Cercospora Leaf Spot Resistance Research Articles

Genetic architecture of Cercospora leaf spot response in table beet with implications for other Beta vulgaris crop types

AbstractTable beet (Beta vulgaris subsp. vulgaris) production is threatened by the fungal disease Cercospora leaf spot (CLS). Infections are common across table beet's closest relatives, including Swiss chard, sugar beet, and fodder beet (all B. v. subsp. vulgaris). This study was conducted to characterize the genetic architecture underlying CLS response in table beet. A secondary objective was to test whether CLS‐associated loci in table beet perform similarly across B. vulgaris crops. A diversity panel comprised of 168 table beet accessions and with an additional 70 accessions from all close relatives of table beet was screened for CLS response in replicated and inoculated field trials. Results from a genome‐wide association study of additive effects revealed seven quantitative trait loci mapped to chromosomes 1, 3, 7, and 9 to explain 30% of the phenotypic variation for CLS response in table beet. When the performance of these loci was compared between a table beet background and a background of Swiss chard, sugar beet, and fodder beet, two loci exhibited significantly different responses. Among the B. vulgaris crops, these loci may be unique to table beet germplasm and could be useful for the improvement of CLS resistance in other crop types. For the improvement of CLS resistance in table beet, this study identified the cultivar Winter Keeper as a potentially valuable source of resistance. The architecture of CLS response points to recurrent selection and backcross methods as effective strategies for the improvement of CLS resistance in table beet.

Morpho-biochemical and Molecular Characterization of New Mung Bean [Vigna radiata (L.) Wilczek] Landraces for Cercospora Leaf Spot (CLS) Disease Resistance

Mung bean production is significantly lowered by Cercospora leaf spot (CLS) in various parts of the globe. The most effective way to increase mung bean resilience to this stress is to to identify new CLS resistance sources. Therefore, a panel population of 13 landraces along with 2 susceptible check cultivar, and 11 SSR markers were taken for the present experiment. Correlation analysis suggested significant relationships between the quantitative traits, retained resistance (Banapur local, and Kalampur local), and moderately resistance (Dikhitapada local, and Fakirpur local 1) to CLS. However, total chlorophyll content (TCL) showed strong positive correlations with phenolic content (PHE) (0.984), peroxidase activity (POX) (0.931), and polyphenol oxidase activity (PPO) (0.969). Moreover, PHE (-0.769) and POX (-0.867) were also found negatively correlated with CLS disease reaction. The eigenvalues from the principal component analysis (PCA) indicated the first three principal components collectively explained 84.88% of the total variance. Molecular analysis of the panel population suggested a PIC value range from 0.30 to 0.88, with an average 0.696, and markers such as cp01713 (0.84), cp02181 (0.87), and CEDG147 (0.88) had higher PIC values. Principal coordinate analysis (PCoA) suggested capturing of 69.06% of the total variance by the first three axes, and the landraces were categorizing into three clusters (cluster A, B and C). The genetic distances among the landraces ranged from 0 to 0.608, and phylogenetic tree differentiated them into three major clusters at respective Jaccard’s similarity coefficient i.e., Cluster I (0.68), II (0.75) and III (0.83). Meanwhile, the resistance and moderately resistance landraces were observed in cluster A and cluster B, and in cluster II and cluster III respectively. The resistance landraces obtained from the present study could be used as potential donor for breeding process towards CLS resistance in mung bean.

Morpho-genetic assessment and dissecting the genetic architecture for Cercospora leaf spot (CLS) resistance in mung bean [Vigna radiata (L.) Wilczek

