**3. Genetic potential of maize populations**

Maize genetic diversity accounted by the locally adapted populations (landraces) within a traditional agricultural system is not static; it varies from 1 year to the another as a consequence of many factors such as migration (seed, pollen), selection, genetic drift [18], and adaptation to changes and interactions with external factors within the ecosystem development, as part of the evolutionary process and selection [19]. Thus, genetic variation is closely related to the environmental and production conditions and to the different uses of the crop, in particular the grain (color and flavor). The knowledge and understanding of the genetic variation, the environmental interaction and its potential use, may determine both the genetic conservation strategy and the possible utilization in breeding programs to improve local populations or for developing novel germplasm for particular goals.

#### **3.1. Yielding potential and environmental response**

The maize genetic diversity in the Coahuila state was determined initially by the description of 90 native maize populations that were collected during 2008 [10]. At the same time, those populations were established on field experiments for agronomic evaluation for 2 years (2008–2009), at two contrasted locations to determine the grain yielding potential. The agronomic evaluation was conducted in: El Mezquite, Galeana, Nuevo Leon (1890 masl), and General Cepeda, Coahuila (1350 masl). These locations are representative of both, the highland and intermediate environmental conditions in the area of study. The combination of two locations and 2 years of evaluation was named as four different environments. To analyze the environment response, the native populations were grouped based on the adaptation altitude: lowland (0–1000), intermediate (1001–1800), transition (1801–2000), and highland (greater than 2000 masl).

The maize populations represented in the transition and highland groups, showed a contrasted yielding response when evaluated at the General Cepeda area (intermediate altitude), in comparison with El Mezquite environment; whereas those populations adapted to the lowland and intermediate altitudes showed an adequate yield performance in both environments. Similar response pattern has been reported by [22], who also mentioned that populations adapted to highland areas have a difficult performance when established at lowland altitudes; on the other hand, those populations with an adaptation to lowland to intermediate areas have an acceptable agronomic performance. Thus, populations from lowland and intermediate altitudes have better adaptation range with satisfactory yielding potential. The above performance pattern is important because it may be useful to identify favorable alleles that, in a local population *per se* or through genetic combination among different racial complexes, resulting in population changes in allele frequencies controlling traits of interest, consequently, it could mitigate the effects of climate changes, particularly in maize populations

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**Figure 2.** Groups of native maize populations by the environment interaction based on grain yield.

In a different study, carried out in the southeast of the Coahuila state, an agronomic evaluation of native maize populations was performed in 2013 (unpublished data). The objectives of the research work were to determine the agronomic performance and yield potential of local maize populations, and to define the area of adaptation using two contrasting and

adapted to highland altitudes [23].

The local population × environment interaction analysis allowed to identify three groups that describe the specific adaptation of the maize populations [20]: the first one with adaptation to El Mezquite (33.3%), the second adapted to General Cepeda (42.2%), and a third group (24.4%) with an average yielding potential across environments, indicating a form of stability [16, 21]. In this study, it was shown that the racial types are associated to the locations of evaluation: the race Conico Norteño to El Mezquite (highland) and the races Raton, Tuxpeño, and Tuxpeño Norteño to the General Cepeda site (intermediate), which are also associated to the adaptation origin as indicated in **Table 1**. In Mexico, the maize genetic diversity is associated to the agro-ecological conditions that determine the different races types and their ear and grain distinctiveness and uses [17]. Results of the study determined the yielding potential and population response to the environmental evaluation, outstanding the racial groups Tuxpeño, Tuxpeño Norteño, and Raton with the highest yielding potential.

The assigned groups of native maize populations and the groups × environments were statistically different (P ≤ 0.01), explained by the diversity in altitudinal origin of maize populations and the differential response on the evaluation environments. A relative comparison of the average grain yield of the groups of native populations evaluated in the two contrasted environments during 2 years is presented in **Figure 2**.

**Figure 2.** Groups of native maize populations by the environment interaction based on grain yield.

**3. Genetic potential of maize populations**

104 Rediscovery of Landraces as a Resource for the Future

developing novel germplasm for particular goals.

