Distribution and diversity of russian wheat aphid (Hemiptera: Aphididae) biotypes in North America

Wheat, Triticum aestivum L., with Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) resistance based on the Dn4 gene has been important in managing Russian wheat aphid since 1994. Recently, five biotypes (RWA1-RWA5) of this aphid have been described based on their ability to differentially damage RWA resistance genes in wheat. RWA2, RWA4, and RWA5 are of great concern because they can kill wheat with Dn4 resistance. In 2005, 365 Russian wheat aphid clone colonies were made from collections taken from 98 fields of wheat or barley, Hordeum vulgare L., in Oklahoma, Texas, New Mexico, Colorado, Kansas, Nebraska, and Wyoming to determine their biotypic status. The biotype of each clone was determined through its ability to differentially damage two resistant and two susceptible wheat entries in two phases of screening. The first phase determined the damage responses of Russian wheat aphid wheat entries with resistance genes Dn4, Dn7, and susceptible 'Custer' to infestations by each clone to identify RWA1 to RWA4. The second phase used the responses of Custer and 'Yuma' wheat to identify RWA1 and RWA5. Only two biotypes, RWA1 and RWA2, were identified in this study. The biotype composition across all collection sites was 27.2% RWA1 and 72.8% RWA2. RWA biotype frequency by state indicated that RWA2 was the predominant biotype and composed 73-95% of the biotype complex in Texas, Oklahoma, Colorado, and Wyoming. Our study indicated that RWA2 is widely distributed and that it has rapidly dominated the biotype complex in wheat and barley within its primary range from Texas to Wyoming. Wheat with the Dn4 resistance gene will have little value in managing RWA in the United States, based on the predominance of RWA2.     

Distribution and diversity of Russian wheat aphid (Hemiptera: Aphididae) biotypes in South Africa and Lesotho

Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) was recorded for the first time in South Africa in 1978. In 2005, a second biotype, RWASA2, emerged, and here we report on the emergence of yet another biotype, found for the first time in 2009. The discovery of new Russian wheat aphid biotypes is a significant challenge to the wheat, Triticum aestivum L., industry in South Africa. Russian wheat aphid resistance in wheat, that offered wheat producers a long-term solution to Russian wheat aphid control, may no longer be effective in areas where the new biotypes occur. It is therefore critical to determine the diversity and extent of distribution of biotypes in South Africa to successfully deploy Russian wheat aphid resistance in wheat. Screening of 96 Russian wheat aphid clones resulted in identification of three Russian wheat aphid biotypes. Infestations of RWASA1 caused susceptible damage symptoms only in wheat entries containing the Dn3 gene. Infestations of RWASA2 caused susceptible damage symptoms in wheat entries containing Dn1, Dn2, Dn3, and Dn9 resistant genes. Based on the damage-rating scores for the seven resistance sources, a new biotype, which caused damage rating scores different from those for RWASA1 and RWASA2, was evident among the Russian wheat aphid populations tested. This new biotype is virulent to the same resistance sources as RWASA2 (Dn1, Dn2, Dn3, and Dn9), but it also has added virulence to Dn4, whereas RWASA2 is avirulent to this resistance source.     

Identification of Russian wheat aphid (Homoptera: Aphididae) populations virulent to the Dn4 resistance gene

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a serious worldwide pest of wheat and barley. Russian wheat aphid populations from Hungary, Russia, and Syria have previously been identified as virulent to D. noxia (Dn) 4, the gene in all Russian wheat aphid-resistant cultivars produced in Colorado. However, the virulence of Russian wheat aphid populations from central Europe, North Africa, and South America to existing Dn genes has not been assessed. Experiments with plants containing several different Dn genes demonstrated that populations from Chile, the Czech Republic, and Ethiopia are also virulent to Dn4. The Czech population was also virulent to plants containing the Dnx gene in wheat plant introduction PI220127. The Ethiopian population was also virulent to plants containing the Dny gene in the Russian wheat aphid-resistant 'Stanton' produced in Kansas. The Chilean and Ethiopian populations were unaffected by the antibiosis resistance in Dn4 plants. There were significantly more nymphs of the Chilean population on plants of Dn4 than on Dn6 plants at both 18 and 23 d postinfestation, and the Ethiopian population attained a significantly greater weight on Dn4 plants than on plants containing Dn5 or Dn6. These newly characterized virulent Russian wheat aphid populations pose a distinct threat to existing or proposed wheat cultivars possessing Dn4.     

