Mapping polygenes for tuber resistance to late blight in a diploid Solanum phureja × S. stenotomum hybrid population

Potato tuber blight is a disease caused by the oomycete Phytophthora infestans (Mont.) de Bary. Due to the significant economic impact of this disease, introgression of durable resistance into the cultivated potato is one of the top priorities of breeding programmes worldwide. Though numerous resistance loci against this devastating disease have already been mapped, most of the detected loci are contributing towards foliar resistance while specific information on tuber resistance is limited. To identify the genetic components of tuber resistance and its relationship to foliar resistance and plant maturity we have investigated the host‐pathogen interaction in a segregating diploid hybrid Solanum phureja × S. stenotomum family. Mature tubers from this mapping family were inoculated with a sporangial suspension of P. infestans (US‐8 clonal lineage) and evaluated for lesion expansion. No significant correlation was detected between late blight resistance in foliage and tubers, and between plant maturity and tuber resistance. Four chromosomal regions were significantly associated with tuber resistance to the disease. The largest effect was detected near the marker locus PSC (LOD 10.7) located on chromosome 10. This locus explained about 63% of the total phenotypic variation of the trait. The other three resistance‐related loci were mapped on chromosomes 8 (GP1282, LOD 4.4), 6 (CP18, LOD 4.0) and 2 (CP157, LOD 3.8). None of the four tuber resistance loci coincides with the foliage resistance loci detected in this same family. Tuber blight resistance quantitative trait loci (QTL) on chromosomes 2, 8 and 10 are distinct from the maturity QTLs and have an additive effect on tuber resistance. These results indicate that different genes are involved in foliar and tuber resistance to P. infestans in the present family and that some of the resistance genes might be associated with late maturity.     

Somatic hybrids of vegetable brassicas as source for new resistances to fungal and virus diseases

Somatic hybrids were produced by PEG-induced symmetric and asymmetric protoplast fusions in order to transfer resistance to Alternaria brassicicola, A. brassicae, Phoma lingam, Plasmodiophora brassicae and Turnip mosaic virus (TuMV) into Brassica oleracea var. capitata (cv. ‘Toskama’) and botrytis (cv. ‘Korso’). As resistance donors, ten species belonging to several genera of the family Brassicaceae including wild relatives were used. Of 2,189 plants (somatic hybrids, partially in vitro cloned) tested, 1,616 (73.8%) were resistant against at least one of the pathogens, indicating that, mostly, a successful resistance transfer has taken place. Five hundred and twenty-two hybrids showed multiple resistances to two, three and, in a single case, to four pathogens. Irrespective of the donor parents used in the fusion, a broad variability in symptom manifestation ranging from 0 (without symptoms) to 9 (highly susceptible) could be observed. With regard to the Alternaria pathogens, Sinapis alba, B. nigra and B. juncea were the most effective resistance donors, whereas fusions with Raphanus sativus resulted in the most hybrids with resistance to clubroot and TuMV. As could be shown especially in asymmetric fusions with S. alba, Barbarea vulgaris and Hesperis matronalis, transferred resistance to a pathogen may not correspond with resistance exhibited by the donor parent. Some combinations in which both parents were highly susceptible, e.g. R. sativus (+) B. oleracea var. capitata, yielded hybrids that exhibited strong resistance, e.g. to A. brassicicola, revealing that a new type of resistance might be occurring. With regard to the Alternaria pathogens, resistance expression was very unstable. Many hybrids into which (also variable) resistance of some donors, such as B. vulgaris, S. alba and B. carinata, was transferred became as highly susceptible as those of which the fusion parents did not show any resistance reaction (e.g. R. sativus). For reliable characterization of the resistance response, hybrids should be subjected to several resistance tests during growth period of the host, at least until flowering.     

