Wheat diseases on the prairies: A Canadian story

Canada is one of the largest wheat producers in the world, and wheat is grown over an area spanning most of the southern latitudes, with the prairie region (provinces of Saskatchewan, Alberta, and Manitoba) being the main producer. Several pathogens and pests attack wheat, but at present fusarium head blight (FHB), stripe rust, and leaf spots are the most damaging diseases to wheat production in Canada. Historically, smuts, stem rust, and leaf rust caused major crop losses in Canada and can still pose serious threat if management practices are relaxed. Cropping practices used by Canadian farmers to grow and harvest wheat over the last century have influenced disease development and pathogen biology, affecting the severity, incidence, and prevalence of crop diseases over time. Changes such as reduced tillage coincide with emergence of residue-borne diseases, such as FHB and leaf spots, while the deployment of resistant cultivars and increased fungicide use has resulted in the reduction of common bunt, stem, and leaf rust. This review will discuss the influence of long-term cropping practices, alone or in combination, on the biology, emergence, and prevalence of wheat diseases in Canada over the last century.     

A unique race of the wheat stem rust pathogen with virulence on Sr31 identified in Spain and reaction of wheat and durum cultivars to this race

Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a re-emerging disease, posing a threat to wheat production. In Spain, stem rust has been rarely detected since the 1970s, but infection was observed in wheat fields in 2018. We analysed six stem rust samples collected in Rota, Cádiz province and one from Monteagudo del Castillo, Teruel province. All the samples from Rota were typed as race TKTTF, whereas the sample from Monteagudo del Castillo, collected in a wheat field adjacent to barberry bushes, was typed as race TKHBK. This race has a unique and significant virulence combination that includes virulence to Sr31, Sr33, Sr53 and Sr59, and is avirulent to Rusty, a durum line developed for universal susceptibility to the wheat stem rust pathogen. TKHBK is the first race outside the Ug99 race group with virulence to Sr31 and the first known race with virulence to Sr59. Genotyping studies indicate that race TKHBK does not belong to the Ug99 or TKTTF race groups and constitutes a previously unknown lineage. Two hundred bread and durum wheat cultivars and breeding lines from Spain were evaluated against TKHBK, TKTTF, and six additional races. Resistance was observed to all the races evaluated. Molecular markers confirmed the presence of Sr7a, Sr24, Sr31, Sr38 and Sr57 in bread wheat, and Sr13 in durum wheat. The re-emergence of wheat stem rust in Spain and the occurrence of unique virulences underscore the need to continue surveying and monitoring this disease.     

Breeding cereals for rust resistance in Australia

Rust diseases have caused significant losses to Australian cereal crops, and continue to pose a serious threat. Because Australian cereal crop yields are generally low, genetic resistance remains the most economical means of rust control. Resistant cultivars also contribute significantly to reducing over-summer rust survival. A policy of releasing only rust resistant wheats in northern New South Wales and Queensland has resulted in industry-wide protection from rust in this region for the past 40 years. The Australian Cereal Rust Control Program conducts annual pathogenicity surveys for all cereal rust pathogens, undertakes genetic research to identify and characterize new sources of resistance, and provides a germplasm screening and enhancement service to all Australian cereal breeding groups. These three activities are interdependent, and are closely integrated with particular emphasis on linking pathology and genetics to ensure breeding outcomes. Recent changes in the wheat rust pathogens, including the development of virulences for Yr17 , Lr24 , Lr37 and Sr38 resistance genes, and the introduction of a new pathotype of the wheat stripe rust pathogen, have provided new and significant challenges for wheat rust resistance breeding. Similar challenges exist in breeding barley and oats for rust resistance. Examples are discussed to illustrate the ways in which rust isolates are providing information that can be used in breeding for rust resistance. In future, as more markers linked to durable rust resistance sources become available, it is likely that the use of marker-assisted selection will become more common-place in rust resistance breeding.     

