Introduction

In 2013 in Mexico, 3.3 million tonnes of wheat were produced and 4.6 million tonnes were imported to cover domestic demand. Thus, wheat production (Triticum aestivum L.) in Mexico had an annual deficit close to 70%, which represents the import of 4.6 million tons form EE. UU and Canada. In this same year from the total national production 94.4% was under irrigation conditions during the autumn-winter cycle 2013-2014, under these production conditions the wheat crop is facing water shortage, and the conversion to crops of greater cost effectiveness. An alternative to counteract dependence on wheat consumption is to increase common wheat production under temporary conditions, which is characterized by growing under variable environmental conditions (^{Hortelano et al., 2013}) and by its low production volume, which in 2014 was 5% of the national production (^{SIAP, 2015}). In addition, it presents marketing problems due to the harvesting of heterogeneous production lots and the lack of collection centers.

Of the total imports, during 2013, 63% corresponded to common wheat (^{CANIMOLT, 2014}). The quality characteristics of imported hard wheats are protein percentages of 12.6 to 15% associated with gluten strength of 350 to 500*10^-4 J and ratio of tenacity/extensibility balanced to extensible, from 1.2 to 0.9, respectively, which Is reflected in the production of bread volumes exceeding 800 cm³ (^{Maghirang et al., 2006}; ^{McCallum and DePauw, 2008}). Therefore, in addition to increasing the area sown under temporary conditions, common wheat flour be harvested with industrial quality comparable to that of imported wheat and its market price. According to ^{Villaseñor and Espitia, 2000}, there is potential for the planting of temporary wheat flour, in more than 500 000 ha in the states of Mexico and Tlaxcala, in addition, the proximity to the main grinding and consumption centers, as Mexico City and Estado de México, that demand more than 60% of ground grain (^{CANIMOLT, 2014}), it would increase the profitability due to savings by means of transportation.

Based on the above the production of temporary, must compete in industrial quality, with imported wheat. Therefore, genetic sources must be evaluated to improve the physical quality of the grain and the dough quality to increase the quality of baking. According to ^{Espitia et al. (2004)} there is a need to increase the genetic variability in hectoliter weight, grain protein and flour, sedimentation volume and bread volume. The above with the aim of improving the response to selection, which depends on genetic variability and heritability. According to ^{Ehdaie and Waines (1989)} the coefficient of genetic variation allows to know the amplitude of its variability to use and high values of heritability indicate that the variation is due to genetic effects and that its improvement is easy to perform.

Bread volume is the determinant variable that expresses the dough functionality; so it is sought trhough breeding to select genotypes with more bread volumen per flour used and also to improve its stability through environments, which has not been widely studied yet (^{Hristov et al., 2010}). A limitation for the selection, in the initial stages of segregation, based on bread volume is the sample size harvested, so it is necessary to identify variables that estimate it in these sample sizes (^{Seabourn et al., 2012}). Therefore, the objective of this paper was to determine the genetic variability, its heritability and its association of industrial quality variables that favor bread volume and stability through environments, in US nnd Canadian common wheat, grown under temporary conditions in the high valleys of central Mexico.

Materials and methods

Sixteen genotypes were used: Kulm, Keene, Waldron, SD3249, SD3195 and SD3236 originate from the United States of America and Blue Sky, Ac Vista, BW725, HY437, HY439, HY632 from Canada; The advanced lines GAVIA/ROM/3/PIRUL/GUI//TEMP/AGR/4/JUCH (line 1) and PAMDOLY-PABG-Tardía-C4 (line 2), as well as the Náhuatl F2000 and Kronstad F2004 as witnesses, which were released by INIFAP’s wheat breeding program. These genotypes were planted during June in temporary conditions in the localities known as Santa Lucía 2009, Chapingo first date 2009, Chapingo second date 2009, Coatepec 2009, Juchitepec 2009, Chapingo 2010, Coatepec 2010 and Juchitepec 2010, all localities are in the Estado de México, Santa Lucia de Prías and Chapingo are characterized by being subhumid temperate climate C (Wo) (W)b(y)g. Chapingo is located at 19° 13’north latitude and 98° 51’ west longitude at 2 250 masl and Santa Lucia de Prías is located at 19° 44’ north latitude and 98° 87’ west longitude at 2 260 masl. Juchitepec and Coatepec are classified as wet weather, Juchitepec is located at 2 571 msnm between 19° 06’ north latitude and 98° 53’ west longitude and Coatepec at 2 320 msnm (^{García, 1981}).

