Late Blight Resistance Research Articles

Mapping Quantitative Trait Loci (QTL) for Resistance to Late Blight in Tomato.

Late blight caused by Phytophthora infestans (Montagne, Bary) is a devastating disease of tomato worldwide. There are three known major genes, Ph-1, Ph-2, and Ph-3, conferring resistance to late blight. In addition to these three genes, it is also believed that there are additional factors or quantitative trait loci (QTL) conferring resistance to late blight. Precise molecular mapping of all those major genes and potential QTL is important in the development of suitable molecular markers and hence, marker-assisted selection (MAS). The objective of the present study was to map the genes and QTL associated with late blight resistance in a tomato population derived from intra-specific crosses. To achieve this objective, a population, derived from the crossings of NC 1CELBR × Fla. 7775, consisting of 250 individuals at F2 and F2-derived families, were evaluated in replicated trials. These were conducted at Mountain Horticultural Crops Reseach & Extension Center (MHCREC) at Mills River, NC, and Mountain Research Staion (MRS) at Waynesville, NC in 2011, 2014, and 2015. There were two major QTL associated with late blight resistance located on chromosomes 9 and 10 with likelihood of odd (LOD) scores of more than 42 and 6, explaining 67% and 14% of the total phenotypic variation, respectively. The major QTLs are probably caused by the Ph-2 and Ph-3 genes. Furthermore, there was a minor QTL on chromosomes 12, which has not been reported before. This minor QTL may be novel and may be worth investigating further. Source of resistance to Ph-2, Ph-3, and this minor QTL traces back to line L3707, or Richter’s Wild Tomato. The combination of major genes and minor QTL may provide a durable resistance to late blight in tomato.

Potato NAC43 and MYB8 Mediated Transcriptional Regulation of Secondary Cell Wall Biosynthesis to Contain Phytophthora infestans Infection

Resistance to late blight is highly complex and quantitative in nature but has proven difficult to harness due to poor understanding of its molecular and biochemical mechanisms. Secondary cell wall (SCW) biosynthesis is a critical process in late blight resistance, regulated by an array of transcription factors (TF). In the present study, metabolo-transcriptomics approaches were used to functionally characterize that the upregulated StNAC43 and StMYB8 in potato genotypes were linked to SCW biosynthetic phenylpropanoid metabolites produced in high fold change following Phytophthora infestans infection. The promoter analysis of StNAC43 revealed the presence of ethylene responsive element (ERE), which is the proposed binding site for ethylene responsive factor, ERF3. Sequencing of the ERF3 revealed a frameshift mutation in the susceptible potato genotype. Simultaneous induction of both the ERF3 and StNAC43, following pathogen invasion, enables functioning of the latter to interact with the ERE present in the resistant StNAC43 promoter region. Further, the StNAC43 binds to the secondary NAC binding element in StMYB8 promoter and activates StMYB8 TF. A luciferase transient expression assay elucidated a direct regulatory role of the StMYB8 on SCW biosynthetic genes, by binding to promoters of downstream genes: HCT, PHT, CHS, and flavanone 3-hydroxylase (F3H). Silencing of StNAC43 and StMYB8 affected the late blight resistance by significantly increasing pathogen biomass and decreasing the amounts of hydroxycinnamic acid amides (HCAAs) and flavonoid glycosides. The StNAC43 and StMYB8 TFs are positive activators of SCW biosynthetic genes, which deposit resistance-related metabolites to reinforce SCW and improve resistance against late blight.

English

Late blight of tomato (Solanum lycopersicum L.) caused by the heterothallic oomycete Phytophthora infestans (Mont.) de Bary, is one of the most destructive and serious diseases of tomato in cool and wet environments. Tomato breeders have developed late blight-resistant tomato lines and cultivars based on Ph resistance genes derived from S. pimpinellifolium, but resistance can be short-lived because P. infestans is highly diverse and can readily develop virulence towards the Ph resistance genes. Studies were carried out to assess the resistance level of four tomato genotypes and 48 wild relatives of cultivated tomato to P. infestans. The highest late blight resistance was detected in S. habrochaites accessions LA1777, LA1352, LA2855, LA1347, LA1718 and LA1295, with disease severities ranging from 4.5 to 13.5%. Interestingly, tomato genotypes containing Ph-2 and Ph-3 had significantly lower disease severity indices compared with the susceptible control 'Super Strain B' when inoculated with a highly virulent isolate. However, when a different isolate was used in 2014, the Ph-2 and Ph-3 containing tomato genotypes were as susceptible as 'Super Strain B'.  The overall results demonstrate that LA1777, as previously reported, had a high level of resistance against all isolates of P. infestans and is a useful genetic resource for future tomato breeding programs. Key words: Tomato, late blight, Phytophthora infestans, disease resistance, Ph-genes, Solanum habrochaites.