Pod shatter resistance evaluation in cultivars and breeding lines of Brassica napus, B. juncea and Sinapis alba

Pod shatter susceptibility was investigated in Brassica napus germplasm and shatter resistant species of B. juncea and Sinapis alba. The comparisons were made by measuring seed yield in field plots, detached pod rupture energy (RE) and the half‐life of pod‐opening. Pod shatter resistance was significantly greater in B. napus lines derived from interspecific hybridizations of B. napus with B. rapa, B. carinata and B. juncea, than common B. napus cultivars. While these lines exhibited no significant difference in resistance to pod shatter than B. juncea, an entry of S. alba had no yield loss caused by pod shatter. Resistance to pod shatter was characterized in the field as little or no yield loss after full maturity, delayed shattering in time, and stable yield performance under variable climatic conditions during pod maturity. Yield loss caused by pod shatter ranged from a low of 4% for the B. juncea cv. ‘AC Vulcan’ to a high of 61% for the black seeded B. napus line DH12075 in 2‐year field trials after 1 month maturity. Pod shatter resistance was not significantly associated with specific plant and pod morphological traits, except pod length (P = 0.005) in tested materials. Field visual scores of pod shatter through inspections of average pod shatter per plant within plots were highly correlated with plot yield loss. Indoor quantitative evaluations of pod strength using a pendulum machine to measure pod RE and random impact test to measure half‐life of pod‐opening resistance were highly correlated with field yield loss. Multiple evaluations of pod shatter in method and in time after pod maturity are recommended for reliable evaluation of pod shatter resistance.     

Screening of Portuguese cole landraces (Brassica oleracea L.) with Peronospora parasitica and Plasmodiophora brassicae

Summary Forty-four landraces of Portuguese coles (Brassica oleracea L.), representing different morphotypes, were screened at the cotyledon stage for downy mildew resistance, caused by Peronospora parasitica. Two isolates of the pathogen, PHW 630 and PHW 828, were used in the experiment. The mean disease interaction phenotype varied among the landraces. Overall, the Portuguese coles have shown resistance to both isolates, particularly to isolate PHW 828. Some landraces were identified with differential reaction to the two P. parasitica isolates. Some of the Portuguese coles are, therefore, good sources of resistance genes to P. parasitica, and could be used in breeding programs or in the development of a downy mildew host differential set. Among the morphotypes tested, Couve Algarvia (ISA 207), Couve Galega (ISA 243 and 187) and Couve Glória de Portugal (ISA 84) have presented the highest resistance interaction. For the development of host differential sets, the landraces ISA 2 (Penca de Mirandela), ISA 35 (Couve de Valhascos) and ISA 600 (Penca Espanhola) could be further selected for the differentiation of P. parasitica isolates. They are resistant to PHW 828 and susceptible to PHW 643.The same morphotypes and landraces were also screened at the seedling stage for resistance to clubroot, caused by Plasmodiophora brassicae Woron.. Although some variation for resistance could be noticed in some the landraces tested, mainly Galega kale types, none of them presented a sufficient level of resistance as to be directly be useful in breeding for resistance to race 6 of P. brassicae.     

Molecular markers for Ve1 and Ve2 Verticillium resistance genes from Italian tomato germplasm

The so‐called Rosa (= pink) tomatoes, which are typically grown in the Southern Italian area, are characterized by the pink colour of the fruit, due to the gene y, colourless fruit skin. In a preliminary survey, it was found that among these Rosa tomatoes there were some ‘Rosa di Sorrento’ local landraces showing resistance to Verticillium wilt (race 1). In tomato, resistance to race 1 of V. dahliae and V. albo‐atrum is conferred by two strictly associated genes, Ve1 and Ve2, which independently confer resistance to the same pathogen. The development of two new markers for Ve1 and Ve2, based respectively on selective allele‐specific PCR amplification and on a PCR amplification followed by enzymatic restriction, is reported. These two markers allow the identification of both allelic forms at the Ve loci and they are of potential interest for use in marker‐assisted selection. Furthermore, ‘Rosa di Sorrento’‐resistant lines have the same resistance alleles as those found in the Ve‐resistant cultivars.     

