Quantitative evaluation of the pollination process of european larch (Larix decidua mill.) in seed orchard

Abstract

The pollination of European larch (Larix decidua MILL.) was investigated in the seed orchard Dolné Mlynárovo (Low Tatra Mts, Central Slovakia) during years 1991-1993. The pollen in the air was captured on horizontally and veritically placed microscopical glasses in different areas of the seed orchard. After the pollination period, ovules were isolated from the fermale strobili in order to find out the percentage of the pollinated ovules and number of the pollen grains per collecting apparatus. Approximately 140 pollen grains per square centimeter on average were captured on the vertically placed microscopical glasses in 1991, up to 400 in 1992, and only 40 in 1993. The most rapid course of the pollination was observed in 1991. Most pollen grains (in some cases more than 2,000 per square centimeter) were intercepted on the 5th and 7th day of observation and in next days the numbers of captured pollen were significantly lower. In 1992 the pollination period was much longer and more harmonious. This fact is probably associated with stable temperatures and small amount of precipitation (unlike to 1991). When comparing the number of pollen grains on horizontally placed microscopical glasses, approximately 25 pollen grains on average were captured in 1992, 6 in 1991, and only 2 per square centimeter in 1993. Days with the maximum numbers of intercepted pollen did correspond with the maximum values obtained from the vertically placed interceptive glasses. Almost all of analyzed ovules were pollinated in 1992 and up to 27 pollen grains were found on their pollen collecting apparatus in some extreme cases. In 1991 the situation was similar to 1992 (more than 85% ovules pollinated), but in 1993 only 40-85% ovules were pollinated (depending upon the grafted plants and different parts of the crowns) and only 1-3 pollel grains were found in the majority of pollinated ovules.