Effect of Growth Stage and Initial Inoculum Level on Leaf Rust Development and Yield Loss Caused by Puccinia recondita f. sp. tritici

The effects of the combinations of leaf rust inoculation at different growth stages and initial inoculum levels on leaf rust development and yield of winter wheat cultivars, McNair 1003 and Coker 762 were evaluated. Disease onset stage and initial inoculum level affected the rate of leaf rust development and shape of the disease progress curves in both cultivars. Epidemics with common onset stages and different initial inoculum levels differed in area under the disease progress curve (AUDPC). Leaf rust epidemics initiated at Feeke's growth stages 5, 7, and 10 reduced yield in both cultivars. Leaf rust epidemics initiated early with high inoculum levels had the greatest deleterious effect on yield. Maximum losses due to leaf rust were 30–40 %. Yield loss was directly related to AUDPC when the AUDPC varied from 500 to 1700 in McNair 1003 and from 250 to 1700 in Coker 762. Yield reduction was mainly due to reduction in grain weight.     

Observed and hypothetical leaf rust progress curves of some genotypes of wheat

Summary The hypothetical leaf rust progress curves of 15 genotypes of wheat were generated by integrating the components of slow rusting resistance determined in the glasshouse. The area under the disease progress curve (AUDPC) from the hypothetical and observed leaf rust progress curves were compared. It was found that the hypothetical AUDPC values of all the genotypes studied were smaller than their respective observed AUDPC values. Possible causes for the discrepancies in the observed and hypothetical values are discussed.     

Assessment of sorghum genetic resources of Ethiopia for anthracnose (Colletotrichum sublineolum Henn.) resistance and agronomic traits

Sorghum anthracnose caused by Colletotrichum sublineolum Henn. is one of the key diseases limiting sorghum production and productivity. Development of anthracnose‐resistant sorghum genotypes possessing yield‐promoting agronomic traits is an important breeding goal in sorghum improvement programs. The objective of this study was to determine the responses of diverse sorghum genetic resources for anthracnose resistance and agronomic traits to identify desirable lines for breeding. A total of 366 sorghum collections and three standard checks were field evaluated during the 2016 and 2017 cropping seasons. Lines were artificially inoculated with a virulent pure isolate of the pathogen. Anthracnose disease severity was assessed to calculate the area under disease progress curve (AUDPC). Agronomic traits such as panicle length (PL), panicle width (PW), head weight (HW) and thousand grain weight (TGW) were measured. Lines showed highly significant differences (p < .001) for anthracnose severity, AUDPC and agronomic traits. Among the collections 32 lines developed levels of disease severity between 15% and 30% in both seasons. The following sorghum landraces were selected: 71708, 210903, 74222, 73955, 74685, 74670, 74656, 74183, 234112, 69412, 226057, 214852, 71420, 71484, 200126, 71557, 75120, 71547, 220014, 228179, 16212, 16173, 16133, 69088, 238388, 16168 and 71570. These landraces had a relatively low anthracnose severity possessing farmer‐preferred agronomic traits. The selected genotypes are useful genetic resources to develop anthracnose‐resistant sorghum cultivars.     

Plant competition and disease in genetically diverse wheat populations

Summary The direct and indirect effects of plant genetic diversity on epidemics and the influence of disease on plant competition were investigated using the wheat (Triticum aestivum)/stripe rust (Puccinia striiformis) system. Replacement series consisting of a susceptible and a resistant wheat genotype or two wheat genotypes susceptible to different races of stripe rust were grown in the presence and absence of the pathogen. Stripe rust severity, number of seed heads, seed yield, and seed weight were determined separately for each wheat genotype in the mixtures and the pure stands. The frequency of susceptible genotypes in a mixture explained up to 67% of the variation in disease severity. However, competitive interactions among plant genotypes sometimes appeared to alter susceptibility and obscured the relationship. In pure stands of single genotypes, disease severity explained between 52 and 58% of the variation in seed yield. In mixtures, coefficients of determination were only 10 and 31%, suggesting a strong influence of plant-plant interactions on seed yield. These results suggest that host-parasite coevolutionary models need to account for the strong effect that specific plant genotype combinations may have on disease severity and plant reproduction.Paper No. 9818 of the journal series of the Oregon Agricultural Experiment Station     

Phenotypic and Molecular Assessment of Wheat Genotypes Tolerant to Leaf Blight,Rust and Blast Diseases