**3.1. Yielding potential and environmental response**

Maize genetic diversity accounted by the locally adapted populations (landraces) within a traditional agricultural system is not static; it varies from 1 year to the another as a consequence of many factors such as migration (seed, pollen), selection, genetic drift [18], and adaptation to changes and interactions with external factors within the ecosystem development, as part of the evolutionary process and selection [19]. Thus, genetic variation is closely related to the environmental and production conditions and to the different uses of the crop, in particular the grain (color and flavor). The knowledge and understanding of the genetic variation, the environmental interaction and its potential use, may determine both the genetic conservation strategy and the possible utilization in breeding programs to improve local populations or for

The maize genetic diversity in the Coahuila state was determined initially by the description of 90 native maize populations that were collected during 2008 [10]. At the same time, those populations were established on field experiments for agronomic evaluation for 2 years (2008–2009), at two contrasted locations to determine the grain yielding potential. The agronomic evaluation was conducted in: El Mezquite, Galeana, Nuevo Leon (1890 masl), and General Cepeda, Coahuila (1350 masl). These locations are representative of both, the highland and intermediate environmental conditions in the area of study. The combination of two locations and 2 years of evaluation was named as four different environments. To analyze the environment response, the native populations were grouped based on the adaptation altitude: lowland (0–1000), inter-

The local population × environment interaction analysis allowed to identify three groups that describe the specific adaptation of the maize populations [20]: the first one with adaptation to El Mezquite (33.3%), the second adapted to General Cepeda (42.2%), and a third group (24.4%) with an average yielding potential across environments, indicating a form of stability [16, 21]. In this study, it was shown that the racial types are associated to the locations of evaluation: the race Conico Norteño to El Mezquite (highland) and the races Raton, Tuxpeño, and Tuxpeño Norteño to the General Cepeda site (intermediate), which are also associated to the adaptation origin as indicated in **Table 1**. In Mexico, the maize genetic diversity is associated to the agro-ecological conditions that determine the different races types and their ear and grain distinctiveness and uses [17]. Results of the study determined the yielding potential and population response to the environmental evaluation, outstanding the racial groups

The assigned groups of native maize populations and the groups × environments were statistically different (P ≤ 0.01), explained by the diversity in altitudinal origin of maize populations and the differential response on the evaluation environments. A relative comparison of the average grain yield of the groups of native populations evaluated in the two contrasted

mediate (1001–1800), transition (1801–2000), and highland (greater than 2000 masl).

Tuxpeño, Tuxpeño Norteño, and Raton with the highest yielding potential.

environments during 2 years is presented in **Figure 2**.

The maize populations represented in the transition and highland groups, showed a contrasted yielding response when evaluated at the General Cepeda area (intermediate altitude), in comparison with El Mezquite environment; whereas those populations adapted to the lowland and intermediate altitudes showed an adequate yield performance in both environments. Similar response pattern has been reported by [22], who also mentioned that populations adapted to highland areas have a difficult performance when established at lowland altitudes; on the other hand, those populations with an adaptation to lowland to intermediate areas have an acceptable agronomic performance. Thus, populations from lowland and intermediate altitudes have better adaptation range with satisfactory yielding potential. The above performance pattern is important because it may be useful to identify favorable alleles that, in a local population *per se* or through genetic combination among different racial complexes, resulting in population changes in allele frequencies controlling traits of interest, consequently, it could mitigate the effects of climate changes, particularly in maize populations adapted to highland altitudes [23].