The relationship between wheat yield and stripe rust as affected by length of epidemic and temperature at the grain development stage of crop growth

Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici. was associated with mean losses of up to 84% in the yield of wheat in southern New South Wales, Australia, between 1984 and 1987. Yield loss became smaller in cultivars with increasing levels of resistance in adult plant reaction and did not appear in cultivars with seedling susceptibility and moderate or better adult plant reaction levels in the 3 years when epidemics began after emergence of the flag leaf. However, in 1984 the stripe rust epidemic began during stem elongation, and yield losses of up to 21% occurred in cultivars with seedling susceptibility and a moderate or better adult plant reaction.
Yield was significantly negatively correlated with the proportion of leaf area affected by stripe rust at stages of crop development from the end of heading to late milk. The correlation was greatest at the early milk stage of growth where the relationship was logarithmic. Two factors significantly influenced this relationship. Yield loss increased as the length of the epidemic increased, and decreased as temperature increased during grain development. The relationship that was developed for predicting yield loss accounted for 80-5% of the variance across all experiments, and was:
y = 100(1- e ^10-4×(393+165 L -141 T ))
where y = yield loss (%); X = stripe rust (leaf area affected, range 0-99%) at early milk; L = time from 1% disease to early milk (range 0-70 days); and T = mean daily maximum temperature from 7 days before to 14 days after early milk (range 198-27.5°C).     

Influence of intra-row cruciferous surrogate weed growth on crop yield in organic spring cereals

In Northern Europe, inter-row hoeing has become a popular tactic for controlling weeds in organic cereals. Hoeing is highly effective and can be implemented from crop emergence until stem elongation to maintain a nearly weed-free inter-row zone. However, hoeing has a lesser effect on weeds growing in the intra-row zone, where crop–weed proximity results in heightened competition. In the hoed cereal system, it is investigated whether tall-growing, competitive, cruciferous weeds in the intra-row zone affect crop biomass, yield and thousand kernel weight (TKW). An additive experimental design is employed to enable the fitting of rectangular hyperbolas, describing and quantifying the effects of increasing intra-row surrogate weed density on crop growth parameters. Regressions were studied under the influence of crop (spring barley and spring wheat), row spacing (narrow [12.5 or 15.0 cm] and wide [25.0 cm]) and nitrogen rate (50 and 100 kg NH₄-N/ha). Cruciferous surrogate weeds were found to impact crop yield and quality severely. For example, ten intra-row plants/m² of surrogate weed Sinapis alba reduced grains yields by 7%–14% in spring barley and by 7%–32% in spring wheat with yield losses becoming markedly greater in wheat compared to barley as weed density increases. Compared to wheat, barley limited yield and quality losses and suppressed intra-row weed growth more. Row spacing did not have a consistent effect on crop or weed parameters; in one of six experiments, the 25 cm row spacing reduced yields and increased intra-row weed biomass in wheat. Nitrogen rate did not affect crop or weed parameters. Results warrant the implementation of additional tactics to control intra-row weeds and limit crop losses.     

Yield reduction in wheat by simulated rat damage

Abstract

A study of simulated rat damage was done to determine the loss of wheat yield when O (control). 10, 30 and 50% ot the wheat stems were cut at tillering, booting, dough and mature crop stages. The yields at harvest from each of 128 1‐m² plots were compared by analysis of variance and least significant difference tests. Yield at the tillering stages was not significantly different from the controls but yields at all other stages differed significantly. Yield losses in tillering and booting stages were not significant for the different damage levels except for 50% stem cutting at the booting stage. The yields from dough and mature crop stages at all damage levels were significantly lower than yields from controls. No significant differences in yield at all growth stages were observed between control plots and those receiving 10% damage, but 30 and 50% damage gave significant losses.     

Hyperspectral signal decomposition and symptom detection of wheat rust disease at the leaf scale using pure fungal spore spectra as reference

This study establishes a method to detect and distinguish between brown rust and yellow rust on wheat leaves based on hyperspectral imaging at the leaf scale under controlled laboratory conditions. A major problem at this scale is the generation of representative and correctly labelled training data, as only mixed spectra comprising plant and fungal material are observed. For this purpose, the pure spectra of rust spores of Puccinia triticina and P. striiformis, causal agents of brown and yellow rust, respectively, were used to serve as a spectral fingerprint for the detection of a specific leaf rust disease. A least-squares factorization was used on hyperspectral images to unveil the presence of the spectral signal of rust spores in mixed spectra on wheat leaves. A quantification of yellow and brown rust, chlorosis and healthy tissue was verified in time series experiments on inoculated plants. The detection of fungal crop diseases by hyperspectral imaging was enabled without pixel-wise labelling at the leaf scale by using reference spectra from spore-scale observations. For the first time, this study shows an interpretable decomposition of the spectral reflectance mixture during pathogenesis. This novel approach will support a more sophisticated and precise detection of foliar diseases of wheat by hyperspectral imaging.     

