Powdery Mildew Populations Research Articles

Study of new spring bread wheat cultivar quartet in multi location test according to the KASIB system

The results of the study of a new spring bread wheat cultivar Quartet, production by introgressive breeding for economically useful traits are presented. This cultivar have a combination genes Lr39(=Lr41) (from Aegilops tauschii), Lr19/Sr25 (7DS-7DL-7Ae#1L translocation from Agr. elonga-tum) and Lr26/Sr31/Yr9/Pm8 (1BL·1R#1S translocation from S. cereale) It has been established that this cultivar has good adaptability and plasticity both in the conditions of the Saratov region Russia and when tested according to the KASIB system (. This cultivar was not inferior to local cultivar standards, but in many regions significantly exceeded them in grain productivity. At the same time, the cultivar Quartet have the good bread making quality, even though it contains the 1BL·1R#1S translocation from S. cereale. The resistance of the cultivar Quartet to leaf rust populations has been established, both in the Lower Volga region and in Western Siberia and Kazakhstan, as well as to most local stem rust populations, including the dangerous Ug99 race of this pathogen. Cultivar Quartet was slightly affected by powdery mildew. When evaluating this cultivar according to the KASIB system, it gave a differentiated degree of damage by local powdery mildew populations and had a reaction from 0 to 3 points and a degree of damage from 0% to 40%, but it should be noted that Quartet was resistant to most pathogen populations. Evaluation of a new spring bread wheat cultivar Quartet for a number of agronomic valuable traits and adaptability, revealed the prospects of using a combination of translocations 7DS-7DL-7Ae#1L + 1BL•1R#1S, in combination with chromatin from Aegilops tauschii. At the same time, a compensatory effect of the cultivar L505 was observed in the Quartet, which reduces the negative impact on the quality of flour and dough of 1BL•1R#1S translocation.

Establishment of a strong Powdery Mildew Population – Experimental approaches to Remediation

Establishment of a strong Powdery Mildew Population – Experimental approaches to Remediation

Genetic control of juvenile resistance to powdery mildew in spring bread wheat cultivars from the VIR collection

Background. Bread wheat (Triticum aestivum L.) is one of the major food crops of humankind. Powdery mildew, caused by Blumeria graminis f. sp. tritici, is the most destructive foliar disease capable of causing great yield losses in epidemic years. Breeding for resistance to powdery mildew is the most economical and effective way to control this disease. By now, 68 loci were identified to contain more than 90 alleles of resistance to powdery mildew in wheat. However, there is a permanent necessity in finding new sources of resistance.The objective of the present study was to characterize the seedling powdery mildew resistance in some spring bread wheat varieties from the VIR collection and determine the inheritance of powdery mildew resistance in these accessions.Materials and methods. The powdery mildew resistant varieties ‘SW Kungsjet’ (k-66036), ‘SW Kronjet’ (k-66097), ‘Boett’ (k-66353), ‘Batalj’ (k-67116), ‘Stilett’ (k-67119) ‘Pasteur’ (k-66093) were crossed with a resistant line ‘Wembley 14.31’ (k-62557) containing the Pm12 gene, and with ‘SW Milljet’ (k-64434); the variety ‘Sibirka Yartsevskaya’ (k-38587) was used as a susceptible parent and control. The hybrid populations F2 were inoculated with the fungus population from local field and evaluated. The powdery mildew population manifested virulence to Pm1a, Pm2, Pm3a-f, Pm4a-b, Pm5a, Pm6, Pm7, Pm8, Pm9, Pm10, Pm11, Pm16, Pm19, Pm28, and avirulence to Pm12. The degree of resistance was assessed on days 8 and 10 after the inoculation using the Mains and Dietz scale (Mains, Dietz, 1930). The castrated flowers in the spikes were pollinated using the twell-method (Merezhko et al., 1973). Chi-squared for goodness of fit test was used to determine deviation of the observed data from the theoretically expected segregation.Results. According phytopathological and genetic tests, juvenile resistance in the varieties ‘SW Kungsjet’, ‘SW Kronjet’, ‘Boett’, ‘Batalj’, ‘Stilett’ and ‘Pasteur’ is controlled by dominant genes, which differ from Pm1a, Pm2, Pm3a-f, Pm4a-b, Pm5a, Pm6, Pm7, Pm8, Pm9, Pm10, Pm11, Pm12, Pm16, Pm19, and Pm28. The varieties ‘SW Milljet’, ‘SW Kronjet’ and ‘Pasteur’ had identical resistance genes. Genetic control of juvenile resistance to powdery mildew in ‘Batalj’, ‘Boett’, ‘Stilett’, ‘SW Milljet’, ‘SW Kungsjet’, ‘Pasteur’ was governed by different genes.Conclusions. The varieties ‘SW Kungsjet’, ‘SW Kronjet’, ‘Boett’ have been maintaining adult and seedling resistance since 2005, and ‘Batalj’, ‘Stilett’ and ‘Pasteur’ since 2017. Seedling resistance of these varieties to local powdery mildew population is controlled by dominant genes. A high degree of resistance was displayed by ‘SW Kungsjet’ and ‘SW Kronjet’ in the Novosibirsk Province, while ‘SW Kungsjet’ was resistant to mildew populations of Tatarstan. The variety ‘Pasteur’ manifested seedling resistance to leaf rust, and ‘SW Kungsjet’ was resistant to loose smut. By summing all the results, it may be suggested that the varieties ‘SW Kungsjet’, ‘SW Kronjet’, ‘Boett’, ‘Batalj’, ‘Stilett’ and ‘Pasteur can serve as good donors of powdery mildew resistance in wheat breeding.

