Regeneration and evaluation of sugarcane somaclonal variants for drought tolerance

The regeneration of drought tolerant variants from embryogenic callus of sugarcane (Saccharum hybrids) of three varieties (Q77N1232-tolerant, Co6519-moderate and Cadmus-sensitive) on a selective medium containing Polyethylene glycol (PEG) corresponded with the degree of tolerance to drought they possess. The three varieties produced 55%, 7% and 4% respectively, of the number of plants produced in the absence of PEG. A total of eight plants regenerated from the moderate and sensitive varieties were selected and grown in a greenhouse for further testing under water stress. Plants were decapitated and microsets were used to clonally propagate them in soil. Plants were further screened for drought tolerance by measuring parameters including Drought Tolerance Capacity (DTC), chlorophyll content, peroxidase activity, proline content and stomata dimensions were assessed at 93 days-old plants, three days after water withholding. DTC of the tolerant variety (Q77N1232) was high for both the control plants regenerated in the absence of PEG and three selected plants in the presence of PEG. There was no significant (p > 0.05) difference in DTC between the parental line and its generants. On the contrary, DTC was significantly higher (p < 0.05) for the regenerants of the moderate (Co6519) and sensitive (Cadmus) regenerants as compared to their control. These significant difference may qualify the obtain regenerants as Somaclones, with improved tolerance to drought, especially because the value of DTC of the regenerants were comparable to that of the tolerant variety, Q77N1232. The variants have shown a dramatic increase in proline content as a result of exposure to water stress under PEG, as compared to their respective controls. Differences among all tested plants in chlorophyll content were not significant (p > 0.05). Similarly, the trend in peroxidase activity was similar in all blots within treatment and among varieties. Stomata dimensions including length and width have shown significant reduction in the somaclonal variants as compared to their respective controls and due to exposure to water stress under PEG. No inferior agronomic traits were observed on the obtained somaclonal variants. The improved tolerance to drought found amongst the somaclonal variants would be valuable in enhancing the diversity of varieties with high degree of drought tolerance suitable for different areas in the tropics and subtropics prune to drought.