The use of host resistance in disease management of rust in common bean

Bean rust, caused by Uramyces appendiculatus, is one of the major diseases in dry and snap bean production world-wide. Numerous advancements in disease management have been made to reduce rust losses. Host resistance is an important component of rust management. However, durability of disease resistance has often been short due to the use of single genes for resistance interacting with extremely high virulence diversity of the bean rust fungus. The challenge to increase durability of resistance has led to strategies such as gene pyramiding of race-specific resistance, selection and use of partial resistance, and investigation and discovery of leaf morphological features that may slow the rust epidemic. Germplasm with multiple sources of rust resistance has been developed in specific bean seed classes and released for public and commercial use in intensive production systems such as those in the United States. However, progress to develop rust resistant germplasm for the subsistence agriculture of Latin America and Africa where intercropping and mixed cultivars dominate the production system has been slow. Incorporation of high yielding, disease-resistant components as partial replacement in farmer's mixtures has the potential to reduce severity in the crop and increase yield in the presence of rust. This strategy would not erode the genetic diversity that is historically known to enhance resistance durability and for many years has given stability in production in the subsistent agriculture systems.     

Crop damage and yield loss caused by two species of rodents in irrigated fields in northern Nigeria

We investigated the damage and yield loss caused by two rodent species, Arvicanthis niloticus and Mastomys (Praomys) natalensis, in cereal crops in fields near Kano, northern Nigeria from August, 1990 to April, 1992. Using the random cluster technique, we selected 100 clusters of 30 hills in each rice and wheat field, and assessed damage fortnightly, using the Cut Tiller Count method. In premature crops, damage increased from tillering stages to the dough stages. Differences in the percentages of damage (yield loss) in mature rice (4.8% in 1990 and 12.6% in 1991) and in wheat (30.0% in 1991 and 21.7% in 1992) were statistically significant between years. Severe yield losses in wheat, compared to low and moderate levels in rice (grown for the most part during the rains), were probably a result of greater consumption of the wheat, grown entirely by irrigation during the dry season when other rodent food sources were less abundant. Results of ANOVA showed significant effects of developmental stage of the crop, year of cultivation, and their interactions on the magnitude of crop damage.     

小麦条锈病抗病遗传及菌源基地基因布局研究进展

小麦条锈病是世界范围内严重影响小麦生产安全的重要病害。我国是世界上最大的小麦条锈病流行区,自成独立的流行体系。培育和种植抗病品种是防治病害最有效的措施。然而,小麦品种对条锈病的抗性常常由于病菌新小种的产生而丧失,这既是一个重大科学问题,也是一个亟待研究解决的生产实际问题。如何有效、合理地利用小麦的抗病性,植病学家和育种学家进行了一个多世纪的研究与探索,提出了各种理论与策略,开展了各种实践与探索。该文就小麦抗条锈病遗传及其基因布局研究进展进行综述,主要包括抗性鉴定评价、抗病基因发掘与利用、数量抗性位点定位、抗病基因克隆与功能解析、近等基因系创建与应用,以及抗源创制、抗病生态育种和大区基因布局等,并对深入开展抗条锈病基因发掘与利用和大区基因布局进行展望,以期为抗病育种和病害持续治理提供参考。     

An SMS based system for surveillance of wheat rust diseases: a pilot initiative in Central Anatolia region in Turkey

