Andean beans (Phaseolus vulgaris L.) with resistance to the angular leaf spot pathogen (Phaeoisariopsis griseola) in southern and eastern Africa

Common beans (Phaseolus vulgaris) are separated into two distinct groups: Andean and Middle American. We identified CAL 143 as the first Andean bean with resistance to angular leaf spot disease caused by Phaeoisariopsis griseola. Angular leaf spot is the most widespread and economically important bean disease in southern and eastern Africa, and it is especially severe on the extensively grown Andean beans. Cal 143 was resistant in Malawi, South Africa, Tanzania, and Zambia, but it was susceptible in Uganda. This was attributed to the presence of races of P. griseola in Uganda not present in the other countries. We identified two additional Andean bean lines, AND 277 and AND 279, with resistance to angular leaf spot in Malawi. We also characterized the virulence diversity of 15 isolates of P. griseola from southern and eastern Africa into nine different races. Five of six isolates from Malawi and two of seven from Uganda, obtained from large-seeded Andean beans, were characterized into four different races considered Andean. These were compatible only or mostly with large-seeded Andean cultivars. The other eight isolates from Uganda, Malawi, and the Democratic Republic of Congo, obtained from a small- or medium-seeded Middle American beans, were characterized into five different Middle American races. These were compatible with Middle American and Andean cultivars. CAL 143 was resistant or intermediate under greenhouse conditions to all but one of the same 15 isolates from southern and eastern Africa, but it was susceptible to an isolate from Uganda obtained from a medium-seeded Middle American bean. This revised version was published online in July 2006 with corrections to the Cover Date.     

New sources of resistance to anthracnose and angular leaf spot of beans (Phaseolus vulgaris L.)

Summary over 13000 CIAT bean accessions were evaluated for their reactions to the anthracnose (Colletotrichum lindemuthianum) and angular leaf spot (Isariopsis griseola) pathogens over a 3 yr period. Among these accessions, 156 were resistant to all races of the anthracnose pathogen collected from Popayán, Colombia. Thirty were resistant to numerous races obtained from other parts of the world, including Europe. Although many of these new resistant sources originated in Mexico and Central America, they are quite diverse for geographic origin, plant type, seed color and seed size. In addition, more than 50 of the 156 lines were also resistant to isolates of I. griseola with diverse sources of origin throughout Colombia.     

Characterization of resistance to angular leaf spot of common bean (Phaseolus vulgaris L.) breeding line SPS50HB

The common bean (Phaseolus vulgaris L.) makes an important contribution to the human diet, particularly in Africa and Latin America. Because angular leaf spot (ALS), caused by the fungal pathogen Pseudocercospora griseola, is one of the most severe foliar diseases of the bean plant, an important priority is to identify genes encoding resistance. The present study focused on the resistance shown by the Mesoamerican common bean breeding line SPS50HB. From the pattern of segregation for resistance displayed in an F₂ population bred from a cross between SPS50HB and the ALS-susceptible Ethiopian variety Red Wolaita, it was concluded that the resistance of SPS50HB is controlled by two unlinked dominant genes. An allelism test indicated that one of these genes was either identical with, allelic to, or closely linked to the major gene Phg-2 carried by variety Mexico 54. The sequence-characterized amplified region assays OPEO4 and PF13, which are diagnostic for an ALS resistance gene carried by the germplasm accession G10909, both tracked a possible second gene present in SPS50HB.     

