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Barley (Hordeum vulgare) is a cereal whose production is used for animal and human consumption. In Mexico it is cultivated mainly as raw material for the brewing industry using awned varieties with six and two-grain rows on the ear. The SIAP (2022) reported in 2021 that the planted area in the country was 345.4 thousand hectares, of which 21% were under irrigation conditions during the autumn-winter cycle and 79% under rainfed conditions in the spring-summer cycle.
In Mexico, barley production has been an alternative for producers in the Highland Valleys of Central Mexico. According to González et al. (2021), in recent years the malting-brewing industry demand has increased in requirement of two-row varieties, with yield potential, quality and disease tolerance.
Among the main diseases of economic importance worldwide are those of fungal origin, where those caused by the genus Puccinia stand out (Dean et al., 2012). Hamwieh et al. (2018) indicate that the most important limiting factors in barley-producing areas are yellow rust caused by Puccinia striiformis f. sp. hordei, leaf rust (P. hordei) and stem rust (P. graminis). Yellow rust of barley is a disease of economic importance in producing areas throughout the world. Large epidemics have been reported worldwide. Gonzalez et al. (2021) mention that in 1988 yellow rust caused losses of up to 50% of the yield of all the improved Mexican barley varieties sown in rainfed conditions in the Highland Valleys of Central Mexico. Smaller losses were determined in the El Bajío crops under irrigated conditions. Rodriguez et al. (2021) report losses in grain yield up to 53% due to yellow rust effect. In the last production cycles in Mexico, yellow rust has regained importance (Rodríguez et al., 2021), partly due to climate change, the lack of resistance in the currently planted varieties and pathogen virulence change. Rodriguez et al. (2010) indicated that rusts in cereals could overcome the specific resistance of resistant varieties by evolving towards new pathogen biotypes or physiological races with new virulence genes, in addition, the pathogens reproduce rapidly and can move long distances.
Physiological races of economically important yellow rust have been identified in barley, such was the case of race 24 identified in Colombia in 1975 as mentioned by Dubin and Stubbs (1986) and which later spread over South America. In Mexico it appeared in 1988 and later this same race was reported in Texas in 1991 as indicated by Roelfs et al. (1992). Marshall and Sutton (1995) report for the United States the dominance of race 24 and the existence of race 23, later Chen (2007) reports the presence of 22 new physiological races identified since 2000 in the United States. Prashar et al. (2014) report for India five pathotypes of P. striiformis f. sp. hordei identified during the years 2004-2005 to 2010-2011. In Iran, Safavi et al. (2017) identified the presence of 10 new physiological races during 2012-2013 and indicated that it was the first report of physiological races of P. striiformis f. sp. hordei in that country.
Rodriguez et al. (2019), Brown et al. (2001) and Gangwar et al. (2018) indicate that the best strategy to battle rusts in cereals worldwide is genetic control, based on the use of varieties with resistance to the various physiological races of rusts that exist in the producing regions. Sandoval et al. (1999; 2007), Niks (2014), and Gangwar et al. (2018) mention that two types of resistance have been identified in barley pathosystem; seedling resistance, which is correlated in the adult plant, and partial resistance, which is characterized by presenting susceptible seedlings, but low percentages of damaged leaf area in the adult plant. Chen and Line (2002) report 27 resistance genes for barley yellow rust.
Currently in Mexico the sowing of barley with two grain rows in the ear has increased, largely displacing the sowing of six-row genotypes, for which the objective of the present work was to identify the pathogenic variability of P. striiformis f. sp. hordei and identify genotypes of two rows with resistance to yellow rust and good agronomic behavior.
