Co-segregation analysis and mapping of the anthracnose Co-10 and angular leaf spot Phg-ON disease-resistance genes in the common bean cultivar Ouro Negro.

Anthracnose (ANT) and angular leaf spot (ALS) are devastating diseases of common bean (Phaseolus vulgaris L.). Ouro Negro is a highly productive common bean cultivar, which contains the Co-10 and Phg-ON genes for resistance to ANT and ALS, respectively. In this study, we performed a genetic co-segregation analysis of resistance to ANT and ALS using an F2 population from the Rudá × Ouro Negro cross and the F2:3 families from the AND 277 × Ouro Negro cross. Ouro Negro is resistant to races 7 and 73 of the ANT and race 63-39 of the ALS pathogens. Conversely, cultivars AND 277 and Rudá are susceptible to races 7 and 73 of ANT, respectively. Both cultivars are susceptible to race 63-39 of ALS. Co-segregation analysis revealed that Co-10 and Phg-ON were inherited together, conferring resistance to races 7 and 73 of ANT and race 63-39 of ALS. The Co-10 and Phg-ON genes were co-segregated and were tightly linked at a distance of 0.0 cM on chromosome Pv04. The molecular marker g2303 was linked to Co-10 and Phg-ON at a distance of 0.0 cM. Because of their physical linkage in a cis configuration, the Co-10 and Phg-ON resistance alleles are inherited together and can be monitored with great efficiency using g2303. The close linkage between the Co-10 and Phg-ON genes and prior evidence are consistent with the existence of a resistance gene cluster at one end of chromosome Pv04, which also contains the Co-3 locus and ANT resistance quantitative trait loci. These results will be very useful for breeding programs aimed at developing bean cultivars with ANT and ALS resistance using marker-assisted selection.

Linkage mapping of the Phg-1 and Co-1(4) genes for resistance to angular leaf spot and anthracnose in the common bean cultivar AND 277.

The Andean common bean AND 277 has the Co-1(4) and the Phg-1 alleles that confer resistance to 21 and eight races, respectively, of the anthracnose (ANT) and angular leaf spot (ALS) pathogens. Because of its broad resistance spectrum, Co-1(4) is one of the main genes used in ANT resistance breeding. Additionally, Phg-1 is used for resistance to ALS. In this study, we elucidate the inheritance of the resistance of AND 277 to both pathogens using F(2) populations from the AND 277 × Rudá and AND 277 × Ouro Negro crosses and F(2:3) families from the AND 277 × Ouro Negro cross. Rudá and Ouro Negro are susceptible to all of the above races of both pathogens. Co-segregation analysis revealed that a single dominant gene in AND 277 confers resistance to races 65, 73, and 2047 of the ANT and to race 63-23 of the ALS pathogens. Co-1(4) and Phg-1 are tightly linked (0.0 cM) on linkage group Pv01. Through synteny mapping between common bean and soybean we also identified two new molecular markers, CV542014(450) and TGA1.1(570), tagging the Co-1(4) and Phg-1 loci. These markers are linked at 0.7 and 1.3 cM, respectively, from the Co-1(4) /Phg-1 locus in coupling phase. The analysis of allele segregation in the BAT 93/Jalo EEP558 and California Dark Red Kidney/Yolano recombinant populations revealed that CV542014(450) and TGA1.1(570) segregated in the expected 1:1 ratio. Due to the physical linkage in cis configuration, Co-1(4) and Phg-1 are inherited together and can be monitored indirectly with the CV542014(450) and TGA1.1(570) markers. These results illustrate the rapid discovery of new markers through synteny mapping. These markers will reduce the time and costs associated with the pyramiding of these two disease resistance genes.

Quantitative proteomic analysis of bean plants infected by a virulent and avirulent obligate rust fungus.

Plants appear to have two types of active defenses, a broad-spectrum basal system and a system controlled by R-genes providing stronger resistance to some pathogens that break the basal defense. However, it is unknown if the systems are separate entities. Therefore, we analyzed proteins from leaves of the dry bean crop plant Phaseolus vulgaris using a high-throughput liquid chromatography tandem mass spectrometry method. By statistically comparing the amounts of proteins detected in a single plant variety that is susceptible or resistant to infection, depending on the strains of a rust fungus introduced, we defined basal and R-gene-mediated plant defenses at the proteomic level. The data reveal that some basal defense proteins are potential regulators of a strong defense weakened by the fungus and that the R-gene modulates proteins similar to those in the basal system. The results satisfy a new model whereby R-genes are part of the basal system and repair disabled defenses to reinstate strong resistance.