The experimental design was of randomized complete blocks with two replicates in each locality and the experimental unit was four rows of 3 m in length with a separation of 30 cm. Seed density was 120 kg ha^-1, fertilized with the formula 40-20-00, all N and all P₂O₅ at planting. As fertilization source, urea (CO (NH₂)₂) was used with 46% N and triple calcium superphosphate (Ca (H₂PO₄)₂) with 46% P₂O₅. Narrow-leaf weeds were controlled with Topik 24EC^® and broad-leafed weeds with Esteron 47^®. During the embedding stage 500 mL ha^-1 of Folicur^® was applied to control the incidence of diseases. It was harvested with a mini combined when the grain moisture was less than 14%.

The industrial quality analyzes were carried out in the Laboratory of Farinology of CEVAMEX-INIFAP. The hectolitric weight (kg hL^-1) was determined on a 500 g sample of clean grain in a volumetric balance (Seedburo Equipment CO., Chicago, IL.). From the bean the refined flour was obtained using a Brabender mill (Quadrumat Senior, C.W. Brabender OHG, Germany) with a sifting through a mesh of 129 μm in diameter. The protein content in flour (%) was measured with the NIR analyzer Infralyzer 300 (method 39-10; ^{AACC, 2005}). The sedimentation volume (mL) was determined in a sample of 3.2 g refined flour by the presence of lactic acid and isopropyl alcohol (^{Zeleny, 1947}), indicating the hydration and expansion capacity of the protein; to greater volume greater strength. Using the method 54-30A of the ^{AACC (2005)}, the alveogram was obtained from Chopin’s Alveograph (Tripette and Renaud, France), using a sample of 60 g of refined flour, from which strength (W) and the dough tenacity/extensibility ratio (PL) were obtained.

The doughs based on their W and PL can be classified by their W are grouped into strong doughs greater than 300*10^-4 J, strong medium masses of 200*10^-4 J to 300*10^-4 J and smaller weak masses of 200*10^-4 J and by its PL in balanced (PL= 1.1), extensible (PL <1) and tenacious (PL> 1.2). The bread volume (mL) was obtained by the direct dough method (^{AACC, 2005}) from 100 g of refined flour, 3 g of milk powder, 3 g of vegetable fat, to which 25 mL of a 24% yeast solution and 25 mL of a sugar-salt solution were added to 20 and 4%, respectively; the fermentation process was 3 h and 25 min, with a relative humidity of 90% at 35 °C. Baking was carried out in a Despatech Oven Co. oven (Minneapolis USA) at 220 °C for 25 min, the volume was measured in a voltmeter by means of displacement of rapeseed (Brassica campestris L.).

A joint variance analysis was performed for the eight locations for all variables evaluated. Prior to the analysis of variance of protein content in flour, a logarithmic transformation of the percentage data was performed. Genotypes were considered as fixed effects and environments were considered as random effects, analysis of variance was performed using the SAS GLM procedure (^{SAS, 2002}), and means were compared using the least significant significant difference (p≤ 0.05) in order to identify the differences between genotypes and environments. Table 1 presents the structure of the analysis of variance and mean square expectations.

Table 1 Structure of combined variance analysis and mean squares expectations of 16 wheat genotypes in eight temporal environments. Spring-summer cycle, 2009 and 2010. 

FV= fuentes de variación; GL= grados de libertad; SC= suma de cuadrados; CM= cuadrados medios; ECM= esperanzas de cuadrados medios; σ² _g= varianza de genotipos; σ² _ag= varianza de genotipos por ambiente; σ² _e= varianza del error.

The coefficient of genetic variation was calculated by the quotient of the genetic standard deviation between the mean. Coefficients less than 20 are classified as high genetic variability, from 12 to 20 intermediate genetic variability and greater than 10 low variability. Heritability was obtained by dividing the genetic variance between the phenotypic variance. In addition, the Pearson correlations were obtained by the SAS procedure CORR.

