Crop Breeding and Applied Biotechnology - 20(1): e27242016, 2020 BRS 372 and BRS 416: high-yielding cotton cultivars with multiple disease resistance

: BRS 372 and BRS 416 are cotton cultivars with high lint yield and genetic resistance to the main cotton diseases in Brazil, particularly to Ramularia Leaf Spot. They have stable yields, good fiber quality and can contribute to a sustainable cotton disease management in tropical environments. 2007-423 progenies were bulk-harvested and tested in 2008/2009 as preliminary breeding line (F 9 ). Line CNPA 2007-423 was evaluated as advanced breeding line (F 10 ) in the states of Goiás, Bahia, Mato Grosso and Mato Grosso do Sul, in 2009/2010. In the 2010/2011 and 2011/2012 growing seasons, it was evaluated as final breeding line (F 11 ) in 26 official variety trials for value of cultivation and use (VCU), in the states of Bahia, Goiás, Mato Grosso do Sul, Mato Grosso, Minas Gerais, Maranhão, Piauí, and Rondônia.


INTRODUCTION
Cotton (Gossypium hirsutum L.) is an important commodity in the global agricultural economy. Since the 1980's, the cotton-growing area in the Brazilian savannah (cerrado) was significantly increased, mainly due to the development of genetically improved cotton cultivars, with e.g., higher lint yield and adapted to the cerrado, and because of adjustments and enhanced production systems (Silva Neto et al. 2016). Currently, more than 90% of the Brazilian cotton-growing areas are located in this ecosystem. Particular characteristics of these production systems are extensive areas, high inputs and use of high yielding cultivars that are frequently susceptible to tropical diseases (Ferreira Filho and Alves 2007). In this scenario, diseases previously considered secondary or new diseases, e.g., Ramularia Leaf Spot (RLS), caused by the fungus Ramulariopsis pseudoglycines, can become epidemic. The latter cotton disease has a high economic relevance since up to eight fungicide applications per season are required to control it in a production area of more than 1.000,000 hectares (Silva et al. 2019).
In Brazil, much effort has been invested in developing new cotton cultivars (Morello et al. 2010, Morello et al. 2012, Morello et al. 2015, Barroso et al. 2017, Suassuna et al. 2018, to ensure high lint yields and the competitiveness of Brazilian cotton on the international market. However, most of the released cultivars are RLS-susceptible. Moreover, the prevalent weather conditions (long periods of high air humidity and daytime temperature between 25 and 30 o C) throughout the growing season in the cerrado ecosystem are conducive to RLS development (Rathaiah 1977). This must have contributed to proliferate the initial inoculum over years and let the disease become epidemic. Consequently, more fungicide sprays per season in cotton fields are now required, increasing the cost for RLS management.
The cotton breeding program of EMBRAPA (Brazilian Agricultural Research Corporation) was established in 1975, and since 1989, cultivars adapted to ND Suassuna et al. the cerrado have been released. After 2004, efforts were made to develop germplasm resistant to the major diseases, mainly to RLS. For this specific purpose, the breeding program, in partnership with the private sector, was financially supported by FIALGO (Fundo de Incentivo à Cultura do Algodão) and technically by the Fundação Goiás. This paper describes the development of the conventional cotton cultivars BRS 372 and BRS 416 as part of an ongoing effort to create new cotton lines and cultivars with improved yield potential and resistance to one or several diseases, adapted to the Brazilian cerrado.  2003, 2003/2004, 2004/2005, 2005/2006 and 2006/2007 Plants of both cultivars have trichomes on the leaves and main stem. Leaves and bracts (7 -12 lobes) are normally shaped and have glands and nectaries. The first reproductive branch is generally inserted at the fifth node. BRS 372 has short fruiting branches, forming an oblique angle with the main stem, while BRS 416 has normal fruit branches with a more perpendicular insertion in relation to the main stem, resulting in cylindrical or cone-shaped plants, respectively. Flowers have cream-colored petals, anthers, and pollen. Full-size green bolls have greater length than width and are broader in the middle. Bolls have five, occasionally four locks. Open bolls resist shattering but are not stormproof and Table 1. T-test comparison of cottonseed yield (CY -kg ha -1 ) and lint yield (LY -kg ha -1 ) for BRS 372 and FMT 701 (control) in /2011and 2011/2012   Based on data of cv. BRS 372 from five independent field trials without fungicide spraying, a mean RLS disease score of 1.17 was recorded on a scale from 1 (immune) to 5 (highly susceptible). For cv. BRS 372, fungicide foliar sprays were not necessary to avoid losses caused by ramularia leaf spot ). Cultivar BRS 416 had a mean RLS score of 1.3 across three independent field trials, on the same 1-5 disease score scale.

GENETIC ORIGIN AND DEVELOPMENT
Disease resistance to cotton blue disease and bacterial blight was confirmed by molecular markers. The fluorochromelabeled SSR primers DC20027 and CIR246 were used for genotyping. These primers were selected because they are physically linked to resistance genes that confer total resistance to blue disease and bacterial blight. Cultivar Delta Opal was used as resistant control. Polymerase chain reactions (PCR) were performed in a multiplex system using the Kit PCR Multiplex (Qiagen), as described by Carvalho et al. (2017). For marker CIR 246, the control (Delta Opal), all BRS 372 samples and 98% of the BRS 416 samples amplified a 146-bp band, associated with the bacterial blight resistance gene B12 . In 2% of the BRS 416 samples, which were heterozygous but resistant, the 146/156 band pattern was observed. All samples of BRS 372, BRS 416 and Delta Opal (control) amplified a 202-bp band for marker DC 20027. This band pattern is associated with a resistance gene against the blue disease ).

SEED MAINTENANCE AND DISTRIBUTION
Cultivars BRS 372 and BRS 416 are protected (certificates no. 20140173 and 20170145, respectively) by the Brazilian Ministry of Agriculture, Livestock and Food Supply. Genetic seed is available at Embrapa Cotton.  ); c Disease severity (grades from 1 = resistant to 5 = highly susceptible); d For bacterial blight, resistance confirmed by the SNP marker ); e Data of plants artificially inoculated with Colletotrichum gossypii var. cephalosporioides in a field trial.