This study examines the potential, magnitude, and causes of enhanced biological N2 fixation (BNF) by common beans (Phaseolus vulgaris L.) through bio-char additions (charcoal, biomass-derived black carbon). Bio-char was added at 0, 30, 60, and 90 g kg−1 soil, and BNF was determined using the isotope dilution method after adding 15N-enriched ammonium sulfate to a Typic Haplustox cropped to a potentially nodulating bean variety (CIAT BAT 477) in comparison to its non-nodulating isoline (BAT 477NN), both inoculated with effective Rhizobium strains. The proportion of fixed N increased from 50% without bio-char additions to 72% with 90 g kg−1 bio-char added. While total N derived from the atmosphere (NdfA) significantly increased by 49 and 78% with 30 and 60 g kg−1 bio-char added to soil, respectively, NdfA decreased to 30% above the control with 90 g kg−1 due to low total biomass production and N uptake. The primary reason for the higher BNF with bio-char additions was the greater B and Mo availability, whereas greater K, Ca, and P availability, as well as higher pH and lower N availability and Al saturation, may have contributed to a lesser extent. Enhanced mycorrhizal infections of roots were not found to contribute to better nutrient uptake and BNF. Bean yield increased by 46% and biomass production by 39% over the control at 90 and 60 g kg−1 bio-char, respectively. However, biomass production and total N uptake decreased when bio-char applications were increased to 90 g kg−1. Soil N uptake by N-fixing beans decreased by 14, 17, and 50% when 30, 60, and 90 g kg−1 bio-char were added to soil, whereas the C/N ratios increased from 16 to 23.7, 28, and 35, respectively. Results demonstrate the potential of bio-char applications to improve N input into agroecosystems while pointing out the needs for long-term field studies to better understand the effects of bio-char on BNF.

http://www.css.cornell.edu/faculty/lehmann/publ/BiolFertSoils%2043,%20699-708,%202007%20Rondon.pdf

Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions

Breeding for resistance to biotic and abiotic stresses of global importance in common bean is reviewed with emphasis on development and application of marker-assisted selection (MAS). The implementation and adoption of MAS in breeding for disease resistance is advanced compared to the implementation of MAS for insect and abiotic stress resistance. Highlighted examples of breeding in common bean using molecular markers reveal the role and success of MAS in gene pyramiding, rapidly deploying resistance genes via marker-assisted backcrossing, enabling simpler detection and selection of resistance genes in absence of the pathogen, and contributing to simplified breeding of complex traits by detection and indirect selection of quantitative trait loci (QTL) with major effects. The current status of MAS in breeding for resistance to angular leaf spot, anthracnose, Bean common mosaic and Bean common mosaic necrosis viruses, Beet curly top virus, Bean golden yellow mosaic virus, common bacterial blight, halo bacterial blight, rust, root rots, and white mold is reviewed in detail. Cumulative mapping of disease resistance traits has revealed new resistance gene clusters while adding to others, and reinforces the co-location of QTL conditioning resistance with specific resistance genes and defense-related genes. Breeding for resistance to insect pests is updated for bean pod weevil (Apion), bruchid seed weevils, leafhopper, thrips, bean fly, and whitefly, including the use of arcelin proteins as selectable markers for resistance to bruchid seed weevils. Breeding for resistance to abiotic stresses concentrates on drought, low soil phosphorus, and improved symbiotic nitrogen fixation. The combination of root growth and morphology traits, phosphorus uptake mechanisms, root acid exudation, and other traits in alleviating phosphorus deficiency, and identification of numerous QTL of relatively minor effect associated with each trait, reveals the complexity to be addressed in breeding for abiotic stress resistance in common bean.

Common bean breeding for resistance against biotic and abiotic stresses: From classical to MAS breeding

Evolutionary aspects of the trade-off between seed size and number in crops

Knowledge, access, and use of diversity available in cultivated and wild relatives are essential for broadening the genetic base of cultivars to sustain improvement. My objectives are to review briefly the origin, domestication, and organization of genetic diversity in Phaseolus beans, highlight production problems and traits deficient in the common bean (P. vulgaris L.) cultivars, cite sources of useful gemplasm, and review progress achieved in broadening the genetic base of cultivars. Phaseolus beans originated in the Americas. Only five species, P. acutifolius A. Gray, P. coccineus L., P. lunatus L., P. polyanthus Greenman, and P. vulgaris L. were domesticated. The interspecies diversity in relation to common bean is organized in primary, secondary, tertiary, and quaternary gene pools. Intraspecies diversity in common bean is separated into two major gene pools (Andean and Middle American). Cultivars are further divided into races, each with their distinguishing characteristics. Also, cultivars of dry seed and snap bean exist. Abiotic and biotic stresses limit common bean production. The genetic base of cultivars within market classes is narrow and inadequate level of resistance to common bacterial blight [caused by Xanthomonas campestris pv. phaseoli (Smith) Dye] and white mold [caused by Sclerotinia sclerotiorum (Lib) de Bary] exist in cultivars. High levels of resistance to these and other desirable traits exist in the relatives and gene pools of P. vulgaris. Early maturity, adaptation to higher latitude, upright plant type, high pod quality and seed yield, and resistance to Bean common mosaic virus (a potyvirus) andlor rust [caused by Uromyces appendiculatus (Pers.:Pers.) Unger] have been bred into cultivars. However, most of the genetic variability available in the common bean races, gene pools, and wild relatives remains to be utilized. To maximize and sustain bean production, high yielding, high quality cultivars that are less dependent on water, fertilizer, pesticides, and manual labor should be developed. This need warrants sustained, comprehensive, and integrated genetic improvement, in which favorable alleles from cultivated and wild relatives are accumulated in superior cultivars. A three-tiered breeding approach involving:(i) gene introgression from alien germplasm, (ii) pyramiding favorable alleles from different sources, and (iii) simultaneous improvement of multiple traits for common bean cultivars would be the most appropriate strategies to meet theses needs.