Exploiting the natural variation of <Emphasis Type="Italic">Arabidopsis</Emphasis><Emphasis Type="Italic">thaliana</Emphasis> for the seed-specific production of proteins

The seed-specific expression of recombinant proteins in transgenic plants offers several interesting advantages over other production platforms. The aim of this study was to select accessions of Arabidopsis thaliana with the highest potential as a platform for seed-specific production of recombinant proteins. A. thaliana was chosen because of its flexibility, high seed yield per m2, high natural protein content and its non-food status. Seven characteristics were measured for 96 accessions; days to first flower bud, days to complete senescence, rosette size, number of main bolts, dry biomass of plant, seed yield and protein content of seeds. Three characteristics (length of life cycle, seed yield and protein content) were used to select accessions with a maximal yield. A variation of length of life cycle between 87 ± 11 days (Ler-1) and more than 200 days (several accessions) was registered. Seed yields per accession varied between 18 ± 16 mg (Wa-1) and 274 ± 76 mg (Mr-0). Protein content ranged between 30% (Ws-2) and 38% (Cvi-0). Based on the results of this study, accession Nok-3 is selected as the accession best suited for exploitation as a seed-based platform for the production of recombinant proteins. Nok-3 has a high seed yield (194 ± 66 mg) combined with a moderate protein content of 34.8% and short life cycle of 126 ± 17 days, resulting in a calculated protein yield per year three times higher than reference accession Col-0. In conclusion, this study illustrates the unexploited variability present in the Arabidopsis gene pool that can be used directly for further optimization of Arabidopsis seeds as production platform. In combination with A. thaliana’s rapid life cycle, flexibility, and high fertility, this makes it an attractive platform for the production of specific groups of recombinant proteins, such as high-purity products produced on a relatively small scale.     

Heritability of spotted wilt resistance in a Florida‐EP™ “113”‐derived peanut (Arachis hypogaea) population

Spotted wilt, caused by tomato spotted wilt virus (TSWV), is a major disease of peanut (Arachis hypogaea ) in the south‐eastern United States. Cultivar resistance is the most important factor in disease control. However, spotted wilt resistance in current cultivars still carries risk in the absence of other practices when disease is severe. In contrast, a newly developed cultivar, Florida‐EP? “113,” has demonstrated excellent resistance even when spotted wilt is severe. Information on heritability of this resistance can help breeders better utilize it in breeding. F₂‐derived populations from the cross Florida‐EP? “113”/Georgia Valencia were developed and tested in field experiments in Florida from 2012 to 2014. Disease symptoms were evaluated visually, and the frequency of TSWV infection was measured by ImmunoStrip^®. Heritability estimated from ImmunoStrip^® was higher (0.66) compared to visual ratings (0.48). Genetic correlations among evaluation methods (r _A = 0.92–0.99) and environments (r _B = 0.86–0.99) were high. These results indicate that resistance in Florida‐EP? “113” is highly heritable and that selection in a high disease risk environment is feasible without significant erosion of genetic gain.     

Sources of resistance to Indian pathotypes of Puccinia graminis tritici and P. triticina in durum wheat

Stem rust and leaf rust are important diseases affecting durum wheat production in India. Inheritance and extent of diversity in resistance were studied in five durum genotypes, viz. ?B 662', ?ED 2398‐A', ?HG 110', ?IWP 5019' and ?Line 1172? using Pgt pathotypes 40A and 117‐6, and Pt pathotypes 12‐2 and 104‐2. F₂ and F₃ analyses showed that resistance was conferred by one or two genes in each line. In all, four genes for resistance to 40A, and eight each for pathotypes 117‐6 and 12‐2 were identified among the five genotypes, and three for resistance to 104‐2 among B 662, ED 2398‐A and IWP 5019 were indicated by tests of allelism. Although the gene identities are not known, at least some of them should be different from Sr2, Sr7b, Sr8a, Sr8b, Sr9e, Sr9g, Sr11, Sr12, Sr13, Sr14, Sr17, Sr23 and Sr28; and from Lr3, Lr14a, Lr23 and Lr27 + Lr31. These genotypes enrich the diversity of resistance to stem rust and leaf rust for durum wheat improvement.     