Sources of resistance to angular leaf spot (Phaeoisariopsis griseola) in common bean core collection, wild Phaseolus vulgaris and secondary gene pool

Angular leaf spot (ALS) is one of the most devastating diseases of common bean (Phaseolus vulgaris L.) in tropical and subtropical countries. The causal fungus, Phaeoisariopsis griseola(Sacc.) Ferr. is highly variable and a diverse source of resistance genes is required to manage this disease. We evaluated a common bean core collection,primary and secondary gene pools and lines derived from inter-specific crosses of P. vulgaris and P. coccineus or P. polyanthus (secondary gene pool) for resistance to angular leaf spot. Of the 1441 accessiones in the core collection, only 2.2% were resistant to both Andean and Mesoamerican races of P. griseola, 28% were resistant only to Andean and 9% to Mesoamerican races. Of the 32 resistant accessions, 68%originated from Bolivia, Colombia,Guatemala and Mexico. More accessions from these countries should be examined for P. griseola reaction. Very few wild P. vulgaris accessions (4%), were resistant to ALS. In contrast, high levels of resistance (62%) were found in the secondary gene pool. Among the 1010 lines from inter-specific crosses, 109 lines were highly resistant. These genotypes from the primary and secondary common bean gene pools resistant to Andean and Mesoamerican races of P. griseola offer a potential for developing broad and durable ALS resistance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of angular leaf spot resistance in common bean line BAT 332 and identification of RAPD markers linked to the resistance gene

The existence of genetic variability for angular leaf spot (ALS) resistance in the common bean germplasm allows the development of breeding lines resistant to this disease. The BAT 332 line is an important resistance source to common bean ALS. In this work we determined the inheritance pattern and identified RAPD markers linked to a resistance gene present in BAT 332. Populations F₁, F₂,BCs and BCr derived from crosses between BAT 332 and cultivar Rudá were used. Rudá is a commercial cultivar with carioca type grains and susceptible to ALS. The resistance of BAT 332 to race 61.41 of the pathogen was confirmed. Segregation analysis of the plants indicated that a single dominant gene confers resistance. For identification of RAPD markers linked to the resistance gene, bulk segregant analysis (BSA) was used. Two RAPD markers,OPAA07₉₅₀ and OPAO12₉₅₀, linked in coupling phase at 5.10 and 5.83 cM of this gene, respectively, were identified. These molecular markers are important for common bean breeders and geneticists as source of genetic information and for marker assisted selection in breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth analysis in a reduced leaf mutant of common bean (Phaseolus vulgaris L.)

Summary A comparison between the Royal Red bean variety and a reduced leaf mutant on the basis of growth indices is reported. The mutants has lower leaf area index (LAI) and leaf area duration (LAD) (–43.7%), higher specific leaf weight (SLW) (on the mean +33.3%) and accumulates less dry matter (–7.7%) than the normal genotype. When the net assimilation rate (NAR) is considered, the mutant is superior to the normal (+62.3%). It is concluded that the unit area of the mutant leaves accumulates dry matter more efficiently than that of the corresponding normal variety.     

Pathogenic variation in, sources of, and breeding for resistance to Phaeoisariopsis griseola causing angular leaf spot in common bean

If we are to breed common bean (Phaseolus vulgaris L.) for durable resistance to diseases, we must understand pathogenic variation and find sources of resistance. Our first objective was to determine the patterns of pathogenic variation found among isolates of Phaeoisariopsis griseola (PG), the fungus that causes angular leaf spot (ALS) in common bean. We characterized 433 PG isolates from 11 Latin American and 10 African countries, using differential cultivars, isozymes, and/or random amplified polymorphic DNA (RAPD) markers. We also systematically screened, for ALS resistance, common bean accessions from the world collection held at CIAT, and assessed the progress so far made in breeding for resistance to ALS. Despite their great diversity within and between countries on both continents, the PG isolates were classified into two major groups: Andean, and Middle American. Although each group had internal differences for virulence, and biochemical and molecular characteristics, the ‘Andean’ PG isolates were more virulent on common beans of Andean origin, than on those of Middle American origin, thus, suggesting a host-pathogen co-evolution. The ‘Middle American’ PG isolates, although more virulent on common beans from Middle America, also attacked Andean beans, thus, exhibiting a much broader virulence spectrum. To find sources of resistance, we tested 22,832 common bean accessions against naturally occurring PG isolates in the field at CIAT's Experiment Station, Quilichao, Colombia, between 1985 and 1992. The resulting 123 intermediate (scores of 4 to 6) and resistant (scores of 1 to 3) accessions were then tested in the greenhouse against selected 14 PG isolates of diverse origins. Nineteen accessions were intermediate or resistant to at least 13 of 14 PG isolates. Similarly, of 13,219 bred lines tested in the field between 1978 and 1996, 89 were intermediate or resistant. Of these, 33 bred lines proved intermediate or resistant to at least eight of nine PG isolates to which they were challenged in the greenhouse. We suggest that, to breed for durable resistance to ALS, common bean populations should be developed from crosses between Andean and Middle American gene pools. The populations should then be systematically evaluated and selected against the broadest range of the most virulent PG isolates of diverse evolutionary origins. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of pod cross-section in beans (Phaseolus vulgaris L.)