Virulence Structure of the Wheat Powdery Mildew Population in Serbia

Powdery mildew is a common, economically important disease in the wheat growing area of Serbia. A large-scale virulence survey of its causal agent Blumeria graminis f. sp. tritici population was performed in the period 1995–2013. A total of 1013 isolates were recovered from the collected chasmothecial samples. Among them, 862 unique pathotypes were identified using a differential set of 20 wheat lines with known powdery mildew (Pm) resistant genes. The pathogen was highly diverse. Number of virulence genes (virulence complexity) per isolate was large, supporting a constant need to extend the differential set of wheat with newly identified Pm genes. Virulence frequencies to Pm6, Pm7, and Pm5+8 were high throughout the 19-year period, in contrast with that to Pm5+6, which was consistently at a low level. The most significant change in the population was observed for virulence to the Pm2+4b+6 gene combination, with an increasing frequency of virulence to this gene combination over the years. High virulence complexity and genetic diversity of the population are the most influential factors for the damaging epidemics that this pathogen can cause.

Virulence Structure of Blumeria graminis f. sp. avenae Populations in Poland across 2014-2015.

The purpose of this study was to determine the virulence structure of oat powdery mildew (Blumeria graminis f. sp. avenae, Bga) populations in Poland collected in 2014 and 2015. Powdery mildew isolates were collected from 18 locations in Poland. In total, nine lines and cultivars of oat, with different mildew resistance genes, were used to assess virulence of 180 isolates. The results showed that a significant proportion of the Bga isolates found in Poland were virulent to differentials with Pm1, Pm3, Pm6, and Pm3 + Pm8 genes. In contrast Pm4, Pm5, Pm2, and Pm7 genes were classified as resistant to all pathogen isolates used in the experiment. Based on obtained results we can state that there are differences in virulence pattern and diversity parameters between sites and years, but clear trends are not deducible.

Powdery mildew resistance of Nordic spring bread wheat accessions from the collection of the Vavilov Institute (VIR)

Background. Powdery mildew is one of the harmful and destructive foliar diseases of cereal crops, caused by the fungus Вlumeria graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal. Annual harvest losses may reach 10–15%, and up to 30% in an epidemic year. The VIR collection contains rich diversity of wheat, a valuable source of original material for wheat resistance breeding programs.The aim of this study was to generalize the results of long-term field and laboratory investigations on powdery mildew resistance in spring bread wheat of Nordic origin from the VIR collection and search for accessions resistant in all development phases.Materials and methods. Powdery mildew resistance was analyzed in 279 accessions originated from Sweden, Finland, Norway and Denmark. The tests were performed from 1961 to 2019 against a natural population of the fungus in VIR’s experimental field (Pushkin, St. Petersburg). Field and laboratory studies were carried out in accordance with the guidelines developed by VIR.Results. The analysis of the field data on powdery mildew resistance in spring bread wheat accessions against the Pushkin population of the fungus showed that many Nordic accessions were resistant from 1970 till 1990. These data were retested in 2012–2013. One hundred and five accessions of old landraces and modern cultivars of Nordic origin were studied under field and laboratory conditions for their response to a natural population of the fungus. Accessions resistant in all phases of plant development were identified.Conclusion. Swedish cultivars ‘Sunnan’ (k-58177), ‘Canon’ (k-60992), ‘Sober’ (k-61080) ‘Dragon’ (k-61515) and ‘Dacke’ (k-63479) preserved their resistance to the powdery mildew population beginning from 1993. Spring bread wheat cultivars ‘SW Vals’ (k-64436), ‘SW Milljet’ (k-64434), ‘SW Estrad’ (k-64435), ‘SW Vinjet’ (k-64436), ‘Zebra’ (k-64707), ‘SW Kungsjet’ (k-66036), ‘SW Kronjet’ (k-66097) and ‘Boett’ (k66353) demonstrated adult and seedling resistance in the period from 2005 to 2019.

