Disease Management

Plants can be attacked by a variety of parasitic microorganisms, primarily fungi, bacteria, nematodes, and viruses. From 2001 to 2003, an average of 7% to 15% of the major world crops (wheat, rice, potato, maize, and soybean) were lost due to fungi and bacteria (Oerke, 2005). Along with weeds and insects, plant pathogens are the major biotic limitation to crop health and yield. Many of these pathogens are foliar and attack aboveground parts of plants, with inoculum spread by wind and rain. Examples are rust, powdery mildew, and foliar leaf pathogens such as the fungus Septoria. However, some of the most severe, intractable, and difficult to control pathogens are soil-borne pathogens, which live in the soil for part or all of their life cycle and interact with the soil biota and the edaphic environment. These pathogens can survive in the soil and infect the root systems of plants. Fungi, fungus-like Stramenopiles (Oomycetes) and nematodes are probably the most important of the soil-borne pathogens. Fungi are eukaryotic organisms that form threadlike filamentous hyphae that can spread through the soil and form resistant structures such as oospores or sclerotia. These structures allow the fungus to survive in the absence of the host, or during unfavorable environments such as heat, cold, or dry soils. When these resting structures encounter a seed or root in the soil, they are stimulated to germinate, chemotactically grow toward the root, and infect the epidermal cells. Some fungi can also destroy seedlings before they emerge from the soil. Once the root is infected, fungi can spread inside the root, rotting the root by producing enzymes and toxins. Fungi also destroy lateral roots, feeder roots, and root hairs. As a result, the plant loses its ability to absorb water and nutrients. Above ground, plants are stunted and show nutrient deficiencies, and yields are reduced. Some pathogens can also move up the roots to the base of the plant, girdling the base or infecting the lower stem. Finally, another group of fungal pathogens can induce wilt by colonizing the xylem system, restricting the conduction of water to the leaves

Impacts of previous crops on Fusarium foot and root rot, and on yields of durum wheat in North West Tunisia

The impacts of ten previous crop rotations (cereals, legumes and fallow) on Fusarium foot and root rot of durum wheat were investigated for three cropping seasons in a trial established in 2004 in Northwest Tunisia. Fungi isolated from the roots and stem bases were identified using morphological and molecular methods, and were primarily Fusarium culmorum and F. pseudograminearum. Under low rainfall conditions, the previous crop affected F. pseudograminearum incidence on durum wheat roots but not F. culmorum. Compared to continuous cropping of durum wheat, barley as a previous crop increased disease incidence more than fivefold, while legumes and fallow tended to reduce incidence.  Barley as a previous crop increased wheat disease severity by 47%, compared to other rotations. Grain yield was negatively correlated with the incidence of F. culmorum infection, both in roots and stem bases, and fitted an exponential model (R2 = -0.61 for roots and -0.77 for stem bases, P<0.0001). Fusarium pseudograminearum was also negatively correlated with yield and fitted an exponential model (R2 = -0.53 on roots and -0.71 on stem bases, P < 0.0001) but was not correlated with severity

Controlling root and crown diseases of small grain cereals [2012]

Published November 2012. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalogThis publication describes practices to manage and minimize losses from root and crown diseases of wheat and barley throughout the Pacific Northwest.Keywords: green bridge effect, wheat, seed treatment, small grain cereals, crown disease, barley, root disease, crop rotation, cereal crops, pathoge

Identification of Resistance to Pratylenchus neglectus and Pratylenchus thornei in Iranian Landrace Accessions of Wheat

The pathogenic nematodes Pratylenchus neglectus (Rensch, 1924) Filipjev and Schuurmans Stekhoven, 1941 and Pratylenchus thornei Sher and Allen, 1953 cause severe yield losses in wheat (Triticum aestivum L.). The objectives in this study were to assay a collection of Iranian landrace accessions collected from 12 provinces in Iran to identify novel sources of resistance to both species and to characterize agronomic traits critical for consideration in wheat breeding. Seventy-eight accessions were assayed for dual resistance to parasitic nematodes P. neglectus and P. thornei in controlled environment assays. Field trials conducted in Pullman, WA, and Pendleton, OR, evaluated stripe rust (Puccinia striiformis f. sp. tritici) resistance, days to heading, grain volume weight, plant height, seed protein content, seed kernel characterization, glume tenacity, and pubescence. The accessions were assayed with simple-sequence repeat (SSR), single-nucleotide polymorphism (SNP), and known vernalization markers for hierarchical cluster analysis to identify relatedness among accessions. Thirty-two accessions were identified as resistant or moderately resistant to both Pratylenchus species. Six were identified with moderate adult plant resistance to stripe rust in the field. The range of mean agronomic traits over locations was 53 to 105 cm for plant height, 46 to 84 d for post planting days to heading, and 151 to 728 kg m⁻³ for grain volume weight. The genetic cluster analysis identified three clusters based on the number of rare polymorphisms in the subset. The nematode resistance was distributed over the three clusters. The diversity within this subset could be useful for wheat breeders to integrate genetic variation and resistance to both Pratylenchus spp

