The antioxidant protein ZmPrx5 contributes resistance to maize stalk rot

Maize(Zea mays L.)stalk rot is a devastating disease worldwide,causing severe yield losses.Although previous studies have focused on the genetic dissection of maize resistance to stalk rot,the mechanisms of resistance remain largely unknown.We used a comparative proteomics approach to identify candidate proteins associated with stalk rot resistance.Statistical analyses revealed 763 proteins differentially accumulated between Fusarium graminearum and mock-inoculated plants.Among them,the antioxidant protein ZmPrx5,which was up-accumulated in diseased plants,was selected for further study.ZmPrx5 transcripts were present in root,stalk,leaf,ear,and reproductive tissues.The expression of ZmPrx5 in three inbred lines increased significantly upon F.graminearum infection.ZmPrx5 was localized in the cytoplasm.Compared to control plants,maize plants overexpressing ZmPrx5 showed increased resistance to F.graminearum infection,and ZmPrx5 mutant plants were more susceptible than wild-type plants.Defense-associated pathways including plant–pathogen interactions,phenylalanine metabolism,and benzoxazinoid and flavonoid biosynthesis were suppressed in ZmPrx5 homozygous mutant plants compared with wild-type plants.We suggest that ZmPrx5 positively regulates resistance against stalk rot in maize,likely through defense-oriented transcriptome reprogramming.These results lay a foundation for further research on the roles of Prx5 subfamily proteins in resistance to plant fungal diseases,and provide a potential genetic resource for breeding disease-resistance maize lines.

Genome-wide association mapping and genomic prediction of stalk rot in two mid-altitude tropical maize populations

Maize stalk rot reduces grain yield and quality.Information about the genetics of resistance to maize stalk rot could help breeders design effective breeding strategies for the trait.Genomic prediction may be a more effective breeding strategy for stalk-rot resistance than marker-assisted selection.We performed a genome-wide association study(GWAS)and genomic prediction of resistance in testcross hybrids of 677 inbred lines from the Tuxpe?o and non-Tuxpe?o heterotic pools grown in three environments and genotyped with 200,681 single-nucleotide polymorphisms(SNPs).Eighteen SNPs associated with stalk rot shared genomic regions with gene families previously associated with plant biotic and abiotic responses.More favorable SNP haplotypes traced to tropical than to temperate progenitors of the inbred lines.Incorporating genotype-by-environment(G×E)interaction increased genomic prediction accuracy.

Effect of Potassium on Ultrastructure of Maize Stalk Pith and Young Root and Their Relation to Stalk Rot Resistance

To study the mechanism of potassium （K） application on improvement of maize resistance to stalk rot at cellular level, scanning electron microscope and transmission electron microscope were used to observe the effect of K on the ultrastructure of maize stalk pith tissue and young root tip cell influenced by K and pathogen. In K deficient treatment, parenchyma cells of stalk pith had abnormal structure, and the cell wall between upper and lower adjacent cell was damaged, resulting in the loss of connections between vascular cells and insufficient supporting capacity. However, an improved K nutrition helped to keep a quite tight arrangement of root cell with thick cell wall, and prevent the invasion of pathogen effectively. Moreover, K treated root cell had abundant golgi apparatus, which could excrete large amount of secretions to degrade mycelium. Papillary and highly electronic intensity dot were accumulated at the invading point to prevent the deveJopment of the mycelium. Improved K nutrition could increase the resistant ability of maize plant to stalk rot, through keeping cell structure stability, preventing the expansion of intracellular space to reduce the chances of pathogen invasions, and through reinforcing cell wall and formation of intercellular and intracellular material to restrict further development of pathogen in host cell.

Screening of antagonistic Trichoderma strains and their application for controlling stalk rot in maize

Maize is one of the major crops in China, but maize stalk rot occurs nationwide and has become one of the major challenges in maize production in China. In order to find an environment-friendly and feasible technology to control this disease, a Trichoderma-based biocontrol agent was selected. Forty-eight strains with various inhibition activities to Fusarium graminearum, and Fusarium verticillioides were tested. A group of Trichoderma strains(DLY31, SG3403, DLY1303 and GDFS1009) were found to provide an inhibition rate to pathogen growth in vitro of over 70%. These strains also prevented pathogen infection over 65% and promoted the maize seedling growth for the main root in vivo by over 50%. Due to its advantage in antifungal activity against pathogens and promotion activity to maize, Trichoderma asperellum GDSF1009 was selected as the most promising strain of the biocontrol agent in the Trichoderma spectrum. Pot experiments showed that the Trichoderma agent at 2–3 g/pot could achieve the best control of seedling stalk rot and promotion of maize seedling growth. In the field experiments, 8–10 g/hole was able to achieve over 65% control to stalk rot, and yield increased by 2–11%. In the case of natural morbidity, the control efficiency ranged from 27.23 to 48.84%, and the rate of yield increase reached 11.70%, with a dosage of Trichoderma granules at 75 kg ha^-1. Based on these results, we concluded that the Trichoderma agent is a promising biocontrol approach to stalk rot in maize.

Pyramiding the disease resistant genes to southern rust and stalk rot in maize(Zea mays L.) with marker-assisted selection

Southern corn rust(SCR) caused by Puccinia polysora Underw and maize stalk rot caused by Pythium inflatum Matthews(MSR-2) are two destructive diseases of maize(Zea mays L.) in China.Our previous studies indicated that maize inbred line Qi319 is highly resistant to SCR but susceptible to MSR-2,while inbred line 1145 is highly resistant to MSR-2 but susceptible to SCR.The SCR resistant gene(RppQ) in Qi319 and MSR-2 resistant gene(Rpi1) in 1145 have been mapped on chromosome 10 and 4 respectively.In this research,through marker-assisted selection(MAS) with the molecular markers,bnlg1937 tightly linked to Rpi1 and phi041 tightly linked to RppQ,pyramid breeding of the two kinds of disease resistant genes were carried out from the year of 2003 to 2007.Two homozygotic inbred lines of F5 generation,DR94-1-1-1 and DR36-1-1-1 were identified.MAS result suggested DR94-1-1-1 and DR36-1-1-1 contained the two resistance genes RppQ and Rpi1.Field inoculation tests confirmed their high resistance to the two diseases.In addition,field investigation indicated that the two selected inbred lines,particularly DR94-1-1-1,had excellent agronomic traits such as plant height,ear height and yield-relating traits including ear length,ear diameter,ear weight,kernels per ear,kernels per row and kernel weight per ear.The two selected inbred lines DR94-1-1-1 and DR36-1-1-1 can either be directly developed into commercial variety or used as immediate donors of SCR and MSR resistance breeding programs in maize.