Globally among biotic stresses, diseases like blight, rust and blast constitute prime constraints for reducing wheat productivity especially in Bangladesh. For sustainable productivity, the development of disease-resistant lines and high yielding varieties is vital and necessary. This study was conducted using 122 advanced breeding lines of wheat including 21 varieties developed by Bangladesh Wheat and Maize Research Institute (BAMRI) with aims to identify genotypes having high yield potential and resistance to leaf blight, leaf rust and blast diseases. These genotypes were evaluated for resistance against leaf blight and leaf rust at Dinajpur and wheat blast at Jashore under field condition. Out of 122 genotypes tested, 20 lines were selected as resistant to leaf blight based on the area under the diseases progress curve (AUDPC) under both irrigated timely sown (ITS) and irrigated late sown (ILS) conditions. Forty-two genotypes were found completely free from leaf rust infection, 59 genotypes were identified as resistant, and 13 genotypes were identified as moderately resistant to leaf rust. Eighteen genotypes were immune against wheat blast, 42 genotypes were categorized as resistant, and 26 genotypes were identified as moderately resistant to wheat blast. Molecular data revealed that the 16 genotypes showed a positive 2NS segment among the 18 immune genotypes selected against wheat blast under field conditions. The genotypes BAW 1322, BAW 1295, and BAW 1203 can be used as earlier maturing genotypes and the genotypes BAW 1372, BAW 1373, BAW 1297 and BAW 1364 can be used for lodging tolerant due to short plant height. The genotypes WMRI Gom 1, BAW 1349 and BAW 1350 can be selected for bold grain and the genotypes WMRI Gom 1, BAW 1297, BAW 1377 can be used as high yielder for optimum seeding condition but genotypes BAW 1377 and BAW 1366 can be used for late sown condition. The selected resistant genotypes against specific diseases can be used in the further breeding program to develop wheat varieties having higher disease resistance and yield potential.     

Molecular Detection of Stripe Rust Resistance Gene(s) in 115 Wheat Cultivars (lines) from the Yellow and Huai River Valley Wheat Region

Stripe rust (yellow rust), caused by Puccinia striiformis f.sp. tritici (Pst), is a serious disease of wheat worldwide, including China. Growing resistant cultivars is the most cost‐effective and environmentally friendly approach to control the disease. To assess the stripe rust resistance in commercial wheat cultivars and advanced lines in the Yellow and Huai River Valley Wheat Region, 115 wheat cultivars (lines) collected from 13 provinces in this region were evaluated with the most prevalent Chinese Pst races CYR32, CYR33 and the new race V26 at seedling stage. In addition, these wheat entries were inoculated with the mixed races of CYR32 and CYR33 at the adult‐plant stage in the field. The results indicated that 53 (46.1%) cultivars (lines) had all‐stage resistance to all the three races, and 16 (13.9%) cultivars (lines) showed adult‐plant resistance. The possible stripe rust resistance genes in these entries were postulated by the closely linked markers of all‐stage resistance genes Yr5, Yr9, Yr10, Yr15 and Yr26 and adult‐plant resistance gene Yr18. Molecular analysis indicated that resistance genes Yr5, Yr9, Yr10, Yr18 and Yr26 were found in 5 (4.3%), 38 (33.0%), 1 (0.9%), 2 (1.7%) and 8 (7.0%) entries, respectively. No entry was found to carry the Yr15 gene. In future breeding programs, Yr5, Yr15 and Yr18 should be used to pyramid with other effective genes to develop wheat cultivars with high‐level and durable resistance to stripe rust, whereas Yr9, Yr10 and Yr26 should not be used or used in a limited way due to the virulent races present in China.     

Selection of parents for crossing based on genotyping and phenotyping for stripe rust (<Emphasis Type="Italic">Puccinia striiformis</Emphasis>) resistance and agronomic traits in bread wheat breeding

