Leakage of electrolytes and phenols and altered activity profile of peroxidase and its isoenzymes from wheat leaves inoculated withPuccinia recondita

Second and third leaves of 25-day old wheat (Triticum aestivum L.) planta, cultivar WL-711, were inoculated with three races of the brown rust pathogen,Puccinia recondita f. sp.tritici. The host reflected a differential interaction response towards these races, viz., susceptible reaction to race 77 (reaction type 4) intermediate reaction to race 104 (reaction type 1 - 3) and resistant reaction to race 63 (reaction type 0). Post-inoculation mutual interaction brought about observable changes in peroxidase activity along with leakage of electrolytes and phenolic constituents indicating altered permeability of host tissue. Differential increase in leakage of electrolytes and phenols occurred with increase of peroxidase activity during 12 h and 24 h post-inoculation, however, during 36 h, 48 h and 72 h post-inoculation, electrolyte leakage increased continuously with corresponding increases in peroxidase activity in all three interactions, while leakage of phenols showed a differential pattern. The differential changes in isoenzymic pattern of peroxidase activity were also noted during the progressive infection process which may also be an indication of altered permeability of the host issue at the very onset of brown rust infection.     

Pathogen race determines the type of resistance response in the stripe rust –Triticum dicoccoides pathosystem

Wild relatives of crop plants may serve as a promising source for screening for new disease resistance genes that can be utilized in breeding programs. Triticum dicoccoides, the wild progenitor of most cultivated wheats, was shown to harbor many resistance genes against the major diseases attacking cultivated wheat. Stripe rust is a devastating fungal disease that attacks wheat in many regions of the world. New races of Puccinia striiformis Westend. f. sp. tritici, the causative agent of stripe rust, have overcome most of the known Yr resistance genes in wheat. Therefore, there is a need to search for new resistance genes in the T. dicoccoides gene pool. A set of 120 T. dicoccoides accessions, collected from 13 populations representing different habitats in Israel and vicinity, was tested for resistance to three prevalent stripe rust races (38E134, 6E16 and 6E0). Of these 120 accessions, 14, 8 and 12% were resistant to races 38E134, 6E16 and 6E0, respectively, while 57, 2 and 4% were moderately resistant to these races, respectively. A unique resistance was found in the population of Mt Hermon where >80% of the accessions showed resistance to all races. Distribution of infection types (ITs) of race 38E134 showed a normal distribution that can fit a quantitative pattern of response, while the distributions of ITs of races 6E16 and 6E0 had excess of extreme values and therefore showing a qualitative pattern of response. anova testing the main factor effects and interaction showed significant effects of population, race and their interaction on IT. Significant positive correlations were obtained between the resistance to races 6E16 and 6E0 and humidity variables of the collections sites, while resistance to race 38E134 was positively correlated with temperature variables. These results show that the pathogen race can determine the type of resistance response, qualitative or quantitative, in the stripe rust—T. dicoccoides pathosystem. The obtained results also reveal that the distribution of resistance to different pathogen races can be affected by different climatic factors.     

小麦隐匿柄锈菌与小麦互作不同阶段的基因差异表达分析

[目的]小麦叶锈病是影响小麦生产主要病害之一,其病原菌新小种的出现和劣势小种上升为优势小种导致抗病品种的抗病性不断被克服.小麦隐匿柄锈菌与小麦互作不同阶段差异表达谱分析对于揭示该病菌致病的分子机制,进而有效防控小麦叶锈病具有重要意义.[方法]利用转录组分析小麦隐匿柄锈菌致病生理小种与感叶锈病小麦品种MuTcLr19亲和...     

