Effect of planting date and soybean cultivar on the development of sudden death syndrome, caused by Fusarium solani f. sp. glycines, in Tucumán, Argentina

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

Foz do Iguassú, Paraná, Brasil

Conferencia; VII World Soybean Research Conference (VII WSRC).; 2004

Embrapa SOJA y WSRC Continuing Committee

Sudden death syndrome (SDS), caused by Fusarium solani f. sp. glycines, is one of the most important soybean diseases in Tucumán as well as in other provinces of northwestern Argentina. Several practices are recommended to manage the disease, including the use of resistant cultivars.  The objective of this study was to evaluate the effect of planting date on the development of SDS in cultivars differing in resistance to the disease.  This field test was conducted in the 2002/03 growing season in La Invernada, Tucumán.  Six commercial cultivars (Maturity Groups IV to VIII) were planted on three dates (11 December, 20 December, and 7 January) in a field where high levels of the disease had been observed in previous years.  The experimental design was a randomized complete block with 3 replications.  Plots 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, and 5= >70% of the foliar area with chlorosis or necrosis.  All cultivars had the MI in R6.  For all cultivars the highest DI was observed in the plots with the first planting date, although there were significant differences among them.  Differences among cultivars were not as marked for the second and third planting dates.  Some cultivars, such as A 7636 RG (MG VII) and A 6401 RG (VI), had low DI values, with no significant differences among the 3 dates.  Qaylla RR (VII), Munasqa RR (VIII), A 8100 RG (VIII), and AW 4902 RR (IV) showed the highest DI for the first date, with no significant differences among cultivars.  AW 4902 RR had one of the highest DI in the first date (16.5), but low DIs in the second and third dates (2.3 and 2.4, respectively).  No significant differences were observed between the DI values of the first and second dates for A 8100 RG, although the DI for the third date was significantly lower.  DIs for Munasqa RR and Qaylla RR significantly decreased from the first to the third planting date.  These results indicate that less disease occurred as planting was delayed, and that the extent of this reduction was influenced by the soybean cultivar.