Cercospora leaf spot (CLS) has a substantial negative impact on mung bean production across the world. It is crucial to identify and incorporate alleles that might be helpful in combating CLS in order to maintain mung bean health, and productivity. Therefore, 90 mung bean genotypes, including four check varieties, and 66 polymorphic SSR markers were included in the present study during pre-rabi 2018 and pre-rabi 2019. Morpho-genetic analysis revealed a higher value of GCV for yield, cluster and pod numbers per plant, and plant height. All traits had excellent genetic advance (GA), with the exception of the number of seeds per pod, which was medium. PCA was used to separate up to 85.656 % of the variation in the characteristics between the two primary PCs. Molecular dissection revealed, the markers CEDG118 and CEDG074 to yield more genetic diversity, followed by CEDG073, CEDG030 and CEDG147. Estimation of allele frequencies revealed some alleles of the markers found linked to CLS resistance, i.e., CEDG001 (111 bp and 135 bp), CEDG006 (135 bp), CEDG153 (117 bp), CEDG210 (193 bp), CEDG117 (112 bp), CEDG020 (143 bp), CEDG067 (93 bp), CEDG146 (111 bp), and CEDG071 (231 bp and 267 bp). The highest private allelic frequency was employed by the markers CEDG153 and CEDG146. The dendrogram divided the panel population into two major clusters. However, two distinct genetic structure were found within the population. According to these findings, the mung bean germplasm panel used in the present study may have the ability to improve the local gene pool and aid in the development of CLS resistance breeding strategies using genomic tools and techniques.

Identification and characterisation of Cercospora leaf spot(CLS) resistance in mungbean (Vigna radiata L.) genotypes through SSR markers

Identification and characterisation of Cercospora leaf spot(CLS) resistance in mungbean (Vigna radiata L.) genotypes through SSR markers

GENETICS OF CERCOSPORA LEAF SPOT RESISTANCE IN MUNG BEAN

Pulses are notably good nutritive complements of carbohydrate-rich staple diets, such as, wheat, maize, and rice. Mung bean is an essential pulse crop with different proteins and antioxidants proven beneficial for health. The yield of mung bean in Pakistan is comparable to the world average, but overall production is low because of several biotic and abiotic factors. Cercospora leaf spot (CLS) is one of mung bean’s most damaging diseases, limiting its productivity, causing significant losses in yield and an overall gap in production. The presented investigation progressed to comprehending the genetics of resistance to CLS in mung bean. A minicore set of 293 mung bean genotypes developed and maintained by the World Vegetable Center, Taiwan, served as samples in the study. Observed CLS attacks occur during flowering and reduce the yield by decreasing the number of pods per plant. The genetics to resistance against CLS has a single recessive gene controlling it; hence, homozygous recessive plants will be CLS-resistant. Therefore, single gene transfer methods, such as, backcross breeding, are recommendable for incorporating CLS resistance in high-yielding mung bean genotypes.

QTL discovery for resistance to black spot and cercospora leaf spot, and defoliation in two interconnected F1 bi-parental tetraploid garden rose populations.

Garden roses are an economically important horticultural crop worldwide, and two major fungal pathogens, black spot (Diplocarpon rosae F.A. Wolf) and cercospora leaf spot of rose (Rosisphaerella rosicola Pass.), affect both the health and ornamental value of the plant. Most studies on black spot disease resistance have focused on diploid germplasm, and little work has been performed on cercospora leaf spot resistance. With the use of newly developed software tools for autopolyploid genetics, two interconnected tetraploid garden rose F1 populations (phenotyped over the course of 3 years) were used for quantitative trait locus (QTL) analysis of black spot and cercospora leaf spot resistance as well as plant defoliation. QTLs for black spot resistance were mapped to linkage groups (LGs) 1-6. QTLs for cercospora resistance and susceptibility were found in LGs 1, 4, and 5 and for defoliation in LGs 1, 3, and 5. The major locus on LG 5 for black spot resistance coincides with the previously discovered Rdr4 locus inherited from Rosa L. 'Radbrite' (Brite Eyes™), the common parent used in these mapping populations. This work is the first report of any QTL for cercospora resistance/susceptibility in tetraploid rose germplasm and the first report of defoliation QTL in roses. A major QTL for cercospora susceptibility coincides with the black spot resistance QTL on LG 5 (Rdr4). A major cercospora resistance QTL was found on LG 1. These populations provide a genetic resource that will further the knowledge base of rose genetics as more traits are studied. Studying more traits from these populations will allow for the stacking of various QTLs for desirable traits.

Pedigree-based analysis in multi-parental diploid rose populations reveals QTLs for cercospora leaf spot disease resistance.

