Differences in needle morphology between blister rust resistant and susceptible western white pine stocks

Abstract

Needle traits were evaluated on three groups of western white pine (Pinus monticola Dougl.) seedlings: four open-pollinated families that ranked high for the "reduced needle lesion frequency" type of resistance to blister rust; four blister rust susceptible families; and two bulk lots from a seed orchard selected for blister rust resistance. No statistically significant differences were found for most traits in pairwise comparisons among the three groups. However, needles of susceptible families had significantly wider and larger stomata (greater area) than did those of resistant families and seed orchard lots; their stomata were also rounder (smaller ratio of stomatal length to width) than those of the seed orchard lots. Needles of the resistant stocks were significantly shorter than those from seed orchard bulks. Contact angles of water droplets on adaxial needle surfaces were also significantly larger on resistant families compared with the other genetic stocks. Results suggest the possibility of some threshold stomatal size and (or) critical stomatal shape related to infection by the blister rust fungus, Cronartium ribicola J.C. Fisch. ex Rabenh., and possible differences among the groups in wax chemistry and (or) surface textures, both of which may alter behavior of blister rust germ tubes and (or) be altered by blister rust infection.