/pdf/broadening-the-genetic-base-of-common-bean-cultivars-2hhrt8jd18.pdf

Broadening the Genetic Base of Common Bean Cultivars

An estimated 60% of common bean (Phaseolus vulgaris L.) production worldwide is at risk of drought. A breeding program was developed at the International Center of Tropical Agriculture (CIAT) to create drought resistant breeding lines with varietal potential in the small red, small black, cream (mulatinho) and cream-striped (carioca) grain classes. Breeding populations were created from triple or double crosses. Field screening under terminal drought was performed at Palmira, Colombia in the dry season in F 2 , F 3:5 , and F 6:8 generations over two cycles of recurrent selection in the small red and small black classes, and one cycle in the mulatinho and carioca classes. Drought resistant lines yielded significantly more than commercial check cultivars under drought in all color classes. Some outyielded the respective checks by 15 to 25% (depending on color class and trial) in one or more of three favorable environments, or in the combined analysis across favorable environments, and were also earlier to mature. Drought resistant lines presented up to 36% greater yield d -1 in favorable environments. Some also expressed superior yields in a phosphorus-limited environment. Thus, selection for drought resistance has improved yield potential and plant efficiency across different environments. It is suggested that selection under drought stress reveals genes that correct inefficiencies inherited from the wild Phaseolus vulgaris, and are key to yield improvement of common bean.

Selection for Drought Resistance in Common Bean Also Improves Yield in Phosphorus Limited and Favorable Environments

Common bean (Phaseolus vulgaris L.) is highly susceptible to common bacterial blight (CBB), caused by Xanthomonas campestris pv. phaseoli (Smith) Dye. High levels of cultivar resistance would minimize yield losses, reduce bactericide use and production costs, and facilitate integrated disease-and-crop management and the production and distribution of pathogen-free seed. We aimed to (i) assess the levels of CBB resistance of different Phaseolus species in the tropics, (ii) determine the CBB reaction of resistant cultivars and advanced breeding lines, and (iii) report on CBB resistance of lines developed from P. vulgaris × P. acutifolius (tepary bean) hybridization and gene pyramiding at CIAT. Between 1994 and 1998, we evaluated, in the field, 162 accessions of tepary, scarlet runner (P. coccineus), lima (P. lunatus), and common beans, 119 CBB-resistant cultivars and advanced breeding lines of common bean, and six lines recently developed by interspecific hybridization and gene pyramiding. For inoculation, we used aspersion, surgical blades, and/or multiple needles. The highest levels (scores of 1.2-2.0) of CBB resistance were found in P. acutifolius accessions, G40029 and G40156, followed by P. lunatus (scores of 4.2-6.2), P. coccineus (scores of 4.8-5.5), and P. vulgaris (scores of 4.5-6.4). Resistance available in P. coccineus and P. vulgaris landraces has already been transferred to common bean. But resistance transferred from P. acutifolius was much lower (scores of 3.8-4.5) than those available. Gene pyramiding produced lines with high CBB resistance (scores of 1.5-2.4), and is thus, a suitable method for developing CBB-resistant cultivars of different market classes.

Resistance to Common Bacterial Blight amongPhaseolus Species and Common Bean Improvement

