Ultraviolet-B radiation effects on sweetpotato growth and development

Abstract

In spite of the success of the implementation of Montreal Protocol, the ozone level is not expected to return to 1980's levels until this mid-century because of the remaining chloroflurocarbon (CFCS) in the atmosphere. Therefore, ground-level ultraviolet-B will still stay in a high level in the next several decades and be a significant factor on the growth and development of all crops including sweetpotatoes. Two experiments were conducted using sunlit plant growth chambers and greenhouse facilities at Mississippi State, MS from July to November, 2016. In Experiment 1, the influence of three levels of UV-B (0, 5 and 10 kJ m-2 d-1) on growth, development, and yield of three contrasting cultivars, Beauregard, Hatteras and LA 1188, were studied. In Experiment 2, interactive effects of three levels of nitrogen (100, 60 and 20%) and two levels of UV-B (0 and 10 kJ m-2 d-1) on one cultivar, Beauregard, growth and development evaluated. In both the experiments, growth and developmental parameters including storage root yield and physiological parameters, were measured at the final harvest and during the experiment. Vine length, measured at – days of planting, were shorter by 15 and 39% in Beauregard), and 1.4 and 18% in LA 1188 at ambient (5 kJ) and elevated (10 kJ) of UV-B, respectively,. Similarly, total biomass was reduced by 62% (Beauregard) and 30% (Hatteras) due to the dysfunction of photosynthesis and total leaf area development. Moreover, in response to the ambient and projected UV-B, leaf thickness was reduced by 25-45% and 32-54% for three cultivars, respectively. Leaf wax and phenolic were increased in response to ambient and elevated UV-B in all cultivars. Based on the combined response index (CRI), Beauregard was classified as UV-B sensitive and Hatteras and LA 1188 were classified as UV-B tolerant. The greenhouse experiment showed that compared to 100% nitrogen (optimum) and 0 UV-B, 20% of nitrogen deficiency and projected UV-B reduced the longest vine length, the storage root dry weight and the total biomass by 29, 59 and 59%, respectively. Both elevated UV-B and nitrogen deficiency suppressed the sweetpotato growth, but the optimal nitrogen offset some of the damaging effects of UV-B. These results demonstrate that maintaining optimal nitrogen could reduce the damaging of UV-B on sweetpotato plants. Developing cultivars tolerant to UV-B will not only benefit in the current UV-B levels, but also in the projected UV-B radiation environments.