Introduction

Foliar diseases such as yellow rust (Puccinia striiformis f. sp. tritici), leaf rust (P. triticina), Septoria sp., Cochliobolus sativum and Pyrenophora tritici-repentis, are biotic factors that affect productivity. Yellow rust (Triticum aestivum L.) in bread wheat in rainfed conditions in Mexico, and there are grain productions losses greater than 60 % due to yellow rust (^{Huerta and Singh, 2000}), by leaf rust between 5.5 % and 25.9 % (^{Leyva et al., 2003}) and Septoria tritici 44 % (^{Rodriguez-Contreras et al., 2008}).

In a climate change scenario, it is likely that wheat diseases that did not affected productivity may affect it (^{Duveiller et al., 2007}) and there are severe cases of yellow rust in unsuitable environments for their presence (^{Milus et al., 2009}). In Mexico, in the two main producer states of rainfed flour wheat, Tlaxcala and the Estado de Mexico, in 2014 the yellow rust caused yield losses of 70 %, so it was necessary to use chemical control. Wheat production in Mexico competes in price and industrial quality with the hard red spring wheat from the USA and Canada. The red spring wheat represents 63 % of wheat imports; therefore, wheat production should be a profitable option for the farmers and domestic industry (^{CANIMOLT, 2014}). Chemical control of leaf diseases does not affect the content of protein, dough strength and tenacity/extensibility relationship (^{Blandino and Reyneri, 2009}), although ^{Ruske et al. (2004)} showed that disease control decreases protein content and loaf volume, but ^{Gooding (2007)} indicates that rust control promotes protein concentration and the control of Septoria tritici reduces protein concentration.

To minimize yield losses and obtain the desired grain quality by the domestic industry, the control of foliar diseases should be tested using tolerant genotypes or with fungicides; assessed both in terms of yield and in the quality of the grains and dough. Therefore, the objective of this research was to evaluate the performance of agronomic variables and the industrial quality of the grain and dough in terms of disease control (rusts, stains and leaf blights) in resistant and susceptible rainfed bread wheat genotypes in the high valleys of central Mexico. The hypothesis was that application of fungicides in the plant prevents disease incidense and consequently increases the yield and improves physical grain quality and dough functionality.

Materials and Methods

The following genotypes were used: Pavon F76, Galvez M87, Temporalera M87, Batan F96, Romoga F96, Juchi F2000, Nahuatl F2000, Rebeca F2000 and Tlaxcala F2000. The numbers (76, 87, 96, and 2000) indicates the year when the genotypes were released, and they are recommended for planting under rainfed conditions by The National Research Institute of Forestry, Agriculture and Livestock (INIFAP). Varieties Galvez M87 and Temporalera M87 are classified, based on the strength of its dough, as mid-strong and the other varieties are strong, which are recommended to the mechanized baking industry. Juchi F2000, Nahuatl F2000, Rebeca F2000 and Tlaxcala F2000, released in the year 2000, have more resistant genes to yellow rust compared to other genotypes. The genotypes were planted in Bellavista, (state of Morelos); Chapingo, Juchitepec and Coatepec (Estado de Mexico). The experimental design was a randomized complete block with two replications in an arrangement of split plot treatments; in which the largest plot were the treatments with and without fungicide and in the small plots were the varieties. The experimental unit was of four rows of 3 m length and 30 cm apart from each other. The applied fungicides were Folicur^® and Sportak^®, whose active ingredients are tebuconazole and prochloraz, respectively. Applications were of 500 mL ha^-1 of Folicur^® at the anthesis stage to control rusts and 15 d after 1000 mL ha^-1 of Sportak^® to control blights and leaf spots. The incidence of foliar diseases was natural.

The evaluated agronomic variables were: days to flowering, days to maturity, plant height, percentage of damaged leaf area and grain yield (Mg ha^-1). In a clean 500 g grain sample the test weight (kg h L^-1) was determined in a volumetric scale (Seedburo Equipment CO., Chicago, IL). Samples were then grounded in a Brabender mill (Senior Quadrumat CW Brabender OHG, Germany) and by sifting them through a 129 µm diameter mesh refined flour was obtained. Their protein content (%) was determined with the NIR infralyzer 300 analyzer (method 39-10, AACC, 2005). The strength (W) and ratio tenacity/extensibility (PL) of the dough were calculated from the alveograph, which was originated from 60 g of refined flour in Chopin’s Alveograph (Tripette & Renaud, France), using method 54-30A from the AACC (2005). The doughs were classified as: 1) by W in strong doughs, of a value greater than 300×10^-4 J, mid-strong doughs ranging from 200×10^-4 J to 300×10^-4 J, and weak doughs under 200(10^-4 J; 2) by PL, in balanced (PL=1.1), extensible (PL˂1) and tenacious (PL>1.2). The bread volume (mL) was measured using the method of direct dough (method 10-09, AACC, 2005) with 100 g of refined flour and was determined in a volutometer by rapeseed displacement (Brassica campestris L.).