Results and discussion

The variables dough strength and tenacity/extensibility ratio presented the highest coefficients of genetic variation, with 24.3 and 21.7, respectively. Both values for these characteristics of the dough are similar to those found by ^{Espitia et al. (2004)} in a group of Mexican varieties of wheat produced under temporary. Its amplitude for dough strength was 661*10^-4 J and of 2.1 for the tenacity/extensibility ratio. These high values indicate high genetic variation, which will allow the selection of genotypes with specific characteristics of strength and extensibility, which can be used as genetic sources for these characteristics within the breeding program.

On the other hand, the variables sedimentation volume, flour protein, bread volume and hectoliter weight showed coefficients of genetic variation lower than 10, which indicates that the introduced genotypes have a reduced genetic variation for these characteristics (Table 2). So it would be complicated to apply the selection for these characters in this group of genotypes as well as to obtain genetic sources for these characters. However, it is important to indicate that in the materials introduced the maximum value for protein in flour was greater than 15 mg g^-1 and the mean value for bread volume was higher than 850 mL, both values are higher than the Mexican materials according to that reported by ^{Espitia et al. (2004)} so it is possible to identify outstanding genotypes for these characteristics.

Table 2 Estimated genetic parameters for industrial quality variables of common wheat genotypes evaluated under temporal. Spring-Summer cycle, 2009 and 2010. 

CVG= coeficiente de variación genética; h²= heredabilidad.

The highest heritability values were for dough strength, protein in flour and sedimentation volume with 0.37, 0.33 and 0.23 respectively, which indicates that these characteristics are essentially due to genetic effects which will favor these characters to be recombined and inherited in the progeny. Contrary behavior showed volume of bread, protein in flour and hectoliter weight, that presented heritabilities less than 0.2, so that their breeding is more complicated since these characteristics are mostly influenced by the environment.

Since bread quality refers to the ability to obtain a larger volume of bread with the same amount of flour used and this characteristic must be maintained through the environments it is necessary to use in the breeding process correlated variables favoring bread volume. The bread volume was positively correlated with the protein content in the flour, which is consistent with that found by ^{Dowell et al. (2008)} and ^{Barak et al. (2013)}, this positive relationship was also shown with dough strength and sedimentation volume and was inversely related to the tenacity/extensibility ratio, same results were obtained by ^{Li et al. (2013)}.

This indicates that in order to select genotypes with higher bread volume, it is necessary to increase the protein content in flour, the dough strength as well as its extensibility, which coincides with that reported by ^{Nash et al. (2006)} who indicated that there must be a balance between strength and extensibility to favor bread volume and not only increase the dough strengt. Since the variable tenacity/extensibility was not correlated with sedimentation volume which is a predictive test (Table 3) it is necessary to implement in early stages of segregation a selection variable that favors the dough extensibility, which indirectly favors bread volume.

Table 3 Pearson’s correlations among quality variables of 16 common wheat genotypes evaluated under temporal conditions. Spring-Summer cycle, 2009 and 2010. 

SVP= estabilidad de volumen de pan; ns, ^*, ^**= no significativo, significativo y significativo, respectivamente.

The highest correlation was between dough strength and sedimentation volume (Table 3), the above is similar to that obtained by ^{Axford et al. (1979)} and ^{Zečević et al. (2007)}, since high values of sedimentation volume have been used as a tool to select genotypes of greater dough strength indirectly in segregating stages of genetic improvement as well as low values of sedimentation are characteristic of genotypes with low masses. Positive correlations were also found between flour protein and sedimentation volume, which is in agreement with ^{Espitia et al. (2004)}. The stability of bread volume was positively related to bread and protein volume in flour and inversely with hectolitric weight and the tenacity/extensibility ratio, while there was no relation with sedimentation volume and dough strength.

Figure 1 shows the correlations between bread volume and its stability. The Nahuatl F2000, Waldron, Ac Vista, Line 2, Kronstad F2004 and Kulm genotypes associated greater stability, given their lower value in the numerical scale, with bread volumes greater than 800 mL.

Figure 1 Comparison of bread volume (DSH = 48.5) in relation to the stability of bread volume of common wheat genotypes evaluated under temporal. Spring- Summer cycle, 2009 and 2010. 3= BW725; 4= HY437; 5= HY439; 6= HY632; 7= AC Vista; 8= Blue sky; 10= Keene; 11= Kulm; 14= Waldron; 15= SD3249; 16= SD3195; 17= SD3236; 20= Línea 1; 21= Línea 2; 24= Náhuatl F2000; y 25= Kronstad F2004. 