Genetic Overlap in the Quantitative Resistance of Rice at the Seedling and Adult Stages to <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis>

The genetic components responsible for the qualitative and quantitative resistance of rice to three Chinese races (C2, C4, and C5) of Xanthomonas oryzae pv. oryzae (Xoo) were investigated at the seedling and adult stages in two successive years in set of Lemont/Teqing cross introgression lines (ILs) in a Teqing background, to create a complete linkage map using 160 well-distributed SSR markers. Teqing was resistant to C2 and C4, but moderately susceptible to C5, whereas Lemont was susceptible to all three races. Highly significant correlations were detected among the resistance to different races at different developmental stages. A major gene (Xa4), 14 main-effect QTLs (M-QTLs), and 18 epistatic QTLs were identified in the two developmental stages over 2 years, and were largely responsible for the segregation of resistance in the ILs. In 2007, the Lemont alleles at all loci in the seedling stage, except QBbr10 to C4, increased lesion length (LL) or decreased resistance. The Teqing allele at the Xa4 locus acted as a resistance gene against C2 and C4, but acted as a M-QTL when its resistance was overcome by the virulent race C5. M-QTLs showed a degree of race specificity and had a cumulative effect on resistance. Most M-QTLs (94%) consistently expressed resistance to the same race at the seedling and adult stages, indicating that a high degree of genetic overlap exists between Xoo resistance at both developmental stages in rice. Among the digenic interactions, most co-introgressed Lemont alleles at the two epistatic loci lead to significantly smaller LL with all three races, compared to other types of interacting alleles at both development stages. The results indicate that a high level of resistance may be achieved by the cumulative effect of multiple M-QTLs, including the residual effects of “defeated” major resistance genes and the epistatic effects of co-introgression from diverse susceptible varieties.     

Response to Gamma Irradiation and Induced Virulent Mutation in Melampsora medusae of Poplars

When the urediniospores of three races of Melampsora medusae, the causal agent of leaf rust of poplars, were exposed to Co⁶⁰ gamma irradiation (range 100–1000 Gy), there were significant differences in the radiosensitivity of the races as assessed, in vitro, by incubation period to flecking and the uredinial survivability percentage. In race 5A the frequency of mutation to virulence on Populus deltoides cv. T-173, normally a resistant cultivar, was maximum (1.688 %) at an irradiation dose of 400 Gy. Importance of mutations as source of variability in pathosystems and usefullness of artificially induced mutations in the context of host-pathogen interactions are discussed.     

Chitinases of <Emphasis Type="Italic">Coffea arabica</Emphasis> genotypes resistant to orange rust <Emphasis Type="Italic">Hemileia vastatrix</Emphasis>

Two Coffea arabica — Hemileia vastatrix incompatible interactions (I₁: coffee cv. Caturra — rust race VI and I₂: coffee cv S4 Agaro — rust race II) and a compatible interaction (coffee cv. Caturra — rust race II) were compared in relation to the infection process and chitinase activity. In the two incompatible interactions the fungus ceased growth in the early infection stages, while in the compatible interaction no fungus growth inhibition was observed. A high constitutive level of chitinase activity was detected in the intercellular fluid of healthy leaves. Upon infection, chitinase isoforms were more abundant in incompatible interactions than in the compatible interaction. Immunodetection showed that class I chitinases are particularly relevant in the incompatible interactions and might participate in the defence response of the coffee plants.     