Seed yield of common bean (Phaseolus vulgaris L.) can be improved by exploiting the genetic variability available in the crop's cultivated races and gene pools. The objectives of this study were to (i) compare yield gains obtained through two cycles of recurrent selection, based on S 1 family tests, in two types of populations [interracial Middle American (MA) and inter-gene-pool Andean × Middle American (AMA)], and (ii) estimate genetic variance, heritability, and expected gains from selection. The MA population comprised 11 parents from race Mesoamerica, three from Jalisco (Mexico), and two from Durango (Mexico). The AMA population had six parents from race Mesoamerica, one from Jalisco, five from Nueva Granada (northern Andes), and two from Chile (also Andean). From the initial cycle (C 1 ) of each population, 45 S 2 families were evaluated at three locations in Colombia in 1992 to select the 10 highest yielding families to be intermated in a diallel fashion (excluding reciprocals) to generate 45 S 1 families for cyde 1 (C 1 ). Similarly, 45 S 1 families from C 1 and cycle 2 (C 2 ) were evaluated in 1993 and 1995, respectively. The 10 highest yielding selected families from each of C 0 , C 1 , and C 2 and a corresponding bulk of all 45 S 1 families from each of the three cycles were evaluated at three sites in 1997. Data were recorded for seed yield, seed weight, and maturity. Genetic variance among 45 S 1 families in C 1 and C 2 was greater in the AMA population than in the MA, diminishing from C 1 to C 2 in MA and increasing in AMA. Heritability for seed yield ranged from 0.31 to 0.46, for seed weight from 0.75 to 0.86, and for maturity from 0.50 to 0.81. Expected gains from selection for seed yield was lower (3-4%) in C 2 compared with C 1 (7.9-13.2.%). The mean yields of C 0 , C 1 , and C 2 of the MA were significantly (P < 0.05) higher than those of the AMA. The C 2 of both MA and AMA out yielded their respective C 1 and C 0 families. The average realized yield gain per selection cyde was 15% or higher in both populations. These results justify the use of recurrent selection in interracial and inter-gene-pool populations for improving seed yield of common bean.

Two Cycles of Recurrent Selection for Seed Yield in Common Bean

Registration of Common Bacterial Blight Resistant Dry Bean Germplasm VAX 1, VAX 3, and VAX 4

Soil mineral defidendes or toxicities adversely affect common bean (Phaseolus vulgaris L.) production worldwide. Cultivars tolerant to low soil fertility (LF) should support sustainable farming systems and reduce production costs and farmers' dependence on fertilizes Our objective was to identify LF tolerant landraces and improved common bean genotypes. We systematically screened 5000 to 5500 landraces and improved genotypes for LF tolerance at Popayan and Quilichao, Colombia, between 1978 and 1998. Mean LF intensity index across locations for seed yield ranged from 0.35 to 0.68. Average seed yield reduction over five cropping seasons was 53%. Seed yield, biomass, and HI were positively associated in LF and high soil fertility (HF). LF tolerance was identified in eight landraces and 14 improved genotypes. All landraces were from Middle America (MA), belonging to common bean races Durango, Jalisco, and Mesoamerica. All improved genotypes except one (A 36) also possessed characteristics of and involved one or more LF tolerant MA landraces in their pedigree. There was considerable variation for seed, plant, and maturity characteristics among LF tolerant genotypes. In LF, mean seed yield for landraces ranged from 856 kg ha -1 for 'Apetito' to 332 kg ha -1 for G 19833. Among improved genotypes, A 774 had the highest (948 kg ha -1 ) and CAP 4 the lowest (651 kg ha -1 ) seed yield. Reduction in seed yield due to LF ranged from 31% for A 36 to 63% for CAP 4. All landraces and seven improved genotypes had either a below average or average LF susceptibility index. Use of these LF tolerant landraces and improved genotypes should be maximized in breeding and genetic studies to enhance sustainable farming systems.

http://ciat-library.ciat.cgiar.org/articulos_ciat/singh2003.pdf

Low soil fertility tolerance in landraces and improved common bean genotypes

The inheritance of resistance to bean golden yellow mosaic virus (BGYMV) was studied in common beans (Phaseolus vulgaris L.). The original cross was made between breeding line PR9556-158, which produces deformed pods when infected with BGYMV, and PR9556-171, which has normal pod development when inoculated with the virus. Pod type was evaluated on plants from six generations (parental lines, F1, F2, F2:3, F3:4, and backcrosses of the F1 to both parents) at mid-pod fi ll (R8), ≈65 days after planting. The segregation patterns from the F2, F2:3, F3:4, and backcross populations were consistent with the hypothesis that a single dominant gene confers normal pod development in PR9556-171. When inoculated with BGYMV, the deformed pods of PR9556-158 produced fewer seeds per pod than PR9556-171, resulting in lower seed yield. The gene symbol Bgp-1 has been assigned for this dominant resistance gene that controls the normal pod reaction to BGYMV in common bean.

/pdf/inheritance-of-normal-pod-development-in-bean-golden-yellow-5addtb05b8.pdf

Carlos German Muñoz

Papers

Resistance to Common Bacterial Blight amongPhaseolus Species and Common Bean Improvement

Two Cycles of Recurrent Selection for Seed Yield in Common Bean

Registration of Common Bacterial Blight Resistant Dry Bean Germplasm VAX 1, VAX 3, and VAX 4

Low soil fertility tolerance in landraces and improved common bean genotypes

Inheritance of Normal Pod Development in Bean Golden Yellow Mosaic Resistant Common Bean