April 14, 2003

A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases
Source: Amer Phytopathol Soc, DISEASE NOTES [edited]
M Scandiani and D Ruberti, Laboratorio Agricola Rio Parana, Moreno 225 (2930) San Pedro, Argentina; R Pioli, Facultad Ciencias Agrarias, (2123) Zavalla, Argentina; A Luque, CEREMIC, Facultad Ciencias Bioquimicas y Farmaceuticas, UNR, (2000) Rosario, Argentina; and L Giorda, EEA, INTA Manfredi, (5988) Manfredi, Argentina. Plant Dis. 87:447, 2003; published on-line as D-2003-0129-02N, 2003. Accepted for publication 3 Jan 2003.

Foliage symptoms on soybean resembling those of sudden death syndrome (SDS) were detected in Argentina during 1991 and 1992 in the Pampas Region and during 1992 and 1993 in the Northwest Region. Isolations were made in 1999, 2000, and 2001 from soybean plants (_Glycine max_ (L.) Merr.) showing these symptoms.

5 fungal isolates obtained from taproot tissue and blue sporulation on taproot exteriors were selected for further evaluation. These isolates were plated on potato dextrose agar supplemented with streptomycin (PDAS). Based on spore morphology, colony growth rate, morphology and pigmentation on PDAS, and lack of microconidia (1) 5 isolates were identified as _Fusarium solani_ f. sp. _glycines_ (Fsg).

In pathogenicity tests, soybean cvs. Ripley, Spencer, Pioneer 9492RR, and A6445 RG were inoculated in greenhouse tests with each of the isolates using toothpick and soil infestation methods for a total of 6 experiments. Isolate 171 provided by J. Rupe (University of Arkansas, Fayetteville) was
tested as a positive control.

Foliar symptoms typical of SDS and similar to those in the field were observed 14 and 25 days, respectively, after inoculation.

Lesions produced on leaves averaged 3.6 for all 5 isolates and 4 for the reference strain using a disease severity scale where: 1 = no symptoms; 2 = slight symptom development with mottling and mosaic on leaves (1 to 20 percent foliage affected); 3 = moderate symptom development with
interveinal chlorosis and necrosis on foliage (21 to 50 percent foliage affected); 4 = heavy symptom development with interveinal chlorosis and necrosis (51 to 80 percent foliage affected); and 5 = severe interveinal chlorosis and necrosis (81 to 100 percent foliage affected). Noninoculated controls were symptomless.

Differences in virulence were observed among the isolates. Based on disease symptoms in the greenhouse and cultural morphology on PDAS, the isolates were classified as Fsg.

Isolates recovered from symptomatic plants resembled Fsg on PDAS and peptone/p-chloro-nitrobenzene agar amended with streptomycin, confirming Koch's postulates. Fsg was recovered from 60 percent of inoculated plants.

Reference: (1) K. W. Roy et al. Plant Dis. 81:1100,1997.

[This appears to be the first report of SDS outside the USA. Have any of  our readers observed SDS in their jurisdictions? In a twist of fate, SDS is more common in well-managed fields. The disease is more likely to be widespread during wet and cool weather. SDS can reduce yields from 5 to 80 percent, mainly because of pod abortion, poor pod fill, and low seed weight. Unfortunately, SDS-infested fields remain infective for several years. Disease management involves selection of appropriate cultivars and use of cultural practices (crop rotation for 2-3 years, early planting dates, and soil drainage). - Mod.DH]

[see also:
2003
Sudden death syndrome, soybean - USA (MN)      20030328.0776
2002
Heterodera glycines, soybean - Europe: alert      20020802.4914
Sudden death syndrome, soybean - USA (DE & MD)      20020710.4721
2000
Soybean Fusarium infection, improved detection      20000920.1622
Soybean crop deaths - USA (Midwest)      20000827.1431

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