December 30, 2002

A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases
Source: Amer Phytopathol Soc, DISEASE NOTES [edited]


First Report of Phakopsora pachyrhizi, the Causal Organism of Soybean Rust in the Province of Misiones, Argentina

R. L. Rossi, Programa Soja, Nidera Semillas S.A., Ruta 8 km 376, C.P. 2600, Venado Tuerto, Santa Fe, Argentina. Plant Dis. 87:102, 2003; published on-line as D-2002-1118-02N, 2002. Accepted for publication 8 Oct 2002.

In April 2002, _Phakopsora pachyrhizi_ [Pr] Sydow was observed for the first time in Leandro Alem,  Province of Misiones, Argentina. Misiones is nearly surrounded by Paraguay and Brazil, where it was
discovered recently (2) and where it causes serious disease (3).

Symptoms were observed on leaves in the upper half of plants at the R6 stage in a soybean research field trial. Symptoms included reddish-brown lesions on leaves especially on the abaxial surface, and uredinia (spore-bearing structures) were observed in the lesions. Leaf defoliation was observed due to the disease after the R5 stage, and the environment (high humidity and air temperatures) was particularly conducive to disease development.

The field trial area was 2500 square meters and included soybean genotypes of maturity groups V to IX. Symptoms were detected in the later maturity groups. Field trials were surrounded by kudzu
(_Pueraria_ sp.),  a common weed introduced in South America as a forage plant by Asian farmers. It was reported to be the main host of Pr in Paraguay (2).

To confirm the identity of the pathogen, leaf samples from the middle part of plants were collected and sent to the Foreign Disease-Weed Science Research Unit, Ft. Detrick, MD, USA. Samples were analyzed using a real-time PCR (1). Identification of Pr was confirmed in May, 2002 (R. Frederick, personal communication).

The soybean production area in Misiones is a small area in Argentina lying 600 km northeast of the main soybean area in the north central part of the country. SENASA (Servicio Nacional de Sanidad Vegetal Nacional Service of Plant Health]) and SAGPYA (Secretary of Agriculture) were formally informed about these results on 19 Jun 2002.

A program to assess the risk of disease spread is under development.

References:
(1) R. D. Frederick et al. Phytopathology 92:217, 2002.
(2) W. Morel Paiva. AnaisII Congresso Brasilero de Soja e Mercosoja. Foz de Iguazu, Brazil, 2002.
(3) T. Yorinori. Anais II Congresso Brasilero de Soja e Mercosoja. Foz de Iguazu, Brazil, 2002.

Soybean rust in South Africa

From: Eve du Preez <eve.dupreez@dae.kzntl.gov.za>

The first report of soybean rust caused by the fungus Phakopsora pachyrhyzi in the 2002/2003 season was announced on 30 Dec 2002 at Cedara, an agricultural research station in KwaZulu-Natal Province. It was found in an early-planted trial which is in early pod set. The infection is still at a very early stage, with only a few lesions visible on lower leaves.

Soybean rust was first identified in South Africa in late February 2001,when it was believed to have blown in from neighbouring Zimbabwe. It reoccurred in 2002, with the first report on 4 Feb 2002. This latest report is the third successive season in which the disease has occurred and is now thought to be endemic in the area. What is of considerable interest is how much earlier it has been identified this season.

Eve du Preez
Plant Pathologist
Crop Protection
KwaZulu-Natal Department of Agriculture & Environmental Affairs
<eve.dupreez@dae.kzntl.gov.za>

[Soybean rust, first reported in Hawaii in 1994, has been reported in several areas (Australia, Brazil, China, India, Japan, central and southern Africa, and Thailand). Yield losses of 10 to 90 percent have
been reported for some of these areas. There are 2 species, _Phakopsora meibomiae_ and _P. pachyrhizi_, the latter being the more aggressive pathogen. _P. pachyrhizi_ was reported in South America for the first time in 2001, and again in 2002. Yield loss estimates for Paraguay and Brazil range from 10 to 50 percent for 2002, respectively, in some fields. This disease also has the potential to cause significant losses in the United States. The fact that the pathogen may be endemic in the region is cause for concern, since spores can be spread by wind, causing the disease in other regions of Africa.

Two excellent references are:
http://www.ag.uiuc.edu/cespubs/pest/articles/200213k.html
http://www.aphis.usda.gov/ppq/ep/pestdetection/soybean_rust/soybeanrust.html
- Mod.DH]

[see also:
Phakopsora sp., soybean rust - South Africa      20020206.3495
Phakopsora sp., rust, soybean - Zimbabwe      20020110.3220
2001
Phakopsora sp., soybean rust - South Africa (03) 20011213.3014
Phakopsora sp., soybean rust - South Africa (02) 20010405.0679
Phakopsora sp., soybean rust - South Africa      20010312.0505
Phakopsora sp., soybean rust - S. Africa (confirmed)      20010322.0569
Phakopsora sp., soybean rust - Nigeria      20010309.0486
Phakopsora sp., soybean rust - Africa (02) 20010310.0491
Phakopsora sp., soybean rust - Africa      20010309.0487]
.............................dh/pg/lm

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