Bread wheat (Triticum aestivum L.) germplasm consisting of 45 genotypes were clustered phenotypically using ten morphological traits and Area Under Disease Progress Curve (AUDPC) as measure of stripe rust resistance. The clustering was ratified by using twenty three molecular markers (SSR, EST and STS) linked to stripe rust (Puccinia striiformis f. sp. tritici) resistant QTLs. The aim was to asses the extent of genetic variability among the genotypes in order to select the parents for crossing between the resistant and susceptible genotypes with respect to stripe rust. The Euclidian dissimilarity values resulted from phenotypic data regarding morphological traits and AUDPC were used to construct a dendrogram for clustering the accessions. Using un-weighted pair group method with arithmetic means, another dendrogram resulted from the similarity coefficient values was used to distinguish the genotypes with respect to stripe rust. Clustering based on phenotypic data produced two major groups and five clusters (with Euclidian dissimilarity ranging from 2.44 to 16.16) whereas genotypic data yielded two major groups and four clusters (with percent similarity coefficient values ranging from 0.1 to 46.0) to separate the gene pool into highly resistant, resistant, moderately resistant, moderately susceptible and susceptible genotypes. With few exceptions, the outcome of both type of clustering was almost similar and resistant as well as susceptible genotypes came in the same clusters of molecular genotyping as yielded by phenotypic clustering. As a result seven genotypes (Bakhtawar-92, Frontana, Saleem 2000, Tatara, Inqilab-91, Fakhre Sarhad and Karwan) of diverse genetic background were selected for pyramiding stripe rust lesistant genes as well as some other agronomic traits after hybridization.     

Identification of sources of resistance to common bacterial blight in common bean in Ethiopia

Common bacterial blight (CBB) caused by Xanthomonas axonopodis pv. phaseoli and X. axonopodis pv. phaseoli var. fuscans is one of the major biotic constraints limiting common bean (Phaseolus vulgaris L.) production and productivity in Ethiopia. The objective of this study was to identify new sources of CBB resistance from a diverse panel of genotypes to develop CBB-resistant common bean varieties. One hundred and ten diverse accessions were evaluated for CBB resistance at three hotspot sites (Melkassa, Arsi Negelle and Mieso) for two seasons (2017 and 2018) in Ethiopia. Data on mean disease severity on leaf (SL) and mean disease severity on pod (SP), the area under disease progress curve (AUDPC), number of pods per plant (PP), number of seeds per pod (SPP) and grain yield (GY) were collected. Data were subjected to standard analysis of variance and principal component analysis. The genotype × site interaction (G × E) had significant (p < .05) effect on all assessed traits. This indicated the presence of marked variation among tested genotypes in CBB resistance across the testing sites. Genotypes including SEC21, SEC23, SMC21, VAX6, SEC12, SEC25, SMC22, VAX5, SEC20, SEC22, SEC24, SEC26, SMC16 SMC24, VAX6, SEC25, SEC21, SEC23 and SMC21 exhibited lower values of SL, SP and AUDPC which are useful genetic resources for future CBB resistance breeding programmes. Nasir provided a grain yield of 3.45 ton/ha followed by VAX1 (2.86 ton/ha) and Hawassa Dume (2.83 ton/ha). Further, CBB-resistant and high yielding genotypes had the higher PPP and SPP making them ideal candidates for common bean breeding in Ethiopia or similar agro-ecologies emphasizing CBB resistance and enhanced agronomic traits.     

Valuable New Leaf or Inflorescence Resistances Ensure Improved Management of White Rust (Albugo candida) in Mustard (Brassica juncea) Crops

Field resistances/susceptibilities against Albugo candida race 2V were determined for 29 Indian Brassica juncea varieties and compared with resistant varieties from China (6) and Australia (7). ‘Basanti’ (AUDPC incidence 46.7; AUDPC severity 29.2) represents the first high‐level resistance to race 2V in Indian varieties. Several others showed lower but still useful levels of resistance, including Narendra Ageti Rai‐4 (AUDPC incidence 150.6; AUDPC severity 66.8) and JM1 (AUDPC incidence 167.1; AUDPC severity 83.7). Highly susceptible Indian varieties had AUDPC incidence values >200 and severity >100. ‘Basanti’ had least stagheads/plant (0.32), while Narendra Ageti Rai‐4 had lowest % plants with stagheads (2.48). In contrast, almost half of Indian varieties had stagheads/plant >1 and % plants with stagheads >4, and >26 for ‘Kranti’. The resistance in ‘Basanti’ paves the way forward towards significantly improved white rust management in mustard in India. JM06011, JM06021, JR049 from Australia and CJB‐003 from China had zero leaf incidence. There were significant (P < 0.001) relationships between disease incidence with severity (R² 0.92), stagheads/plant (R² 0.69) and also % plants with stagheads (R² 0.60); between disease severity with stagheads/plant (R² 0.68) and also % plants with stagheads (R² 0.69); and between stagheads/plant with % plants with stagheads (R² 0.59).     