Rust diseases (Puccinia spp.), namely stripe, leaf and stem rusts, are among the major diseases of wheat. Their management requires integrated approaches including timely surveillance, speedy communication and rapid response. This surveillance system was developed in order to facilitate participation of extension offices (in provinces/districts) in the survey of wheat rust diseases and sharing of information quickly. The SMS based system was tested as a pilot tool in the Central Anatolia region of Turkey connecting 25 districts in 5 provinces through an SMS network during the rust development period (April–July) in 2013. The observations from 268 fields indicated that leaf rust and stem rust development was insignificant in the districts covered, occurring in only 2.3% and 1.9% of the fields respectively. Stripe rust prevalence was higher occurring in 44.8% of the fields. Of the inspected fields 2.5% had infected plant incidences between 15% and 40% requiring control measures. Using the SMS reports received from the extension officers, the system facilitated daily monitoring of rust development and exchange of observations among the relevant institutions, also sending out alert messages to designated authorities as necessary. The study demonstrated that the system can serve as a rapid surveillance and communication tool to facilitate timely decision making and rapid response to prevent wheat rust epidemics.     

PUCREC/PUCTRI – a decision support system for the control of leaf rust of winter wheat and winter rye*

During a three‐year project from 2003 to 2006, two models have been developed to predict leaf rust (Puccinia recondita and P. triticina) occurrence and to simulate disease incidence progress curves on the upper leaf layers of winter rye (PUCREC) and winter wheat (PUCTRI). As input parameters the models use air temperature, relative humidity and precipitation. PUCREC and PUCTRI firstly calculate daily infection favourability and a cumulative infection pressure index and, in a second step, disease incidence is estimated. An ontogenetic model (SIMONTO) is used to link disease predictions to crop development. PUCREC and PUCTRI have been validated with data from 2001 to 2005. Both models give satisfactory results in simulating leaf rust epidemics and forecasting dates when action thresholds for leaf rust control are exceeded.     

Characterisation of kernel resistance against <Emphasis Type="Italic">Fusarium</Emphasis> infection in spring wheat by baking quality and mycotoxin assessments

Fusarium head blight (FHB) of wheat heads by Fusarium culmorum causes serious yield losses and compromises the end-use quality by accumulation of mycotoxins and alteration of baking characteristics. The most promising control strategies against the disease combine adequate cropping techniques (i.e. crop rotation avoiding maize as a preceding crop) with the use of resistant varieties. Different types of resistance against this disease have been described such as the resistance to primary infection of the spikelets and the reduction of spread of the infection in other parts of the ear. In recent years, the ability of the kernels to prevent penetration of the fungus and mycotoxin accumulation has received increasing attention. Yet, the detection of kernel resistance for breeding purposes is rather difficult, as the corresponding resistance mechanisms are not fully understood. The aim of the present work is to compare different aspects of kernel resistance in order to define the most significant criteria for breeding purposes. The experimental set up included eight modern Swiss spring wheat varieties grown on small irrigated yield plots (3 × 1.5 m) inoculated at anthesis with a mixture of Fusarium culmorum isolates. Disease ratings from 7 to 28 days post-inoculation were completed with post-harvest analyses for the accumulation of the mycotoxin deoxynivalenol and different baking quality parameters. Results indicate that the accumulation of the mycotoxin deoxynivalenol in the kernels is correlated with visible symptoms on the ear before harvest. In terms of baking quality parameters, water absorption, dough softening and dough resistance are impaired in susceptible varieties after FHB infection, while resistant varieties are not affected. The results obtained here indicate that kernel resistance can be defined by low deoxynivalenol accumulation in the kernels and by stability of several baking quality parameters under conditions of high FHB infection pressure.     

Genetic variation in partial resistance to leaf rust in winter wheat: disease progress,foliage senescence and yield reduction