Summary OSU 5062, a green bean line with a tendency for pods to become creasebacked (wider than deep) in cross-section, was crossed to near-round-podded cultivars Oregon 83 and Slenderette, oval-podded Bountiful, and flat-podded Roma, to further clarify the inheritance of pod cross-section. Differences among generations in pod cross-section index (PCS), calculated as pod width/depth, were small in the near-round x creaseback crosses (1.07 and 1.01 for Oregon 83 and Slenderette versus 1.20 for OSU 5062). Bountiful (0.63) and Roma (0.50) differed to a greater extent from 5062. Generation means of individual plant PCS of the F₁ and F₂ were almost identical, were almost exactly intermediate between parents, and strongly supported additive inheritance. Backcross data generally supported additive inheritance, but in some cases indicated degrees of dominance of higher PCS. A generation means analysis indicated additive gene action, but deviations from an additive-dominance model were significant in each cross.     

Breeding the common bean (Phaseolus vulgaris L.) for resistance to bean common mosaic virus: alternatives to backcrossing

A series of field experiments was undertaken in order to determine whether resistance to bean common mosaic virus (BCMV) could be incorporated into genotypes of the common bean (Phaseolus vulgaris L.) suitable for cultivation in Zimbabwe without recourse to backcrossing. Six inbred genotypes carrying the resistance-conferring alleles at the loci I and Bc-3 were crossed with five locally-adapted inbred genotypes. The first experiment comprised F₃ progeny rows, each derived from a single unselected F₂ plant, the second, F₃ bulks selected for resistance, and the third, a comparison of selected and unselected F₂-derived F₄ lines. The number of days to flowering and to maturity, the incidence of mosaic and necrosis symptoms, seed yield and seed size were recorded. There was evidence that late flowering and maturity were associated with BCMV resistance in some crosses, though not strongly enough to present an obstacle to plant breeding. The incidence of virus symptoms and seed yield were influenced by genetic factors additional to the major resistance genes, and variation in seed yield was present not only between bulk populations of crosses, but also between single-row plots of lines within crosses. This indicates that early-generation selection for yield in the presence of BCMV, even among progeny selected for BCMV-resistace, is likely to be effective. However, the variation in yield among F₄ lines was least in the highest-yielding crosses, which may represent a limit to successful selection for yield. Seed size was partly under additive genetic control, but there was also evidence of non-allelic interactions. There was no association between large seed size, preferred by consumers, and susceptibility to BCMV in the progeny, indicating that the association between these characters in the parent lines is fortuitous and will not present an obstacle to plant breeding. It is noted that a considerable amount of useful genetic information can be obtained without recourse to elaborate crossing schemes, provided that unselected progeny are included in experiments as controls. The evidence presented indicates that resistance to BCMV can be combined with appropriate values of maturity date, yield and seed size without the need for backcrossing.     

Inheritance of temperature sensitivity of the photoperiod response in common bean (Phaseolus vulgaris L.)

