Common Bacterial Blight Resistance Research Articles

Mapping yield and yield-related traits using diverse common bean germplasm.

Common bean (bean) is one of the most important legume crops, and mapping genes for yield and yield-related traits is essential for its improvement. However, yield is a complex trait that is typically controlled by many loci in crop genomes. The objective of this research was to identify regions in the bean genome associated with yield and a number of yield-related traits using a collection of 121 diverse bean genotypes with different yields. The beans were evaluated in replicated trials at two locations, over two years. Significant variation among genotypes was identified for all traits analyzed in the four environments. The collection was genotyped with the BARCBean6K_3 chip (5,398 SNPs), two yield/antiyield gene-based markers, and seven markers previously associated with resistance to common bacterial blight (CBB), including a Niemann-Pick polymorphism (NPP) gene-based marker. Over 90% of the single-nucleotide polymorphisms (SNPs) were polymorphic and separated the panel into two main groups of small-seeded and large-seeded beans, reflecting their Mesoamerican and Andean origins. Thirty-nine significant marker-trait associations (MTAs) were identified between 31 SNPs and 15 analyzed traits on all 11 bean chromosomes. Some of these MTAs confirmed genome regions previously associated with the yield and yield-related traits in bean, but a number of associations were not reported previously, especially those with derived traits. Over 600 candidate genes with different functional annotations were identified for the analyzed traits in the 200-Kb region centered on significant SNPs. Fourteen SNPs were identified within the gene model sequences, and five additional SNPs significantly associated with five different traits were located at less than 0.6Kb from the candidate genes. The work confirmed associations between two yield/antiyield gene-based markers (AYD1m and AYD2m) on chromosome Pv09 with yield and identified their association with a number of yield-related traits, including seed weight. The results also confirmed the usefulness of the NPP marker in screening for CBB resistance. Since disease resistance and yield measurements are environmentally dependent and labor-intensive, the three gene-based markers (CBB- and two yield-related) and quantitative trait loci (QTL) that were validated in this work may be useful tools for simplifying and accelerating the selection of high-yielding and CBB-resistant bean cultivars.

Release of tepary bean cultivar ‘USDA Fortuna’ with improved disease and insect resistance, seed size, and culinary quality

AbstractTepary bean (Phaseolus acutifolius A. Gray) is a viable and nutritious alternative to common bean (P. vulgaris L.) in areas with excessively high temperatures and/or chronic drought. Tepary bean is a traditional crop of the Tohono O'odham Indians of the Sonoran Desert in the Southwest United States and Mexico, as well as other Indigenous peoples of the United States, Mexico, and Central America. Despite its potential for broad applications for reduced water‐input agriculture or for hot, semi‐arid, marginal production zones, tepary bean remains an orphan crop. ‘USDA Fortuna’ (Reg. no. CV‐352, PI 698459) is an improved tepary bean cultivar with enhanced seed size, seed quality, tolerance to Bean golden yellow mosaic virus, and resistance to local strains of rust in Puerto Rico. It has leafhopper pest resistance, common bacterial blight resistance, and moderate resistance to powdery mildew. USDA Fortuna is a high‐yielding tepary bean with an attractive black speckled seed color and a quick cooking time. This cultivar was developed cooperatively by the USDA‐ARS, the University of Puerto Rico, Zamorano University, the Instituto Dominicano de Investigaciones Agropecuarias y Forestales (IDIAF) of the Dominican Republic, Quisqueya University of Haiti, the National Seed Service of Haiti, Instituto Nacional de Innovación y Transferencia en Tecnología Agropecuaria (INTA) of Costa Rica, and Iowa State University.