Cercospora leaf spot (CLS) (Cercospora rosicola) is a major fungal disease of roses (Rosa sp.) in the southeastern U.S. Developing CLS-resistant cultivars offers a potential solution to reduce pesticide use. Yet, no work has been performed on CLS resistance. This study aimed to identify QTLs and to characterize alleles for resistance to CLS. The study used pedigree-based QTL analysis to dissect the genetic basis of CLS resistance using two multi-parental diploid rose populations (TX2WOB and TX2WSE) evaluated across five years in two Texas locations. A total 38 QTLs were identified across both populations and distributed over all linkage groups. Three QTLs on LG3, LG4, and LG6 were consistently mapped over multiple environments. The LG3 QTL was mapped in a region between 18.9 and 27.8 Mbp on the Rosa chinensis genome assembly. This QTL explained 13 to 25% of phenotypic variance. The LG4 QTL detected in the TX2WOB population spanned a 35.2 to 39.7 Mbp region with phenotypic variance explained (PVE) up to 48%. The LG6 QTL detected in the TX2WSE population was localized to 17.9 to 33.6 Mbp interval with PVE up to 36%. Also, this study found multiple degrees of favorable allele effects (q-allele) associated with decreasing CLS at major loci. Ancestors 'OB', 'Violette', and PP-M4-4 were sources of resistance q-alleles. These results will aid breeders in parental selection to develop CLS-resistant rose cultivars. Ultimately, high throughput DNA tests that target major loci for CLS could be developed for routine use in a DNA-informed breeding program.

Cercospora Leaf Spot Resistance of Crapemyrtle Cultivars in Tennessee

Crapemyrtle (Lagerstroemia sp.) is a top-selling deciduous flowering tree in the United States, and its salability is often compromised by cercospora (Cercospora lythracearum Heald & F. A. Wolf) leaf spot. To compare cercospora leaf spot resistance, 32 crapemyrtle cultivars belonging to Lagerstroemia indica, Lagerstroemia fauriei, L. indica × L. fauriei, and L. indica × L. fauriei × Lagerstroemia limii and 12 cultivars or unnamed selections belonging to L. indica, L. indica × L. fauriei, L indica × L. fauriei × L. limii, L. limii, and Lagerstroemia subcostata were planted in field plots in 2004 and 2011, respectively. The experiment was a completely randomized block design with three and four replications in the 2004 and 2011 plantings, respectively. Plants were evaluated for cercospora leaf spot disease severity and defoliation using a scale of 0% to 100% foliage affected from August to October of 2015, 2016, and 2017. Area under the disease progress curve (AUDPC) was calculated for the evaluation period of each year. L. fauriei cultivars Fantasy, Kiowa, Townhouse, and Woodlander’s Chocolate Soldier and L. indica × L. fauriei Apalachee from the 2004 planting, and the L. subcostata and L. limii selections from the 2011 planting had lowest cercospora leaf spot disease severity ratings, AUDPC, and defoliation. L. indica × L. fauriei cultivars Choctaw, Miami, Natchez, Osage, Sarah’s Favorite, Tonto, Tuscarora, and Tuskegee, and L. indica × L. fauriei × L. limii Arapaho were moderately resistant to cercospora leaf spot, whereas cultivars belonging to L. indica and L. indica × L. fauriei × L. limii Cheyenne were highly susceptible to cercospora leaf spot. Results from this research may aid breeders, nursery producers, and landscapers in selecting crapemyrtle species and cultivars with cercospora leaf spot resistance.

