The objective of this study is to investigate the mechanism of maize resistance to corn smut disease induced by the secreted protein gene UM01240 of Ustilago maydis.

The wild-type strain SG200 of U. maydis, the UM01240 overexpression strain SG200-OE-UM01240, and the UM01240 deletion strain SG200ΔUM01240 were individually inoculated onto the maize variety Jidan209, which is highly susceptible to U. maydis. The three inoculated maize samples were named as S1, S2, and S3, respectively. After 7 d of inoculation, the pathogenicity differences among the tested strains on maize were evaluated. Using high-throughput RNA-Seq technology, the differential expression of genes between the S2 maize leaves and the S1 and S3 maize leaves was compared. Resistance-related genes involved in plant-pathogen interactions, flavonoid biosynthesis, phenylpropane metabolism, and plant hormone signal pathways were screened and subsequently validated through qRT-PCR.

The overexpression strain SG200-OE-UM01240 exhibited significantly reduced pathogenicity compared to the SG200 strain, with the corresponding maize sample S2 displaying the mildest leaf symptoms. In contrast, the SG200ΔUM01240 strain demonstrated significantly increased pathogenicity, with the maize sample S3 displaying the most severe leaf symptoms. In comparison to the S1 and S3 maize leaves, the S2 maize leaves exhibited 1 613 differentially expressed genes. Among these genes, 31 were associated with the plant-pathogen interaction pathway, primarily including protein-coding genes such as WRKY1, WRKY33, WRKY52, PR1, and PIT5. Additionally, 15 genes were linked to the flavonoid biosynthesis pathway, primarily including the synthesis of pinocembrin, naringenin, luteolin, and dihydroquercetin. Furthermore, 23 genes related to the phenylpropane metabolism pathway were identified, mainly associated with the synthesis of lignin, cinnamaldehyde, p-hydroxycinnamic acid, coniferylaldehyde, and sinapaldehyde. Lastly, 33 genes connected to plant hormone signal transduction pathways were also found, primarily concerning the synthesis of salicylic acid, cytokinins, gibberellins, and jasmonic acid. The results of qRT-PCR analysis for the selected genes were consistent with the transcriptome data.

The secreted protein gene UM01240 plays a crucial role in the pathogenicity of U. maydis in maize. The expression level of UM01240 is negatively correlated with the pathogenicity of U. maydis in maize. UM01240 achieves a balanced symbiotic relationship between U. maydis and the maize host by regulating pathways including plant-pathogen interaction, flavonoid and phenylpropanoid compound biosynthesis, and plant hormone signal transduction.

Rice blast poses a serious threat to the safe production of rice in Jilin Province, China. Breeding and utilizing resistant varieties are the most economical, safe, and effective measures to control rice blast. On the basis of clarifying the physiological race forms, distribution, and pathogenicity of Magnaporthe oryzae, the resistance evaluation to rice blast and variety combination utilization value analysis for major japonica rice varieties in Jilin Province were carried out. It will provide a theoretical basis for rational variety deployment and the efficient utilization of resistant varieties.

In the autumn of 2021, 62 dominant single spore strains were selected from 115 strains of M. oryzae collected and isolated from the main rice-growing areas of Jilin Province. These strains were then subjected to physiological race identification and pathogenicity analysis using seven Chinese differential varieties (CDVs). To assess the resistance of primary japonica rice varieties in Jilin Province, single pathogen inoculation at the seedling stage and field-induced resistance evaluation at various locations were carried out. Utilizing the results acquired from both the seedling stage and field identification, the resistance association coefficient (RAC) and virulence association coefficient (VAC) were used to analyze the disease resistance effect of various combinations of varieties.

According to the resistance phenotype of different varieties (CDVs), 62 M. oryzae strains could be divided into 7 groups and 22 physiological races. The dominant physiological groups were ZG and ZA, with frequencies of 35.48% and 32.26%, respectively. The dominant physiological races were ZG1, ZA1, and ZA17, with frequencies of 35.48%, 9.68%, and 8.06%, respectively. The moderately virulent races with a pathogenicity rate of over 40% were ZA49, ZA1, ZB15, ZB23, and ZC15. The results of single-strain inoculation at the seedling stage of the main japonica rice varieties in Jilin Province showed that 48.89% of the tested rice varieties had a seedling blast resistance frequency above 80%. According to the field evaluation of panicle blast resistance, 14 varieties demonstrated moderately resistant (MR), accounting for 15.56% of the evaluated varieties. Additionally, 27 varieties exhibited moderately susceptible (MS), representing 30% of the evaluated varieties. Furthermore, 35 varieties were classified as susceptible (S), making up 38.88% of the evaluated varieties. Finally, 14 varieties exhibited highly susceptible (HS), representing 15.56% of the total. The analysis of disease resistance through the combinations of varieties revealed that the combinations simultaneous presence of a high RAC and low VAC have a good application prospect.

The physiological race structure of the 62 M. oryzae strains in Jilin Province is complex and diverse, with different dominant physiological races in different rice-growing regions. Additionally, the major japonica rice varieties in Jilin Province exhibit strong resistance and a broad resistance spectrum against the rice blast. Moreover, some combinations of varieties possess significant application value.