ABSTRACT
The rust fungi parasitize most green plants and have worldwide distribution, ranging from tropical to arctic regions, from desert to marsh, and from valley bottoms to mountain tops. This chapter focuses on the disease caused by G. asiaticum. G. asiaticum infects leaves, petioles, and fruits of Japanese pear. Photosynthetic activity is remarkably reduced in heavily infected leaves. In the early spring, young pear leaves become infected by airborne basidiospores, which are disseminated form the telial horns on infected junipers in the vicinity. A penetration peg emerging from an appressorium of the basidiospore develops into a binucleate haustorium in the upper epidermis of the pear leaf. Aeciospores deposited on the surface of juniper leaves produce a long germ tube under a favorable humid condition. When a germ tube encounters a stoma, a rectangular appressorium is formed at the apex of the germ tube on guard cells of the stoma.
