Reactions of Hordeum spontaneum to infection with two cultures of Puccinia hordei from Israel and United States

Summary The reactions to infection with two cultures of Puccinia hordei were determined for 292 Hordeum spontaneum (syn. H. vulgare ssp. spontaneum) accessions, collected at 16 sites which encompassed the ecological range of H. spontaneum in Israel. Culture Tel-Aviv was from Israel and culture 57.19 was from the United States. Fifty-two percent of the accessions were resistant to culture Tel-Aviv and 67% were resistant to culture 57.19. Forty-three percent of the accessions were resistant to both cultures. The average infection type (IT) of accessions within sites ranged from 2.7 to 7.5 on a 0–9 rating scale. The results showed that the presence of Ornithogalum species, the alternate hosts of P. hordei, may increase the percentage of H. spontaneoum accessions resistant to P. hordei. More accessions were resistant at sites where humidity at 1400 was higher, the annual evaporation was lower, and where the glumes were shorter. Kernel weight and annual rainfall was not correlated with resistance. A lower percentage of H. spontaneum accessions were resistant to P. hordei culture Tel-Aviv from Israel than to culture 57.19 from the United States. In a previous study a lower percentage of H. spontaneum accessions also was found to be resistant to a culture of Erysiphe graminis hordei from Israel than to cultures from other countries. Previous studies also have shown that cultures of P. hordei and E. graminis hordei from Israel have many genes for virulence on barley, and that H. spontaneum accessions from Israel have many genes for resistance to these two pathogens. Previous results and the results reported in this paper support the hypothesis of coevolution of resistant host genes and virulent pathogen genes where hosts and pathogens have coexisted for many thousand years.     

The genetics of seedling resistance to leaf rust,Puccinia hordeiOtth. in some spring barley cultivars

Summary The three Dutch isolates studied carried virulence genes against the resistance genes Pa, Pa-2, Pa-4 and Pa-5, substantiating the widespread occurrence of these virulences in Western Europe as reported by others. The cultivars Cebada Capa, La Estanzuela, Gondar and Dabat carry the same dominant to semi-dominant gene, which is also found in Forrajera Klein and H2212. It is proposed to designate this gene Pa-7. This gene segregated independently from the Pa-3 gene in Rika x (Baladi x Rika) substantiating the data of Johnson (1968), but disagreeing with those of Roane & Starling (1970). EP 75 seems to carry a single dominant or semi-dominant gene conferring an intermediate resistance to the isolates used. This gene, tentatively designated as Pa-z, is different from the Pa, Pa-2, Pa-4, Pa-5 and Pa-7 genes. The intermediate resistance of Monte Christo is probably based on gene(s) different from EP 75.     

Pathogenicity of the Rhynchosporium secalis population in the Western Cape province of South Africa

The virulence spectra of 50 Rhynchosporium secalis isolates from a population in the Western Cape province of South Africa were determined, and 21 races were detected when evaluated against 17 differential cultivars. The virulence spectrum of the R. secalis population shows considerable variation, and carries unnecessary virulence genes which is quite unexpected, since chiefly susceptible barley cultivars are grown in the south Western Cape. The two most prevalent races, namely races 4 and 7 had three and four virulence genes respectively. Both race 4 and 7 were virulent on the most susceptible cultivars, West China, Steudelli, C.I.8618 and C.I.2226. Considering the resistance genes reported for the cultivars Atlas 46, Turk, and C.I.3515 which showed no susceptible cultivar-pathogen interaction, it would appear that the Rh-Rh3-Rh4 complex is primarily involved in conferring resistance to the local R. secalis isolates This revised version was published online in July 2006 with corrections to the Cover Date.     

Adaptation of wheat rusts to the wheat cultivars in former Czechoslovakia

Summary In former Czechoslovakia virulence of rusts attacking wheat was studied since the sixties. Since the same time genes for resistance in the registered cultivars were identified. The role of Berberis and Thalictrum as alternate hosts for stem rust and leaf rust, respectively, was investigated as well. Determined changes of virulence in rust populations could only partially be ascribed to changes of resistance genes in the grown cultivars. Unnecessary genes for virulence had no negative effect on the fitness of the pathogen. All tested samples of aeciospores from barberries attacked rye, not wheat. None of Thalictrum species occurring in the Czech and Slovak Republics was found to host wheat leaf rust. However, the sexual stage of wheat stem rust and wheat leaf rust could be induced on Berberis vulgaris and Thalictrum speciosissimum, respectively. General epidemiological conclusions are drawn from the results and experience of the last 35 years.     

