Viability and in vitro germination rate of pollen grains of D. kaki Thunb., D. lotus L. and D. virginiana L. in relation to storage time and temperatures

Most persimmon production relies on parthenocarpy; nevertheless male fertility is a relevant issue for breeding and, secondarily, when, for specific environmental or productive conditions, fruit-set needs to be improved. One of the bottle-necks in breeding is the natural sex-expression of persimmon (a polygamous dioic species) linked to the effect of anthropic selection of progenies, which leads to a small amount of monoic cultivars. In non-native areas of persimmon, germplasm collections usually hold a very limited number of pollen donors. Hence pollen storage is an important step in order to conserve/transport viable pollen grains for breeding purposes. In this study pollen grains of three accessions of D. kaki, one of D. lotus and one of D. virginiana have been stored at +4, -20, -80°C and in liquid nitrogen, for 0, 15, 30, 90, 180 and 360 days. Pollen grain viability and in vitro germinability depended mostly on temperature and duration of storage. After one year of conservation, storage in liquid nitrogen allowed to have rates of viable and germinable pollen grains ranging from 11 to 18% and from 5 to 9%, respectively; on the contrary, pollen grains stored for the same time at +4 and -20°C, even if viable in small amounts, did not germinate.