Materials and methods
Isolate identification. 45 samples of leaves with yellow rust urediniospores were collected during the spring-summer/2021 cycle from the towns of Terrenate, Nanacamilpa and Tlaxco, Tlaxcala; Apan, Hidalgo; Chapingo and Santa Lucia, Texcoco and Toluca, State of Mexico, included within the rainfed barley producing areas of the Highland Valleys of Central Mexico. The samples were transferred, for their evaluation and conservation, to National Laboratory for Rust and other Cereal Diseases (Laboratorio Nacional de Royas y Otras Enfermedades de Cereales- LANAREC) located in Valley Mexico Experimental Field (Campo Experimental Valle de Mexico-CEVAMEX), belonging to National Forestry, Agriculture and Husbandry Institute (Instituto Nacional de Investigaciones Forestales Agricolas y Pecuarias - INIFAP). The samples with yellow rust urediniospores were increased for the Apizaco variety because it was considered from susceptible to moderately susceptible to yellow rust. To do this, in polystyrene cups containing a mixture of sterile soil and Peat Moss, 60:40, 12 seeds per cup were sown. Five days after sowing, all the seedlings were treated with maleic acid (MH30®) to regulate their growth. Each sample was inoculated in a glass with eight-day-old Apizaco seedlings, suspending the urediniospores in mineral oil (Sotrol® 170; Chevron Phillips Chemical Company, The Woodlands, Texas, United States), and spraying on the leaf blades with an atomizer connected to an electric compressor. The inoculated seedlings were allowed to dry for a period of 20 min, then they were transferred to a bioclimatic chamber with temperatures of 4 °C and 100% dew for 24 hours. After that period, the inoculated seedlings were transferred to a greenhouse whose temperature fluctuated between 18-20 °C. Each glass containing the seedlings was placed in individual plastic cages. Fifteen days after inoculation, isolated urediniospores were collected from each isolate, using special collectors connected to an electric compressor and storing in gelatin capsules. To obtain sufficient and pure inoculum, the collected urediniospores were increased again for the Apizaco variety, following the procedure described above.
For isolates identification, a group of 16 barley genotypes listed in Table 1 were used, which were planted, per group, in 20 × 30 × 6 cm plastic trays containing a mixture of sterile soil and Peat moss, 60:40. During planting, small holes were marked in the substrate of each tray and 8 to 9 seeds were placed per genotype, originating the same number of seedlings; subsequently, 15 days after sowing, the group of genotypes were inoculated individually with each of the isolates (45) previously increased and following the methodology described above for the purification and increase of the inoculum. 15 days after inoculation, the reaction of the genotypes was recorded using the 0-9 scale described by Roelfs et al. (1992). For isolation designation, the abbreviation MEXC was used, which indicates that it is an isolation identified in Mexico in the barley crop, followed by the year and number of the registered isolation.
Table 1 Genotypes used to identify isolates of P. striiformis f. sp. hordei in laboratory.
| No. | Genotipo o variedad | No. | Genotipo o variedad |
|---|---|---|---|
| 1 | Heils Franken | 9 | Armida |
| 2 | Apizaco | 10 | Doña Josefa |
| 3 | Puebla | 11 | ABI Growler |
| 4 | Kaputar | 12 | ABI Voyager |
| 5 | Esmeralda | 13 | AC Metcalfe |
| 6 | Guanajuato | 14 | Maravilla |
| 7 | Esperanza | 15 | Brennus |
| 8 | Alina | 16 | Meztli |
Evaluation of genotypes in seedling. At LANAREC, under greenhouse conditions (T min. 18 °C - T max. 20 °C), the seedling resistance of 15 advanced two-row barley lines from the Barley Genetic Breeding Program of INIFAP was evaluated. CEVAMEX and a control variety (Meztli). The 16 genotypes were sown in plastic trays, small holes were marked and 8 to 9 seeds per genotype were placed, 13 days after sowing the seedlings were inoculated with a suspension of urediniospores of the isolates MEXC/21.5 and MEXC/21.9, at a concentration of 1 x 106 urediniospores/mL-1. The MEXC/21.5 isolate was identified as the one with the lowest virulence spectrum, while MEXC/21.9 was one of the most virulent and frequent. The urediniospores were suspended in mineral oil (Soltrol® 170) and sprayed with an atomizer connected to a compressor. The inoculated seedlings were placed in a bioclimatic chamber with temperatures of 4-7 °C for 24 hours and dew at 100%. Subsequently, they were transferred to the greenhouse and 15 days after inoculation, the response to yellow rust was recorded on the 0-9 scale proposed by Roelfs et al. (1992), where the values of 0, 1, 2, 3, 4, 5 and 6 are considered as a resistance reaction and 7, 8 and 9 as a susceptibility reaction.
