Seed treatments are applied to soybean (Glycine max L. Merrill) seeds to control early season diseases and insects. Unsold, treated soybean seed must be disposed in a different manner than untreated seed. To minimize treated seed disposal costs, it is necessary to improve seed storage. The objective of this study was to determine the best storage environments that would minimize deterioration of chemically treated soybean seed from different maturity groups and seed compositions. Twenty-four soybean varieties, different in lipid and protein contents, and from four maturity groups, were treated either with fungicide, a mixture of fungicide + insecticide, and untreated and were stored in three storage environments differing in temperature and relative humidity: a cold storage (CS), 10°C; a warm storage (WS), 25°C; and a warehouse, (WH). The seed viability and vigor were evaluated each 4 mo for 20 mo using standard germination and accelerated aging tests. Seed viability remained high throughout the study for seeds stored in CS (>92%) and moderate in the WS (>78%), but decreased to almost 0% after 20 mo in the WH. The seed viability of treated seed was significantly higher than that of untreated seed after 16 mo in the WH, while in the CS and WS the positive effects lasted for 20 mo. Maturity groups and protein content did not affect seed vigor, but seed lipid content did for seeds stored for 12 mo, regardless of storage environment. Treated soybean seeds could be carried over for two seasons if the storage temperature is maintained at 10oC and the relative humidity is below 40%. Disciplines Agricultural Science | Agronomy and Crop Sciences | Plant BiologyComments This is a manucript of an article published as Mbofung, Gladys CY, A. Susana Goggi, Leonor FS Leandro, and Russell E. Mullen. "Effects of storage temperature and relative humidity on viability and vigor of treated soybean seeds." ABSTRACTSeed treatments are applied to soybean (Glycine max L. Merrill) seeds to control early season diseases and insects. Unsold, treated soybean seed must be disposed in a different manner than untreated seed. To minimize treated seed disposal costs, it is necessary to improve seed storage. The objective of this study was to determine the best storage environments that would minimize deterioration of chemically treated soybean seed from different maturity groups and seed compositions. Twenty-four soybean varieties, different in lipid and protein contents, and from four maturity groups, were treated either with fungicide, a mixture of fungicide + insecticide, and untreated and were stored in three storage environments differing in temperature and relative humidity: a cold storage (CS), 10°C; a warm storage (WS), 25°C; and a warehouse, (WH). The seed viability and vigor were evaluated each 4 mo for 20 mo using standard germination and accelerated aging tests. Seed viability remained high throughout the study for seeds stored in CS (>92%) and moderate in the WS (>78%), but decreased to almost 0% after 20 mo in the WH. The seed viab...

A nested polymerase chain reaction-based (nPCR) assay was developed and evaluated for the rapid detection of Fusarium oxysporum f. sp. lactucae in seed of lettuce. Three primers were designed from sequences of the intergenic spacer region of the rDNA and were used in the PCR amplifications. The first amplification employed the primer pair GYCF1 and GYCR4C and produced a product of 2,270 bp. The second amplification employed the forward primer GYCF1 and the nested primer R943 and produced a single 936-bp PCR product. The nPCR protocol developed successfully detected the target sequence in genomic DNA at 1 fg/μl. A seed assay was tested that included a 4-day incubation step in which seed were maintained under high humidity conditions to increase fungal biomass for DNA extraction. In seed lots prepared by mixing known amounts of F. oxysporum f. sp. lactucae–infested seed with noninfested seed, this assay permitted the detection of the pathogen from lots with infestation rates as low as 0.1%. Samples of lettuce seed obtained from 88 commercial lettuce seed lots were assayed for the pathogen by direct plating and by using the nPCR assay. The pathogen was not detected by either diagnostic method, suggesting the seed lots were pathogen free or the level was below detection limits.

The quantification of the soilborne pathogen Fusarium virguliforme inoculum in soil is important for epidemiological studies of soybean sudden death syndrome (SDS). Classical dilution plating methods to determine inoculum density in soil have yielded inconsistent results due to slow growth, variable colony morphology of the pathogen, and the presence of other fungi with similar phenotype. A TaqMan real-time polymerase chain reaction assay was developed based on sequences of the FvTox1 gene of F. virguliforme. The gene differed by four single-nucleotide proteins from the other SDS-causing species. Assay specificity was tested on 48 fungal isolates that varied in taxonomic relatedness. Assay sensitivity was appraised on 10-fold serial dilutions of genomic DNA, conidia suspensions, and soil spiked with conidia. Applicability of the assay was evaluated on field and greenhouse soil samples, and on roots of symptomatic plants. The assay detected only DNA sequences specific to F. virguliforme. The detection limit of the assay was 5 pg/μl, 1,000 conidia/ml, and 1,000 conidia/g soil for genomic DNA, conidial suspensions, and soil with conidia, respectively. The assay was specific to F. virguliforme and was used successfully to quantify inoculum density in soil and soybean roots. The assay can be used as a diagnostic tool for rapid screens of field and greenhouse soil, and for symptomatic and asymptomatic plants.

Clavibacter michiganensis subsp. nebraskensis causes Goss’s bacterial wilt and blight on maize and is managed primarily with C. michiganensis subsp. nebraskensis-resistant hybrids. To understand the mechanisms of resistance to infection by C. michiganensis subsp. nebraskensis, leaves of a susceptible and a resistant maize hybrid at the V4 to V5 developmental stage were wound inoculated with the pathogen. Blight lesion length was monitored, C. michiganensis subsp. nebraskensis colonizing ability was determined, and structural changes were observed using microscopy. Bacterial colonization preceded lesion development that occurred 4 to 5 days postinoculation in both hybrids. Lesion expansion in the susceptible hybrid was associated with a faster rate of C. michiganensis subsp. nebraskensis spread and multiplication in the tissues. In the resistant hybrid, spread and multiplication was reduced (P < 0.0001) and, at 16 days postinoculation, became imperceptible. Initially, C. michiganensis subsp. nebraskensis showed a preference for colonization of the metaxylem vessels in both hybrids. Spread from cell to cell was accomplished through disruption of cell walls, presumably from abundance of bacterial cells or enzymatic activity. Morphological responses of the resistant maize hybrid to infection by C. michiganensis subsp. nebraskensis were similar to those reported in maize inbred lines that were resistant to Stewart’s wilt caused by Pantoea stewartii. Resistance to C. michiganensis subsp. nebraskensis was associated with production of a dense matrix in the xylem that deformed and restricted movement of the bacterial cells.