Disease Resistance Breeding Programs Research Articles

TABLE GRAPE BREEDING AT THE ARC INFRUITEC-NIETVOORBIJ, SOUTH AFRICA; ITS IMPACT ON THE SA INDUSTRY AND LATEST DEVELOPMENTS

Since its inception in 1952 and first releases in 1965, the ARC table grape breeding program released a total of 28 cultivars. In 1985 one ARC cultivar (?Bien Donne?) made a noteworthy contribution to export (3%), while the contribution of six ARC cultivars was 25,9% of the total export in 2006. Changes in consumer preferences necessitate regular revision of aims. For example, export of seedless cultivars from SA grew from a minimal contribution in 1985 to over 52% in 2006 and is still growing. New seedless cultivars are developed by in vitro embryo rescue techniques, while crosses to develop seeded cultivars with unique characteristics are also made. The first seedless cultivar was released in 1986, followed by another five seedless cultivars. Two new, early ripening, red seedless cultivars will be released in the near future to the SA industry. Since 2004, DNA technologies and molecular approaches were introduced as an essential component of the disease resistance breeding program. An extensive DNA fingerprint of table grape cultivars/selections was constructed and is used to solve identity issues. ?Regent?, an interspecies hybrid, is resistant to powdery and downy mildew (Fisher et al., 2004) and was used to introduce resistance into the ARC table grape breeding program. We report validation of the resistance loci previously identified, following a QTL approach in a ?Regent? × ?RedGlobe? population. We identified plants that phenotypically displayed resistance to both downy and powdery mildew, whilst also carrying flanking markers for both resistance QTL. These plants are prime candidates to be used in future crosses to introduce resistance, whilst also selecting for good fruit quality. The population and the genetic map is a valuable resource that can be used in future to map other disease resistance loci present in Regent or fruit quality traits of ?RedGlobe?.

Occurrence of barley pathogenicPyrenophoraspecies and their mating types in Hungary

Net blotch and leaf stripe caused by Pyrenophora teres and P. graminea, respectively, are two major foliar diseases of barley. These two species are able to infect wheat, too. The species composition of these pathogens was examined, for the first time, in four different regions of Hungary in 2006–2010. Altogether 204 isolates were obtained from 99 winter barley, 55 spring barley and 50 wheat leaf samples collected in commercial fields and experimental stations, and species assignment was carried out using species-specific PCR reactions. Most isolates belonged to P. teres f. teres (68%), 26% to P. teres f. maculata and only 6% of the isolates were assigned to P. graminea. Interestingly, all but one of the P. graminea isolates came from the western part of Hungary, while both forms of P. teres occurred in each region. The distribution of mating type genes was also examined in 144 isolates. The overall ratio of MAT1 and MAT2 genes in P. graminea, P. teres f. maculata and P. teres f. teres was 5:3, and close to 2:1 and 1:1, respectively. Both MAT1 and MAT2 isolates of each fungal species/form were distributed in almost all regions over several years, indicating a high potential for sexual outcrossing within local populations of these pathogens. Our survey may be helpful to determine priorities in disease resistance breeding programs. Further studies are in progress to examine the population structure of the most abundant pathogen P. teres f. teres.

Evaluation of maize inbred lines currently used in Chinese breeding programs for resistance to six foliar diseases

Foliar diseases are common in most maize-producing regions and have caused serious yield reduction in China. To evaluate genetic resistance of parental lines actively used in maize breeding programs to major foliar diseases, 152 maize inbred lines were tested against northern corn leaf blight (NCLB), southern corn leaf blight (SCLB), Curvularia leaf spot (CLS), gray leaf spot (GLS), common rust, and southern rust from 2003 to 2005. A small number of lines exhibited highly resistant reactions to common rust and southern rust, but none were highly resistant to NCLB, SCLB, CLS, and GLS. Although 53.3%, 40.8%, and 80.7% of lines were resistant to NCLB, SCLB, and common rust, the resistance in most lines was moderate. Resistance to CLS, GLS, and southern rust was rare in this collection of maize lines. Five lines, 313, Chang 7-2, Qi 319, Qi 318, and Shen 137, were resistant to five diseases tested. Lines belonging to heterotic subgroup PB exhibited better resistance to the foliar diseases than lines from other heterotic subgroups, such as BSSS, PA, Lancaster, LRC, and PA. The results will be of benefit to breeders for selecting lines in disease resistance breeding programs.