Dr. Heinz rogoll‐70 Jahre

The wheat crop remains vulnerable to all three rust diseases (leaf rust, stem rust and yellow rust) caused by Puccinia spp. according to the prevalence of the pathogen in different wheat-growing areas worldwide. Stripe rust or yellow rust caused by Puccinia striiformis f. sp. tritici is the most significant rust pathogen which prefers cool, moist areas and highlands. The pathogen is recognised as responsible for huge production losses in wheat. Genetic variation in pathogen makes its control difficult. Therefore, resistance against all the races of the pathogen known as durable or race-non-specific resistance is preferred. The present study was carried out to identify durable resistance against stripe rust in selected wheat cultivars from Pakistan through seedling testing, field evaluation at adult stage, morphological marker studies and marker-assisted selection. Results revealed that 4% of the cultivars were resistant at the seedling stage while the rest were susceptible or intermediate. To confirm their field resistance, the same cultivars were evaluated under field conditions at Cereal Crops Research Institute Pirsabak (located in Khyber Pakhtunkhwa, KP) a hot spot of stripe rust in Pakistan. Observations exhibited that at the adult stage 4% of the cultivars were resistant, 70% intermediate or moderately resistant while the others were highly susceptible. Leaf tip necrosis was observed in 30% of the cultivars. Wheat cultivars showing susceptibility at the seedling stage were highly to moderately resistant at adult stage showing durable resistance. For further validation, morphological markers were also observed in cultivars indicating the presence of Yr18/Lr34 gene. Eleven cultivars (C-518, Mexipak, Kohinoor-83, Faisalabad-83, Zardana-93, Shahkar-95, Moomal-2002, Wattan-94, Pasban-90, Kiran-95, and Haider-2000) were identified, having durable or race non-specific resistance against stripe rust. These cultivars can further be utilised in wheat breeding programmes for deploying durable resistance to attain long lasting control against stripe rust.     

Seedling and adult‐plant stage resistance of a world collection of barley genotypes to stripe rust

Barley stripe rust caused by Puccinia striiformis f.sp. hordei (PSH) is one of the major diseases in barley production regions worldwide. A total of 336 barley genotypes with diverse genetic backgrounds targeted for low‐input barley production were tested for seedling and adult‐plant stage resistance against six PSH races (0S0, 0S0‐1, 1S0, 4S0, 5S0 and 7S0) originated from India. The seedling resistance was evaluated by inoculating the barley genotypes with six races separately under controlled conditions in Shimla, India. The same barley genotypes were evaluated for adult‐plant stage resistance in the Agricultural Research Station (ARS) of Rajasthan Agriculture University, Durgapura, Rajasthan, India. Out of the 336 barley genotypes tested for seedling resistance, 119 (35.4%), 101 (30.1%), 87 (25.9%), 100 (29.8%), 91 (27.1%) and 70 (20.8%) genotypes were resistant to races 0S0, 0S0‐1, 1S0, 4S0, 5S0 and 7S0, respectively. In the field, 102 (30.3%) genotypes showed the resistance response of which 18 (5.3%) genotypes were highly resistant to PSH. Barley genotypes AM‐14, AM‐177, AM‐37, AM‐120, AM‐300, AM‐36, AM‐103, AM‐189, AM‐291, AM‐275 and AM‐274 showed resistance response to all six races at seedling and adult‐plant stages. Seedling resistance reported in the current study is effective against the newly emerged race 7S0 and previously reported five races in India. Therefore, resistant barley genotypes identified in the current study provided effective protection against all six races at seedling and adult‐plant stages. The stripe rust resistance identified in the current studies may be potential donors of stripe rust resistance to barley breeding programmes in India and elsewhere.     

Identification and mapping in spring wheat of genetic factors controlling stem rust resistance and the study of their epistatic interactions across multiple environments

Stem rust (Puccinia graminis f. sp. tritici) is responsible for major production losses in hexaploid wheat (Triticum aestivum L.) around the world. The spread of stem rust race Ug99 and variants is a threat to worldwide wheat production and efforts are ongoing to identify and incorporate resistance. The objectives of this research were to identify quantitative trait loci (QTL) and to study their epistatic interactions for stem rust resistance in a population derived from the Canadian wheat cultivars AC Cadillac and Carberry. A doubled haploid (DH) population was developed and genotyped with DArT^® and SSR markers. The parents and DH lines were phenotyped for stem rust severity and infection response to Ug99 and variant races in 2009, 2010 and 2011 in field rust nurseries near Njoro, Kenya, and to North American races in 2011 and 2012 near Swift Current, SK, Canada. Seedling infection type to race TTKSK was assessed in a bio-containment facility in 2009 and 2012 near Morden, MB. Eight QTL for stem rust resistance and three QTL for pseudo-black chaff on nine wheat chromosomes were identified. The phenotypic variance (PV) explained by the stem rust resistance QTL ranged from 2.4 to 48.8 %. AC Cadillac contributed stem rust resistance QTL on chromosomes 2B, 3B, 5B, 6D, 7B and 7D. Carberry contributed resistance QTL on 4B and 5A. Epistatic interactions were observed between loci on 4B and 5B, 4B and 7B, 6D and 3B, 6D and 5B, and 6D and 7B. The stem rust resistance locus on 6D interacted synergistically with 5B to improve the disease resistance through both crossover and non-crossover interactions depending on the environment. Results from this study will assist in planning breeding for stem rust resistance by maximizing QTL main effects and epistatic interactions.     