Genes for resistance in barley to Finnish isolates of Rhynchosporium secalis

Summary Twenty Finnish isolates of Rhynchosporium secalis (Oud.) J.J. Davis, the causal agent of scald, were taken from infected barley (Hordeum vulgare L.) plants and inoculated on to seedlings of a differential series of barley containing a range of major genes for resistance to the fungus, as well as on to six Nordic 6-row spring barleys and three winter ryes (Secale cereale L.). These fungal isolates derived from four sites and three host varieties. Disease development was monitored on two leaves of seedlings in the greenhouse employing a standard scale, and on adult plants in the field by assessing the diseased area on the three uppermost leaves. A comparison was also made between the pathogenicity and virulence of ten Finnish and ten Canadian R. secalis isolates. The Finnish isolates varied in virulence, but with the exception of Algerian (CI 1179) seedlings and adult La Mesita (CI 7565) all seedlings and adult plants of the entire differential series were resistant to all isolates. Canadian isolates were, on average, less virulent than Finnish isolates. All the Nordic checks were susceptible to all Finnish and seven Canadian isolates, but differences in the degree of susceptibility were evident. Isolates of R. secalis from barley were non-pathogenic on rye, isolates from Elymus repens L. were non-pathogenic on barley and rye, and isolates from rye were only pathogenic on rye. Finnish R. secalis isolates contain no redundant pathogenic diversity. The differential series represents a useful, but as yet untapped, source of resistance to R. secalis for Finnish barley breeders.     

Race differentiation and search for sources of resistance to Rhynchosporium secalis in barley in Italy

Summary Barley in Italy has recently been seriously affected by Rhynchosporium secalis. The pathogenic variation of the fungus was studied and 17 races were differentiated on 13 barley cultivars carrying most of the currently known genes for resistance. RC 1, the most virulent and most frequent race, was virulent on 10 out of the 13 differentials and the remaining races proved to be less virulent variants of RC 1. Atlas (C.I. 4118), Atlas 46 (C.I. 7323) and Osiris (C.I. 1622) were the only three differentials resistant to all the analyzed single-spore isolates.Differential cultivars previously assumed to have identical resistance factors did not react in the same way to all the Italian races, thereby revealing either undisclosed differences in the genes described or the presence of additional unidentified ones.Our findings were compared with previous data about virulence of scald populations from different countries, on the basis of tests with common differentials: fundamental differences were found between the Italian population and those of other countries with regard to virulence patterns.The susceptible reactions to race RC 1 of most barley cultivars grown in Italy indicate the urgent need for resistance genes to be incorporated in the cultivated material. Seventy-one barley accessions, known as sources of resistance in different parts of the world, were screened for their behaviour to races RC 1 and RC 13. Twenty-two appeared resistant to both of them.     

Diversity among Finnish net blotch isolates and resistance in barley

Summary Seedlings of a differential barley (Hordeum vulgare L.) series (21 genotypes) and of six check genotypes were used in the greenhouse to assess variation in virulence among 20 single-spore isolates of the net blotch pathogen. Pyrenophora teres Drechs. f.teres Smedeg., collected from various sites in Finland. The experiment was run twice and symptom expression was recorded on the first three leaves. Analysis of second leaf symptom scores from Run 1 indicated differences in virulence between isolates, all of which were pathogenic, and differential resistance among the barleys. The virulence of P. teres isolates appeared to be conditioned by the host barley from which the isolate derived; the average virulence of isolates collected from a susceptible host was greater than that of isolates collected from a less susceptible host. Results from Run 2 were similar regarding resistance within the barleys, but variation in virulence among the P. teres isolates was not consistent with that from Run 1. CI 9819 caries duplicate genes for resistance to P. teres (Rpt1b and Rpt1c), and CI 7548 possesses Rpt3d. Both genotypes were highly resistant to all isolates. The Rpt1a gene of Tifang (CI4407) conferred resistance to all isolates in Run 2, but only to about half of the isolates in Run 1. The checks, including two of the symptomatically most resistant Nordic barley genotypes, were universally susceptible during these stringent tests. No selective pressure has been placed on Finnish isolates of P. teres through previous deployment of major resistance genes, and it is speculated that any variation in virulence among isolates is likely to be due to a combination of evolutionary forces including, natural selection, random genetic drift and gene flow.     

