Resistant Parent Research Articles

Screening for Resistance to PVY in Australian Potato Germplasm.

Potatoes are an important human food crop, but have a number of yield limiting factors, including disease susceptibility. Potato virus Y (PVY) is found worldwide, and is one of the main virus problems for potato growers. PVY is transmitted by aphids and mechanically by machinery, tools and people, and symptoms are variable across cultivars and strains, including being symptomless in some cultivars. Therefore, breeding resistant cultivars is the best way to control this virus. This study phenotypically screened 74 of the main commercial cultivars and a few other select cultivars grown in Australia, in order to identify sources of resistance to PVY. The cultivars were screened against PVYO and PVYNTN, with 23 out of 71 resistant to PVYO and 13 out of 74 resistant to PVYNTN, and all these 13 were resistant to both strains. When the phenotypic screening was compared to the results listed on the European Cultivated Potato Database, the majority of results were found to be consistent. We then evaluated three molecular markers RYSC3, M45, and STM0003 for the extreme resistance genes Ryadg and Rysto, to validate the usefulness of the markers for marker-assisted selection (MAS) on Australian germplasm. The degree of correlation between the resistance phenotypes and the RYSC3, M45, and STM0003 markers for Ryadg and Rysto conferred PVY resistance was determined. Three cultivars amplified the RYSC3 marker, while the M45 marker amplified the same 3 and an additional 9. Of the 12 cultivars, 11 phenotyped as resistant, but 1 was susceptible. The STM0003 marker was amplified from only 2 cultivars that both had resistant phenotypes. The RYSC3, M45, and STM0003 markers were therefore able to identify all the 13 cultivars that were resistant to both strains of PVY. Therefore, these markers will enable the identification of genotypes with resistance to PVY, and enable PVY resistant parents to be used for the development of superior progeny; these genetic markers can be used for MAS in the Australian potato breeding program.

Identification of additional /novel QTL associated with resistance to cassava green mite in a biparental mapping population.

Cassava green mite [CGM, Mononychellus tanajoa (Bondar)] is the most destructive dry-season pest in most cassava production areas. The pest is responsible for cassava fresh root yield losses of over 80%. Deployment of CGM resistant cultivars is the most cost-effective and sustainable approach of alleviating such production losses. The purposes of this study were to validate the stability of CGM resistance genes found in previously published results, to identify new genes for CGM resistance in bi-parental mapping population and estimate the heritability of the trait. A total of 109 F1 progeny derived from a cross between CGM resistant parent, TMEB778 and a very susceptible parent, TMEB419 were evaluated under CGM hotspot areas in Nigeria for two cropping seasons. A total of 42,204 SNP markers with MAF ≥ 0.05 were used for single-marker analysis. The most significant QTL (S12_7962234) was identified on the left arm on chromosome 12 which explained high phenotypic variance and harboured significant single nucleotide polymorphism (SNP) markers conferring resistance to CGM and leaf pubescence (LP). Colocalization of the most significant SNP associated with resistance to CGM and LP on chromosome 12 is possibly an indication of a beneficial pleiotropic effect or are physically linked. These significant SNPs markers were intersected with the gene annotations and 33 unique genes were identified within SNPs at 4 – 8MB on chromosome 12. Among these genes, nine novel candidate genes namely; Manes.12077600, Manes.12G086200, Manes.12G061200, Manes.12G083100, Manes.12G082000, Manes.12G094100, Manes.12G075600, Manes.12G091400 and Manes.12G069300 highly expressed direct link to cassava green mite resistance. Pyramiding the new QTL/genes identified on chromosome 12 in this study with previously discovered loci, such on chromosome 8, will facilitate breeding varieties that are highly resistant CGM.

Construction of High-Density Linkage Maps and Identification of Quantitative Trait Loci Associated with Verticillium Wilt Resistance in Autotetraploid Alfalfa (Medicago sativa L.).