Association mapping for common bacterial blight in carioca beans

Common bacterial blight (CBB) is an important disease in Phaseolus vulgaris L. A carioca diversity panel (CDP) composed of 149 cultivars of common bean was genotyped with 1,616 SNPs and evaluated for Xanthomonas phaseoli pv. phaseoli (Xap) resistance aiming to identify QTLs. Phenotypic evaluation was done in controlled conditions. The plants displayed in a randomized block design, with 3 replications were evaluated ten days after inoculation. GWAS analysis using the BLINK model identified one SNP on chromosome Pv07, with a different genomic location in relation to previous studies. Considering a confidence interval of 100 kb, gene annotation identified 13 candidate genes related to defense-associated genes, and their key functional motives were discussed. The marker identified may constitute an important resource for future marker assisted CBB resistance breeding.

Registration of the slow‐darkening pinto common bean cultivar ‘Wildcat’

AbstractSlow‐darkening pinto common bean (Phaseolus vulgaris L.) cultivar ‘Wildcat’ (Reg. no. CV‐345, PI 698190) was released by the University of Nebraska dry bean breeding program in 2018. It was bred for adaptation to western Nebraska growing conditions and enhanced resistance to bean rust, common bacterial blight (CBB), and Bean common mosaic virus (BCMV). The yield of Wildcat was comparable to conventional and slow‐darkening pinto bean cultivars grown in Nebraska from 2015 to 2020. During the 2017 Western Regional Bean Trial, 2017 Midwest Regional Performance Nursery, and 2018 Cooperative Dry Bean Nursery, Wildcat had a higher seed yield than ‘Twin Falls’, ‘Nez Perce’, ‘Black Foot’, ‘Montrose’, ‘Buster’, ‘ND‐Palomino’, and ‘La Paz’ at some locations. Wildcat has the Ur‐11 gene that confers resistance to all but one known bean rust race and carries the Indel NDSU_IND_11_48.459.896 marker tagging the Ur‐11 locus. Wildcat also has the SAP6 sequence characterized amplified region (SCAR) marker linked to a major CBB resistance quantitative trait locus, with an intermediate CBB rating (5.0) under field conditions at western Nebraska in 2020. Wildcat also carries the single dominant I gene that confers resistance to all non‐necrotic strains of BCMV and the SW13 SCAR marker linked to the I gene for resistance to BCMV. Wildcat has white flowers, blooms 46 d after planting, and is a full‐season bean, maturing 93 d after planting. The seed size of Wildcat, 43.3 g 100 seeds–1 on average, was significantly larger than current conventional and slow‐darkening pinto beans.

Release of tepary bean TARS‐Tep 23 germplasm with broad abiotic stress tolerance and rust and common bacterial blight resistance

AbstractTepary bean (Phaseolus acutifolius A. Gray) is a drought and high ambient temperature tolerant crop native to the Sonoran Desert, the hottest and driest region in the United States and Mexico. Although tepary bean is an orphan crop with little current commercial production, there was a brief period of larger scale production in the early 1900s in California. Tepary bean has great potential as a novel crop in a warmer world climate and can be introduced as an alternative pulse crop in hot and/or dry regions worldwide. TARS‐Tep 23 (Reg. no. GP‐309, PI 698457) is an improved tepary bean germplasm with wide‐ranging adaptation to tropical and temperate regions experiencing high temperature and drought stress conditions, with broad resistance to bean rust and with resistance to common bacterial blight. It has a flat, mottled black seed type with good seed size, a Type III plant habit, and a short crop cycle of 55–61 d in the environments tested. This germplasm was developed cooperatively by the USDA‐ARS, Zamorano University, the University of California–Davis, and the University of Nebraska. The use of this improved germplasm by farmers in production zones affected by abiotic and biotic stresses, or by breeding programs, can potentially increase seed yields of this climate‐resilient crop.

The Induction of the Isoflavone Biosynthesis Pathway Is Associated with Resistance to Common Bacterial Blight in Phaseolus vulgaris L.

