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A method for in vitro germination and tube growth of English walnut ( Juglans regia L.) pollen is described. The medium contained 20% sucrose, 1.0 mM CaCl 2 and 0.16 mM boric acid solidified with 0.65% agar, and was suitable for freshly collected pollen from each of the 21 clones tested. Pollen collection and storage conditions were evaluated using pollen germination on this medium as an indicator. There was considerable variation in results among the clones examined, but in general the results indicated that pollen collection should be made when catkins begin to shed pollen in the field; germination of pollen from catkins forced in the laboratory was generally low. The ability of pollen to germinate declined rapidly when held at ambient conditions. Storage in closed vials at −20°C resulted in complete loss of pollen germination ability by 3 months for some clones and by 8 months for all clones tested. When the relative humidity of the −20°C storage environment was maintained near 30%, germinability was retained, although at reduced levels, for up to 1 year. Cryopreservation using liquid nitrogen (−196°C) was satisfactory for pollen of 2 cultivars which retained the ability to germinate and grow in vitro, but not for 2 others which did not.

Pollen was collected from 7 male clones of Pistacia vera selected to cover the range of staminate bloom dates represented in an extensive collection of the species. Pollen was incubated at a range of controlled temperatures from 11 to 39°C, in 1–4°C increments, and analyzed for germination percentages. High rates of pollen germination occurred over a broad range of temperatures for all clones. Germination of pollen from the early-blooming clones showed greater tolerance for low temperatures. Curves for pollen germination vs. temperature in the early-blooming clones showed a broader peak at the low-temperature end.