A Polysaccharide of Ganoderma lucidum Enhances Antifungal Activity of Chemical Fungicides against Soil-Borne Diseases of Wheat and Maize by Induced Resistance

Ganoderma lucidum polysaccharide (GLP), which is the primary active ingredient in G. lucidum, has been widely used in functional food and clinical medicine. However, it is rarely reported in the prevention and control of plant diseases. In this study, we found that the GLP can increase the germination rates and seedling heights of maize and wheat. We also found that the combination of GLP and chemical fungicides as a seed coating chemical compound has a control effect of more than 75% on the primary soil-borne diseases of the wheat and maize growing areas in both greenhouse and field trials. Furthermore, the combination of GLP and chemical fungicides prolongs the lasting period and reduces the application dosage of the chemical fungicides by half. In addition, GLP seed dressing could increase the resistance-related gene expression of the TPS and WRKY53 in maize and WMS533, NbPR1a, and RS33 in wheat. The combination of GLP and low-dose chemical fungicides proved to be an effective way to effectively prevent wheat sharp eyespot, root rot, and maize stalk rot in the wheat and maize continuous cropping areas in the North China Plain and to reduce pesticide use and increase crop yield.

The Wheat Wall-Associated Receptor-Like Kinase TaWAK-6D Mediates Broad Resistance to Two Fungal Pathogens Fusarium pseudograminearum and Rhizoctonia cerealis

The soil-borne fungi Fusarium pseudograminearum and Rhizoctonia cerealis are the major pathogens for the economically important diseases Fusarium crown rot (FCR) and sharp eyespot of common wheat (Triticum aestivum), respectively. However, there has been no report on the broad resistance of wheat genes against both F. pseudograminearum and R. cerealis. In the current study, we identified TaWAK-6D, a wall-associated kinase (WAK) which is an encoding gene located on chromosome 6D, and demonstrated its broad resistance role in the wheat responses to both F. pseudograminearum and R. cerealis infection. TaWAK-6D transcript induction by F. pseudograminearum and R. cerealis was related to the resistance degree of wheat and the gene expression was significantly induced by exogenous pectin treatment. Silencing of TaWAK-6D compromised wheat resistance to F. pseudograminearum and R. cerealis, and repressed the expression of a serial of wheat defense-related genes. Ectopic expression of TaWAK-6D in Nicotiana benthamiana positively modulated the expression of several defense-related genes. TaWAK-6D protein was determined to localize to the plasma membrane in wheat and N. benthamiana. Collectively, the TaWAK-6D at the plasma membrane mediated the broad resistance responses to both F. pseudograminearum and R. cerealis in wheat at the seedling stage. This study, therefore, concludes that TaWAK-6D is a promising gene for improving wheat broad resistance to FCR and sharp eyespot.

TaWAK2A-800, a Wall-Associated Kinase, Participates Positively in Resistance to Fusarium Head Blight and Sharp Eyespot in Wheat

Fusarium head blight (FHB) and sharp eyespot are important diseases of the cereal plants, including bread wheat (Triticum aestivum) and barley. Both diseases are predominately caused by the pathogenic fungi, Fusarium graminearum and Rhizoctonia cerealis. The roles of the wheat-wall-associated kinases (WAKs) in defense against both F. graminearum and R. cerealis have remained largely unknown. This research reports the identification of TaWAK2A-800, a wheat WAK-coding gene located on chromosome 2A, and its functional roles in wheat resistance responses to FHB and sharp eyespot. TaWAK2A-800 transcript abundance was elevated by the early infection of R. cerealis and F. graminearum, or treatment with exogenous chitin. The gene transcript seemed to correspond to the resistance of wheat. Further functional analyses showed that silencing TaWAK2A-800 compromised the resistance of wheat to both FHB (F. graminearum) and sharp eyespot (R. cerealis). Moreover, the silencing reduced the expression levels of six defense-related genes, including the chitin-triggering immune pathway-marker genes, TaCERK1, TaRLCK1B, and TaMPK3. Summarily, TaWAK2A-800 participates positively in the resistance responses to both F. graminearum and R. cerealis, possibly through a chitin-induced pathway in wheat. TaWAK2A-800 will be useful for breeding wheat varieties with resistance to both FHB and sharp eyespot.

Genetics of Resistance to Common Root Rot (Spot Blotch), Fusarium Crown Rot, and Sharp Eyespot in Wheat

Due to soil changes, high density planting, and the use of straw-returning methods, wheat common root rot (spot blotch), Fusarium crown rot (FCR), and sharp eyespot (sheath blight) have become severe threats to global wheat production. Only a few wheat genotypes show moderate resistance to these root and crown rot fungal diseases, and the genetic determinants of wheat resistance to these devastating diseases are poorly understood. This review summarizes recent results of genetic studies of wheat resistance to common root rot, Fusarium crown rot, and sharp eyespot. Wheat germplasm with relatively higher resistance are highlighted and genetic loci controlling the resistance to each disease are summarized.