Effect of different cole crops on the biological parameters of <Emphasis Type="Italic">Pieris brassicae</Emphasis> (L.) (Lepidoptera: Pieridae) under laboratory conditions

The effect of different cole crops was studied on biological parameters of Pieris brassicae (L.) in the laboratory at 28 °C, 65% RH, and 12L:12D photoperiod. The results indicated that host plants significantly affected the life history, i.e. survival of developmental stages, oviposition period, and sex ratio of P. brassicae. Comparative study on different host plant revealed that P. brassicae required a maximum of 40 days to complete generation on cabbage, cauliflower, and broccoli. The survivorship and expectation of life declined gradually with the advancement of age; the life expectancy of newly deposited eggs was 23.96 days while it was 8.12 days at the time of adult emergence on cabbage. However, the fluctuations of mortality parameter were seen on all the cole crops. On cabbage, 100% hatching of eggs with low larval mortality were noticed. The highest net reproductive rate (R₀) occurred on cauliflower, i.e. 27.1 followed by cabbage 24.89, females per female per generation. Intrinsic rate of increase (r_m), was found to be highest (0.09558954) on cauliflower followed by broccoli and cabbage, 0.078886 and 0.077551 females per female per day, respectively. The smallest r_m (0.059469 females per female per day) occurred on radish which shows that P. brassicae did not perform well on radish. In addition, P. brassicae may double in 7.2 days on cauliflower, 8.7 days on broccoli, and 8.9 days on cabbage. The sex ratio was computed as 1.5:1, female:male, respectively on cabbage.     

Microstructure of a Brassica rapa genome segment homoeologous to the resistance gene cluster on Arabidopsis chromosome 4

Genome evolution is a continuous process and genomic rearrangement occurs both within and between species. With the sequencing of the Arabidopsis thaliana genome, comparative genetics and genomics offer new insights into plant biology. The genus Brassica offers excellent opportunities with which to compare genomic synteny so as to reveal genome evolution. During a previous genetic analysis of clubroot resistance in Brassica rapa, we identified a genetic region that is highly collinear with Arabidopsis chromosome 4. This region corresponds to a disease resistance gene cluster in the A. thaliana genome. Relying on synteny with Arabidopsis, we fine-mapped the region and found that the location and order of the markers showed good correspondence with those in Arabidopsis. Microsynteny on a physical map indicated an almost parallel correspondence, with a few rearrangements such as inversions and insertions. The results show that this genomic region of Brassica is conserved extensively with that of Arabidopsis and has potential as a disease resistance gene cluster, although the genera diverged 20 million years ago.     

Resistance of 12 rose genotypes to 14 isolates of Diplocarpon rosae Wolf (rose blackspot) collected from eastern North America

Blackspot disease, caused by the fungus Diplocarpon rosae Wolf, is the most serious disease problem of roses worldwide. From a breeding perspective, the documented occurrence of races in the pathosystem necessitates the characterization of the race structure for the pathogen, identification of resistance genes in rose germplasm, and determination of the nature of genetic resistance to breed stably resistant rose cultivars. The objective of this study was to characterize the diversity of eastern North American races of D. rosae and to simultaneously determine the degree to which partial resistances existed in rose hosts. Twelve rose genotypes were inoculated with 14 single‐conidial isolates collected from eastern North America. Three distinct D. rosae races were identified based on presence/absence of infection in the differential array. There were five distinct reaction patterns across pathogen isolates among the 12 rose genotypes. The partial resistance components of leaf area with symptoms, lesion length and incubation period were evaluated for all inoculated plants. Variation for expression of partial resistance was noted, and partial resistance appears to behave in a race‐specific manner for some rose genotypes. Early defoliation differed between genotypes and may prove to be another component of partial resistance.     