Evaluation of genotypes in the field. The field evaluation was carried out during the spring-summer cycle of 2021 in three representative localities of the rainfed barley producing area of the Highland Valleys of Central Mexico: 1) Terrenate, Tlaxcala, located at 19° 26’ 55.9 “ LN and 97° 56’ 23.3” LW and at an altitude of 2,530 masl; 2) Nanacamilpa, Tlaxcala, at 19° 30’ 8.3” LN, 98° 31’ 9.6” LW and an altitude of 2,701 masl, 3) Chapingo, Texcoco, State of México, at 19° 29’ 14.8” LN, 98 ° 53’ 49.3” LW at 2,252 masl. The experimental design used was complete randomized blocks with 16 treatments (genotypes) and four repetitions, giving a total of 64 experimental units or plots for each location. The experimental unit consisted of four furrows three meters long and spaced at 30 cm, corresponding to a surface of 3.6 m2, considered a useful plot. Fifteen advanced lines were evaluated (three of them in the process of being described for their official registration with the National Seed Inspection and Certification Service - SNICS) and the Meztli variety, recently introduced to Mexico. All germplasm was from two rows. The incidence of yellow rust occurred naturally from the growth stage of booting (development stage 41-49; Zadoks et al., 1974) since the three locations present favorable climatic conditions for the development of the disease, such as cold to warm temperatures (5 to 18 °C) and the formation of dew. The registered variables were: 1) Days to heading (DE), days elapsed from sowing to the moment in which 50% of the plants presented visible spikes; 2) Days to physiological maturity (DM), days elapsed from sowing to the moment the spike peduncle turned hay yellow ; 3) Plant height (AP), height in centimeters from the soil surface to the tip of the terminal or higher spike; 4) Grain yield (REND), grain weight produced by all the spikes of each useful plot, registered in grams, which was subsequently transformed into kg ha-1; 5) Test weight (PH), grain weight per unit volume (kg hL-1); 6) Final disease severity (SFE), maximum level of damaged leaf area, registered as a percentage and using the scale suggested by Roelfs et al. (1992). With the severity readings taken in time intervals (three), the Area Under the Disease Progress Curve (AUDPC) was calculated using the equation described by Bjarko and Line (1988). The data of the variables obtained in the three locations were analyzed statistically in jointly with the SAS 9.3 program (SAS, 2016) and mean comparisons were made for the variables under study using the DMS test (p≤ 0.01).
Results and discussion
Virulence of P. striiformis f. sp. hordei
In the spring-summer 2021 cycle, nine isolates of P. striiformis f. sp. hordei were identified in seven locations in Tlaxcala, State of Mexico, and Hidalgo. These isolates are shown in Table 2, where MEXC/21.9, MEXC/21.16 and MEXC/21.23 were the most virulent, while MEXC/21.5 was the least virulent. All the isolates were avirulent in the Heils Franken, Esperanza, Alina, Armida, Doña Josefa, Maravilla and Brennus genotypes, and virulent to ABI Growler.
