Bean Anthracnose Research Articles

The spore coat of the bean anthracnose fungus Colletotrichum lindemuthianum is required for adhesion, appressorium development and pathogenicity

The spores (conidia) of the bean anthracnose fungal pathogen, Colletotrichum lindemuthianum, adhere to the aerial parts of plants to initiate the infection process. In previous studies we have shown that the Colletotrichum spores are surrounded by a fibrillar spore coat, comprising several major glycoproteins. Previous evidence showed that a monoclonal antibody (UB20) that recognised these glycoproteins was able to inhibit adhesion of spores to a hydrophobic surface. In this paper we have further studied the role of the spore coat in adhesion, germination and fungal development by studying the effects of UB20 and protease treatment of spores. The latter treatment has previously been shown to remove the spore coat. Spores germinate on glass, polystyrene and water agar, however, appressoria only develop on glass or polystyrene, showing a requirement for a hard surface. Removal of the spore coat with protease inhibits adhesion at 30 min, before the secretion of ECM glycoproteins. Protease treatment also inhibits the development of appressoria and reduces pathogenicity on leaves. Incubation of spores with the MAb UB20 inhibits adhesion at 30 min, but does not affect appressorium formation or pathogenicity. The results suggest that an intact spore coat has two functions; it is required for adhesion to a hydrophobic surface and for the detection of a hard surface necessary for appressorium formation. We suggest that contact with a hard surface, rather than adhesion, is the key event leading to appressorium formation.

Genetic characterization of anthracnose resistance genes Co-4 3 and Co-9 in common bean cultivar tlalnepantla 64 (PI 207262)

Tlalnepantla 64 (PI 207262) is an important source of genes for resistance to common bean anthracnose, caused by Colletotrichum lindemuthianum. However, these genes have not been fully characterized. Inheritance studies using crosses involving PI 207262 show that two independent genes confer resistance to anthracnose. Allelism tests showed that the genes are located at distinct loci from the previously identified resistance genes Co-1, Co-2, Co-3, Co-5, Co-6, and Co-10. Also, no segregation was observed in relation to Co-4, Co-4 2, Co-9, and to the gene present in cultivar Widusa, indicating that PI 207262 harbors alleles of these genes. We conclude that PI 207262 harbors two anthracnose resistance genes, Co-4 and Co-9. The Co-4 allele of PI 207262 would be different from Co-4 and Co-4 2 and it is proposed Co-4 3 as the genetic symbol for this resistance allele. As PI 207262 is the parent of BAT 93, the Co-9 symbol represents the gene of both cultivars. Also, one allele of Co-9 gene was detected in cultivar Widusa.

Pathological and molecular diversity inColletotrichum lindemuthianum(bean anthracnose) across Himachal Pradesh, a north-western Himalayan state of India

Ninety isolates of Colletotrichum lindemuthianum collected from commercial bean growing areas of Himachal Pradesh were characterised on international differential bean varieties and analysed by random amplified polymorphic DNA (RAPD) analysis for elucidation of variability. Virulence analysis of 90 isolates on a differential set categorised them into 29 pathogenic races. Out of these, 12 races resembled American and European virulences, whereas 17 races (101, 103, 115, 119, 131, 195, 537, 551, 581, 598, 613, 615, 631, 639, 707, 775 and 935) were identified as new, thereby enhancing the total race number to more than 140 globally. RAPD data analysis with nine 10-mer random primers producing polymorphic bands, grouped 90 isolates into two major clusters accommodating 36 and 54 isolates, respectively. There was no congruence between the RAPD pattern and virulence phenogram. Interaction analysis among the races and the two Phaseolus vulgaris gene pools indicated that most of the races were virulent on both Andean and Mesoamerican gene pools. Virulence and avirulence interactions between isolates and differential cultivars provided valuable information for resistance to Indian virulences of the anthracnose pathogen, as four differential cultivars (AB 136, Cornell 49242, G 2333 and TO) possessing different resistance genes were resistant to most of the Indian races.

