Impact of solar UV-B radiation on seedling emergence, chlorophyll fluorescence, and growth and yield of radish (Raphanus sativus)

Abstract

We report the impact of present-day solar UV-B radiation on seedling emergence, its association with the accumulation of UV-absorbing compounds, and the growth and yield of radish (Raphanus sativus L.). Two field experiments were conducted at intermediate latitudes in South America (Buenos Aires, Argentina) using two cultivars of radish (`Scarlet Globe' and `Sparkler National'). Solar UV-B reduced the emergence of seedlings by nearly 20% for the Scarlet radish cultivar, and delayed emergence for both cultivars by least one day. Using a chlorophyll fluorescence method to estimate the degree of UV penetration into photosynthetic tissue, we found significant differences in the levels of UV-B-absorbing compounds between seedlings grown under contrasting levels of solar UV-B. The increase of specific UV-absorbing compounds in the cotyledons required an initial lag period of 4 d after the emergence of seedlings. We could not detect any relationship between the accumulation of UV-B-screening compounds in cotyledons and leaves of the same plant, suggesting that solar UV-B induced a localized response in green tissues. Ambient UV-B affected the biomass partitioned to tubers, resulting in an increase of at least 17% in tuber diameter and 26% in tuber fresh weight at the end of the life cycle. Our results indicate that the early effects of UV-B on seedling development involve a cost for young plants, but it appears to be advantageous to increase the carbon partitioning to the tubers at harvest. These findings suggest ways to improve the yield of radish crops.