Jianjun Wang

Northern corn leaf blight (NCLB) is a leaf disease caused by Setosphaeria turcica that infects maize at multiple growth stages and severely impairs photosynthesis and grain yield. Breeding for resistance to NCLB would be an effective strategy to mitigate the damage caused by this disease. Mapping of resistance genes provides an opportunity to understand the resistance mechanisms and to utilize the information in developing an introgression breeding strategy. The resistance of 421 maize inbred lines with extensive genetic variation to NCLB was evaluated over three consecutive years in Xinzhou, Shanxi. The proportions of maize lines classified as highly resistant, resistant, moderately resistant, susceptible, and highly susceptible were 1.06, 7.16, 20.16, 37.13, and 34.48%, respectively. A total of 39,676 high-quality SNP markers were employed for genome-wide association study (GWAS). In the early and late stages, 85 SNPs associated with NCLB resistance were identified, of which 11 stable SNPs were detected across the two environments. Through comparative transcriptome analysis, 4,758 and 3,779 differentially expressed genes (DEGs) were identified in the resistant inbred line Jing724 and the susceptible inbred line PH4CV after infection with S. turcica, respectively. GO and KEGG analyses indicated that more DEGs were enriched in plant defense pathways in the resistant line. Furthermore, two candidate genes were identified by integrating GWAS and transcriptome analyses. These findings could provide a foundation for cloning resistance genes and breeding resistant varieties.

Northern corn leaf blight (NCLB), caused by the fungus Exserohilum turcicum, is one of the most significant foliar diseases in maize worldwide, with its severity being highly influenced by environmental conditions. An effective strategy used to control NCLB involves screening diverse maize germplasm for resistant sources through multi-environment inoculation assays, ultimately aiming to develop resistant varieties. This study systematically evaluated 711 maize germplasm accessions with rich genetic diversity. The evaluation was conducted under four location–year environment combinations (Shangluo, Shaanxi Province, China in 2014–2015 and Xinzhou, Shanxi Province, China in 2021–2022) using artificial inoculation with physiological race 123N (or races 1, 2, 3, N). The results showed that the estimated variances of genotype, environment, and genotype-by-environment interaction were all highly significant (p < 0.01). Significant correlations (p < 0.01) were observed among replicates within each environment, with correlation coefficients (r) ranging from 0.67 to 0.88. At the Xinzhou trial in 2021, four replicates were inoculated with four physiological races (1, 2, 3, and N), revealing highly significant correlations (r = 0.77–0.80, p < 0.01) among them. The disease severity of the tropical germplasm was significantly lower (p < 0.001) than that of the temperate germplasm. Among the temperate subgroups, the PA and PB (groups A and B germplasms derived from modern US hybrids) subgroups exhibited lower disease severity, with the PB subgroup showing the lowest, while the Iodent and Reid subgroups exhibited higher susceptibility. The disease severity responses to the four physiological races were highly positively correlated (r = 0.77–0.80, p < 0.001), and their correlations with the composite inoculation (race 123N) ranged from 0.65 to 0.83. Based on the resistance evaluations across four location–year environment combinations, the 711 maize accessions were classified into five categories: 20 were highly resistant, 236 resistant, 205 moderately resistant, 237 susceptible, and 13 highly susceptible. The findings indicate that the tropical germplasm and the temperate PB subgroup are major sources of NCLB resistance.

Ear rot caused by the Fusarium species has led to a decline in maize yield and kernel quality worldwide. The changes in the population structure of pathogens and the widespread planting of susceptible maize varieties have exacerbated the occurrence and harm of ear rot in China. Therefore, it is very important to establish the species composition of Fusarium and evaluate the resistance of the main cultivated hybrids. In this study, 366 single conidial isolates of Fusarium spp. were obtained from three provinces of Northeast China. F. verticillioides, F. subglutinans, F. proliferatum, F. oxysporum, and F. graminearum species complex (FGSC) were identified, with F. verticillioides being the most prevalent with a frequency of 44.0%. Based on the TEF-1α gene sequences analysis, the FGSC populations consisted of two independent species: F. boothii and F. graminearum, which account for 23.8% and 5.7% of the total isolates, respectively. Additionally, the resistance to ear rot by 97 maize hybrids commonly planted in Northeast China was evaluated by inoculation with F. verticillioides during 2021 and 2022. The results showed that the disease parameters of different hybrids varied significantly (p < 0.05). Approximately half of the hybrids had damage rates ranging from 0 to 15%, and 79.4% of the hybrids had a severity rating of less than 5.5. In total, 49 (50.5%) hybrids were rated as moderately resistant, which was the dominant resistance category, and 71 hybrids (73.2%) were identified as moderately to highly resistant to ear rot. Current research confirms that Fusarium ear rot in maize is mainly caused by F. verticillioides in Northeast China, and many hybrids are resistant to the disease. This study will guide growers to scientifically deploy resistant commercial hybrids to control ear rot.

Maize rough dwarf disease (MRDD) caused by pathogenic viruses in the genus Fijivirus in the family Reoviridae is one of the most destructive diseases in maize. The pyramiding of effective resistance genes into maize varieties is a potential approach to reduce the damage resulting from the disease. Two major quantitative trait loci (QTLs) (qMrdd2 and qMrdd8) have been previously identified. The resistance genes ZmGLK36 and ZmGDIα-hel have also been cloned with the functional markers Indel-26 and IDP25K, respectively. In this study, ZmGLK36 and ZmGDIα-hel were introgressed to improve MRDD resistance of maize lines (Zheng58, Chang7-2, B73, Mo17, and their derived hybrids Zhengdan958 and B73 × Mo17) via marker-assisted selection (MAS). The converted lines and their derived hybrids, carrying one or two genes, were evaluated for MRDD resistance using artificial inoculation methods. The double-gene pyramiding lines and their derived hybrids exhibited increased resistance to MRDD compared to the monogenic lines and the respective hybrids. The genetic backgrounds of the converted lines were highly similar (90.85–98.58%) to the recurrent parents. In addition, agronomic trait evaluation demonstrated that pyramiding lines with one or two genes and their derived hybrids were not significantly different from the recurrent parents and their hybrids under nonpathogenic stress, including period traits (tasseling, pollen shedding, and silking), yield traits (ear length, grain weight per ear and 100-kernel weight) and quality traits (protein and starch content). There were differences in plant architecture traits between the improved lines and their hybrids. This study illustrated the successful development of gene pyramiding for improving MRDD resistance by advancing the breeding process.

The gray leaf spots caused by Cercospora spp. severely affect the yield and quality of maize. However, the evolutionary relation and pathogenicity variation between species of the Cercospora genus ...