Xanthomonas axonopodis infects common bean (Phaseolus vulgaris L.) causing the disease common bacterial blight (CBB). The aim of this study was to investigate the molecular and metabolic mechanisms underlying CBB resistance in P. vulgaris. Trifoliate leaves of plants of a CBB-resistant P. vulgaris recombinant inbred line (RIL) and a CBB-susceptible RIL were inoculated with X. axonopodis or water (mock treatment). Leaves sampled at defined intervals over a 48-h post-inoculation (PI) period were monitored for alterations in global transcript profiles. A total of 800 genes were differentially expressed between pathogen and mock treatments across both RILs; approximately half were differentially expressed in the CBB-resistant RIL at 48 h PI. Notably, there was a 4- to 32-fold increased transcript abundance for isoflavone biosynthesis genes, including several isoflavone synthases, isoflavone 2′-hydroxylases and isoflavone reductases. Ultra-high performance liquid chromatography-tandem mass spectrometry assessed leaf metabolite levels as a function of the PI period. The concentrations of the isoflavones daidzein and genistein and related metabolites coumestrol and phaseollinisoflavan were increased in CBB-resistant RIL plant leaves after exposure to the pathogen. Isoflavone pathway transcripts and metabolite profiles were unaffected in the CBB-susceptible RIL. Thus, induction of the isoflavone pathway is associated with CBB-resistance in P. vulgaris.

Sources of Resistance to Common Bacterial Blight and Charcoal Rot Disease for the Production of Mesoamerican Common Beans in the Southern United States.

The gene pool of Mesoamerican common beans (Phaseolus vulgaris L.) includes genotypes in the small-to-medium-size seeded dry beans, as well as some snap beans from hotter environments adapted to the Southeastern United States. However, the warm and humid climate of the Southeastern United States is conducive to diseases such as Common Bacterial Blight (CBB) and Charcoal Rot (CR). The pathogens for these two diseases can survive long periods in infested soil or on seeds and are difficult to control through pesticides. Hence, field-level resistance would be the best management strategy for these diseases. The goals of this study were (1) to evaluate field-level resistance from the various commercial classes and subgroups represented in the Mesoamerican gene pool as sources for breeding beans for the region and (2) to evaluate genome-wide marker × trait associations (GWAS) using genetic markers for the genotypes. A total of 300 genotypes from the Mesoamerican Diversity Panel (MDP) were evaluated for CBB and CR in field experiments for three years. CBB resistance was also tested with a field isolate in controlled greenhouse conditions. The analysis of variance revealed the presence of variability in the MDP for the evaluated traits. We also identified adapted common bean genotypes that could be used directly in Southeastern production or that could be good parents in breeding programs for CBB and CR resistance. The GWAS detected 14 significant Single-Nucleotide Polymorphism (SNP) markers associated with CBB resistance distributed on five chromosomes, namely Pv02, Pv04, Pv08, Pv10, and Pv11, but no loci for resistance to CR. A total of 89 candidate genes were identified in close vicinity (±100 kb) to the significant CBB markers, some of which could be directly or indirectly involved in plant defense to diseases. These results provide a basis to further understand the complex inheritance of CBB resistance in Mesoamerican common beans and show that this biotic stress is unrelated to CR resistance, which was evident during a drought period. Genotypes with good yield potential for the Southeastern U.S. growing conditions were found with resistant to infection by the two diseases, as well as adaptation to the hot and humid conditions punctuated by droughts found in this region.

Using Breeding Populations With a Dual Purpose: Cultivar Development and Gene Mapping-A Case Study Using Resistance to Common Bacterial Blight in Dry Bean (Phaseolus vulgaris L.).