Radiation‐Use Efficiency,Biomass Production,and Grain Yield in Two Maize Hybrids Differing in Drought Tolerance

Drought‐tolerant (DT) maize (Zea mays L.) hybrids have potential to increase yield under drought conditions. However, little information is known about the physiological determinations of yield in DT hybrids. Our objective was to assess radiation‐use efficiency (RUE), biomass production, and yield in two hybrids differing in drought tolerance. Field experiments were conducted in 2013 and 2014 with two hybrids, P1151HR (DT hybrid) and 33D49 (conventional hybrid) under well‐watered (I₁₀₀) and drought (I₅₀) conditions. I₁₀₀ and I₅₀ refer to 100 % and 50 % evapotranspiration requirement, respectively. On average, P1151HR yielded 11–27 % greater than 33D49 at I₁₀₀ and about 40 % greater at I₅₀, At I₁₀₀, greater yield in P1151HR was due to greater biomass at physiological maturity (BM_pm) resulting from greater post‐silking biomass accumulation (BM_post). At I₅₀, both hybrids had similar BM_pm but P1151HR showed a higher harvest index and greater BM_post. RUE differed significantly (P < 0.05) between the hybrids at I₁₀₀, but not at I₅₀. At I₁₀₀, the RUE values for P1151HR and 33D49 were 4.87 and 4.28 g MJ^?1 in 2013, and 3.71 and 3.48 g MJ^?1 in 2014. At I₅₀, the mean RUE was 3.89 g MJ^?1 in 2013 and 3.16 g MJ^?1 in 2014. Results indicate that BM_post is important for maintaining high yield in DT maize.     

Utilization of Asymmetric Somatic Hybridization for the Transfer of Disease Resistance from Brassica nigra to Brassica napus

Asymmetric somatic hybrid calli were produced between Brassica napus and a transgenic (Hyg ^R) line of B. nigra using a donor recipient fusion method for the production of cybrids. The transgenic line of B. nigra used as a donor also possessed genetic resistance to the pathogenic fungi Phoma lingam and Plasmodiophora brassicae. Using hygromycin for selection, 332 hybrid calli were obtained from which 30 produced shoots (1—-20 per callus) which were rooted on a hormone-free culture medium. The rooted shoots were transferred into soil and cultivated in a growth chamber where the plants were tested for resistance against the two pathogens. Out of 129 hybrid plants tested for resistance against P. brassicae, 30 (23.3 %) plants proved to be resistant and from 78 plants tested for resistance against P. lingam, 41 (52.6 %) plants remained disease-free after infection.     

Pollen and pistil morphology, in vitro pollen grain germination and crossing success of Lens cultivars and species

Morphological and in vitro germination characteristics of pollen altogether with pistil and style length were analysed, so as to carry out a morphological comparison between different lentil (Lens culinaris Medik.) cultivars and wild species, as well as to correlate the morphological and functional statistics with data regarding crossing success. Pollen length and width in the different genotypes were found to have a positive and highly significant correlation with pistil and style length and in vitro pollen tube length. A cluster analysis detected two different plant groups, namely, (i) large‐seeded L. culinaris (macrosperma), and (ii) a second group formed by two subgroups, a first subgroup with L. ervoides standing alone and a second subgroup including small‐seeded L. culinaris (microsperma) and the wild L. culinaris ssp. orientalis, L. odemensis, L. nigricans. A high and significant correlation was detected between crossing success and phenotypic similarity (r > 0.98; P < 0.05), therefore implying that phenotypic similarity, based on pollen morphology and in vitro pollen length together with pistil and style length, is a good predictor of hybridization success.     

Genetic control of resistance to the aphid Brevicoryne brassicae in the wild species Brassica fruticulosa

Initial studies have shown variable resistance in Brassica fruticulosa to the aphid Brevicoryne brassicae The aim of this work was to fix high levels of resistance to B. brassicae in true breeding lines of B. fruticulosa and obtain data on the genetic control of resistance. Plants from initially variable B. fruticulosa accessions were selfed to produce inbred resistant and susceptible lines that were studied in three separate experiments to determine the extent to which resistance to B. brassicae had been fixed. Results from three experiments using successive generations of resistant and susceptible inbred lines showed that continued selection resulted in resistant inbred lines that supported an average of three aphids per plant compared with an average of 96 aphids per plant for susceptible inbred lines. Data collected from an experiment determining the resistant phenotype of lines including the selfed progenies and the F₁ and F₂ progeny of a cross between resistant and susceptible individual plants indicated that the resistance was not controlled by a single gene.     