Development of Molecular Marker Linked with Cercospora Leaf Spot (CLS) Disease Resistance in Vigna radiata, Cloning, and Expression for Evaluating Antifungal Activity against Cercospora canescens

We developed a molecular marker for MAS of mungbean resistant varieties against CLS from the consensus sequence (MB-CLsRG) of identified RGAs (MB-ClsRCaG1 and MB-ClsRCaG2). The MB-CLsRG sequence-specific primer pair was used to screen Cercospora leaf spot (CLS) resistant varieties of mungbean in genomic analysis that showed congruency with phenotypic screening. Validation of molecular marker linkage with CLS resistance was performed using rtPCR in transcriptomic analysis. The sequenced PCR products showed 100% homology with MB-CLsRG sequence and putative disease resistance proteins that confirmed the linkage of molecular marker with CLS resistance in mungbean. The antifungal potential of MB-CLsRG gene encoding protein was assessed. The MB-CLsRG gene sequence was cloned in the E. coli expression vector for recombinant protein production. The recombinant protein was then investigated for its in vitro antifungal potential against Cercospora canescens. The in vitro investigation showed strong antifungal activity of recombinant protein as it restricted the growth of fungal mycelial mass. The results validated the linkage of developed marker with CLS-resistant mungbean varieties; therefore, it can be used to screen resistant varieties from a large population in MAS. Moreover, the recombinant protein of the MB-CLsRG gene sequence revealed antifungal potential, which proved the gene sequence could be suitable to use in transgenic plants technology to develop fungal-resistant transgenic crops.

Seed Bio-priming Mediated Control of Cercospora Leaf Spot and Bacterial Wilt Disease Resistance in Chilli (Capsicum annuum L.) under New Alluvial Zone

The potential bio-control agents Trichoderma harzianum, and Pseudomonas fluorescens in alone or combinationwere used as seed bio-priming for reviewing their efficacy in the reduction of the devastating diseases, theCercospora leaf spot (Cercosporacapsici) and Bacterial wilt (Ralstonia solanacearum) of chilli (Capsicum annuumL.). Considering two important seasons, the Rabi season was comparatively vital as its disease severity wasmore. In chilli, the disease index was significantly reduced in combining the Trichoderma harzianum +Pseudomonas fluorescens treated seeds, followed by the T. harzianum treatment compared to the control (hydroprimed)against cercospora leaf spot of chilli. In case of Bacterial wilt, it was found that T3 followedbyPseudomonas fluorescens treated seeds. Chilli seeds were primed with Trichoderma harzianum + Pseudomonasfluorescens revealed maximum disease protection that was displaying favour in pre-kharif and early stage(35DAS) in comparison to rabi and 60DAS of chilli production. The ability of genotype indicated variationwhere the distinct variation was noticeable in V2 (G-4) mentioning its high tolerance at 35DAS. Theapplication of combined bio-priming may be suitable to control both Cercospora leaf spot and Bacterial wiltof chilli.

Understanding the genetics of Cercospora leaf spot (CLS) resistance in mung bean (Vigna radiata L. Wilczek)

Understanding the genetics of Cercospora leaf spot (CLS) resistance in mung bean (Vigna radiata L. Wilczek)

Identification of mung bean germplasm for resistance against Cercospora canescens and to study the association of biochemical parameters with defense mechanisms

AbstractSizable loss in crop yields resulting from Cercospora leaf spot (CLS), caused by Cercospora canescens and is a major disease in mung bean [Vigna radiata (L.) R. Wilczek] crops, demands a thorough evaluation of various parameters dealing with the infection. Determination of components for CLS resistance is associated with leaf spot intensity in the field, which is estimated from the area under the disease progress curve (AUDPC). The present study showed that out of 261 genotypes screened in the field for CLS, 88, 89, 51 and, 33 genotypes were found to be resistant, moderately resistant, moderately susceptible, and susceptible, respectively, on the basis of the AUDPC values. Further, five resistant and five susceptible genotypes were selected from the screened genotypes for bioassay analysis and were subjected to artificial inoculation with three different isolates of Cercospora canescens to study the effectiveness in polyhouse. The morphological data along with disease incidence, chlorophyll content, proline content, phenol content and enzymatic activities of phenylalanine ammonia‐lyase (PAL), peroxidase (POX), and superoxide dismutase (SOD) were estimated. The findings showed that there was a significant increase in the enzymatic activities, total phenol, and proline contents in inoculated resistant and susceptible genotypes vs. control (without inoculation). However, the total chlorophyll content reduced in both resistant and susceptible genotypes after inoculation. Moreover, higher enzyme activities were marked in the resistant genotypes than the susceptible genotypes. This study will help to identify the resistant and susceptible mung bean genotypes against Cercospora canescens for further agronomic study as well as breeding programs.

