Overgrazing and loss of native forage species is an ongoing problem in the rangelands. In the state of Chihuahua, 40 % of the 4.6 million hectares of open grasslands are extremely deteriorated^1,2. Therefore, it is necessary to establish management plans that include rangeland restoration practices, using improved native species. Among these species is sideoats grama grass [Bouteloua curtipendula (Michx.) Torr.], native from the arid and semi-arid areas of Northern Mexico. These grass plants produce abundant forage widely accepted by livestock. It adapts to different types of soil and climatic conditions, in addition, plants of this species persist when low rainfall occurs^3,4. Usually located in plains and rocky hillocks, it produces about 1,900 kg DM ha^-1 with rainfall of about 350 mm. They have digestibility values of 50 to 70 % depending on their growth stage⁵.

The critical step for the establishment of pastures is the emergence of seedlings, which is important to the success of replanting. However, the selection of the species and variety suitable for the site conditions is a fundamental decision, because within the same species there are productive changes in behavior according to the region. Therefore, it is important to consider the behavior of the species and varieties that have been developed, and can demonstrate desirable characteristics in different agro-ecological sites that use^6,7. In addition, seed quality is another determinant for germination, emergence and establishment, which contribute to whether the seed meets the quality standards of the species in question^8,9. In another study of seed production, 13 sideoats grama grass genotypes were evaluated and reported that best caryopsis yields were 6.64 and 8.6 kg ha^-1 for the 125 and 303 ecotypes originating in Durango and Zacatecas, respectively¹⁰. Given the importance of this species, it is necessary to characterize and identify sideoats grama grass varieties with potential for establishment in grassland restoration programs. The aim of this study was to characterize the productive behavior of five varieties recommended for reseeding of sideoats grama grass.

The study was conducted in a greenhouse located at the Facultad de Zootecnia y Ecología, Universidad Autónoma de Chihuahua during the summer in 2013. Five commercial varieties of sideoats grama grass were used: Niner (Ni), Vaughn (Va) El Reno (Re), Kansas native-6107 (K-07) and Kansas native-6113 (K-13). The experiment was divided into two tests.

For test one, 20 plastic trays 0.33 m wide x 0.54 m long (0.18 m²) and 5 cm deep were used; each tray was an experimental unit. In each tray 12 perforations were made at the same distance, and covered with a layer of 4 cm of soil with sandy loam and pH 6, obtained from Rancho Experimental La Campana located at 29° 16' 01" N and 106° 21' 16" W. Watering was conducted for 30 d before planting in order to remove seeds from the soil and avoid the emergence of other species. Planting began on August 8, 2013 and the distribution of seed was random. Five kilograms of pure viable seed were applied per hectare (kg SPV ha^-1) for each variety (Table 1)¹¹. The seed was sown at a depth of 0.5 cm. The trays were distributed in randomized blocks with four replicates per variety to avoid exposure effect. An initial irrigation of 1.5 L of water per tray was applied, and the irrigation were similar for each experimental unit (1.0 and 0.5 L) spaced between one and four days; later, soil was maintained at field capacity. Temperatures inside the greenhouse fluctuated between 14 and 41 °C. The variables evaluated were: emergence (EM%), plant density (PD), plant height (PH), dry matter of the first cut (DM1), height of regrowth (HR), dry matter regrowth (DM2), and survival (SV%). Measurements of PD started three days after seeding and daily counts were taken during a month. To PD it took into account the last count before the first cut. For PH three plants were measured at random for each experimental unit and at the same time the first cut was made for DM1. These three variables were evaluated at 60 d after planting. Biomass was dried at constant temperature, of 65 °C for 24 h in an oven (Felisa brand) to constant weight. Later samples were weighed on an analytical scale (Sartorius brand). Work continued on the irrigation and grown regrowth for 21 d to make the second cut; on this date HR and DM2 were measured. The drying and weighing was carried out with the same technique as the first cut. Estimate of SV% took into account the highest recorded density and the number of live plants that regrew.

For test two, in order to evaluate plant growth and development sideoats grama seed were planted in cylindrical pots. Each pot was 30 cm deep by 10 cm in diameter. The bags were filled to 25 cm with the same soil used in the trays. A total of 20 seeds per variety were seeded 0.5 cm deep at each pot. Three seedlings were allowed to growth per pot for further evaluation. The pots were placed on a table in the greenhouse, distributed in randomized blocks with four replications. The soil into the pots was maintained at field capacity. The plants were removed from the pots and left in the ground for 35 d after sowing. The above ground biomass of the radicle was separated, dried and weighed using the same methodology. The variables evaluated were: root length (RL), height, above ground biomass (aDM) and ratio root-biomass r(R-aDM).