Table 2 Isolates of P. striiformis f. sp. hordei identified in the spring-summer/2021 cycle.
| No. | Aislamiento | Virulenciaz | Avirulenciaz | Frecuencia (%) |
|---|---|---|---|---|
| 1 | MEXC/21.5 | 2,11 | 1,3,4,5,6,7,8,9,10,12,13,14,15,16 | 9 |
| 2 | MEXC/21.7 | 2,3,4,11,12,13,16 | 1,5,6,7,8,9,10,14,15 | 13 |
| 3 | MEXC/21.9 | 2,3,4,6,11,12,13,16 | 1,5,7,8,9,10,14,15 | 27 |
| 4 | MEXC/21.10 | 2,4,11,12,13,16 | 1,3,5,6,7,8,9,10,14,15 | 11 |
| 5 | MEXC/21.11 | 2,3,4,6,11,12,13 | 1,5,7,8,9,10,14,15,16 | 7 |
| 6 | MEXC/21.16 | 2,3,4,5,6,11,12,13,16 | 1,7,8,9,10,14,15 | 7 |
| 7 | MEXC/21.18 | 3,4,6,11,12,13,16 | 1,2,5,7,8,9,10,14,15 | 4 |
| 8 | MEXC/21.23 | 3,4,5,6,11,12,13,16 | 1,2,7,8,9,10,14,15 | 11 |
| 9 | MEXC/21.35 | 4,11,12,13,16 | 1,2,3,5,6,7,8,9,10,14,15 | 11 |
z The number refers to the barley genotypes indicated in Table 1.
Table 3 shows the isolates identified by locality and state, where it is observed that the greatest diversity (four isolates) was identified in Terrenate, Tlax. In this locality, the MEXC/21.9 isolate was also identified with greater frequency, 27%, and it was also identified in Nanacamilpa, Tlax. On the other hand, the isolate MEXC/21.18 was identified in Tlaxco, Tlax. and Apan, Hgo. It is worth mentioning that these locations are within the most important barley production areas in the states of Hidalgo and Tlaxcala.
Table 3 Isolates of P. striiformis f. sp. hordei identified in seven locations in Valles Altos during the spring-summer/2021 cycle.
| Estado | Localidad | Aislamiento |
|---|---|---|
| Tlaxcala | Terrenate | MEXC/21.7, MEXC/21.9 MEXC/21.10, MEXC/21.35 |
| Nanacamilpa | MEXC/21.9 | |
| Tlaxco | MEXC/21.18, MEXC/21.9 | |
| Estado de México | Chapingo | MEXC/21.5, MEXC/21.16 |
| Santa Lucia | MEXC/21.23 | |
| Toluca | MEXC/21.11 | |
| Hidalgo | Apan | MEXC/21.16, MEXC/21.18 |
Barley yellow rust (Figure 1) did not exist in Mexico until 1986 and according to Calhoun et al. (1988) and Sandoval et al. (1999), during the summer of 1987, this disease was detected in the Highland Valleys of Central Mexico, by 1988 it caused yield losses of up to 50% as indicated by González et al. (2021). This epidemic was attributed mainly to race 24, which was characterized by its virulence for the Heils Franken genotype as indicated by Stubbs (1985) and Line (2002) and which possesses the resistance genes Rps4 and RpsHF. None of the nine isolates identified showed virulence for Heils Franken; however, they share some similarity with race 23 previously identified by Stubbs (1985) and later reported by Marshall and Sutton (1995), this race is avirulent to Heils Franken. The virulence/avirulence results observed in Heils Franken suggest that the isolates identified in this study could be derived from race 23 and not from race 24.
Figure 1 Symptoms of P. striiformis f. sp. hordei in seedling and adult plant in barley genotypes. A. Adult plants with susceptibility reaction; B. Adult plants with resistance reaction; C. Uredia in leaf of adult plant; D. Uredia and telia in grains and awns; E. Telias in sheath; F. Susceptibility response in the seedling stage; G. Uredias on seedling leaf.
The Esperanza, Alina, Armida and Maravilla barley varieties were resistant to all the isolates identified. Esmeralda was only susceptible to the isolates MEXC/21.16 and MEXC/21.23. This variety has been moderately resistant to yellow rust since its release and was described by Zamora et al. (1997) as the first variety developed in Mexico for rainfed conditions that has tolerance to yellow rust and that, until 2015, occupied 80% of the sown area of rainfed barley. However, González et al. (2021) indicate that INIFAP has obtained great achievements in varieties release, the most important being Esperanza and Esmeralda, which due to their resistance to stripe or yellow rust, allowed the production of barley for brewing both under irrigation and rainfed conditions; achieving national self-sufficiency in the year 2000.