A Novel, Sensitive Method to Evaluate Potato Germplasm for Bacterial Wilt Resistance Using a LuminescentRalstonia solanacearumReporter Strain

Several breeding programs are under way to introduce resistance to bacterial wilt caused by Ralstonia solanacearum in solanaceous crops. The lack of screening methods allowing easy measurement of pathogen colonization and the inability to detect latent (i.e., symptomless) infections are major limitations when evaluating resistance to this disease in plant germplasm. We describe a new method to study the interaction between R. solanacearum and potato germplasm that overcomes these restrictions. The R. solanacearum UY031 was genetically modified to constitutively generate light from a synthetic luxCDABE operon stably inserted in its chromosome. Colonization of this reporter strain on different potato accessions was followed using life imaging. Bacterial detection in planta by this nondisruptive system correlated with the development of wilting symptoms. In addition, we demonstrated that quantitative detection of the recombinant strain using a luminometer can identify latent infections on symptomless potato plants. We have developed a novel, unsophisticated, and accurate method for high-throughput evaluation of pathogen colonization in plant populations. We applied this method to compare the behavior of potato accessions with contrasting resistance to R. solanacearum. This new system will be especially useful to detect latency in symptomless parental lines before their inclusion in long-term breeding programs for disease resistance.

Evaluation of rice germplasm for multiple disease resistance under artificial inoculation conditions

One thousand and eighteen rice germplasm lines were evaluated against the prevalent pathotypes viz., PbXo-7 and PbXo-10 of Xanthomonas oryzae pv. oryzae causing bacterial blight, brown spot and sheath blight diseases under artificial inoculation conditions. Virulence/avirulence of the two pathotypes to Xa/xa genes indicated that all the pathotypes were virulent on the most of bacterial blight resistant single Xa/xa gene (s). Pathotype PbXo-7 was virulent to known Xa genes namely Xa 1, Xa 3, Xa 4, xa 5, Xa 7, xa 8, Xa 10 and Xa 11 and cultivars PR 114, PR 116 and PR 118 growing in Northern regions of India. PbXo-10 was virulent on all these genes including newly identified gene Xa38. None of the single gene is effective against the pathotypes prevalent in Punjab. Two years data revealed that 46 lines (5.4%) showed resistant reaction to pathotype PbXo-7 and 30 lines (2.9%) showed resistance to newly emerged pathotype PbXo-10. Twenty two lines showed resistant reaction to both the pathotypes. Most of the entries which were resistant to PbXo-10 also showed resistant to the PbXo-7. Germplasm line IC No.346207 showed resistant reaction and IC Nos. 114315 and 320826 showed moderately resistant reaction to brown spot. None of the germplasm line showed resistance to sheath blight. These resistant entries can either be released as new varieties or further utilized as donors in multiple disease resistance breeding programmes.

Diallel analysis for yield, yield traits and foliar disease resistance traits in groundnut [Arachis hypogaea(l.)

Combining ability of eight diverse genotypes for yield and foliar disease resistance traits was estimated to assess the type of gene action governing the yield and disease resistance traits and to identify genotypes suitable for use as parents in breeding for high yielding associated with foliar disease resistance. Twenty-eight F1s (excluding reciprocals) from an eight parental diallel cross and their parents were evaluated in a randomized block design. Data were recorded on sixteen traits including morphological, yield and yield traits and foliar disease resistance traits. Highly significant GCA and SCA effects recorded for almost all the studied traits, but the SCA effects were lesser than the GCA effects indicated the additive type of gene action suggested that the selection for high yield and for foliar disease resistance should be effective in early generations. Strong association between parental means and GCA effects for yield and disease resistance traits suggested that the per se performance of the parental line could be used as a predictor of the capability of a line to transmit the foliar disease resistance and yielding traits to its progenies. The parental lines, GPBD 4 and ICG (FDRS) 79 were found to be suitable as good donors in a foliar disease resistance breeding program.