Verticillium wilt (VW) of alfalfa is a devastating disease that causes forage yield reductions of up to 50% in the northern United States and Canada. The most effective method for controlling the disease is through the development and use of resistant varieties. To identify quantitative trait loci (QTL) for VW resistance in alfalfa, we used a full-sib population segregating for VW resistance. High-density linkage maps for both resistant and susceptible parents were constructed using single-dose alleles of single-nucleotide polymorphism markers generated by genotyping-by-sequencing. Five QTL associated with VW resistance were identified and they were in four linkage groups (4D, 6B, 6D, and 8C). Of those, three QTL (qVW-6D-1, qVW-6D-2, and qVW-8C) had higher logarithm of odds. Two putative candidates of nucleotide-binding site leucine-rich repeat disease resistance genes were identified in the QTL intervals of qVW-6D-2 and qVW-8C, respectively. The result agreed with our previous studies, in which similar resistance loci were identified in an association panel using genome-wide association. The results provide insight into the quantitative resistance to VW in alfalfa. The resistance loci and closely linked markers identified in the present study can be used in developing new alfalfa varieties with enhanced resistance to VW.

Genetic inheritance and identification of germplasm sources for anthracnose resistance in soybean [Glycine max (L.) Merr.

Soybean anthracnose caused by Colletotrichum truncatum (Schw.) Andrus & W.D. Moore is a devastating disease in Central and Southern India. Chemical control of this disease is neither economical nor eco-friendly and genetic resistance is considered to be an efficient means for its management. Therefore, in the current study, a total of 225 soybean [Glycine max (L.) Merr.] germplasm accessions were evaluated for anthracnose resistance which resulted in the identification of five genotypes viz., EC 538828, EC 34372, EC 457254, AKSS 67 and Karune as highly resistant. Genetics of anthracnose resistance in three F2 populations derived from EC 34372 × JS 95-60, EC 457254 × JS 95-60 and AKSS 67 × JS 95-60 revealed that the resistance in all the three resistant parents was governed by two major genes interacting in complementary fashion. The χ2 test for goodness of fit revealed that F2 plants in each of the three populations segregated in 9 resistant: 7 susceptible ratio. This is the first report on genetics of anthracnose resistance in soybean and will aid soybean breeders to develop a strategic anthracnose resistance breeding program and to map the genes governing resistance. Research findings from this study indicated the potential role of exotic germplasm in Indian soybean improvement against anthracnose disease.

Marker assisted screening of breeding population of wheat segregating for stripe rust resistance using SSR markers

Screening of F2 population from cross WH711 (susceptible parent) and PBW698 (resistant parent) against stripe rust was done on the basis of field reaction of yellow rust and 12 morphlogical traits. The genotyping of parents was done by using 80 SSR markers out of which 11 were found polymorphic. These 11 markers were used to screen 250 individuals of F2 population. Mendelian inheritance was followed by five markers viz. Xgwm631, Cfa2040, Xsps3000, Barc76 and Xgwm 130 which segregated according to expected ratio of 1:2:1 with chisquare values 5.78, 4.23, 2.75, 9.2 and 7.6 respectively. Single marker analysis showed markers Xgwm631, Cfa2040 (Yr2, Yr6), Xsps3000 (Yr10), Xgwm130 (Yr7), Xwmc407 (Lr17), Barc46, Xgwm413 (Yr15), Barc187 (Yr27) and Xgwm273 (YrH52) were linked with yellow rust locus at 0.01% of significance hence these genes may be present in the breeding population. Cfa2040 was found linked with flag leaf area, number of spikelets and Barc181 with spike weight locus. Markers on chromosomes 7A and 1B showed LOD values 6.64 and 6.86 conferring tight linkage with yellow rust locus thus can be used for MAS.

Four Consistent Loci Confer Adult Plant Resistance to Leaf Rust in the Durum Wheat Lines Heller#1 and Dunkler.

