**2.1. Relationship among local populations**

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

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

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

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 improve-

In any crop system, the genetic diversity is determined—among other factors—by the use of diverse types of local varieties. Conceptually, two types of genetic materials are commonly developed, those obtained from preferences (color, flavors, crop type, etc.) and those selected for adaptability to biotic or abiotic micro-environments [4]. In addition to the native population for a particular environment, maize genetic diversity is associate to other factors that may change the genetic structure in a population such as the seed exchange among farmers within a community or among different communities, and, depending on the migration index and introgression of foreign germplasm, would contribute to the genetic variation in a native

. The climate in the state is dry to very dry, semi warm (75% of total area), average

forage.

151,571 km2

different communities [2, 3].

100 Rediscovery of Landraces as a Resource for the Future

population [5, 6].

ment to resolve current and future aims.

**2. Regional maize genetic diversity**

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 represents the maize genetic diversity in the region of study.

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

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].


**Table 1.** Racial classification of local native populations from the Southeast of Coahuila State in Mexico.

The races Conico Norteño and Elotes Conicos (the ear conical type) are adapted from the transition to the highland areas, in altitudes above 1700 m; whereas, Raton, Tuxpeño, and Tuxpeño Norteño (the ear cylindrical type), the adaptation area is widely: Raton (84–1300 m), Tuxpeño (0–1950 m), and Tuxpeño Norteño (1400–1701) [17]. The maize diversity in the Coahuila state is represented mainly by three racial complexes: Conico Norteño, Raton, and Tuxpeño Norteño [10].

The eight racial complexes and the four adaptation groups were statistically different (P ≤ 0.01) for most traits, indicating relative differences among the race type and the adaptation of landrace populations in the region; the populations within racial complexes and populations within adaptation groups were significant (P ≤ 0.01), indicating the variation associated within race groups, the genetic combination among populations and race complexes (**Table 1**), and the specific adaptation to the different ecological environments within the region.

The scatter plot of the interaction among the 77 native maize populations with the 10 quantitative traits is presented in **Figure 1**.

Dispersion in **Figure 1** shows the identification of two main groups: the group of maize populations with the conical ear type (transition and highland altitudes) and those with the cylindrical ear type (lowland to intermediate altitudes) (**Table 1**). This indicates the usefulness of the ear and grain traits in exploring the association among maize populations as suggested by [12, 13]. The continuous pattern among the different races within the two main groups is explained by the adaptation of the local populations (**Table 1**), and the genetic combination among races as a consequence of seed exchange by farmers within the community and with other communities [5, 6]. The seed exchange among farmers is a common practice in the area of study, is evident by the presence of some maize populations located at a different adaptation area (**Table 1**), explained by the genetic combinations among different races, and further adaptation to micro-environments as was verified in

**Figure 1.** Scatter plot of the first two principal component scores showing the dispersion of the 77 maize populations and relationship among traits. Populations are identified by the population number and combinations of letters that indicate the race classification: C = Celaya; CN = Conico Norteño; EC = Elotes Conicos; EC = Elotes Occidentales; O = Olotillo;

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

http://dx.doi.org/10.5772/intechopen.71360

103

several regional studies [3, 11].

R = Raton; T = Tuxpeño; and TN = Tuxpeño Norteño.

The maize populations and the traits studied are all distributed along **Figure 1**, where individual points (maize population or traits) reached a vector from the origin indicates the joint association that makes the distinctions among maize populations and the relationship with the associated traits. The group of populations indicated by the dashed oval corresponds to the Conico Norteño and Elotes Conicos, two races adapted to highland altitude, characterized by a conical ear type. Populations outside the oval show the cylindrical ear type represented mainly by the races Raton, Tuxpeño, and Tuxpeño Norteño (**Table 1**). By the exploration of dispersion of these population × racial groups in **Figure 1**, it is possible to detect a continuous pattern among the races Raton and Tuxpeño Norteño. Similar genetic variation pattern was found among racial groups through the landraces analyses in the state of Coahuila [11].