In a different study, carried out in the southeast of the Coahuila state, an agronomic evaluation of native maize populations was performed in 2013 (unpublished data). The objectives of the research work were to determine the agronomic performance and yield potential of local maize populations, and to define the area of adaptation using two contrasting and representative environments of the southeast of the Coahuila state in Mexico. The agronomic evaluation of 63 maize populations and 7 improved checks was carried at 2 locations and 2 replications (blocks) under irrigation conditions: El Mezquite, Galeana, N. L. (1890 masl) and General Cepeda, Coah. (1350 masl). The combination of two locations and two replications was named as four different environments (GC1, GC2, MEZ1, and MEZ2). In both locations, replications were established independently, and in General Cepeda, the two replications represented two planting dates. The genetic diversity was represented by eight racial complexes: Celaya (3), Conico Norteño (26), Elotes Conicos (4), Elotes Occidentales (1), Olotillo (3), Raton (16), Tuxpeño (6), and Tuxpeño Norteño (4). The improved materials used as checks have variability on maturity and grain type: an experimental variety (POBAM), two improved varieties (VAN210 and JAGUAN), and four synthetic populations (6221, 6222, Pool31, and Pool32). The yield potential was analyzed across environments and the genotype × environment interaction based in the model of the additive main effects and multiplicative interaction (AMMI) [24].

The analysis of variance showed differences (P ≤ 0.01) among environments, genotypes (populations and checks) and genotype × environment interaction. Among the 25 outstanding populations, the racial groups with higher yield grain potential correspond mainly to the Raton races (9 populations), Tuxpeño (6 populations), and Tuxpeño Norteño (4 populations). Also, there were five native maize populations adapted to intermediate areas: three of the Tuxpeño race (I38T, I52T, and I54T) and two of the Raton race (I13R and I40R) with similar yields to the best improved check. In a previous study, the races Raton, Tuxpeño, and Tuxpeño Norteño had also the highest yield potential [20].

In the environmental response analysis based on the AMMI model, (**Figure 3**) shows the main effects for grain yield (Genotype and Environment) on the abscissa axis, and the first interaction principal component (IPC1) on the ordinate axis.

The AMMI model (**Figure 3**) allowed identifying genotypes with specific adaptation to the two contrasting environments, and the average response across environments. For instance, using an approximate range of −0.25 ≤ 0 ≤ 0.25 of the IPC1 as criteria to identify those genotypes with an average performance across environments, represents a form of stability stability [21]. There were five populations identified with good yield potential and a type of stability across environments: two Conico Norteño (H28CN and H27CN), one of Tuxpeño Norteño (I59TN), and two of Raton race (I56R and I40R). Likewise, in addition to the two Conico Norteño populations (H43CN and T08CN), there were four populations with adaptation to intermediate areas, with good potential in high altitude valleys: Tuxpeño race (I52T and I54T), a population of Elotes Occidentales (I33EO), and another Raton population (I35R). Most of the populations with the highest grain yield on **Figure 3** (positive values of main effects) have adaptation to intermediate areas, and have a potential performance in the two contrasting environments and the stability as well. This pattern agrees with the results presented in **Figure 2**, suggesting that those native populations may be used in a breeding strategy, individually, or as a combination with populations adapted to highland altitudes to identify useful alleles for developing novel germplasm that could mitigate the climate change.

**4. Strategies for crop improvement**

Occidentales, O = Olotillo, R = Raton, T = Tuxpeño, and TN = Tuxpeño Norteño.

In a traditional agricultural system, the native maize populations are developed and maintained by farmers through multiple cycles of empirical mass selection. Those populations are commonly the only source of genetic variation available for sowing, due to their flexible response to adverse situations, and usually two types of local varieties may be distinguished: the local varieties that are planted in a very small area for special uses, basically for consumption, and

**Figure 3.** Scatter plot of AMMI model for grain yield of 70 maize genotypes evaluated at 2 contrasting environments (GC1, GC2, MEZ1, and MEZ2). Population's data points are indicated by combinations of letters and numbers. The first character indicates the adaptation area L = lowland, I = intermediate, T = transition and H = highland; followed by the population number and finally, the racial group: C = Celaya, CN = Conico Norteño, EC = Elotes Conicos, EO = Elotes

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**Figure 3.** Scatter plot of AMMI model for grain yield of 70 maize genotypes evaluated at 2 contrasting environments (GC1, GC2, MEZ1, and MEZ2). Population's data points are indicated by combinations of letters and numbers. The first character indicates the adaptation area L = lowland, I = intermediate, T = transition and H = highland; followed by the population number and finally, the racial group: C = Celaya, CN = Conico Norteño, EC = Elotes Conicos, EO = Elotes Occidentales, O = Olotillo, R = Raton, T = Tuxpeño, and TN = Tuxpeño Norteño.