A rapid method for measuring production of yellow rust spores on single seedlings to assess differential interactions of wheat cultivars with Puccinia striiformis

Uredospore production of Puccinia striiformis in single wheat seedlings was assessed by weighing spores on an electrical microbalance, by counting on a haemocytometer or by measuring turbidity of spore suspensions with a spectrophotometer and compared with production from groups of seedlings determined by weighing spores on an analytical balance. The data were used to assess differential interaction of wheat cultivars Hybrid 46 and Joss Cambier with two isolates of race 104 E137 of P. striiformis and cvs Maris Templar and Joss Cambier with two isolates of race 41 E136. A significant differential interaction was shown in both experiments by each method but most rapidly and with the minimum of materials by the single-plant microbalance technique. Measurements of spore production demonstrated differences between isolates within races more clearly than the conventional visual assessment of yellow rust symptoms.     

The inheritance of restriction fragment length polymorphisms in the flax rust Melampsora lini

Summary Random cDNA sequences synthesized from poly A⁺ RNA extracted from germinated urediospores of the flax rust fungus, Melampsora lini, were used as probes to detect restriction fragment length polymorphisms (RFLPs) in three races of M. lini originating from cultivated flax, Linum usitatissimum, and one race originating from Australian native flax, L. marginale. Fourteen out of 22 probes tested detected RFLPs in the three races from cultivated flax while 19 of the probes detected polymorphisms between these three races and the race from L. marginale. The segregation of seven RFLPs was determined in a family of 19 F₂ progeny derived from a cross between two of the rust races. With six of these the inheritance was consistent, in each case, with the segregation of alleles at a single locus. Inheritance of the seventh was unusual and an explanation involving two loci with null alleles at each was proposed. No linkage was detected between any of the RFLP loci and nine unlinked loci specifying avirulence.     

Genetic control of durable resistance to yellow rust (Puccinia striiformis) in the wheat cultivar Hybride de Bersée

The wheat cultivar Hybride de Bersee is described as possessing durable resistance to yellow rust. Some races of Puccinia striiformis can infect it at the seedling stage but not severely in the field. Using euploid and aneuploid stocks of Bersee it was shown that a large part of this resistance was controlled by chromosome 5BS-7BS, the effect being detectable in seedlings and at later growth stages. Measurements of spore production from infected seedlings showed that the line ditelosomic for the 5BS arm of the chromosome was more resistant than the line ditelosomic for the 7BS arm under environments favouring high spore production, but more susceptible under environments favouring low spore production. Thus both arms of the chromosome could contribute to resistance in appropriate environments. Chromosome 5BS-7BS did not carry the factors controlling the race-specific resistance to race 37 E132 of P. striiformis. The possibility of exploiting the resistance carried by chromosome 5BS-7BS in wheat breeding programmes is discussed.     