Differential Response of Common Bean Cultivars to Phakopsora pachyrhizi.

Soybean rust (Phakopsora pachyrhizi) has been reported on common bean (Phaseolus vulgaris) in Asia, South Africa, and the United States. However, there is little information on the interaction of individual isolates of Phakopsora pachyrhizi with common bean germplasm. A set of 16 common bean cultivars with known genes for resistance to Uromyces appendiculatus, the causal agent of common bean rust, three soybean accessions that were sources of the single gene resistance to P. pachyrhizi, and the moderately susceptible soybean 'Ina' were evaluated using seedlings inoculated with six isolates of P. pachyrhizi. Among the common bean cultivars, Aurora, Compuesto Negro Chimaltenango, and Pinto 114, were the most resistant to all six P. pachyrhizi isolates, with lower severity, less sporulation, and consistent reddish-brown (RB) lesions associated with resistance in soybean. A differential response was observed among the common bean cultivars, with a cultivar-isolate interaction for both severity and sporulation levels, as well as the presence or absence of the RB lesion type. This differential response was independent of the known genes that condition resistance to U. appendiculatus, suggesting that resistance to P. pachyrhizi was independent of resistance to U. appendiculatus.

Fusarium Wilt Disease Caused by Fusarium oxysporum f. sp. phaseoli on a Common Bean Cultivar, G 2333, in Rwanda and the Democratic Republic of Congo.

The common bean (Phaseolus vulgaris L.) is an important source of dietary protein for poor resource families in Rwanda and the Kivu region of the Democratic Republic of Congo (DRC). During the second season of 1990, symptoms consisting of chlorosis, premature defoliation, stunting, wilting, and vascular discoloration were observed for the first time on an improved popular climbing bean cultivar, G 2333, in the prefectures of Butare and Gikongoro, in southwest Rwanda. Between 1991 and 1994, surveys to determine disease occurrence were conducted in the two prefectures and in Kigali North, Gitarama, Cyangugu, and Kibuye in Rwanda, and in the south Kivu region of the DRC. Aseptic isolation from diseased plant samples yielded the fungus Fusarium oxysporum f. sp. phaseoli. Pathogenicity tests on G 2333 seedlings by the root-dip inoculation method resulted in symptoms similar to those observed in the field, and recovery of the fungus, fulfilling Koch's postulate. Control seedlings gave no symptoms. Disease incidence was 44 and 53% in Butare and Gikongoro, respectively, during the first season of 1991 and 50 and 70% in the second season, while crop loss in some fields was as high as 100%. Between 1992 and 1994 the disease was also observed in the four other prefectures in Rwanda, and in south Kivu. Climbing bean cultivars Gisenyi-2-bis, G 865, Flora de Mayo, and Puebla 444 Criollo, and several bush local varietal mixtures grown where the disease occurred, were unaffected. CIAT bean Fusarium wilt differentials IPA 1, RIZ 30, A 211, Mortiño, Diacol Calima, BAT 477, HF 465-63-1, and Ecuador 650, and lines A 300 and XAN 112, were inoculated with three isolates (FOP-RW1, FOP-RW2, FOP-RW3) from Rwanda. Only IPA 1, RIZ 30, and A 211 were susceptible, indicating the isolates' likeness to the Brazilian race (1). This was the first report of Fusarium wilt disease on G 2333 in the two countries despite the cultivar having been grown for about 5 years. Reference: (1) R. L. D. Ribeiro and D. J. Hagedorn. Phytopathology 69:272, 1979.

Clover Proliferation Group (16SrVI) Subgroup A (16SrVI-A) Phytoplasma is a Probable Causal Agent of Dry Bean Phyllody Disease in Washington.

