The identification of two new strains of bean common mosaic virus

Two sap-transmissible virus isolates from bean (Phaseolus vulgaris L.) were identified as bean common mosaic virus (BCMV) on the basis of particle size and morphology, serology, non-persistent aphid transmission, very limited host range, and symptoms and seed transmission in bean. In bean varietal reaction both isolates differed from each other and all six Dutch BCMV strains described before. From literature data it may be concluded that they also differ from thirteen other strains described elsewhere. The isolate from Peruvian seed may be related to strains reported from Costa Rica and Peru, but these have been described incompletely. The two isolates obtained at Wageningen are therefore described as new strains and designated BCMV-NL7 and BCMV-NL8. The latter seems unusual in its extremely high dilution end point, in its serological affinity to both BCMV and BYMV, and in not being infectious toChenopodium amaranticolor andC. quinoa. Tetragonia expansa proved to be a new local lesion host of BCMV. There is an urgent need for international standardization of strains of BCMV.     

Characterization of <Emphasis Type="Italic">Bean common mosaic virus</Emphasis> and <Emphasis Type="Italic">Bean common mosaic necrosis virus</Emphasis> isolates in common bean growing areas in Turkey

Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) are well-known legume-infecting potyviruses. The incidences of BCMV and BCMNV infections were determined by ELISA in 367 seed and leaf samples which were collected in 15 common bean-growing provinces of Turkey. Of the samples tested, 67 (18.2 %) occurred to be infected with BCMV, however only 5 (1.4 %) were infected with BCMNV. A total of 45 ELISA-positive samples were selected from single-virus infected ones to determine BCMV and BCMNV pathogenicity groups (PGs) by using a set of bean cultivars that contain different combinations of resistance genes. Some BCMV populations exhibiting unusual pathogenicity were identified. One of them, named TR-180, was found to overcome resistance conferred by bc-1, bc-1 ² , bc-2 and bc-2 ² recessive alleles in common bean and assigned to PG VII. This isolate shared high (99 %) sequence identity with previously identified BCMV RU-1 and RU-1-related strains (RU1-OR-B and RU1-OR-C) according to a BLAST analysis of the nucleotide sequences of RT-PCR amplified products comprising the complete coat protein and 3′ partial NIb regions. The isolates TR-203 and TR-256 produced a distinctive reaction pattern in the dominant I gene-bearing bean cultivars Amanda and Isabella at lower (<30 °C) temperatures and were classified into PG IVb. These isolates were found to be 99 % identical to US-1 strain based on 3′ terminal nucleotide sequences of the BCMV genome. A fourth isolate, TR-243, involved mixed BCMV populations, as confirmed by partial nucleotide sequence analysis; one was classified as belonging to PG VII being similar to TR-180, and another was assigned to PG IVb. In conclusion, on the basis of both the reactions of differential bean cultivars and ELISA results, most of BCMV isolates were assigned to pathogroup PG VII and BCMNV isolates to PG VIb. This study is the first to show that four recessive resistance alleles of common bean can be overcome by a single field isolate of BCMV, and that a wide range of BCMV pathogroups are present in Turkey.     

Genetic Characterization of Differential Reactions Among Host Group 3 Common Bean Cultivars to NL-3 K Strain of Bean common mosaic necrosis virus

ABSTRACT A previously unrecognized recessive resistance gene (or allele) was identified in three host group (HG) 3 common bean (Phaseolus vulgaris) cvs. Olathe, Victor, and UI 37, based on genetic analysis of plants from five populations screened with the NL-3 K strain of Bean common mosaic necrosis virus (BCMNV). The gene (or allele) was associated with resistance to leaf stunting and deformity and reduction in plant height. The gene (or allele) provides similar, but slightly better resistance than the bc-1(2) gene that is characteristic of HG 3 cultivars. Traditional HG 3 cultivars like Redlands Greenleaf B with bc-1(2) are susceptible to NL-3 K, whereas this newly identified gene (or allele) conditions resistance to NL-3 K. Other slight variations in disease reaction pattern to a wide array of bean common mosaic (BCM)-inducing strains were noted among HG 3 differentials, indicating that additional resistance to BCM exists in common bean that remains to be exploited. To gauge the full breeding value of this newly identified gene (or allele), allelism tests with existing genes, namely bc-1(2), and further characterization of responses to all Bean common mosaic virus (BCMV) and BCMNV strains need to be conducted. Meanwhile, breeders should consider introgressing this more effective gene (or allele) into susceptible cultivars while plant pathologists continue to decipher the genetic variability present among HG 3 differential cultivars.     

