Analysis of pathogens and pathogenicity characteristics of potato early blight in Yunnan Province

Abstract:

[Background] Early blight is one of the main potato diseases and the pathogen Alternaria has complex species composition and different pathogenicity. [Objective] To clarify the virulence characteristics and functional gene differences of two pathogenic species of potato early blight in Yunnan Province. [Methods] In this study, Alternaria solani (TA-0410) and Alternaria alternata (TB-1129) were collected, isolated, and purified from the main potato production area in Heqing County, Dali Prefecture, Yunnan Province, with the aim of clarifying the virulence characteristics and functional gene differences between the two species through spore morphological observation, pathogenicity verification, whole genome sequencing, and comparative analysis. [Results] TA-0410 was a large-spored species with brown or yellow conidia, spore size of (37.4–151.9(±28.1)) μm×(4.3–22.9(±4.1)) μm, and long beak. TB-1129 was a small-spored species with grayish-brown conidia, spore size of (18.6–42.6(±9.3)) μm× (6.1–15.3(±2.3)) μm, and short beak. The pathogenicity verification showed that TA-0410 was the only pathogenic species, as TB-1129 failed to induce early blight in the case of direct inoculation. However, in the instance of wounded-leaf inoculation, TB-1129 successfully infected the leaves and the lesions were expanded. The genome of TA-0410 was 32.26 Mb, with contig N₅₀=1 158 607 bp, and 177 unique genes, and the genome of TB-1129 was 33.30 Mb, with scaffold N₅₀=2 338 721 bp, and 600 unique genes. In addition, the secretory proteins of TA-0410 were analyzed and 12 candidate secretory proteins containing the RxLx[EDQ] motif were screened out, all of which were annotated as putative proteins. The secretory proteins ASR_2859 and ASR_19579 contained the pathogenic BID_1 and UBA domain, respectively. [Conclusion] Both A. solani and A. alternata can cause potato early blight, with A. alternata only in the case of wounded-leaf inoculation. The phenotypes of the two in the infection and expansion stages are mainly controlled by spore viability and biotoxicity-associated proteins.