Barrier zone anatomy in red pine roots invaded by Heterobasidionannosum

Abstract

Resin production and decay were localized or, more specifically, compartmentalized in roots of Pinusresinosa Ait. invaded by Heterobasidionannosum Fr. Bref, (formerly Fomesannosus (Fr.) Krast). Distinctive tissues constituted the barrier zone which separated the resin-impregnated or decayed wood from the younger rings of normal, unaffected wood.The barrier zone tissues included distinctive tangential bands of parenchyma, many resin ducts, and disordered abnormal tracheids. The parenchyma cells of the barrier zone were thin walled and unlignified, and contained polyphenols. These cells were nucleate and remarkably similar to the secondary phloem parenchyma once fully differentiated.The barrier zone was most obvious when observed in close proximity to a site of injury or fungal colonization. However, the barrier zone appeared as a complete ring in many of the roots observed.