Genetic Potential and Usefulness of Native Maize Populations in Developing Novel Germplasm… http://dx.doi.org/10.5772/intechopen.71360 103

The races Conico Norteño and Elotes Conicos (the ear conical type) are adapted from the transition to the highland areas, in altitudes above 1700 m; whereas, Raton, Tuxpeño, and Tuxpeño Norteño (the ear cylindrical type), the adaptation area is widely: Raton (84–1300 m), Tuxpeño (0–1950 m), and Tuxpeño Norteño (1400–1701) [17]. The maize diversity in the Coahuila state is represented mainly by three racial complexes: Conico Norteño, Raton, and

**Table 1.** Racial classification of local native populations from the Southeast of Coahuila State in Mexico.

**Intermediate (1001–1800)**

Celaya C 4 4 Cónico Norteño CN 3 8 23 34 Elotes Cónicos EC 1 1 1 3 Elotes Occidentales EO 2 2 Olotillo O 1 1 Ratón R 4 16 1 21 Tuxpeño T 1 1 Tuxpeño Norteño TN 1 9 1 11 Total 5 37 11 24 77

**Transition (1801–2000)** **Highland (>2000)**

**Total**

The eight racial complexes and the four adaptation groups were statistically different (P ≤ 0.01) for most traits, indicating relative differences among the race type and the adaptation of landrace populations in the region; the populations within racial complexes and populations within adaptation groups were significant (P ≤ 0.01), indicating the variation associated within race groups, the genetic combination among populations and race complexes (**Table 1**), and

The scatter plot of the interaction among the 77 native maize populations with the 10 quantita-

The maize populations and the traits studied are all distributed along **Figure 1**, where individual points (maize population or traits) reached a vector from the origin indicates the joint association that makes the distinctions among maize populations and the relationship with the associated traits. The group of populations indicated by the dashed oval corresponds to the Conico Norteño and Elotes Conicos, two races adapted to highland altitude, characterized by a conical ear type. Populations outside the oval show the cylindrical ear type represented mainly by the races Raton, Tuxpeño, and Tuxpeño Norteño (**Table 1**). By the exploration of dispersion of these population × racial groups in **Figure 1**, it is possible to detect a continuous pattern among the races Raton and Tuxpeño Norteño. Similar genetic variation pattern was found among racial groups through the landraces analyses in the state of Coahuila [11].

the specific adaptation to the different ecological environments within the region.

Tuxpeño Norteño [10].

tive traits is presented in **Figure 1**.

**Race classification Race ID Lowland** 

102 Rediscovery of Landraces as a Resource for the Future

**(<1000)**

**Figure 1.** Scatter plot of the first two principal component scores showing the dispersion of the 77 maize populations and relationship among traits. Populations are identified by the population number and combinations of letters that indicate the race classification: C = Celaya; CN = Conico Norteño; EC = Elotes Conicos; EC = Elotes Occidentales; O = Olotillo; R = Raton; T = Tuxpeño; and TN = Tuxpeño Norteño.

Dispersion in **Figure 1** shows the identification of two main groups: the group of maize populations with the conical ear type (transition and highland altitudes) and those with the cylindrical ear type (lowland to intermediate altitudes) (**Table 1**). This indicates the usefulness of the ear and grain traits in exploring the association among maize populations as suggested by [12, 13]. The continuous pattern among the different races within the two main groups is explained by the adaptation of the local populations (**Table 1**), and the genetic combination among races as a consequence of seed exchange by farmers within the community and with other communities [5, 6]. The seed exchange among farmers is a common practice in the area of study, is evident by the presence of some maize populations located at a different adaptation area (**Table 1**), explained by the genetic combinations among different races, and further adaptation to micro-environments as was verified in several regional studies [3, 11].