The Wall-Associated Receptor-Like Kinase TaWAK7D Is Required for Defense Responses to Rhizoctonia cerealis in Wheat

Sharp eyespot, caused by necrotrophic fungus Rhizoctonia cerealis, is a serious fungal disease in wheat (Triticum aestivum). Certain wall-associated receptor kinases (WAK) mediate resistance to diseases caused by biotrophic/hemibiotrophic pathogens in several plant species. Yet, none of wheat WAK genes with positive effect on the innate immune responses to R. cerealis has been reported. In this study, we identified a WAK gene TaWAK7D, located on chromosome 7D, and showed its positive regulatory role in the defense response to R. cerealis infection in wheat. RNA-seq and qRT-PCR analyses showed that TaWAK7D transcript abundance was elevated in wheat after R. cerealis inoculation and the induction in the stem was the highest among the tested organs. Additionally, TaWAK7D transcript levels were significantly elevated by pectin and chitin treatments. The knock-down of TaWAK7D transcript impaired resistance to R. cerealis and repressed the expression of five pathogenesis-related genes in wheat. The green fluorescent protein signal distribution assays indicated that TaWAK7D localized on the plasma membrane in wheat protoplasts. Thus, TaWAK7D, which is induced by R. cerealis, pectin and chitin stimuli, positively participates in defense responses to R. cerealis through modulating the expression of several pathogenesis-related genes in wheat.

High-quality genome assembly-based and functional analyses reveal the pathogenesis mechanisms and evolutionary landscape of wheat sharp eyespot Rhizoctonia cerealis

Wheat (Triticum aestivum) is one of the most important staple crops. The necrotrophic binucleate fungus Rhizoctonia cerealis is the causal agent for the devastating disease wheat sharp eyespot and additional diseases of other agricultural crops and bioenergy plants. In this study, we present the first high-quality genome assembly of R. cerealis Rc207, a highly aggressive strain isolated from wheat. The genome encodes expand and diverse sets of virulence-related proteins, especially secreted effectors, carbohydrate-active enzymes (CAZymes), metalloproteases, Cytochrome P450 (CYP450), and secondary metabolite-associated enzymes. Many of these genes, in particular those encoding secretory proteins and CYP450, showed markedly up-regulation during infection in wheat. Of 831 candidate secretory effectors, ten up-regulated secretory proteins, such as CAZymes, metalloproteases and antigens, were functionally validated as virulence factors required for the fungal infection in wheat. Further intra-species and inter-species comparative genomics analyses showed that repeat sequences, accounting for 17.87% of the genome, are the major driving force for the genome evolution, and frequently intraspecific gene duplication contributes to expansion of pathogenicity-related gene families. This is the first genome-scale investigation elucidating the pathogenesis mechanisms and evolutionary landscape of R. cerealis. Our results provide essential tools for further development of effective disease control strategies.

Yield losses and control by sedaxane and fludioxonil of soil-borne Rhizoctonia, Microdochium and Fusarium species in winter wheat

Soil-borne Rhizoctonia, Microdochium and Fusarium species are major causal agents of seedling and stem-base diseases in wheat and currently seed treatments are considered the most effective solution for their control. Rhizoctonia solani anastomosis groups (AGs) 2-1 and 5, R. cerealis, Microdochium and Fusarium spp. were used in series of field experiments to determine their capability to cause soil-borne and stem-base disease and to quantify their comparative losses in establishment and yield of wheat. The effectiveness and the response to seed treatment formulated of 10 g sedaxane and 5 g fludioxonil 100 kg-1 against these soil-borne pathogens were also determined. Our results showed that damping off caused by soil-borne R. cerealis was associated with significant reductions in emergence and establishment resulting in stunted growth and low plant numbers. The pathogen also caused sharp eyespot associated with reductions in ear partitioning index. R. solani AG 2-1 or AG 5 were weakly pathogenic and failed to cause significant damping off, root rot or stem-base disease in wheat. Fusarium graminearum and F. culmorum applied as soil-borne inoculum failed to cause severe disease. Microdochium spp. caused brown foot rot disease and soil-borne M. nivale reduced wheat emergence. Application of sedaxane and fludioxonil increased plant emergence and reduced damping off, early stem-base disease and brown foot rot thus providing protection against multiple soil-borne pathogens. R. cerealis reduced thousand grain weight by 3.6% whilst seed treatment of fludioxonil and sedaxane against soil-borne R. cerealis or M. nivale resulted in 4% yield increase.