The durum wheat lines Heller#1 and Dunkler from the International Maize and Wheat Improvement Center Global Wheat Program showed moderate and stable adult plant resistance to leaf rust under high disease pressure over field environments in northwestern Mexico. Leaf rust phenotyping was performed on two recombinant inbred line (RIL) populations derived from crosses of Heller#1 and Dunkler with the susceptible parent Atred#2, conducted under artificially induced Puccinia triticina epidemics in 2013, 2014, 2015, and 2016. The Atred#2 × Heller#1 and Atred#2 × Dunkler populations were genotyped by single nucleotide polymorphism (SNP) platforms and diversity arrays technology markers, respectively. Four leaf rust resistance quantitative trait loci were detected simultaneously in the two RIL populations: Lr46, QLr.cim-2BC, QLr.cim-5BL, and QLr.cim-6BL based on phenotypic data across all four crop seasons. They explained 11.7 to 46.8%, 7.2 to 26.1%, 8.4 to 24.1%, and 12.4 to 28.5%, respectively, of the phenotypic variation for leaf rust resistance in Atred#2 × Heller#1 and 16.3 to 56.6%, 6.7 to 15.7%, 4.1 to 10.1%, and 5.1 to 20.2% of the variation in the Atred#2 × Dunkler population. Only the resistance allele of QLr.cim-2BC was from the susceptible parent Atred#2, and resistance alleles at other loci came from the resistant parents Heller#1 and Dunkler. The SNP markers closely linked to Lr46 and QLr.cim-2BC were converted to kompetitive allele specific PCR markers for use in marker-assisted selection to improve leaf rust resistance through crosses with Heller#1 and Dunkler sources.

Development of Molecular Marker Linked with Bacterial Fruit Blotch Resistance in Melon (Cucumis melo L.).

Bacterial fruit blotch (BFB) causes losses in melon marketable yield. However, until now, there has been no information about the genetic loci responsible for resistance to the disease or their pattern of inheritance. We determined the inheritance pattern of BFB resistance from a segregating population of 491 F2 individuals raised by crossing BFB-resistant (PI 353814) and susceptible (PI 614596) parental accessions. All F1 plants were resistant to Acidovorax citrulli strain KACC18782, and F2 plants segregated with a 3:1 ratio for resistant and susceptible phenotypes, respectively, in a seedling bioassay experiment, indicating that BFB resistance is controlled by a monogenic dominant gene. In an investigation of 57 putative disease-resistance related genes across the melon genome, only the MELO3C022157 gene (encoding TIR-NBS-LRR domain), showing polymorphism between resistant and susceptible parents, revealed as a good candidate for further investigation. Cloning, sequencing and quantitative RT-PCR expression of the polymorphic gene MELO3C022157 located on chromosome 9 revealed multiple insertion/deletions (InDels) and single nucleotide polymorphisms (SNPs), of which the SNP A2035T in the second exon of the gene caused loss of the LRR domain and truncated protein in the susceptible accession. The InDel marker MB157-2, based on the large (504 bp) insertion in the first intron of the susceptible accession, was able to distinguish resistant and susceptible accessions among 491 F2 and 22 landraces/inbred accessions with 98.17% and 100% detection accuracy, respectively. This novel PCR-based, co-dominant InDel marker represents a practical tool for marker-assisted breeding aimed at developing BFB-resistant melon accessions.

Genetic analysis of partial resistance to vine decline in watermelon [Citrullus lanatus (Thunb.) Matsum&Nakai

Vine decline or sudden wilt caused by a complex of pathogens with unknown etiology is emerging as most destructive disease of watermelon in the southern part of India. In this direction ICAR-IIHR, has identified a prebred line derived from Citrullus amarus viz., BIL-53 to be field tolerant to this disease. This study was planned to understand the genetics of vine decline resistance in this accession. The BIL-53 used as resistant parent was crossed with icebox accession, IIHR‐140–152, a susceptible genotype to develop F1, F2, BC1 and BC2 generations and observe the segregation for disease reaction. The results in F2 and backcross progenies suggested that resistance is governed by a single recessive gene. BIL-53 is also known to possess resistance to WBNV and hence, this line can be used in resistance breeding programs to develop combined resistance to vine decline and watermelon bud necrosis orthotospovirus employing back cross breeding. Further, this line can be tested as a rootstock in overcoming vine decline as an immediate measure.