A System for Identification of Potato Varieties Using SNP Dosage

As in autoteraploids, five genotypes are possible in a biallelic locus, allele dosage could be useful for variety identification in potato. DNA sequences of 13 genes associated with tuber yield, tuber starch content or late blight resistance were surveyed for single nucleotide polymorphism (SNP) in eight tetraploid varieties. A total of 193 potential SNPs was found by Sanger-sequencing, of which 58 were measured for nucleotide frequencies using a pyrosequencer. Of the 58 SNPs, 35 yielded distinct clusters, corresponding to allele dosages. Among these, six were highly correlated with another, leaving 29 independent SNP loci for use in variety discrimination. By using dosage scores at the 29 SNP loci, it was possible to differentiate 115 varieties, except for a sport with red tuber skin color, with at least three different SNP dosages. Therefore, using SNP dosages is a simple, fast and reliable tool for variety identification.

MANAGEMENT OF POTATO LATE BLIGHT THROUGH HOST PLANT RESISTANCE AND FUNGICIDE USE IN SOUTH OMO ZONE, SNNPR, ETHIOPIA

The study was carried out in April 2015 at South Ari district, Senmamer kebele of South Omo Zone Southern Nation Nationality People Regional State to test and demonstrate the effects of integrating host resistance and fungicide application for management of potato late blight disease. In this experiment one relatively late blight resistance improved Irish potato variety (Belete) was collected from Holleta Seed producer Association and susceptible local control potato varieties were used. RCBD with four replications (farmers as replication) were used. A recommended rate of CurzateR R WP fungicide was applied while susceptible local variety developed the first blight symptom. GLM procedures were followed to analyze yield, disease incidence and severity. LSD (P<0.01) values were used to separate treatments mean. Total weight of tubers per plot (kg) was show significant difference (P<0.01) among treatments. The highest total weight of tubers per plot (kg) was given by treated belete (T1) (22.625) followed by untreated belete (T3), untreated local (T4) and treated local (T2) (18.525, 11.875and 10.125) respectively (Table 2). Local potato variety also gave the highest unmarketable tubers weight per plot. The result indicated that there were a significant difference (P<0.01) and (P<0.05) among treatments on late blight incidence and severity respectively. Untreated local variety (T4) showed highest late blight incidence and severity as compare to treated belete variety (T1). The experiment result suggested that application CurzateR R WP fungicide twice on variety belete results in significant reduction on late blight progress, with a corresponding increased tubers yield.

Isolation, characterization and genetic diversity of NBS-LRR class disease-resistant gene analogs in multiple virus resistant line of chilli (Capsicum annuum L.)

Viruses are serious threat to chilli crop production worldwide. Resistance screening against several viruses resulted in identifying a multiple virus resistant genotype ‘IHR 2451’. Degenerate primers based on the conserved regions between P-Loop and GLPL of Resistance genes (R-genes) were used to amplify nucleotide binding sites (NBS)—encoding regions from genotype ‘IHR 2451’. Alignment of deduced amino acid sequences and phylogenetic analyses of isolated sequences distinguished into two groups representing toll interleukin-1 receptor (TIR) and non-TIR, and different families within the group confirming the hypotheses that dicots have both the types of NBS-LRR genes. The alignment of deduced amino acid sequences revealed conservation of subdomains P-loop, RNBS-A, kinase2, RNBS-B, and GLPL. The distinctive five RGAs showing specific conserved motifs were subjected to BLASTp and indicated high homology at deduced amino acid level with R genes identified such as Pvr9 gene for potyvirus resistance, putative late blight resistance protein homolog R1B-23 and other disease resistance genes suggesting high correlation with resistance to different pathogens. These pepper RGAs could be regarded as candidate sequences of resistant genes for marker development.