Reduction of Winter Wheat Yield Losses Caused by Stripe Rust through Fungicide Management

Stripe rust of winter bread wheat (Triticum aestivum L.) causes substantial grain yield loss in Central Asia. This study involved two replicated field experiments undertaken in 2009–2010 and 2010–2011 winter wheat crop seasons. The first experiment was conducted to determine grain yield reductions on susceptible winter wheat cultivars using single and two sprays of fungicide at Zadoks growth stages Z61–Z69 in two farmers’ fields in Tajikistan and one farmer's field in Uzbekistan. In the second experiment, four different fungicides at two concentrations were evaluated at Zadoks growth stage Z69. These included three products from BASF – Opus (0.5 l/ha and 1.0 l/ha), Platoon (0.5 l/ha and 1.0 l/ha) and Opera (0.75 l/ha and 1.5 l/ha) – and locally used fungicide Titul 390 (0.5 l/ha and 1.0 l/ha). One and two sprays of fungicides did not differ significantly (P > 0.05) in increasing grain yield. Stripe rust reduced grain yield and 1000‐kernel weight (TKW) from 24 to 39% and from 16 to 24%, respectively. The benefits from the two concentrations of the same fungicide did not consistently resulted in significantly higher grain yield, suggesting that the lower concentrations could be more cost effective. Our study provides important information about the selection of fungicides, spray concentrations and number of spray to control stripe rust and increase grain yield. The findings could play an important role in developing stripe rust management approaches such as fungicide rotation and strategic fungicide applications in Central Asian countries.     

Phenotypic and Molecular Characterization of Wheat for Slow Rusting Resistance against Puccinia striiformis Westend. f.sp. tritici

Race‐specific resistance of wheat (Triticum aestivum L.) to yellow rust caused by Puccinia striiformis Westend. f.sp. tritici is often short‐lived. Slow‐rusting resistance has been reported to be a more durable type of resistance. A set of sixteen bread wheat varieties along with a susceptible control Morocco was tested during 2004–05 to 2006–07 in field plots at Peshawar (Pakistan) to identify slow rusting genotypes through epidemiological variables including final rust severity (FRS), apparent infection rate (r), area under disease progress curve (AUDPC), average coefficients of infection (ACI) and leaf tip necrosis (LTN). Epidemiological parameters of resistance were significantly (P < 0.01) different for years/varieties in three seasons, while variety × year interactions remained non‐significant. Sequence tagged site (STS) marker, csLV34 analyses revealed that cultivars Faisalabad‐83, Bahawalpur‐95, Suleman‐96, Punjab‐96, Bakhtawar‐93, Faisalabad‐85, Shahkar‐95 and Kohsar‐95 possessed Yr18 linked allele. Faisalabad‐83, Bahawalpur‐95, Suleman‐96, Punjab‐96, Bakhtawar‐93 and Faisalabad‐85 were relatively more stable over 3‐years where FRS, AUDPC and r values reduced by 80, 84 and 70% respectively compared to control Morocco. These six varieties therefore could be exploited for the deployment of Yr18 in breeding for slow rusting in wheat. Both FRS and ACI are suitable parameters for phenotypic selection.     

Phytophthora Crown and Root Rot of Apricot Caused by Phytophthora palmivora in Turkey

Forty‐nine Phytophthora isolates were obtained from roots and crown of apricot trees with symptoms of decline grown in commercial orchards in Malatya, Elaz?? and Diyarbak?r provinces, Turkey, in 2011 and 2013. All of the recovered isolates were identified as Phytophthora palmivora on the basis of morphological characteristics. Blast analysis of ITS region sequences of rDNA of 5 isolates revealed 100% identity with a reference isolates of P. palmivora from GenBank. Isolates of P. palmivora were pathogenic on 12‐month‐old wild apricot rootstock ‘Zerdali’ plants that were wound inoculated on the roots and on the crown. This study demonstrated that P. palmivora is the cause of the crown and root rot found on apricot in Turkey. To our knowledge, this is the first report of P. palmivora on this host plant.     