Response in seedling and adult plant. Under controlled laboratory and greenhouse conditions, the response was evaluated in seedlings of 15 lines and a two-row barley control variety. Table 4 shows the seedling response to two isolates, MEXC/21.9 with its virulence/avirulence formula: Apizaco, Puebla, Kaputar, Guanajuato, ABI Growler, ABI Voyager, AC Metcalfe, Meztli/Heils Franken, Esmeralda, Esperanza, Alina, Armida, Doña Josefa, Maravilla, Brennus; and MEXC/21.5: Apizaco, ABI Growler/Heils Franken, Puebla, Kaputar, Esmeralda, Guanajuato, Esperanza, Alina, Armida, Doña Josefa, ABI Voyager, AC Metcalfe, Maravilla, Brennus, Meztli. Lines L-3, L-4, L-5 and the Meztli variety were susceptible to the two isolates evaluated, and L-10 was only susceptible to the MEXC/21.5 isolate. In 80% of the lines evaluated, a resistance response was observed with readings of 0 to 6 of infection according to the scale of Roelfs et al. (1992).
Table 4 Response in seedling and adult plant to P. striiformis f. sp. hordei in 16 two-row barley genotypes.
| Línea | Resistencia en plántula | Resistencia en planta adulta | |||
|---|---|---|---|---|---|
| MEXC/21.9 | MEXC/21.5 | Terrenate, Tlax. | Nanacamilpa, Tlax. | Chapingo, Edo. Mex | |
| L-1 | 4 | 5 | 10MSz | 10MS | 5MR |
| L-2 | 5 | 6 | 1R | 0R | 0R |
| L-3 | 7 | 7 | 20MS | 10MS | 5MR |
| L-4 | 8 | 7 | 15MS | 5MR | 5MR |
| L-5 | 7 | 7 | 5MR | 5MR | 5MR |
| L-6 | 4 | 5 | 5MR | 0MR | 0MR |
| L-7 | 4 | 4 | 10MS | 1R | 0R |
| L-8 | 4 | 5 | 0R | 1R | 0R |
| L-9 | 3 | 5 | 0R | 5MR | 0R |
| L-10 | 4 | 8 | 0R | 0R | 0R |
| L-11 | 5 | 6 | 0R | 0R | 0R |
| L-12 | 4 | 4 | 5MR | 1MR | 0R |
| L-13 (Salome “s”) | 4 | 3 | 1R | 0R | 0R |
| L-14 (Frida “s”) | 4 | 4 | 0R | 5MR | 5MR |
| L-15 (Alexia “s”) | 4 | 4 | 0R | 0R | 0R |
| Meztli | 7 | 7 | 15MS | 10MS | 5MS |
z R=Resistant; MR=Moderate Resistance; MS=Moderate Susceptibility.
Regarding resistance in adult plants, Table 4 indicates the percentage of final severity observed in the towns of Terrenate and Nanacamilpa, Tlaxcala and Chapingo, Texcoco, State of Mexico. Most of the lines evaluated showed satisfactory levels of resistance in adult plants with readings of 0 to 10% infection. Lines 3 and 4 were moderately resistant to moderately susceptible, with readings of 15 to 20% infection. The control variety (Meztli) was moderately resistant to moderately susceptible (5 to 15% severity), it should be noted that it is a recently introduced variety for cultivation under the two planting conditions in Mexico (irrigated and rainfed) and it is likely that share a similarity with the germplasm introduced from other countries (USA and Canada) by the brewing consortia, for which its observed resistance levels are not satisfactory. In the candidate lines for release (Frida “s” and Alexia “s”) good resistance was observed to P. striiformis f. sp. hordei in seedlings, as well as in adult plants in all evaluation locations.