Undescribed wheat gene for partial leaf rust and stripe rust resistance from Thatcher derivatives RL6058 and 90RN249 carryingLr34

Inheritance of partial leaf rust and stripe rust resistance of a Thatcher wheat 90RN2491, earlier reported to carry two doses of the gene pairLr34-Yr18 and the reference line RL6058 (6*Thatcher/PI58548) for theLr34-Yr18 gene pair was studied against predominant and highly virulent Indian races. Thatcher derivatives 90RN2491 and RL6058 were intercrossed as well as crossed with the leaf rust and stripe rust susceptible Indian cultivar WL711. The F₁, F₂ and F₃ generations from these crosses were assessed for rust severity against leaf rust race 77-5 and stripe rust race 46S119. The F₂ and F₃ generations from the crosses of RL6058 and 90RN2491 with WL711, segregated 15 resistant : 1 susceptible (F₂) and 7 homozygous resistant : 8 segregating : 1 homozygous susceptible (F₃) ratios, respectively, both for leaf rust and stripe rust severity. Therefore, partial resistance against each of the leaf rust and stripe rust races in both RL6058 and 90RN2491 is ascribed to two independently inherited dominant genes. One of the two genes for leaf rust and stripe rust resistance in 90RN2491 and RL6058 isLr34 and the linked geneYr18, respectively. The second leaf rust resistance gene in both the Thatcher lines segregated independently of stripe rust resistance. Therefore, it is notLr34 and it remains unidentified.     

Determination of Physiological Races and Evaluation of Sunflower for Resistance to Puccinia helianthi Schw

Sunflower rust, caused by Puccinia helianthi Schw., is a widespread disease of sunflower (Helianthus annuus L.) in China. To study physiological races, sunflower field surveys were undertaken in major sunflower growing areas of China in 2010. Forty‐four rust‐infected sunflower leaf samples were collected from 25 geographical locations. Freshly produced spores were used to study physiological race differentiation on a set of nine differentials. Race 300 was the most prevalent race observed over all locations with a 59% frequency followed by races 735, 310, 500, 724 and 737. To evaluate hybrids and varieties for resistance screening, spores of race 300 were used to inoculate 65 hybrids, and five open‐pollinated varieties selected from breeding programmes and from the seed market. None of the confection hybrids and open‐pollinated varieties was immune to race 300. Conversely, among oilseed hybrids, 3% of them showed immunity, 12% highly resistant, 59% resistant and 26% showed susceptible reactions. Open‐pollinated varieties were the most susceptible to race 300 followed by confection and oilseed sunflower hybrids. Results from this study are projected to assist breeders in selection of hybrids and varieties against prevalent race as our results showed a diversity of resistance levels to race 300.     

Reaction of some wheat cultivars and breeding lines to Puccinia striiformis f. sp. tritici hot races in Iran

Many physiological races of Puccinia striiformis f. sp. tritici which cause stripe rust in wheat can be determined in different parts of the world. The emergence of new races with different pathogenicity which happens very quickly breaks cultivars resistant and cause disease. Therefore, breeding cultivar for resistance to different pathogenic races should be continued. In this research, pathogenicity of two isolates collected from two regions of Iran were determined by using wheat yellow rust differential lines, which indicated race 70E50A+ and 6E18A+ The responses of 30 wheat genotypes were separately evaluated in the forms of randomized complete block design with three replicates in the seedling stage under greenhouse condition. The components of resistance including latent period and infection type were recorded. Results indicated genotypes were evaluated in terms of both traits and were significant at 1% level. Also, the results from pathogenicity study indicated of effective gene/s included Yr1, Yr2+, Yr3, Yr4, Yr5, Yr10, Yr15, Yr24, Yr26, YrSP, YrND, YrSD and YrSU. From the genotypes studied in the greenhouse condition, 39% of the genotypes showed complete resistance to both races. Probably, resistance genes, Yr32 and YrCV, or the other unknown genes which are types of seedling resistance are either alone or in combination of one another cause strength in resistant genotypes.     