#### **4. Strategies for crop improvement**

representative environments of the southeast of the Coahuila state in Mexico. The agronomic evaluation of 63 maize populations and 7 improved checks was carried at 2 locations and 2 replications (blocks) under irrigation conditions: El Mezquite, Galeana, N. L. (1890 masl) and General Cepeda, Coah. (1350 masl). The combination of two locations and two replications was named as four different environments (GC1, GC2, MEZ1, and MEZ2). In both locations, replications were established independently, and in General Cepeda, the two replications represented two planting dates. The genetic diversity was represented by eight racial complexes: Celaya (3), Conico Norteño (26), Elotes Conicos (4), Elotes Occidentales (1), Olotillo (3), Raton (16), Tuxpeño (6), and Tuxpeño Norteño (4). The improved materials used as checks have variability on maturity and grain type: an experimental variety (POBAM), two improved varieties (VAN210 and JAGUAN), and four synthetic populations (6221, 6222, Pool31, and Pool32). The yield potential was analyzed across environments and the genotype × environment interaction based in the model of the additive main effects and

The analysis of variance showed differences (P ≤ 0.01) among environments, genotypes (populations and checks) and genotype × environment interaction. Among the 25 outstanding populations, the racial groups with higher yield grain potential correspond mainly to the Raton races (9 populations), Tuxpeño (6 populations), and Tuxpeño Norteño (4 populations). Also, there were five native maize populations adapted to intermediate areas: three of the Tuxpeño race (I38T, I52T, and I54T) and two of the Raton race (I13R and I40R) with similar yields to the best improved check. In a previous study, the races Raton, Tuxpeño, and Tuxpeño Norteño

In the environmental response analysis based on the AMMI model, (**Figure 3**) shows the main effects for grain yield (Genotype and Environment) on the abscissa axis, and the first interac-

The AMMI model (**Figure 3**) allowed identifying genotypes with specific adaptation to the two contrasting environments, and the average response across environments. For instance, using an approximate range of −0.25 ≤ 0 ≤ 0.25 of the IPC1 as criteria to identify those genotypes with an average performance across environments, represents a form of stability stability [21]. There were five populations identified with good yield potential and a type of stability across environments: two Conico Norteño (H28CN and H27CN), one of Tuxpeño Norteño (I59TN), and two of Raton race (I56R and I40R). Likewise, in addition to the two Conico Norteño populations (H43CN and T08CN), there were four populations with adaptation to intermediate areas, with good potential in high altitude valleys: Tuxpeño race (I52T and I54T), a population of Elotes Occidentales (I33EO), and another Raton population (I35R). Most of the populations with the highest grain yield on **Figure 3** (positive values of main effects) have adaptation to intermediate areas, and have a potential performance in the two contrasting environments and the stability as well. This pattern agrees with the results presented in **Figure 2**, suggesting that those native populations may be used in a breeding strategy, individually, or as a combination with populations adapted to highland altitudes to identify useful alleles for developing novel germplasm that could

multiplicative interaction (AMMI) [24].

106 Rediscovery of Landraces as a Resource for the Future

had also the highest yield potential [20].

mitigate the climate change.

tion principal component (IPC1) on the ordinate axis.

In a traditional agricultural system, the native maize populations are developed and maintained by farmers through multiple cycles of empirical mass selection. Those populations are commonly the only source of genetic variation available for sowing, due to their flexible response to adverse situations, and usually two types of local varieties may be distinguished: the local varieties that are planted in a very small area for special uses, basically for consumption, and represent the diversity of the crop; whereas, in the second case, varieties are planted in a larger areas, widely distributed, and are frequently used for seed exchange among farmers within the same community or with other communities. In either case, strategies for the efficient use of the germplasm need to be determined. For instance, in the first case, the recurrent selection strategy applied is basically to improve it; while, the second group, in addition to *per se* selection, those varieties are eligible for any form of genetic combination with external exotic germplasm.