Dry bean (Phaseolus vulgaris L.) is an important worldwide legume crop with low to moderate levels of resistance to common bacterial blight (CBB) caused by Xanthomonas axonopodis pv. phaseoli. A total of 852 genotypes (cultivars, preliminary and advanced breeding lines) from the North Dakota State University dry bean breeding program were tested for their effectiveness as populations for genome-wide association studies (GWAS) to identify genomic regions associated with resistance to CBB, to exploit the associated markers for marker-assisted breeding (MAB), and to identify candidate genes. The genotypes were evaluated in a growth chamber for disease resistance at both the unifoliate and trifoliate stages. At the unifoliate stage, 35% of genotypes were resistant, while 25% of genotypes were resistant at the trifoliate stage. Libraries generated from each genotype were sequenced using the Illumina platform. After filtering for sequence quality, read depth, and minor allele frequency, 41,998 single-nucleotide polymorphisms (SNPs) and 30,285 SNPs were used in GWAS for the Middle American and Andean gene pools, respectively. One region near the distal end of Pv10 near the SAP6 molecular marker from the Andean gene pool explained 26.7–36.4% of the resistance variation. Three to seven regions from the Middle American gene pool contributed to 25.8–27.7% of the resistance, with the most significant peak also near the SAP6 marker. Six of the eight total regions associated with CBB resistance are likely the physical locations of quantitative trait loci identified from previous genetic studies. The two new locations associated with CBB resistance are located at Pv10:22.91–23.36 and Pv11:52.4. A lipoxgenase-1 ortholog on Pv10 emerged as a candidate gene for CBB resistance. The state of one SNP on Pv07 was associated with susceptibility. Its subsequent use in MAB would reduce the current number of lines in preliminary and advanced field yield trial by up to 14% and eliminate only susceptible genotypes. These results provide a foundational SNP data set, improve our understanding of CBB resistance in dry bean, and impact resource allocation within breeding programs as breeding populations may be used for dual purposes: cultivar development as well as genetic studies.

Common bacterial blight (Xanthomonas axonopodis pv. phaseoli) resistance reaction in common bean genotypes and their agronomic performances in Southern Ethiopia

Common bacterial blight (CBB) is an economically important disease of common beans and causes significant yield losses worldwide, including Ethiopia. Therefore, development and use of resistant cultivars are important options to manage the disease. Thus, field reactions of common bean genotypes to CBB and their agronomic performances were conducted at two locations in Southern Ethiopia, during 2018/2019. The experiment was arranged in a randomized complete block design with three replications. Analysis of variance revealed significant (P < 0.01) genotypic variation for disease and yield parameters at both locations. The results showed wide ranges of variation in incidence (26.05–82.75%), severity (23.75–70.70%), AUDPC (773.9–2544%-days) and disease progress rate (0.024–0.142 unit day−1) on average for both locations. And also, remarkable genotypic variation for quantitative growth and yield characters such as plant height, days to 50% flowering, days to 90% maturity, number of pods, number of seeds, seed weight and grain yield were observed. Based on mean severity and R8_severity score, genotypes were grouped as 20% resistant, 55% moderately resistant and 25% susceptible at JARC, and 15% resistant, 80% moderately resistant and only 5% susceptible at Debub Ari. Variable relationships were found among and between parameters studied. The overall results indicated that SER119 and MALB135 showed consistent resistance reaction to CBB, and SER119 also gave high yield across fields. It is recommended to use SER119 with proper management practices for bean production and MALB135 as parent for CBB resistance development in plant breeding programs of the country.

Genotype-by-environment interaction and stability of resistance in mungbean landraces against common bacterial blight across semi-arid environments

Common bacterial blight (CBB) of mungbean (Vigna radiata [L.] Wilczek var. radiata) is a major limitation to mungbean production in semi-arid areas of the world where mungbean is a major crop. Deployment of resistant varieties is a significant sustainable strategy for controlling CBB in marginal production systems. The objective of this study was to identify sources of resistance and the stability of mungbean landraces to CBB attack across drought-endemic environments. A total of 240 mungbean genotypes were evaluated for CBB resistance and performance of agronomic traits in an alpha lattice design at four locations for 2 years (2019, 2020). Data were subjected to residual maximum likelihood (REML) analysis to partition variance components attributed to main effects and interactions, respectively. REML analysis revealed significant main effects for genotype, environment (combination of cropping season and location) and genotype-by-environment interaction (p < 0.01), demonstrating the influence of environment on genotypic expression. A genotype main effect plus genotype-by-environment biplot was used to analyse the multi-location trial data based on CBB score to determine genotypic stability. The GGE analysis demonstrated that the Kambi Ya Mawe location in 2019 was the most suitable environment for the assessment of CBB resistance. Accessions GBK 004852, GBK 004789, GBK 026986, GBK 004970, GBK 004961, GBK 004882 and GBK 043573 were selected as having high and stable resistance across all environments. The identification of high and stable resistance sources is a first step towards deploying resistance in mungbean breeding programmes against CBB and the future deployment of resistant cultivars.