Selection of parents for crossing based on genotyping and phenotyping for stripe rust (Puccinia striiformis) resistance and agronomic traits in bread wheat breeding

Bread wheat (Triticum aestivum L.) germplasm consisting of 45 genotypes were clustered phenotypically using ten morphological traits and Area Under Disease Progress Curve (AUDPC) as measure of stripe rust resistance. The clustering was ratified by using twenty three molecular markers (SSR, EST and STS) linked to stripe rust (Puccinia striiformis f. sp. tritici) resistant QTLs. The aim was to asses the extent of genetic variability among the genotypes in order to select the parents for crossing between the resistant and susceptible genotypes with respect to stripe rust. The Euclidian dissimilarity values resulted from phenotypic data regarding morphological traits and AUDPC were used to construct a dendrogram for clustering the accessions. Using un-weighted pair group method with arithmetic means, another dendrogram resulted from the similarity coefficient values was used to distinguish the genotypes with respect to stripe rust. Clustering based on phenotypic data produced two major groups and five clusters (with Euclidian dissimilarity ranging from 244 to 16.16) whereas genotypic data yielded two major groups and four clusters (with percent similarity coefficient values ranging from 0.1 to 46.0) to separate the gene pool into highly resistant, resistant, moderately resistant, moderately susceptible and susceptible genotypes. With few exceptions, the outcome of both type of clustering was almost similar and resistant as well as susceptible genotypes came in the same clusters of molecular genotyping as yielded by phenotypic clustering. As a result seven genotypes (Bakhtawar-92, Frontana, Saleem 2000, Tatara, Inqilab-91, Fakhre Sarhad and Karwan) of diverse genetic background were selected for pyramiding stripe rust resistant genes as well as some other agronomic traits after hybridization.     

Deoxynivalenol accumulation and other scab symptoms in six romanian wheat genotypes inoculated withFusarium graminearum

At anthesis, under field conditions at Fundulea, each of 6 Romanian winter wheat genotypes was inoculated with 3Fusarium graminearum isolates used individually.Fusarium head blight (FHB) was assessed according to the following traits: relative weight of spikes (RWS), percentage of Fusarium damaged kernels (FDK), relative weight of kernels per head (RWKH), area under the disease progress curve (AUDPC) and deoxynivalenol (DON) content in total sample of kernels. Correlations between these traits and parameters revealed important differences between examined wheat genotypes in: DON accumulation, progress of FHB development, yield reduction, and models of host — pathogen interactions in theTriticum - Fusarium pathosystem. Significant correlations between different attributes of FHB were found forFusarium isolate 1 which is a moderate producer of DON (0.89 μg g^-1). Weight of spike was significantly correlated with weight of kernels per spike (r = 0.93**) and with percentage of damaged kernels (r = - 0.87**), while FDK was highly correlated with RWKH (r = - 0.85*) and with DON content (r = 0.82*). Area under the disease progress curve was also found to be significantly correlated with DON content (r = 0.86*).     

Effect of yellow rust on yield components of barley cultivars with race-specific and slow rusting resistance to yellow rust

Yellow rust caused by Puccinia striiformis f. sp. hordei is an important disease of barley (Hordeum vulgare L.) in some parts of the world. We compared the effectiveness of different types of resistance in field plots at Ardabil Agricultural Research Station (Iran) during 2010–2011. Yield components along with slow rusting parameters including final rust severity (FRS), apparent infection rate (r), relative area under disease progress curve (rAUDPC) and coefficient of infection (CI) were evaluated for 25 barley cultivars. In all, two barley cultivars with race-specific resistance, 19 cultivars with different levels of slow rusting resistance and four susceptible cultivars were included in two experiments with and without fungicide protection under high disease pressure. Barley cultivars with slow rusting resistance displayed a range of severity responses indicating phenotypic diversity. Mean thousand kernels weight (TKW) losses for susceptible, race-specific and slow rusting genotypes were 31, 3 and 12%, respectively, and mean kernels per spike (KPS) losses for susceptible, race-specific and slow rusting genotypes were 19, 0.2 and 8%, respectively. Correlation coefficient of mean TKW and KPS losses with epidemiological parameters; rAUDPC, r, CI and FRS were highly significant. Slow rusting cultivars with low values of different parameters as well as genotypes with low yield component losses despite moderate disease levels were identified. Such genotypes can be used for breeding barely genotypes with high levels of resistance and negligible yield losses.     