#### **4.1. Selection strategies applied to a locally adapted maize population**

In the southeast of the Coahuila state, a wide adapted local maize population was identified to apply different selection strategies [25]. The native variety named JAGUEY, representative of the race Conico Norteño, is adapted to Jagüey de Ferniza, Saltillo, Coahuila (2100 masl). This variety was exposed to different management and selection procedures where four populations were obtained: (1) the original adapted population (OP); (2) the first generation from the local population (G1), obtained through a seed production scheme (detasseled rows); (3) and (4) two populations generated by the combination of the original population with an improved population, using a divergent selection for early (EM) and late (LM) maturities, respectively. After the populations were developed, a set of 25 half sib families was randomly obtained from each of the 4 populations for evaluation in 2 locations during 2003: El Mezquite, Galeana, Nuevo Leon (1890 m) and Jagüey de Ferniza, Saltillo, Coahuila (2100 m), being the irrigated and rain-fed environments, respectively. The four populations were compared to analyze the effects of selection procedures on agronomic traits using the site and the local population as references. Data were recorded for days to anthesis, plant height (m), husk cover (%), stalk and root lodging (%), moisture content of seed (%), number of ears per plant, and ear yield (t ha−1) adjusted to a 15% moisture content.

population. These results indicate that genetic variation of local populations can be managed attending different goals including conservation of genetic variation and crop improvement

**Table 2.** Squared distances among pairs of maize populations based on agronomic traits evaluated at two environments.

\*\*, Significant at 0.01 probability level; OP = Original local population; G1 = Fist generation obtained through a seed production scheme; EM and LM = Early and Late maturity populations obtained through the local **×** improved

Based on the results of the research paper carried out by [25], plants of the local population JAGUEY were crossed with an improved population to determine the value of a breeding material to enhance a local adapted maize population. Introgression of exotic germplasm to adapted material in maize has been a powerful tool to increase genetic variability in the local population, as well as to transfer favorable alleles, such as insect or disease resistance. The proportion of the exotic germplasm has been addressed in several studies to determine the usefulness of the foreign material on the foundation of breeding base populations [26–28]. The relevance of the introgression of foreign or exotic germplasm to an adapted population may change depending on the particular objectives. For instance, the improvement of a local farmer population by the introgression of exotic or foreign germplasm requires the identification of a good source donor and the establishment of the selection strategy. However, the application of breeding techniques to local maize populations may change their genetic structure, being the level of change related to the breeding methodology and the selection pressure. Besides the improvement of the local material, it is essential to preserve as much as possible the genetic variation accounted by the local material. In this case, the maize population JAGUEY adapted to Jagüey de Ferniza, Saltillo, Coah., Mexico, was considered the local material (L), and used to assess the contribution of an improved material introgressed to the local population [25]. This local population is a white dent type of the race Conico Norteño, adapted to rainfall conditions, such as low fertilizer inputs and limited water supply, and it is maintained by farmers through an empirical mass selection. The improved material (I), considered the foreign material, was an

**4.2. Potential of local × improved combination to enhance a locally adapted maize** 

**Populations† G1 EM LM**

OP 0.338 3.636\*\* 11.396\*\* G1 2.850\*\* 12.267\*\* EM 9.844\*\*

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OP 0.609 3.219\*\* 11.258\*\* G1 2.806\*\* 10.628\*\* EM 6.462\*\*

Jagüey, Saltillo, Coahuila (Rain-fed)

El Mezquite, Galeana, Nuevo Leon (Irrigation)

by the introgression of exotic germplasm.

germplasm; adapted from Rincón and Ruiz [25].

**population**

†

Results showed significant differences (P ≤ 0.01) among populations for most traits. A relative comparison among pairs of populations from a multivariate analysis, based on the agronomic traits evaluated is presented in **Table 2**.

