Evaluation on Potential Risk of the Emerging Yr5-Virulent Races of Puccinia striiformis f. sp. tritici to 165 Chinese Wheat Cultivars

In 2017, a new race (TSA-6) of the wheat stripe rust pathogen, Puccinia striiformis f. sp. tritici, virulent to resistance gene Yr5 were detected in China. However, whether Chinese wheat cultivars are resistant to the new races was unknown. In this study, two isolates (TSA-6 and TSA-9) with virulence to Yr5 were tested on other wheat Yr gene lines for their avirulence/virulence patterns and used, together with prevalent races CYR32 and CYR34 without the Yr5 virulence, to evaluate 165 major Chinese wheat cultivars for their reactions. Isolates TSA-6 and TSA-9 had similar but different virulence spectra, and therefore should be considered as two different races. Their avirulent/virulence patterns were remarkably different from that of CYR34 but quite similar to that of CYR32. Of the 165 wheat cultivars, 21 had all-stage resistance to TSA-6, 34 to TSA-9, and 20 to both races. Adult-plant resistance (APR) was detected in 35 cultivars to TSA-6 and 27 to TSA-9, but only 3 cultivars showed APR to both new races. Slow rusting resistance was observed in 24 cultivars to TSA-6 and of 33 to TSA-9. Analysis of variance (ANOVA) of disease index indicated a significant difference among cultivars, but not among the four races. Based on the molecular marker data, a low percentage of wheat cultivars carried Yr5, Yr7, Yr10, Yr15, Yr26, and/or YrSP. As TSA-6 and TSA-9 can be a serious threat to wheat production in China, monitoring TSA-6, TSA-9, and other races are continually needed.

Response of durum wheat lines to the cause agent of leaf rust Puccinia triticina

Аbstract. The response of 1262 durum wheat lines to the cause agent of leaf rust Puccinia triticina was studied. The investigation was carried under infection field conditions during 2013-2015 at Dobrudzha Agricultural Institute (DAI) – General Toshevo, Bulgaria. Over the years of investigation, a maximum high infection background was developed by the cause agent of the disease, including all pathogen pathotypes identified during this period. The race variability in the population of the pathogen during the period was determined at the Plant Pathology Laboratory of DAI according to a validated methodology for working with rusts. Seventy-one phenotypically different virulent pathotypes were established. Fifteen new races of P. triticina were also identified, which have not been present during the previous 15 years in Bulgaria. Seventeen lines and one cultivar with a certain degree of resistance to the pathogen were selected. The selected lines can be involved in the breeding programs for developing initial material with resistance to leaf rust P. triticina.

To artificial inoculation of sunflower plants with modern pathotypes of rust for breeding on immunity

Under global warming of the last decade, there is observed an intensive spread of rust in sunflower fields in the Russian Federation, due to the emergence of new races of the pathogen. It is obvious that there is a need to breed sunflower for resistance to new pathotypes and to correct the technique of artificial inoculation of plants in relation to them. Sunflower breeding for rust resistance has not been carried out since the 1980s. Objective of the study is determining the optimal temperature range for artificial inoculation of sunflower leaves with modern pathotypes (300 and 700) of the rust pathogen. The work was performed in the laboratory of immunity of the V.S. Pustovoit All-Russian Research Institute of Oil Crops in 2020–2021 using monopustular isolates of Puccinia helianthi with virulence codes 300 and 700. The germination of mature urediniospores, the duration of the incubation period and the degree of damage to sunflower plants at different temperatures were studied. The incubation period of pathotypes 300 and 700 of P. helianthi at a temperature of 26–28 °C is reduced by 2–3 days, which is essential both for the rapid identification of the racial identity of the pathogen isolates and for shortening the period for assessing sunflower genotypes when breeding for immunity. To speed up this work, the infection of sunflower plants should be carried out in the phase of the first pair of true leaves at a temperature of 22 °C, followed by a 24-hour stay in a humid chamber at 20 °C and a further increase in the growing temperature to 26–28 °C.