Validation of molecular markers linked to Cercospora leaf spot disease resistance in mungbean (Vigna radiata [L.] Wilczek)

Cercospora leaf spot (CLS) resistance is a highly desirable trait for mungbean (Vigna radiata [L.] Wilczek) production in Thailand. ‘V4718’ is a vital resistance source that shows high and stable resistance to CLS disease. A previous study identified a major quantitative trait locus (QTL) (qCLSC72V18-1) controlling CLS resistance and found the marker (I16274) that was located closest to the resistance gene by using F2:9 and F2:10 recombinant inbred line populations derived through a cross between ‘V4718’ and the susceptible variety ‘Chai Nat 72’ (‘CN72’). Here, we evaluated three newly reported simple sequence repeat (SSR) markers and one InDel marker together with six previously identified markers that were linked to qCLSC72V18-1 to further identify the markers that were located close to this QTL. By performing bulk segregant analysis on two validation populations, we found that two SSR markers (Vr6gCLS037 and Vr6gCLS133) and one InDel marker (VrTAF5_indel) were putatively associated with CLS resistance. Of these markers, only the VrTAF5_indel marker showed a significant association with the CLS resistance gene with a logarithm of odds score > 3 across the phenotypic data for 2016 and 2018. QTL analysis with inclusive composite interval mapping revealed that the VrTAF5_indel marker was integrated into the genetic map with other previously identified markers. The I16274 and VrTAF5_indel markers flanking the QTL of interest accounted for 41.56%-60.38% of the phenotypic variation with genetic distances of 4.0 and 5.0 cM from the resistance gene, respectively. Both markers together permitted only 0.40% recombination with the CLS resistance gene in marker-assisted selection and thus could be useful in future breeding efforts for CLS resistance in mungbean.

Improvement of Cercospora leaf spot and powdery mildew resistance of mungbean variety KING through marker-assisted selection

AbstractThe development of resistant mungbean varieties is one of the most efficient strategies to control major diseases such as Cercospora leaf spot (CLS) and powdery mildew (PM). The objectives of this study were to pyramid a CLS resistance gene and two PM resistance genes from the donor parent D2 into a susceptible variety KING through marker-assisted backcrossing (MABC) and to evaluate their agronomic traits and disease resistance under field conditions. Five markers linked to the resistance genes were used for foreground selection, while two marker sets [Set A containing 15 polymorphic simple sequence repeat (SSR) and expressed sequence tag-SSR (EST-SSR) markers and Set B containing 34 polymorphic inter-simple sequence repeat (ISSR) loci] were also used for background selection. Two pyramided backcross (BC) lines, namely H3 and H4, were homozygous at all five marker loci when confirmed in BC4F4 and BC4F5 generations. Their recurrent parent genome (RPG) recovery ranged from 96.4 to 100.0%, depending on the marker sets. During field evaluation, a moderate to high level of CLS and PM resistance was observed in both BC lines compared to the susceptible recurrent parent KING. One of these BC lines (H3) had all agronomic traits similar or superior to the recurrent parent KING at all environments, and had a higher yield than KING (18.0–32.0%) under CLS and PM outbreaks. This line can be developed into a new resistant mungbean variety in Thailand in the future. These results substantiate the usefulness of MABC for transferring multiple resistance genes into an elite variety.

Genetics of Cercospora Leaf Spot Resistance in Mungbean [Vigna radiata (L.) Wilczek] through Generation Mean Analysis