Fungicide efficacy trials for the control of powdery mildew (Podosphaera cerasi) on sweet cherry trees (Prunus avium)

ABSTRACT Powdery mildew is a detrimental foliar disease of sweet cherry trees. The disease is predominantly managed by spraying synthetic fungicides throughout the growing season. The emergence of resistant powdery mildew populations, to some commonly used synthetic fungicides, highlights the need for research into alternative control methods. Between 2012 and 2015, the efficacy of two different biofungicides (Bacillus subtilis and Bacillus pumilus) and electrolysed oxidised (EO) water were evaluated to determine if they could be a viable replacement for four commonly used synthetic fungicides (fluopyram/trifloxystrobin, triflumizole, quinoxyfen and myclobutanil) in a greenhouse, nursery and commercial orchard. Electrolysed oxidised water and fluopyram/trifloxystrobin significantly lowered disease severity and incidence in all of the locations tested, however, biweekly applications of EO water had little effect on the fungus and weekly applications were phytotoxic in the nursery and greenhouse. Before EO water is implemented into integrated pest management programmes, the optimal spray frequency needs to be evaluated to eliminate its phytotoxic effects. The biofungicides evaluated in this study had minimal effects on powdery mildew severity and incidence and should not be recommended for control on sweet cherry trees. Currently, synthetic fungicides are the best method for the control of powdery mildew as fluopyram/trifloxystrobin was the only fungicide that was successful in lowering disease incidence and severity over the duration of the powdery mildew epidemic in both the nursery and greenhouse. Future research should evaluate integrated pest management strategies, including additional biofungicides, that could supplement and reduce synthetic fungicide applications.

Improved DNA extraction and quantitative real-time PCR for genotyping Erysiphe necator and detecting the DMI fungicide resistance marker A495T, using single ascocarps

DNA extraction from minute fungal samples is challenging in all genetic studies. Identification of genetic groups and population biology mostly rely on the laborious production of single conidium isolates or on field samples, including infected plant materials. This paper reports a simple and cost-effective protocol for DNA extraction from individual chasmothecia of Erysiphe necator for subsequent applications. It is a less laborious alternative for genotyping purposes than production and analysis of single conidium isolates or analysis of infected plant material from the field. Using the protocols described here for 186 E. necator samples tested, genetic groups A and B were assigned. Based on CYP51 sequences, all the samples belonged to group B, while TUB2 sequences exhibited SNPs also diagnostic for group A. Additionally, a quantitative real-time PCR detection method of single nucleotide polymorphism in the CYP51 gene associated with DMI fungicide resistance was applied. The A495T marker, associated with DMI resistance, and here reported for the first time from Hungary, was detected by quantitative real-time PCR assays and direct sequencing of CYP51. The methods developed in this study can be applied as routine tests to monitor powdery mildew populations for fungicide resistance and other genetic characteristics.

Improved DNA extraction and quantitative real-time PCR for genotyping Erysiphe necator and detecting the DMI fungicide resistance marker A495T, using single ascocarps

DNA extraction from minute fungal samples is challenging in all genetic studies. Identification of genetic groups and population biology mostly rely on the laborious production of single conidium isolates or on field samples, including infected plant materials. This paper reports a simple and cost-effective protocol for DNA extraction from individual chasmothecia of Erysiphe necator for subsequent applications. It is a less laborious alternative for genotyping purposes than production and analysis of single conidium isolates or analysis of infected plant material from the field. Using the protocols described here for 186 E. necator samples tested, genetic groups A and B were assigned. Based on CYP51 sequences, all the samples belonged to group B, while TUB2 sequences exhibited SNPs also diagnostic for group A. Additionally, a quantitative real-time PCR detection method of single nucleotide polymorphism in the CYP51 gene associated with DMI fungicide resistance was applied. The A495T marker, associated with DMI resistance, and here reported for the first time from Hungary, was detected by quantitative real-time PCR assays and direct sequencing of CYP51. The methods developed in this study can be applied as routine tests to monitor powdery mildew populations for fungicide resistance and other genetic characteristics.

