IAC 2051: common bean cultivar of carioca type with slow seed coat darkening

IAC 2051 is a common bean (Phaseolus vulgaris L.) cultivar with carioca-type seed coat, mean 1000 seed weight of 300g, indeterminate semiupright type II growth habit, slow post-harvest seed coat darkening, resistance to Fusarium wilt, common bacterial blight, and three races of anthracnose, and mean yield of 2729 kg ha-1.


INTRODUCTION
Common bean (Phaseolus vulgaris L.) is rich in protein, carbohydrates, vitamins, minerals, fibers, and antioxidant phenolic compounds (Silva et al. 2009). Brazilians consume an average of 17 kg inhab -1 year -1 of common bean, with frequency of three to seven times a week (Ribeiro et al. 2019). Among the different types of common bean grown, preference in the Brazilian consumer market is for carioca-type (cream-colored seed coat with brown streaks), followed by black bean, and then other types of bean grain (Faria et al. 2008).
In the 2018/2019 crop season, Brazil produced around 3.02 million metric tons of common bean in an area of 2.93 million hectares, led by the states of Paraná. In the same crop year, mean Brazilian yield was approximately 1031 kg ha -1 , though the mean yield for the state of São Paulo was much higher: 2363 kg ha -1 (CONAB 2020).
The increase in grain yield of common bean observed over the years is a result of improvement of crop management through use of inputs, suitable agronomic practices, and improved cultivars. Common bean breeding programs are important for increasing crop yield, and annual genetic gains obtained in common bean grain yield in Brazil range from 1.07% to 6.74% , Barili et al. 2016).
Adoption of a common bean cultivar by farmers depends not only on grain yield but also on other characteristics, such as resistance/tolerance to biotic and abiotic factors that can interfere in bean development, nutritional quality, technological aspects, such as seed-coat darkening and cooking time, and post-harvest characteristics of the grain , Chiorato et al. SAM Carbonell et al. 2015. For the consumers, post-harvest quality merits consideration, especially slow seed darkening during storage since consumers associate dark bean grain color with difficulty in cooking ).

GENETIC ORIGIN AND DEVELOPMENT
The line Gen 2017-26-3-DA410 (IAC 2051) was developed from 2016 to 2018. In the winter of 2016, the carioca cultivar TAA Dama and the line SXB 410 (from the International Center for Tropical Agriculture [CIAT]), were crossed. From this cross, 20 F 1 seeds were obtained. These seeds were sown in a greenhouse in the rainy season of 2016 to obtain seeds of the F 2 generation. This multiplication provided 350 F 2 seeds.
In 2017, in the dry crop season, a sample of 50 pre-germinated F 2 seeds were transplanted to 5-liter pots in a greenhouse to identify plants with light-colored grain and with slow seed coat darkening after storage for 90 days. From this evaluation, 30 plants that exhibited slow seed-coat darkening and high 100-seed weight, characteristics of line SXB 410, were separated. The 30 plants selected in F 2 were identified as Gen 2017-1-DA410 to Gen 2017-30-DA410, in which Gen is the abbreviation used by the Common Bean Plant Breeding Program of the IAC; 2017 is the year in which the progenies were obtained; the sequence from 1 to 30 represents the total of 30 progenies selected in the F 2:3 generation; and the abbreviation DA410 refers to the parents used, with DA for the cultivar TAA Dama and 410 for the line SXB 410.
In the winter season of 2017, the 30 progenies were sown in a field on the Santa Elisa Farm of the Instituto Agronômico -IAC, Campinas, São Paulo. The seeds of each progeny were sown in 5-m rows at a spacing of 50 cm between rows. The aim of the experiment was to select plants within the progenies resistant to the soil pathogen Fusarium oxysporum f. sp. phaseoli. From this experiment was selected the progeny Gen 2017-26-DA410.
In the rainy season of 2017, each progeny of the F 2:4 generation was sown in a 5-m row, spaced 0.5 m apart, in the municipality of Capão Bonito, São Paulo. Growth habit, grain yield, yield components, and grain quality after harvest were evaluated. Five plants were selected within Gen 2017-26-DA410, which were identified as Gen 2017-26-1-DA410 to Gen 2017-26-5-DA410, thus obtaining the F 2:5 generation.
In 2018, in the dry season, the F 2:5 progenies were sown in the municipality of Mococa, São Paulo. The randomized block experimental design, with three replications, was adopted. Growth habit, grain yield, resistance to soil pathogens, and post-harvest seed coat darkening were evaluated. To evaluate the seed coat darkening, a chamber with ultraviolet light was used for selection of lines with seed coats that did not darken at 24 hours of exposure to ultraviolet light (Spitti et al. 2019). The line Gen 2017-26-3-DA410 exhibited slow darkening of grain and was incorporated in the Value for Cultivation and Use (VCU) trials. These trials began in the winter season of 2018 and finished in the dry season of 2020.
In combined analysis (Table 2)

OTHER CHARACTERISTICS
The cultivar IAC 2051 has an indeterminate semi-upright type II growth habit, mean 1000 seed weight of 300 grams, mean cycle of 90 days from emergence to physiological maturity, mean grain cooking time of 30 min, and mean protein content of 20%. In artificial inoculations with the pathogens that cause anthracnose (races 65, 83, and 89), Fusarium wilt (race 6), and common bacterial blight (XAP 19 isolate) (Table 3), under controlled conditions in the laboratory and greenhouse, the cultivar IAC 2051 exhibited resistance to these races and pathogens.
A between-row spacing of 50 cm and 12 plants per meter, which result in 240.000 plants per hectare, is recommended for the three cropping seasons. The yield of the cultivar IAC 2051 depends on the period of sowing, growing region, and technological level of the farmer (fertilization, disease and weed control, water supply, and other production factors).

TECHNICAL RECOMMENDATIONS AND SEED PRODUCTION
Considering its high mean yield and 1000-seed weight in addition to its slow seed-coat darkening, the cultivar IAC 2051 is recommended for growing in the rainy, dry, and winter crop seasons in the state of São Paulo, and for the rainy and dry crop seasons in the states of Paraná, Santa Catarina, Rio Grande do Sul, and Mato Grosso do Sul.
The IAC 2051 cultivar was registered in the National Cultivar Registry (Registro Nacional de Cultivares -RNC) of the Brazilian Ministry of Agriculture (Ministério da Agricultura, Pecuária e Abastecimento -MAPA) on August 3, 2020, under number 44819 and has seed production available in the Núcleo de Produção de Sementes do Instituto Agronômico -IAC.  (1995) using notes from 1 to 9. The plants with scores 1.0 to 3.0 were classified as resistant; from 3.1 to 6.0 as moderately resistant and from 6.1 to 9.0 as susceptible. b scoring scale adapted from Pastor-Corrales and Abawi (1987) using notes from 1 to 9. The plants with scores 1.0 to 3.0 were classified as resistant; from 3.1 to 6.0 as moderately resistant and from 6.1 to 9.0 as susceptible. c scoring scale adapted from Rava (1984) using notes from 1 to 6. The plants with scores 1.0 to 2.0 were classified as resistant; from 2.1 to 4.0 as moderately resistant and from 4.1 to 6.0 as susceptible.