Expression of a cDNA encoding palmitoyl-acyl carrier protein desaturase from cat's claw (Doxantha unguis-cati L.) in Arabidopsis thaliana and Brassica napus leads to accumulation of unusual unsaturated fatty acids and increased stearic acid content in the seed oil

A cDNA encoding palmitoyl‐acyl carrier protein (ACP)‐desaturase from cat's claw (Doxantha unguis‐cati L.) was expressed in Arabidopsis thaliana and Brassica napus L. with the goal of decreasing the saturated fatty acid (FA) content of the seed oil. In general, transformation of Arabidopsis resulted in a greater change in the FA composition of the seed oil than for B. napus. An increase in palmitoleic acid (16:1cisΔ⁹) was obtained in transgenic lines, suggesting that the 16:0‐ACP‐desaturase cDNA was expressed in the manner originally intended. Other effects on lipid metabolism, however, were observed in the seed of transgenic plants. In Arabidopsis, there was a large increase in the proportions of cis‐vaccenic acid (18:1cisΔ¹¹) and cis‐13‐eicosenoic acid (20:1cisΔ¹³), possibly generated through elongation of 16:1cisΔ⁹. Elongation of 18:1cisΔ¹¹ to 20:1cisΔ¹³, however, was not observed in B. napus indicating that certain aspects of lipid metabolism in the model plant, Arabidopsis, may not apply to B. napus. As well, the appearance of 18:1cisΔ¹¹ was accompanied by a decrease in the proportion of oleic acid (18:1cisΔ⁹). Although the introduced ACP‐desaturase resulted in synthesis of some unsaturated FAs, the overall saturated FA content was maintained at similar levels to the control or was enhanced. Increased levels of saturation were mainly associated with an increase in stearic acid, which unlike 16:0, is considered non‐atherogenic. The results suggest that a mechanism exists further downstream in oil biosynthesis to counteract the decrease in saturation brought about by the 16:0‐ACP‐desaturase action.     

Resistance spectra of wheat genotypes and virulence patterns of <Emphasis Type="Italic">Mycosphaerella graminicola</Emphasis> isolates in Iran

Co-evolution of wheat and its devastating pathogen Mycosphaerella graminicola (anamorph Septoria tritici), the causal agent of septoria tritici blotch, a foliar disease of wheat, is suggested to occur in Fertile Crescent as their center of origin and, thus, interaction between pathogen virulence and host resistance is important subject to be addressed. We have investigated resistance spectra of 54 wheat genotypes including a set of differentials carrying known resistance genes and virulence patterns of 14 M. graminicola isolates at seedling stage under controlled environmental conditions. The isolates were collected in Iran from five provinces. Diversity in virulence and aggressiveness was observed among the isolates from four provinces. Isolates collected from Golestan province were virulent to all wheat genotypes from germplasm of Iran, while specific resistances were identified to the isolates from other provinces. Among wheat genotypes, cvs. Chamran, Morvarid and Hirmand had the greatest number of specific resistances as well as partial resistance. Wheat genotypes of the differential set also differed in their reactions to the isolates. Arina, Flame and TE 9111 were specifically resistant to the greatest number of isolates from different provinces. Most isolates were virulent to the other differentials such as cvs. Shafir, Estanzuela federal and Courtot indicating that extensive adaption of virulence to most of the known resistance genes (Stb) has occurred in these regions. The new sources of resistance to highly virulent isolates from Iran may also be utilized in wheat breeding programs to develop resistant cultivars against pathogen populations in other countries.     

Selection for resistance to Plasmodiophora brassicae Wor. in oriental subspecies of Brassica rapa L.