Summary Photoperiod response of flowering in common bean (Phaseolus vulgaris L.) is thought to be controlled by the genes Ppd and Hr. However, cultivars also vary in the degree that cooler temperatures reduces their sensitivity to photoperiod. To examine the inheritance of this temperature sensitivity, crosses of cvs. Gordo x de Celaya and Flor de Mayo × Rojo 70 were evaluated at two sites differing in mean temperature and using 12.5-h natural photoperiod or 18-h artificially extended photoperiod. Under 18-h photoperiod at the warmer site, Palmira, no plants of the parents or of the F₂ populations flowered, confirming that the parents were sensitive to photoperiod. Under 12.5-h photoperiod at the cooler site, Popayan, the parents for each cross flowered at similar dates and no segregation for days to flower was observed. However, under 18-h photoperiod, de Celaya and Rojo 70 and the F₁ populations did not flower within 100 days after planting, while the F₂ and F₃ populations showed segregation that was consistent with single gene inheritance, late flowering being dominant. Late flowering at Popayan under 18-h photoperiod indicates a lack of temperature sensitivity, so temperature insensitivity of the photoperiod response was dominant to sensitivity. The name Tip, for temperature insensitivity of photoperiod response, is proposed for this gene, with the recessive form of this gene conditioning earlier flowering at cooler temperatures with long daylengths. It is recognized that the observed segregation patterns could represent the effect of multiple alleles at the Ppd or Hr loci, and studies are proposed to test this possibility with molecular markers and recombinant inbred lines.     

Genetics of angular leaf spot resistance in the Andean common bean accession G5686 and identification of markers linked to the resistance genes

Angular leaf spot (ALS), caused by the fungus Phaeoisariopsis griseola is an economically important and widely distributed disease of common bean. Due to the co-evolution of P. griseola with the large and small seeded bean gene pools, stacking Andean and Mesoamerican resistance genes is a strategy most likely to provide lasting resistance to ALS disease. This strategy requires identification and characterization of effective Andean and Mesoamerican resistance genes, and the development of molecular markers linked to these genes. This study was conducted to elucidate the genetics of ALS resistance in the Andean accession G5686 using an F₂ population derived from a G5686 × Sprite cross. Segregation analysis revealed that three dominant and complementary genes conditioned resistance of G5686 to P. griseola pathotype 31-0. Three microsatellite markers, Pv-ag004, Pv-at007 and Pv-ctt001 segregated in coupling phase with the resistance genes in G5686. Microsatellites Pv-ag004 and Pv-ctt001, located on opposite ends of linkage group B04 segregated with resistance genes Phg _G5686A , Phg _G5686B at 0.0 and 17.1 cM, respectively, while marker Pv-at007, localized on linkage group B09 segregated with resistance gene Phg _G5686C at 12.1 cM. Parental surveys showed that these markers were polymorphic in Andean and Mesoamerican backgrounds. The usefulness of G5686 ALS resistance genes in managing the ALS disease, and the potential utility of identified molecular markers for marker assisted breeding are discussed.     

Male sterility in beans (Phaseolus vulgaris L.)

Summary Male sterile bean plants were discovered at Embu Agricultural Research Station, Kenya. The character is controlled by one recessive gene.The Grain Legume Project is a joint project of the Kenya Ministry of Agriculture and The Netherlands Ministry of Foreign Affairs.     

Genetics of resistance to bean golden mosaic virus in Phaseolus vulgaris L.

Summary The genetics of resistance to bean golden mosaic virus (BGMV) was studied in an 8×8 complete diallel cross of common bean, Phaseolus vulgaris L. The 28F₁ hybrids, their reciprocals, and eight parents were artificially inoculated with BGMV under glasshouse conditions. Data were recorded and analyzed for foliar yellowing, plant dwarfing, flower abortion, and pod formation, using a randomized complete block design with two replications.General combining ability (GCA) mean squares were highly significant (P<0.01) and larger than values for specific combining ability for all traits. Reciprocal and maternal effects were nonsignificant. Cultivars Royal Red and Alubia Cerrillos possessed significant negative and positive GCA for all traits, respectively. Porrillo Sintetico also had negative GCA for all traits except plant dwarfing. None of the GCA effects were significant for Great Northern 31 and PVA 1111. Positive associations existed among all traits studied.     