Registration of Great Northern Common Bean Cultivar ‘Panhandle Pride’ with Enhanced Disease Resistance to Bean Rust and Common Bacterial Blight

‘Panhandle Pride’ (Reg. no. CV‐325, PI 691461) great northern common bean (Phaseolus vulgaris L.) cultivar was developed by the dry bean breeding program at the University of Nebraska and released in 2016. It was bred specifically for adaptation to western Nebraska growing conditions and for enhanced resistance to bean rust and common bacterial blight (CBB). Seed yield of Panhandle Pride was comparable to the other cultivars in the on‐station and on‐farm trials conducted in Nebraska and was greater than ‘Orion’ and lower than ‘Matterhorn’ in regional trials. Seed size (100‐seed weight) for Panhandle Pride was larger than Marquis and Beryl‐R in trials grown in Nebraska, and larger than Orion and Matterhorn in regional trials. Panhandle Pride carries the sequence characterized amplified region (SCAR) markers SAP6 and SU91 linked to a major CBB resistance quantitative trait locus, and its reaction to the CBB pathogen under field conditions was consistent across 3 yr at the West Central Research and Extension Center, North Platte, NE, with disease ratings of 6.0, 4.3, and 5.2. Panhandle Pride has the Ur‐3 and Ur‐6 genes for resistance to bean rust and carries the SS68 Kompetitive Allele Specific polymerase chain reaction (KASP) and SK14 SCAR markers linked the Ur‐3 bean rust resistance locus. It also carries the single dominant hypersensitive I gene that provides resistance to all non‐necrotic strains of the Bean common mosaic virus (BCMV) and the SW13 SCAR marker linked to the I gene for resistance to BCMV. Panhandle Pride has bright white seed, blooms 44 d after planting, and is a midseason bean, maturing 87 d after planting.

Identification of common bean genotypes with dual leaf and pod resistance to common bacterial blight disease in Uganda

Common Bacterial Blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap) and Xanthomonas axonopodis pv. phaseoli var. fuscans (Xapf), is a serious disease that affects common bean production worldwide. In Uganda, it is the most severe and widely occurring bacterial disease, causing significant yield losses in common bean. Although various sources of resistance have been developed around the world, none of the varieties grown in Uganda is known to be resistant. The objective of this study was to identify lines with combined leaf and pod resistance for introgression into locally adapted but susceptible Ugandan genotypes. A total of 132 common bean accessions was evaluated in a screenhouse and under field conditions, in an 11x12 alpha lattice design. Genotypes were inoculated with a local isolate in a screenhouse; while the plants were left to undergo natural infestation in field. Results indicated significant differences (P<0.001) in genotypic reactions against the CBB disease, with a range of disease scores of 2.2 - 7.8 on leaves and 2.6 - 7.1 on pods (1-9 CIAT disease scale), suggesting high genetic variability among the tested germplasm. Relatively low correlation (r = 0.39) was observed between leaf and pod reactions, suggesting differential expression of CBB resistance in these two plant organs. Overall, four genotypes, NE2-14-8, NE17-14-29, NE14-09-78 and VAX3, consistently showed resistance in both screenhouse and field evaluations, leaf and pod inoculations and at all sampling stages. These genotypes were, therefore, identified for transferring CBB resistance into Ugandan susceptible market class bean varieties. Key words: CBB, Phaseolus vulgaris , Xanthomonas axonopodis