Late blight and virus host-plant resistances, crossing ability and glycoalkaloids in Nordic potato germplasm

ABSTRACTOld potato cultivars from the Nordic Genetic Resource Center (NordGen) and advanced breeding clones from the Swedish University of Agricultural Sciences (SLU) were evaluated for susceptibility to Potato Virus Y (PVY) and Potato Leafroll Virus (PLRV), foliar and tuber resistance to late blight – caused by Phytophthora infestans – as well as for glycoalkaloid content and crossing ability. Enzyme-Linked Immunosorbant Assay (ELISA) tests were used for PVY and PLRV screening during two years that were characterized by intensive virus incidence and severity in the field, while foliar and tuber resistances to late blight were assessed under artificial inoculation with an aggressive Swedish isolate of P. infestans. Hybrid seeds were obtained by crossing cultivars such as ‘Kiva’, ‘Sarpo Mira’, ‘Rosamunda’ and ‘Superb’ with SLU advanced breeding clones and a selected clone of Solanum tuberosum Group Andigena. Some cultivars (‘Hårek’, ‘Sarpo Mira’) and breeding clones (04-2662, 04-2085) with late blight resistance did not show virus infection. The α-solanin and α-chaconin contents of some of the old Nordic potato cultivars and breeding clones were similar to the known Dutch table cultivar ‘Bintje’ after 3 years of testing. This research allows identification of promising Nordic potato cultivars and SLU breeding clones for further use in developing germplasm aiming at organic and conventional farming systems.

RB and Ph resistance genes in potato and tomato minimize risk for oospore production in the presence of mating pairs of Phytophthora infestans

Late blight caused by the heterothallic oomycete Phytophthora infestans, is a constraint of potato and tomato production worldwide. Currently, pathogen populations within the U.S. are primarily asexual with limited recombination or soil persistent oospores. Both mating types, however, were isolated from Wisconsin during 2009, 2010, and 2013, posing risk for oospores. Late blight resistance genes can be useful in disease reduction against currently predominant U.S. clonal lineages, however, resistance is not complete. To assess disease and oospores with US-22 (A2), US-23 (A1), and US-24 (A1) clonal lineages, fifteen solanaceous hosts with different resistance genetics were investigated. Potato and tomato transformed with the RB gene and tomato ‘Mountain Magic,’ carrying Ph-2 and Ph-3, were the most tolerant to all pathogen lineages with significantly less disease severity (<30%) than the other twelve varieties (40–100% severity). Oospores formed in plant tissues after inoculation with both mating pairs on susceptible and moderately resistant hosts at 12–20 °C, with the greatest number of oospores at 16 °C. The US-24 x US-22 cross produced significantly more oospores than the US-23 x US-22 cross. No oospores were detected in tomato with Ph2 and Ph3, or potato and tomato with RB using whole plant assays. Varieties with these genes could play an important part of an integrated late blight management program by limiting disease and the sexual phase of the pathogen. Deployment of Ph and RB could greatly reduce the risk of oospores and sexual recombination, thereby reducing population variation and development of soilborne P. infestans.

Are We Getting Better at Using Wild Potato Species in Light of New Tools?

Potato (Solanum tuberosum L.), mankind's third most consumed food crop, originated as an interspecific hybrid in the Andean highlands. More than 100 species closely related to potato exist throughout Central and South America. Potato was introduced to Europe, Asia, and North America in the 16th and 17th centuries, but most cultivars were destroyed by late blight epidemics in the mid‐19th century. Late blight resistance genes from the wild relative Solanum demissum Lindl. were subsequently introduced into cultivated potato. Thus, a precedent for the use of wild relatives in potato genetic improvement was established a century ago. Intensive efforts have been made to collect and maintain wild relatives of potato in public germplasm repositories. Genetic diversity in these species is high, and most are sexually compatible with cultivated potato. Perhaps more than any other vegetable crop, potato can benefit from the introgression of genes for valuable traits from wild relatives. However, a century of breeding has realized that potential on only a few notable occasions. Important examples include improved processing quality and resistance to viruses and nematodes. Substantial barriers prevent the facile incorporation of genetic material from wild relatives into potato cultivars. Overcoming these barriers may require an expansion of germplasm collections to include well‐characterized individuals as a complement to population‐based accessions. To be most useful for potato improvement, individual wild species plants will need to be cataloged by allelic composition, haplotype, biochemical properties, and physiological responses to stress. Effectively using the genetic diversity in wild relatives is likely to rely heavily on alternative methods of potato breeding, augmenting reassortment, and selection at the tetraploid level with diploid breeding and genetic modification using biotechnology.

Expression of the Potato Late Blight Resistance Gene Rpi-phu1 and Phytophthora infestans Effectors in the Compatible and Incompatible Interactions in Potato.