Mapping Quantitative Trait Loci Associated With Resistance to Aflatoxin Accumulation in Maize Inbred Mp719.

Aflatoxins are carcinogenic and toxic compounds produced principally by fungal species Aspergillus flavus (Link: Fries) and A. parasiticus (Speare), which are common contaminants of food and feed. Aflatoxins can be found at dangerously high levels and can readily contaminate pre-harvest maize (Zea mays L.) grain. Sources of resistance to aflatoxin accumulation in maize have been identified, however, the highly quantitative nature and complex inheritance of this trait have limited the introgression of aflatoxin accumulation resistance into agronomically desirable lines. Mapping of quantitative trait loci (QTL) was performed on a bi-parental population comprised of 241 F2:3 families derived from the cross of inbred lines Mp705 (susceptible) × Mp719 (resistant). The mapping population was phenotyped in replicated field trials in three environments for resistance to aflatoxin accumulation under artificial inoculation with an A. flavus spore suspension. The genetic linkage map was constructed with 1,276 single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) molecular markers covering a total genetic distance of 1,642 cM across all ten maize chromosomes. Multiple interval mapping revealed that majority of the aflatoxin-reducing alleles and the source for the larger effect QTL identified in this study were contributed from Mp719, the resistant parent. Two QTL identified on chromosome 1 (bin 1.06–1.07) and chromosome 3 (bin 3.09) were the most stable across different environments and when combined, explained 24.6% of the total phenotypic variance across all three environments. Results from the study showed that these chromosomal regions harbor important QTL for influencing aflatoxin accumulation, which is consistent with previous reports with other different mapping populations. These stable QTL were the most promising for controlling aflatoxin accumulation in maize grain. Identifying beneficial alleles derived from Mp719 and closely linked molecular markers through QTL analysis for implementation of MAS could accelerate breeding efforts to reduce aflatoxin accumulation in maize.

Hybridization between resistant and susceptible fenugreek accessions and evaluation of Cercospora leaf spot resistance in segregating generations

Cercospora leaf spot (CLS), caused by Cercospora traversoana, is an important phyto-pathological problem of self-pollinated fenugreek (Trigonella-foenum graecum). Developing resistant genotypes in crop plants has been considered the best option to control diseases for economic, environmental, and social reasons. However, before this can be accomplished, knowledge about the inheritance of disease-resistant genes is necessary for creating high-yielding resistant genotypes. One susceptible fenugreek cultivar, Tristar, and two resistant accessions L3717 and PI138687 were used in two-way crosses using hand emasculation and pollination technique in a greenhouse. F1 plants were grown in a greenhouse and allowed to grow till maturity to produce F2 seeds. Some flowers from F1 plants were crossed back to both resistant and susceptible parents separately to generate backcross (BC1) seeds. Parents, F1, F2, and BC1 populations were grown in the greenhouse using a RCBD with four replications. Plants were inoculated 30 d after sowing with a suspension of C. traversoana at 2 × 105 conidia mL−1. Symptoms were observed and rated on individual plants 25 d after inoculation, and plants were categorized according to susceptible or resistant reactions based on rating scores. Mean disease score was significantly different (p < 0.0001) among generations. In both the cross combinations, results showed CLS resistance in fenugreek (from L3717 and PI138687) was governed by a single dominant gene which is moderately heritable (46% narrow sense heritability). This indicates a relatively simple pathway for transfer of genes to adapted fenugreek cultivars.