Molecular diversity in <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> isolates from common bean fields in Brazil

The common bean (Phaseolus vulgaris L.) is widely cultivated in Brazil and is known as a very important crop for families in this country. Fusarium wilt severely harms common beans and has become a big issue for this crop. In order to assist the breeding programs that target resistance to this disease, the evaluation of genetic diversity of the pathogen and its molecular characterization are crucial. Thus, the present goal was to identify Fusarium isolates obtained from several places in Brazil using molecular tools; select molecular markers for these isolates; and analyze their diversity. All of isolates were molecularly identified as Fusarium oxysporum f. sp. phaseoli (Fop). By using seven selected SSR markers, the results of diversity obtained by the dendrogram and the Bayesian analysis formed four groups where a large diversity of this fungus was found within each state. However, the groups were more homogenous according to the collection source and the pathogenicity test. More specifically, group 2 was composed of the most virulent strains and originated from Minas Gerais State – UFV, and group 3 was mostly composed by isolates from Goias state. Group I was also more diverse in terms of location and virulence. The overall results indicated a positive correlation between Fusarium diversity and its virulence to common bean. Furthermore, the use of these markers was effective in molecular identification and in detecting polymorphism within F. oxysporum f. sp. phaseoli.     

Elimination of Bean common mosaic virus using an electrotherapy technique

Journal of Plant Diseases and Protection - Bean common mosaic virus (BCMV) is a major seed transmitted virus of common bean (Phaseolus vulgaris). The use of virus-free germplasm is a prerequisite...     

First report of <Emphasis Type="Italic">Bean common mosaic virus</Emphasis> in yam bean [<Emphasis Type="Italic">Pachyrhizus erosus</Emphasis> (L.) Urban] in Indonesia

Severe mosaic with leaf malformation and green vein banding was observed on yam bean in West and Central Java, Indonesia. Virions of the causal virus were flexuous filaments, about 700 nm in length, with a coat protein of 30 kDa. The virus was transmitted by mechanical inoculation and by aphids in a nonpersistent manner. The nucleotide sequence of the coat protein gene had the highest identity with that of Bean common mosaic virus (BCMV, genus Potyvirus) isolate VN/BB2-5. Based on demarcation criteria, including the genome sequence and host range, we tentatively designate this isolate as BCMV-IYbn (Indonesian yam bean). The nucleotide sequence reported is available in the DDBJ/EMBL/GenBank databases under accession number AB289438.     

Phylogenetic analysis of <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> subgroups associated with web blight symptoms on common bean based on ITS-5.8S rDNA

Sixty-eight Rhizoctonia solani isolates (31 AG-1, 37 of AG-2-2) associated with web blight (WB) of common bean, Phaseolus vulgaris, were examined for sequence variations in the ITS-5.8S rDNA region. The isolates were collected in bean-growing lowland and mountainous regions in Central and South America. Sequences of these isolates were aligned with other known R. solani sequences from the NCBI GenBank and distance and parsimony analysis were used to obtain phylogenetic trees. WB isolates of AG-1 formed two clades separated from known AG-1 subgroups. WB isolates of AG-2-2 formed one clade separated from known AG-2-2 subgroups. Other isolates belonged to AG-1 IA and AG-1 IB. Based on phylogenetic analysis, we confirmed that at least five genetically different subgroups incite WB of common beans. Three new subgroups of R. solani have been identified and designated as AG-1 IE, AG-1 IF and AG-2-2 WB. DNA sequences of these isolates provided needed information to design taxon-specific primers that can be employed in ecological/epidemiological studies and seed health tests.     