This study describes late blight resistance of potato breeding lines resulting from crosses between cultivar 'Sárpo Mira' and Rpi-phu1 gene donors. The progeny is investigated for the presence of Rpi-Smira1 and Rpi-phu1 resistance (R) genes. Interestingly, in detached-leaflet tests, plants with both R genes withstood the infection of the Phytophthora infestans isolate virulent to each gene separately, due to either interaction of these genes or the presence of additional resistance loci. The interaction was studied further in three chosen breeding lines on the transcriptional level. The Rpi-phu1 expression, measured over 5 days, revealed different patterns depending on the outcome of the interaction with P. infestans: it increased in infected plants whereas it remained low and stable when infection was unsuccessful. The expression patterns of P. infestans effectors Avr-vnt1, AvrSmira1, and Avr8, recognized by the Rpi-phu1, Rpi-Smira1, and Rpi-Smira2 genes, respectively, were evaluated in the same experimental setup. This is the first report that the Avr-vnt1 effector expression is not switched off permanently in virulent isolates to avoid recognition by an R protein but can reappear in a postbiotrophic phase and is present constantly when infecting plants without the corresponding R gene. Both a plant and a pathogen can react to the other interacting side by changing the transcript accumulation of R genes or effectors.

Genotypic background of the recipient plant is crucial for conferring RB gene mediated late blight resistance in potato

BackgroundLate blight, caused by oomycetes pathogen Phytophthora infestans (Mont.) de Bary, is the most devastating potato disease in the world. RB gene from Solanum bulbocastanum has been shown to impart broad spectrum resistance against P. infestans races. In this study Katahdin transgenic event SP951 was used as male parent to cross with the popular Indian potato cultivars viz., Kufri Bahar (KB) and Kufri Jyoti (KJ) to enhance the late blight resistance.ResultsPopulations of 271 F1seedlings from the crosses KB × SP951 (87) and KJ × SP951 (184) were screened for inheritance of RB transgene through PCR and bioassay. Disease response based on AUDPC of different hybrid lines varied from immunity to complete susceptibility. High degree of resistance (<25% infection) was observed in KJ × SP951 derived seedlings (85.2%), whereas level of resistance in KB × SP951 (36.4% infection) derived seedlings was of low order.ConclusionThis study provides valuable genetic materials for development of potentially durable late blight resistant potato varieties. Besides, it also corroborates the fact that efficacy of R gene is not solely dependent on its presence in the variety but largely depends on the genetic background of the recipient genotype.

DNA Markers for Selection of Late Blight Resistant Potato Breeding Lines

Potato late blight, caused by the oomycete Phytophthora infestans, is one of the most devastating diseases in the agricultural sector around the world. Many genes (R genes) conferring resistance to late blight have been identified in various potato species and most of these R genes have been used in potato breeding. The aim of this study was to develop and validate PCR-based assays for the R genes Rpi-blb1, Rpi-blb2, Rpi-blb3 and Rpi-bt1, to distinguish between late blight resistant and late blight susceptible potato progeny in the given breeding background. A total of 100 breeding progeny were screened for the presence of these R genes and tested for resistance against P. infestans mating type A2, genotype US-8 strain, using detached leaf and tuber rot assays. PCR products for the Rpi-blb1 and Rpi-bt1 resistance genes were identified in the resistant progeny but were absent in the susceptible ones; therefore these PCR assays could differentiate between late blight resistant and susceptible plants. Genotypic data from the DNA markers derived from the Rpi-blb1 and Rpi-bt1 genes was found to correlate with the phenotypic data for foliar late blight but not with data for tuber rot. Our results demonstrate that markers derived from these two R genes could be useful for marker-assisted selection (MAS) for foliar late blight resistance in potato breeding programs.

北海道のバレイショ品種の1983年から2011年におけるジャガイモ疫病抵抗性の変動

北海道のバレイショ品種の1983年から2011年におけるジャガイモ疫病抵抗性の変動

Yield, Yield-related Traits and Response of Potato Clones to Late Blight Disease, in North-Western Highlands of Ethiopia

Late blight disease of potato caused by Phytophthora infestans poses a significant threat to potato production in Ethiopia. The development of new high yielding genotypes with adequate late blight disease resistance will provide a strong component of an integrated management strategy for farmers. The objective of this study was to determine late blight resistance and yield of potato clones under field condition in north-western Ethiopia. Twenty-four clones (17 from the International Potato Centre B3C2 population and seven widely grown cultivars) were evaluated at three locations. The experiment was laid in a randomized complete block design with two replications. Late blight resistance and yield-related traits were determined. Results showed that clones differ significantly for all traits across locations. The following five clones combine high to moderate resistance to late blight with high yields: 396029.250, 395017.229, 396004.263, 396034.103 and 395077.12. These clones are useful genetic resources for resistance breeding against late blight disease and for enhanced yields.