Introgression of bacterial blight resistance gene Xa7 into popular Indonesian rice varieties through backcross and molecular breeding

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of major diseases in rice production. The BB resistance gene Xa7 is one of effective genes against Xoo strains in Indonesia. This study aimed to introgress BB resistance gene Xa7 into submergence tolerant rice variety Inpara 5 (IR64 Sub1) and brown plant hopper (BPH) resistant rice variety Inpari 13. Stable BB resistant rice lines have been successfully developed after three backcrossing and four generations of fixation (BC3F4). Screening for BB resistance were conducted in generative stage using Xoo strains IV and VIII. The reaction pattern of the backcross lines against these two Xoo strains were similar to the BB resistant parent Conde. The introgression of the Xa7 gene in Inpara 5 and Inpari 13 genome have been confirmed by using SSR markers RM20589 and RM20590; and Xa7 gene specific marker Xa7-LD34. Agronomic characters and grain quality properties of the backcross lines were comparable to the recurrent parents. Other desirable traits from recurrent parents including submergence tolerance and BPH resistance retained in the selected backcross lines. The BB resistance rice lines with popular rice varieties genetic background developed through this study have potential to be released for farmers adoption.

Evaluation and genome-wide association study of Verticillium wilt resistance in a MAGIC population derived from intermating of eleven Upland cotton (Gossypium hirsutum) parents

Vertcillium wilt (VW, Verticillium dahliae Kleb.) is one of the most important soil-borne fungal diseases affecting world cotton production. Numerous studies have been conducted to investigate the genetic basis of VW resistance using bi-parental or association mapping populations. In this study, a multi-parent advanced generation inter-cross (MAGIC) population of 550 recombinant inbred lines (RILs) together with their 11 Upland cotton parents with a total of 473,516 polymorphic SNP markers was used to identify chromosomal regions for VW resistance based on foliar disease severity ratings (DSR) in two replicated greenhouse tests. Among the 11 parents, Acala Ultima, Coker 315, and Deltapine Acala 90 in the two tests and FiberMax 966 in one test and on average were significantly more resistant than the susceptible check parent- Phytogen PSC 355, while Paymaster HS 26, SureGrow 747, Stoneville 474, Stoneville 825, and Tamcot Pyramid performed similarly to PSC 355. Although a significant genotype × test interaction was detected for DSR, 37 MAGIC lines were consistently resistant to VW. Of 13 and 12 VW resistance QTL declared in Test 1 and 2, respectively, through a genome-wide association study (GWAS), three QTL on chromosome A01, D02 and D08 were in common and three QTL clusters were detected on chromosome A01, A13, and D01 between the two tests. The narrow chromosomal regions for the three common resistance QTL allowed identification of possible candidate genes for VW resistance. This greenhouse study identified VW resistant parents and RILs and common resistance QTL for VW resistance, providing useful information for developing VW resistant cultivars and further genomic studies towards the identification of VW resistance genes in cotton.

Evaluation of the resistance of the breeding material beetroot to Cercospora amid epiphytoty in greenhouses the Moscow region

Relevance.An important feature that determines the technological qualities of varieties and hybrids of beetroot is an erect, compact leaf rosette that persists until the end of the vegetation of plants. In this regard, much attention is paid to the selection of resistance to diseases affecting the leaves of plants, including Cercospora beticola Sacc. When creating resistant to Cercospora interline hybrids based on CMS, the selection of parent components plays an important role. In agroclimatic conditions of the Moscow region, Cercospora on industrial beetroot rarely reaches an economically significant threshold of harmfulness. However, in 2019, epiphytic development of Cercospora on summer first-year crops was observed in the block film greenhouse of the «Federal Scientific Vegetable Center», which allowed to assess the promising breeding material.Material and method. Phytomonitoring on beetroot plantings and sowing of the experimental production Department of the «Federal Scientific Vegetable Center» growing was carried out by methods of visual diagnostics and microscopy. Cercospora lesion in the breeding nursery was evaluated on an 11-point scale, the ranking of samples into five groups of resistance - according to the degree of disease development (R%). Analyzed: 28 sterile lines (А); 13 fertile lines of fixers (В); 25 lines of pollinators (С) and 38 hybrid F1 (АхВхС).Results. It was found that more than half of the studied lines were receptive to Cercospora. The share of relatively resistant lines was 13%. Most of them (8%) are ms - lines « obtained by pollination of CMS with mf-lines В. A close relationship (r=0.86-0.89) between the index of lesion of fixators and the degree of disease development of ms- lines was revealed, in some simple combinations a positive effect of heterosis on resistance to Cercospora relative to mf-В was noted. In the submitted sample F1 hybrids mainly observed between the nature of inheritance according to the degree of disease development (R, %), mixed effects the base line stability of pollinator mf-С (r=0,32) and a closer correlation of the stability of hybrid offspring the F1 with the resistant parent ms-line А (r=0.55). As a result of the evaluation, the most resistant to Cercospora ms- and mf-lines and derived from them hybrid F1, among which only 9% were included in the group of relatively resistant to C. beticola.