Lines resistant to downy mildew in the sunflower genetic collection at VIR

Background. Downy mildew (DM) caused by the fungus Plasmopara halstedii (Farl) Berl. & De Toni) is one of the most harmful diseases of sunflower (Helianthus annuus L.). Due to the pathogen’s attacks, annual seed harvest losses range between 30% and 70%. Lines resistant to new races of the pathogen should be obtained for the development of commercial sunflower hybrids.Materials and methods. Downy mildew resistance of 323 lines and 10 cultivars from the sunflower collection was assessed in the field at the Kuban Experiment Station of VIR in 2017–2018. Line VIR 845, susceptible during all years of observations, was used as a control. Resistance genes were identified by means of the molecular analysis using diagnostic markers of the Plarg, Pl6 and Pl8 genes that confer resistance to many known P. halstedii races.Results. The founder varieties of VIR’s lines were susceptible to a varying extent. Thirty-nine lines were resistant in 2016 and 2018; among those, 36 lines were susceptible in 2017. Presumably, a more virulent P. halstedii race became widespread in 2017, compared to the races that prevailed in 2016 and 2018, so the genes that determined resistance in 2016 and 2018 turned out to be ineffective. Lines ТА 716-18, VIR 768, and VIR 800, having originated from interspecific hybrids, exhibited absence of pathogenic damage during 3 years of the trials. Molecular markers of the Plarg, Pl6 and Pl8 genes were detected in most lines that demonstrated resistance in 2016 and 2018. There were no markers in lines VIR 768 and VIR 800, whereas in ТА 716-18 the markers of Plarg and Pl8 were present.Conclusion. As a result of the long-term studies, a trait-specific genetic collection was established for sunflower. It comprises genotyped lines with various effective DM resistance genes. Lines ТА 716-18, VIR 768 and VIR 800 appeared highly resistant to the pathogen and probably possess new resistance genes/alleles introgressed from wild species.

Biological and Transcriptomic Characterization of Pre-Haustorial Resistance to Sunflower Broomrape (Orobanche cumana W.) in Sunflowers (Helianthus annuus)

Infestations with sunflower broomrape (Orobanche cumana Wallr.), an obligatory root parasite, constitute a major limitation to sunflower production in many regions around the world. Breeding for resistance is the most effective approach to reduce sunflower broomrape infestation, yet resistance mechanisms are often broken by new races of the pathogen. Elucidating the mechanisms controlling resistance to broomrape at the molecular level is, thus, a desirable way to obtain long-lasting resistance. In this study, we investigated broomrape resistance in a confectionery sunflower cultivar with a robust and long-lasting resistance to sunflower broomrape. Visual screening and histological examination of sunflower roots revealed that penetration of the broomrape haustorium into the sunflower roots was blocked at the cortex, indicating a pre-haustorial mechanism of resistance. A comparative RNA sequencing between broomrape-resistant and -susceptible accessions allowed the identification of genes that were significantly differentially expressed upon broomrape infestation. Among these genes were β-1,3-endoglucanase, β-glucanase, and ethylene-responsive transcription factor 4 (ERF4). These genes were previously reported to be pathogenesis-related in other plant species. This transcriptomic investigation, together with the histological examinations, led us to conclude that the resistance mechanism involves the identification of the broomrape and the consequent formation of a physical barrier that prevents the establishment of the broomrape into the sunflower roots.

Sexual selection as race making

Charles Darwin's theory of sexual selection, as described in The Descent of Man, and Selection in Relation to Sex (1871), should be viewed as a significant transitional point in the modern expression of race. Unlike earlier race theorists, Darwin proposed that sexual reproduction was not merely a testing ground of racial character, but was itself a causal force that could create new races. His account of race was distinctly modern – viewing race not in terms of blood but as a collection of population-level characteristics. Recognizing this feature of Darwin's sexual-selection theory allows us to situate Darwin's work not solely within the history of evolutionary science, but also within the structures of racism that became the governing principles of modern nation states. In other words, sexual selection is an expression of Michel Foucault's biopolitics, in which political power is exercised by states not through the contracts of liberal governance but through the management of population-level phenomena. Furthermore, by contextualizing sexual selection in this theoretical framework, it becomes possible to more clearly emphasize the importance of race in the rise of modern biopolitics.

