June 22, 2012

Good Progress Reported for Varieties Resistant to Soybean Rust

Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.

Soybean rust continues to be the most serious long-term chronic diseases affecting the soybean crop in Brazil. It was first discovered in Brazil during the 2000/01 growing season and it made its way to the soybean fields of Mato Grosso, which is the largest soybean producing state in Brazil, by the 2003/04 growing season. The disease has cost Brazilian farmers many billions of dollars in lost revenues and increased chemical costs.

The ultimate solution to this problem is the development of soybean varieties resistant to the disease and Brazilian scientists have made substantial progress in this area. Immediately after the disease was discovered in Brazil, scientists started to screen thousands of soybean varieties looking for resistance. Within five years after its discovery, scientists had developed soybean varieties that had increased tolerance to the disease and they named the new varieties Inox soybeans.

During the 2009/10 growing season, two conventional Inox soybean varieties were available for Brazilian farmers, one adapted to the growing conditions of Mato Grosso and one adapted for Bahia. In 2010/11 a new Inox variety was introduced containing improved resistance to the disease as well as herbicide tolerance. During the 2011/12 growing season the Inox varieties yielded significantly higher than the non-Inox varieties and 2011/12 was a good test because of the high levels of rust present in Mato Grosso. Inox varieties in the state averaged approximately 60 sacks per hectare (3,600 kg/ha or 52.2 bu/ac) compared to the state average of 52 sacks per hectare (3,120 kg/ha or 45.2 bu/ac)

The first generation of Inox soybeans had only one added gene that offered improved tolerance. Shortly thereafter they introduced the second generation of Inox soybeans that offered two genes of resistance to the disease. Brazilian scientists have now announced that a third generation of Inox soybeans will be available for planting during the 2013/14 growing season. These new varieties not only offer improved rust resistance, but they also contain resistance to cyst nematodes as well. Additionally, these third generation Inox varieties will be available as short maturing soybeans, which are in high demand by farmers in Mato Grosso.

Complete resistance to soybean rust is not yet available and it may never be due to the nature of the disease, but these new more tolerant varieties allow farmers to reduce in half the amount of chemicals needed to control the disease. Even with these new varieties, scientists recommend two fungicide applications during the growing season. Not only will the fungicides control soybean rust, but the added benefit is the control of various other foliar diseases as well.

The cost of the new Inox varieties is 2% to 3% more than for conventional varieties, but the benefits far outweigh the costs. If managed correctly, the Inox soybean varieties could yield 16 sacks per hectare more than the conventional varieties (960 kg/ha or 14 bu/ac), which equates to R$ 600 more per hectare.

Rust is present in all regions of Mato Grosso and nematodes are a problem for 90% of the soybeans grown in Mato Grosso.