Grasses are able to harbor the oversummering of urediospores and the overwintering of teliospores of Puccinia striiformis f. sp. tritici in China

Puccinia striiformis f. sp. tritici ( Pst ), the cause of wheat stripe rust, is a biotrophic and heteroecious rust fungus with five spore types. Cool and humid climatic conditions are conducive for the development of wheat stripe rust, and in turn, temperatures above 22 °C limit or even cease the disease. The survival of Pst during summer after wheat harvest is responsible for the infection on autumn-sown wheat to maintain disease cycle all the year round. Teliospores formed at late stage of wheat growth are essential for initiating sexual reproduction in spring. Although Chinese native grasses have been experimentally testified as susceptible hosts for Pst and teliospores produced on wheat have been shown to be potential inoculum sources causing infection on alternate hosts (mainly Berberis ) in spring, the roles of grass hosts in harboring the survival of urediospores and teliospores of Pst and promoting the emergence of diverse races under field conditions in China have not been known. Herein, Gansu, as a hotspot and an important oversummering region for Pst , was exemplified to demonstrate these roles of grass hosts. As a result, 63 Pst isolates, derived from 2184 uredial samples collected from grass hosts during harvesting period (from mid-June to mid-to-late July) and seeding period (mid to late September) in 2012 and 2013, were identified as 52 diverse phenotypes (82.5%) on the Chinese differential hosts. Subsequently, after inoculation of barberry, 52 Pst isolates with high infection type, 20 known races and 32 new races, were recovered from 1,712 single aecium, which are derived from 35 telial samples of grass hosts. Our experiments showed that Pst urediospores can oversummer on grass species in Gansu or other oversummering regions with similar ecological and climatic conditions. Pst teliospores, which are produced on these grass hosts, are important inoculum source for barberry infection in spring. Therefore, treatment of grasses hosts should be taken into consideration in management of wheat stripe rust.