PHYSIOLOGICAL RACES OF PHYTOPHTHORA INFESTANS: A COMPARISON OF THE DIFFERENTIAL HOSTS AT THE PLANT BREEDING INSTITUTE, CAMBRIDGE, WITH THOSE OF THE SCOTTISH SOCIETY FOR RESEARCH IN PLANT BREEDING

At the Plant Breeding Institute, Cambridge, there have been recognized three physiological races of blight ( Phytophthora infestans ), A, B and C ; and at the Scottish Society for Research in Plant Breeding, Edinburgh, there have been used five races, A, B ¹, B ², C and D , obtained in the British Isles.
It is shown that the two Cambridge types of differential hosts, AbC and ABc (where A = resistant to race A, a = susceptible to race A , etc.), are Ab ¹ b ² CD and AB ¹ B ² cD respectively on the Scottish scheme, and that the Cambridge races A, B and C correspond to the Scottish races A, B ¹ and C respectively.
A number of blight isolates were tested on both the Cambridge and Scottish differential hosts. Isolates of race types A, B ¹, B ¹, C and D were found.
The identification and origin of physiological races of blight, and the breeding of blight-resistant potatoes, are discussed.     

Rust resistance in Triticum cylindricum Ces. (4x, CCDD) and its transfer into durum and hexaploid wheats.

In order to counteract the effects of the mutant genes in races of leaf rust (Puccinia recondita f.sp. tritici Rob. ex Desm.) and stem rust (P. graminis f.sp. tritici Eriks. &Henn.) in wheat, exploration of new resistance genes in wheat relatives is necessary. Three accessions of Triticum cylindricum Ces. (4x, CCDD), Acy1, Acy9, and Acy11, were tested with 10 races each of leaf rust and stem rust. They were resistant to all races tested. Viable F1 plants were produced from the crosses of the T. cylindricum accessions as males with susceptible MP and Chinese Spring ph1b hexaploid wheats (T. aestivum, 6x, AABBDD), but not with susceptible Kubanka durum wheat (T. turgidum var. durum, 4x, AABB), even with embryo rescue. In these crosses the D genome of hexaploid wheat may play a critical role in eliminating the barriers for species isolation during hybrid seed development. The T. cylindricum rust resistance was expressed in the F1 hybrids with hexaploid wheat. However, only the cross MP/Acy1 was successfully backcrossed to another susceptible hexaploid wheat, LMPG-6. In the BC2F2 of the cross MP/Acy1//LMPG-6/3/MP, monosomic or disomic addition lines with resistance to either leaf rust race 15 (infection types (IT) 1=, 1, or 1+; addition line 1) or stem rust race 15B-1 (IT 1 or 1+; addition line 2) were selected. Rust tests and examination of chromosome pairing of the F1 hybrids and the progeny of the disomic addition lines confirmed that the genes for rust resistance were located on the added T. cylindricum C-genome chromosomes rather than on the D-genome chromosomes. The T. cylindricum chromosome in addition line 2 was determined to be chromosome 4C through the detection of RFLPs among the genomes using a set of homoeologous group-specific wheat cDNA probes. Addition line 1 was resistant to the 10 races of leaf rust and addition line 2 was resistant to the 10 races of stem rust, as was the T. cylindricum parent. The added C-genome chromosomes occasionally paired with hexaploid wheat chromosomes. Translocation lines with rust resistance (2n = 21 II) may be obtained in the self-pollinated progeny of the addition lines through spontaneous recombination of the C-genome chromosomes and wheat chromosomes. Such translocation lines with resistance against a wide spectrum of rust races should be potentially valuable in breeding wheat for rust resistance.     

Identification of additional sources of resistance to Puccinia striiformis f. sp. hordei (PSH) in a collection of barley genotypes adapted to the high input condition