Variation for pathogenicity among isolates of bean common mosaic virus in Africa and a reinterpretation of the genetic relationship between cultivars of Phaseolus vulgaris and pathotypes of BCMV

Bean common mosaic virus (BCMV) isolates were collected from crops of Phaseolus vulgaris (bean) and from wild legume species in 13 African countries. Isolates of pathotype VIa from both beans and wild legume species were predominant in central, eastern and southern Africa. Isolates of pathotypes I, III, IVa, IVb and Va were also found. Some isolates did not conform to previously published pathotypes, and therefore represent records of novel pathotypes. The susceptibility of various wild legume species to BCMV was investigated and isolates of the virus obtained from Crotalaria incana, Rhynchosia sp., Macroptilium atropurpureum and Cassia occidentalis (synonym Senna occidentalis) were aphid-transmitted both from P. vulgaris to their original host species and to P. vulgaris. Isolates of BCMV from wild legume species were seed-transmitted in bean and in several other legume species. The natural occurrence of BCMV in wild legume species in Africa is probably a significant factor in the ecology and epidemiology of the virus and possibly the evolution of isolates of the 'A' serotype which induce necrotic reactions in cultivars carrying the I gene for resistance. The occurrence of viruses other than BCMV from P. vulgaris and other legume hosts is also reported. The gene-for-gene model described by Drijfhout (1978) is reinterpreted to explain the variation for pathogenicity, and it is proposed that there may be genes which control the temperature sensitivity of necrosis in combination with the I gene.     

Characterization of white mold disease avoidance in common bean

White mold, caused by Sclerotinia sclerotiorum, is a devastating fungal disease of common bean (Phaseolus vulgaris L.) worldwide. Physiological resistance and disease avoidance conferred by plant architecture-related traits contribute to white mold field resistance. Our objective was to further examine white mold disease avoidance in common bean. A comparative map composed of 79 quantitative trait loci (QTL) for white mold resistance (27), disease avoidance traits (36) and root traits (16) was generated. Thirteen white mold resistance QTL, six with strong and seven with weak associations with disease avoidance traits, were observed. Root length and lodging QTL co-located in three regions. Canopy porosity and height, and lodging were highly correlated with disease severity score in field screening trials conducted from 2000 to 2011. Resistance to lodging was extremely important for reducing disease severity in both dry and snap bean (r?=?0.61 across 11 trials). Avoidance traits were less effective in reducing disease severity in trials with heavy disease pressure. Dry bean lines with physiological resistance in combination with disease avoidance traits did not require fungicide application to protect yield potential under moderate and heavy disease pressure. Given the complexity of disease resistance as evidenced by the comparative QTL map, marker-assisted breeding for disease avoidance is not recommended at this time. Instead, selecting for resistance to white mold in the field, in combination with high yield potential and acceptable maturity, is the recommended strategy for improving both disease avoidance and physiological resistance to white mold in cultivars with commercially acceptable agronomic traits.     

Adult attractiveness and oviposition preference of <Emphasis Type="Italic">Zabrotes subfasciatus</Emphasis> toward genotypes of common bean <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis>

The Mexican bean weevil Zabrotes subfasciatus (Coleoptera: Chrysomelidae: Bruchinae) is among the key pests of common bean Phaseolus vulgaris L. around the world. Identifying resistance sources and the resistance types involved is important for development of pest-resistant bean varieties. This study assessed the adult attractiveness and oviposition preference of Z. subfasciatus toward eight genotypes of common bean, including seven pre-selected resistant genotypes and one standard for susceptibility. Attraction to the genotypes was assessed at one and four days after infestation. Oviposition preference was tested under free- and no-choice (confinement) conditions. We observed that IAC 853 was the least oviposited genotype in the free-choice test. However, this finding was not confirmed by the no-choice test. Therefore, IAC 853 could not be characterized as resistant to Z. subfasciatus. Presence of the toxic protein arcelin does not appear to influence host selection by Z. subfasciatus.     

