Unveiling the genetic diversity and host specificities of rust: morphological and molecular characterization of Berberis species

Berberis species serve as an alternate host of the aecial phase of many rust diseases causing pathogens including wheat stem rust (WSR), wheat yellow rust (WYR) and oat stem rust (OSR). Barberry, as an alternate host, has recently gained attention due to the emergence of new races after genetic recombination during the aecial stage on barberry. Different Berberis species also serve as a seasonal bridge for stem and stripe rust pathogen in Pakistan and neighbouring countries. The aim of this study was to identify the role of Berberis species and to examine the genetic diversity of rust on Berberis spp. at species and formae speciales levels collected from different geographical areas of Pakistan using molecular and morphological techniques. Initially, PCR based approach was applied using simple sequence repeat (SSR) markers to investigate the presence of WSR, WYR, and OSR in 95 aecial samples grown under natural conditions. Based on aecial growth and spore morphology, rust was divided into 2 groups i.e., localized (Puccina graminis) and systematic (Puccina arrhenatheri). For molecular study, DNA was extracted from infected leaf aecial lesion using different methods (CTAB, SDS and Kit) to avoid degradation. Positive control (DNA) of WSR, WYR and OSR were first screened using SSR markers and then Kits extracted DNA were successfully amplified by species and formae speciales specific SSR markers. In total, 25 of 46 SSR markers were found to be useful for the screening of selected rusts collected from barberry. SSR analysis revealed 3 Berberis species namely Berberis balochistanica, Berberis pachyacantha and Berberis lycium as alternate hosts of WSR, while B. lycium was also identified as an alternate host of OSR. Additionally, no barberry was found as an alternate host of stripe rust in natural conditions. This study also showed the specificity of SSR markers at species and formae speciales level. The result of present study indicated that spore morphology and aecium appearance on leaf of barberry is an imperative tool to screen rust diversity. In conclusion, this study confirms that barberry serves as an alternate host for only stem rust in Pakistan. This study just focused on aecial stage, so in future relationship of all stages like survival of urediniospores, teliospore germination and basidiospore production and initiation of pycnial stage on Berberis should be studied.