ФИТОФТОРОУСТОЙЧИВОСТЬ ГИБРИДОВ ОТ СКРЕЩИВАНИЙ SOLANUM TUBEROSUM L. С ДИПЛОИДНЫМИ БОЛИВИЙСКИМИ ВИДАМИ КАРТОФЕЛЯ

This paper presents the data of evaluation of late blight resistance in hybrids derived from crosses of Solanum tuberosum L. with the diploid Bolivian potato species S. berthaultii Hawk. and S. ruiz-ceballosii Card. selected previously for their resistance. In field and laboratory evaluation large share of resistant phenotypes was found. Both hybrids produced tubers in the field under long daylight conditions. S. berthaultii possesses a triploid number of chromosomes (2n = 36) and is completely sterile. Pollen grains of S. ruiz-ceballosii hybrid are partially fertile.

Breeding Potential of Potato Somatic Hybrids: Evaluations for Adaptability, Tuber Traits, Late Blight Resistance, Keeping Quality and Backcross (BC1) Progenies

Ten tetraploid interspecific potato somatic hybrids developed earlier through protoplast fusion between the dihaploid Solanum tuberosum L. ‘C-13’ and the diploid wild species Solanum pinnatisectum Dun. were used in this study. Somatic hybrids and standard control cultivars were evaluated for adaptability, tuber traits, late blight resistance and keeping quality attributes (dormancy, sprouting, weight loss and appearance after 75 days of storage) during two successive winter crop seasons (short-days) in the sub-tropical plains of India, where nearly 90% of India’s potatoes are grown. Somatic hybrids showed medium to good plant vigour and late to very late plant maturity. Though none of the somatic hybrids produced equal or higher tuber yield than the control cultivars, except clone P7, all other somatic hybrids produced significantly higher marketable and total tuber yield after a 90-day growth than the parent C-13. Most of the somatic hybrids possessed higher tuber dry matter concentration, resistance to late blight and better keeping quality attributes than the control cultivars. Notably, the tubers of somatic hybrids showed a tendency for colour change from white to purple on exposure to sunlight. Breeding potential of somatic hybrids was further assessed by crossing them with commonly grown local potato cultivars for the development of backcross (BC1) progenies. In the hybridization programme, berries were formed while somatic hybrids were used either as male or female parents with common cultivars. Our results revealed that the use of bulk pollen of somatic hybrids not only resulted in higher pollination success but also helped to achieve higher numbers of true potato seeds (TPS) per berry. Despite the formation of berries, TPS was absent in 22 crosses using somatic hybrids as a female or male parent which may be due to ovule or embryo abortions. Segregating BC1 generations were evaluated under the same sub-tropical conditions for further exploitation in potato breeding. Based on our study, the somatic hybrids P4, P8 and P10 can be utilized for the introgression of important characters such as high tuber dry matter concontration, resistance to late blight and excellent keeping quality attributes into the cultivated potato via conventional breeding methods for cultivar development in the sub-tropical plains of India.

Comparative Transcriptomic Analyses of Differentially Expressed Genes in Transgenic Melatonin Biosynthesis Ovine HIOMT Gene in Switchgrass.

Melatonin serves pleiotropic functions in prompting plant growth and resistance to various stresses. The accurate biosynthetic pathway of melatonin remains elusive in plant species, while the N-acetyltransferase and O-methyltransferase were considered to be the last two key enzymes during its biosynthesis. To investigate the biosynthesis and metabolic pathway of melatonin in plants, the RNA-seq profile of overexpression of the ovine HIOMT was analyzed and compared with the previous transcriptome of transgenic oAANAT gene in switchgrass, a model plant for cellulosic ethanol production. A total of 946, 405, and 807 differentially expressed unigenes were observed in AANAT vs. control, HIOMT vs. control, and AANAT vs. HIOMT, respectively. Two hundred and seventy-five upregulated and 130 downregulated unigenes were detected in transgenic oHIOMT line comparing with control, including the significantly upregulated (F-box/kelch-repeat protein, zinc finger BED domain-containing protein-3) genes, which were potentially correlated with enhanced phenotypes of shoot, stem and root growth in transgenic oHIOMT switchgrass. Several stress resistant related genes (SPX domain-containing membrane protein, copper transporter 1, late blight resistance protein homolog R1A-6 OS etc.) were specifically and significantly upregulated in transgenic oHIOMT only, while metabolism-related genes (phenylalanine-4-hydroxylase, tyrosine decarboxylase 1, protein disulfide-isomerase and galactinol synthase 2 etc.) were significantly upregulated in transgenic oAANAT only. These results provide new sights into the biosynthetic and physiological functional networks of melatonin in plants.

