Identification of Fusarium oxysporum f. sp. ciceris Physiological Races in Chickpea Cultivated Areas in Al-Ghab Region, Syria

Alloush, L., S. Al-Maghribi and B. Barhom. 2021. Identification of Fusarium oxysporum f. sp. ciceris Physiological Races in Chickpea Cultivated Areas in Al-Ghab Region, Syria. Arab Journal of Plant Protection, 39(4): 231-240. https://doi.org/10.22268/AJPP-39.4.231240 Fusarium wilt disease caused by Fusarium oxysporum f. sp. ciceris is one of the diseases that cause significant economic losses to the chickpea crop around the world, as infection with FOC can occurs during the different stages of plant growth. One of the best approaches to reduce the damage caused by FOC is by using resistant chickpea varieties. Hence, this study aimed to determine the physiological races of 25 FOC isolates collected from 20 agricultural sites belonging to six regulatory zones in the Al-Ghab region in Syria, based on their pathogenicity on 13 differential chickpea cultivars (C-104, JG -74, CPS-1, BG-215, BG-212, WR-315, Anniger, Chaffa, ILC482, L-550, K850-3/27, UC-27). The study was carried out during 2020 at the Agricultural Scientific Research Center in Al-Ghab. The results obtained showed that the tested isolates belong to races 0, 1B/C, 2, 3, 5, and 6. This is the first report of races 2 and 3 in Syria, and each of them constituted 28% of the total tested isolates, whereas 24% of the isolates were represented by race 0, and both races 5 and 1B/C occurred at 8% frequency, and race 6 included one isolate obtained from Abu Faraj site. Keywords: Chickpea, vascular wilt, physiological races, pathogenicity, Al-Ghab, Syria

Southern corn rust caused by Puccinia polysora Underw: a review

Southern corn rust (SCR) caused by Puccinia polysora Underw is one of the most devastating maize diseases, resulting in substantial yield losses worldwide. The pathogen is an obligate biotrophic parasite that is difficult to culture on artificial media. In recent years, the disease has become prevalent—both globally and in China—and increasing difficult to control because of its wide distribution, long-distance migration, multiple physiological races and fast evolution, all of which have contributed to a considerable increase in the risks of associated epidemics. In this review, we summarize the current knowledge of P. polysora, with emphasis on its global distribution (particularly in China), life and disease cycle, population genetics, migration, physiological races, resistance genes in maize and management. Understanding the underlying factors and processes in SCR epidemics should facilitate management of the disease and breeding for resistant maize varieties.

Molecular Cytogenetic Analysis of the Introgression between Agropyroncristatum P Genome and Wheat Genome

Agropyroncristatum (2n = 4x = 28, PPPP) is an important wild relative of common wheat (Triticum aestivum L., 2n = 6x = 42). A previous report showed that the wheat-A. cristatum 6P translocation line WAT655 carrying A. cristatum 6PS (0.81–1.00) exhibited high resistance to prevalent physiological races of stripe rust (CYR32 and CYR33). In this study, three disease resistance-related transcripts, which were mapped to A. cristatum 6PS (0.81–1.00) through the analysis of specific molecular markers, were acquired from among A. cristatum full-length transcripts. The BC5F2 and BC5F2:3 genetic populations of the translocation line WAT655 were analyzed by using three disease resistance-related gene markers, A. cristatum P genome-specific markers, and fluorescence in situ hybridization (FISH). The results revealed that the introgression between A. cristatum P genome and wheat genome was observed in progenies of the genetic populations of the translocation line WAT655 and the physical positions of the three genes were considerably adjacent on A. cristatum 6PS (0.81–1.00) according to the FISH results. Additionally, kompetitive allele-specific PCR (KASP) markers of the three genes were developed to detect and acquire 24 breeding lines selected from the progenies of the distant hybridization of wheat and A. cristatum, which showed resistance to physiological races of stripe rust (CYR32 and CYR33) and other desirable agronomic traits according to the field investigation. In conclusion, this study not only provides new insights into the introgression between A. cristatum P genome and wheat genome but also provides the desirable germplasms for breeding practice.

