Genetic Diversity and Pathogenicity of Verticillium dahliae Isolates and Their Co-occurrence with Fusarium oxysporum f. sp. vasinfectum Causing Cotton Wilt in Xinjiang, China

Genome-Wide Identification and Expression Analysis of RLCK-VII Subfamily Genes Reveal Their Roles in Stress Responses of Upland Cotton

Receptor-like cytoplasmic kinase VII (RLCK-VII) subfamily members are vital players in plant innate immunity and are also involved in plant development and abiotic stress tolerance. As a widely cultivated textile crop, upland cotton (Gossypium hirsutum) attaches great importance to the cotton industry worldwide. To obtain details of the composition, phylogeny, and putative function of RLCK-VII genes in upland cotton, genome-wide identification, evolutionary event analysis, and expression pattern examination of RLCK-VII subfamily genes in G. hirsutum were performed. There are 129 RLCK-VII members in upland cotton (GhRLCKs) and they were divided into nine groups based on their phylogenetic relationships. The gene structure and sequence features are relatively conserved within each group, which were divided based on their phylogenetic relationships, and consistent with those in Arabidopsis. The phylogenetic analysis results showed that RLCK-VII subfamily genes evolved in plants before the speciation of Arabidopsis and cotton, and segmental duplication was the major factor that caused the expansion of GhRLCKs. The diverse expression patterns of GhRLCKs in response to abiotic stresses (temperature, salt, and drought) and V. dahliae infection were observed. The candidates that may be involved in cotton's response to these stresses are highlighted. GhRLCK7 (GhRLCK7A and D), which is notably induced by V. dahliae infection, was demonstrated to positively regulate cotton defense against V. dahliae by the loss-of-function assay in cotton. These findings shed light on the details of the RLCK-VII subfamily in cotton and provide a scaffold for the further function elucidation and application of GhRLCKs for the germplasm innovation of cotton.

Self-assembled thiophanate-methyl/star polycation complex prevents plant cell-wall penetration and fungal carbon utilization during cotton infection by Verticillium dahliae

No effective fungicides are available for the management of Verticillium dahliae, which causes vascular wilt disease. In this study, a star polycation (SPc)-based nanodelivery system was used for the first time to develop a thiophanate-methyl (TM) nanoagent for the management of V. dahliae. SPc spontaneously assembled with TM through hydrogen bonding and Van der Waals forces to decrease the particle size of TM from 834 to 86 nm. Compared to TM alone, the SPc-loaded TM further reduced the colony diameter of V. dahliae to 1.12 and 0.64 cm, and the spore number to 1.13 × 10⁸ and 0.72 × 10⁸ cfu/mL at the concentrations of 3.77 and 4.71 mg/L, respectively. The TM nanoagents disturbed the expression of various crucial genes in V. dahliae, and contributed to preventing plant cell-wall degradation and carbon utilization by V. dahliae, which mainly impaired the infective interaction between pathogens and plants. TM nanoagents remarkably decreased the plant disease index and the fungal biomass in the root compared to TM alone, and its control efficacy was the best (61.20 %) among the various formulations tested in the field. Furthermore, SPc showed negligible acute toxicity toward cotton seeds. To the best of our knowledge, this study is the first to design a self-assembled nanofungicide that efficiently inhibits V. dahliae growth and protects cotton from the destructive Verticillium wilt.

The Genome of Fusarium oxysporum f. sp. phaseoli Provides Insight into the Evolution of Genomes and Effectors of Fusarium oxysporum Species

Fusarium oxysporum f. sp. phaseoli, the causal agent of cowpea fusarium wilt, is a serious threat to cowpea production in China. In this study, a sample of cowpea fusarium wilt was identified as Fusarium oxysporum f. sp. phaseoli using the methods of morphological characters and molecular detection. We further reported the first genome assembly for Fusarium oxysporum f. sp. phaseoli, with 53.7 Mb genome sequence comprising 14,694 genes. Comparative genomic analysis among five Fusarium oxysporum genomes showed that four accessory chromosomes in the five Fusarium oxysporum display similar characteristics, with low sequence similarity (55.35%, vs. overall average of 81.76%), low gene density (2.18 genes/10 kb vs. 3.02 genes/Mb) and highly transposable element density (TEs) (15.01/100 kb vs. 4.89/100 kb), indicating that variable accessory chromosomes are the main source of Fusarium oxysporum evolution. We identified a total of 100 Fusarium oxysporum f. sp. phaseoli-specific effectors in the genome and found 13 specific effector genes located in large insertion or deletion regions, suggesting that insertion or deletion events can cause the emergence of species-specific effectors in Fusarium oxysporum. Our genome assembly of Fusarium oxysporum f. sp. phaseoli provides a valuable resource for the study of cowpea fusarium wilt, and the comparative genomic study of Fusarium oxysporum could contribute to the knowledge of genome and effector-associated pathogenicity evolution in Fusarium oxysporum study.

Genetic Diversity and Population Structure of Fusarium oxysporum f. sp. conglutinans Race 1 in Northern China Samples

Fusarium oxysporum f. sp. conglutinans (FOC), the causal agent of cabbage fusarium wilt, is a serious threat to cabbage production in northern China, and most Chinese FOC isolates were identified as FOC race 1 (FOC1). To better understand the genetic diversity of FOC1 in northern China, we collected FOC isolates from five provinces in northern China and identified them as FOC1 through pathogenicity and race test. To evaluate the genome-level diversity of FOC1, we performed a genome assembly for a FOC1 isolate (FoYQ-1) collected from Yanqing, Beijing, where cabbage fusarium wilt was first reported in China. Using resequencing data of FOC1 isolates, we conducted a genome-wide SNP (single nucleotide polymorphism) analysis to investigate the genetic diversity and population structure of FOC1 isolates in northern China. Our study indicated that Chinese FOC1 can be grouped into four populations and revealed that the genetic diversity of FOC1 were closely associated with geographical locations. Our study further suggests that genetic differentiation occurred when FOC1 spread to the northwest provinces from Beijing Province in China. The FOC1 genetic diversity based on whole-genome SNPs could deepen our understanding of FOC1 variation and provide clues for the control of cabbage fusarium wilt in China.

Detection and Genotyping of Fov4 (Race 4, VCG0114), the Fusarium Wilt Pathogen of Cotton

Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum (Fov), is an important disease of cotton. More than 14 different genotypes as determined by VCG and sequence analyses are known to occur in the United States. Fov4 (race 4, VCG0114), originally found in India, was first detected in the United States in 2001 in California and recently in 2017 and 2019 in Texas and New Mexico, respectively. Four sub-genotypes of Fov4 have been identified, with Fov4 N, T, and MiT genotypes occurring in California, and Fov4 T and MT genotypes occurring in Texas. Unlike other genotypes of Fov in the United States, Fov4 does not require the presence of root-knot nematodes (Meloidogyne incognita) to cause severe wilt in cotton and is a major concern to US cotton growers. Fov4 can be spread through a variety of mechanisms including through infected seed. Once a field is infested, the fungus becomes endemic since there are no economically viable means to eradicate the pathogen from infested fields. Therefore, a rapid and accurate detection method is essential for early identification of infested fields and seed lots to prevent further spread of Fov4. This chapter describes multiplex and singleplex PCR diagnostics for detection of Fov4, and for detection and genotyping N, T, MiT, and MT genotypes of Fov4 from wilted cotton plants.