Allelic relationships of anthracnose (Colletotrichum lindemuthianum) resistance in the common bean (Phaseolus vulgaris L.) cultivar Michelite and the proposal of a new anthracnose resistance gene, Co-11

The genetic resistance of Phaseolus vulgaris L. cultivar Michelite to races 8 and 64 of Colletotrichum lindemuthianum, causal agent of bean anthracnose, was characterized. Crosses were made between Michelite and Mexico 222 cultivars and the F2 population was inoculated with race 64 in order to study the inheritance of resistance to anthracnose in Michelite. The segregation of F2 population fitted in a ratio of 3R:1S, showing the presence of a dominant gene in Michelite gene conditioning resistance to race 64. Allelism tests were conducted with F2 populations derived from crosses between Michelite and AB 136, AND 277, BAT 93, Cornell 49-242, G 2333, Kaboon, Mexico 222, Michigan Dark Red Kidney (MRDK), Ouro Negro, Perry Marrow, PI 207262, TO, TU, and Widusa. All the cultivars (except Mexico 222) were resistant to race 64. While F2 derived from the Michelite x Mexico 222 was inoculated with race 8. Additionally, allelism tests indicated that the gene present in Michelite is independent from Co-1, Co-2, Co-3, Co-4, Co-5, Co-6, Co-7, Co-9 and Co-10 genes. The monogenic inheritance observed in Michelite and the independence of this gene from those previously characterized allow the authors to propose that the anthracnose resistant gene in Michelite should be named Co-11.

Development of a molecular genetic linkage map for Colletotrichum lindemuthianum and segregation analysis of two avirulence genes

A framework genetic map was developed for the fungal pathogen Colletotrichum lindemuthianum, the causal agent of anthracnose of common bean (Phaseolus vulgaris L.). This is the first genetic map for any species within the family Melanconiaceae and the genus Colletotrichum and provides the first estimate of genome length for C. lindemuthianum. The map was generated using 106 haploid F1 progeny derived from crossing two Mexican C. lindemuthianum isolates differing in two avirulence genes (AvrclMex and AvrclTO). The map comprises 165 AFLP markers covering 1,897 cM with an average spacing of 11.49 cM. The markers are distributed over 19 major linkage groups containing between 5 and 25 markers each and the genome length was estimated to be approximately 3,241 cM. The avirulence genes AvrclMex and AvrclTO segregate in a 1:1 ratio supporting the gene for gene hypothesis for the incompatible reaction between C. lindemuthianum and P. vulgaris, but could not be incorporated into the genetic map. This initial outline map forms the basis for the development of a more detailed C. lindemuthianum linkage map, which would include other types of molecular markers and allow the location of genes previously isolated and characterized in this species.

Geoestatística como metodologia para estudar a dinâmica espaço-temporal de doenças associadas a Colletotrichum spp. transmitidos por sementes

Objetivou-se no presente trabalho caracterizar o progresso espaço-temporal da severidade da antracnose do feijoeiro comum e da ramulose do algodoeiro por meio da Geoestatística. Os experimentos foram conduzidos no campo, durante o período das águas, em diferentes épocas. Sementes inoculadas pelo método da restrição hídrica foram semeadas no centro de parcelas experimentais constituindo fonte de inóculo do tipo ponto. Foram realizadas semanalmente seis avaliações da severidade das doenças com base em escalas de notas. Pelos modelos de semivariograma isotrópicos esféricos e gaussianos ajustados aos dados, verificou-se o padrão de distribuição agregado e a dependência espacial de ambos os patossistemas. Com o mapeamento da severidade das doenças pelo método da krigagem ordinária em blocos, verificou-se menor severidade das doenças nos primeiros estádios, com aumento gradual ao longo do tempo. A antracnose apresentou formação inicial de focos de inóculo secundário, além do foco com inóculo inicial, que coalesceram com o tempo. A severidade da ramulose diminuiu gradualmente de forma radial e contínua do centro da parcela para as extremidades, com maior capacidade de infecção de plantas vizinhas, quando comparada à antracnose, possivelmente pela maior agressividade do patógeno e hábito de crescimento arbustivo do algodoeiro.