Inheritance Pattern and Molecular Markers for Resistance to Blackleg Disease in Cabbage.

The inheritance and causal loci for resistance to blackleg, a devastating disease of Brassicaceous crops, are yet to be known in cabbage (Brassica oleracea L.). Here, we report the pattern of inheritance and linked molecular marker for this trait. A segregating BC1 population consisting of 253 plants was raised from resistant and susceptible parents, L29 (♀) and L16 (♂), respectively. Cotyledon resistance bioassay of BC1 population, measured based on a scale of 0–9 at 12 days after inoculation with Leptosphaeria maculans isolate 03–02 s, revealed the segregation of resistance and ratio, indicative of dominant monogenic control of the trait. Investigation of potential polymorphism in the previously identified differentially expressed genes within the collinear region of ‘B. napus blackleg resistant loci Rlm1′ in B. oleracea identified two insertion/deletion (InDel) mutations in the intron and numerous single nucleotide polymorphisms (SNPs) throughout the LRR-RLK gene Bol040029, of which six SNPs in the first exon caused the loss of two LRR domains in the susceptible line. An InDel marker, BLR-C-InDel based on the InDel mutations, and a high resolution melting (HRM) marker, BLR-C-2808 based on the SNP C2808T in the second exon were developed, which predicated the resistance status of the BC1 population with 80.24%, and of 24 commercial inbred lines with 100% detection accuracy. This is the first report of inheritance and molecular markers linked with blackleg resistance in cabbage. This study will enhance our understanding of the trait, and will be helpful in marker assisted breeding aiming at developing resistant cabbage varieties.

A recombination bin-map identified a major QTL for resistance to Tomato Spotted Wilt Virus in peanut (Arachis hypogaea)

Tomato spotted wilt virus (TSWV) is a devastating disease to peanut growers in the South-eastern region of the United States. Newly released peanut cultivars in recent years are crucial as they have some levels of resistance to TSWV. One mapping population of recombinant inbred line (RIL) used in this study was derived from peanut lines of SunOleic 97R and NC94022. A whole genome re-sequencing approach was used to sequence these two parents and 140 RILs. A recombination bin-based genetic map was constructed, with 5,816 bins and 20 linkage groups covering a total length of 2004 cM. Using this map, we identified three QTLs which were colocalized on chromosome A01. One QTL had the largest effect of 36.51% to the phenotypic variation and encompassed 89.5 Kb genomic region. This genome region had a cluster of genes, which code for chitinases, strictosidine synthase-like, and NBS-LRR proteins. SNPs linked to this QTL were used to develop Kompetitive allele specific PCR (KASP) markers, and the validated KASP markers showed expected segregation of alleles coming from resistant and susceptible parents within the population. Therefore, this bin-map and QTL associated with TSWV resistance made it possible for functional gene mapping, map-based cloning, and marker-assisted breeding. This study identified the highest number of SNP makers and demonstrated recombination bin-based map for QTL identification in peanut. The chitinase gene clusters and NBS-LRR disease resistance genes in this region suggest the possible involvement in peanut resistance to TSWV.