On-farm performance of rainbow trout (Oncorhynchus mykiss) selectively bred for resistance to bacterial cold water disease: Effect of rearing environment on survival phenotype

Selective fish breeding programs for disease resistance comprise an increasingly important role in aquaculture production and offer an additional management tool for reducing bacterial-caused disease losses. Bacterial cold water disease (BCWD) is one of the most frequent causes of elevated mortality in juvenile salmonids, and we have selectively bred three genetic lines of rainbow trout for varying resistance to BCWD. These lines, designated ARS-Fp-R (resistant), ARS-Fp-C (control) and ARS-Fp-S (susceptible), differ in survival following standardized laboratory challenges with the causative agent of BCWD, Flavobacterium psychrophilum. This study evaluated survival of the genetic lines in laboratory challenges and in a production environment. Evaluations of disease resistance demonstrated a reproducible, 30% or greater, survival difference between ARS-Fp-R and ARS-Fp-S lines at body weights ranging from 0.7 to 13g. Farm trials were performed to evaluate survival over an 80-day growth period starting after the trout began feeding. After a BCWD epizootic, the ARS-Fp-R line displayed significantly greater risk-adjusted survival (95.7%) than the ARS-Fp-S line (91.2%, P<0.0001) and the ARS-Fp-C line (92.4%, P<0.0001). Phenotype stability in farm-trial fish was also evaluated using laboratory challenges. The ARS-Fp-R line consistently displayed a higher, but not always statistically significant, survival percentage compared to the other lines and the data suggest that the magnitude of the survival phenotype difference is sensitive to environmental influence. In summary, the overall greater survival of the ARS-Fp-R line provides evidence of genetic improvement under production conditions.

Resistance to Foliar Diseases in a Mini-Core Collection of Sorghum Germplasm.

Anthracnose, leaf blight, and rust are important biotic constraints to grain and forage sorghum production worldwide and are best managed through host plant resistance. A sorghum mini-core collection, consisting of 242 germplasm accessions developed from a core collection of 2,246 landrace accessions originating from 58 countries, was evaluated to identify sources of resistance to foliar diseases. The mini-core accessions were evaluated in anthracnose- and leaf-blight-screening nurseries under artificial inoculation in the rainy and late rainy seasons, respectively, during 2009 and 2010. For rust resistance, screening was done under artificial inoculation in the greenhouse as well as in the field under natural infection. In all, 13 accessions were found resistant (score ≤3.0 on a 1-to-9 scale) to anthracnose and 27 to leaf blight in both 2009 and 2010. Six accessions exhibited resistance to rust in both the greenhouse and the field. In the resistant accessions, a wide range of diversity was observed for agronomic traits such as days to 50% flowering, plant height, and grain yield/plant, and morphological characteristics such as grain or glume color, glume coverage, endosperm texture, and panicle type (ear head compactness). Three mini-core accessions (IS 473, IS 23684, and IS 23521) exhibited resistance to all three diseases. These accessions with multiple disease resistance will be useful in sorghum disease resistance breeding programs.

Standardizing resistance screening to Pseudomonas fuscovaginae and evaluation of rice germplasm at seedling and adult plant growth stages

Sheath lesions, grain sterility and grain discolouration of rice caused by Pseudomonas fuscovaginae can cause yield losses of up to 100 %. The most sustainable method of managing this disease is the use of host plant resistance. To identify sources of resistance an inoculation method that is practical, rapid and reliable is needed. We compare three different inoculation methods. Results showed that the pin-prick method is appropriate for identifying sources of resistance to P. fuscovaginae, while the spray method could be useful for mass screening of rice genotypes. The seed-soaking method was also evaluated and has showed potential in detection of early disease resistance. A total of 16 Multiparent Advanced Generation Inter-Crosses and 20 OryzaSNP set varieties from the International Rice Research Institute were evaluated using the pin-prick and seed-soaking methods. All growth stages were susceptible to the pathogen and the 107 cfu mL−1 inoculum concentration was optimal for discriminating between resistant and susceptible genotypes. For the pin-prick method, a single point assessment of disease severity at 14 days post-inoculation could be used instead of the AUDPC values to classify genotypes. An index of reduction in seedling height 10 days after seed soaking was established for the classification of the genotypes reaction to the disease. Resistant varieties identified using both the pin-prick and seed-soaking methods could be verified for use in disease resistance breeding programs. Of the 36 genotypes evaluated 22 were found to be resistant at the late booting or early panicle exsertion stage by pin-prick method, while 25 were resistant at the seed to germination stage. No correlation was found between the resistance classification of varieties between the two inoculation methods, indicating that there could be different mechanisms of resistance to P. fuscovaginae in rice.