Inheritance of anthracnose resistance in the common bean cultivar Widusa

Snap bean (Phaseolus vulgaris L.) cultivar, Widusa, was crossed to Michigan Dark Red Kidney (MDRK), Michelite, BAT 93, Mexico 222, Cornell 49–242, and TO cultivars to study the inheritance of resistance to anthracnose in Widusa. The segregation patterns observed in six F2 populations supported an expected 3R:1S ratio suggesting that Widusa carries a single dominant gene conditioning resistance to races 7, 65, 73, and 453 of Colletotrichum lindemuthianum, the causal organism of bean anthracnose. Allelism tests conducted with F2 populations derived from crosses between Widusa and Cornell 49–242 (Co-2), Mexico 222 (Co-3), TO (Co-4), TU (Co-5), AB 136 (Co-6), BAT 93 (Co-9), and Ouro Negro (Co-10), inoculated with races 7, 9, 65 and 73, showed a segregation ratio of 15R:1S. These results suggest that the anthracnose resistance gene in Widusa is independent from the Co-2, Co-3, Co-4,Co-5, Co-6, Co-9, and Co-10 genes. A lack of segregation was observed among 200 F2 individuals from the cross Widusa/MDRK, and among 138 F2 individuals from the cross Widusa/Kaboon inoculated with race 65, suggesting that Widusa carries an allele at the Co-1 locus. We propose that the anthracnose resistance allele in Widusa be named Co-15 as Widusa exhibits a unique reaction to race 89 compared to other alleles at the Co-1 locus. RAPD marker A181500 co-segregated in repulsion-phase linkage with the Co-15 gene at a distance of 1.2 cM and will provide bean breeders with a ready tool to enhance the use of the Co-15 gene in future bean cultivars.

Influence of growth habit, row spacing, and seed infection on bean anthracnose development

Bean anthracnose, caused by Colletotrichum lindemuthianum, has been responsible for severe seed yield and quality losses in many dry bean (Phaseolus vulgaris) producing regions of the world. A 2-year study conducted at two field locations in Manitoba examined the effect of differences in seed-borne infection level, row spacing, and growth habit on anthracnose development and any associated losses in seed yield and quality in four navy bean entries and two pinto bean entries. Row spacing had little or no effect on anthracnose severity, but the narrow row spacing (30 cm) always produced the highest yield. A seed-borne infection level of 10% resulted in a significant decrease in the percent seedling emergence of the navy bean entries but usually did not reduce the emergence of the pinto bean cultivars. Nevertheless, anthracnose ratings were most severe on the pinto bean cultivars early in the growing season. The results suggest that the larger seed size of the pinto bean cultivars might have resulted in the emergence of a higher percentage of infected seedlings, which would have caused the disease to rapidly spread in these cultivars. The effect of seed-borne anthracnose infection on the crop canopy and on the pods became evident late in the growing season and resulted in higher incidences of anthracnose seed discoloration. Growth habit did not consistently influence anthracnose severity, since the entries with the lowest disease ratings were a viny navy bean line and an indeterminate, upright navy bean line.

Efeito de fontes de silício na incidência e na severidade da antracnose do feijoeiro