Based on the resistance response to yellow rust observed in the evaluated genotypes, it can be inferred that monogenic resistance predominates over polygenic resistance in the barley program, since of the 15 lines evaluated, 10 were resistant in seedlings and adult plants; however, three lines were also identified (L-3, L-4 and L-5) that were susceptible in seedlings while in adult plants they were moderately resistant to moderately susceptible, which infers that they have polygenic type resistance. The results shown coincide with what was reported by Sandoval et al. (1999; 2007); Niks (2014); Gangwar et al. (2018) who indicate that in the barley-yellow rust pathosystem, two types of resistance have been identified; seedling resistance, which is correlated in the adult plant, and partial resistance, which is characterized by presenting susceptible seedlings, but low percentages of damaged leaf area in the adult plant.
Agronomic behavior. In barley as in other crops, agronomic variables are the main factors to consider when generating and releasing a variety, so evaluating the agronomic behavior in the field allows us to observe the potential of each genotype. Table 5 shows the comparison of means by location of the variables days to heading (DE), days to maturity (DM), plant height (AP), test weight (PH) and grain yield (REND) of the 15 lines and control variety. For DE, the town of Chapingo was where the genotypes expressed greater earliness. For DM, Nanacamilpa and Terrenate were statistically the same; in both locations, the crop cycle was longer, unlike Chapingo, where the average physiological maturity of the germplasm was 105 days. Similar results were reported by González et al. (2016), who indicate that the specific conditions of each environment determine the duration of the crop cycle. Regarding AP, in the town of Terrenate the largest plant sizes were observed and the smallest in Nanacamilpa (Table 5). For PH, the highest values for this variable were obtained in Chapingo (61.06 kg hL-1), followed by Nanacamilpa (59.49 kg hL-1). Only the town of Terrenate registered an average PH value lower than what is established in the standard for the commercialization of the products. According to González et al. (2013), the test weight (PH) is a quality factor related to the texture of the endosperm or the protein content of the grain, being a very important parameter in the industrialization of malting barley because its values directly influence the performance and quality of finished products. The grain yield (REND) was higher in Chapingo with 5,282 kg ha-1; for the towns of Nanacamilpa and Terrenate, no significant statistical differences were observed in the yield obtained. In general, the best agronomic performance was observed in Chapingo, State of Mexico, and although the best PH and yield values were recorded in this locality, these variables are not correlated. However, genotypes with high values for these two variables are preferred.
Table 5 Comparison of means of the agronomic behavior of 16 two-row barley genotypes in three locations in Tlaxcala and State of Mexico, during the Spring-Summer cycle, 2021.
| Localidades | Días a espigamiento | Días a madurez fisiológica | Altura de planta | Peso hectolítrico (kg ha-1) | Rendimiento de grano means-1) |
|---|---|---|---|---|---|
| Chapingo | 52 cz | 105 b | 92 b | 61.06 a | 5282 a |
| Nanacamilpa | 64 a | 126 a | 78 c | 59.49 b | 4356 b |
| Terrenate | 61 b | 121 a | 104 a | 55.57 c | 4166 b |
| media | 59 | 117 | 91 | 58.71 | 46012 |
| DMS | 0.75 | 6.41 | 6.94 | 0.60 | 253.15 |
zMeans with the same letter within columns are not statistically different (DMS, p≤ 0.01).