Relations between leaf rust progress, foliage senescence and yield reduction were studied for seven winter wheat genotypes, differing in their partial resistance to leaf rust. Leaf rust accelerated leaf and ear senescence. Photosynthesis measurements showed, however, that the photosynthetic capacity of the remaining green surface was not affected. Differences between genotypes in yield reduction were largely explained by differences in leaf senescence and, therefore, in cumulative light interception (r=0.83) and crop photosynthesis. Reduction in cumulative light interception was closely related to the area under the disease-progress-curve (r=0.85), which was also closely associated with yield reduction (r=0.88). However, the time taken to reach a 50% reduction of green leaf area and the pustule density on 1 July (i.e. halfway through the epidemic) were just as good predictors of yield reduction as cumulative light interception and area under disease-progress-curve, suggesting that the former are useful criteria in the selection for partial resistance to leaf rust.Samenvatting De relatie stussen de epidemiologie van bruine roest, bladveroudering en oprengstderving werden bestudeerd bij zeven wintertarwegenotypen die verschilden in partiële resistentie tegen bruine roest. Bruine roest versnelde de veroudering van blad en aar. Fotosynthesemetingen wezen echter uit dat de fotosynthesecapaciteit van het resterende groene oppervlak niet werd beïnvloed. Verschillen tussen de genotypen in opbrengstderving werden voornamelijk veroorzaakt door verschillen in bladveroudering en daarmee in cumulatieve lichtinterceptie (r=0.83) en gewasfotosynthese. De reductie in cumulatieve lichtinterceptie was nauw gerelateerd aan de cumulatieve ziektedruk (in puistdagen) (r=0.85), welke ook nauw was geassocieerd met de opbrengstderving (r=0.88). De opbrengstreductie werd echter even goed voorspeld door de tijdsduur tot 50% reductie van het groene bladoppervlak en de puistdichtheid halverwege de epidemie als door cumulatieve lichtinterceptie en cumulatieve ziektedruk, waardoor beide eerste criteria gebruikt kunnen worden in de selectie voor partiële resistentie tegen bruine roest.     

Fourth International Conference on Spices

Abstract

The present article suggests a simple procedure for estimating yield and production losses in a given crop and region. The utility of the procedure is illustrated by an empirical application to bean production in Cauca Valley, Colombia. Using data obtained from direct field observations on a panel of farms, a production function approach is used to estimate yield and production losses caused by each of the yield constraints identified. It is expected that such estimates will be useful for establishing agricultural research priorities. In an empirical analysis of bean production in Cauca Valley, six important yield limiting factors were identified. Unfavourable rainfall conditions caused a yield loss of about 32% and a total production loss of about US $1.2 million for the region during one growing season. The production losses caused by rust and bacterial blight were slightly smaller. Other important yield constraints were Empoasca kraemeri, angular leaf spot and the use of noncertified seed. Small production increases could be obtained by increasing input use and plant population.     

Simulation of yield reduction by leaf rust in winter wheat,applied to the analysis of genetic variation in partial resistance

Differences in yield reduction among seven winter wheat genotypes due to leaf rust, as observed in a field experiment, were analysed using a simulation model. In this model, the effects of the disease on crop growth and yield were described on the basis of light interception, photosynthesis, respiration and assimilate partitioning. The model properly described the observed yield difference between the genotypes, both in the absence and in the presence of leaf rust. According to the model, 66% of total yield reduction was due to an accelerated decrease in green leaf area and 18% was due to light capture by dead leaf tissue at the top of the canopy. Genetic variation in yield reduction was, therefore, mainly explained by variation in leaf senescence. Leaf rust did not affect the photosynthetic rate of the remaining green leaf area. Opportunities of selection for individual damage components were assessed from their simulated effect on grain yield, together with their estimated genetic and environmental variance.Samenvatting Verschillen tussen zeven wintertarwegenotypen in opbrengstderving door bruine roest, zoals waargenomen in een veldexperiment, werden geanalyseerd met een simulatiemodel. In dit model werd het effect van de ziekte op gewasgroei en opbrengst beschreven op basis van lichtinterceptie, fotosynthese, ademhaling en assimilatenverdeling. Het model gaf een goede beschrijving van de waargenomen opbrengstverschillen tussen de genotypen, zowel bij aanwezigheid als bij afwezigheid van bruine roest. Van de totale opbrengstreductie werd, volgens modelberekeningen, 66% veroorzaakt door versnelde afname van groen bladoppervlak en 18% door het wegvangen van licht door dood bladweefsel boven in het gewas. De genetische variatie in opbrengstreductie werd zodoende vooral verklaard uit de waargenomen verschillen in bladveroudering tussen de genotypen. De fotosynthese per eenheid resterend groen bladoppervlak werd niet beïnvloed door bruine roest. Respectieven voor selectie op afzonderlijke schadecomponenten werden geëvalueerd op basis van hun gesimuleerde effect op korrelopbrengst, in combinatie met hun genetische en toevalsvariatie.     

