**1. Introduction**

The *Fusarium* genus includes several fungi species considered as the most important soil and seedborne pathogens causing plant diseases with high yield, quality and economic impact in several food and cash crops sown in the highlands of México [1]. The main effect of the *Fusarium* genus is the root and crown rot observed in vascular bundles of common bean (*Phaseolus vulgaris* L.), chili pepper (*Capsicum annuum* L.), maize (*Zea mays* L.) and other crops used as food, fodder and to obtain cash for urgent expenditures by the poor farmers in Northern México [2]. The main *Fusarium* symptoms in the plants are observed at the soil surface or

below the ground including damage in root crown and embryonic root, losses of root water-absorbing surface, leaf wilting and plant death [3, 4]. As a result, low plant densities are commonly observed in common bean and chili commercial plantings in most of the producing areas of Northern México [5, 6].

Under rainfed conditions losses in plant population are aggravated in years registering drought stress [7] after the common bean seedlings emergence. Plant losses are also observed under irrigation [8] when high temperatures and fast drying of the soil surface are registered, mainly after plant emergence (V1) and the primary leaves unfolded (V2) stages in common beans [9] and the second week after chili seedlings transplant in cultivated soil. Under those conditions, no post-embryonic adventitious root growth and plant death are observed due to severe damage in the embryonic root caused by the fungi complex (*Fusarium* spp., *Rhizoctonia* spp., and *Pythium* spp.) [10].

Plant losses in the early stages of growth in common bean and chili are considered one of the main causes of reducing yield and the quality of the commercial product (seed and chili pepper: fresh, dried, or processed fruits) [5, 11–13]. Decrement of the income is also observed by farmers, considering that low-input agriculture is the best option for reducing risks in crop production thus obtaining low yields. The actual measurement of the incidence and severity levels of plant pathogens causing root and crown rot, as well as diseases in the aerial plant organs is necessary to establish control strategies according to agroecological and sustainable agriculture. Identification of plant disease agents is the key to the development of effective control and management strategies [14]. Actual evaluation of disease problems related to the *Fusarium* genus in the state of Durango was included in this study regarding the importance of common bean and chili peppers as important food-producing crops.

### **2. Common bean**

Common bean is an important cash crop used as a food, nitrogen-fixing plant and organic matter source [15], thus helping to reach sustainability in the agriculture performed under drought-prone and irrigated areas in the Mexican highlands of Northern México, including the states of Zacatecas, Durango and Chihuahua. In this area near 1.6 million of hectares are annually sown and more than 1.0 million of tons of grain are produced, at a rate of 0.69 t ha−1 [16]. Common bean cultivars Pinto Saltillo (improved) and Negro San Luis (landrace) are the most important varieties, according to the planted area and grain volume produced. Sowing recommendations include 35 to 50 kg ha−1 of seed [17] to obtain plant densities ranging from 100,000 to 120,000 plants ha−1. In despite of recommendations low plant densities (<80,000 plants ha−1) are very common in commercial plantings through the common bean-producing areas of Northern México, thus lower seed yield is also observed across locations and years [2].

Reduction in plant densities reached values lower than 20% of the recommended levels, and the lowest levels (12,500 plants ha−1) were related to the lowest seed yield [5]. Plant densities reduction in early stages of crop growth were related to the low seeding rates, mechanical soil impedance and seedlings death caused by the fungi complex including *Fusarium solani* f. sp. *phaseoli*. Identification and predominance studies of pathogenic fungi are important to establish control strategies to reduce disease problems. Studies on fungi genetic and pathogenic diversity are also important for efficient disease control in several crop-producing areas of Northern México. Several strategies were used for fungal disease control including

crop genetic breeding, crop rotation and other modern agroecological and chemical management technologies.