Analysis of TIR- and non-TIR-NBS-LRR disease resistance gene analogous in pepper: characterization, genetic variation, functional divergence and expression patterns

BackgroundPepper (Capsicum annuum L.) is one of the most important vegetable crops worldwide. However, its yield and fruit quality can be severely threatened by several pathogens. The plant nucleotide-binding site (NBS)-leucine-rich repeat (LRR) gene family is the largest class of known disease resistance genes (R genes) effective against such pathogens. Therefore, the isolation and identification of such R gene homologues from pepper will provide a critical foundation for improving disease resistance breeding programs.ResultsA total of 78 R gene analogues (CaRGAs) were identified in pepper by degenerate PCR amplification and database mining. Phylogenetic tree analysis of the deduced amino acid sequences for 51 of these CaRGAs with typically conserved motifs ( P-loop, kinase-2 and GLPL) along with some known R genes from Arabidopsis and tomato grouped these CaRGAs into the non-Toll interleukin-1 receptor (TIR)-NBS-LRR (CaRGAs I to IV) and TIR-NBS-LRR (CaRGAs V to VII) subfamilies. The presence of consensus motifs (i.e. P-loop, kinase-2 and hydrophobic domain) is typical of the non-TIR- and TIR-NBS-LRR gene subfamilies. This finding further supports the view that both subfamilies are widely distributed in dicot species. Functional divergence analysis provided strong statistical evidence of altered selective constraints during protein evolution between the two subfamilies. Thirteen critical amino acid sites involved in this divergence were also identified using DIVERGE version 2 software. Analyses of non-synonymous and synonymous substitutions per site showed that purifying selection can play a critical role in the evolutionary processes of non-TIR- and TIR-NBS-LRR RGAs in pepper. In addition, four specificity-determining positions were predicted to be responsible for functional specificity. qRT-PCR analysis showed that both salicylic and abscisic acids induce the expression of CaRGA genes, suggesting that they may primarily be involved in defence responses by activating signaling pathways.ConclusionThe identified CaRGAs are a valuable resource for discovering R genes and developing RGA molecular markers for genetic map construction. They will also be useful for improving disease resistance in pepper. The findings of this study provide a better understanding of the evolutionary mechanisms that drive the functional diversification of non-TIR- and TIR-NBS-LRR R genes in pepper.

Resistance to blast (Magnaporthe grisea) in a mini-core collection of finger millet germplasm

Blast caused by Pyricularia grisea [teleomorph: Magnaporthe grisea] is an economically important and widespread disease of finger millet in the world. Host resistance is the most economical and effective means of combating this disease as finger millet is predominantly grown by resource-poor and marginal farmers. At the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), we evaluated a finger millet mini-core collection of 80 germplasm accessions (about 1 % of the total germplasm collection representing major trait variability) for blast resistance both in the field and greenhouse. Field evaluation was done using a refined screening technique that included new improved rating scales for leaf, neck and finger infection. Sixty six of the 80 accessions showed combined resistance to leaf, neck and finger blast in two seasons (2009 and 2010) of field screening. A highly significant and positive correlation was found between neck and finger blast ratings (r = 0.92), whereas small but significant correlations were found between leaf blast and neck blast (r = 0.25) and between leaf blast and finger blast (r = 0.30). These accessions were also screened for leaf blast resistance in the greenhouse by artificial inoculation of seedlings to confirm field observations. Fifty-eight of the 80 accessions were resistant to leaf blast in the greenhouse screen as well. These resistant accessions represented one wild (africana) and four cultivated races (vulgaris, plana, elongate and compacta) of finger millet that originated from 13 countries in Asia and Africa and exhibited considerable diversity for agronomic traits, such as maturity period, plant height and panicle type. These blast resistant accessions from the mini-core collection would be useful in finger millet disease resistance breeding programs.

