**The Asian Soybean Rust in South America**

Gustavo B. Fanaro and Anna Lucia C. H. Villavicencio *Instituto de Pesquisas Energéticas e Nucleares (IPEN)* 

 *Brazil* 

#### **1. Introduction**

474 Soybean Physiology and Biochemistry

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Soybean is infected by two species of fungi that cause the rust: the *Phakopsora meibione* (Arth.) Arth. (American soybean rust), which is native from American continent, existing from Puerto Rico to southern Brazil and not cause concerns for farmers and the *Phakopsora pachyrhizi* Sydow & Sydow (Asian soybean rust), a serious disease which causes a high yield losses. The differentiation of these two species is only possible through DNA testing (Yorinori & Lazzarotto, 2004).

The *P. meibione* is the less aggressive soybean rust species and was reported in the western hemisphere, South and Central America and Caribbean. It was reported in Puerto Rico in 1913, Mexico in 1917 and Cuba in 1926 on hyacinth bean and some other leguminous species, but only in Puerto Rico in 1976 was related on soybean (Pivonia & Yang, 2004). This species occurs under mild temperatures (average below 25 °C) and high relative humidity (Yorinori & Lazzarotto, 2004).

The *P. pachyrhizi* was described as a pathogen on the legume *Pachyrhizus erosus* (L.) Urb. (well-know as jacatupé in Brazil; jícama or pois patate in France; jícama, yam and mexican turnip in English language and jícama, pipilanga, yacón or nabo mexicano in Spanish language) in Taiwan, published by Sydow & Sydow in 1914 and can infect many leguminous species in numerous orders of the family Leguminosae (Deverall et al., 1977).

The *P. pachyrhizi* was first identified in Japan in 1902, and then was detected in India (1906), Australia (1934), China (1940), in Southeast Asia (1950s) and Russia (1957). For many years it remained confined to Asia and Australia, until to be found in Hawaii in 1994 and in Africa continent (from Uganda to South Africa) in 1997 (Begenisic et al., 2004).

*P. pachyrhizi* was first identified in the America continent in March 2001 in Paraguay, which caused yield reduction of 1,100 kg/hectare. In May, it was also found in Paraná (Brazil). In 2001/02 harvest, the disease recurred throughout Paraguay and was also found in Argentina, Bolivia and in several states of Brazil. In the worst hit places, the reductions in grain yield were estimated between 10% and 80% (Yorinori, 2002).

The fungal inoculum, for the initial outbreak in South America, is thought to originated from southern Africa where soybean rust has been observed since the late 1990s (Scherm et al., 2009). Since 1994, the disease has been identified by several countries, damaging up to 40% of crops in Thailand, 90% in India, 50% in the south of China and 40% in Japan (Hartman et al., 1991; Mendes et al., 2009). In the United States, this disease was first reported at the Louisiana State University AgCenter Research Farm in 2004, but yield loss was not as high as those reported from other countries (Cui et al., 2010).

Soybean plants are susceptible to the fungus at all growth stages. As a general rule, the earlier a crop is attacked, the higher will be the loss (Mendes et al., 2009), however, if the attack occurs at flowering and pod filling stage, which is commonly observed in soybean fields, the yield reducing can be higher than in others stages (Kawuki et al., 2004).
