Evaluation of Maize Hybrids for Identifying Resistance to Northern Corn Leaf Blight in Northeast China

Northern corn leaf blight (NCLB) caused by Setosphaeria turcica is one of the most devastating foliar diseases in maize (Zea mays), resulting in great economic losses worldwide. The mutation of the pathogen exacerbates the occurrence and harmfulness of NCLB in China. Therefore, there is an urgent need for evaluating and cultivating resistant hybrids. Here, the response of 239 maize hybrids approved in Northeast China to NCLB was evaluated during 2019 and 2020. The results showed that 92 (38.49%) and 75 (31.38%) hybrids were rated as moderately resistant and resistant, respectively, which together constituted the predominant resistant categories. We observed that maize hybrids from different certified sources had different levels of resistance to NCLB, whose disease parameter values varied significantly (P <0.05) among 52 main cultivated hybrids. In 2019 and 2020, the average size of the lesions increased from 21.02 to 21.06 cm2, the average lesion density decreased from 1.36 to 1.33 lesions/100 cm2, and more than 30% of the hybrids registered final disease severity scores between 10% and 30%. The area under the disease progress curve of the main cultivated hybrids ranged from 57.96 to 986.86 cm2 in 2019 and from 50.75 to 1028.65 cm2 in 2020. Correlation analysis revealed a significant relationship (P <0.0001) among four disease parameters. Current research has shown that many maize hybrids in Northeast China are resistant to NCLB. This study should assist growers in purposefully selecting resistant commercial hybrids to contribute to the management of NCLB.

CO477, CO478, CO479, and CO480 inbred lines

CO477, CO478, CO479, and CO480 are mid- to late-season (75 – 81 days to flowering, CHU=1720–1855) corn (Zea mays L.) inbred lines with high stalk sugar levels. The level of sugar in the stalks are very high especially when grown as inbred lines. On average, the inbreds yield three times more sugar than their testcrosses. These inbred lines are the first to be developed and released for biofuel production, from the corn breeding program of Agriculture and Agri-Food Canada. Additionally, these inbred lines can be used for sugar and/or silage production. They have moderate to intermediate resistance to common rust, eyespot, northern corn leaf blight and fusarium stalk rot but are susceptible to gibberella ear rot.

Genetic Mapping And Genomic Prediction For Northern Corn Leaf Blight (Exserohilum Turcicum (Pass.) Leonard And Suggs) Resistance

Background: Northern corn leaf blight (NCLB) of maize caused by Exserohilum turcicum is a serious foliar disease. Resistance to NCLB is complexly inherited and the highly significant genotype x environment interaction effect makes selection of resistant genotypes difficult through conventional breeding methods. Hence an attempt was made to identify the genomic regions associated with NCLB resistance and perform genomic selection (GS) in two F2:3 populations derived from the crosses CM212 × MAI172 (Population-1) and CM202 × SKV50 (Population-2). Results: Two populations, each comprising of 366 progenies, were phenotyped at three different locations in the disease screening nurseries. Linkage analysis using 297 polymorphic SNPs in Population-1 and 290 polymorphic SNPs in Population-2 revealed 10 linkage groups spanning 3623.88cM and 4261.92cM with an average distance of 12.40 cM and 14.9 cM, respectively. Location-wise and pooled data across locations indicated that QTL expression was population and environment specific. The genomic prediction accuracies of 0.83 and 0.79 were achieved for NCLB Population 1 and Population 2, respectively. The resistant progenies from both populations were advanced to derive inbred lines and crossed with four different testers in line x tester mating design to test for their combining ability. High overall general combining ability was exhibited by 21 inbred lines. Among crosses 48 % were assigned high overall specific combining ability status. Out of 136 single crosses, seven recorded significant positive standard heterosis over the best check for grain yield. The clustering pattern of inbred lines developed from the two populations revealed high molecular diversity. Conclusions: In this study, comparatively better genomic prediction accuracies were achieved for NCLB and the worth of F3 progenies with high genomic predictions was proved by advancing them to derive inbred lines and establishing their higher combining ability for yield and yield related traits.

Genetic Differentiation and Mixed Reproductive Strategies in the Northern Corn Leaf Blight Pathogen Setosphaeria turcica From Sweet Corn in Fujian Province, China

The northern corn leaf blight (NCLB) pathogen Setosphaeria turcica (Luttrell) Leonard and Suggs is one of the main biotic constraints on sweet corn (Zea mays L.) yield and quality in Fujian Province, China. Currently, however, there is comparatively little information available regarding the distribution of mating types, population genetics, and reproductive strategies of this pathogen in Fujian. In this study, we investigated the distribution of mating types and population genetics of 117 isolates of S. turcica collected from seven of the main sweet corn-growing regions in Fujian Province, based on multiple polymerase chain reaction analyses using two mating type-specific primer pairs and 11 inter-simple sequence repeat markers. Furthermore, we examined the mode of reproduction of Fujian S. turcica populations. Both MAT1-1 and MAT1-2 mating types were detected throughout all seven sampling locations. The majority of MAT1-2 isolates were detected from Dongyou, Jian’ou, Pingnan, Songxi, and Longyan, whereas a large proportion of the detected MAT1-1 isolates were among those collected from Dongfeng and Nanjing. Furthermore, we detected five shared multi-locus haplotypes among S. turcica isolates from Dongyou, Jian’ou, Pingnan, Nanjing, and Songxi, whereas no shared haplotypes were observed between the Dongfeng (or Longyan) population and these five populations. Pairwise comparisons of the indices ΦPT and Nm, and population structure and principal coordinate analyses indicated genetic differentiation between both the regional and the mating type populations of S. turcica in Fujian. The skewed mating type ratio associated with low a haplotypic diversity and evident linkage disequilibrium reveals a mixed reproductive strategy for S. turcica populations in Fujian Province. The findings of this study advance our current understanding of the genetic diversity, population structure, and reproductive strategies of S. turcica populations infecting sweet corn in Fujian Province, and will potentially contribute to further resistance breeding efforts.

Complete Genome Sequence Data of Xenorhabdus budapestensis strain C72, a Candidate Biological Control Agent, from China.

Xenorhabdus budapestensis strain C72 isolated from the entomopathogenic nematode of Steinernema bicornutum possesses excellent biocontrol effect to southern corn leaf blight. However, its genomic information is lacking. Here, we report a high-quality complete and annotated genome sequence of X. budapestensis strain C72. Fifteen secondary metabolite biosynthetic gene clusters are identified in the genome, which are responsible for the production of a diverse group of antimicrobial compounds to help host plants against agricultural pathogenic diseases. This genome sequence could contribute to investigations of the molecular basis underlying the biocontrol activity of this Xenorhabdus strain.