Reaction of soybean cultivars to sudden death syndrome in Tucumán, Argentina, 2002/03

ZAMORANO, M A; PLOPER, L.D.; GONZÁLEZ, V; GÁLVEZ, M R; JALDO, H E; DÍAZ, C G; DEVANI, M R

Biological And Cultural Tests

The American Phytopathological Society

Lugar: St. Paul, MN, USA; Año: 2004 p. 1 - 1

0887-2236

Reaction to sudden death syndrome (SDS) was evaluated on 24 commercial soybean cultivars, maturity groups (MG) IV to IX, in La Invernada, Tucumán, Argentina.  The experiment was conducted in a field cropped to soybean and with high levels of the disease in previous years.  The planting date was 11 Dec 02 and treatments were arranged in a randomized complete block design with 3 replications.  Each plot consisted of four 6-m rows spaced 0.5 m apart.  Evaluations were carried out, starting at growth stage V1, every 15 days until the appearance of SDS foliar symptoms, and weekly thereafter. To analyze the data a Disease Index (DI) was calculated, based on the Maximum Incidence (MI) and its corresponding Severity (S), according to the following formula: DI= (MI x S)/5.  Incidence was determined as the percentage of diseased plants in the plot, and the Maximum Incidence was the highest incidence observed in each plot during the season.  Severity was estimated using a 0 to 5 scale, where 0= no foliar symptoms, 1= less than 10% of the foliar area with chlorosis, 2= 10-30% of the foliar area with chlorosis or less than 10% with necrosis, 3= 10-30% of the foliar area necrosis, 4= 31-70 % of the foliar area with necrosis, and 5= more than 70% of the foliar area with necrosis.  Rainfall between Nov and Apr was 721.0 mm (average 763.8 mm), however, precipitation was less than average in Feb (30.0 mm, average 154.8 mm) and Mar (113.0 mm, average 169.4 mm).  In most cultivars, the first foliar symptoms of SDS appeared between R1 and R3; only two of them showed symptoms before flowering (A 8100 RG and Munasqa).  All cultivars showed the Maximum Incidence between R5 and R6 with an average severity of 3.5.  There were significant differences in Disease Index among cultivars. None of the cultivars showed high levels of resistance or susceptibility to the disease, however, based on these data, there are cultivars in the region with acceptable levels of resistance to SDS.