Monitoring Methyl Benzimidazole Carbamate-Resistant Isolates of the Cucurbit Powdery Mildew Pathogen, Podosphaera xanthii, Using Loop-Mediated Isothermal Amplification.

Powdery mildew, caused by the fungus Podosphaera xanthii, is one of the most economically important diseases affecting cucurbit crops in Spain. Currently, chemical control offers the most efficient management of the disease; however, P. xanthii isolates resistant to multiple classes of site-specific fungicides have been reported in the Spanish cucurbit powdery mildew population. In previous studies, resistance to the fungicides known as methyl benzimidazole carbamates (MBCs) was found to be caused by the amino acid substitution E198A on β-tubulin. To detect MBC-resistant isolates in a faster, more efficient, and more specific way than the traditional methods used to date, a loop-mediated isothermal amplification (LAMP) system was developed. In this study, three sets of LAMP primers were designed. One set was designed for the detection of the wild-type allele and two sets were designed for the E198A amino acid change. Positive results were only obtained with both mutant sets; however, LAMP reaction conditions were only optimized with primer set 2, which was selected for optimal detection of the E198A amino acid change in P. xanthii-resistant isolates, along with the optimal temperature and duration parameters of 65°C for 75 min, respectively. The hydroxynaphthol blue (HNB) metal indicator was used for quick visualization of results through the color change from violet to sky blue when the amplification was positive. HNB was added before the amplification to avoid opening the lids, thus decreasing the probability of contamination. To confirm that the amplified product corresponded to the β-tubulin gene, the LAMP product was digested with the enzyme LweI and sequenced. Our results show that the LAMP technique is a specific and reproducible method that could be used for monitoring MBC resistance of P. xanthii directly in the field.

ПРОЯВЛЕНИЕ УСТОЙЧИВОСТИ К МУЧНИСТОЙ РОСЕ У ОБРАЗЦОВ ЯРОВОЙ МЯГКОЙ ПШЕНИЦЫ ИЗ КОЛЛЕКЦИИ ГЕНЕТИЧЕСКИХ РЕСУРСОВ РАСТЕНИЙ ВИР

Background. Powdery mildew caused by Blumeria graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal. is a widespread foliar disease of common wheat in regions with cool and wet conditions. The disease infects the foliage, stem and spike of the wheat host. The most economical and environmentally safe method for controlling powdery mildew is the development of resistant bread wheat cultivars. The objective of this work was to analyze wheat (Triticum aestivum L.) cultivars for resistance to a powdery mildew population. Materials and methods . The VIR collection of plant genetic resources is a rich source of genetic materials. The study of resistance to the fungus employed 465 common wheat cultivars. The plants were inoculated at the seedlings, heading and flowering stages of plant development. The population of fungus was virulent to Pm1, Pm2, Pm3a-d, Pm4a-b, Pm5a, Pm6, Pm7, Pm8, Pm9, Pm16, Pm19 and avirulent to Pm12. For the estimation of plant damage, a scale from 0 (no damage) to 4 (abundant pustules) was used. Results and conclusions . The estimation of powdery mildew resistance was made in the field on adult plants. Out of 465 cultivars, resistant accessions amounted to 10,5%, intermediate ones to 16.8%, and susceptible ones to 72.7%. Generally, the resistant varieties originated from Europe and Russia. The group of the resistant cultivars (adult plants) was inoculated with fungus at the seedling stage and the plant damage was estimated. The cultivars 'Kandela', 'Arabeska', 'Batalj', 'Stillet' were resistant at all growth stages. The genetic control of powdery mildew resistance at different wheat growth stages was discussed.

