**1. Introduction**

The maize (*Zea mays* L.) is a native crop of Mexico adapted to the most diverse environmental conditions; planted around the country in altitudes ranging from sea level to altitudes

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greater than 2550 m. In Mexico, 78.3% of the maize production is sown under rain-fed conditions, mainly with native (landrace) adapted varieties [1]. Those varieties are usually grown in non-optimum agronomic conditions, therefore they are adapted to variable rainfall, and are in some extent, tolerant to biotic and abiotic stresses. These varieties are available to the farmers for sowing, due to their flexible response to adverse situations, and are frequently used for seed exchange among farmers, within the same community or with other communities. In the Coahuila state, 24,900 ha of maize for grain production were sown during 2016, 84.7% was sown in the southeast region, mainly with local adapted populations (landrace populations), and 94.8% of these were sown under rain-fed conditions [1]. Typically, the native maize production is mainly for local consumption, both human and livestock as forage.

The maize (*Z. mays* L.) is a native crop of Mexico, and it is the place where the highest genetic diversity is found. This crop is adapted to the most diverse environmental conditions; thus, the specific local adapted populations (landrace) have been developed, with particular attributes that differentiate each other, within and among regions, circumstances that make possible to recognize Mexico as center of origin and diversification [7]. Commonly, the maize diversity has been described by the racial classification approach, which allowed to identify the first 25 races of maize in Mexico, based on morphological data (plant, ear, and tassel) [8]. In the region of study, the maize diversity has been documented by the presence of representative race populations in Coahuila state, such as Tuxpeño [8], Raton and Tuxpeño Norteño [9], Celaya, Conico Norteño, Elotes Conicos, and Olotillo [10]. A case study carried out in native populations from Coahuila State in Mexico, indicated that genetic diversity shows a continuous pattern among racial complexes, and is associated to the altitudinal and

Genetic Potential and Usefulness of Native Maize Populations in Developing Novel Germplasm…

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In this section, several quantitative traits of the ear and grain were considered to analyze the maize genetic diversity and the relationship among local populations within the southeast region of the Coahuila state in Mexico. The racial classifications and relationship among the native adapted populations (landraces) were studied with a sample of 77 maize populations that were collected in the region from altitudes ranged from 774 to 2557 masl. A total of 51 of these populations were collected in 2008 [10] and 26 during 2010 (unpublished data), which

Sample sizes of 10 representative ears were first used for a visual classification of the maize populations based on the primary race classification [8]. In addition to the race classification, a set of quantitative traits from the ear and grain were used to analyze the relationship among the native maize populations. Several authors have emphasized that the reproductive organ traits such as the ear traits, are the most useful for race classification in maize [12, 13]. Thus, eight racial complexes were identified: Celaya, Conico Norteño, Elotes Conicos, Elotes Occidentales, Olotillo, Raton, Tuxpeño, and Tuxpeño Norteño. At the same time, maize populations were grouped by an altitudinal stratum: lowland (0–1000 m), intermediate (1001–1800 m), transition

Ten quantitative ear and grain traits were obtained from the collected sample to analyze the maize diversity. Five ear traits: ear and cob diameter (EAR\_DIAM, COB\_DIAM) (cm), ear length (EAR\_LENG) (cm), ear rows (EAR\_ROWS), shelling percent (SHELL\_PCT), and five kernel traits: Kernel measurements such as kernel length (KER\_LENG), width (KER\_WIDTH) and thickness (KER\_THICK) (mm), kernel per row (KER\_PER\_ROW), weight of 100 dry kernel (WT\_100\_KER) (g) [14]. Data were explored by the analysis of variance to test adaptation groups and racial complexes differences. In both cases, populations within groups and populations within races were analyzed using the PROC GLM procedure of SAS [15]. Data means were used to explore maize

diversity by principal component analysis using the quantitative traits as testers [16].

ecological regions [11].

**2.1. Relationship among local populations**

represents the maize genetic diversity in the region of study.

(1801–2000 m), and highland (above 2000 m) (**Table 1**).

The area of study is located in the southeast of the Coahuila state in Mexico, and it is represented by five counties (Arteaga, General Cepeda, Parras, Ramos Arizpe, and Saltillo). Coahuila state is situated in the central part of the North of Mexico, with a territorial area of 151,571 km2 . The climate in the state is dry to very dry, semi warm (75% of total area), average temperature ranging from 18 to 20°C; annual average precipitation of 316 mm. Based on the environmental conditions, the region of study is considered as critical, determined by an average annual precipitation ranging between 350 and 450 mm; average temperature of 16.8°C; with presence of drought and frost seasons in the year. Moreover, to the environmental and ecological conditions in the region, the maize diversity is determined by the adaptation, and genetic combinations among race complexes allowed by seed exchange within and among different communities [2, 3].

Exploring and understanding the genetic potential of adapted cultivars on traits of interest may determine and guide further research for a particular environment or crop system, as well as the efficient use of both economic and human resources. Thus, the objectives of research work were to describe the regional maize genetic diversity, determine the genetic potential of locally adapted maize populations and to identify strategies for crop improvement to resolve current and future aims.
