Three formae speciales of Puccinia striiformis were identified as heteroecious rusts based on completion of sexual cycle on Berberis spp. under artificial inoculation

Abstract

Abstract Puccinia striiformis Westend. is an obligate biotrophic parasite that could infect wheat and grasses to cause stripe rusts. P. striiformis, a species of rust fungi, is divided into several formae speciales based on host specialization, including P. striiformis f. sp. tritici, P. striiformis f. sp. hordei, P. striiformis f. sp. elymi, P. striiformis f. sp. agropyri, and P. striiformis f. sp. secalis. Among the five forms of P. striiformis, sexual stage was confirmed only for the wheat form of the rust, P. striiformis f. sp. tritici, but not known for the rest four forms. In the present study, we investigated the host specialization of three forms of P. striiformis including P. striiformis f. sp. agropyri, P. striiformis f. sp. elymi, and P. striiformis f. sp. hordei, compared the morphology of their urediniospores and teliospores, and analyzed the molecular phylogenic tree of the three forms of P. striiformis and other related species in the genus Puccinia. Each of the three forms was able to infect barberry to complete pycnial and aecial stages under artificial inoculation. Further inoculations of grass, barley cv. Guoluo and wheat cv. Mingxian 169, highly susceptible to P. striiformis f. sp. tritici, using the resultant aeciospores showed that the aeciospores could successfully infect their respective hosts and produce uredinia with high infection types, with the exception on wheat cv. Mingxian 169 where only necrosis was observed. The results suggested that Berberis spp. were alternate hosts for the three formae speciales of P. striiformis, and confirmed that the three rusts were macrocyclic and heteroecious rust fungi completing the whole life cycle on primary hosts and alternate hosts. Our study provides a basis for studying pathogenic variation of the rust fungi through sexual hybridization between formae speciales of P. striiformis.

Keywords

• Puccinia striiformis
• Grass
• Barley
• Stripe rust
• Alternate host
• Sexual reproduction