A relative comparison among pairs of populations based on a multivariate analysis, showed significant differences (P ≤ 0.01) among the OP and G1, with the two populations obtained by the introgression with improved germplasm, in the two environments evaluated (EM and LM), indicating the contribution of the improved material to the original population. On the other hand, there was not any evidence of a difference among the OP and the G1; at the same time, they were comparatively more diverse than EM and LM, as an effect of the selection methodology. Thus, populations showed significant differences in the agronomic traits, determined by both, procedures and selection applied criteria, which determine the selection strategy and management for the conservation and use of genetic diversity.

Contribution of selection methodologies after the first selection cycle, indicated by the average difference in grain yield between G1 and OP, was 1.7%; whereas, the contribution associated to the germplasm combination, the EM against OP was in the order of 24.0%. In both cases, the first cycle of selection was associated with reduction in root and stalk lodging percentages, asynchrony silk interval, husk cover, and plant and ear height, in reference to the original


represent the diversity of the crop; whereas, in the second case, varieties are planted in a larger areas, widely distributed, and are frequently used for seed exchange among farmers within the same community or with other communities. In either case, strategies for the efficient use of the germplasm need to be determined. For instance, in the first case, the recurrent selection strategy applied is basically to improve it; while, the second group, in addition to *per se* selection, those varieties are eligible for any form of genetic combination with external exotic germplasm.

In the southeast of the Coahuila state, a wide adapted local maize population was identified to apply different selection strategies [25]. The native variety named JAGUEY, representative of the race Conico Norteño, is adapted to Jagüey de Ferniza, Saltillo, Coahuila (2100 masl). This variety was exposed to different management and selection procedures where four populations were obtained: (1) the original adapted population (OP); (2) the first generation from the local population (G1), obtained through a seed production scheme (detasseled rows); (3) and (4) two populations generated by the combination of the original population with an improved population, using a divergent selection for early (EM) and late (LM) maturities, respectively. After the populations were developed, a set of 25 half sib families was randomly obtained from each of the 4 populations for evaluation in 2 locations during 2003: El Mezquite, Galeana, Nuevo Leon (1890 m) and Jagüey de Ferniza, Saltillo, Coahuila (2100 m), being the irrigated and rain-fed environments, respectively. The four populations were compared to analyze the effects of selection procedures on agronomic traits using the site and the local population as references. Data were recorded for days to anthesis, plant height (m), husk cover (%), stalk and root lodging (%), moisture content of seed (%), number of ears per plant,

Results showed significant differences (P ≤ 0.01) among populations for most traits. A relative comparison among pairs of populations from a multivariate analysis, based on the agronomic

A relative comparison among pairs of populations based on a multivariate analysis, showed significant differences (P ≤ 0.01) among the OP and G1, with the two populations obtained by the introgression with improved germplasm, in the two environments evaluated (EM and LM), indicating the contribution of the improved material to the original population. On the other hand, there was not any evidence of a difference among the OP and the G1; at the same time, they were comparatively more diverse than EM and LM, as an effect of the selection methodology. Thus, populations showed significant differences in the agronomic traits, determined by both, procedures and selection applied criteria, which determine the selection

Contribution of selection methodologies after the first selection cycle, indicated by the average difference in grain yield between G1 and OP, was 1.7%; whereas, the contribution associated to the germplasm combination, the EM against OP was in the order of 24.0%. In both cases, the first cycle of selection was associated with reduction in root and stalk lodging percentages, asynchrony silk interval, husk cover, and plant and ear height, in reference to the original

strategy and management for the conservation and use of genetic diversity.

**4.1. Selection strategies applied to a locally adapted maize population**

and ear yield (t ha−1) adjusted to a 15% moisture content.

traits evaluated is presented in **Table 2**.

108 Rediscovery of Landraces as a Resource for the Future

† \*\*, Significant at 0.01 probability level; OP = Original local population; G1 = Fist generation obtained through a seed production scheme; EM and LM = Early and Late maturity populations obtained through the local **×** improved germplasm; adapted from Rincón and Ruiz [25].

**Table 2.** Squared distances among pairs of maize populations based on agronomic traits evaluated at two environments.

population. These results indicate that genetic variation of local populations can be managed attending different goals including conservation of genetic variation and crop improvement by the introgression of exotic germplasm.