Resistance to Marssonina coronaria and Alternaria alternata Apple Pathotype in the Major Apple Cultivars and Rootstocks Used in China

A comparison of field tolerance of 25 apple (Malus ×domestica) cultivars and 39 apple rootstocks to the pathogens Marssonina coronaria and Alternaria alternata apple pathotype was performed. Although most apple cultivars grown in China were susceptible or highly susceptible to both pathogens causing two diseases, considerable variation in the level of resistance to both pathogens was observed. Only three cultivars, Qinguan, Jiguan, and Xiangyanghong, exhibited resistance to both pathogens. Among the rootstocks tested, 30 of 39 (77%) were susceptible or highly susceptible to M. coronaria and 32 (82%) were susceptible to the A. alternata apple pathotype. Four rootstocks, ‘P.22’, ‘SH12’, ‘Za’ai 76’, and ‘Qingdao598’, were resistant to both pathogens. The correlation between resistance to both pathogens was highly significant in the 74 apple cultivars and rootstocks tested suggesting common genetic resistance factors to these two pathogens. Data represented horizontal resistance in the germplasm. The resistant local germplasm should be used in disease resistance breeding programs.

Identification and multi-environment validation of resistance to Fusarium oxysporum f. sp. ciceris in chickpea

Chickpea wilt incited by Fusarium oxysporum f. sp. ciceris is one of the most important constraints to chickpea production worldwide and best managed through host plant resistance. The aim of this work was to find new sources of resistance to wilt disease and validate their stability across different environments. One-hundred and twenty three lines with wilt incidence <10% were selected from preliminary evaluation of 948 lines including germplasm and breeding lines from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) for wilt resistance in the sick plot during 2003/2004 crop season at ICRISAT, Patancheru, India. Sixty lines were selected for second round of evaluation (2005/2006) and from those 57 lines were selected for third round of evaluation (2006/2007). In order to validate resistance stability, a Chickpea Wilt Nursery was constituted with 27 lines (7 germplasm accessions, 19 breeding lines and a highly susceptible check) and further tested in multi-location experiment for wilt resistance at 9 locations in India for three years (2007/2008–2009/2010). Variability in wilt incidence due to genetic differences among the genotypes, among the environments, and that due to genotype×environment interaction was highly significant (P<0.001). Although complete resistance across the locations was not found, the genotype and genotype×environment (GGE) biplot analyses allowed the selection of three breeding lines (ICCV 05527, ICCV 05528 and ICCV 96818) and one germplasm accession (ICC 11322) with moderate level of disease resistance and stable performance across the environments. Genotype×environment (G×E) interaction contributed 36.7% of total variation of the multi-environment evaluation, revealing instability of the phenotypic expression across environments. The identified resistant sources should be useful to chickpea disease resistance breeding programs.

Tissues Expression, Polymorphisms Identification of FcRn Gene and Its Relationship with Serum Classical Swine Fever Virus Antibody Level in Pigs.

Neonatal Fc receptor (FcRn) gene encodes a receptor that binds the Fc region of monomeric immunoglobulin G (IgG) and is responsible for IgG transport and stabilization. In this report, the 8,900 bp porcine FcRn genomic DNA structure was identified and putative FcRn protein included 356 amino acids. Alignment and phylogenetic analysis of the porcine FcRn amino acid sequences with their homologies of other species showed high identity. Tissues expression of FcRn mRNA was detected by real time quantitative polymerase chain reaction (Q-PCR), the results revealed FcRn expressed widely in ten analyzed tissues. One single nucleotide polymorphism (SNP) (HQ026019:g.8526 C>T) in exon6 region of porcine FcRn gene was demonstrated by DNA sequencing analysis. A further analysis of SNP genotypes associated with serum Classical Swine Fever Virus antibody (anti-CSFV) concentration was performed in three pig populations including Large White, Landrace and Songliao Black pig (a Chinese indigenous breed). Our results of statistical analysis showed that the SNP had a highly significant association with the level of anti-CSFV antibody (At d 20; At d 35) in serum (p = 0.008; p = 0.0001). Investigation of expression and polymorphisms of the porcine FcRn gene will help us in further understanding the molecular basis of the antibody regulation pathway in the porcine immune response. All these results indicate that FcRn gene might be regarded as a molecular marker for genetic selection of anti-CSFV antibody level in pig disease resistance breeding programmes.