Foram realizados três experimentos para estudar a influência do silício na redução da antracnose, causada por Colletotrichum lindemuthianum, em feijoeiro (Phaseolum vulgaris). No primeiro experimento plantas tratadas com silicato de cálcio foram inoculadas com 0, 10³, 10(4), 5x10(4), 10(5), 5x10(5) e 10(6) conídios/ml de C. lindemuthianum. Na concentração de 10(6) conídios/ml avaliou-se a diferença entre o silicato de cálcio e uma fonte de cálcio (óxido de cálcio). No segundo experimento foi avaliado o silicato de cálcio e de sódio na redução da antracnose. No terceiro experimento, por meio da microscopia eletrônica de varredura (MEV) e da microanálise de raios-X (MAX), estudou-se o efeito do silício nos mecanismos de resistência. Foram realizadas cinco avaliações da doença, utilizadas para calcular a área abaixo da curva de progresso da incidência (AACPI), da severidade (AACPS) e a duração da área foliar sadia (HAD), nos dois primeiros experimentos. Com o aumento da concentração do inóculo houve aumento na AACPI e AACPS e redução na HAD, porém a testemunha inoculada com a maior concentração de inóculo, e tratada apenas com cálcio (CaO), sem silicato, teve maiores AACPI e AACPS do que as plantas tratadas com silicato de cálcio. No segundo experimento, a menor AACPS e maior HAD foram obtidas no tratamento com silicato de sódio via foliar, que proporcionou redução de 62,4% na AACPS. Na MEV e na microanálise de raios X não se observaram a formação de barreira física e o acúmulo de silício externamente com a aplicação de silicato de cálcio, embora o elemento tenha contribuído para reduzir a antracnose.

Co-evolução entre raças fisiológicas de colletotrichum lindemuthianum e feijoeiro

O agente causal da antracnose (Colletotrichum lindemuthianum) em feijoeiro comum é classificado, assim como seu hospedeiro, em Andino e Mesoamericano, sendo a resposta à infecção dependente da origem genética de um e de outro. Desta forma, o objetivo do presente trabalho foi avaliar 220 acessos do Banco de Germoplasma de feijoeiro (Phaseolus vulgaris) do Instituto Agronômico, IAC, quanto à infecção por três raças fisiológicas do patógeno (31, 65 e 89), caracterizando uma possível co-evolução entre a origem do acesso e do patógeno. No estudo, foram utilizados 120 acessos de origem mesoamericana, 57 andinos e 43 cultivares geneticamente melhoradas. Além dos dados relacionados à infecção, foram avaliados 23 descritores morfo-agronômicos com finalidade de melhor caracterizar os acessos em relação aos seus respectivos centros de origem. As análises estatísticas foram baseadas em componentes principais a fim de exibir graficamente a variabilidade em função da origem do patógeno e dos acessos. Dentre os acessos mesoamericanos, 50% foram suscetíveis às três raças, enquanto nos andinos apenas 33% foram suscetíveis. Entre as cultivares geneticamente melhoradas, 79% foram resistentes a pelo menos uma das raças, provavelmente devido a seleções para resistência ao C. lindemuthianum. Nos gráficos da análise de componentes principais, a maioria dos acessos resistentes foi agrupada na região de dispersão dos acessos andinos. Os resultados permitiram estabelecer uma associação entre a origem do feijoeiro e do patógeno da antracnose, ajudando assim no conhecimento biológico da reação dos acessos ao C. lindemuthianum e orientando a escolha de genitores para realização de cruzamentos visando à resistência a essa doença.

