The life cycle of Puccinia digitariae on Digitaria eriantha and Solanum species in South Africa

Rust fungi are important plant pathogens and have been extensively studied on crops and other host plants worldwide. This study describes the heterecious life cycle of a rust fungus on Digitaria eriantha (finger grass) and the Solanum species S. lichtensteinii (large yellow bitter apple), S. campylacanthum (bitter apple), and S. melongena (eggplant) in South Africa. Following field observations, inoculation studies involving telial isolates collected from Digitaria plants produced spermogonia and aecia on S. lichtensteinii, S. campylacanthum, and S. melongena. Likewise, inoculation of finger grass with aeciospores collected from the aforementioned Solanum species produced uredinia on D. eriantha. Pennisetum glaucum (pearl millet varieties Milkstar and Okashana, as well as 17 experimental lines) and S. elaeagnifolium (silverleaf nightshade or bitter apple) were resistant to the rust isolates. Morphological descriptions and molecular phylogenetic data confirmed the identity of the rust on Digitaria as P. digitariae, herein reinstated as a species and closely related to P. penicillariae the pearl millet rust, also reinstated. Puccinia digitariae has a macrocyclic, heterecious life cycle in which teliospores overwinter on dormant D. eriantha plants. Aecia sporulate on species of Solanum during spring and early summer to provide inocula that infect new growth of Digitaria.锈菌（rust fungi）是一类重要的植物病原菌，目前已在全球范围内的农作物及其他寄主植物中得到广泛研究。本研究记述了南非地区一种锈菌在长穗马唐（Digitaria eriantha，俗称手指草）以及茄属植物利希滕施泰因茄（S. lichtensteinii，俗称大黄色苦苹果）、弯棘茄（S. campylacanthum，俗称苦苹果）和茄子（S. melongena）上的转主寄生生活史（heterecious life cycle）。经野外观察后，以从长穗马唐植株上采集的冬孢子分离物（telial isolates）开展接种试验，结果显示该分离物可在S. lichtensteinii、S. campylacanthum及S. melongena上诱导形成性孢子器（spermogonia）与锈孢子器（aecia）。同理，用上述茄属植物上采集的锈孢子（aeciospores）接种手指草，可在长穗马唐上形成夏孢子堆（uredinia）。御谷（Pennisetum glaucum，其珍珠粟品种包括Milkstar、Okashana及17个试验品系）与银叶茄（S. elaeagnifolium，俗称银叶龙葵或苦苹果）对该锈菌分离物表现出抗性。形态学描述（morphological descriptions）与分子系统发育数据（molecular phylogenetic data）证实，长穗马唐上的锈菌为马唐柄锈菌（P. digitariae），本研究恢复其物种分类地位；该菌与同样被恢复物种地位的珍珠粟锈菌——笔形柄锈菌（P. penicillariae）亲缘关系密切。马唐柄锈菌具有长循环型转主寄生生活史，其冬孢子（teliospores）可在休眠的长穗马唐植株上越冬。锈孢子器于春季和初夏在茄属植物上产孢，产生的接种体可侵染马唐的新生组织。