Systematic analysis and comparison of nucleotide‐binding site disease resistance genes in maize

Nucleotide-binding site (NBS) disease resistance genes play an integral role in defending plants from a range of pathogens and insect pests. Consequently, a number of recent studies have focused on NBS-encoding genes in molecular disease resistance breeding programmes for several important plant species. Little information, however, has been reported with an emphasis on systematic analysis and a comparison of NBS-encoding genes in maize. In the present study, 109 NBS-encoding genes were identified based on the complete genome sequence of maize (Zea mays cv. B73), classified as four different subgroups, and then characterized according to chromosomal locations, gene duplications, structural diversity and conserved protein motifs. Subsequent phylogenetic comparisons indicated that several maize NBS-encoding genes possessed high similarity to function-known NBS-encoding genes, and revealed the evolutionary relationships of NBS-encoding genes in maize comparede to those in other model plants. Analyses of the physical locations and duplications of NBS-encoding genes showed that gene duplication events of disease resistance genes were lower in maize than in other model plants, which may have led to an increase in the functional diversity of the maize NBS-encoding genes. Various expression patterns of maize NBS-encoding genes in different tissues were observed using an expressed-sequence tags database and, alternatively, after southern leaf blight infection or the application of exogenous salicylic acid. The results reported in the present study contribute to an improved understanding of the NBS-encoding gene family in maize.

Field evaluation of mulberry accessions for susceptibility to foliar diseases in Uasin-Gishu district, Kenya

The incidence and severity of foliar disease pathogens in five mulberry accessions (Embu, Thika, Thailand, Kanva-2 and S41) grown in Kenya were evaluated under field conditions in Eldoret. The plants were rated for disease incidence and severity in two mulberry growth cycles over a period of 10 months (May 2009 to February 2010). A high incidence of 58.3% bacterial leaf blight (Xanthomonas campestris pv. mori) disease prevalence was recorded on Embu accession, 36.6% incidence of fungal leaf blight (Alternaria alternata) on Thika and 26.0% for S41 accessions. Black leaf spot (Pseudocercospora mori) disease was high (48.93%) on the Thailand accession, while brown leaf spot (Myrothecium roridum) was recorded with a low (3.61%) incidence on the Kanva-2. Susceptibility of accessions to diseases was highest in Embu, followed by Thailand, Thika and S41 that were moderately susceptible, while Kanva-2 accession was resistant. Our results suggest that Kanva-2 accession can be utilized in future disease resistance breeding programmes to confer disease resistant trait in mulberry varieties.

Identification, Mapping, Isolation of the Genes Resisting to Bacterial Blight and Application in Rice

Bacterial blight, caused by Xanthomonas oryzae pv. Oryzae , is the most devastating plant bacterial disease in Asia. Exploration, identification and utilization of new resistant germplasms to rice breeding are the effective pathway to control the disease. Mapping and cloning the resistant genes makes MAS (marker-assisted selection) and transgenic technology play a great role in breeding program for disease resistance and let people have a profound insight on molecular mechanism of resistance to bacterial blight. In this paper, mapping, cloning and application of the genes resisting to bacterial blight were summarized, and also some suggestions were put forward to relieve the damaging extent caused by bacterial blight via utilizing disease resistant breeding program.

