Identification of Wheat Stripe Rust Inoculum Sources and Dispersal Routes Responsible for Initial Rust Establishment in Southern Henan of China

Wheat stripe rust (yellow rust), caused by <i>Puccinia striiformis</i> f. sp. <i>tritici</i> (<i>Pst</i>), is an important airborne disease worldwide. <i>Pst</i> inoculum strength in southern Henan in winter or early spring is important for spring epidemics in the main autumn-sown wheat-growing regions of China. However, there is limited knowledge about the source and time of initial infection on winter wheat in southern Henan. The first occurrence of wheat stripe rust in southern Henan was recorded annually from 2011 to 2022, from which we used the backward trajectory approach to infer the likely source of <i>Pst</i> inoculum responsible for the initial disease occurrence. The results suggested that the <i>Pst</i> inoculum responsible for initial rust established in the winter in southern Henan originated from the Gansu <i>Pst</i> oversummering area in China, whereas it originated from the adjacent winter <i>Pst</i> sporulation regions in southern Shaanxi and northwestern Hubei if <i>Pst</i> symptoms were first observed in early spring in southern Henan. Another possible <i>Pst</i> source is southern Hubei where <i>Pst</i> can also sporulate in the winter. Thus, early <i>Pst</i> development in winter in the main wheat production region in China (Henan) is likely to be caused by <i>Pst</i> inoculum spread from the oversummering inocula or <i>Pst</i> epidemics in autumn seedlings in Gansu.