A set of differential Glycine hosts for the identification of races of Phakopsora pachyrhizi Syd.

Summary Variation in the responses of a wide range of accessions of four native Australian species of Glycine (viz. G. canescens, G. clandestina, G. tabacina and G. tomentella) to infection by eight Australian isolates of Phakopsora pachyrhizi was analyzed.Differences in the infection type responses of the various wild Glycine species were sufficient to recognize six different virulence combinations amongst the eight pathogen isolates.A set of differential hosts useful in the identification of different races of the pathogen is presented to facilitate further examination of the virulence structure of the pathogen population.     

Verifying the genetic relationships between three leaf rust resistance genes in barley

Summary The genetic relationships between three known genes for resistance to Puccinia hordei in barley, Pa 3, Pa5 and Pa 7, were re-examined because of conflicting reports in the literature. PA 3 was found to be independent of Pa 5 and Pa 7, but the latter two are linked with an estimated recombination value of 7.6±1.4%. Trisomic analysis confirmed Pa 7 to be on chromosome 3, but Pa 3 could not be associated with chromosomes 3 to 7 and, therefore, is inferred to be either on chromosome 1 or 2     

Pathotypes and NIP1 gene sequences of Finnish Rhynchosporium secalis isolates from barley, couch grass and rye

Rhynchosporium secalis (Oud.) J.J. Davis, causal agent of scald of barley (Hordeum vulgare L.), was isolated from barley, couch grass (Elymus repens L.) and rye (Secale cereale L.). Isolates were used to inoculate seedlings of a differential barley series containing several sources of major gene resistance to the disease. The series included Atlas46, (resistance gene Rrs1) and the isogenic line Atlas, which lacks the gene (rrs1). The necrosis-inducing peptide NIP1 has been suggested to be the product of the avirulence gene AvrRrs1 (NIP1) that with the barley resistance gene Rrs1 determines the incompatibility of the pathogen-host interaction. All R. secalis isolates were virulent only on the susceptible barley cultivars Arve and Chan, irrespective of spore concentration or original host species. There were no indications of redundant virulence among the R. secalis isolates. The NIP1 gene was sequenced from each isolate and there was no correlation with source of the isolate or sequence modification and virulence. Four isolates, from barley and couch grass, were characterised by a basic Type I NIP1sequence. The recorded NIP1 sequence changes are consistent withR. secalis populations not receiving selection through deployment of the Rrs1 gene in commercial barley cultivars in Finland. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of resistance to Puccinia graminis tritici and Puccinia recondita tritici in Kenya Plume wheat

Summary Seven genes, viz. Sr5, Sr6, Sr7a, Sr8a, Sr9b, Sr12 and Sr17 were associated with seedling resistance to Puccinia graminis tritici in Kenya Plume wheat. The predominant field cultures were avirulent on seedlings with Sr7a, but possessed virulence for the other six genes. However, Sr7a did not confer adult-plant resistance when present on its own. Adult-plant resistance was attributed to Sr2 and possibly also to the interaction of Sr7a and Sr12.Two genes, Lr13 and Lr14a, were identified in seedling tests with various cultures of Puccinia recondita tritici. Lr13 conferred adult-plant resistance to the predominant field strains. Genetic recombination between Lr13 and Sr9b was estimated at 17.6±3.1%.     

The response of field-inoculated wheat cultivars to mixtures of Septoria tritici isolates

Summary Wheat cultivars of diverse genetical background and response to Septoria tritici were inoculated during 2 years in the field with single or mixtures of isolates. Significant reductions in pycnidial coverage were recorded for mixtures of 2 or 5 isolates relative to the virulent isolate ISR8036 under the moderate 1989/1990 epidemic. The interactions between cultivars and all possible combinations among ISR398A1, USR8036 and the 1:1. mixture of the 2 isolates were highly significant. Cultivars exposed to mixtures of isolates expressed differential response in pycnidial coverage compared to the single isolate response. The coverage in the mixtures was significantly less than that of the arithmetic mean between the two isolates. Under the severe 1990/1991 epidemic pycnidial coverage on cultivars inoculated with the mixture of the same 2 isolates did not differ statistically from that of ISR8036, yet, ISR398A1 differed from ISR8036 and the isolate mixture. Losses in 1000-kernel weight for 12 wheat cultivars which were repeated during the 2-trial-years were significantly lower in the isolate mixture relative to that of ISR8036. The suppression of symptoms in isolate mixture relative to the expected expression of the most virulent component may be indicative of differential aggressiveness of isolates regardless of their virulence. The phenomenon may affect screening and selection procedures in breeding for resistance.     