Plant damage and yield response to the Russian wheat aphid (Homoptera: Aphididae) on susceptible and resistant winter wheats in Colorado

Plant damage and yield response to the Russian wheat aphid, Diuraphis noxia (Mordvilko), were evaluated on a susceptible (TAM 107) and a resistant (RWA E1) winter wheat, Triticum aestivum L., in three Colorado locations in the 1993 and 1994 crop years. Russian wheat aphid was more abundant on TAM 107 than on RWA E1. Russian wheat aphid days per tiller were greater at the higher infestation levels. Yield losses as a result of Russian wheat aphid infestation occurred most of the time with TAM 107 but rarely with RWA E1. Seed densities were reduced at higher infestation levels in TAM 107 at two locations. Russian wheat aphids per tiller had a negative relationship to yield in TAM 107 but not in RWA E1. In TAM 107 yield decreased as aphid densities increased, but yield remained constant regardless of initial aphid abundance on RWA E1 in all environments. Seed densities were reduced at higher infestation levels in TAM 107 at two locations. The resistance conferred by the Dn4 gene seems to be an effective management approach across a range of field conditions.     

Response of resistant and susceptible barley to infestations of five Diuraphis noxia (Homoptera: Aphididae) biotypes

Since 2003, four new biotypes of the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae), RWA2-RWA5, have been discovered that have the ability to damage most of the wheat germplasm resistant to the original Russian wheat aphid population (RWA1). Barley germplasm lines with resistance to RWA1 have not yet been evaluated against the newest biotypes. Our study compared how biotypes RWA1-RWA5 affected the growth and leaf damage of RWA1-resistant germplasm (STARS 9301B, STARS 9577B), moderately resistant germplasm (MR-015), and susceptible varieties (Schuyler, Harrington, and Morex) under greenhouse conditions. Russian wheat aphid population levels also were determined 14 d after plant infestation. STARS 9301B exhibited strong resistance by showing only small differences in leaf damage and growth parameters from the feeding by the biotypes. STARS 9577B showed greater differences in damage by the Russian wheat aphid biotypes than STARS 9301B, yet, the ratings were still within the resistant category (e.g., chlorosis rating 2.3-4.9). Leaf chlorosis ratings for MR-015 ranged from 5.0 to 6.9 and fell within the moderately resistant to susceptible categories for all the biotypes. The greatest difference in leaf chlorosis occurred in Morex where RWA2 showed less virulence than the other biotypes. Feeding by the Russian wheat aphid biotypes produced only small differences in leaf rolling and plant growth within plant entries. Population levels of the Russian wheat aphid biotypes did not differ within barley entries (n = 610-971) at the termination of the study (14 d). From our research, we conclude that the new Russian wheat aphid biotypes pose no serious threat to the key sources of resistance in barley (STARS 9301B and 9577B).     

Comparison of Dn4- and Dn7-carrying spring wheat genotypes artificially infested with Russian wheat aphid (Homoptera: Aphididae) biotype 1

Genetic resistance is a useful control strategy for managing Russian wheat aphid, Diuraphis noxia (Mordvilko), in wheat, Triticum aestivum L. In 2003, a Russian wheat aphid population (denoted as biotype 2) identified in Colorado was virulent to genotypes carrying the Dn4 Russian wheat aphid resistance gene, necessitating the rapid identification and deployment of new sources of resistance. Although the Dn7 gene had shown excellent resistance to Russian wheat aphid biotypes 1 and 2 in evaluations in the greenhouse, no information is available on the amount of protection provided by Dn7 under field conditions. The objective of this study was to compare the reaction of Dn4- and Dn7-carrying spring wheat genotypes under artificial infestation by Russian wheat aphid biotype 1 in the field. Irrigated field experiments were conducted in 2003 and 2004 in a split-split plot arrangement with six replications. The whole plot treatment was infestation level (control, 1x, and 10x Russian wheat aphids), and the subplot treatment was resistance source (Dn4- and Dn7-carrying genotypes). The sub-subplot treatment consisted of side-by-side planting of resistant and susceptible genotypes. The Dn4 subplot was significantly more damaged than the Dn7 subplot in 2003, but not in 2004. Interaction effects observed in 2004 suggested an advantage of Dn7 relative to Dn4 in terms of reduced Russian wheat aphid abundance and plant damage. Deployment of the Dn7 Russian wheat aphid resistance gene should provide protection in the field comparable with that provided by the Dn4 resistance gene for management of Russian wheat aphid biotype 1.     