Virulence variation of cucurbit powdery mildews in the Czech Republic – population approach

Kosman diversity models were applied to analyses of virulence (disease reaction patterns) variation of 115 isolates of two cucurbit powdery mildew (CPM) species, Golovinomyces orontii (Go) and Podosphaera xanthii (Px), collected in the Czech Republic from 2010 through 2012. Diversity within and distances between Go and Px populations and each other in a spatio-temporal context and with regard to original host plant species were analyzed based on virulence patterns of individual isolates on a set of 21 melon (Cucumis melo L.) race differential genotypes. Significant differentiation among the Go and Px pathogen populations was revealed, and the results clearly demonstrate and confirm that the set of differential C. melo genotypes is well composed because of high differentiation capacity. Differentiation of pathogens among years was significant for both species. No significant difference between Go isolates from different host plant species was established due to high variability among Go isolates, but there was significant host-specific differentiation among Px isolates. Differentiation of pathogens among regions was not detected. These results revealed high virulence variation in isolates of Go and Px, and their spatio-temporal fluctuations. High diversity in virulence of Go isolates supports the treatment of Go as a complex of different (sub)species with distinct virulence factors. Similar relationships of selected Go isolates in a UPGMA dendrogram in a previously reported multigene phylogenetic tree support the logic and suitability of the Kosman assignment based approach to population studies of organisms with asexual or mixed modes of reproduction. The approach applied in this study provides a complex view of virulence structures of powdery mildew populations, and when combined with race determination and denomination on melon, it may serve as a base to understandvirulence variation of these CPM species from a spatio-temporal viewpoint.

Characterizing the pathotype structure of barley powdery mildew and effectiveness of resistance genes to this pathogen in Kazakhstan

BackgroundPowdery mildew of barley is a wind-borne and obligate biotrophic pathogen, which ranks among the most widespread barley pathogens worldwide. However, purposeful research towards studying the structure of the barley powdery mildew populations, of their virulence and of effectiveness of certain resistance genes against the infection was not conducted in Kazakhstan till present time. This paper is the first to describe characteristics of the pathotype structure of Blumeria graminis f.sp. hordei (Bgh) population and effectiveness of resistance genes in two regions of barley cultivation in the republic.ResultsOne hundred and seven isolates of Bgh were obtained from seven populations occurring on cultivated barley at two geographically locations in Kazakhstan during 2015 and 2016. Their virulence frequency was determined on 17 differential lines Pallas. All isolates were virulent on the resistance gene Mla8 and avirulent for the resistance genes Mla9, Mla1 + MlaAl2, Mla6 + Mla14, Mla13 + MlRu3, Mla7 + MlNo3, Mla10 + MlDu2, Mla13 + MlRu3 and Mlo-5. The frequencies of isolates overcoming the genes Mla3, Mla22, Mlat Mlg + MlCP and Mla12 + MlEm2 were 0.0–33.33%, and frequencies of isolates overcoming the genes Mlra, Mlk, MlLa and Mlh ranged from 10.0 to 78.6%. Based on reactions of differential lines possessing the genes Mla22, Mlra, Mlk, Mlat, MlLa and Mlh, pathotypes were identified. In total, 23 pathotypes with virulence complexity ranging from 1 to 6 were identified. During both years in all populations of South Kazakhstan and Zhambyl regions pathotypes 24 and 64 mainly prevailed.ConclusionsObtained data suggest that low similarity of populations Bgh in Kazakhstan to European, African, Australian and South-East Asian populations. The present study provides a foundation for future studies on the pathogenic variability within of Bgh populations in Kazakhstan and addresses the knowledge gap on the virulence structure of Bgh in Central Asia. Complete effectiveness of the resistance genes, for which no corresponding virulence was found, will allow Kazakhstanean breeders to access many modern barley cultivars that those possessing the resistance effectiveness genes.

Winter fungicide sprays impact the dynamics of vineyard Botrytis populations


 
 
 Botrytis populations in vineyards often show seasonal differences. Early season populations tend to be less pathogenic than those at harvest. This change probably reflects differences in competitive ability in winter versus summer conditions. Such a seasonal pattern was observed in a Waipara vineyard from 2008 to 2012. The population at owering was dominated by a Botrytis cinerea low pathogenicity haplotype; the population at harvest was dominated by a high pathogenicity haplotype. Since the 2013/2014 season, there has been a sudden change in this dynamic, with the high pathogenicity haplotype now dominant at both owering and harvest. This change in the seasonal dynamic was confirmed using microsatellite analysis. A possible explanation for the change in behaviour of the Botrytis populations was a change in management practice, with the addition over the past 2-3 seasons of a winter GelSeal spray for control of vascular pathogens. GelSeal is a trizole fungicide effective against Botrytis. The change to the vineyard spray programme may have disrupted the competitive advantage the low-pathogenicity population previously enjoyed over winter. The possible impact of this change on levels of disease will be discussed in relation to similar seasonal changes in European grape powdery mildew populations, where there is a strong relationship between early season populations and disease at harvest.
 