Registration of ‘Condor’ Black Bean

‘Condor’ black bean (Phaseolus vulgaris L.) (Reg. no. CV-233, PI 635117) was developed cooperatively by the Michigan Agricultural Experiment Station and the USDA-ARS and released in 2004 as an upright, midseason, disease-resistant cultivar. Condor, tested as B00101, was derived from a cross made in 1996 between black bean cultivars Phantom and Black Jack. Phantom is a mid-to-full season, upright, indeterminate growth habit Type II black bean cultivar (2) with resistance to Races 7 and 73 of Colletotrichum lindemuthianum (Sacc. & Magnus) Lams.-Scrib., the cause of bean anthracnose. Black Jack is a more prostrate black bean cultivar with excellent canning quality. F1 plants were advanced in the greenhouse and F2 seed was space-planted in a nursery at the Saginaw Valley Bean and Sugarbeet Research Farm near Saginaw, MI. A single F2 plant possessing the desired agronomic and black bean seed traits was selected. The F3 progeny row was planted at the University of Puerto Rico Research Station at Isabela and mass selected based on agronomic and seed traits. A single-plant selection was made in a space-planted F4 nursery in Michigan based on agronomic and black bean seed traits and resistance to bean rust [caused by Uromyces appendiculatus (Pers.:Pers.) Unger]. The F5 progeny row was advanced at Isabela, Puerto Rico and the reaction to virus and anthracnose was confirmed by inoculating remnant seed in the greenhouse for resistance to Races 7 and 73 of C. lindemuthianum and to the NL 3 strain of Bean common mosaic necrosis virus (BCMNV). The F4:6 breeding line, coded B00101, was tested for yield and agronomic traits at 29 locations in Michigan from 2000 to 2003 before release. Condor averaged 3100 kg ha−1 and was equivalent in yield to ‘Midnight’ at 13 locations. Condor outyielded three commercial black bean cultivars, namely ‘Jaguar’, ‘T-39’, and Black Jack by a margin of 5, 6, and 8% at 24, 29, and 12 locations, respectively. Condor averages 49 cm in height and exhibits an upright indeterminate growth habit Type II, with moderate resistance to lodging. Condor has purple flowers and blooms 49 d after planting. Condor is a midseason bean, maturing 94 d after planting and has a range in maturity from 83 to 99 d, depending on season and location. Condor matures 1 d later than Jaguar (3), T-39, and Black Jack, and 5 d earlier than Midnight. Plants of Condor mature uniformly and show excellent dry-down across a broad range of environments. Condor carries the dominant I gene for resistance to Bean common mosaic virus (BCMV) but is sensitive to the temperature-insensitive necrosis-inducing strains of BCMNV such as NL 3 and NL 8. Condor carries the Co-1 and Co-2 genes, which condition resistance to Races 7, and 73 of C. lindemuthianum, and the Ur-3 rust resistance gene, which conditions resistance to Race 53 and all indigenous bean rust pathogen races prevalent in Michigan. Condor is tolerant to Michigan isolates of root rot [caused primarily by Fusarium solani (Mart.) Sacc. f. sp. phaseoli (Burkholder) W.C. Snyder & H.N. Hans.] but is susceptible to common blight [caused by Xanthomonas axonopodis pv. phaseoli (Smith) Dye]. Condor has a higher level of tolerance (35% incidence) to white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary], as compared to T-39 (49% incidence), but exhibits less white mold avoidance (4) compared to the more erect Jaguar (21% incidence). Condor has flat-to-round seed, which averages 23 g 100 seed−1 (range: 19–25 g 100 seed−1). The seed is similar in color and shape to T-39. In canning trials, Condor scored 4.7 on a seven-point hedonic scale (where 7 is most desirable, 1 is least desirable, and 4 is average); whereas T-39, Jaguar, and Black Jack scored 3.9, 4.4, and 5.1, respectively. After processing, Condor retains color better than Jaguar and T-39 but it does not differ significantly from other black bean cultivars for texture, hydration, and drained weight ratios (1). Condor was released as a public nonexclusive variety, with the option that Condor may be sold for seed by name only under the Certified class. A research fee will be assessed on each hundredweight unit of Foundation seed sold. Breeder seed is maintained by the Michigan Agricultural Experiment Station, East Lansing, MI 48824, in cooperation with the Michigan Crop Improvement Association.