Of this group of genotypes, those that associated greater stability and bread volumes above 840 mL were Nahuatl F2000 and Waldron. The Náhuatl F2000 variety associated strong dough (W> 500*10^-4 J) with a close to tenacity/extensibility ratio as well as flour protein greater than 11 mg g^-1 (Figure 2A). The introduced Waldron genotype showed greater extensibility, because its PL was lower than 0.9 and strong dough with a protein content in the flour similar to Nahuatl F2000.

Figure 2 Comparison of bread volume (DSH = 48.5) as a function of flour protein (A), dough strength (B) and tenacity/ extensibility (C) ratio of common wheat genotypes evaluated under temporary. Spring-summer cycle, 2009 and 2010. 3= BW725; 4= HY437; 5= HY439; 6= HY632; 7= AC Vista; 8= Blue sky; 10= Keene; 11= Kulm; 14= Waldron; 15= SD3249; 16= SD3195; 17= SD3236; 20= Línea 1; 21= Línea 2; 24= Náhuatl F2000; y 25= Kronstad F2004.  

The genotypes Line 2 and Ac Vista, presented similar stability among them but was lower with respect to Náhuatl F2000 and Waldron, both presented volumes of bread near 820 mL. Line 2 was characterized by strong dough at its W near 400*10^-4 J and extensible by its PL< 1.1 (Figure 2 B and C) which allowed it to reach the indicated volumes of bread. On the other hand, Ac Vista was characterized by lower values of protein and dough strength with contents lower than 10.5 mg g^-1 and W< 250*10^-4 J, respectively, classified by their strength as mean dough; however, due to its excellent extensibility by its PL< 0.8, which was the lowest of all genotypes analyzed, it obtained acceptable bread volume, the above agrees with ^{Różyło and Laskowski, (2011)} who indicated that high bread volumes are favored by a greater dough extensibility.

The Kronstad F2004 and Kulm genotypes presented intermediate stability values and were associated with bread volumes greater than 850 mL. Both genotypes presented strong dough for their W> 400*10^-4 J and their PL close to one were classified as balanced. However, Kulm added intermediate stability and 870 mL of bread volume higher than Kronstad F2004, which is due in part to its protein content in flour greater than 12 mg g^-1, which is in agreement with ^{Barak et al. (2013)} who indicated that the protein content in the flour increases the bread volume.

The genotypes Keene, SD3249, HY437, BW725 and Blue sky presented values of bread volume higher than 870 mL; however, they showed low stability due to their high value on the numerical scale (Figure 1). The characteristics of these materials were flour protein contents greater than 11.5 mg g^-1. Their mass forces were greater than 400*10^-4 J, with the exception of BW 725, associated with PL< 1.2. On the other hand, the materials SD3195 and SD3236 presented good stability values, however, they were associated with the lower bread volumes <800 mL, which is due to their masses being classified as tenacious, by their PL> 1.5, which according to ^{Li et al. (2013)} reduces the bread volume.

The genotypes Keene and SD3249 presented the highest values of bread volume which were superior to 900 mL; however, they showed low stability. These genotypes were characterized by their flour protein content greater than 12 mg g^-1 associated with mass strength of 550*10^-4 J and with a lower tenacity/extensibility ratio of one for Keene and close to 1.1 for SD3249. The above combination of high flour protein content, strong dough with good extensibility ie with PL values less than 1.2 favors bread volumes which has also been indicated by ^{Battenfield et al. (2016)}.

Based on the above, in the introduced genotypes there is diversity in their protein content as well as in the strength and extensibility of the dough which consequently affects bread volume. According to ^{Lemelin et al. (2005)}, these variations in bread strength, extensibility and volume are also due to the type of allelic variants of glutenins and gliadins that intrinsically presents each genotype which is recognized as protein quality and which would also allow to select which alleles associate greater volume and better stability through environments; however, such variants were not considered in this study.

Conclusions

In the introduced wheat germplasm, the dough strength conjugated high values of genetic variation and heritability, which may be exploited by the INIFAP breeding program, while the bread volume and hectoliter weight showed an inverse behavior.

In addition to selecting for higher protein content and higher sedimentation volume in early stages of common wheat planting, it is necessary to perform it to favor its dough extensibility, which will consequently increase bread volume.

The introduced genotypes Waldron, Ac Vista and Kulm associated good bread volumes with adequate stability so they should be used as genetic sources to improve baking quality.