Residual effects of the Xa-4 resistance gene in three rice cultivars when exposed to a virulent isolate of Xanthomonas campestris pv. oryzae

Summary F₂ plants of five, and F₃ plants of three, crosses between genotypes carrying the race-specific resistance gene Xa-4 and genotypes not carrying this gene were inoculated with two isolates of Xanthomonas campestris pv. oryzae. Half the tillers of each plant received isolate PX061, avirulent on the Xa-4 gene, the other half of the tillers received isolate PX099, virulent for the Xa-4 gene. The F₂ and F₃ populations segregated for a single dominant resistance gene, Xa-4.The parental, F₂ and F₃ genotypes not carrying Xa-4 had mean lesion lengths between 28 and 29 cm for both isolates. The Xa-4 carrying parents showed a mean lesion length of 2.7 cm with the avirulent isolate and of 12.4 cm with the virulent isolate. The Xa-4 carrying F₂ and F₃ genotypes had mean lesion lengths of 5.2 and 20.1 cm for the two isolates, respectively. These observations strongly indicate that the Xa-4 gene, carried by the rice genotypes studied (IR28, Cisadane and BR51-282-8), had a considerable residual effect when exposed to virulent isolate PXO99.     

Evolution of virulence patterns in yellow rust races and its implications for Ereeding for resistance in wheat in Kenya

Summary Virulence patterns of yellow rust isolates collected in Kenya between 1986–1989 were compared with earlier results. The number of virulence factors per race and the range in virulence factors both increased considerably. Before 1976 races carried on average 4.5 to 5.0 virulence factors, whereas the races after 1986 had a mean of 6.5 virulence factors. The range in the number of virulence factors increased from some seven to eight in the first period to 12 in the second out of the 17 evaluated. In the period 1986–1989 another three virulence factors (2, 9 and A) were assessed. All three occurred at a high frequency.Virulence neutralizing the resistance genes Yr2, Yr2+, Yr6, Yr6+, Yr7, Yr7+, Yr8, Yr9, Yr9+ and those in the cultivars Anza (A), Strubes Dickkopf (SD) and Suwon92/Omar (SU) occurred at a high frequency, while virulence for Yr3V, Yr4+, Yr5, CV and SP (resistance in Carstens V and Spaldings Prolific resp.) were not found. The remaining three virulence factors for Yr1, 10 and 3N were rare.In the past ten years the resistance of most released cultivars became ineffective in less than six years. They were shown to carry race-specific major resistance genes such as Yr7+, Yr9+, SD and A. However, in the field, the resistance of the cultivars was not completely neutralized. A residual resistance, ranging from moderate to fairly high, was observed in all cultivars in which the major gene resistances were neutralized by corresponding virulence genes.Other wheat cultivars such as Africa Mayo, Kenya Kudu, Enkoy, Kenya Leopard, Bounty, Frontatch, Bonny and Kenya Plume appeared to keep their resistance over a condiserable period of time. They are considered to be durably resistant to the Kenyan yellow rust populations. This form of resistance, together with the residual resistance, can be recommended for use in breeding programmes.     

Pathogenic variation among isolates of Rhynchosporium secalis from cultivated barley growing in Victoria,Australia

Summary Three hundred and nineteen Rhynchosporium secalis isolates from cultivated barley were divided into five groups on the basis of their virulence on 15 differential barley varieties. Pathogenic variation was also demonstrated for isolates from different scald lesions within the same crop and amongst different spores from the same lesions.     

Production of aneuploids of the cotton hybrid G. barbadense × <Emphasis Type="Italic">G. hirsutum</Emphasis> L. via intergeneric pollination with <Emphasis Type="Italic">Abelmoschus esculentus</Emphasis>

The possibility to induce embryo development after pollination of F₁ interspecific cotton hybrids (Gossypium barbadense × Gossypium. hirsutum) with pollen from Abelmoschus esculentus was investigated to determine if wide-cross hybrid, haploid or other types of progeny might result. Small numbers of progeny (Pa) were indeed recovered after numerous alien pollinations and in-planta development or in-vitro culture. The Pa plants were characterized phenotypically and studied cytogenetically and microscopically to help establish their origin documenting their reproductive basis. Root-tip chromosome counts and meiotic Metaphase-I analyses revealed that chromosome numbers among cells of the Pa plants ranged from 33 to 44 and that the differences in chromosome number among cells of the same plant ranged from 1 to 3, indicating somatic instability. Flow cytometric analysis also indicated the aneuploid nature of Pa plants. Although the reproductive mechanisms need to be characterized more extensively by cytological and molecular means, the observations suggest that alien pollinations may have resulted in parthenogenetic (Pa) egg cell development, or some other unusual reproductive events. The production of wide-crosses and high degrees of aneuploidy could be of use for several types of genomic studies, e.g., functional genomic characterization of genome shock, deletion mapping, and germplasm introgression.     

