**2.2. Reactions of common bean germplasm to root rot pathogens under field conditions**

Previous works indicated us that soils of Chapingo and Sandovales are highly, naturally and homogeneously infested in most cases by FSP [12, 13]. We divided the characterizations into two groups.

The first group included 6 (experiment I), 75 (experiment II) and 36 (experiment III) (**Table 1**) common bean genotypes under rainfall conditions at Sandovales, Aguascalientes. Experiments were established on June 27 (E-I and E-II) and July 11 (E-III), 2002 under randomized complete block (RCB) design with four replications (E-I), where experimental unit was three rows 5 m-length. The germplasm of E-II was divided into three groups based on color seed coat: 25 pinto seed-type bean genotypes, 25 Flor de Mayo seed-type and 20 black seed beans. Each group of genotypes was randomized in a RCB design with three replications, and where experimental unit was two rows 6 m-length. Finally, germplasm in E-III was randomized on 6×6 lattice design with three replications and experimental unit of 2 rows 6 m in length.

In the second group of experiments, 49 common bean genotypes (**Table 1**) were evaluated under two levels of soil moisture: irrigated and rainfed conditions. Germplasm was randomized in 7 × 7 lattice design with four replications. Two replications were carried out under irrigated conditions, while the other two under rainfed conditions (irrigation was stopped when the most of germplasm initiated flowering and no irrigation was supplied until harvest). Experiments were established in Sandovales and Chapingo, México.

In both groups of experiments, FSP root rot severity ratings were determined at 28 and 56 days after sowing. Five plants were randomly picked off from each experimental unit and damage was evaluated by using the scale described by Abawi and Pastor-Corrales [6]. The scale has nine degrees of damage (1–9) where 1 = no symptoms and 9 = more than 75% of root or stem tissues infected by the pathogen. We took the values 1–3 as a reaction of resistance, while

values of 4–9 indicated susceptibility. Plants were analyzed at laboratory in order to ratify the infection by FSP [11]. Days to flowering and to maturity were registered in each experimental unit in all experiments, and grain yield (kg h−1) registered after physiological maturity.

Data were subjected to analysis of variance (ANOVA). When ANOVA detected significant (P < 0.05) differences among treatments, Tukey significant difference values (Tukey LSD, P = 0.05) were calculated for mean comparisons. Statistical analysis was performed using

We selected two common bean genotypes based on their contrasting reaction to FSP under both controlled and field conditions: BAT 477 (resistant) and Pinto UI-114 (susceptible). Crosses between the two parents were carried out under greenhouse conditions at Chapingo,

of México. Reactions to a highly virulent isolate of FSP were measured in F9:10 recombinant inbred lines [3]. A genetic linkage map was built with genotypic data obtained with 30 + 3/+3 AFLP. QTLs associated with resistance to FSP were identified using R software ver. 2.10.1

Nineteen isolates of *Fusarium* were obtained from different locations of Aguascalientes, although most of them were collected in Pabellón. Ten isolates were FSP and the other nine were *F. oxysporum* f. sp. *phaseoli* (FOP). As controls, isolates from Guanajuato, México and Veracruz were included. FSP and FOP isolates showed a great variability on morphology (**Figure 1**). Most of the isolates showed radial growth of colony, purple color of colony and variation on mycelial production and conidia size and shapes (**Table 2**). Most of the common bean cultivars were susceptible to most of FSP isolates, mainly those from Mesoamerican genetic race. AFLP molecular markers clearly separated FSP isolates from FOP isolates, but pathogenicity patterns were not associated with *Fusarium* species

Significant differences were found in morphology, pathogenicity and AFLP genotype among isolates. Isolates from Veracruz, Guanajuato and Aguascalientes grew faster *in vitro* than those from México and showed the largest conidia. The most pathogenic isolates were from Aguascalientes and Mexico. Bean cultivars with Flor de Mayo (Jalisco race) and Pinto (Durango race) seed coat showed the highest frequencies of resistance to the most of FSP isolates (**Table 2**). Isolates from the State of Mexico were genetically different from the other

seeds were obtained in successive sowings in different locations

Analysis of *Fusarium*-Common Beans Pathosystem in Aguascalientes, Mexico

http://dx.doi.org/10.5772/intechopen.72875

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Statistical Analysis System version 6.12 and Statistica version 6.0 for Windows.

**2.3. Genetic basis of resistance to root rot pathogens in selected common bean** 

**cultivars**

[14, 15].

**3. Results**

(**Table 3**) [11].

México during 2002. F1

to F<sup>8</sup>

**3.1. Variability of FSP isolates from Aguascalientes, México**

isolates with genetic dissimilarity of >9% [4].


Prefix indicates seed coat color or commercial type: PT = 'Pinto', AZ = 'Azufrado' (Yellow), FM = 'Flor de Mayo', BY = 'Bayo' (Cream or beige), FJ = 'Flor de Junio' and NG = Black.

**Table 1.** Germplasm included on field experiments at Sandovales and Chapingo, México.

values of 4–9 indicated susceptibility. Plants were analyzed at laboratory in order to ratify the infection by FSP [11]. Days to flowering and to maturity were registered in each experimental unit in all experiments, and grain yield (kg h−1) registered after physiological maturity.

Data were subjected to analysis of variance (ANOVA). When ANOVA detected significant (P < 0.05) differences among treatments, Tukey significant difference values (Tukey LSD, P = 0.05) were calculated for mean comparisons. Statistical analysis was performed using Statistical Analysis System version 6.12 and Statistica version 6.0 for Windows.
