Auxin (indole-3-acetic acid, IAA) has been implicated as a susceptibility factor in both beneficial and pathogenic molecular plant-microbe interactions. Previous studies have identified a large number of auxin-related genes underlying quantitative disease resistance loci (QDRLs) for Phytophthora sojae. Thus, we hypothesized that auxin may be involved the P. sojae-soybean interaction. The levels of IAA and related metabolites were measured in mycelia and media supernatant as well as in mock and inoculated soybean roots in a time course assay. The expression of eleven soybean Pin-formed (GmPIN) auxin efflux transporter genes was also examined. Tryptophan, an auxin precursor, was detected in the P. sojae mycelia and media supernatant. During colonization of roots, levels of IAA and related metabolites were significantly higher in both moderately resistant Conrad and moderately susceptible Sloan inoculated roots compared to mock controls at 48 hours post inoculation (hpi) in one experiment and at 72 hpi in a second, with Sloan accumulating higher levels of the auxin catabolite IAA-Ala than Conrad. Additionally, one GmPIN at 24 hpi, one at 48 hpi, and three at 72 hpi had higher expression in inoculated compared to the mock control roots in Conrad. The ability of resistant cultivars to cope with auxin accumulation may play an important role in quantitative disease resistance. Levels of jasmonic acid (JA), another plant hormone associated with defense responses, were also higher in inoculated roots at these same time points, suggesting that JA also plays a role during the later stages of infection.

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Fusarium head blight (FHB) and the associated mycotoxin deoxynivalenol (DON) negatively impact the wheat industry worldwide. In North America, FHB is mainly caused by Fusarium graminearum sensu stricto. The purpose of this study was to evaluate, under storage conditions, the expression of the DON biosynthetic gene trichodiene synthase (Tri5) of F. graminearum in grain of hard red winter wheat cultivars 'Overley' (FHB-susceptible) and 'Overland' (moderately resistant to FHB) from field plots treated or untreated with the triazole fungicide Prosaro and the strobilurin fungicide Headline. Infected grain was stored and periodically sampled to determine gene expression by qRT-PCR analysis. The F. graminearum housekeeping gene GAPDH was consistently detected, indicative of metabolically active fungi, and Tri5 detection was significantly higher in 'Overley' compared with 'Overland'. Tri5 gene expression and DON concentrations showed little to no correlation; consequently, Tri5 expression levels did not accurately predict DON concentrations. The strobilurin did not significantly reduce Tri5 gene expression compared with untreated wheat. In the triazole treatment, a significant reduction in the relative expression of Tri5 was detected after 120 days, as well as a downregulation of Tri5 from 60 to 120 days of storage in 'Overley'. In grain from strobilurin-treated plots of both cultivars, the expression of Tri5 increased from 0 to 30 days after tempering. Genetic expression of Tri5 that is necessary for the production of DON can increase during storage of high-moisture grain. Fusarium fungi can persist in wheat kernels for several months postharvest and may actively produce toxin during this period.

The Soybean Nested Association Mapping (SoyNAM) populations were developed from 40 parents and have been used to map genes underlying complex traits such as yield and disease resistance. Soil borne pathogens that affect soybean seed and seedlings result in significant losses due to reduced stands and costs associated with replanting. This study compared the response of these 40 SoyNAM parent genotypes to seed- and seedling-rot pathogens, Fusarium graminearum, Phytophthora sojae, Globisporangium ultimum var. ultimum, G. ultimum var. sporangiiferum, and G. irregulare groups 1, 2 and G. cryptoirregulare. None of the parental genotypes conferred high levels of resistance to F. graminearum nor G. ultimum var. sporangiiferum. Of the 40 parental genotypes, 15 were resistant to P. sojae OH1 (vir 7) indicating they contain Rps genes while the remaining (including the common parent IA 3023) do not have Rps genes. Based on inoculations with known P. sojae pathotypes, Rps1c was the most common followed by Rps1a as both Rps genes confer resistance to isolates OH4 (vir 1a, 1c, 7) and OH25 (vir 1a, 1b,1c, 1k, 7). Eight of the SoyNAM parents had higher levels of partial resistance to P. sojae than Conrad (cultivar with moderate resistance). There was moderate resistance to G. ultimum var ultimum among the 40 parents and to G. irregulare subpopulations among the 6 parents that were evaluated. The SoyNAM parental lines and populations are an excellent resource available for soybean breeders to advance the development of new cultivars with improved resistance to some soilborne pathogens.

Field trials were conducted in two years to evaluate persistence of B. thuringiensis and Bacillus pumilus under field conditions. Strains of B. thuringiensis (3971) and B. pumilus (4185) were isolated from coffee agro-ecosystem in Puerto Rico. Field trials consisted in plots of nine coffee trees arranged in a randomized complete block design, sprayed with Bt-3971 and Bp-4185 at 108, 109, or 1010 colony forming units CFU ml-1 or non-inoculated. In year 1, B. thuringiensis and B. pumilus survived up to six months after inoculation. Monitoring carried out during year 2, re-confirmed the survival of Bt-3971 and Bp-4185 inoculated in coffee trees under field conditions. Overall, Bt-3971 had significantly more recovery rates than Bp-4185. However, the higher bacterial recoveries were 1.24x1013 CFU ml-1 in coffee trees treated with Bt-3971 and 2.48x1013 CFU ml-1 in coffee trees treated with Bp-4185 in year 1 and year 2, respectively, both sprayed with 1010 spores ml-1. B. thuringiensis (3971) and B. pumilus (4185) isolated from coffee fields of Puerto Rico are well adapted to the environmental conditions of the island, and are valuable biological control agents against coffee berry borer.