Inheritance of resistance to angular leaf spot in common bean and validation of the utility of resistance linked markers for marker assisted selection out side the mapping population

Inheritance of resistance to angular leaf spot (ALS) disease caused by Phaeoisariopsis griseola (Sacc.) Ferr was investigated in two common bean cultivars, Mexico 54 and BAT 332. Both Andean and Mesoamerican backgrounds were used to determine the stability of the resistance gene in each of the two cultivars. Resistance to P. griseola was phenotypically evaluated by artificial inoculation with one of the most widely distributed pathotypes, 63–39. Evaluation of the parental genotypes, F₁, F₂ and backcross populations revealed that the resistance to angular leaf spot in the cultivars Mexico 54 and BAT 332 to pathotype 63–39 is controlled by a single dominant gene, when both the Andean and Mesoamerican backgrounds were used. Allelism test showed that ALS resistance in Mexico 54 and BAT 332 to pathotype 63–39 was conditioned by the same resistance locus. Resistant and susceptible segregating populations generated using Mexico 54 resistant parent were selected for DNA extraction and amplification to check for the presence /absence of the SCAR OPN02 and RAPD OPE04 markers linked to the Phg-2 resistance gene. The results indicated that the SCAR OPN02 was not polymorphic in the study populations and therefore of limited application in selecting resistant genotypes in such populations. On the other hand, the RAPD OPE04 marker was observed in all resistant individuals and was absent in those scored susceptible based on virulence data. Use of the RAPD OPE04 marker in marker-assisted selection is underway.     

Development of common bean (Phaseolus vulgaris L.) lines resistant to the bean pod weevil,Apion godmani Wagner,in Central America

Summary The larva of the bean pod weevil (BPW), Apion godmani Wagner (Coleoptera: Curculionidae), causes serious yield losses in common bean (Phaseolus vulgaris L.) in Mexico and Central America, by consuming the seed as it develops in the immature pod. Resistance to the BPW was identified in bean germplasm of highland Mexican origin, and these sources of resistance were incorporated into a pedigree breeding program to recover locally adapted lines resistant to Bean Common Mosaic Virus and BPW, with commercial grain for Guatemala, Honduras and El Salvador. These lines yielded as well as or better than local cultivars in the absence of the insect, and better than local cultivars when the BPW was present. Resistance appeared to be governed by several genes, and was stable across geographic areas, seasons and planting systems.     

Phenotypic variation within a Hungarian landrace of runner bean (Phaseolus coccineus L.)

Summary A landrace seed lot of runner bean (Phaseolus coccineus L.), obtained from the Budapest region, Hungary, was separated into five seed groups according to seed coat colour. 131 plants were grown randomly, and observed for 27 morphological and physiological characters. The collected data were analysed by ANOVA.Numerical taxonomy of the data employed Principal Components Analysis to generate scatter diagrams and Cluster Analysis to generate dendrograms, both before and after removing data on the four anthocyanin colour characters (seed coat, calyx, stem and flower colour) as these characters are probably controlled by a single major gene. The progenies from the five distinct parental seed groups showed much overlap in characteristics, indicating that they were not distinct lines but comprised a largely panmictic population.Some character associations were detected: plants from white seeds matured significantly later than those from black seeds, plants from white seeds with a few dark spots produced seeds significantly heavier than average, whereas those from white or black seeds produced significantly lighter seeds, although the average seed yield per plant did not differ significatly.     

Interaccession variation of electrophoregrams of cotyledon protein of field bean (Phaseolus vulgaris L.)

Summary Polyacrylamide gel electrophoresis at acidic pH showed substantive qualitative pattern difference among accessions that had been classified into one cultivar by conventional taxonomic procedures.Join publication of Food Science Department, University of Manitoba (No. 109) and Centro Internacional de Agricultura Tropical-CIAT.     

