**2. Materials and methods**

Despite the states of Aguascalientes and México, other states do not outstand as bean producers in México that three Mexican northern states (Chihuahua, Zacatecas and Durango) produce 60% of common beans at country while other four southern states (Chiapas, Oaxaca, Veracruz and Puebla) produce 20%, and both groups produce 80% of total beans in Mexico, they are considered by Mexican bean breeders as good locations for germplasm evaluation and/or selection for resistance to drought stress and root rot diseases caused by *Fusarium* sp., *Rhizoctonia solani* and *Pythium* sp., among other diseases such as common blight (*Xanthomonas axonopodis* pv. *phaseoli*) and anthracnose (*Glomerella lindemuthiana*) [8, 9].

Field trials included in this report were conducted in one location of the State of Aguascalientes: Sandovales and one from the State of México: Chapingo. Sandovales is located at 22°09′N, 102°18′W, and 2000 m above sea level and shows dry land conditions with summer rainfall. Annual average precipitations range from 350 to 400 mm, with average temperature ranges from 12 to 18°C. Chapingo is located at 19°28′N, 98°52′W; 2250 m above sea level and has a temperate climate with fresh summer and low variable temperatures (15–18°C) and the annual average precipitations range from 600 to 700 mm [10].

#### **2.1. Variability of FSP isolates from Aguascalientes, México**

of 690 kg ha−1 was reported [1]. Grain yields of common bean in México are low since potential yields are estimated to be ≈3 t h−1. Several factors such as biotic (diseases, insect pest, weeds) and abiotic (drought, freeze, low-fertility soils, high temperatures, salinity) stresses reduce common bean production [2]. Drought stress and root rots caused by *Fusarium solani* f. sp. *phaseoli* (FSP), alone or combined, affect bean grain yield in major regions producing common beans in México. Both stresses reduce grain yields due to increase the percentages of seedling death and, consequently, reduce the crop standing (root rots) or reduce growth and develop-

102 Fusarium - Plant Diseases, Pathogen Diversity, Genetic Diversity, Resistance and Molecular Markers

Grain yield reductions decrease crop profits. More than 70% of common bean growers use low inputs for production, or in some cases, common bean is a subsistence crop. We consider that production of common bean germplasm with combined resistance to drought stress and diseases could be an appropriate strategy for grain yield improvement because it is a cheap, sustainable and durable strategy for grain yield stabilization [5]. The control of major root rot pathogens includes chemical, cultural and biological strategies, but most of them are not enough efficient to control pathogens or they have poor possibilities to be applied under

Mexican common bean breeding programs need the former analysis of plant-pathogen pathosystem to perform the selection of those genotypes with improved resistance to root rot pathogens and the best environmental adaptation. Another challenge is the characterization of pathogenic variability of root rot pathogen populations to identify molecular genetic factors of parasitic capability of the pathogen, since these characteristics affect the variation on reactions of common bean germplasm to the fungus. Then, the development of molecular marker technologies to improve the evaluation and selection of resistant common bean germ-

This research includes three objectives: (1) to characterize the genetic variability patterns of *Fusarium* isolates from Aguascalientes and other regions of México; (2) to assess the reactions of each root rot pathogen in *Phaseolus* sp. germplasm under field and controlled conditions and (3) to define the genetic basis of resistance to each root rot pathogen in common

Despite the states of Aguascalientes and México, other states do not outstand as bean producers in México that three Mexican northern states (Chihuahua, Zacatecas and Durango) produce 60% of common beans at country while other four southern states (Chiapas, Oaxaca, Veracruz and Puebla) produce 20%, and both groups produce 80% of total beans in Mexico, they are considered by Mexican bean breeders as good locations for germplasm evaluation and/or selection for resistance to drought stress and root rot diseases caused by *Fusarium* sp., *Rhizoctonia solani* and *Pythium* sp., among other diseases such as common blight (*Xanthomonas* 

*axonopodis* pv. *phaseoli*) and anthracnose (*Glomerella lindemuthiana*) [8, 9].

ment and seed production (water deficits) [3, 4].

Mexican bean grower conditions because they are expensive [6].

plasm under marker-assisted selection strategy is needed [7].

beans.

**2. Materials and methods**

The procedures for *Fusarium* isolates characterization by using *in vitro*, pathogenicity and AFLP genotype strategies were described when we analyzed the isolates from the State of Aguascalientes [11] and Aguascalientes, México, Guanajuato and Veracruz [4].
