Soilborne wheat mosaic disease (SBWMD), originally attributed to infections by Soilborne wheat mosaic virus (SBWMV) and Wheat spindle streak mosaic virus (WSSMV), is one of the most frequent virus diseases and causes economic losses in wheat in southern Brazil. This study aimed to characterize molecularly the viral species associated with wheat plants showing mosaic symptoms in Brazil. Wheat leaves and stems displaying mosaic symptoms were collected from different wheat cultivars in Passo Fundo municipality, Rio Grande do Sul State, southern Brazil. Double‐stranded RNA was extracted and submitted to cDNA library synthesis and next‐generation sequencing. No sequences of SBWMV and WSSMV were detected but the complete genome sequence of a putative new member of the family Benyviridae was determined, for which the name wheat stripe mosaic virus (WhSMV) is proposed. WhSMV has a bipartite genome with RNA 1 and RNA 2 organization similar to that of viruses belonging to Benyviridae. WhSMV RNA 1 has a single open reading frame (ORF) encoding a polyprotein with putative viral replicase function. WhSMV RNA 2 has six ORFs encoding the coat protein, the major protein (read‐through), triple gene block movement proteins (TGB 1, 2 and 3) and ORF 6 (hypothetical protein). In addition to the genomic organization and nucleotide and amino acid sequence identities, phylogenetic analyses also corroborated that WhSMV is a virus species of the Benyviridae. However, isolates of WhSMV formed a clade distinct from members of the genus Benyvirus. It was also demonstrated that the plasmodiophorid Polymyxa graminis is associated with wheat roots showing SBWMD symptoms and infected by WhSMV.

Soil-borne wheat mosaic disease (SBWMD) caused by wheat stripe mosaic virus (WhSMV) is one of the most important viral diseases of wheat in Brazil. Farmers have used crop rotation (CR) successfully to reduce the incidence of many diseases in wheat. CR can contribute along with genetic resistance in the management of SBWMD. The objective of this study was to evaluate the effect of CR in SBWMD incidence and wheat yield as compared with wheat monoculture (W). During 2017 and 2018 growth seasons, in a long-term experiment, W and three CR: W1white oats-wheat; W2vetch-white oats-wheat; and W3black oatsbarley-black oats-wheat were evaluated using three wheat cultivars: BRS Parrudo (resistant), BRS Reponte (moderately resistant) and BRS Guamirim (susceptible). The rainiest season (2018) was more favorable to the development of the disease. In this year, CR W2 and W3 significantly decreased SBWMD incidence by 90% compared to wheat monoculture. Also, grain yield (GY) differences between CR were higher in the rainiest season. GY increases up to 58% (BRS Reponte), 81% (BRS Guamirim) and 106% (BRS Parrudo) in W2 and W3. The use of plant species that are non-hosts of WhSMV may be one of the main factors that contribute to the reduction of SBWMD levels.

No-till system and high plant density are common practices in soybean crops of the Brazilian southern region, which has increased the incidence of stem and pod diseases. The objective of this study was to evaluate the effect of plant populations on stem blight incidence. The experiments were conducted in Muitos Capões Municipality, Rio Grande do Sul State, during the seasons 2006/07 and 2007/08, using cultivars BRS 255 RR and CD 213 RR. The evaluated populations had 12, 18, 24, 30 and 36 plants m-2, spaced 0.45 m between rows. The experimental plot units consisted of 5m width and 10m length, arranged in randomized blocks with four replicates. Stem blight incidence was quantified at phenological stages R5.1, R5.5, R6 and R7 and the collected data underwent regression analysis. Higher soybean plant densities caused a positive and significant increase on stem blight incidence in all four phenological stages for both cultivars and seasons. There was no significant difference for soybean grain yield according to the increase in plant population. Results indicated that soybean management preventing high plant densities can contribute to reduce stem blight incidence.

Occurrence of rice seeds infected by Fusarium graminearum has shown the importance of identifying the most favorable phenological stage of panicles to grain infection. The experiments were conducted in two crop seasons under greenhouse conditions, using the rice hybrid INOV CL. The phenological stages during inoculation were complete booting, full heading and flowering. All plots were inoculated using two isolates of Fusarium graminearium species complex 15A (F. graminearium - 15-ADON) and FmNiv (F. meridionale - Nivalenol). Disease severity was estimated at weekly intervals and was used to calculate the area under the disease progress curve (AUDPC), while panicles were collected to determine the percentage of spotted grains and Fusarium incidence. Percentage of spotted grains and incidence of F. graminearum and F. meridionale were greater when inoculation was made during flowering stage, significantly differing from heading and booting stages. Rice flowering stage is more susceptible to infection by F. graminearum and F. meridionale, inducing higher disease severity and incidence of spotted grains, as well as presence of fungi in the grains. Flowering was the most susceptible stage in the two crop seasons for both isolates, and the complete booting stage presented the lowest values of AUDPC.