The effects of uv-b irradiation during the seedling stage on plant growth, crop yield and quality of lettuces

The aim of the present study is to investigate the effects of supplemental UV-B irradiation applied during the seedling stage on plant growth, crop yield and quality. The seedlings of curly lettuce (L.sativa var.crispa cv. Caipira) and iceberg (L.sativa var.capitata cv. Fortunas) were exposed to different doses (4.8 and 9.6 kJ/m2/day) of supplemental UV-B for 12 days. An untreated control group was also included. Plants which completed the seedling stage development were grown in soilless culture composed of peat + soil. During the seedling and vegetation stages, plant height, leaf number, leaf width, root collar diameter, root length, dry matter yield, macro and micro element content, total amount of chlorophyll and color values were studied. In addition, in harvested lettuces head weight and some yield parameters were assessed. As a consequence of supplemental UV-B irradiation at different doses during the seedling stage, reductions in plant height, root length and chlorophyll content in the seedling stage of lettuce were detected. Additionally, increasing UV-B dosages increased the content of Ca, K, Zn and Fe while they decreased the content of Cu and P in the Caipira variety. On the other hand, in the Fortunas variety they led to decreases in the content of Fe, K and Ca. The measurements carried out during plant growth revealed a decrease in the chlorophyll content of Fortunas variety, whereas in Caipira variety head weight was found to decrease. Although there was a decline in yield and marketable yield values in both varieties compared with the control group, this was not statistically important. In addition, in Caipira variety the contents of mineral matters Ca, K and Mg increased while the contents of Zn and Cu decreased. As to Fortunas variety, the content of Ca, K, Zn, Cu, Fe and Mn increased.