Variation to cause host injury between Russian wheat aphid (Homoptera: Aphididae) clones virulent to Dn4 wheat

Biotypes are infraspecific classifications based on biological rather than morphological characteristics. Cereal aphids are managed primarily by host plant resistance, and they often develop biotypes that injure or kill previously resistant plants. Although molecular genetic variation within aphid biotypes has been well documented, little is known about phenotypic variation, especially virulence or the biotype's ability to cause injury to cultivars with specific resistance genes. Five clones (single maternal lineages) of Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae), determined to be injurious to wheat, Triticum aestivum L., with the Dn4 gene, were evaluated on resistant and susceptible wheat and barley, Hordeum vulgare L., for their ability to cause chlorosis, reduction in plant height, and reduction in shoot dry weight. Variation to cause injury on resistant 'Halt' wheat, susceptible 'Jagger' wheat, and resistant 'STARS-9301B' barley was found among the Dn4 virulent clones. One clone caused up to 30.0 and 59.5% more reduction in plant height and shoot dry weight, respectively, on resistant Halt than other clones. It also caused up to 29.9 and 55.5% more reduction in plant height and shoot dry weight, respectively, on susceptible Jagger wheat. Although STARS-9301B barley exhibited an equal resistant response to feeding by all five clones based on chlorosis, two clones caused approximately 20% more reduction in plant height and shoot dry weight than three other clones. The most injurious clones on wheat were not the most injurious clones on barley. This is the first report of variation to cause varying degrees of plant damage within an aphid biotype virulent to a single host resistance gene. A single aphid clone may not accurately represent the true virulent nature of a biotype population in the field.     

Influence of three resistance sources in winter wheat derived from TAM 107 on yield response to Russian wheat aphid

A study to determine yield response to the Russian wheat aphid, Diuraphis noxia (Mordvilko), was conducted during the 1997-1998 and 1998-1999 growing seasons at three eastern Colorado locations, Akron, Fort Collins, and Lamar, with three wheat lines containing either Russian wheat aphid-resistant Dn4 gene, Dn6 gene, or resistance derived from PI 222668, and TAM 107 as the susceptible control. Russian wheat aphids per tiller were greater on TAM 107 than the resistant wheat lines at the 10x infestation level at Fort Collins and Akron in 1999. Yield, seed weight, and number of seeds per spike for each wheat line were somewhat affected by Russian wheat aphid per tiller mainly at Fort Collins. The infested resistant wheat lines harbored fewer Russian wheat aphids and yielded more than the infested susceptible wheat lines. Wheat lines containing the Dn4, Dn6, and PI 222668 genes contain different levels of antibiosis or antixenosis and tolerance. Although differences existed among sites and resistance, there is a benefit to planting resistant wheat when there is a potential for Russian wheat aphid infestations.     

Population growth rate and relative virulence of the two South African biotypes of Russian wheat aphid,Diuraphis noxia,and bird cherry‐oat aphid,Rhopalosiphum padi,on resistant and non‐resistant barley

In South Africa a new biotype of the Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), RWASA2, has appeared which exhibits an improved performance compared to the original biotype (RWASA1) on wheat containing the Dn1 resistance gene. We examined population growth rates as well as damage caused by RWASA1 and RWASA2, in addition to a different aphid species, the bird cherry‐oat aphid (BCA), Rhopalosiphum padi L. (Hemiptera: Aphididae), on three RWA‐resistant barley [Hordeum vulgare L. (Poaceae)] lines (STARS‐9577B, STARS‐0502B, and STARS‐9301B) and one susceptible control (PUMA). RWASA2 had a higher reproductive rate than RWASA1 on all barley lines tested, which is consistent with previous results on wheat. Two of the RWA‐resistant lines (STARS‐0502B and STARS‐9301B) also exhibited a similar resistance phenotype against BCA. In our experiments, severe chlorosis and leaf roll appeared earlier on the control PUMA barley variety as a result of RWASA2 feeding than was the case with RWASA1, probably due to the differences in reproductive rate. Although chlorosis appeared earlier on resistant plants after RWASA2 feeding, this symptom developed much faster during RWASA1 feeding on all three resistant lines tested. As chlorosis did not correlate well with aphid population numbers, we surmise that the differential chlorosis effects may be related to differences in the amount of saliva introduced by the two aphid clones during feeding. Our results indicate that the difference between RWASA2 and RWASA1 are broader than a ‘gene for gene’ interaction with the Dn1 resistance (R) gene in wheat, and that these biotypes also differ in important aspects of their biology.     

