Rates of non-suberized impervious tissue development after wounding at different times of the year in three conifer species

Abstract

Rates of development of a non-suberized impervious tissue (NIT), which is a prerequisite to necrophylactic periderm formation, vary on the same tree with the changing environment at different times of the year. In Abies amabilis (Dougl.) Forbes, rates varied from 14 days in June, slowing gradually to 35 days in fall, virtually ceasing in winter, and resuming slowly (70 days) in spring. This cyclical pattern in rates of NIT formation was also found in Tsuga heterophylla (Raf.) Sarg. and Thuja plicata Donn. Fluctuations in the environment occasioned by year-to-year within-season variations appear to affect the physiology of NIT formation; in July, NIT developed after 21 days in 1968 and after 16 days in 1969, on the same A. amabilis. Preliminary observations indicate presence of intraspecific variations in the rates. Rates were consistently faster on the resistant than on the susceptible A. amabilis heavily infested with balsam woolly aphid, Adelges piceae Ratz. Possible causes of these variations and implications of the findings, in relation to process of NIT formation as a basic physiological host component in pathogenic interactions of bark, are discussed.