English

In the present investigation, the genetic variability of 64 speckled type common bean genotypes were evaluated at Haramaya University during 2015 cropping season using 8 × 8 simple lattice design with three replications. The analysis of variance indicated highly significant (P<0.01) differences among genotypes for all the nine characters studied. High genotypic coefficient of variation (GCV) was observed for grain yield, while high phenotypic coefficients of variation (PCV) were recorded for number of seeds plant-1, grain yield ha-1 and common bacterial blight resistance. For all the traits, estimates of PCV were higher than GCV indicating the presence of environmental influence. High heritability values and genetic advances were recorded in grain yield. Cluster analysis using Mahalanobis distance delineated the genotypes into six main groups. Cluster I contain the largest number of genotypes (43.75%) followed by clusters II (26.56%) and III (10.94%) while clusters IV, V and VI contain four genotypes each. The D2 analysis indicated that there was a significant difference among the clusters. The maximum inter cluster distance was observed between cluster IV and V. Principal component analysis (PCA) was performed to assess the variation and correlation among genotypes for the traits and grouped them based on their performance. The combination of the first four principal components explained more than 85.74% of the genotypic variations. Therefore, exploiting the genetic diversity among clusters would broaden the genetic base of speckled bean breeding populations. Key words: Clustering, genetic distance, genetic variability, Phaseolus vulgaris, speckled bean.

Genome-Wide Association Study Identifies NBS-LRR-Encoding Genes Related with Anthracnose and Common Bacterial Blight in the Common Bean.

Nucleotide-binding site and leucine-rich repeat (NBS-LRR) genes represent the largest and most important disease resistance genes in plants. The genome sequence of the common bean (Phaseolus vulgaris L.) provides valuable data for determining the genomic organization of NBS-LRR genes. However, data on the NBS-LRR genes in the common bean are limited. In total, 178 NBS-LRR-type genes and 145 partial genes (with or without a NBS) located on 11 common bean chromosomes were identified from genome sequences database. Furthermore, 30 NBS-LRR genes were classified into Toll/interleukin-1 receptor (TIR)-NBS-LRR (TNL) types, and 148 NBS-LRR genes were classified into coiled-coil (CC)-NBS-LRR (CNL) types. Moreover, the phylogenetic tree supported the division of these PvNBS genes into two obvious groups, TNL types and CNL types. We also built expression profiles of NBS genes in response to anthracnose and common bacterial blight using qRT-PCR. Finally, we detected nine disease resistance loci for anthracnose (ANT) and seven for common bacterial blight (CBB) using the developed NBS-SSR markers. Among these loci, NSSR24, NSSR73, and NSSR265 may be located at new regions for ANT resistance, while NSSR65 and NSSR260 may be located at new regions for CBB resistance. Furthermore, we validated NSSR24, NSSR65, NSSR73, NSSR260, and NSSR265 using a new natural population. Our results provide useful information regarding the function of the NBS-LRR proteins and will accelerate the functional genomics and evolutionary studies of NBS-LRR genes in food legumes. NBS-SSR markers represent a wide-reaching resource for molecular breeding in the common bean and other food legumes. Collectively, our results should be of broad interest to bean scientists and breeders.

Interaction of quantitative trait loci for resistance to common bacterial blight and pathogen isolates in Phaseolus vulgaris L.

Common bacterial blight (CBB) is a major disease of common bean (Phaseolus vulgaris L.) worldwide. Genetic resistance is the most effective and environmentally safe approach for controlling CBB, and identification of resistance quantitative trait loci (QTL) can improve response to selection when breeding for CBB resistance. Interactions of CBB resistance QTL and pathogen isolates with different levels of aggressiveness were studied using an F4:5 recombinant inbreed line (RIL) population, derived from a cross between the susceptible cultivar “Sanilac” and the resistant breeding line “OAC 09-3.” Disease phenotyping was performed under field and growth room conditions using multiple bacterial isolates with differential levels of aggressiveness. QTL analysis was performed with 237 molecular markers. The effect of pathogen isolate on the average phenotypic value in the RIL population and the interaction of RILs and the pathogen isolates were highly significant. Two QTL underlying CBB resistance were detected on Pv08 and Pv03. A major QTL (R2p between 15 and 56%) was identified in a 5-cM (380 kbp) interval in the distal end of the long arm of Pv08. This genomic region was significantly associated with multiple disease evaluation traits in field and growth room assays and against different isolates of the pathogen, which included the previously known CBB marker SU91. A new QTL on Pv03 (Xa3.3SO), associated with the PvSNP85p745405 allele from the susceptible parent, Sanilac, appeared to be an isolate-specific QTL against the aggressive fuscans isolate ISO118. Interaction between the SU91 and Xa3.3SO QTL resulted in a significant reduction in mean disease severity for almost all disease evaluation traits after plants were challenged with the isolate ISO118. The 7.92 and 7.79% diseased areas in RILs with both QTL, compared with 14.92 and 13.81% in RILs without either in test1 and in test2 quantified by image analysis, showed a 44 and 47% reduction of percent diseased areas, indicating that the two QTL interact to limit the expansion of CBB symptoms after infection by ISO118. The information obtained in this study indicates that while the broad-spectrum SU91 QTL is useful in breeding programs, isolate-specific QTL, such as Xa3.3SO, will aid in breeding bean varieties with enhanced resistance against aggressive regional isolates.