Ação fungicida do acaricida azocyclotin sobre a antracnose do feijoeiro comum

A cultura do feijoeiro (Phaseolus vulgaris L.) pode ser afetada por muitas doenças e dentre elas destaca-se a antracnose, causada pelo fungo Colletotrichum lindemuthianum. O acaricida azocyclotin (AZ) foi avaliado in vitro, em plântulas e em condições de campo, quanto ao efeito em C. lindemuthianum. Foram avaliados sete tratamentos in vitro: 1) testemunha; 2) AZ-1 mg L-1; 3) Trifenil hidróxido de estanho (THE)-1 mg L-1; 4) AZ-10 mg L-1; 5) THE-10 mg L-1; 6) AZ-100 mg L-1 e 7) THE-100 mg L-1 e 13 tratamentos in vivo: 1) testemunha; 2) AZ aplicado 24 horas antes da inoculação (AZ-24); 3) THE-24; 4) AZ-48; 5) THE-48; 6) AZ-72; 7) THE-72; 8) AZ-96; 9) THE-96; 10) AZ-120; 11) THE-120; 12) AZ-144 e 13) THE-144. Azocyclotin foi avaliado à dose de 125 g i.a.100 L-1 de água e trifenil hidróxido de estanho a 41,25 g i.a.100 L-1. Os delineamentos experimentais foram inteiramente ao acaso, com cinco repetições. Em condições de campo, foi realizado um experimento com seis tratamentos. Os tratamentos e as doses em g ha-1 de i.a foram: 1) tebuconazole + trifenil hidróxido de estanho (100 + 200); 2) tebuconazole + trifloxystrobin (40 + 100); 3) trifloxystrobin (125); 4) tebuconazole + azocyclotin (100 + 500); 5) azocyclotin (500) e 6) testemunha. O delineamento foi em blocos ao acaso, com quatro repetições. Para a avaliação in vitro foram medidos diâmetros ortogonais do crescimento micelial do fungo em BDA; in vivo e no campo usou-se escala de notas de 1 a 9, sendo 1 = sem sintoma e 9 = igual ou mais de 25% de área foliar afetada. In vitro, o tratamento 7 proporcionou maior inibição do desenvolvimento micelial. Em plântulas, observou-se controle de C. lindemuthianum até 144 horas, pelos dois produtos. Uma nova constatação em campo foi o controle de antracnose pelo acaricida azocyclotin, em que se observou também efeito sobre mancha-angular e mancha-de-alternária. Concluiu-se que o acaricida azocyclotin é eficiente no controle da antracnose do feijoeiro, semelhante ao trifenil hidróxido de estanho.

Effect of foliar fungicide application timing on the control of bean anthracnose in the navy bean ‘Navigator’

Bean anthracnose, caused by Colletotrichum lindemuthianum, can severely reduce bean yield and seed quality. A 2-year field study at two sites in southern Manitoba examined the effect of the timing of foliar applications of the fungicide pyraclostrobin (Headline® 250 EC) on the control of bean anthracnose in navy bean (Phaseolus vulgaris) ‘Navigator’. Single and (or) sequential applications of pyraclostrobin at a rate of 0.1 kg active ingredient (a.i.)/ha were made at four growth stages. Single applications of pyraclostrobin, at either 3 to 5 trifoliolate leave stage, early flowering (40% bloom), late flowering (80% bloom), or 10 days after flowering, reduced disease development in the crop canopy, but had inconsistent effects on pod infection, seed discoloration, and yield. Sequential applications of pyraclostrobin at the early and late flowering stages usually resulted in the lowest disease severity on all parts of the plant and in the highest yield. Sequential applications of pyraclostrobin at the late flowering stage and 10 days after flowering were less effective in reducing anthracnose severity and seed discoloration than the earlier sequentialapplication treatment. Both sequential-application treatments of pyraclostrobin had similar yields. Under Manitoba growing conditions, seed-borne infection by C. lindemuthianum resulted in yield reductions that ranged from 15.2% to 32.1% in the untreated bean plots.

Effect of Organic Amendments on Soilborne and Foliar Diseases in Field-Grown Snap Bean and Cucumber.

Several paper mills in Wisconsin have programs for spreading paper mill residuals (PMR) on land. A growing number of vegetable farmers recognize the agronomic benefits of PMR applications, but there have been no investigations on the use of PMR for control of vegetable crop diseases. Our objective was to determine the effect of PMR amendments on soilborne and foliar diseases of cucumber and snap bean grown on a sandy soil. Raw PMR, PMR composted without bulking agent (PMRC), or PMR composted with bark (PMRBC) were applied annually in a 3-year rotation of potato, snap bean, and pickling cucumber. Several naturally occurring diseases were evaluated in the field, along with in situ field bioassays. All amendments suppressed cucumber damping-off and Pythium blight and foliar brown spot of snap bean. Both composts reduced the incidence of angular leaf spot in cucumber. In a separate field experiment planted with snap bean for two consecutive years, all amendments reduced common root rot severity in the second year. In a greenhouse experiment, the high rate of PMRBC suppressed anthracnose of snap bean. These results suggest that the application of raw and composted PMR to sandy soils has the potential to control several soilborne and foliar diseases.

