Origin and process of obtaining

‘San Blas’ originated from the simple cross Jamapa Plus/XRAV-187-3 carried out in 2010 in The Bajío Experimental Field (CEBAJ) of the INIFAP (Table 1). The Jamapa Plus variety was used as a progenitor due to its wide adaptation to the humid tropics and The Bajío and because of its high commercial acceptance grain; the XRAV-187-3 line was used as a source of resistance to BCMV, BCMNV. Jamapa Plus was derived through mass selection of the Jamapa variety under pressure of a viral complex under field conditions (Comun. Pers. Ernesto Lopez Salinas CECOT-INIFAP, 2010).

The XRAV-187-3 line was developed from the PR0003-124 Raven cross (^{Beaver et al., 2014}), Raven contains genes II and bc-3 that confer broad spectrum resistance to BCMV and BCMNV (^{Kelly et al., 1994}). ‘San Blas’ was obtained by the genealogical method, carrying out two generations per year until its standardization and inclusion in yield tests.

In the F₂ and F₄ generations, under irrigation during the early season of the year, in CEBAJ healthy plants were selected under pressure of BCMV and BCMNV under natural field conditions, which was confirmed by reverse transcription and polymerase chain reaction (RT-PCR) following the protocol described by ^{Chiquito-Almanza et al. (2017)}. Subsequently, individual selection was made in generations F₅ and F₆.

In 2013, the F₈ lines were evaluated in Guanajuato under storm and natural presence of diseases such as rust, powdery mildew, common mosaic, common blight and halo blight. During the autumn-winter cycle (A-W) 2013/14 the trial was established in Nayarit, the line (Jamapa Plus/XRAV-187-3)-M-M-9-M-3, which gave rise to ‘San Blas’, showed resistance in the field to BCMV and BCMNV viruses. In 2015, together with other 70 bean genotypes, it was phenotyped by artificial inoculation with the BCMNV NL-3 strain at CEBAJ facilities under greenhouse containment conditions and genotyped with molecular markers (MMs) SW13 (^{Melotto et al., 1996}) and ENM (^{Naderpour et al., 2010}), associated with resistance genes I and bc-3, respectively, following the methodology described by ^{Anaya-López et al. (2018)}. From 2016 to 2019, the line that gave rise to the ‘San Blas’ variety was evaluated in Guanajuato and Nayarit. Table 1 summarizes the development of the ‘San Blas’ variety.

Agronomic characteristics of the San Blas variety

The San Blas plant is of indeterminate type II semi-erect habit, with lilac-purple flowers, medium-sized dark green leaves, straw-colored pods at maturity, and grain similar to Jamapa, Negro Opaco in color and small in size. In The Bajío, its flowering and physiological maturity occurs around 45 and 92 days after sowing, respectively (Tables 2 and 4), while in Nayarit at 40 and 80 dds, respectively (Table 4). The average yield of San Blas in six different environments in Guanajuato was 1841 kg ha^-1, 12% more than Negro 8025; while in three different environments in Nayarit it was 1927 kg ha^-1, 50 and 36% more than Jamapa and Coranay (Table 4).

In the 2013 storm cycle in CEBAJ, Celaya presented high pressure of common blight, halo blight, ash and rust. With the exception of the experimental line (Jamapa Plus/XRAV-187-3)-M-4-10 and the Jamapa Plus and Negro Guanajuato varieties, the San Blas variety had yield values slightly higher than the average of the other materials, in weight of 100 seeds, its value was similar to all materials and showed lower values of reaction to naturally occurring diseases (Table 2).

Regarding the incidence of viruses causing black root, Verdin, Jamapa, Negro Guanajuato and Negro 8025 showed a low percentage of infected plants, while San Blas and other sister lines were not affected. For common blight, the line (Jamapa Plus/XRAV-187-3)-M-2-8 and the Negro 8025 variety showed the highest incidence. For halo blight, the line (Jamapa Plus/XRAV-187-3)-M-4-10 and Jamapa Plus showed the highest incidence. For mildew only Negro Comapa showed a value above 3 and for rust only (Jamapa plu/XRAV-187-3)-M-4-10. In days of flowering and maturity, Verdin showed the least number, while Jamapa Plus and Negro Guanajuato were the latest.

In the evaluation of San Blas y Negro 8025 in Celaya, Guanajuato under three fertilization treatments during the S-S 2017 cycle in rainfed conditions plus supplementary irrigation to flowering, the highest average yield corresponded to San Blas (Table 3); this result was partly due to the characteristic of resistance to the BCMV and BCMNV viruses of San Blas, since it did not show incidence of common mosaic or black root under any fertilization treatment, while Negro 8025 showed incidence of black root through treatments (>10%). Across varieties, the average dose was higher in yield (p< 0.01) and the sub-optimal and optimal doses showed a similar yield. Regarding the weight of 100 seeds, the two varieties were similar and were within the acceptable commercial range for beans of the small Negro Opaco type, similar to that of the Jamapa variety to which they belong (Table 3).

In rainfed and irrigated conditions in The Bajío, San Blas was occasionally superior to Negro 8025, both in seed weight and yield (Table 4). As for the days to start flowering, in general San Blas starts in less time than Negro 8025 and as the maturity is similar, San Blas has a longer reproductive period.

In 2017, under a storm plus an aid irrigation, the maximum yield of San Blas in the locality was observed, of 2 731 kg ha^-1, while the lowest was obtained in the late 2018 sowing under temporary and under strong pressure by leafhopper (Empoasca kraemeri).

Regarding the weight of the seed, San Blas and Negro 8025 were similar. In an average of six different environments, San Blas exceeded the yield of Negro 8025 by 12% (Table 4). In residual humidity conditions in the A-W 2017/2018 cycle in the towns of Ruiz, Santiago Ixcuintla and San Blas, Nayarit; the average yield was 1 927 kg ha^-1, 50 and 36% more than the Jamapa and Coranay varieties, respectively (Table 4). San Blas showed values of 1 in the reaction to the common mosaic and the black root on the ^{Shoonhoven and Pastor-Corrales scale (1987)} across all the test locations, while the control varieties showed values between 2 and 4 (Table 4), which confirmed the resistance to BCMV and BCMNV of San Blas.

Conclusions

The ‘San Blas’ variety was resistant to BCMV and BCMNV in all the test locations. This is the first variety in Mexico that includes the combination of resistance genes I and bc-3. In The Bajío, the San Blas variety with an average yield of 1 841 kg ha^-1 was 12% higher than Negro 8025. In Nayarit the average yield was 1 927 kg ha^-1, 50 and 36% higher than that of the varieties local Jamapa and Coranay. The first author can be contacted to obtain seed samples for research purposes or to be used as a parent by giving the corresponding credits to the National Institute of Forestry, Agricultural and Livestock Research.