Common Bacterial Blight Resistance QTL BC420 and SU91 Effect on Seed Yield, Seed Weight, and Canning Quality in Dry Bean

Common bacterial blight (CBB) disease limits dry bean (Phaseolus vulgaris L.) production worldwide. Resistance quantitative trait loci (QTL) from tepary bean (Phaseolus acutifolius A. Gray) have been used to develop dry bean lines with high levels of CBB resistance. This study examines the effects that two QTL from tepary bean BC420 (B) on chromosome Pv06 and SU91 (S) on Pv08 have on agronomic (seed yield and seed weight) and canning quality traits (water uptake, percentage washed drained weight [PWDWT], texture, and visual appearance). Sixteen small white dry bean near‐isogenic lines, representing four homozygous genotypes for the BC420 and SU91 QTL BBSS, bbSS, BBss, and bbss, the donor resistant parent Teebus‐BC5 (BBSS), and the recurrent susceptible parent ‘Teebus’ (bbss) were tested in replicated, inoculated and non‐inoculated field plots across five environments in South Africa. Plots were inoculated with a mixture of Xanthomonas axonopodis pv. phaseoli and X. fuscans sbsp. fuscans isolates. The BC420 and SU91 QTL did not cause a yield penalty in non‐inoculated plots in environments with low to no disease. SU91 provided yield protection under severe disease pressure, and both QTL in combination reduced disease severity score under moderate to high disease pressure. Seed weight was maintained in lines with the QTL under severe to moderate pressure and was unaffected by the QTL in low‐ to no‐disease environments. Water uptake was significantly reduced in genotypes with BC420 (BBSS, BBss) and likely influenced traits measured subsequently: lower PWDWT, firmer texture, and less attractive visual appearance, which contributed to a reduced canning quality overall. Deployment of BC420 and SU91 QTL can be safely recommended for control of CBB, as no agronomic penalty was observed in CBB‐free conditions, but canning quality should be closely monitored in lines with BC420 QTL.

Mapping of Common Bacterial Blight Resistance Gene in Common Bean

Mapping of Common Bacterial Blight Resistance Gene in Common Bean

QTL and candidate genes associated with common bacterial blight resistance in the common bean cultivar Longyundou 5 from China

Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli and Xanthomonas fuscans subsp. fuscans (Xff), is a worldwide disease of common bean (Phaseolus vulgaris L.). Longyundou 5, a Chinese cultivar in the Mesoamerican gene pool of common bean, displays resistance to the Xff strain XSC3-1. To identify the genetic mechanisms behind this resistance, we crossed Long 5 with a susceptible genotype to develop a mapping population of F2 plants. Plant resistance to CBB was identified at 14 and 21days after inoculation with Xff strain XSC3-1. A major QTL at 14 and 21days after inoculation was mapped on chromosome Pv10 with LOD scores of 6.41 and 5.35, respectively. This locus was associated with SAP6, a previously-identified and much-used dominant marker, but in a 4.2cM interval between new codominant markers BMp10s174 and BMp10s244. Ten candidate genes were found between markers BMp10s174 and BMp10s244 on chromosome Pv10 and could encode defense response proteins responding to CBB pathogens. Four pairs each of epistatic QTL for CBB resistance were detected at 14 and 21days after inoculation. Phenotypic variation explained by the epistatic QTL ranged from 7.19% to 12.15% and 7.72% to 8.80% at 14 and 21days after inoculation, respectively. These results confirmed the importance of epistasis in CBB resistance in common bean. The adjacent markers found may be more efficient for marker assisted selection in common bean breeding for CBB resistance owing to their closer linkage to the target QTL.