Monitoring of host suitability and defense-related genes in wheat to Bipolaris sorokiniana

Spot blotch caused by Bipolaris sorokiniana is a destructive disease of wheat worldwide. This study investigated the aggressiveness of B. sorokiniana isolates from different wheat-growing areas of Bolu province in Turkey on the cultivar Seri-82. Host susceptibility of 55 wheat cultivars was evaluated against the most aggressive isolate. Our results indicated that the cultivars Anafarta and Koç-2015 were the most resistant. A specific and sensitive qPCR assay was developed for detecting the pathogen in plant tissues and evaluating wheat plants with different resistance levels. Three primer sets, BsGAPDHF/BsGAPDHR, BsITSF/BsITSR, and BsSSUF/BsSSUR, were designed based on glyceraldehyde-3-phosphate dehydrogenase, internal transcribed spacers, and 18S rRNA loci of B. sorokiniana with detection limits of 1, 0.1, and 0.1 pg of pathogen DNA, respectively. The qPCR assay was highly sensitive and did not amplify DNA from the other closely related fungal species and host plants. The protocol differentiated wheat plants with varying degrees of resistance. The assay developed a useful tool for the quantification of the pathogen in the early stages of infection and may provide a significant contribution to a more efficient selection of wheat genotypes in breeding studies. In the present study, expression levels of PR proteins, phenylalanine ammonia-lyase, catalase, ascorbate peroxidase, and superoxide dismutase enzymes were upregulated in Anafarta (resistant) and Nenehatun (susceptible) cultivars at different post-infection time points, but more induced in the susceptible cultivar. The results showed considerable variation in the expression levels and timing of defense genes in both cultivars

Relationship Between Climatic Factors and Distribution of Pratylenchus spp. in the Dryland Wheat-Production Areas of Eastern Washington

Field surveys were conducted by collecting soil samples to estimate nematode densities in soil from winter wheat, spring wheat, spring barley, and spring legumes (lentil, chickpea, and pea) fields during 2010 and 2011. Pratylenchus spp. were observed in 60% of sampled fields. However, nematodes were detected in nearly all of the survey fields in high numbers where crops were grown every year. To identify climatic variables associated with density of Pratylenchus spp. in soil, correlation and regression analyses were performed using climate data of survey sites from 1979 to 2010. Fifty-seven climate variables were significantly correlated with densities of Pratylenchus spp. All precipitation variables were significantly positively correlated with nematode abundance. Summer maximum air temperature was negatively correlated and winter minimum air temperature was positively correlated with nematode densities. In addition, both years’ nematode densities were significantly correlated with cropping intensity. Five multivariate regression models for 2010 and seven models for 2011 nematode abundance levels were developed. The majority of the climate variables selected in the models were related to precipitation. Knowledge of root-lesion nematode distribution in the dryland region of eastern Washington and associated climate variables may be helpful to determine risk and apply management practices to minimize crop damage

Acid soils How do they interact with root diseases?

Soil pH can have an influence on the outcome of root diseases caused by soilborne pathogens, but it depends on the pathogen. Cereal growers in the Pacific Northwest (PNW) have been experiencing an increase in soil acidity (lower pH) primarily due to a long history of ammonium fertilizer use. In eastern Washington and northern Idaho, soil acidification tends to be worse in areas that are annually cropped, do not include nitrogen-fixing legumes in the crop rotation, and in areas that were historically forested. Plant disease is the outcome of three interacting components: the pathogen, the plant, and the environment. Soil pH, a component of the environment, influences both the pathogen and the host

Acid soils : how do they interact with root diseases?

Soil pH can have an influence on the outcome of root diseases caused by soilborne pathogens, but it depends on the pathogen. Cereal growers in the Pacific Northwest (PNW) have been experiencing an increase in soil acidity (lower pH) primarily due to a long history of ammonium fertilizer use. In eastern Washington and northern Idaho, soil acidification tends to be worse in areas that are annually cropped, do not include nitrogen-fixing legumes in the crop rotation, and in areas that were historically forested. Plant disease is the outcome of three interacting components: the pathogen, the plant, and the environment. Soil pH, a component of the environment, influences both the pathogen and the host