Background: Cercospora leaf spot (CLS) is a fungal disease of mungbean [Vigna radiata (L.) Wilczek] caused by Cercospora canescens and now emerged as an important biotic stress. A better understanding of the genetics of CLS resistance will help in formulating efficient breeding procedures in mungbean.Methods: The present investigation focused on genetics of CLS resistance through generation mean analysis (six parameter model) in two intra-specific mungbean crosses namely, Kopergaon × HUM12 and Kopergaon × ML1720. Four quantitative disease resistance components, viz., Area under disease progress curve (AUDPC), Incubation period (IP), Latent period (LP) and degree of sporulation (SP) were studied.Result: A high correlation of AUDPC with latent period (r = –0.68 to –0.79, P less than 0.0001) and SP (r = 0.72 to -0.81, P less than 0.0001) advocated that both are main contributor for CLS disease development. High heterosis along with high heritability in terms of AUDPC ( greater than 0.09) indicated the importance of genetic factor(s) in controlling CLS resistance. Generation mean analysis of both the crosses revealed duplicate epistatic interaction and involvement of two genes for CLS resistance in terms of AUDPC. This study supports oligogenic nature of inheritance, advocating AUDPC along with IP, LP and SP as important disease indicator for selection of CLS resistance in mungbean.

Apomictic lines of sugar beet: development and studying

Background. While working with such cross-pollinated crops as sugar beet, the greatest problem is the fixation of valuable genotypes. Using apomixis to produce breeding material helps to accelerate the breeding process and save the desired combination of genes.Materials and methods. The research objects were 110 accessions of sugar beet from the VIR collection. Field experiments and assessments of the resistance to Cercospora leaf spot, monogermity, and non-bolting were performed according to VIR’s guidelines in 2016–2018 at Pushkin and Pavlovsk Laboratories of VIR and Maikop Experiment Station of VIR. The sugar level in roots was measured using an optical refractometer.Results. A comprehensive study of sugar beet accessions resulted in the development of apomictic lines with cytoplasmic male sterility, followed by an evaluation of their economically important characters. An extremely rare occurrence of biotypes with the 0-type sterility (less than 0.5%) was observed in the population. The seeds obtained from apomixis-prone lines demonstrated a significant difference during inbreeding from the seeds of fertile inbred genotypes: no inbreeding depression was observed in apomictic lines. Lines combining sterility and monogermity in their genotype were produced. Testing parent accessions and apomictic forms did not reveal significant differences in the sugar content and root yield, so the resulting forms can be efficiently used in future breeding programs.Conclusion. Using apomixis to develop sugar beet lines helped to fixate the sugar content level, biennial plant development cycle, and Cercospora leaf spot resistance. Thus, apomixis is promising for ensuring maternal inheritance and preserving the desired combination of genes in sugar beet, thereby accelerating the breeding process.

Fine mapping of QTL conferring Cercospora leaf spot disease resistance in mungbean revealed TAF5 as candidate gene for the resistance.

This paper reports fine mapping of qCLS for resistance to Cercospora leaf spot disease in mungbean and identified LOC106765332encoding TATA-binding-protein-associated factor 5 (TAF5) as the candidate gene for the resistance Cercospora leaf spot (CLS) caused by the fungus Cercospora canescens is an important disease of mungbean. A QTL mapping using mungbean F2 and BC1F1 populations developed from the "V4718" (resistant) and "Kamphaeng Saen 1" (KPS1; susceptible) has identified a major QTL controlling CLS resistance (qCLS). In this study, we finely mapped the qCLS and identified candidate genes at this locus. A BC8F2 [KPS1 × (KPS1 × V4718)] population developed in this study and the F2 (KPS1 × V4718) population used in a previous study were genotyped with 16 newly developed SSR markers. QTL analysis in the BC8F2 and F2 populations consistently showed that the qCLS was mapped to a genomic region of ~ 13Kb on chromosome 6, which contains only one annotated gene, LOC106765332 (designated "VrTAF5"), encoding TATA-binding-protein-associated factor 5 (TAF5), a subunit of transcription initiation factor IID and Spt-Ada-Gcn5 acetyltransferase complexes. Sequence comparison of VrTAF5 between KPS1 and V4718 revealed many single nucleotide polymorphisms (SNPs) and inserts/deletions (InDels) in which eight SNPs presented in eight different exons, and an SNP (G4,932C) residing in exon 8 causes amino acid change (S250T) in V4718. An InDel marker was developed to detect a 24-bp InDel polymorphism in VrTAF5 between KPS1 and V4718. Analysis by RT-qPCR showed that expression levels of VrTAF5 in KPS1 and V4718 were not statistically different. These results indicated that mutation in VrTAF5 causing an amino acid change in the VrTAF5 protein is responsible for CLS resistance in V4718.