Microsatellite markers linked to six Russian wheat aphid resistance genes in wheat

The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is a serious economic pest of wheat and barley in North America, South America, and South Africa. Using aphid-resistant cultivars has proven to be a viable tactic for RWA management. Several dominant resistance genes have been identified in wheat, Triticum aestivum, including Dn1 in PI 137739, Dn2 in PI 262660, and at least three resistance genes (Dn5+) in PI 294994. The identification of RWA-resistant genes and the development of resistant cultivars may be accelerated through the use of molecular markers. DNA of wheat from near-isogenic lines and segregating F₂ populations was amplified with microsatellite primers via PCR. Results revealed that the locus for wheat microsatellite GWM111 (Xgwm111), located on wheat chromosome 7DS (short arm), is tightly linked to Dn1, Dn2 and Dn5, as well as Dnx in PI 220127. Segregation data indicate RWA resistance in wheat PI 220127 is also conferred by a single dominant resistance gene (Dnx). These results confirm that Dn1, Dn2 and Dn5 are tightly linked to each other, and provide new information about their location, being 7DS, near the centromere, instead of as previously reported on 7DL. Xgwm635 (near the distal end of 7DS) clearly marked the location of the previously suggested resistance gene in PI 294994, here designated as Dn8. Xgwm642 (located on 1DL) marked and identified another new gene Dn9, which is located in a defense gene-rich region of wheat chromosome 1DL. The locations of markers and the linked genes were confirmed by di-telosomic and nulli-tetrasomic analyses. Genetic linkage maps of the above RWA resistance genes and markers have been constructed for wheat chromosomes 1D and 7D. These markers will be useful in marker-assisted breeding for RWA-resistant wheat. Received: 17 May 2000 / Accepted: 13 June 2000     

Proteomic analysis of secreted saliva from Russian Wheat Aphid (Diuraphis noxia Kurd.) biotypes that differ in virulence to wheat

Diuraphis noxia, Russian Wheat Aphid (RWA), biotypes are classified by their differential virulence to wheat varieties containing resistance genes. RWA salivary proteins, unlike those of most aphid species, cause foliar damage and physiological alterations in plants. A comparative proteomic analysis of secreted saliva from four differentially virulent RWA biotypes identified thirty-four individual proteins. The five major proteins were glucose dehydrogenase, lipophorin, chitinase, CiV16.8g1-like, and lava lamp. Fourteen proteins quantitatively varied among biotypes; trehalase, β-N-acetylglucosaminidase (chitinase), two separate glucose dehydrogenases, calreticulin, aminopeptidase, acetylglucosaminyltransferase, hydroxymethylglutaryl-CoA lyase, acyltransferase, ficolin-3, lava lamp, retinaldehyde-binding protein, and two proteins of unknown function. Fifty-four percent of spectral counts were associated with glucose dehydrogenase, which is thought to detoxify plant defensive compounds. One-dimensional electrophoresis detected nine protein bands from 9 to 60 kDa that quantitatively differed. Two-dimensional electrophoresis identified six major gel zones with quantitative and qualitative variance in proteins. Our findings reveal that the salivary proteome of RWA, a phytotoxic aphid, differs considerably from those reported for nonphytotoxic aphids. The potential roles of proteins used in the general plant feeding processes of aphids and those that are potential phytotoxins related to aphid virulence are discussed.     

