Breeding new cotton varieties in Brazil: 15 years of collaboration between Coodetec and Cirad.

摘要

Since 1990, Coodetec (Cooperativa central de pesquisa agricola) and Cirad (Centre de cooperation internationale en recherche agronomique pour le developpement) have been developing a program in Brazil to breed improved cotton cultivars for South America. The objectives of cotton breeding are geared towards meeting the needs of specific agrosystems due to the broad range of different cotton pests and cropping systems - ranging from labour-intensive but relatively non-intensified systems in Southern Brazil and Paraguay to highly intensive and completely mechanized systems in the Central-Western Brazilian cerrados region. The goal is to overcome the main constraints by introducing traits of resistance or tolerance to viral (blue disease), bacterial (bacterial blight) and fungal (ramulose and grey mildew) diseases and nematodes. Farmers are constantly striving to increase their cotton yields, especially in the current setting of highly fluctuating world market prices for cotton fibre, but it is even more crucial to enhance fibre quality since this product is targeted for export markets. Improved cotton cultivars are created using a pedigree-breeding schedule applied to populations obtained via broad-based intraspecific crossing of cotton varieties and lines from all over the world. The efficiency of this cotton improvement program could be boosted by taking advantage of a new molecular biology tool - marker-assisted selection - especially with respect to introgressing blue disease resistance characters. New cotton varieties can now be officially recommended on the basis of results obtained in a varietal and agronomic experimental network that spans eight Brazilian States (Parana, Sao Paulo, Mato Grosso do Sul, Minas Gerais, Goias, Bahia, and Mato Grosso) and Paraguay. Since it was founded, 15 years ago, this program has released a series of improved varieties, i.e. CD401 to CD407, which are all resistant or tolerant to blue disease and bacterial blight, CD405 being the most nematode-tolerant variety. The very early CD401 variety yields excellent fibre and has been very well received by smallholders, while CD406, with the most indeterminate growth cycle, is designed for intensive cerrado cropping conditions. These varieties have accounted for around 15% of the Brazilian market and 30% of the Paraguayan market in 2003-2004 despite very tight competition from many other public and private breeder companies. This commercial success has enabled Coodetec to entirely self-finance its cotton research program and Cirad to set up a multidisciplinary team to deal with a broad range of new research issues. The challenge is now to breed and promote cultivars tailored to specific cropping systems (direct seeding, mulch-based, cropping systems (DMC), secondary crop systems called safrinha systems, and high-density cropping - Ultra Narrow Row Cotton) and to prepare for the imminent release of genetically-modified cotton varieties.