Principal component analysis (PCA) and cluster analysis (CA) by Ward linkage method for grouping varieties¹² was performed. The varieties were compared with each other through multivariate analysis (MANOVA) and statistics of orthogonal contrasts under the Wilks' Lambda, Pillai's Trace, Hotelling-Lawley Trace and Roy's Greatest Root. The statistical program used was SAS¹². The scatter plots and dendrogram were obtained through MINITAB.

Table 2 shows a wide variation in the variables evaluated in the five varieties of sideoats grama grass. The higest variation was on % MS and PD; lowest variation was obtained for HR and r(R-aDM). The high variability represent potential for selection the most appropriated varieties in order to ensure establishment. The PCA showed that the first two components explain 76.9 % of the variance (Table 3). The PC1 presents a balance in almost all variables evaluated (Table 4), except EM% and SV%. This component is characterized by grouping variables related to forage production and related capacity reflects growth traits. In PC2 variables that contributed most were SV%, PD and PRBA (Table 3). The differences in these varieties could be related to ability for survival during the critical stage of establishment, as they originate from different agro-ecological environments^13-17.

To obtain the coefficient of determination (R²) for each of the original variables, with respect to the first two PC, significant correlations were presented in different varieties, and with respect to PC one significant difference (P<0.05) were presented at the most of the evaluated variables (Table 4). It is noted that the coefficient of determination in correlation PC1 with the original variables, showed that only the variables EM% and SV % had no significant contribution. The PC2 was significantly correlated (r= 85.1 %; P<0.0.0001) with SV %.

The dispersion shown in Figure 1 reflects existing morphological diversity in these varieties; variables that contributed most were SV%, r(R-aDM), aDM and PD. Morphological variation of sideoats grama grass can predict varieties more able according to the ability to adapt to different temperatures, rainfall and soil types, is possible to establish groups with characteristics of interest, rather than locations or source features^18,19,20.

Figure 1 Distribution of the diversity of five varieties of sideoats grama grass based on the first two principal components obtained with the correlation matrix of 10 variables 

The cluster analysis was based on the method of WARD linkage consisting of three groups. Group one (G-I) was composed of the Niner and Vaughn varieties originating from Socorro, New Mexico, USA and Vaughn, New Mexico, USA, respectively. In general, these varieties were characterized as having the highest values in the variables evaluated. For the two varieties, Niner had the highest values of PD, DM1, HR, ABDM, and RL; however, only the variety Vaughn had the highest values in PH and DM2. Group two (G-II) only consisted of one variety (El Reno), originally from El Reno, Oklahoma, USA This variety was characterized with intermediate values. However, other authors mention good performance at environments with low temperatures²¹. Group Three (G-III) integrated varieties K-07 and K-13, originating from Kansas, USA. These varieties were characterized by having the lowest values. The K-07 variety showed the lowest values in % EM, PD, PH, DM1, DM2 and SV%. The K-13 variety showed the lowest values in HR, RL and ABDM (Figure 2). An important aspect is that the morphological variation observed is probably the result of selection and breeding performed on those varieties. With regard to these results, different authors report morphological variations within this species^22,23,24.

Figure 2 Dendrogram analysis of 10 variables for five varieties of sideoats grama grass based on the method of Ward linkage 

By comparing the variables with multivariate analysis (MANOVA), the varieties can be classified for its productive importance at 2 mo of establishment as follows: Niner and Vaughn, no differences between them, but they were higher (P<0.05) than El Reno, K-07 and K-13. Likewise, El Reno was higher (P<0.05) than K-07 and K-13. Table 5 shows the values of the statistics; Wilks' Lambda, Pillai's Trace, Hotelling-Lawley Trace and Roy's Greatest Root. From the above results, it is important to consider that the productive capacity of a plant, is related to the quality of seed, as well as the genetic potential of each variety¹⁷. However, location and weather conditions depend largely on the productive response, of either species or variety of grass^25,26. Previous work has reported that Niner and Vaughn cultivars with outstanding production performance in the states of Colorado and New Mexico in environments with 200 to 400 mm of precipitation²⁷. Also, it has been reported that the variety El Reno was lower in some productive parameters compared to sideoats grama grass ecotypes collected in Durango and Zacatecas¹⁰. Regarding Kansas native varieties it was only found that they were used in 2012 in reseeding programs in the state of Chihuahua, but low rates of establishment and production were obtained.

The Niner and Vaughn varieties were identified with morphological features reflecting high forage potential. The El Reno variety presented an intermediate potential for forage production, according to the variables considered. The Kansas native-6107 and Kansas native-6113, are the varieties that had the lowest potential for forage production in greenhouses. The study of attributes of sideoats grama grass varieties that are of a more productive and morphological variation importance shows which varieties to incorporate in replanting programs in order to achieve results in a shorter time. The evaluation herein under field conditions shows with greater certainty a recommended inclusion of varieties Niner and Vaughn for reseeding programs on rangelands state of Chihuahua.