Impact of solar ultraviolet UV-B radiation on seedling emergence, chlorophyll fluorescence, and growth and yield of radish.

ZAVALA, J.A.; BOTTO, J.F.

Functional Plant Biology

Año: 2002 vol. 29 p. 797 - 804

1445-4408

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 seedling by nearly 20% for the Scarlet radish cultivar, and delayed emergence for both cultivars by least 1 day. Using a chlorophyll fluorescent 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 compunds in the cotyledons requiered 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 partiotioned to tubers, resulting in an increase of at least 17 % in tuber diameter and 26% in fresh weight at the end of the life cycle. Our results indicate that the early effects of UV-B on seedlings development involve a cost for young plants, but it appears to be  adventageous to increase the carbon partitioning to the tubers at harvest. These findings suggest ways to improve the yield of radish crop.