Results and Discussion

There were significant differences among locations, genotypes and for interactions locality-genotype and genotype-fungicide in all the quality variables. These results are similar to those found by ^{Gooding (2007)} and ^{Ruske et al. (2004)}. Nevertheless, there were no differences in days to flowering with and without fungicide application, as well as for this variable and plant height in the interaction variety-fungicide (Table 1), which is consistent with the results reported by ^{Lackermann et al. (2011)} and ^{Villaseñor et al. (2012)}. These results show the contrast between environmental conditions and genotypes with different agronomic characteristics and quality. The data also shows that the application of fungicides and their interaction with the locality and genotype influenced the agricultural and industrial quality bread wheat variables.

The localities of Bellavista and Juchitepec showed higher grain yields, they also presented the higher values of damaged leaf area, contrary to what was observed in the localities of Coatepec and Chapingo (Table 2). This could be due to a higher incidence of disease but its severity was milder; based on the results of ^{Rodríguez-Pérez et al. (2005)}. The localities of Bellavista and Juchitepec are classified as suitable environments for wheat production; Coatepec and Chapingo are classified as mild environments.

The genotypes Rebeca F2000, Tlaxcala F2000 and Juchi F2000 had less damaged leaf area and had high production, which is partially explained by its genetic resistance to yellow rust, according VillaseñorEspin et al. (2009). Rebeca F2000 was the most productive due to its longer crop cycle, as indicated by the fact that it takes more days to reach maturity, which could be associated with a larger period of time dedicated to fill the grains and this is consistent with the report of Villaseñor et al. (2004) where they classify Rebeca F2000 as a variety of late cycle. The application of fungicides reduced the incidence of foliar diseases, which in turn decreased the damaged leaf area and increased grain yield; whereas the disease shortened the crop cycle and reduced plant height (Table 2).

The diseases reduced the days of the maturity cycle in the varieties Rebeca F2000 and Juchi F2000, compared with the days in the maturity cycle of varieties Galvez M87 and Temporalera M87. This is caused by diseases given that they accelerate senescence of leaves and these varieties do not have resistance genes to the yellow rust (^{Villaseñor-Espin et al., 2009}) (Figure 1A). The plant height of Rebeca F2000 and Tlaxcala F2000 was not affected, contrary of what was observed in Romoga F96 and Temporalera M87 (Figure 2) this is consistent with the reports of ^{Leyva et al. (2003)}, ^{Rodriguez-Contreras et al. (2008)} and ^{Wiik (2009)}. Based on the above, the genotypes that have resistance genes to yellow rust, even without the application of fungicides, showed less damaged leaf area and a smaller loss in grain yield, compared with varieties that do not have these genes. This validates the importance of accumulating resistance genes using improvement against the complex of foliar diseases.

Figure 1 Behavior of A) Days to flowering and B) Days maturity, in terms of the application of fungicides in bread wheat under rainfed conditions. CF and SF: with and without fungicide application, respectively. HSD: honest significant difference. 

Figure2.Variations in plant height depending on the application of fungicide in flour wheat in rainfed conditions. HSD: honest significant difference CF and SF: with and without fungicide application, respectively 

The presence of foliar diseases caused yield losses between 7.3 % and 28.6 % depending on the variety, this is consistent with the reports of ^{Ransom and McMullen (2008)} and ^{Thompson et al. (2014)}. They reported values ranging from 5.5 % to 44.0 %, depending on the tolerance of the genotypes to disease. The genotypes Rebeca F2000, Juchi F2000 and Tlaxcala F2000 showed lower losses in damaged leaf area and production, whereas Pavon F76 and Galvez M87 presented an opposite behavior (Table 3). This situation is partially explained because the first genotypes have the gene Yr18 and three lesser genes with additive effects to resistance to yellow rust (^{Villasenor-Espin et al., 2009}), as well as an increased tolerance to Septoria sp. and by its higher potential yield, which is consistent with that indicated by ^{Ramirez et al. (2016)}. Batan F96 showed a reduction of 63 % in leaf area, this is associated with a minimal decrease in production, which may be due to its increased ability to translocate leaf assimilates to the wheat’s ear, a mechanism reported by ^{Leyva et al. (2003)}. The application of fungicides decreased the incidence of the disease and prevented losses in a grain yield average of 19.2%, which is smaller than the 42 % loss reduction documented by ^{Wegulo et al. (2009)}.