Identification of Late Blight Resistance Gene Homologues in Wild Solanum Species

Solanum wild species represent diverse population harbouring myriad of resistance (R) genes which could be tapped for incorporating durable biotic and abiotic stress resistance in cultivated genotypes. In the present study, the authors report the screening of eleven Solanum wild species viz., Solanum avilesii, S. berthaultii, S. tuberosum sp andigena, S. arnezii, S. cardiophyllum, S. alandiae, S. albicans, S. sparsipilum, S. spegazzinii, S. pinnatisectum and S. demissum for the presence of late blight resistance genes through molecular markers linked to genes RB/Rpi-blb1, Rpi-ber1, R1 and R3. These markers were able to amplify specific sequences across species indicating universal distribution of R genes. The amplified marker specific sequences matched well with sequences in NCBI database with known function in governing late blight resistance. Phylogenetic analysis grouped the sequences to their known counterpart’s. e.g. sequences amplified with Rpi-blb1 gene specific marker grouped with known sequence corresponding to Solanum bulbocastanum protein genes and so forth in other sequence-marker combinations. The presence of such genes was not immediately linked to resistance against late blight in the wild species accession but may have a role in maintaining/developing their resistance against novel pathogenic races. The newly identified R gene homologues (fragments) in the highly resistant wild potato accessions can serve as a novel source of genes for late blight resistance breeding. The complementary late blight resistant genes from different species can be pyramided in cultivated genotypes for providing stable late blight resistance.

A survey of metabolic changes in potato leaves by NMR-based metabolic profiling in relation to resistance to late blight disease under field conditions.

Non-targeted nuclear magnetic resonance (NMR)-based metabolic profiling was applied to potato leaves to survey metabolic changes associated with late blight resistance under field conditions. Potato plants were grown in an experimental field, and the compound leaves with no visible symptoms were collected from 20 cultivars/lines at two sampling time points: (i) the time of initial presentation of symptoms in susceptible cultivars and (ii) 12 days before this initiation. 1 H NMR spectra of the foliar metabolites soluble in deuterium oxide- or methanol-d4 -based buffers were measured and used for multivariate analysis. Principal component analysis for six cultivars at symptom initiation showed a class separation corresponding to their levels of late blight resistance. This separation was primarily explained by higher levels of malic acid, methanol, and rutin and a lower level of sucrose in the resistant cultivars than in the susceptible ones. Partial least squares regression revealed that the levels of these metabolites were strongly associated with the disease severity measured in this study under field conditions. These associations were observed only for the leaves harvested at the symptom initiation stage, but not for those collected 12 days beforehand. Subsequently, a simple, alternative enzymatic assay for l-malic acid was used to estimate late blight resistance, as a model for applying the potential metabolic marker obtained. This study demonstrated the potential of metabolomics for field-grown plants in combination with targeted methods for quantifying marker levels, moving towards marker-assisted screening of new cultivars with durable late blight resistance. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluation of the Ph‐3 gene‐specific marker developed for marker‐assisted selection of late blight‐resistant tomato

AbstractLate blight caused by Phytophthora infestans is one of the most destructive diseases of tomato (Solanum lycopersicum L.) that mainly occurs in cool and wet environments. With the spread of the A2 mating type and new clonal lineages, fewer fungicides provide effective control of the disease, which has increased its worldwide threat. Host resistance could contribute significantly to sustainable disease control. Ph‐3 is a race‐specific late blight resistance gene commonly used in commercial tomato breeding. Availability of precise and easy to use gene‐based markers would facilitate selection. In this study, a Ph‐3 on‐gene cleaved amplified polymorphic sequence (CAPS) marker, Ph3.gsm/HincII, was developed based on the published gene sequence of Ph‐3. The effectiveness of the marker was evaluated along with other published Ph‐3 markers using an F9 recombinant inbred line (RIL) population derived from NC 23E‐2(93) × L3708. Markers Ph3.gsm/HincII and TG328/BstNI accurately genotyped the RIL population for Ph‐3. In addition, Ph3.gsm/HincII was able to differentiate variable susceptible alleles. This reliable codominant DNA marker would be very useful in marker‐assisted selection, particularly for resistance gene pyramiding.