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.

Sensory assessment of Cercospora beticola sporulation for phenotyping the partial disease resistance of sugar beet genotypes

BackgroundDue to its high damaging potential, Cercospora leaf spot (CLS) caused by Cercospora beticola is a continuous threat to sugar beet production worldwide. Breeding for disease resistance is hampered by the quantitative nature of resistance which may result from differences in penetration, colonization, and sporulation of the pathogen on sugar beet genotypes. In particular, problems in the quantitative assessment of C. beticola sporulation have resulted in the common practice to assess field resistance late in the growth period as quantitative resistance parameter. Recently, hyperspectral sensors have shown potential to assess differences in CLS severity. Hyperspectral microscopy was used for the quantification of C. beticola sporulation on sugar beet leaves in order to characterize the host plant suitability / resistance of genotypes for decision-making in breeding for CLS resistance.ResultsAssays with attached and detached leaves demonstrated that vital plant tissue is essential for the full potential of genotypic mechanisms of disease resistance and susceptibility. Spectral information (400 to 900 nm, 160 wavebands) of CLSs recorded before and after induction of C. beticola sporulation allowed the identification of sporulating leaf spot sub-areas. A supervised classification and quantification of sporulation structures was possible, but the necessity of genotype-specific reference spectra restricts the general applicability of this approach. Fungal sporulation could be quantified independent of the host plant genotype by calculating the area under the difference reflection spectrum from hyperspectral imaging before and with sporulation. The overall relationship between sensor-based and visual quantification of C. beticola sporulation on five genotypes differing in CLS resistance was R2 = 0.81; count-based differences among genotypes could be reproduced spectrally.ConclusionsFor the first time, hyperspectral imaging was successfully tested for the quantification of sporulation as a fungal activity depending on host plant suitability. The potential of this non-invasive and non-destructive approach for the quantification of fungal sporulation in other host–pathogen systems and for the phenotyping of crop traits complex as sporulation resistance is discussed.

Two tightly linked genes coding for NAD-dependent malic enzyme and dynamin-related protein are associated with resistance to Cercospora leaf spot disease in cowpea (Vigna unguiculata (L.) Walp.).

Cercospora leaf spot (CLS) caused by Cercospora canescens is an important disease of cowpea (Vigna unguiculata). A previous study using an F2 population [CSR12906 (susceptible)×IT90K-59-120 (resistant)] identified a major QTL qCLS9.1 for resistance to CLS. In this study, we finely mapped and identified candidate genes of qCLS9.1 using an F3:4 population of 699 individuals derived from two F2:3 individuals segregating at qCLS9.1 from the original population. Fine mapping narrowed down the qCLS9.1 for the resistance to a 60.6-Kb region on cowpea chromosome 10. There were two annotated genes in the 60.6-Kb region; Vigun10g019300 coding for NAD-dependent malic enzyme 1 (NAD-ME1) and Vigun10g019400 coding for dynamin-related protein 1C (DRP1C). DNA sequence analysis revealed 12 and 2 single nucleotide polymorphisms (SNPs) in the coding sequence (CDS) and the 5' untranslated region and TATA boxes of Vigun10g019300 and Vigun10g019400, respectively. Three SNPs caused amino acid changes in NAD-ME1 in CSR12906, N299S, S488N and S544N. Protein prediction analysis suggested that S488N of CSR12906 may have a deleterious effect on the function of NAD-ME1. Gene expression analysis demonstrated that IT90K-59-120 and CSR12906 challenged with C. canescens showed different expression in both Vigun10g019300 and Vigun10g019400. Taken together, these results indicated that Vigun10g019300 and Vigun10g019400 are the candidate genes for CLS resistance in the cowpea IT90K-59-120. Two derived cleaved amplified polymorphic sequence markers were developed to detect the resistance alleles at Vigun10g019300 and Vigun10g019400 in IT90K-59-120.