Population Dynamics of Wheat Root Pathogens Under Different Tillage Systems in Northeast Oregon

Genome-wide characterization and expression analysis of the CINNAMYL ALCOHOL DEHYDROGENASE gene family in Triticum aestivum

BACKGROUND

CINNAMYL ALCOHOL DEHYDROGENASE (CAD) catalyzes the NADPH-dependent reduction of cinnamaldehydes into cinnamyl alcohols and is a key enzyme found at the final step of the monolignol pathway. Cinnamyl alcohols and their conjugates are subsequently polymerized in the secondary cell wall to form lignin. CAD genes are typically encoded by multi-gene families and thus traditionally organized into general classifications of functional relevance.

RESULTS

In silico analysis of the hexaploid Triticum aestivum genome revealed 47 high confidence TaCAD copies, of which three were determined to be the most significant isoforms (class I) considered bone fide CADs. Class I CADs were expressed throughout development both in RNAseq data sets as well as via qRT-PCR analysis. Of the 37 class II TaCADs identified, two groups were observed to be significantly co-expressed with class I TaCADs in developing tissue and under chitin elicitation in RNAseq data sets. These co-expressed class II TaCADs were also found to be phylogenetically unrelated to a separate clade of class II TaCADs previously reported to be an influential resistance factor to pathogenic fungal infection. Lastly, two groups were phylogenetically identified as class III TaCADs, which possess distinct conserved gene structures. However, the lack of data supporting their catalytic activity for cinnamaldehydes and their bereft transcriptional presence in lignifying tissues challenges their designation and function as CADs.

CONCLUSIONS

Taken together, our comprehensive transcriptomic analyses suggest that TaCAD genes contribute to overlapping but nonredundant functions during T. aestivum growth and development across a wide variety of agroecosystems and provide tolerance to various stressors.

Wheat rhizosphere dynamics of Trichoderma gamsii A5MH and suppression of a Pythium root rot-Fusarium crown rot disease complex over two consecutive cropping seasons

AIMS

Determine the wheat rhizosphere competence of Trichoderma gamsii strain A5MH and in planta suppression of the Pythium root and Fusarium crown rot pathogens Globisporangium irregulare and Fusarium pseudograminearum.

METHODS AND RESULTS

Wheat was continuously cropped (eight years) at a minimum tillage, low growing season rainfall (GSR ≤ 170 mm) site shown as highly conducive to Pythium root and Fusarium crown rots. Root isolation frequency (RIF) and qPCR were used to determine the rhizosphere dynamics of strain A5MH and the target pathogens at tillering, grain harvest, and in postharvest stubble over the final 2 years. Strain A5MH actively colonized the wheat rhizosphere throughout both growing seasons, had high root abundance at harvest [log 4.5 genome copies (GC) g-1] and persisted in standing stubble for at least 293-d postinoculation. Globisporangium irregulare was most abundant in roots at tillering, whereas F. pseudograminearum was only abundant at harvest and up to 9-fold greater in the drier, second year (GSR 105 mm). Strain A5MH decreased RIF of both pathogens by up to 40%, root abundance of G. irregulare by 100-fold, and F. pseudogaminearum by 700-fold, but was ineffective against crown rot in the second year when pathogen abundance was >log 6.0 GC g-1 root. Strain A5MH increased crop emergence and tillering biomass by up to 40%.

CONCLUSIONS

Further trials are required to determine if the A5MH-induced pathogen suppression translates to yield improvements in higher rainfall regions where non-cereal rotations reduce crown rot inoculum.

Long-Term Tillage and Crop Rotation Regimes Reshape Soil-Borne Oomycete Communities in Soybean, Corn, and Wheat Production Systems

Soil-borne oomycetes include devastating plant pathogens that cause substantial losses in the agricultural sector. To better manage this important group of pathogens, it is critical to understand how they respond to common agricultural practices, such as tillage and crop rotation. Here, a long-term field experiment was established using a split-plot design with tillage as the main plot factor (conventional tillage (CT) vs. no till (NT), two levels) and rotation as the subplot factor (monocultures of soybean, corn, or wheat, and corn-soybean-wheat rotation, four levels). Post-harvest soil oomycete communities were characterized over three consecutive years (2016-2018) by metabarcoding the Internal Transcribed Spacer 1 (ITS1) region. The community contained 292 amplicon sequence variants (ASVs) and was dominated by Globisporangium spp. (85.1% in abundance, 203 ASV) and Pythium spp. (10.4%, 51 ASV). NT decreased diversity and community compositional structure heterogeneity, while crop rotation only affected the community structure under CT. The interaction effects of tillage and rotation on most oomycetes species accentuated the complexity of managing these pathogens. Soil and crop health represented by soybean seedling vitality was lowest in soils under CT cultivating soybean or corn, while the grain yield of the three crops responded differently to tillage and crop rotation regimes.

Pest categorisation of Fusarium pseudograminearum

The EFSA Plant Health Panel performed a pest categorisation of Fusarium pseudograminearum O'Donnell & T. Aoki. F. pseudograminearum is a soil-borne fungal pathogen, able to cause a disease known as Fusarium crown rot (FCR, also known as foot and root rot) and occasionally Fusarium head blight on small grain cereals, particularly Triticum aestivum L., Triticum turgidum L. spp. durum (Dest.), Hordeum vulgare L. and triticale (xTriticosecale). In addition, F. pseudograminearum has been isolated from soybean (Glycine max L.) and from some grass genera, such as Phalaris, Agropyron and Bromus, which represent potentially important inoculum reservoirs. This pathogen has been reported in arid and semi-arid cropping regions in Australia, New Zealand, North and South America, northern Africa and South Africa, the Middle East and Asia. In the EU, it has been reported in Italy since 1994 and later in Spain on field-grown durum wheat, but uncertainty remains regarding the actual distribution of the pathogen in the EU. The pathogen is not included in the EU Commission Implementing Regulation 2019/2072. Seeds of host plants and soil and other substrates are the main pathways for the entry and spread of the pathogen into the EU. There are no reports of interceptions of F. pseudograminearum in the EU. Host availability and climate suitability occurring in the EU favour establishment of the pathogen and allow it to establish in areas from which it has not been reported. Phytosanitary measures are available to prevent the introduction of the pathogen into the EU, and additional measures are available to mitigate the risk of spread. In the non-EU areas of its present distribution, the pathogen has a direct impact on cultivated hosts (e.g. wheat, barley, triticale and soybean) that are also relevant for the EU. However, no crop losses have been reported so far in the EU. The Panel concludes that F. pseudograminearum satisfies all the criteria to be regarded as a potential Union quarantine pest.