds and their induced tetraploid counterparts were germinated on filter paper moistened with different concentrations of sodium chloride (NaCl) solutions, and seedlings were treated with 500 mM NaCl for 10 days in controlled conditions. The effect of different salt concentrations on germination and seedlings was studied. Results showed that seeds from the induced tetraploid lines despite being bigger had higher germination index and lower median germination time (T50) values compared to the diploid progenitors. At the seedling stage, increase in the ploidy level had a role in conferring improved tolerance to salinity stress. The induced tetraploid lines had an advantage over their diploid counterparts as the induced tetraploid lines had significant reduction in their growth in response to salinity stress, higher relative water content and antioxidant activities.

No abstract

Drought is a critical abiotic stress that disrupts redox homeostasis and is detrimental to plant development. To respond to drought, plants have developed complex mechanisms that allow them to perceive and counter abiotic stresses rapidly. Polyploidy gives rise to many gene expression changes allowing plants to adapt to a broader ecological range. The present study was designed to compare the expression of drought-related genes in diploid cultivars and induced tetraploid lines of Westerwolths ryegrass (Lolium multiflorum ssp. multiflorum). Plants were grown for three weeks in the growth chambers and were subjected to 5 days of water deficit. The relative expression of candidate genes was checked at three-time points, and the relative water content (RWC) was also calculated. The results of the experiment showed critical differences in response to water deficit periods between the diploid cultivars and their respective induced tetraploid lines. The induced tetraploid lines showed a significantly higher expression of drought-related genes than their diploid parents and had higher RWC. Also, out of the genes investigated, dehydrin is the most responsive gene to water deficit periods in Westerwolths ryegrass. Understanding the differential expression pattern of genes involved in drought response provides insight into how cytotypes respond to water deficit periods.