Reproduction and development of Russian wheat aphid biotype 2 on crested wheatgrass, intermediate wheatgrass, and susceptible and resistant wheat

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), is an economically important pest of small grains. Since its introduction into North America in 2003, Russian wheat aphid Biotype 2 has been found to be virulent to all commercially available winter wheat, Triticum aestivum L., cultivars. Our goal was to examine differences in Russian wheat aphid reproduction and development on a variety of plant hosts to gain information about 1) potential alternate host refuges, 2) selective host pressures on Russian wheat aphid genetic variation, and 3) general population dynamics of Russian wheat aphid Biotype 2. We studied host quality of two wheatgrasses (crested wheatgrass, Agropyron cristatum [L.] Gaertn., and intermediate wheatgrass, Agropyron intermedium [Host] Beauvoir) and two types of winter wheat (T. aestivum, one Biotype 2 susceptible wheat, 'Custer' and one biotype 2 resistant wheat, STARS02RWA2414-11). The susceptible wheat had the highest intrinsic rate of increase, greatest longevity and greatest fecundity of the four host studied. Crested wheatgrass and the resistant wheat showed similar growth rates. Intermediate wheatgrass had the lowest intrinsic rate of increase and lowest fecundity of all tested hosts.     

Reproductive rates of Russian wheat aphid (Hemiptera: Aphididae) biotypes 1 and 2 on a susceptible and a resistant wheat at three temperature regimes

The reproductive rates of Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), Biotype 1 (RWA 1) and Biotype 2 (RWA 2) were compared in the laboratory at three temperature regimes on a Russian wheat aphid resistant cultivar ('Prairie Red') and a susceptible cultivar ('TAM 107'). The objective of this study was to expose RWA 1 and RWA 2 to three temperature regimes and two levels of resistance to find whether there were reproductive differences that may occur within each biotype as well as differences in reproduction between biotypes. In addition, temperature effects of the Dn4 gene on biotype reproduction were noted. Differences in reproductive rates between the two biotypes seem to be driven by temperature. For both biotypes, longevity and reproductive rate parameters, except for intrinsic rate of increase, were lower at the 24-29 degree C temperature regime than the 13-18 degree C and 18-24 degree C temperature regimes. The intrinsic rate of increase was higher for both biotypes at the 18-24 degree C and 24-29 degree C temperature regimes than at the 13-18 degree C temperature regime. Reproductive rates between biotypes were similar at the two higher temperature regimes, but the fecundity for RWA 1 was less than RWA 2 at the 13-18 degree C temperature. The change in fecundity rates between RWA 1 and RWA 2 at lower temperatures could have ecological and geographical implications for RWA 2.     

Analysis of the structure of the AVR1-CO39 avirulence locus in virulent rice-infecting isolates of Magnaporthe grisea

The AVR1-CO39 gene that came from a Magnaporthe grisea isolate from weeping lovegrass controls avirulence on the rice cultivar CO39. AVR1-CO39 was not present in the genome of the rice-infecting M. grisea isolate Guyll from French Guyana, suggesting that the gene had been deleted. Molecular analysis of the deletion breakpoints in the AVR1-CO39 locus revealed the presence of a truncated copy of a previously unknown retrotransposon at the left-hand border. At the right-hand border was a truncated copy of another repetitive element that is present at multiple locations in the genome of Guyll. The structures of avr1-CO39 loci were further examined in 45 rice-infecting isolates collected in Brazil, China, Japan, India, Indonesia, Mali, and the Philippines. Most isolates showed no hybridization signal with the AVR1-CO39 probe and had the same locus structure as Guyll. Some isolates from Japan showed a signal with the AVR1-CO39 probe, but the region specifying avirulence activity was rearranged. These findings suggest that widespread virulence to 'CO39' among rice-infecting M. grisea isolates is due to ancestral rearrangements at the AVR1-CO39 locus that may have occurred early in the evolution of pathogenicity to rice.     

