Specific molecular detection of Phytophthora sojae using conventional and real-time PCR

Phytophthora rot, caused by Phytophthora sojae, is one of the most damaging diseases of soybean (Glycine max) worldwide. This disease can be difficult to diagnose and other Phytophthora species can infect soybean. Accurate diagnosis is important for management of Phytophthora rot. The objective of this study was to evaluate polymerase chain reaction (PCR) methods for rapid and specific detection of P. sojae and diagnosis of Phytophthora rot. PCR assays using two sets of primers (PS and PSOJ) that target the ITS region were evaluated for specificity and sensitivity to P. sojae. Genomic DNA extracted from 11 species of Phytophthora and 19 other species of fungal and oomycete pathogens were used to test the specificity of each primer set. The previously published PS primers amplified DNA from P.?sojae and from four other Phytophthora species using conventional PCR, indicating they are not specific for P. sojae. The new PSOJ primers amplified DNA only from P. sojae using conventional and real-time PCR and not from Phytophthora sansomeana, which has been found in soybean production areas, indicating that they are specific for P. sojae. The PSOJ primers were also used to detect P. sojae in diseased soybean tissue and infested soil. The PCR assays based on the PSOJ primers are specific, rapid, and sensitive tools for the detection of P. sojae.     

Radiometric assessment of tillage and seed treatment effect on soybean root rot caused by Fusarium spp. in central Minnesota

Soybean root rot, caused primarily by Fusarium solani f. sp. phaseoli in a complex with F. oxysporum and Rhizoctonia solani, has become an increasing problem for soybeans, dry beans, and other rotation crops in central Minnesota due to soil conditions associated with reduced tillage. This study was conducted, in two field sites in central Minnesota located near Staples and Verndale, to develop methods for nondestructive assessment of root rot severity using plant radiometric properties. Soybean canopy reflectance was measured with a hand-held multi-spectral radiometer. Prior to the radiometer measurements, attempts were made to create differing root rot situations with moldboard or chisel tillage, and with or without a biological seed treatment. Root rot severity was estimated using a visual disease severity scale. Colony-forming units (CFU) were determined to estimate soil populations of pathogenic F. solani and F. oxysporum. Results from the Verndale site consistently showed significant treatment effects in the measured canopy radiometric parameters, and in the visual disease rating and yield (significant for seed treatment). Values of a simple ratio vegetation index from this site exhibited negative relationships with disease rating and F. oxysporum CFU, and a positive linear relationship with yield. Treatment effects were generally not significant at the Staples site because of low initial F. oxysporum populations. The results indicate that remote sensing is potentially a rapid, nondestructive means for assessment of root rot diseases in soybean.