Summary Selection for resistance to Plasmodiophora brassicae Wor. in oriental groups of Brassica rapa L.Two hundred and sixty-five cultivars of leafy, oriental bassicas were tested for resistance to 18 collections of Plasmodiophora brassicae, the causal agent of clubroot. The tests were conducted in the greenhouse at low and high level inoculum concentrations. Eleven cultivars of B. rapa pe-tsai, five cultivars of B. rapa pak-choy and three cultivars of B. rapa choy-sum consistently segregated for resistance at the lower concentration of inoculum (1000 spores/ml). All 265 cultivars were susceptible at the higher concentration (1 000 000 spores/ml). Three cultivars were used in pedigree and recurrent selection schemes for increased resistance. After three cycles of selfing resistant individuals, significantly more resistant S₃ lines were derived from each cultivar. Lines derived from two cultivars. Chinese White and PI 257236, continued to improve with each cycle of selection and demonstrated increased resistance to higher levels of inoculum (up to 1 000 000 spores/ml) New cultivars based on intercrosses of S₂ resistant individuals also had significantly better resistance than the original cultivar. After two cycles of selection in the third cultivar, PI 419007, resistance did not increase and its S₂ mass did not differ significantly from the original cultivar. Evidence that indicates resistance is pathotype-non-differential and offers an alternative to major gene, pathotype-differential types of resistance currently being introduced to the leafy oriental brassicas from other Brassica rapa groups.     

‘CPAN 1842’: a new source of adult plant leaf rust resistance in bread wheat

There is worldwide interest in adult plant resistance (APR) because of greater durability of APR to the cereal rusts. Peruvian bread wheat genotype ‘CPAN (Coordinated Project Accession Number) 1842’ (LM 50–53) has shown leaf rust resistance in disease screening nurseries since its introduction in 1977. However, it is susceptible at the seedling stage to several Puccinia triticina (Pt) pathotypes including the widely prevalent 77‐5 (121R63‐1) that infects bread wheat. Inheritance studies showed that CPAN 1842 carried a dominant gene for APR to pathotype 77‐5, which was different from Lr12, Lr13, Lr22a, Lr34, Lr35, Lr37, Lr46, Lr48, Lr49 and Lr68, based on the tests of allelism; and from Lr67, based on genotyping with the closely linked SSR marker cfd71. This gene should also be different from Lr22b as the latter is totally ineffective against pathotype 77‐5. CPAN 1842 therefore appears to be a new promising source of leaf rust resistance. Also having resistance to stem rust and stripe rust, this line can contribute to breeding for multiple rust resistances in wheat.     

Quantitative trait loci mapping of adult‐plant resistance to leaf rust in a Fundulea 900 × ‘Thatcher’ wheat cross

Wheat leaf rust (LR), caused by the obligate biotrophic fungus Puccinia triticina (Pt), is a destructive foliar disease of common wheat (Triticum aestivum L.) worldwide. The most effective, economic means to control the disease is resistant cultivars. The Romanian wheat line Fundulea 900 showed high resistance to LR in the field. To identify the basis of resistance to LR in Fundulea 900, a population of 188 F_2:3 lines from the cross Fundulea 900/‘Thatcher’ was phenotyped for LR severity during the 2010–2011, 2011–2012 and 2012–2013 cropping seasons in the field at Baoding, Hebei Province. Bulked segregant analysis and simple sequence repeat markers were used to identify the quantitative trait loci (QTLs) for LR adult‐plant resistance in the population. Three QTLs were detected and designated as QLr.hebau‐1BL, QLr.hebau‐2DS and QLr.hebau‐7DS. Based on the chromosome positions and molecular marker tests, QLr.hebau‐1BL is Lr46, and QLr.hebau‐7DS is Lr34. QLr.hebau‐2DS was derived from ‘Thatcher’ and was close to Lr22. This result suggests that Lr22b may confer residual resistance on field nurseries when challenged with isolates virulent on Lr22b, or another gene linked to Lr22b confers this resistance from ‘Thatcher’. This study confirms the value of Lr34 and Lr46 in breeding for LR resistance in China; the contribution of the QTL to chromosome 2D needs further validation.