Molecular Characterization of a Diverse Maize Inbred Line Collection and its Potential Utilization for Stress Tolerance Improvement

ABSTRACTA diverse collection of 359 advanced maize (Zea mays L.) inbred lines from the International Maize and Wheat Improvement Center (CIMMYT) and International Institute for Tropical Agriculture (IITA) breeding programs for drought, low N, soil acidity (SA), and pest and disease resistance was genotyped using 1260 single nucleotide polymorphism (SNP) markers. Model‐based population partition, neighbor‐joining (NJ) clustering, and principal component analysis (PCA) based on the genotypic data were employed to classify the lines into subgroups. A subgroup largely consisting of lines developed from La Posta Sequía (LPS) consistently separated from other lines when using different methods based on both SNP and SNP haplotype data. Lines related by pedigree tended to cluster together. Nine main subsets of lines were determined based on pedigree information, environmental adaptation, and breeding scheme. Analysis of molecular variance (AMOVA) revealed that variation within these subsets was much higher than that among subsets. Genetic diversity and linkage disequilibrium (LD) level were tested in the whole panel and within each subset. The potential of the panel for association mapping was tested using 999 SNP markers with minor allelic frequency (MAF) ≥ 0.05 and phenotypic data (grain yield [GY], ears per plant [EPP], and anthesis to silking interval [ASI]). Results show the panel is ideal for association mapping where type I error can be controlled using a mixed linear model (Q + K). Use of pedigree, heterotic group, and ecological adaptation information together with molecular characterization of this panel presents a valuable genetic resource for stress tolerance breeding in maize.

Resistance to Elsinoë ampelina and expression of related resistant genes in Vitis rotundifolia Michx. grapes.

Muscadine grapes (Vitis rotundifolia Michx) are considered as excellent genetic resources for grape breeding programs as they are known for their hardiness and resistance to pests and diseases. However, contrary to popular belief, our study indicated that not all muscadine cultivars are resistant to anthracnose disease. In order to identify a source of genetic tolerance towards anthracnose among muscadine cultivars, a series of in-situ and ex-situ experiments were conducted through strict and sensitive screening processes. Two consecutive years of field evaluation of 54 grape cultivars showed various levels of anthracnose incidence among the cultivars between a scale of 0 (tolerant) to 5 (highly-susceptible). Resistance bioassay by inoculation of different spore densities of Elsinoë ampelina on 40 cultivars presented similar results and was consistent with those obtained from the field test. A real-time PCR analysis was conducted to investigate differences of gene expression between susceptible and tolerant cultivars and to confirm results by phenotypic identification. Expression of genes encoding chalcone synthase, stilbene synthase, polygalacturonase-inhibiting protein, chitinase and lipid transfer-protein was only detected in tolerant cultivars. Resistant muscadine cultivars identified in this study could be excellent candidates for grape disease resistance breeding programs.

Identification and characterization of NBS-encoding disease resistance genes in Lotus japonicus

Nucleotide-binding site (NBS) disease resistance genes play an important role in defending plants from a range of pathogens and insect pests. Consequently, NBS-encoding genes have been the focus of a number of recent studies in molecular disease resistance breeding programs. However, little is known about NBS-encoding genes in Lotus japonicus. In this study, a full set of disease resistance (R) candidate genes encoding NBS from the complete genome of L. japonicus was identified and characterized using structural diversity, chromosomal locations, conserved protein motifs, gene duplications, and phylogenetic relationships. Distinguished by N-terminal motifs and leucine-rich repeat motifs (LRRs), 92 regular NBS genes of 158 NBS-coding sequences were classified into seven types: CC-NBS-LRR, TIR-NBS-LRR, NBS-LRR, CC-NBS, TIR-NBS, NBS, and NBS-TIR. Phylogenetic reconstruction of NBS-coding sequences revealed many NBS gene lineages, dissimilar from results for Arabidopsis but similar to results from research on rice. Conserved motif structures were also analyzed to clarify their distribution in NBS-encoding gene sequences. Moreover, analysis of the physical locations and duplications of NBS genes showed that gene duplication events of disease resistance genes were lower in L. japonicus than in rice and Arabidopsis, which may contribute to the relatively fewer NBS genes in L. japonicus. Sixty-three NBS-encoding genes with clear conserved domain character were selected to check their gene expression levels by semi-quantitative RT-PCR. The results indicated that 53 of the genes were most likely to be acting as the active genes, and exogenous application of salicylic acid improved expression of most of the R genes.