Determining The Effect of Mass Selection for FHB Resistance in Soft Red Winter Wheat Using an Image-Based Optical Sorter

Fusarium head blight (FHB) or head scab, caused by Fusarium graminearum Schwabe [telomorph: Gibberella zeae Schwein.(Petch)], is one of the most destructive diseases of wheat (Triticum aestivum L.) worldwide. Numerous strategies for scab resistance breeding are in use, including phenotypic selection for low severity and marker-assisted selection for resistance QTL. The most destructive consequences of scab are evidenced through a reduction in grain quality, and the presence of mycotoxins, the most common of which is deoxynivalenol (DON). Thus, there is great interest among breeders in selecting for resistance to both of these traits. To this end, a study was devised as follows. In 2010, 20 bulk F3 SRW wheat populations with scab resistant parents in their pedigrees were harvested by population from unreplicated plots near Lexington, KY. The plots were affected by a naturally occurring mild-moderate scab epidemic. The grain was sorted on a USDA/ARS and National Manufacturing Seed Sorter System with color camera according to a calibration that reflected visual differences between asymptomatic grain and grain showing FHB symptoms. This process was repeated in 2011 using grain from plots that had conidial suspension applied at anthesis. In 2012, an unreplicated plot study of the C0, C1 and C2 cycles of selection, inoculated with grain spawn and conidial suspension, was evaluated for Fusarium damaged kernels (FDK) and DON concentration. An additional cycle of selection was conducted by running the bulk grain through the sorter. In October 2012, 4 selection cycles of the 20 populations were planted in a RCB experiment at Lexington and Princeton, KY. Bulk populations were planted in both scab nursery and plots, and C3 accepted and rejected of all populations and derived lines of 2 populations were planted in the scab nursery in Lexington, KY. Some populations had FDK and DON reduction with selection, and some derived lines had either numerical or significant reduction with selection. Although the accepted fraction had non-significant reduction compared with the rejected fraction over the populations, FDK and DON means were obviously lower in accepted than in rejected fractions.

Genetic resistance to Phytophthora lateralis in Port‐Orford‐cedar (Chamaecyparis lawsoniana) – Basic building blocks for a resistance program

Societal Impact StatementNon‐native pathogens and pests cause high mortality to tree species globally and may imperil the future viability of associated forest ecosystems. Phytophthora lateralis, an oomycete, causes Port‐Orford‐cedar root disease and is a major cause of mortality in the ecologically and economically important conifer species Chamaecyparis lawsoniana (Port‐Orford‐cedar). The P. lateralis resistance program shows promise to help stabilize C. lawsoniana in its native range of northwestern California and southwestern Oregon, USA, and serves as a leading example of disease resistance breeding in forest trees Summary A non‐native, invasive pathogen, Phytophthora lateralis, has caused extensive mortality within the native range, northern California and southern Oregon USA, of Chamaecyparis lawsoniana (Port‐Orford‐cedar), as well as in horticultural and amenity plantings in the USA and Europe. Restoration of affected sites is contingent upon development of populations with genetic resistance. Naturally occurring genetic resistance has been identified in C. lawsoniana, and an active selective breeding program seeks to characterize and increase resistance levels. Two seedling root dip inoculation trials, assessed for mortality for nearly three years each, are used to examine the types and levels of genetic resistance in C. lawsoniana. Most seedlings utilized in these trials are progeny of crosses from parent trees that exhibited apparent resistance to the disease in earlier trials. Seedling trials suggest that both qualitative major gene and quantitative disease resistance occurs in C. lawsoniana. Both types of resistance to P. lateralis appear to be present at levels high enough to be immediately useful for restoration and reforestation. The data suggest that the qualitative resistance is conditioned by a single major gene (designated here as Pla), but nothing is known about the number of genes involved in quantitative disease resistance. Seedling progeny from resistant parent trees in containerized seed orchards are now being used for restoration and reforestation. Resistant seedlings or clones could also be used to re‐establish C. lawsoniana in urban forests.

Molecular mapping of major QTL conferring resistance to orange wheat blossom midge (Sitodiplosis mosellana) in Chinese wheat varieties with selective populations.