 

Virulence structure of the Blumeria graminis DC.f. sp. avenae populations occurring in Poland across 2010\u20132013

The aim of the present study was to determine the virulence structure of powdery mildew of oats (Blumeria graminis DC.f. sp. avena) in Poland in the years 2010–2013. For this purpose, powdery mildew isolates were collected from three experimental stations in Poland. To assess the virulence of the isolates, eight oat varieties with different responses to the pathogen were used. The results showed that a significant proportion of powdery mildew isolates found in Poland overcame the resistance genes of varieties Bruno (Pm6), Jumbo (Pm1) and Mostyn (Pm3). In contrast, lines Av1860 (Pm4), Am27 (Pm5) and Cc3678 (Pm2) were completely resistant to all pathogen isolates involved in the experiment. Changes constantly occurring in the powdery mildew population perfectly reflect diversity indexes, which were the smallest in the first year of observation, where in the following years these parameters were significantly higher. It is worth noting that the presence of powdery mildew is seasonal and local, which is reflected in the prevalence of the disease in a defined area of the country.

Responses of commercial wheat varieties and differential lines to western Australian powdery mildew (Blumeria graminis f. Sp. tritici) populations

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is an important disease of bread wheat (Triticum aestivum L.). Little is known about the powdery mildew population structure and the economic loss that occurs on commercial wheat cultivars in Western Australia. Eighteen wheat lines (including sixteen commercial wheat varieties, line 7HRWSN58 and a susceptible control) and a set of differential lines with known powdery mildew (Pm) resistant genes were evaluated using a cumulative pool of powdery mildew (Pm) inoculum each year to examine the changes in their responses over the years. Trials with a randomised block design were conducted under controlled environment over the years 2011 to 2014. Resistance genes Pm2, Pm3a, Pm3e, Pm4a, Pm13 and Pm27 were postulated to be effective in WA while genes Pm1a, Pm3c, Pm4b, Pm5a, Pm7, Pm17, Pm24 and Pm28 were ineffective. Differential lines carrying Pm6 and Pm8 genes were moderately resistant at adult plant stage but susceptible at seedling stage. Twelve out of sixteen commercial wheat varieties were susceptible or highly susceptible at seedling and adult plant stages lacking gene/s for resistance to powdery mildew. Most of these varieties were stable but some of the differential lines showed a breakdown in resistance over the four years. The cultivars Fortune, Magenta and Yitpi were moderately susceptible (MS) at adult plant stage but susceptible (S) at the seedling stage. The variety Arrino and line 7HRWSN58 were moderately resistant (MR) and resistant (R) to powdery mildew respectively.

Virulence phenotypes in powdery mildew (Blumeria graminis) populations and resistance genes in triticale (x Triticosecale)

Triticale (xTriticosecale) is a new host for powdery mildew (Blumeria graminis) being not infected by this pathogen in Germany before 2001. To evaluate population structure of the pathogen and race-specific resistances in the host, 694 isolates were collected in 12 states of Germany in the years 2007 to 2009 on triticale. They were tested by a newly developed initial differential set of 20 triticale cultivars. Corresponding virulences were found for all differentials except for cultivar Grenado. In total, 272 different virulence phenotypes (=pathotypes) were detected. The virulence complexity of the isolates ranged from 6 to 19 of 20 possible virulences with a mean of 15. In all years, a high level of diversity of the powdery mildew populations was observed with Simpson indices in the range 0.95 to 0.97. The distribution of the pathotypes was even across Germany with an Evenness index in the range 0.82 to 0.88. A set of 19 isolates with different virulence pathotypes and 10 cultivars were selected to be used to identify race-specific resistances of triticale cultivars and breeding lines. Some cultivars susceptible to most of the isolates in seedling stage were moderately resistant in adult-plant stage. The high diversity and complexity of the pathotypes found in German powdery mildew populations as well as an increasing acreage of only a few dominating triticale cultivars accelerate the adaptation of the pathogen to race-specific host resistances suggesting restricted durability only. More durable resistance might be achieved by combining new effective race-specific (qualitative) resistance genes with race-nonspecific (quantitative) resistances effective in the adult-plant stage that are already available.