A total of 336 barley genotypes consisting of released cultivars, advanced lines, differentials and local landraces from the ICARDA barley breeding programme were screened for seedling and adult‐plant resistances to barley stripe rust pathogen (Puccinia striiformis f. sp. hordei [PSH]). Seedling resistance tests were undertaken at Shimla, India by inoculating 336 barley genotypes with five prevalent PSH races [Q (5S0), 24 (0S0‐1), 57 (0S0), M (1S0) and G (4S0)] in India. Barley genotypes were also evaluated at the adult‐plant stage for stripe rust resistance at Durgapura (Rajasthan, India) in 2013 and 2014, and at Karnal (Haryana, India) in 2014 under artificial PSH infection in fields, using a mixture of the five races. Twelve barley genotypes (ARAMIR/COSSACK, Astrix, C8806, C9430, CLE 202, Gold, Gull, Isaria, Lechtaler, Piroline, Stirling, and Trumpf) were resistant to all five PSH races at the seedling and adult‐plant stages. Two of these genotypes, Astrix and Trumpf, were part of international differentials and reveal that five races were avirulent to genes Rps4 (yr4), rpsAst, rpsTr1 and rpsTr2. These genes were highly effective against PSH races prevalent in India. The virulence/avirulence formula reported in this study helped to determine the effectiveness of PSH resistance genes against Indian races. Forty‐five genotypes showed adult‐stage plant resistance (APR) in the field. The identified PSH resistant genotypes may possess novel resistance genes and might serve as potential donors of PSH resistance at seedling and APR in the future. Further research is needed to determine the nature of resistance genes through allelic studies and mapping of these genes.     

Identification of QTL for reaction to three races of <Emphasis Type="Italic">Colletotrichum trifolii</Emphasis> and further analysis of inheritance of resistance in autotetraploid lucerne

Anthracnose, caused by Colletotrichum trifolii, is one of the most serious diseases of lucerne worldwide. The disease is managed through deployment of resistant cultivars, but new pathotypes present a challenge to the successful implementation of this strategy. This paper reports the genetic map locations of quantitative trait loci (QTL) for reaction to races 1, 2 and 4 of C. trifolii in a single autotetraploid lucerne clone, designated W126 from the Australian cv. Trifecta. Resistance was mapped in a backcross population of 145 individuals, and reaction was assessed both by spray and injection inoculation of stems. Resistance to injection inoculation with races 1 and 4 was incompletely dominant and closely linked (phenotypic markers 2.2 cM apart); these resistances mapped to a linkage group homologous to Medicago truncatula linkage group 8. When the spray inoculation data were subjected to QTL analysis, the strongest QTL for resistance was located on linkage group 8; six QTL were identified for race 1 and four for race 4. Resistance to race 2 was incompletely recessive; four QTL were identified and these include one QTL on linkage group 4 that was also identified for race 1. Modelling of the interactions between individual QTL and marker effects allowed a total of 52–63% of the phenotypic variation to be described for each of the different races. These markers will have value in breeding lucerne, carrying multiple sources of resistance to the three known races of C. trifolii.     

Linkage mapping of genes controlling resistance to white rust (Albugo candida) in Brassica rapa (syn. campestris) and comparative mapping to Brassica napus and Arabidopsis thaliana.

Genes for resistance to white rust (Albugo candida) in oilseed Brassica rapa were mapped using a recombinant inbred (RI) population and a genetic linkage map consisting of 144 restriction fragment length polymorphism (RFLP) markers and 3 phenotypic markers. Young seedlings were evaluated by inoculating cotyledons with A. candida race 2 (AC2) and race 7 (AC7) and scoring the interaction phenotype (IP) on a 0-9 scale. The IP of each line was nearly identical for the two races and the population showed bimodal distributions, suggesting that a single major gene (or tightly linked genes) controlled resistance to the two races. The IP scores were converted to categorical resistant and susceptible scores, and these data were used to map a single Mendelian gene controlling resistance to both races on linkage group 4 where resistance to race 2 had been mapped previously. A quantitative trait loci (QTL) mapping approach using the IP scores detected the same major resistance locus for both races, plus a second minor QTL effect for AC2 on linkage group 2. These results indicate that either a dominant allele at a single locus (Acal) or two tightly linked loci control seedling resistance to both races of white rust in the biennial turnip rape cultivar Per. The map positions of white rust resistance genes in B. rapa and Brassica napus were compared and the results indicate where additional loci that have not been mapped may be located. Alignment of these maps to the physical map of the Arabidopsis genome identified regions to target for comparative fine mapping using this model organism.