Effects of desiccation and dilution on germinability of almond pollen

Abstract

SummaryThe effects of desiccation and dilution of almond pollen on its germinability were studied as part of a study of artificial pollination of cultivated crop plants. Insufficient pollination was suggested as an important factor in limiting current yields of almonds. Therefore, since 1994 we conducted experiments on the artificial supplementation of pollen to flowering almond trees, with the aim of increasing yield. We constructed a machine for electrostatic pollination (i.e. transport of electrostatically charged pollen to flowers) and tested it under laboratory and field conditions. We used pure almond pollen of cv. Fritz and found it to be sticky and clumped, and, therefore, unsuitable for this method. We tested several methods for improving the flow of pollen grains, and their effects on pollen germinability: (1) pollen grains were dried, either rapidly in a specially designed drying machine, or slowly under room conditions; (2) the pollen was diluted by mixing the grains with either talc or silica gel, in various proportions. Each diluent was used both with dried and with undried pollen grains. All treatments resulted in improved pollen flow and a reduction in pollen germinability. The higher the concentration of the diluent, the lower the germination rate. Pollen flow was improved immediately by dilution, whereas drying took longer and required special facilities such as drying machines. When pollen was mixed with a diluent, its germinability decreased with drying much faster than that of pure pollen. Although the detrimental effects of mixing with diluents are evident, the interactions between the stigmas and the diluents require further investigation. SEM analysis also supports the conclusion that reduction in germinability could be reinforced by the ability of the diluents to separate individual pollen grains and induce even further desiccation. Our results raise the issue of pollen handling and preparation in supplementary pollination in agriculture, and indicate several simple and inexpensive methods for monitoring the possible detrimental effects of methods used in agriculture today.