Infection through wounds on shoots of pine seedlings by basidiospores of Cronartium orientale

• Published in: Journal of general plant pathology : JGPP 2022, Vol.88 (3), p.161-172
• Main Authors: Yamaoka, Yuichi, Okane, Izumi, Suzuki, Hiroyuki, Ohmachi, Katsura
• Format: Article
• Language: English
• Subjects: Agriculture; Basidiospores; Biomedical and Life Sciences; Cronartium; Fungal Diseases; Galls; Germ tubes; Herbivores; Host plants; Infections; Life Sciences; Microbiology; Pine needles; Pine trees; Pinus thunbergii; Plant Pathology; Rust fungi; Seedlings; Shoots; Stems; Telia; Tubes
• ISSN: 1345-2630; 1610-739X
• DOI: 10.1007/s10327-022-01054-9

Cronartium orientale is a heteroecious rust fungus that causes pine gall rust of two-needle pines, e.g., Japanese black pine ( Pinus thunbergii ) and Japanese red pine ( Pinus densiflora ). Basidiospores are discharged from telia on fagaceous plants, then infect pine shoots and/or stems. To determine the infection site of basidiospores on host plants, we inoculated 1–6-month-old seedlings of Japanese black pine and Japanese red pine. Seedlings with wounds formed by the removal of a few needles by a downward pull or by pruning a tip of the shoot produced galls more frequently than seedlings without wounds. When current-year shoots of 4-year-old Japanese black pine seedlings and new shoots from secondary buds induced by “Mekiri” treatment were inoculated after the removal of several needles from the seedlings, significantly more galls were produced than on shoots without wounds. Histological observations revealed that the germ tubes of basidiospores penetrated host cells exposed in the wounds, whereas basidiospores on the intact surface of needles and stems germinated directly or indirectly but did not invade host tissues. Thus, C. orientale basidiospores require fresh stem wounds for infection.