Identification of Berberis spp. as Alternate Hosts for Puccinia achnatheri-sibirici Under Controlled Conditions and Morphologic Observations of Sexual Stage Development of the Rust Fungus

Abstract

Gramineous grasses are a large group of species, many of which act as accessory (secondary) host for a large number of rust fungi, including devastating rust pathogens of cereals. Among the rust fungi, some are known to be heteroecious and have a complete macrocyclic life cycle with five types of spores on distinct plant species, but for many others the complete life cycle is unknown. Puccinia achnatheri-sibirici, a rust fungus infecting grasses in the genus Achnatherum, has been known for only its uredinial and telial stages; however, the other (pycnial and aecial) stages have not been identified. In this study, we demonstrate that P. achnatheri-sibirici is a heteroecious, macrocyclic fungus with the sexual stage on barberry (Berberis spp.) through inoculation. Pycnia and aecia were successively produced on the inoculated barberry plants. Inoculation of Achnatherum extremiorientale leaves with aeciospores produced yellow-orange uredinia with high infection types, whereas inoculation of wheat variety Mingxian 169, highly susceptible to Puccinia striiformis f. sp. tritici which causes stripe rust on wheat, produced chlorotic flecks but no uredinia. The ITS sequence analysis of P. achnatheri-sibirici did not match with any sequence in the NCBI database and had the highest homology with 94% compared to Puccinia brachypodii and Puccinia aizazii. Observations of the uredinial, telial, and basidial stages on A. extremiorientale and pycnial and aecial stages on Berberis shensiana using light and scanning electron microscopes revealed its characteristics. Morphological characteristics of urediniospores and teliospores are most similar with those of P. achnatheri-sibirici described in the literature. This study proved (1) the life cycle of P. achnatheri-sibirici as heteroecious and macrocyclic and the alternate host as barberry; (2) the description of life stages in the sexual cycle, especially the morphologies of aecial, pycnial, and basidial stages; and (3) the expansion of knowledge on the rust flora on barberry.