Cytogenetics of Colletotrichum lindemuthianum (Glomerella cingulata f. sp. phaseoli)

Cytogenetic and morphological studies were conducted with Colletotrichum lindemuthianum (Glomerella cingulata f. sp. phaseoli), the pathogen responsible for anthracnose of common bean (Phaseolus vulgaris). In this species, there is some evidence of genomic variation but it is unknown whether the process occurs in a manner similar to other fungal genetic models. Six isolates from bean plants were used and sexual reproduction was observed in vitro. Meiosis and ascospore formation were investigated by cytogenetical approaches and light microscopy. To study the nucleus and chromosome numbers, a mixture of carmine and orcein propionic dyes was used. Nucleus divisions as well as ascospore maturation were asynchronous. Meiosis was observed in three isolates. In the asexual form, chromosomal polymorphism in conidia was also observed microscopically and the mitosis process was described.

Sources of Resistance to Colletotrichum lindemuthianum in the Secondary Gene Pool of Phaseolus vulgaris and in Crosses of Primary and Secondary Gene Pools.

Use of genetic resistance is the most practical and economic way to manage anthracnose of common bean. Colletotrichum lindemuthianum, the causal agent of bean anthracnose, is a highly variabile pathogen, and there are no host resistance genes that are effective against all known races of the pathogen. To diversify sources of resistance, we screened the core collection of the secondary gene pool of Phaseolus spp. and interspecific lines derived from simple and complex crosses of primary and secondary genotypes for their resistance to anthracnose. High levels of resistance were observed in the secondary gene pool. None of the 162 accessions tested was susceptible to C. lindemuthianum. Of the two species composing the secondary gene pool, P. polyanthus displayed higher levels of resistance than P. coccineus, and all accessions tested were resistant. The response of P. coccineus was more variable, with six genotypes showing an intermediate reaction. Among the 75 lines from interspecific crosses, 49 were resistant to the three races (races 6, 15, and 3481) used in this study, and higher levels of resistance were found in lines that had P. polyanthus as one of the parents in the crosses than in the lines derived from P. coccineus. These lines constitute a valuable source of resistance and may aid in the development of stable resistance to anthracnose.

Clap1, a gene encoding a copper-transporting ATPase involved in the process of infection by the phytopathogenic fungus Colletotrichum lindemuthianum

A screen for insertional mutants of Colletrichum lindemuthianum, the causative agent of common bean anthracnose, led to the identification of a non-pathogenic, lightly colored transformant. This mutant is unable to induce disease symptoms on intact or wounded primary leaves of seedlings and plantlets of Phaseolus vulgaris. In vitro, it exhibits normal vegetative growth, sporulation and conidial germination, but the cultures remain beige instead of becoming black. Microscopic examination revealed that this mutant forms fewer appressoria than the wild-type strain, and these are misshapen and poorly melanized. Molecular analyses indicated that the mutagenic plasmid had targeted clap1, a gene encoding a putative copper-transporting ATPase sharing 35% identity with the human Menkes and Wilson proteins and the product of the CCC2 gene of Saccharomyces cerevisiae. Complementation of the non-pathogenic beige mutant with a wild-type allele of clap1 restored both pathogenicity and pigmentation. Conversely, replacement of the wild-type allele with a disrupted clap1 gene gave rise to non-pathogenic beige transformants. Compared with the wild-type strain, extracts from clap1 mutants were found to have very low levels of phenol oxidase activity. These observations suggest that the clap1 gene product may be involved in the pathogenicity of C. lindemuthianum strains because of its role in delivering copper to secreted cuproenzymes, such as the phenol oxidases that mediate the polymerization of 1,8-dihydroxynaphthalene to melanin.