Rhizobacteria‐mediated resistance against the blackeye cowpea mosaic strain of bean common mosaic virus in cowpea (Vigna unguiculata)

BACKGROUND: The present study investigated the effect of seven Bacillus‐species plant‐growth‐promoting rhizobacteria (PGPR) seed treatments on the induction of disease resistance in cowpea against mosaic disease caused by the blackeye cowpea mosaic strain of bean common mosaic virus (BCMV). RESULTS: Initially, although all PGPR strains recorded significant enhancement of seed germination and seedling vigour, GBO3 and T4 strains were very promising. In general, all strains gave reduced BCMV incidence compared with the non‐bacterised control, both under screen‐house and under field conditions. Cowpea seeds treated with Bacillus pumilus (T4) and Bacillus subtilis (GBO3) strains offered protection of 42 and 41% against BCMV under screen‐house conditions. Under field conditions, strain GBO3 offered 34% protection against BCMV. The protection offered by PGPR strains against BCMV was evaluated by indirect enzyme‐linked immunosorbent assay (ELISA), with lowest immunoreactive values recorded in cowpea seeds treated with strains GBO3 and T4 in comparison with the non‐bacterised control. In addition, it was observed that strain combination worked better in inducing resistance than individual strains. Cowpea seeds treated with a combination of strains GBO3 + T4 registered the highest protection against BCMV. CONCLUSION: PGPR strains were effective in protecting cowpea plants against BCMV under both screen‐house and field conditions by inducing resistance against the virus. Thus, it is proposed that PGPR strains, particularly GBO3, could be potential inducers against BCMV and growth enhancers in cowpea. Copyright © 2009 Society of Chemical Industry     

Pseudocercospora griseola,the causal agent of common bean angular leaf spot: Strain characterization and sensitivity to fungicides

Angular leaf spot (ALS), an important disease of common bean (Phaseolus vulgaris), is caused by the fungus Pseudocercospora griseola. This pathogen has a wide genetic variability and, therefore, poses a challenge to integrated disease management. The use of resistant cultivars is difficult; hence, the application of fungicides has been a common practice in common bean cultivation. P. griseola strains were morphophysiologically characterized and their sensitivity to common fungicides used to control ALS was studied. The strains were evaluated for sporulation capacity and a representative sample of 34 strains was bioassayed to determine their sensitivity to commercial concentrations of five fungicides, namely pyraclostrobin, mancozeb, pyraclostrobin + metconazole, chlorothalonil and tebuconazole. Another sample of 29 strains was studied for conidial germination and dimensions. Sporulation capacity ranged from 0.88 to 27.67 × 10⁴ conidia/ml and germination percentage ranged from 39% to 72%. The large differences among strains suggest a wide genetic variability among the strains. A wide variability in aggressiveness of P. griseola was observed, which has consequences for breeding programmes aimed at resistance. The behaviour of pathogen strains differed in every fungicide evaluated, even in a population that has not been under selection pressure in the field. These results confirm the need for further studies and may guide future research with this pathogen.     

Cryptic diversity,multilocus phylogeny,and pathogenicity of cercosporoid fungi associated with common bean and cowpea

In recent years, common bean (Phaseolus vulgaris) and cowpea (Vigna unguiculata) plants in the north of Iran have exhibited symptoms resembling Cercospora leaf spot (CLS) disease. This study was initiated to elucidate the taxonomy and pathogenicity of cercosporoid taxa associated with leaf spot diseases of these two legume crops in Iran. A total of 138 samples with CLS symptoms were collected from cultivated common bean and cowpea species in northern Iran and subjected to microscopic examination, resulting in identification of 98 Cercospora and 59 Pseudocercospora samples. A six-locus phylogenetic analysis (ITS, actA, tef1, gapdh, his3, and cmdA) coupled with examination of the morphology of 42 representative isolates from these samples confirmed that several cercosporoid fungi occur on common bean and cowpea in Iran. Five Cercospora species (C. iranica, C. cf. flagellaris, Cercospora sp. G, Cercospora sp. T, and C. vignigena) and two Pseudocercospora species (P. griseola f. griseola and P. cf. cruenta) were found; of these, C. cf. flagellaris was the dominant species, occurring on both common bean and cowpea. Pathogenicity tests confirmed that all seven species could infect leaves of common bean and/or cowpea. This is the first report of C. iranica, Cercospora sp. G, and Cercospora sp. T associated with common bean and/or cowpea in the world. In addition, C. vignigena was recorded for the first time in Iran. Results achieved in this study will assist strategies for the management of CLS disease of common bean and cowpea.     