Temperature-sensitive wheat stem rust resistance gene Sr15 is effective against Puccinia graminis f. sp. tritici race TTKSK

The wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), race TTKSK and related races pose a serious threat to world wheat production. Knowing the effectiveness of wheat stem rust resistance (Sr) genes against Pgt race TTKSK is fundamental in mitigating this threat through resistance breeding. Sr15 was previously identified as being ineffective against Pgt race TTKSK. Here, multirace disease phenotyping data, linkage analyses, allelism testing and haplotype analyses are presented to support the conclusion that Sr15 is effective against Pgt race TTKSK. Resistance to race TTKSK was mapped to Sr15 in a biparental population. Thirty-two accessions with Sr15 displayed seedling resistance phenotypes against race TTKSK. However, these accessions were susceptible as seedlings at high temperatures (22–25 °C), consistent with previous reports that the interaction between avirulent Pgt isolates and Sr15 is temperature-sensitive. Markers STS638, wri4 and KASP_IWB30995 were found to predict the presence of Sr15, suggesting the utility of these assays for marker-assisted selection in breeding programmes. The effectiveness of Sr15 to specific Pgt races and temperatures makes it a less-desirable TTKSK-effective gene. Wheat lines assayed as resistant to race TTKSK at the seedling stage may possess Sr15 and breeders should be aware of the limitations of Sr15 for conferring stem rust resistance.     

Yield Reduction in Wheat in Relation to Leaf Disease From Yellow (tan) Spot and Septoria Nodorum Blotch

Yellow or tan spot (caused by Pyrenophora tritici-repentis) and septoria nodorum blotch (caused by Phaeosphaeria nodorum) occur together and are a constraint to wheat yields in Australia. Recently, higher crop yields and lower fungicide costs have made fungicides an attractive management tool against these diseases. Yield-loss under different rates of progress of yellow spot and septoria nodorum blotch was examined in four experiments over three years to define the relationship between disease severity and yield. In these experiments, differences in disease were first promoted by inoculations either with P. tritici-repentis-infected stubble or aqueous spore suspensions of P. nodorum. Disease progress was further manipulated with foliar application of fungicide. The pattern of disease development varied in each year under the influence of different rainfall patterns. The inoculation and fungicide treatments produced differences in disease levels after flag leaf emergence. The infection of yellow spot or septoria nodorum blotch caused similar losses in grain yield, ranging from 18% to 31%. The infection by either disease on the flag or penultimate leaf provided a good indication of yield-loss. Disease severity on flag leaves during the milk stage of the crop or an integration of disease as area under the disease progress curve on the flag leaves based on thermal time explained more than 80% variance in yield in a simple regression model. The data provided information towards the development of disease management strategies for the control of septoria nodorum blotch and yellow spot.     

Molecular marker mapping of leaf rust resistance gene lr46 and its association with stripe rust resistance gene yr29 in wheat

ABSTRACT Leaf and stripe rusts, caused by Puccinia triticina and P. striiformis, respectively, are globally important fungal diseases of wheat that cause significant annual yield losses. A gene that confers slow rusting resistance to leaf rust, designated as Lr46, has recently been located on wheat chromosome 1B. The objectives of our study were to establish the precise genomic location of gene Lr46 using molecular approaches and to determine if there was an association of this locus with adult plant resistance to stripe rust. A population of 146 F(5) and F(6) lines produced from the cross of susceptible 'Avocet S' with resistant 'Pavon 76' was developed and classified for leaf rust and stripe rust severity for three seasons. Using patterns of segregation for the two diseases, we estimated that at least two genes with additive effects conferred resistance to leaf rust and three to four genes conferred resistance to stripe rust. Bulked segregant analysis and linkage mapping using amplified fragment length polymorphisms with the 'Avocet' x 'Pavon 76' population, F(3) progeny lines of a single chromosome recombinant line population from the cross 'Lalbahadur' x 'Lalbahadur (Pavon 1B)', and the International Triticeae Mapping Initiative population established the genomic location of Lr46 at the distal end of the long arm of wheat chromosome 1B. A gene that is closely linked to Lr46 and confers moderate levels of adult plant resistance to stripe rust is identified and designated as Yr29.