Two novel midge resistance QTL were mapped to a 4.9-Mb interval on chromosome arm 4AL based on the genetic maps constructed with SNP markers. Orange wheat blossom midge (OWBM) is a devastating insect pest affecting wheat production. In order to detect OWBM resistance genes and quantitative trait loci (QTL) for wheat breeding, two recombinant inbred line (RIL) populations were established and used for molecular mapping. A total of seven QTL were detected on chromosomes 2D, 4A, 4D and 7D, respectively, of which positive alleles were all from the resistant parents except for the QTL on 7D. Two stable QTL (QSm.hbau-4A.2-1 and QSm.hbau-4A.2-2) were detected in both populations with the LOD scores ranging from 5.58 to 29.22 under all three environments, and they explained a combined phenotypic variation of 24.4-44.8%. These two novel QTL were mapped to a 4.9-Mb physical interval. The single-nucleotide polymorphism (SNP) markers AX-109543456, AX-108942696 and AX-110928325 were closely linked to the QTL and could be used for marker-assisted selection (MAS) for OWBM resistance in wheat breeding programs.

Differential Expression of Signaling Pathway Genes Associated With Aflatoxin Reduction Quantitative Trait Loci in Maize (Zea mays L.).

The roles of signaling pathway genes related to the aflatoxin reduction trait in maize were studied for the improvement of maize resistance to the fungal pathogen Aspergillus flavus (A. flavus). In this study, 55 maize genes in plant–pathogen interaction signaling pathways were investigated among 12 maize near-isogenic lines (NILs) that carry maize quantitative trait loci (QTL) associated with aflatoxin reduction. These maize NILs were developed from maize inbred lines Mp313E (resistant donor parent) and Va35 (susceptible recurrent parent). The quantitative RT-PCR (qRT-PCR) technique was used to study the gene expression patterns. Seven calcium-dependent protein kinases and one respiratory burst oxidase displayed significant differential expression levels among the maize QTL-NILs. In addition, the gene expression profiles of WRKY transcription factors were also examined. Maize WRKY 52, WRKY 71, and WRKY83 genes displayed significantly differential expression levels among the QTL-NILs. The elucidation of differentially expressed signaling pathway genes involving maize resistance to A. flavus can provide insights into maize disease resistance and enhance maize molecular breeding.

Identification and QTL mapping of resistance to Turnip yellows virus (TuYV) in oilseed rape, Brassica napus

Key messagePartially dominant resistance to Turnip yellows virus associated with one major QTL was identified in the natural allotetraploid oilseed rape cultivar Yudal.Turnip yellows virus (TuYV) is transmitted by the peach-potato aphid (Myzus persicae) and causes severe yield losses in commercial oilseed rape crops (Brassica napus). There is currently only one genetic resource for resistance to TuYV available in brassica, which was identified in the re-synthesised B. napus line ‘R54’. In our study, 27 mostly homozygous B. napus accessions, either doubled-haploid (DH) or inbred lines, representing a diverse subset of the B. napus genepool, were screened for TuYV resistance/susceptibility. Partial resistance to TuYV was identified in the Korean spring oilseed rape, B. napus variety Yudal, whilst the dwarf French winter oilseed rape line Darmor-bzh was susceptible. QTL mapping using the established Darmor-bzh × Yudal DH mapping population (DYDH) revealed one major QTL explaining 36% and 18% of the phenotypic variation in two independent experiments. A DYDH line was crossed to Yudal, and reciprocal backcross (BC1) populations from the F1 with either the susceptible or resistant parent revealed the dominant inheritance of the TuYV resistance. The QTL on ChrA04 was verified in the segregating BC1 population. A second minor QTL on ChrC05 was identified in one of the two DYDH experiments, and it was not observed in the BC1 population. The TuYV resistance QTL in ‘R54’ is within the QTL interval on Chr A04 of Yudal; however, the markers co-segregating with the ‘R54’ resistance are not conserved in Yudal, suggesting an independent origin of the TuYV resistances. This is the first report of the QTL mapping of TuYV resistance in natural B. napus.