Table 6 shows the comparison of means for the 16 genotypes including the control variety, where statistical differences are observed between them for all the variables evaluated. For days to heading (DE) line 13 (L-13) was the earliest (49 days), while the latest (71) was the control variety Meztli. For days to maturity (DM) L-3 and L-13 were the earliest, while Meztli (control) was the latest; the late cycle shown in the control is commonly observed in the introduced materials (Rodríguez et al., 2021) and recommended by the brewing consortiums. It is likely that the main cause is they were not generated for the growing conditions present in Mexico. For plant height (AP), the L-3 was the largest (99 cm), the rest of the genotypes had smaller sizes in relation to this line, with the L-13 line being the genotype with the lowest plant height. According to González et al. (2016) these plant sizes are considered intermediate and suitable for growing barley, higher heights than those registered here favor lodging problems and subsequent problems during harvest. The L-13 was the one that registered the highest test weight (PH) on average (63.12 kg hL-1), followed by L-11, while the lowest value was observed in Meztli (53.71 kg hL-1), being 10 units lower than the value obtained in the best line, which represents a 17% superiority of the experimental line over the control. The registered PH values show a great variation between the germplasm evaluated as a response of the genotype to the production environment (Kangor et al., 2017; González et al., 2016). Regarding grain yield, six lines outperformed the commercial control. The highest yields were observed in L-8 (6,097 kg ha-1), L-9 (5,776 kg ha-1) and L-14 (5,706 kg ha-1), which were statistically equal. The L-8 line yielded 1,200 kg more than the control Meztli, which was equivalent to 24.5% more gain. Regarding Final Disease Severity (SFE) and Area Under the Disease Progress Curve (AUDPC), Meztli was the variety where the highest values were observed (145), followed by L-3 and L- 1 for these variables (Table 6).
Table 6 Comparison of means in 16 two-row barley lines for the variables DE, DM, AP, PH, REND, SFE and AUDPC from three locations during the Spring-Summer cycle, 2021.
| Línea | Días a espigamiento | Días a madurez fisiológica | Altura de planta | Peso hectolítrico (kg hL-1) | Rendimiento de grano (kg ha-1) | Severidad final de la enfermedad | ABCPEy |
|---|---|---|---|---|---|---|---|
| L-1 | 59 de | 117 bcd | 92 cdef | 58.03 cdef | 3611 gh | 4.3 bc | 46.3 cdz |
| L-2 | 60 cd | 117 bcd | 91 def | 57.06 f | 3864 gh | 0.2 d | 2.5 d |
| L-3 | 56 h | 110 gh | 99 a | 58.30 cdef | 4899 de | 7.7 b | 102.5 ab |
| L-4 | 58 efgh | 114 defg | 97 ab | 59.16 bcdef | 3653 gh | 3.7 cd | 55.0 bc |
| L-5 | 59 de | 116 bcdef | 92 bcdef | 58.47 cdef | 3465 h | 1.8 cd | 26.3 cd |
| L-6 | 57 gh | 112 efg | 95 abcd | 60.14 bc | 3935 g | 1.0 cd | 15.0 cd |
| L-7 | 59 de | 118 bcd | 93 bcdef | 59.67 bcde | 5442 bc | 2.0 cd | 28.8 cd |
| L-8 | 62 b | 120 b | 89 f | 59.54 bcde | 6097 a | 0.2 d | 1.3 d |
| L-9 | 60 bcd | 120 b | 92 cdef | 57.54 ef | 5776 ab | 0.3 d | 2.5 d |
| L-10 | 61 bc | 117 bcd | 96 abc | 57.76 ef | 4456 f | 0.0 d | 0.0 d |
| L-11 | 57 gh | 114 defg | 95 abcd | 60.95 ab | 4374 f | 0.0 d | 0.0 d |
| L-12 | 52 i | 112 efg | 83 g | 60.01 bcd | 4539 ef | 1.0 cd | 11.3 cd |
| L-13 (Salome s”) | 49 j | 106 h | 77 h | 63.12 a | 3792 gh | 0.2 d | 2.5 d |
| L-14 (Frida “s”) | 62 b | 119 b | 94 bcde | 58.42 cdef | 5706 ab | 1.0 cd | 8.8 cd |
| L-15 (Alexia “s”) | 62 b | 119 b | 91 ef | 58.35 cedf | 5119 cd | 0.0 d | 0.0 d |
| Meztli | 71 a | 141 a | 83 g | 53.71 g | 4896 de | 14.2 a | 145 a |
| DMS | 1.98 | 4.69 | 4.45 | 2.20 | 433.47 | 3.96 | 49.75 |
YAUDPC = area under the disease progress curve. z Means with the same letter within columns are not statistically different (DMS, p≤ 0.01).
