Response of <i>Pinus sylvestris</i> (Pinaceae) to Inbreeding, and Its Characterization as an Element of Incompatibility System

Abstract

The results of the study of seed reproduction systems of Scots pine (Pinus sylvestris L.) under self-pollination and open-pollination are summarized (2- and 12-year experiment on self-pollination; electron microscopy). It was shown that in optimal years the generative sphere of pine is in equilibrium, with the populations being characterized by a minimum level of self-fertility (Rsf = 0.13–0.14). The ratio between self-sterile, partly self-fertile and self-fertile forms is 8ss : 4psf : 1sf, the proportion of inbred progeny is 7–8%. It was found that self-pollination partially reduces cone yield and increases the share of empty seeds. During self-pollination, the incompatibility of the self-sterile forms is ultrastructurally manifested in formation of the isolation zone at the border of pollen tube and nucellus, or of the embryo and endosperm. In early embryogenesis, the isolation zone between embryo and endosperm reaches a diameter of 1–2 cells, indicating the intensity of incompatibility processes. It has been shown that in slightly anomalous (cold or warm) and dry years the level of self-fertility increases in proportion to the strength of weather stress, and the sample structure changes. The share of inbred progeny increases from 1/12 in optimal years to 1/9, 1/5 and 1/3, in cold and warm, moderately dry and severely dry years, respectively. This confirms the participation of inbreeding in the adaptation of the seed gene pool to the habitat. The organization of the genetic incompatibility system in the pine and its changes in the transition from gymnosperms to angiosperms are discussed.