The effect of quinone outside inhibitor fungicides on powdery mildew in a grape vineyard in Hungary

Powdery mildew, caused by Erysiphe necator Schwein., is one of the most important diseases of grapes worldwide. In the present study, nine treatments consisting of chemical compounds and combinations of these compounds were tested against powdery mildew on Vitis vinifera cv. Merlot CI 181 and cv. Italian Riesling GK1. The aim of this study was to examine the effect of quinone outside inhibitor (QoI) fungicides, also called strobilurins, on powdery mildew and to see if resistant strains of the fungus were present. QoI inhibitors had never been used before in the vineyard or a nearby vineyard. Powdery mildew infection severity was monitored in the experimental vineyard in Cserszegtomaj, Hungary. At the same time, weather conditions and their effect on powdery mildew infection levels were monitored. No differences were found between the cultivars Merlot CI 181 and Italian Riesling GK1 in powdery mildew severity. However, there were differences in powdery mildew severity depending on the chemical compound and combination of compounds tested. The QoI fungicides provided little or no control of powdery mildew infection, and powdery mildew severity was not significantly different from that in the untreated vines. This suggests that the population of powdery mildew in this experimental vineyard was resistant to QoI fungicides. In the other treatments the level of powdery mildew infection was either significantly lower than in the untreated vines or there was no infection at all. These results show that the use of QoI fungicides selected for QoI resistance in the powdery mildew population. These results provide a warning that, QoI-resistant powdery mildew strains are likely to be a problem in Hungary in the future.

Pathogenicity of Blumeria graminis f. sp. hordei in Australia in 2010 and 2011

A survey of the Australian barley powdery mildew (Blumeria graminis f. sp. hordei) population was conducted in 2010 and 2011. Three hundred and sixty-two isolates of the pathogen were collected from 18 locations across all six states of Australia. Thirty-two barley differentials were used and 11 genotypes were able to differentiate the population with virulence frequencies varying from 14.5 % to 96.6 %. Twenty-seven pathotypes were detected. Fifteen of them were found in both years and they represented 92.0 % of all isolates examined. No virulence was found on a further 16 major genes for resistance (Mla1, Mla3, Mla6, Mla7, Mla9, Mla10, Mla12, Mla13, Mla23, MlaN81, Mlh, MlLa, Mlp1, Ml(IM9), Ml(St) and mlo) indicating a relatively simple population and the ready availability of diverse sources of resistance. This paper reports the powdery mildew virulences present in Australia, provides intelligence for future resistance breeding and sets a basis for further virulence studies.

Evaluation of Resistance to Powdery Mildew in Triticale Seedlings and Adult Plants.

Triticale (×Triticosecale) is the intergeneric hybrid between the female parent wheat and the male parent rye. With the expansion of the triticale growing area, powdery mildew emerged on this new host and has become a significant disease on triticale. Recent research demonstrated that this "new" powdery mildew on triticale has emerged through a host range expansion of powdery mildew of wheat. Moreover, this expansion occurred recently and multiple times at different locations in Europe. An effective and environmentally sensitive approach to controlling powdery mildew involves breeding crop plants for resistance. The main goal of this study was to identify the presence of powdery mildew resistance in commercial triticale cultivars. First, the avirulence (AVR) genes and gene complexity carried by this new powdery mildew population on triticale were characterized. Virulence was identified for all the resistance genes evaluated in the present study, and virulence frequencies higher than 50% were recorded on the genes Pm3f, Pm5b, Pm6, Pm7, Pm8, and Pm17. Using molecular markers, the presence of resistance genes Pm3f and Pm17 was identified in certain triticale cultivars. The triticale cultivars were also evaluated for the presence of quantitative resistance at adult plant growth stages in a 2-year field experiment. Despite the high disease pressure, cultivars highly resistant at the adult-plant growth stages were identified. Because 'Grenado' also showed effective race-specific resistance, this cultivar could be of high value for breeding for durable resistance to powdery mildew. Altogether, this study reveals valuable information on the presence of powdery mildew resistance in commercial triticale cultivars, which can be used in breeding programs in triticale. Additionally, this study underscores the need to broaden the base of powdery mildew resistance in triticale through introgression and deployment of new sources of mildew resistance, including quantitative resistance.