In general, most of the lines evaluated showed adequate agronomic and physical characteristics, of which grain yield and hectoliter weight are the most important parameters for choosing the genotypes that can be released. In accordance with the NMX-FF-043-SCFI-2003 standard, the minimum value of two-row barley to be considered for brewing industrialization will be 58 kg hL-1. Of the 15 lines evaluated, 12 of them on average presented test weight values according to the established standard.
Few studies have been reported in Mexico that focus on evaluating the pathogenic variability of P. striiformis in barley; however, in recent agricultural cycles yellow rust is occurring more frequently in the country, as mentioned by Rodríguez et al. (2019). In other countries such as the USA, Chen and Penman (2005) report the presence of 15 physiological races that they identified in 2004 in California and Oregon. Subsequently, Wang and Chen (2012) detected the presence of 11 physiological races in 2008 and five in 2009 in Oregon and Washington. Wang and Chen (2019) reported the presence of 12 races primarily identified in the western USA. Studies conducted by Prashar et al. (2014) reported five pathotypes for India, while Safavi et al. (2017) identified the presence of 10 physiological races in Iran. Recently Bai et al. (2022), mention that in the United States the pathogenic diversity of P. striiformis increased from 2010 to 2017, observing rapid changes in virulence from one year to the next. Given this evidence, it is essential to monitor the pathogenic variability of P. striiformis, which will allow any change in virulence to be known in time, being an important strategy to consider in breeding programs as indicated by Rodríguez et al. (2010) who, when analyzing the virulence of yellow rust in wheat crops, highlight the importance of identifying physiological races of the pathogen, being a useful tool in genetic improvement, which allows creating and releasing new varieties with the most effective genetic combinations for disease control.
Due to its resistance in the field to P. striiformis f. sp. hordei, under natural incidence, lines L-10, L-11 and L-15 were identified as immune; however, in general, the resistance levels observed in most two-row barley lines are satisfactory. These results coincide with what was reported by Xi et al. (2013) who indicated that, when evaluating two-row and six-row barley germplasm, they found a greater number of two-row genotypes with resistance to yellow rust. However, in the INIFAP barley improvement program, in recent years the germplasm obtained has been tested for natural infection in the field and in the greenhouse with selected isolates. This strategy has allowed the selection of lines with high resistance levels, this strategy used in Mexico is also applied in barley improvement programs in various countries, including the USA, as mentioned by Chen (2007). On the other hand, Brown et al. (2001) indicated that genetic resistance is an effective, practical and economic mean for the management of barley yellow rust. Ambula et al. (2022) also indicated that genetic resistance is an effective alternative if resistant genotypes are incorporated into the new varieties, allowing to improve the productivity of the barley crop by reducing the effects of rusts. Furthermore, Czembor et al. (2022) mention that adult plant resistance (APR) is potentially more durable and effective for disease control in barley, avoiding yield losses.
Considering the variability of P. striiformis f. sp. hordei present in Mexico and the level of resistance that the varieties and lines have, it is important to continue with the evaluation and rotation of germplasm in contrasting environments to avoid the decrease in resistance already obtained in breeding programs.
Conclusions
Nine yellow rust isolates of barley were identified in the spring-summer/2021 cycle. No virulence was identified for the Heils Franken genotype, therefore race 24 was not detected. Most of the two-row barley lines showed monogenic resistance. Line L-8 was the one with the highest yield potential and resistance to yellow rust in seedlings and adult plants. Alexia “s” is the candidate line with immunity to yellow rust. The evaluation of resistance in the greenhouse and in the field under contrasting environments is a viable strategy for the identification of germplasm resistant to yellow rust in barley that will allow the release of varieties with genetic resistance.