Identification of physiological races of Colletotrichum lindemuthianum occuring in Slovenia

Bean anthracnose, the most important fungal disease of common bean in Slovenia, is caused by a mitosporic fungus Colletotrichum lindemuthianum (Sacc. et Magnus) Briosi et Cav. The most appropriate measure to control the disease is growing of resistant cultivars. Breeding for resistance is limited by the existence of several physiological races of the pathogen and continuous development and introduction of new ones. It is necessary to constantly monitor the occurrence and dynamic of physiological races existing in certain area. With this aim, 47 isolates were obtained from several bean accessions in different bean growing areas in Slovenia. The fungus was isolated from infected pods and leaves. A set of 12 internationally accepted differential bean cultivars was inoculated with spore suspension obtained from single spore isolates. Plant reaction was screened following I - 10 severity scale. Four physiological races of the pathogen were identified. Using the binary nomenclature system they were assigned to races 23, 55, 103 and 131. The most frequent and widespread were races 55 and 23, named also lambda and delta. The research will continue by screening the autochthonous bean germplasm for susceptibility towards the existing races.

Inhibition of Fungal Spore Adhesion by Zosteric Acid as the Basis for a Novel, Nontoxic Crop Protection Technology

ABSTRACT To explore the potential for nontoxic crop protection technologies based on the inhibition of fungal spore adhesion, we have tested the effect of synthetic zosteric acid (p-(sulfo-oxy) cinnamic acid), a naturally occurring phenolic acid in eelgrass (Zostera marina L.) plants, on spore adhesion and infection in two pathosystems: rice blast caused by Magnaporthe grisea and bean anthracnose caused by Colletotrichum lindemuthianum. We have shown that zosteric acid inhibits spore adhesion to model and host leaf surfaces and that any attached spores fail to develop appressoria, and consequently do not infect leaf cells. Low concentrations of zosteric acid that are effective in inhibiting adhesion are not toxic to either fungus or to the host. The inhibition of spore adhesion in the rice blast pathogen is fully reversible. On plants, zosteric acid reduced (rice) or delayed (bean) lesion development. These results suggest that there is potential for novel and environmentally benign crop protection technologies based on manipulating adhesion.

Gas Exchange and Emission of Chlorophyll Fluorescence during the Monocycle of Rust, Angular Leaf Spot and Anthracnose on Bean Leaves as a Function of their Trophic Characteristics

Measurements related to gas exchange and chlorophyll fluorescence emission were taken from healthy and diseased bean leaves with rust, angular leaf spot, and anthracnose during lesion development for each disease. The experiments were performed at different temperatures of plant incubation, and using two bean cultivars. The main effect of temperature of plant incubation was in disease development. There was no significant difference between cultivars in relation to disease development and in magnitude of physiological alterations when disease severity was the same for each cultivar. These diseases reduced the net photosynthetic rate and increased the dark respiration of infected leaves after the appearance of visible symptoms and the differences between healthy and diseased leaves increased with disease development. The transpiration rate and stomatal conductance were stable during the monocycle of rust, however, these two variables decreased in leaves with angular leaf spot and anthracnose beginning with symptom appearance and continuing until lesion development was complete. Carboxylation resistance was probably the main factor related to reduction of photosynthetic rate of the apparently healthy area of leaves with rust and angular leaf spot. Reduction of the intercellular concentration of CO2, due to higher stomatal resistance, was probably the main factor for leaves with anthracnose. Chlorophyll fluorescence assessments suggested that there was no change in electron transport capacity and generation of ATP and NADPH in apparently healthy areas of diseased leaves, but decreases in chlorophyll fluorescence emission occurred on visibly lesioned areas for all diseases. Minimal fluorescence was remarkably reduced in leaves with angular leaf spot. Maximal fluorescence and optimal quantum yield of photosystem II of leaves were reduced for all three diseases. Bean rust, caused by a biotrophic pathogen, induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens. The magnitude of photosynthesis reduction can be related to the host–pathogen trophic relationships.