&lt;b&gt;Combining ability for common bacterial blight resistance in snap and dry bean (&lt;i&gt;Phaseolus vulgaris&lt;/i&gt; L.)

Common bacterial blight (CBB), which is caused by Xanthomonas axonopodis pv. phaseoli (Xap), is the main bacterial disease in snap beans and controlling this disease using resistant cultivars is still a challenge. This work aimed to study the combining ability for CBB resistance in Phaseolus vulgaris genotypes. Six parents (two genotypes of CBB-resistant dry bean and four susceptible snap bean accessions) were crossed in a complete diallel scheme without reciprocals to estimate the general and specific ability to Xap resistance. CBB resistance was evaluated by the inoculation with two Xap isolates, and its severity was evaluated based on the four following resistance components: area under the disease progress curve; scores in the leaves; latent period and diameter of pod lesion. Differences between the two isolates were observed considering all the disease components. Besides pathogen variability, significant GCA and SCA indicate that additive and non-additive effects are involved in Xap-resistance control for the evaluated genotypes, implying that CBC resistance is a trait with complex inheritance. For breeding purposes, the result demonstrates the need to apply breeding methods that are focused on advanced generations selection.

A New Common Bacterial Blight Resistance QTL in VAX 1 Common Bean and Interaction of the New QTL, SAP6, and SU91 with Bacterial Strains

ABSTRACTCommon bacterial blight (CBB) is a severe disease in common bean (Phaseolus vulgaris L.). New resistance quantitative trait loci (QTL) should facilitate development of cultivars with high levels of resistance. Our objectives were to (i) identify new resistance QTL in VAX 1 and verify its presence in VAX 3, (ii) determine the interaction between QTL with existing SAP6 and SU91 QTL, and (iii) examine the interaction between QTL with less aggressive ARX8AC and aggressive Xcp25 bacterial strains. Sixty‐one F6:7 recombinant inbred lines (RIL) from ‘Othello’/VAX 1 and 100 RIL from Othello/VAX 3 were screened in the greenhouse. Disease severity of inoculated primary leaves, first and second trifoliolate leaves, and pods, was scored from 1 = no symptoms to 9 = completely diseased. Genotyping was performed using 5398 single nucleotide polymorphism (SNP) BeadChip and CBB resistance QTL‐linked sequence characterized amplified region (SCAR) markers, SAP6 and SU91. A novel resistance QTL with major effect was detected on Pv11 linkage group in Othello/VAX 1 and verified in Othello/VAX 3. This Pv11 QTL, defined by the closest marker SNP47467 (45,059,806 bp), explained 23% of the phenotypic variance for resistance in primary and 18% in trifoliolate leaves in Othello/VAX 1, and 13% and 22%, respectively, in Othello/VAX 3 to ARX8AC. The Pv11 QTL, named Xa11.4OV1,OV3, had greater influence against Xcp25, with respective values for variance for resistance explained in primary and trifoliolate leaves of 45% and 51% in Othello/VAX 1 and 26% and 37% in Othello/VAX 3. Conversely, SAP6 was only effective against ARX8AC in both populations, and surprisingly, SU91 was only effective against Xcp25 in Othello/VAX 3. SAP6 was the only QTL to condition resistance in pods. QTL interactions and differential reactions to strains indicate that the new Xa11.4OV1,OV3 QTL is critical in breeding for stable and higher levels of foliage resistance to CBB in common bean.