Breeding of sunflower lines resistant to race G of Broomrape

Relevance. Over the past decades, new and extremely virulent races have appeared in the southern regions of the Russian Federation, which overcame the resistance of domestic and foreign sunflower range of varieties. The most effective, long-term, and biologically safe way to protect sunflower from broomrape is to develop varieties and hybrids resistant to new races.Methods. We identified broomrape seeds of race G using internationally accepted differentiator lines: Record 1-3 (C), S-1358 (D), P-1380 (E), LC1093 and P96 (F). We used sunflower lines and hybrids of the breeding of V.S. Pustovoit All-Russian Research Institute of Oil Crops as a parent material. We carried out the evaluation of broomrape resistance by the method of A.Ya. Panchenko. To develop an infectious background, we introduced seeds of broomrape race G into boxes with a soil and sand mixture at the rate of 200 mg per 1 kg of the mixture, distributing them evenly. We grew sunflower plants at a temperature of 25-27 °С and a 16-hour photoperiod. In 25-30 days after the emergence if seedlings, we dug up plants and counted the broomrape specimens on their roots by a scale.Results. We developed sunflower lines resistant to races of broomrape from A to G. All of them are of branched form, with different lengths of the period from germination to flowering, they differ in height and oil content. The line L 82 is distinguished by a high content of oleic acid in oil — 91%. The lines have a high combinability. We obtained experimental hybrid combinations using these lines.

New races of rust pathogen on sunflower in Russia

Over the past two decades, there was observed a widespread of rust on sunflower in some regions of Russia. The identification of the racial structure of Puccinia helianthi populations in Russia has not been done since the early 80s of the last century. At that time, races 100 and 300 were identified. In our recent study, in addition to these races, new biotypes: 700, 710, 722, 772 were identified for the first time. The purpose of this study is to determine the racial identity of 160 P. helianthi isolates collected from 2018 to 2020 in the Rostov, Saratov, and Krasnodar regions. We used eight standard differentiating lines of sunflower: SM-90, SM 29, R-386, HАR-1, HАR-2, HAR-3, HAR-4, HAR-5. Sunflower variety VNIIMK 8883 was used as a differentiator susceptible to all races of the pathogen. In addition to the six races mentioned above, we identified 11 more new races for the first time: 304, 351, 352, 364, 704, 736, 740, 741, 745, 760, 762. Race 700 prevailed among the isolates collected in the Rostov region in 2020; we also identified single specimens of races 760, 762. Thus, 17 races of P. helianthi were found on sunflower in three regions of the Russian Federation. Other races may be also present here, so further research is required.

Joint action of Pb1 and Pb2 provide dominant complementary resistance against new races of Peronospora belbahrii (Basil Downy Mildew)

Sweet basil (Ocimum basilicum, 2n=4x=48) is susceptible to downy mildew caused by Peronospora belbahrii. Pb1 gene exhibit complete resistance to the disease. However, Pb1 became prone to disease due to occurrence of a new virulent races. Here we show that Zambian accession PI 500950 (O. americanum var pilosum) is highly resistant to the new races. From an interspecies backcross between PI 500950 and the susceptible cv ‘Sweet Basil’ we obtained, by embryo rescue, a population of 131 BC1F1 plants. This population segregated 73 Resistant: 58 Susceptible (1: 1, P=0.22), suggesting the resistance is controlled by one incompletely dominant gene called Pb2. To determine whether allelic relationship is existing between Pb1 and Pb2, we used two differential races, race-0, avirulent to both PI 500945 (Pb1) and PI 500950 (Pb2) and race-1, virulent to PI 500945 but avirulent to PI 500950. F1 plants obtained from ‘12-4-6’ (BC6F3 derived from PI 500945) and ‘56’ (BC3F3 derived from PI 500950) showed resistant superiority to both races due to dominant complementary interaction. F2 plants segregated to race-0 as follow; 12:3:1, immune: incomplete resistant: susceptible, as against to 9:3:4 to race-1, indicating Pb1 and Pb2 are not alleles. Since joint action is contributed in F1 plants and in advanced (BC3F3(56) x BC6F3(12-4-6) F4) populations who carrying both genes, it can be assumed that both accessions carry two unlinked genes but share a common signal transduction pathway which leading to dominant complementation superiority of the resistance against different races of BDM.