A rapid procedure for screening the resistance of bean cultivars (Phaseolus vulgaris L.) to Botrytis cinerea and Sclerotinia sclerotiorum

Summary A method to inoculate detached bean leaves with Botrytis cinerea or Sclerotinia sclerotiorum without using a carbon-nitrogen source is described. Leaves were incubated in plastic trays that were covered with transparent plastic bags to maintain air humidity above 95%. Spores of either fungus inoculated in water alone were generally unable to cause infection. Additions of KH₂PO₄ (62.5 mM) or of mixtures of inorganic phosphate and glucose (1.1 or 5.5 mM) to the inoculum stimulated fungal pathogenicity. Also spore concentration (2×10⁵ or 2× 10⁶ spores ml^–1) influenced the ability to produce lesions. At 2× 10⁶ spores ml^–1 both fungi were able to infect primary bean leaves when inoculated in an inorganic phosphate solution. These conditions were used for a preliminary screening for resistance of 15 bean cultivars to both fungi. Only partial resistance to the pathogens was found. Since the procedure is simple and does not require blooming plants, it can be rapidly adopted in screening and breeding programs.Abbreviations Pi inorganic phosphate     

Identification of a novel source of resistance to angular leaf spot disease of common bean within the secondary gene pool

Phaeoisariopsis griseola (Sacc.) Ferr., the agent of angular leaf spot disease of common bean, is a highly variable pathogen for which resistance gene diversification is required. This study analysed genetic resistance to this disease within genotypes of three Phaseolus species. Twenty-nine genotypes of Phaseolus vulgaris, Phaseolus coccineus and Phaseolus polyanthus were inoculated with 54 isolates of Phaeoisariopsis griseola. The genetic resistance was estimated according to the symptom intensity observed for each plant genotype-pathogen isolate combination. Globally, genotypes of the common bean secondary gene pool were resistant to a higher number of isolates than common bean varieties. Interactions between plant genotypes and pathogen isolates suggested vertical resistance genes within P. vulgaris, as well as within P. coccineus and P. polyanthus. The ‘NI666’accession (P. coccineus) showed resistance to all the fungal isolates inoculated while the variety ‘Aroana’(P. vulgaris) was susceptible to most of the isolates. Interspecific hybridization between these two genotypes gave F₁ hybrid plants which showed resistance to angular leaf spot disease.     

Yield stability in common bean (Phaseolus vulgaris L.) genotypes

An experiment was undertaken to determine the stability of seed yield in 21 common bean genotypes representing three growth habits. Seven genotypes in each growth habit (determinate bush, indeterminate bush and indeterminate prostrate) were evaluated in replicated trials at three locations for three years under rain fed conditions in Ethiopia. A combined analysis of variance, stability statistics and rank correlations among stability statistics and yield-stability statistic were determined. The genotypes differed significantly for seed yield and genotype × environment (year by location) interaction (GE). The different stability statistics namely Type1, Type 2 and Type 3 measured the different aspects of stability. This was substantiated by rank correlation coefficient. There were strong rank correlations among S_i ²d, W_i ²,σ_i ² and S_i ², where as there was weak correlation between b_iand R_i ², S_i ²d, W_i ², σ_i ² and S_i ². R² was significantly and negatively correlated with W_i ², σ_i ² and S_i ². σ_i ² is significantly correlated with W_i ².Yield is significantly correlated with b_i and R_i ².None of the statistics per se was useful for selecting high yielding and stable genotypes except the YS(yield-stability statistic). Most of the high yielding genotypes were relatively stable. Of the 21 genotypes, only 11genotypes were selected for their high yielding and stable performance. Genotypes with growth habit III and I (in determinate prostrate and determinate bush) were generally more stable than in determinate bush. This revised version was published online in July 2006 with corrections to the Cover Date.