Effects of deletion and enhancement of 280–315 nm ultra-violet (UV-B) radiation on pea (Pisum sativus L.), potato (Solanum tuberosum L.), radish (Raphanus sativus L.), and wheat (Triticum aestivum L.) plants were examined at a 3000 m elevation field site, which provided a 49% increase in midday effective (biologically weighted) UV-B radiation relative to near sea level. Wheat plants grown under Aclar or cellulose acetate film, which transmit UV-B radiation, were shorter than plants grown under Mylar film, which excludes UV-B radiation. Effective UV-B radiation levels at solar noon in the open and under the Aclar and cellulose acetate were 61, 55, and 44 mW m−2, respectively. There were no significant differences in potato, radish, and wheat dry weights attributable to UV-B radiation among the above treatments. The dry weights of all 4 species and pea and wheat plant height were not significantly decreased by a supplemental enhancement of 32 mW m−2 effective UV-B radiation from cellulose acetate filtered FS-40 sunlamps for 6 hours each day, relative to control plants that received only solar UV-B radiation. The results suggest that wheat plant height is more sensitive to deletion of UV-B radiation than the other parameters measured, and that the 4 species studied can tolerate the level of enhanced UV-B radiation used with concomitant high levels of visible radiation with no significant reduction in dry weight accumulation.
Dehydration effects on freezing characteristics and survival in liquid nitrogen were studied in 11 species of tropical seeds and in silver maple (Acer saccharinum L.) seeds. Differential thermal analysis was used to determine the threshold moisture level below which seed tissue water was in an unfreezable state. Desiccation-sensitive seeds, areca palm [Chrysalidocarpus lutescens (Bory) Wendl.] and silver maple, did not survive dehydration below the threshold moisture level and did not survive exposure to liquid nitrogen. Nine of 10 desiccation-tolerant seeds [strawberry guava, Psidium cattleianum Sabine; passion fruit, Passiflora edulis f. flavicarpa Deg.; Ceara rubber, Manihot glaziovii Mull. Arg.; dwarf schefflera, Schefflera arboricola (Hayata) Merrill; common guava, Psidium guajava L.; papaya, Carica papaya L., apple of sodom, Solarium sodomeum L.; prickly poppy, Argemone glauca Pope; and seamberry, Sabalparviflora Becc.] survived dehydration to as low as 2% to 12% moisture content (below the threshold moisture levels determined) and in the dehydrated state survived exposure to liquid nitrogen. Coffee (Coffea arabica L. var. Bourbon) seeds tolerated dehydration to as low as 8% moisture content but did not survive exposure to liquid nitrogen. These results demonstrate the feasibility of cryopreserving seed germplasm of several tropical species.