Evaluation of Macroscopic and Microscopic Components of Partial Resistance to Leaf Rust in Durum Wheat

Leaf rust, caused by the fungus Puccinia triticina, is considered one of the most important foliar diseases in durum wheat. Hypersensitive resistance (HR) may be rapidly overcome by the pathogen when resistant cultivars are grown on a large acreage or following changes in virulence in the pathogen population. Prolonging the durability of the resistance requires uses of other types of resistance such as partial resistance (PR). In this study, six durum wheat lines provided by the International Center for Corn and Wheat Improvement (CIMMYT) with a high level of PR to leaf rust were studied in monocyclic tests in a growth chamber. Inoculations were performed on both primary and fifth leaves using the Spanish race DGB/BN. UV fluorescence microscopy was employed to determine microscopic components of the resistance, such as the number of early aborted infection units not associated with plant cell necrosis (EA?) and relative colony size (RCS) of the established infection units. Macroscopic components of PR such as latency period, infection frequency and uredinium size were measured as well. All six resistant lines were characterized by a higher EA? and smaller RCS respect to the susceptible control ‘Don Rafael’. Line 3 showed the highest level of PR. It had 22% of EA? compared with 4% in the susceptible control, and the smallest RCS (17% respect to RCS of ‘Don Rafael’) at adult plant stage. Both EA? and RCS had a high heritability (more than 97%) and the correlation with macroscopic parameters (latency period and uredinium size) was also high (significant at 0.001 level). Hence, PR to leaf rust in these durum wheat genotypes has been revealed at microscopic level (higher EA? and smaller RCS).     

Yield Loss Associated with Soya Bean Rust (Phakopsora pachyrhizi Syd.) in Uganda

Studies were conducted to quantify the yield loss attributable to soya bean rust, a relatively new disease in Uganda. This was carried out for three consecutive seasons in the central, eastern, northern and western parts of the country, using three commercial varieties (Nam 1, Nam 2 and Namsoy 3) and two elite varieties (UG‐5 and GC‐00138‐29). The commercial varieties recorded higher yield losses (26.9–36.3%) and higher rust severities >50%, whereas the elite varieties recorded lesser yield losses of <10% and rust severities of <30%. Yield losses were highest in the central region (22.9%), and lowest in the northern region (15.1%). Yield losses differed significantly between seasons and were associated with reduction in seed weight and filled pod per plant.     

The effect of the accumulation of disease resistance genes on the long-term association of a global sample of environments for testing spring bread wheat

CIMMYT (the International Maize and Wheat Improvement Center) has routinely conducted international wheat yield trials to study the adaptation of spring bread wheat. The first of these, the International Spring Wheat Yield Nursery (ISWYN), was conducted for 31 years from 1964 to 1994 inclusive (30 cycles were conducted as no nursery was distributed in 1993 because of Karnal Bunt). Recently, pattern analysis methods have been developed and a set of computer programs written, which enable retrospective analyses of such historical databases to appraise the relationships among test environments in a way that discriminates among genotypes. Such an analysis was conducted on the 30 years of yield data from ISWYN and the classification derived from these analyses was compared with an agroecological classification of spring wheat test environments derived by CIMMYT. The incidence of foliar diseases (stem rust, leaf rust, yellow rust, Septoria spp. and Fusarium spp.) was important in the distinction between the high-rainfall low-latitude (mega-environment 2) and the high-input-irrigated low-latitude (mega-environment 1) environment types. The accumulation of resistance genes for these diseases has been an objective of the CIMMYT wheat breeding program. It was hypothesized that, as the relevant resistance genes were successfully pyramided into the germplasm, the distinction between these two mega-environment types would disappear. The results of the retrospective analyses support this hypothesis. Received: 19 May 1999 / Accepted: 17 January 2000     

Disease in wheat genotypes naturally infected with Gaeumannomyces graminis var. tritici

Wheat genotypes consisting of seven homozygous lines and 40 segregate families were studied at two sites naturally infested with the take-all pathogen, Gaeumannomyces graminis var. tritici. The numbers of seminal and coronal roots infected with G. graminis and other root pathogens were recorded. The genotypes differed in infection with G. graminis, with little evidence of genotype × environment interactions. The incidence of G. graminis and Rhizoctonia solani was negatively associated, but the association did not greatly influence differences between wheats in infection with G. graminis. The distribution of R. solani was negatively associated with the severity of take-all at only one site. Of symptoms of infection with G. graminis, wheat genotypes differed most in incidence of deadheads, but differences were not consistent over environments, and were associated with earliness of maturity. Wheats differed more in expression of disease than in infection with G. graminis. The course of disease was deduced from associations between the incidence of pathogens and components of plant growth and yield. G. graminis was the dominant pathogen at both sites, and caused a yield loss of 0–15% at one site, and an average 62% loss at the other. More components of yield were affected where disease was most severe.