Pollination and seed setting in certain conifers

Abstract

Four species of Conifers were used in an investigation on the effect of self-, cross- and open pollination on cone and seed setting. Both Cedrus atlantica and Tsuga canadensis are shown to he completely self-incompatible, and in the latter species, incompatibility is associated with parthenocony. In Chamaecyparis lawsoniana. the individual trees behave differently and show either complete or partial self-incompatibility. Pinus silvestris is found to be partially self-incompatible. Possibly because of the small number of pollen parents used, no crossincompatibility has been demonstrated in any of the four species. The behaviour of pollen in the self-incompatible pollinations is shown to be different in the four species. In C. atlantica. all self-pollinated cones fail to develop and fall off the tree within a few months of pollination. Pollen in the cross-pollinated cones remains dormant for about eight months before it germinates. In T. canadensis, self-pollen does not germinate whatever its position on the cone-scales; hut cross-pollen within a certain radius of the ovules germinates after six to eight weeks. In P. silvestris and C. lawsoniana, all pollen germinates, hut in most self-pollinations pollen-tube growth is inhibited either in the nucellus or the embryo-sac. Experiments on pollen germination in vitro show that pollen of all four species germinates readily at 18° C and higher temperatures. The long period of pollen dormancy in the female cones of C. atlantica is partly explained by the direct effect of temperature. The nature of the incompatibility reaction is discussed, and it is suggested that in all four species the reaction is more likely to be oppositional rather than complementary.