The Emergence of New Aggressive Leaf Rust Races with the Potential to Supplant the Resistance of Wheat Cultivars

Characterization of the genetic structure and the physiological races of Puccinia triticina is a growing necessity to apply host genetic resistance against wheat leaf rust as a successful control strategy. Herein, we collected and identified about 130 isolates of P. triticina from 16 Egyptian commercial wheat cultivars grown at different locations, over two seasons (2019/2020 and 2020/2021). The 130 isolates of P. triticina were segregated into 17 different physiological races. TTTST and TTTKS were the most common virulent races, whereas TTTST and MTTGT were the most frequent races. The races were classified into three groups, based on their distinct DNA band sizes (150 bp, 200 bp, and 300 bp) after RAPD analysis. The new wheat cultivars (Sakha-94, Sakha-95, and Shandweel-1) infected with the most virulent race (TTTST), Gemmeiza-12, and Misr-3 were resistant to all physiological races. The resistance of these cultivars was mostly due to the presence of Lr19- and Lr28-resistant genes. Our results serve as a warning about emerging aggressive races capable of supplanting resistance to leaf rust, and help in the understanding of the pathotype–cultivar–location association and its role in the susceptibility/resistance of new wheat cultivars to P. triticina.

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.

New Insights Into the Introgression Between Agropyron Cristatum P Genome and Wheat Genome

Agropyron cristatum (2n = 4x = 28, PPPP) is an important wild relative of common wheat and confers desirable agronomic traits to common wheat. A previous report showed that the wheat-A. cristatum 6P translocation line WAT655 carrying A. cristatum 6PS (0.81–1.00) exhibited high resistance to prevalent physiological races (CYR32 and CYR33). In this study, three disease resistance-related transcriptomes, which were mapped to A. cristatum 6PS (0.81–1.00) through the analysis of specific molecular markers, were searched from among A. cristatum full-length transcriptomes. Then, three disease resistance-related gene markers, A. cristatum P genome-specific markers, and fluorescence in situ hybridization (FISH)/genomic in situ hybridization (GISH) probes made from the DNA of three bacterial artificial chromosome (BAC) clones, three genes, and A. cristatum “Z559” were used to analyze the BC5F2 and BC5F2:3 genetic populations of the translocation line WAT655. The results revealed the introgression can spontaneously occur between A. cristatum P genome and wheat genome, and indicated the three genes could constitute a gene cluster according to the positions of their FISH signals. Additionally, kompetitive allele-specific PCR (KASP) markers of the three genes were developed to detect and acquire 24 wheat-A. cristatum breeding materials, which showed resistance to physiological races (CYR32 and CYR33) and other desirable agronomic traits according to the field investigation. In conclusion, our study not only provides new insights into the introgression between A. cristatum P genome and wheat genome, but also provides the desirable breeding materials for breeding practice.

Complex System Analysis of Blumeria graminis f.sp. tritici Isolates Collected in Central Hebei Province, China

Wheat powdery mildew (WPM), caused by Blumeria graminis f.sp. tritici, is a significant disease of wheat throughout the world and has resulted in substantial yield and economic losses in wheat production. It is particularly important to understand the population distribution and genetic resistance of B. graminis f.sp. tritici. In 2019, the cumulative incidence of wheat powdery mildew in China was nearly 8.7 million hm2, which seriously affected the safe production of wheat in China. However, the proportion of disease-resistant wheat varieties in actual production was relatively low, and effective disease-resistant genes were lacking. As one of the main wheat-producing provinces in China, it is of great significance for normal wheat production to understand powdery mildew resistance in Hebei province. In this study, using wheat seedling culture in vitro, the physiological races of wheat powdery mildew in central Hebei province were identified, and the population toxicity frequency was analyzed. The results were as follows: (1) 36 strains were purified and 20 physiological races were identified. Among them, the dominant race is 015, and the distribution frequency is 16.7%. Race 077 is the second dominant race. (2) The frequency of virulence genes VEra, V8, V1, V3c, and V3f in population toxicity frequency analysis was more than 70%, while the frequency of virulence genes V2, MID, V20, V21, V4b, and V4 was less than 16.7%, and 46% of virulence genes of powdery mildew were higher than 40%. It shows that the virulence gene frequency of powdery mildew in Hebei province is high, and the varieties containing Pm2 + MID, Pm20, Pm21, Pm1b, Pm1, and other disease resistance genes have a certain value inbreeding.

