First report of Microdochium nivale and M. majus associated with brown foot rot of wheat in China

Microdochium nivale and M. majus not only cause seedling blight of wheat (Triticum aestivum L.) in cold dry soils, but also cause foot rot and ear blight of wheat under favorable conditions (Haigh et al. 2009). In May 2017, 2019, and 2020, a serious foot rot of wheat with an incidence of 92%, 45%, and 51% was observed in the field in Xiangcheng County (33.43° N, 114.84° E), Tanghe County (32.43° N, 112.66° E), and Linzhou City (36.13° N, 113.75° E), Henan Province, respectively. The serious brown lesions of the lower leaf sheaths is visible. The pathogens were isolated from brown leaf sheaths on potato dextrose agar (PDA) after being surface-sterilized (70% EtOH for 30 s followed by 3% NaClO for 1.5 min) and rinsed three times in sterile distilled water. After 5 d, mycelia were transferred to fresh PDA, and nine representative isolates (G17ZK2-1, G17ZK2-2, G17ZK2-3, g19TH10-4, g19TH10-5, g19TH10-6, G20LZ1-6, G20LZ1-7, and G20LZ1-8) were further purified by hyphal tipping. Species were identified based on morphological characteristics, and sequence analysis of partial sequences of the translation elongation factor-1α (TEF), the RNA polymerase II subunit (RPB2) gene and β-tubulin gene (Abdelhalim et al. 2020). Among the nine isolates, six isolates belonged to M. majus, three isolates belonged to M. nivale. Sequences of six isolates M. majus and three isolates M. nivale were deposited in GenBank with accession numbers MW428296-MW428298, MZ734119-MZ734121and MZ734139-MZ734141(TEF), MW384889, MW428291, MW428292, MZ734203-MZ734205 and MZ734161-MZ734163(RPB2), MW428293-MW428295, MZ501004-MZ501006 and MZ501024-MZ501026 (β-tubulin). For all the genes, isolates revealed 98-100% similarity to M. majus and M. nivale accessions, respectively. Microscopy of the six M. majus isolates showed: the conidia were falcate, straight to curved, apex pointed or obtuse to subacute, lacking basal differentiation, with 1 to 6 septa, 3.6 to 5.0 × 15.0 to 30.5 μm (av.= 4.5 × 23.2; n = 60). The three M. nivale isolates showed: the conidia were hyaline, 1 to 3 septa, 2.4 to 4.4 × 11.9 to 26.0 μm (av.= 3.5 × 14.7; n = 60). Perithecia of M. majus are dark brown, globose, and 95.2 to 190.5 × 95.2 to 228.6 μm (av.= 144.4 ×152.5; n = 30). Asci are clavate, and 6.8 to 11.0 ×68.2 to 77.3 μm (av.= 8.6×72.0; n = 30), contain eight ascospores. Mature ascospores are ellipsoidal, and 3.8 to 4.9 ×11.5 to 19.2 μm (av.= 4.0 ×15.2; n = 30), with 1 to 3 septa. These morphological characteristics were consistent with previous descriptions of these two species (Glynn et al. 2005). For pathogenicity tests, mycelia of M. nivale and M. majus was prepared using the modified procedure of Zhang et al. (2015). Two-week-old healthy wheat seedlings (cv. Aikang 58) were inoculated using 1 mL of prepared mycelia to one seedling, which was sprayied on soil. Control seedlings were inoculated with 1 mL distilled water containing 0.2% gelatin. After 10 days under 15/10℃, 16h/8h, all the inoculated plants had developed brown spots; while control plants remained healthy. The pathogens were reisolated from inoculated plants and identified as M. nivale and M. majus based on morphological characteristics and molecular methods described above. Although there are reports of M. majus associated with brown foot rot of wheat in Anhui Province and M. nivale associated with seedling blight of oat in Gansu Province (Chen et al. 2021; Tai et al. 2019). To our knowledge, this is the first report of brown foot rot of wheat caused by M. nivale and M. majus in China.

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.

A comparison of management regimes for one-year rotational set-aside within a sequence of winter wheat crops, and of growing wheat without interruption. 3. Effects on diseases

Different management regimes for 1-year rotational set-aside were tested in three experiments that followed winter wheat and started in autumn 1988–90. The regimes included operations that prevented the establishment of volunteers or allowed them to establish and persist until either spring or summer, and also altered the distribution of debris from the winter wheat that preceded the set-aside. For comparison, treatments in the set-aside year also included winter wheat.Samples taken in spring from the first test crop showed that there were few significant or consistent effects on leaf diseases of growing the wheat after different set-aside treatments or after winter wheat. There were significant effects of the set-aside treatments on root and stem base diseases but some of the effects, and the apparent absence of others, are not easily reconciled with current understanding of the biology of the pathogens concerned. In summer, eyespot (Pseudocercosporella herpotrichoides) was most severe after winter wheat and least severe after ryegrass. Severity after the other set-aside treatments did not differ significantly. There was more sharp eyespot (Rhizoctonia cerealis) in plots that had been ploughed at the start of the set-aside year, including those sown with winter wheat, than in those that had not. Brown foot rot (Fusarium spp.) was equally severe where the wheat followed wheat or where it followed set-aside treatments that allowed volunteers to develop, and less so where the development of volunteers was prevented. Take-all (Gaeumannomyces graminis var. tritici) was most severe after winter wheat and more severe after set-aside treatments that allowed volunteers to develop and survive through the winter than after those that did not. Effects of ryegrass (Lolium perenne ssp. multiflorum) on take-all in the following wheat were particularly variable, perhaps because ryegrass is a host of both the take-all fungus and of Phialophora graminicola, one of its principal antagonists.