Variation in virulence and resistance in the bean-bean rust pathosystem in Ecuador

Twenty two Uromyces appendiculatus isolates were tested on 20 differential and 25 Ecuadorian Phaseolus vulgaris cultivars in the seedling stage. Based on the infection types 20 races could be discerned. The Ecuadorian cultivars differed greatly in their reaction to the isolates, from resistant to only one isolate (`Red Small Garden') to resistant to all isolates (’G2333‘). The isolates showed a wide range of virulence to the Ecuadorian cultivars, from virulent to only two cultivars (isolate 13) to virulent to 21 cultivars (isolates 5 and 23). Seven cultivars with a basically susceptible infection type appeared to differ greatly in quantitative resistance when tested in three consecutive crop cycles. The disease severities in percentage leaf area affected averaged over the three cycles ranged between 83.9% for ‘Red Small Garden’ and 13.1% for ‘INIAP-414’. Race-specific resistance does not seem an advisable breeding strategy, but the quantitative resistance offers a good alternative.     

Screening techniques and sources of resistance to root rots and wilts in cool season food legumes

Soilborne, fungal pathogens of cool season food legumes, including seed and seedling blights, rot rots, and wilts are described. Seed and seedling diseases are caused primarily by Pythium and Rhizoctonia spp. The most important fungi causing root rots include Aphanomyces euteiches, Fusarium solani, Pythium spp., Sclerotium rolfsii, and Macrophomina phaseolina. Wilt is caused primarily by various host-specific forms of Fusarium oxysporum. This paper discusses these diseases and screening procedures that emphasize standardization of inoculum levels, maintenance of virulent pathogen cultures, inoculum growth media, environmental conditions, and host plant age. Sources of resistance to these diseases are discussed.     

Plants regenerated from embryo cultures of an apomictic clone of Kentucky bluegrass (Poa pratensis L. ‘Baron’) are not apomictic in origin

Plants were regenerated from tissue cultures of embryos dissected from seeds that were harvested from a self-pollinated clonal selection of Kentucky bluegrass (Poa pratensis L.) ‘Baron’, an apomictic cultivar. Plants were regenerated from 35 embryo-derived callus cultures of the 3280 embryos that were plated. Flow-cytometric (FCM) and RAPD-marker analyses were performed to determine if regenerants were or were not apomictic in origin. Fifteen regenerants with a 3c DNA content were classified as arising from 2n + n aberrant embryos, which was a higher frequency than expected, based on a chi-square analysis. Of the remaining 20 regenerants with a 2c DNA content, a chi-square test showed that all could have arisen from n + n sexually-derived embryos, based on the observed segregation of n + n regenerants, which fit the expected 3:1 ratio of dominant:recessive RAPD-marker phenotypes. The apparent lack of regenerants of apomictic origin, and implications for genetic transformation and breeding of Kentucky bluegrass are discussed.     

Development and characterization of a new 1BL.1RS translocation line with resistance to stripe rust and powdery mildew of wheat

The 1BL.1RS wheat-rye translocation from Petkus rye has contributed substantially to the world wheat production. However, following the breakdown of disease resistance genes in 1RS, its importance for wheat improvement decreased. We have developed a new 1BL.1RS line, R14, by means of crossing rye inbred line L155, selected from Petkus rye to several wheat cultivars. One new gene each, for stripe rust and powdery mildew resistance, located on 1RS of the line R14, are tentatively named YrCn17 and PmCn17. YrCn17 and PmCn17 confer resistance to Puccinia striiformis f. sp. tritici pathotypes that are virulent on Yr9, and Blumeria graminis f. sp. tritici pathotypes virulent on Pm8. These two new resistances, YrCn17 and PmCn17, are now available for wheat improvement programs. The present study indicates that rye cultivars may carry yet untapped variations as potential sources of resistance.