Real‐time quantitative PCR assays for the rapid detection and quantification of Fusarium oxysporum f. sp. phaseoli in Phaseolus vulgaris (common bean) seeds

Fusarium oxysporum f. sp. phaseoli (Fop) is a devastating pathogen that can cause significant economic losses and can be introduced into fields through infested Phaseolus vulgaris (common bean) seeds. Efficient seed health testing methods can aid in preventing long‐distance dissemination of this pathogen by contaminated seeds. In order to improve detection of Fop in seed, a rapid, accurate and sensitive real‐time PCR assay (qPCR) protocol was developed for detection of Fop in common bean seeds. Seed lots of seven cultivars with infection incidence ranging from 0·25 to 20% were prepared by mixing known amounts of Fop‐infected seeds with Fop‐free seeds. Direct comparisons between SYBR Green and TaqMan qPCR methods were performed using primers based on the Fop virulence factor ftf1. The primers developed in this study produced a 63 bp product for highly virulent strains of Fop but did not produce an amplicon for nonpathogenic or weakly pathogenic isolates of F. oxysporum from P. vulgaris or other hosts. Under optimized conditions, both qPCR assays detected Fop infection at low levels (0·25%); however, the results suggest the TaqMan assay was more reliable at quantification than the SYBR Green assay. Linear regression models were fitted to the relationships between results of qPCR assays and infection incidence, but the models differed among cultivars. Fungal biomass per seed differed among cultivars and was related to seed size. The results indicate that the TaqMan assay developed in this study is a useful tool for the detection and quantification of Fop in bean seeds.     

Interaction of common bacterial blight bacteria with disease resistance quantitative trait loci in common bean

Common bacterial blight (CBB) of common bean (Phaseolus vulgaris L.) is caused by Xanthomonas campestris pv. phaseoli and X. fuscans subsp. fuscans, and is the most important bacterial disease of this crop in many regions of the world. In 2005 and 2006, dark red kidney bean fields in a major bean-growing region in central Wisconsin were surveyed for CBB incidence and representative symptomatic leaves collected. Xanthomonad-like bacteria were isolated from these leaves and characterized based upon phenotypic (colony) characteristics, pathogenicity on common bean, polymerase chain reaction (PCR) with X. campestris pv. phaseoli- and X. fuscans subsp. fuscans-specific primers, and repetitive-element PCR (rep-PCR) and 16S-28S ribosomal RNA spacer region sequence analyses. Of 348 isolates that were characterized, 293 were identified as common blight bacteria (i.e., pathogenic on common bean and positive in PCR tests with the X. campestris pv. phaseoli- and X. fuscans subsp. fuscans-specific primers), whereas the other isolates were nonpathogenic xanthomonads. Most (98%) of the pathogenic xanthomonads were X. campestris pv. phaseoli, consistent with the association of this bacterium with CBB in large-seeded bean cultivars of the Andean gene pool. Two types of X. campestris pv. phaseoli were involved with CBB in this region: typical X. campestris pv. phaseoli (P) isolates with yellow mucoid colonies, no brown pigment production, and a typical X. campestris pv. phaseoli rep-PCR fingerprint (60% of strains); and a new phenotype and genotype (Px) with an X. campestris pv. phaseoli-type fingerprint and less mucoid colonies that produced brown pigment (40% of strains). In addition, a small number of X. fuscans subsp. fuscans strains, representing a new genotype (FH), were isolated from two fields in 2005. Representative P and Px X. campestris pv. phaseoli strains, an FH X. fuscans subsp. fuscans strain, plus five previously characterized X. campestris pv. phaseoli and X. fuscans subsp. fuscans genotypes were inoculated onto 28 common bean genotypes having various combinations of known CBB resistance quantitative trait loci (QTL) and associated sequence-characterized amplified region markers. Different levels of virulence were observed for X. campestris pv. phaseoli strains, whereas X. fuscans subsp. fuscans strains were similar in virulence. The typical X. campestris pv. phaseoli strain from Wisconsin was most virulent, whereas X. campestris pv. phaseoli genotypes from East Africa were the least virulent. Host genotypes having the SU91 marker-associated resistance and one or more other QTL (i.e., pyramided resistance), such as the VAX lines, were highly resistant to all genotypes of common blight bacteria tested. This information will help in the development of CBB resistance-breeding strategies for different common bean market classes in different geographical regions, as well as the identification of appropriate pathogen genotypes for screening for resistance.     

