EFFECTS OF SOLAR UV-B RADIATION ON GROWTH, FLOWERING AND YIELD OF CENTRAL AND SOUTHERN EUROPEAN BUSH BEAN CULTIVARS (PHASEOLUS-VULGARIS L)

Different cultivars of bush beans (Phaseolus vulgaris L.) originating from Central and Southern Europe were grown from July to August/Septem ber 1993 up to 7 and 8 weeks, respectively, in two greenhouses covered by different UV-B-absorbing (280-320nm) plastic foils. By using the a mbient W-B radiation of the southern location (Portugal, 38.7 degrees N, 9.1 degrees W) in one of the greenhouses as intense UV-B radiation compared to the reduced radiation in the second greenhouse at the same place, a difference in W-B of about 8-10% was simulated. All cultivar s examined showed significant reductions in height of up to 31,8% in m ost growth phases under intense UV-B. Also fresh and dry weight as wel l as leaf area were reduced under intense W-B in the cultivars Purple Teepee, Cropper Teepee and Goldstrahl, and in early growth phases also in Coco bianco, but with ongoing development this cultivar caught up. Cultivars Hilds Maja, Primel, Manata and Cannellino exhibited no UV-B effects on weight and leaf area. A flowering delay of up to 1 day was observed under intense UV-B in several cultivars. Probably due to thi s delay the yield (fresh weight of fruits) decreased in all cultivars up to 55% under intense W-B at harvest time, while the potential yield (sum of buds, opened flowers and fruits) was reduced only in the cult ivars Cropper Teepee, Purple Teepee, Cannellino and Goldstrahl. The UV -sensitivity index (WSI) calculated according to the UV induced change s in growth, dry weight and yield at the second harvest date has shown that all cultivars are UV-sensitive, however the index was numericall y higher for Southern European cultivars (average = 2.5) than for Cent ral European ones (average = 2.3) which means that the first group was slightly less W-sensitive than the second.