Reaction of soybean cultivars to frogeye leaf spot in Tucumán, Argentina, 2002/03

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

Biological And Cultural Tests For Control Of Plant Disease

The American Phytopathological Society

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

0887-2236

Twenty-four commercial soybean cultivars, maturity groups (MG) IV to IX, were evaluated for their susceptibility to frogeye leaf spot (FLS) in three locations close to each other in Tucumán, Argentina.  Two experiments were conducted in La Invernada and La Cocha with planting dates 11 and 19 Dec 02, respectively, in fields previously cropped to soybean. Trials were arranged in a randomized complete block design with 3 replications.  Each plot consisted of four 6-m rows spaced 0.5 m apart.  At Rumi Punco, the evaluation was carried out on cultivar demonstration plots (20 m wide x 250 m long) planted on 18 Dec 02, also in a field previously cropped to soybean.  Severity was estimated using a 1 to 5 scale, where 1= no visible symptoms, 2= approximately 5% of the leaf tissue affected, 3= approximately 10% of the leaf tissue affected, 4= approximately 25% of foliar tissue affected, and 5= approximately 50% or more of the leaf tissue affected.  Rainfall between Nov and Apr was 721.0 mm (average 763.8 mm), however, precipitation was less than average in Feb (30.0 mm, long term average 154.8 mm) and Mar (113.0 mm, long term average 169.4 mm).  Weather conditions favored the occurrence of the disease. There were clear differences in reaction among cultivars.  The highest level of severity (4.5) was observed at Rumi Punco on A 4910 RG (IV).  Cultivars belonging to MG IV showed high levels of susceptibility to FLS, whereas high levels of field resistance were observed in cultivars from MG VIII and IX.