Southern bean Mosaic Virus the Causal Agent of a New Disease of Phaseolus vulgaris beans in Spain

Southern bean mosaic virus (SBMV) has been identified as the cause of a new disease in greenhouse-cultivated common bean (Phaseolus vulgaris), in the south-east of Spain. The identification was based on host range comparisons, morphological and serological characteristics of the virus, the size of its dsRNA species and the nucleotide sequence of an 810-bp fragment from ORF2. The virus could be clearly discriminated from the related sobemovirus Southern cowpea mosaic virus. This is the first report of SBMV in Spain.     

Genetic diversity of Phaeoisariopsis griseola in Argentina as revealed by pathogenic and molecular markers

Angular leaf spot, a disease of common bean produced by Phaeoisariopsis griseola, an imperfect (Deuteromycotina) fungus, causes significant yield losses in Argentina. The development of a strategy to control and/or reduce the impact of P. griseola requires a previous knowledge of the population structure. Therefore, the purpose of this work was to analyze diversity among 45 isolates of P. griseola collected within the production area of common bean in Northwestern Argentina. Pathotypes diversity was determined based on a set of bean differentials and genomic differences between isolates were determined by means of molecular markers. We confirmed that isolates belonging to Middle American and Andean groups coexist in Northwestern Argentina and the level of diversity between them was considerable and of similar level within each group. Even though the number of isolates analyzed was 45, among them 37 were Middle American and only eight were Andean. The number of haplotypes found based on ISSR and RAPD markers were 18 and as expected, they were unrelated with pathotypes. The wild bean species, Phaseolus vulgaris var. aborigineus, showed a high level of tolerance to most pathotypes of P. griseola except 63.63 and 63.23. This together with the fact that none of the bean differentials was resistant to all pathotypes led us to conclude that the range of pathogenic responses might be conditioned by multigenic interactions between the pathogen and the host. Our results not only provided basic information about the diversity of the causative agent of the disease but it will also help to develop cultivars with enhanced tolerance and/or resistance to the disease.     

Sensitivity to,and metabolism of,phaseollin in relation to the pathogenicity of different isolates of Botrytis cinerea to bean (Phaseolus vulgaris)

The pathogenicity of five isolates ofBotrytis cinerea to bean (Phaseolus vulgaris) was compared with their sensitivity to the phytoalexin phaseollin and their ability to metabolize phaseollin. Three of the five isolates were pathogenic to bean, as they formed spreading lesions on bean leaves; the other two isolates were considered nonpathogenic to bean, since they produced lesions limited in size or no lesions at all. The isolates were about equally sensitive to phaseollin, except for one nonpathogenic strain which was more sensitive than the other ones to higher concentrations of phaseollin. The three pathogenic isolates metabolized phaseollin to 6a-hydroxyphaseollin readily in shake cultures containing 9 μg phaseollin/ml, while nonpathogenic isolates were not able, or less able, to do so.     

实时荧光RT-PCR一步法检测南方菜豆花叶病毒

南方菜豆花叶病毒（Southem bean mosaic virus，SBMV）是我国二类检疫性有害生物，以南方菜豆花叶病毒日本分离物（SBMV-J）总RNA为模板，采用RT-PCR方法扩增病毒外壳蛋白基因及其上游基因的cDNA片断并将其克隆到pMD18．T载体上。序列分析结果表明：SBMV-J cp基因由801个核苷酸组成，编码266个氨基酸，SBMV．J与其它分离物及株系印基因的核苷酸序列同源性为83％-97％，氨基酸序列同源性为86％-97％。由于SBMV各分离物及株系印基因的同源性较低，难于设计出较长的普通PCR引物。通过较短引物设计和TaqMan-MGB探针技术，建立了SBMV的实时荧光RT-PCR一步检测方法。该方法的检测低限是0．16pg，最佳检测总RNA的量是0．16ng。