First Report of Hemileia vastatrix (Coffee Leaf Rust) Physiological Races Emergent in Coffee Germplasm Collections in the Coffee-cropping Regions of China

Coffee leaf rust (CLR), caused by the obligate biotrophic fungus Hemileia vastatrix (Hv), is a devastating disease worldwide leading to severe reductions in yield and economic losses in coffee plantations, especially of Coffea arabica L. (Talhinhas et al. 2017). The frequent emergence of new Hv races is a major constraint on coffee production due to continuous exertion of selective pressure on the pathogen from pathogen-resistant cultivars under the coevolutionary ‘arms race’ (Silva et al. 2018). More than 50 physiological races of Hv have been described globally (Várzea & Marques 2005), while at least 16 Hv races have been detected in China (Bai et al. 2018; Zhang et al. 2014; Chen et al. 1998). Coffee is an important cash crop in China (Yan et al. 2019). Most of the coffee germplasm collections in China are in the main coffee-cropping regions, although documentation on the prevalent Hv races is lacking. A total of 57 CLR samples (each sample contained multi leaves with 20-30 pustules of coffee rust) were collected from 4 germplasm fields situated in the main coffee-cropping regions during the high seasonal incidence of CLR in 2018–2019: Field 1, Coffee Germplasm Collection of Malipo County, Wenshan (23°11′ N, 104°55′ E, 550 m); Field 2, Coffee Germplasm Collection I in Puer (22°47′45″ N, 100°58′59″ E, 1320 m); Field 3, Coffee Germplasm Collection II in Puer (22°37′36″ N, 100°59′50″ E, 1010 m); and Field 4, Coffee Germplasm Collection in Ruili (24°01′ N, 97°51′ E, 1260 m). Urediniospores were recovered on susceptible genotypes 849/1 Matari and 19/1 Cantura and tested on a set of coffee differentials at the CIFC (Oeiras, Portugal) following standard race-typing procedure described by D’ Oliveirar & Rodiagues (1961). The coffee trees where the rusts isolated were used to verify virulence and avirulence. The infection type criteria determining virulence and avirulence based on the classification standards for disease resistance (D’ Oliveirar, 1954-57). Twenty-seven pure-cultured Hv isolates were derived from single rust pustules taken from distinct sample groups. The predominant race XXXVII (v2,5,6,7,9) was present in Field 1, 2, and 3 at high frequency (74.04%) separately derived from the genotypes CATUAÍ, Arabica-Catimor Derivates, T2, CCC 24, Typica, T8667 Catimor HW 26/5 (F2) and Sarchimor. Race XXXIV (v2,5,7,9) was detected in Field 4 (3.70%). Races XXXVII and XXXIV had emerged in China during 2011–2015 (Bai et al. 2017 & 2018). A new race (v2,5,6,7) (7.41%) was isolated from the host DTART 316 and was able to infect the differentiators of physiologic Groups D, E, R, 4, 6, and a. Based on its pathological and genetic characteristics, Hv with high evolutionary potential has inevitably overcome the resistance of released coffee cultivars with increase virulence, thereby adapting to new hosts (Silva et al. 2018; Talhinhas et al. 2017; Zambolim 2016; McCook & Vandermeer 2015). The results obtained in this work corroborate the evidence that the emergence of new Hv races occurs preferentially at germplasm fields since the multi-selection pressures from various hosts. Our findings are of considerable importance given the potential of the coffee germplasm collections in coffee regions to promote evolution of new races. The continued emergence of new Hv races places the current commercial cultivars at risk from a loss of resistance. Monitoring the occurrence, dissemination, distribution, and pathogenicity of new races is essential for targeted resistance breeding and CLR control.