Enzymatic chlorophyll degradation in wheat near-isogenic lines elicited by cereal aphid (Homoptera: Aphididae) feeding

Chlorophyll degradation enzyme (i.e., chlorophyllase, Mg-dechelatase, and chlorophyll oxidase) activities of aphid-infested and uninfested 'Tugela' and Tugela near-isogenic wheat lines (i.e., Tugela-Dn1, Tugela-Dn2, and Tugela-Dn5) were assayed. Chlorophyllase activity was higher in bird cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae),-infested wheat lines compared with Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae)]-infested and uninfested plants. Mg-dechelatase activity was higher in D. noxia-infested wheat lines than in R. padi-infested and uninfested plants. Also, Mg-dechelatase activity was lower in Tugela wheat infested with D. noxia than in Tugela near-isogenic lines with Dn genes. Based on the in vitro assays of chlorophyll degradation enzyme (i.e., chlorophyllase and Mg-dechelatase) activities, we proposed that the chlorotic symptoms observed on D. noxia-infested Tugela wheat were most likely to be elicited by unbalanced chlorophyll biosynthesis and degradation.     

Comparison of chlorophyll and carotenoid concentrations among Russian wheat aphid (Homoptera: Aphididae)-infested wheat isolines

Russian wheat aphid, Diuraphis noxia (Mordvilko), feeding injury on 'Betta' wheat isolines with the Dn1 and Dn2 genes was compared by assessing chlorophyll and carotenoid concentrations, and aphid fecundity. The resistant Betta isolines (i.e., Betta-Dn1 and Betta-Dn2) supported similar numbers of aphids, but had significantly fewer than the susceptible Betta wheat, indicating these lines are resistant to aphid feeding. Diuraphis noxia feeding resulted in different responses in total chlorophyll and carotenoid concentrations among the Betta wheat isolines. The infested Betta-Dn2 plants had higher levels of chlorophylls and carotenoids in comparison with uninfested plants. In contrast, infested Betta-Dn1 plants had the same level of chlorophyll and carotenoid in comparison with uninfested plants. Our data provide essential information on the effect of D. noxia feeding on chlorophyll and carotenoid concentrations for Betta wheat and its isolines with D. noxia-resistant Dn1 and Dn2 genes.     

Biotypic variation among north American Russian wheat aphid (Homoptera: Aphididae) populations

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), has been a major economic pest of small grains in the western United States since its introduction in 1986. Recently, a new Russian wheat aphid biotype was discovered in southeastern Colorado that damaged previously resistant wheat, Triticum aestivum L. Biotype development jeopardizes the durability of plant resistance, which has been a cornerstone for Russian wheat aphid management. Our objective was to assess the relative amount of biotypic diversity among Russian wheat aphid populations collected from cultivated wheat and barley, Hordeum vulgare L. We conducted field surveys from May through June 2002 and August 2003 from seven counties within Texas, Kansas, Nebraska, and Wyoming. Based upon a foliar chlorosis damage rating, three new Russian wheat aphid biotypes were identified, one of which was virulent to all characterized sources of Russian wheat aphid resistance. The future success of Russian wheat aphid resistance breeding programs will depend upon the continual monitoring of extant biotypic diversity and determination of the ecological and genetic factors underlying the development of Russian wheat aphid biotypes.     

Evaluation of Durum Wheat Genotypes for Resistance against Root Rot Disease Caused by Moroccan Fusarium culmorum Isolates

Fusarium culmorum is one of the most important causal agents of root rot of wheat. In this study, 10 F. culmorum isolates were collected from farms located in five agro-ecological regions of Morocco. These were used to challenge 20 durum wheat genotypes via artificial inoculation of plant roots under controlled conditions. The isolate virulence was determined by three traits (roots browning index, stem browning index, and severity of root rot). An alpha-lattice design with three replicates was used, and the resulting ANOVA revealed a significant (P < 0.01) effect of isolate (I), genotype (G), and G × I interaction. A total of four response types were observed (R, MR, MS, and S) revealing that different genes in both the pathogen and the host were activated in 53% of interactions. Most genotypes were susceptible to eight or more isolates, while the Moroccan cultivar Marouan was reported resistant to three isolates and moderately resistant to three others. Similarly, the Australian breeding line SSD1479-117 was reported resistant to two isolates and moderately resistant to four others. The ICARDA elites Icaverve, Berghisyr, Berghisyr2, Amina, and Icaverve2 were identified as moderately resistant. Principal component analysis based on the genotypes responses defined two major clusters and two sub-clusters for the 10 F. culmorum isolates. Isolate Fc9 collected in Khemis Zemamra was the most virulent while isolate Fc3 collected in Haj-Kaddour was the least virulent. This work provides initial results for the discovery of differential reactions between the durum lines and isolates and the identification of novel sources of resistance.