Assessment of physiological races of Exserohilum turcicum isolates from maize in Argentina and Brazil

Northern corn leaf blight (NCLB) is one of the most important diseases in maize worldwide. It is caused by the fungus Exserohilum turcicum, which exhibits a high genetic variability for virulence, and hence physiological races have been reported. Disease control is based mainly on fungicide application and host resistance. Qualitative resistance has been widely used to control NCLB through the deployment of Ht genes. Known pathogen races are designated according to their virulence to the corresponding Ht gene. Knowledge about of E. turcicum race distribution in maize-producing areas is essential to develop and exploit resistant genotypes. Maize leaves showing distinct elliptical grey-green lesions were collected from maize-producing areas of Argentina and Brazil, and 184 monosporic E. turcicum isolates were obtained. A total of 66 isolates were collected from Argentina during 2015, 2018 and 2019, while 118 isolates from Brazil were collected during 2017, 2018 and 2019. All isolates were screened on maize differential lines containing Ht1, Ht2, Ht3 and Htn1 resistance genes. In greenhouse experiments, inoculated maize plants were evaluated at 14 days after inoculation. Resistance reaction was characterized by chlorosis, and susceptibility was defined by necrosis in the absence of chlorosis. The most frequent race was 0 in both Argentina (83%) and Brazil (65%). Frequencies of race 1 (6% and 24%) and race 23N (5% and 10%) were very low in Argentina and Brazil, respectively. The high frequency of race 0 isolates provides evidence that qualitative resistance based on the tested Ht genes is not being used extensively in Argentina and Brazil to control NCLB. This information may be relevant for growers and breeding programs as the incidence of NCLB is increasing in both countries.

Physiological races and virulence dynamics of Setosphaeria turcica in Northeast China

Northern corn leaf blight (NCLB), caused by Setosphaeria turcica, is an important foliar disease in corn. Since 2005, the damage from NCLB has increased in Northeast China, probably due to the emergence of new physiological races. In this study, 883 single conidial isolates of S. turcica were obtained from 12 sites across three provinces of Northeast China between 2007 and 2017. The virulence of the isolates was evaluated in five corn lines (B37, B37Ht1, B37Ht2, B37Ht3, B37HtN). Sixteen physiological races (0, 1, 2, 3, N, 12, 13, 1N, 23, 2N, 3N, 123, 12N, 13N, 23N, and 123N) were obtained, depending on their resistance or susceptibility. Three races (0, 1, and 2) were most prevalent, with frequencies of 40.5%, 19.6%, and 11.3% in all isolates, respectively. Races varied across provinces and years. Virulence to more than one Ht resistance genes occurred in 21.5% of isolates, with 8.5% virulent to three or more genes. Overall, 41% of isolates were avirulent to all Ht genes, 36% were virulent to Ht1, 28% to Ht2, 11% to Ht3, and 16% to HtN. Isolates from Heilongjiang had a greater frequency of virulence to Ht2 and Ht3, whereas isolates from Jilin and Liaoning were more frequently virulent to Ht1 and HtN, respectively. The frequency of isolate virulence to Ht2 ranged from 8% in 2009 to a maximum of 29% in 2015, and in 2015, isolates were more virulent to Ht2 than Ht1. This study will help growers to purposefully select commercial hybrids with multiple effective Ht resistance genes, and reduce the utilization of Ht1 and Ht2 genes in the process of corn production to strengthen NCLB control.