The location in Bellavista presented the highest values of hectolitre weight which in turn will produce higher flour yield (^{Baasandorj et al., 2015}), nevertheless it had the lowest protein values, which is associated with its tenacious dough, its PL higher than 1.2 disfavored the bread’s volume. The other locations had an inverse behavior (Table 4). This concurs with the results of ^{Espitia et al. (2003)} who reported how the variables of industrial quality of bread wheat are affected by environmental conditions.

Most of the genotypes presented test weight greater than 75 kg hL^-1 and were associated with strong doughs, which agree with the report by ^{Hortelano et al. (2013)}. Galvez M87 and Juchi F2000 were classified with excellent extensibility because of its relation tenacity/extensibility, resulting in the highest bread volume; this is contrary to the results of Batan F96 and Rebeca F2000, whose tenacious doughs PL1.2, presented the smallest bread volume (Table 4). This confirms the point by ^{Sanchez Garcia et al. (2015)} that strong and extensible doughs favor volume and tenacious doughs reduce it. The absence of foliar diseases due to the application of fungicides favored the hectolitre weight of the grain, similar to a result reported by ^{Ruske et al. (2003)} and ^{Serrago et al. (2011)}, this will favor the flour’s throughput during the milling. But protein in the flour decreased; therefore, the strength of the dough and consequently the bread volume (Table 4) and this concurs with ^{Watson et al. (2010)} and ^{Ruske et al. (2004)}.

The absence of disease because of the application of fungicides favored the hectolitre weight in all genotypes. Juchi F2000, Rebeca F2000 and Temporalera M87did not show decreases without application; however Nahuatl F200 had a reverse behavior and this was associated with the lowest value (Figure 3). Due to the absence of diseases by the application of fungicides, genotypes Tlaxcala F2000, Rebecca F2000, Nahuatl F2000 and Pavon F76, decreased their protein content and consequently the strength of the dough (Figure 4A and B), which affected the bread’s volume. The decrease of protein may be due to higher grain production, which was higher than 1.2 Mg in Pavon F76 and Nahuatl F2000. The applications increased the bread’s volume of Galvez M87 and Temporalera M87 (Figure 4D), which is explained given that Temporalera M87 presented increased protein contents and consequently the dough had more strength. Galvez M87, Juchi F2000, Tlaxcala F2000 and Nahuatl F2000 had the highest bread volume, with and without fungicide application. The dough’s strength is because of the combination of its characteristics: W 300104 J, PL 1.2 that are balanced to extensible (Figure 4C). Batan F96 and Rebeca F2000, given their PL1.2 are classified as tenacious doughs resulting in smaller bread volumes due to the application of fungicides; whereas without fungicides, meaning with disease, they increased the bread volume. In Rebecca F2000 this could be due to increased flour’s protein, but Batán F96 increased the dough’s strength and decreased the dough’s PL, trait that favors bread volume. This is consistent with ^{Gooding (2007)}, ^{Tanács et al. (2010)} and ^{Devadas et al. (2014)}, who indicated that the application of fungicides differentially affect these characteristics, in which the protein content and the strength of the dough of the genotypes depend. This also affects the protein content depending on the disease (^{Dimmock and Gooding, 2002} and ^{Schierenbeck et al., 2014}). Based on the above, the protein content is the variable that decreases because of the chemical control of foliar diseases, which modifies the strength and tenacity/extensibility relation and consequently changes the volume of the bread; Furthermore, these dough characteristics depend on the genetic traits of each genotype and the conditions of each location.

Figure 3 Behavior of hectolitre weight depending on the application of fungicides in rainfed bread wheat. HSD: honest significant difference. 

Figure 4 Behavior of protein content in flour: A) dough strength, B) relation tenacity/extensibility, C) bread volume, D) in terms of fungicide application in bread rainfed wheat under. HSD: honest significant difference. 

The tolerance to diseases showed by Juchi F2000 and Tlaxcala F2000 resulted in small losses in yield and little damage on leaf area without the use of fungicides. They also displayed high hectolitre weight which is due to their genetic resistance to foliar diseases and high yield potential. Both genotypes showed volumes higher than 800 mL of bread, due to a combination of dough strength and extensibility. Rebeca F2000 in the presence of the disease, showed the smallest yield decline amongst all varieties; however, due to its PL1.5, the highest of all genotypes, it was classified as tenacious dough resulting in bread volumes lower than 750 mL.

Conclusions

Fungicide application prevented the incidence of diseases and decreased losses of leaf area, grain yield and hectolitre weight, but reduced protein content, which consequently lowered dough strength and bread volume. Therefore, by selecting varieties that tolerate diseases by having less damaged leaf area or by applying fungicides it is possible to combine higher production, appropriate hectolitre weight for the milling industry, and strong-balanced or extensible dough that favors the appropriate bread volume for the national baking industry.