During 2003, a new disease, dry bean phyllody (DBPh), was observed in the Columbia Basin of Washington in dry bean (Phaseolus vulgaris L.) cultivars of Andean origin grown in Mattawa and Paterson, WA that caused great reduction in dry bean production. Symptoms of DBPh became apparent during mid-to-late pod development and were characterized by leafy petals (phyllody) and aborted seed pods resembling thin, twisted, and corrugated leaf-like structures. Deformed sterile pods that were small, sickle-shaped, upright, and leathery were also observed. The infected plants generally exhibited chlorosis, stunting, or bud proliferation from leaf axils. Symptoms of DBPh were indicative of possible infection by phytoplasmas. Restriction fragment length polymorphism (RFLP) and phylogenetic analyses of amplified 16S rDNA sequences were used for phytoplasma identification. Four symptomatic bean plants were analyzed and tested positive for phytoplasma infection on the basis of results of initial polymerase chain reaction (PCR) and subsequent nested-PCR amplifications (2). RFLP analyses of 16S rDNA sequences with restriction enzymes, MseI, AluI, HhaI, RsaI, and HpaII indicated that the phytoplasma strains associated with DBPh belonged to the clover proliferation group (16SrVI) subgroup A (16SrVI-A) (2). This subgroup currently consists of three members, clover proliferation (CP; GenBank Accession No. AY500130), potato witches'-broom (PWB; GenBank Accession No. AY500818), and vinca virescence (VR; GenBank Accession No. AY500817), a strain of beet leafhopper-transmitted virescence agent (BLTVA) phytoplasmas (1,2). The taxonomic affiliations of the DBPh phytoplasma strains were confirmed by phylogenetic analysis of cloned 16S rRNA gene sequences (GenBank Accession Nos. DBPh2, AY496002; DBPh3, AY496003). Among the existing members of subgroup 16SrVI-A, the four DBPh strains were closely related to the VR strain with 99.7% 16S rDNA sequence homology and to the CP strain with 99.2% sequence homology. To gain further evidence on the role of 16SrVI-A phytoplasma strains in DBPh disease, a modified test of Koch's postulates was conducted. Infected tissue from one phytoplasma-positive dry bean sample was grafted onto three Pinto UI-114 bean seedlings in the greenhouse. Within 60 days, the bean seedlings exhibited corrugated leaf-like structures from aborted seedpods, a lack of flower formation, general chlorosis, and stunting similar to the original diseased plants. The lower leaves of the inoculated bean plants became epinastic and leathery. The transmitted phytoplasma was detected in each of the grafted symptomatic seedlings, and the RFLP patterns of its 16S rRNA gene sequences were identical to those of the phytoplasmas in the scions. A high correlation between the presence of disease symptoms and the presence of subgroup 16SrVI-A phytoplasmas in the bean plants suggests that these phytoplasmas play an etiological role in DBPh disease. To our knowledge, these findings provide the first confirmed case of phytoplasma-associated DBPh in the United States. References: (1) D. A. Golino et al. Plant Dis. 73:850, 1989. (2) I.-M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998.

Modification of Resistance Expression of Phaseolus vulgaris to Meloidogyne incognita by Elevated Soil Temperatures.

The effect of temperature on the reaction of susceptible (Canario Divex) and resistant (A 211) bean pure lines to Meloidogyne incognita was studied with soil temperature tanks housed in a growth chamber at 22 or 24 C. Soil temperature remained constant at 16, 22, 24, 26, 30, or 32 C in several trials. Bean line A 211 was resistant at 16 and 22 C but was susceptible at 24 C and above. Resistance to root-knot nematode reproduction was affected by a lower temperature (24 C) than was resistance to root galling (26 C) in A 211. Incubation of A 211 at 30 C for 3 and 16 days after inoculation with M. incognita resulted in a significant increase in nematode reproduction and root galling, respectively. The resistant reactions of A 211 to nematode reproduction and root galling were retained when inoculated plants were incubated at 21 C for a minimum of 16 and 23 days, respectively, prior to high temperature treatment.

Inheritance of resistance to bacterial blight in common bean.

Inheritance of resistance to common bacterial blight in the trifoliate leaf, plant canopy, and pods was controlled by a single major gene. Additive followed by dominance effects were more important than epistatic interactions. Narrow-sense heritability values ranged from 0.18 to 0.87 for trifoliate leaf, from 0.26 to 0.76 for canopy, and from 0.11 to 0.36 for pods. Observed gains from selection for resistance were higher than expected gains. Implications of these results in breeding for resistance are discussed.