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

Shujie Huang,Dan Zheng,Shuxia Zuo,Zhensheng Kang,Jie Zhao,Zhimin Du,Yao Liu

doi:10.1186/s42483-019-0021-y

Shujie Huang, Dan Zheng + Show 5 more

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https://doi.org/10.1186/s42483-019-0021-y

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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.

Highlights

Stripe rust, caused by Puccinia striiformis Westend., is a common fungal disease damaging cereal crops and gramineous grasses (Liu and Hambleton 2010)
Host specialization of P. striiformis formae speciales Fifteen days post inoculation of the single uredinium-derived isolates of the three P. striiformis formae speciales on their respective original hosts, heavy sporulation was observed on A. cristatum (Fig. 1a), E. cylindricus (Fig. 1b), and barley cv
Cheng et al (2016) reported that grasses harbor more diverse pathotypes of P. striiformis than cereals based on pathogenicity and DNA polymorphism of urediniospore isolates collected from wheat, barley, rye, grasses, and triticale in the United States

Summary

Introduction

Stripe (yellow) rust, caused by Puccinia striiformis Westend., is a common fungal disease damaging cereal crops and gramineous grasses (Liu and Hambleton 2010). Huge yield losses of crops resulted from epidemics of stripe rust often occurred in temperate areas where the summer is cool and the moisture is adequate for dew formation (Rapilly 1979; Li and Shang 1989; Zadoks and van den Bosch 1994). Stripe rust epidemics are often caused by new virulent races of P. striiformis. In China, seven displacements of major wheat cultivars nationwide have happened since 1950 because of continuous emergence of new races (Wan et al 2007). A few of new highly virulent races, V26 virulent to Yr24 (=Yr26 + YrCH42) (Liu et al 2010), G22–9 virulent to Guinong 22 (Yr10), Chuanmai 42 (YrCH42), 93R137 (Yr26) and Moro (Yr10)

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