Dry Heat and Hot Water Treatments for Disinfesting Cottonseed of Fusarium oxysporum f. sp. vasinfectum.

The potential of low- and high-temperature dry heat, and hot water treatments, for disinfesting cottonseed of Fusarium oxysporum f. sp. vasinfectum was investigated. Naturally infected seeds from Louisiana were air-heated at 30, 35, and 40°C for up to 24 weeks. Seed harvested from bolls inoculated with race 4 of F. oxysporum f. sp. vasinfectum were incubated in dry heat at 60, 70, and 80°C for 2 to 14 days, or were immersed in 90°C water from 45 s to 3 min. The effects on seed germination and vigor of hot water treatment and a subset of the high-temperature dry heat treatments were also examined in seeds of a Pima (Gossypium barbadense) and an Upland (G. hirsutum) cultivar. Low- or high-temperature dry heat did not eliminate Fusarium spp. from the seed, although seed infection declined more rapidly with higher incubation temperatures. High-temperature dry heat treatments effective in eliminating fusaria also significantly reduced seed vigor in both the Pima and Upland cultivars. Seed from all times of immersion in hot water were less frequently infected with Fusarium spp. than nontreated seed. Incidence of seed infection did not differ significantly among immersion times ranging from 75 s to 3 min. Immersion in 90°C water did not reduce germination or vigor at exposure times ≤120 s and ≤150 s for seeds of Pima and Upland cotton, respectively. Results from the hot water treatments suggest that thermotherapy may be optimized to provide a tactic to prevent the spread of virulent F. oxysporum f. sp. vasinfectum genotypes into uninfested areas through infected seed.

A two-locus DNA sequence database for typing plant and human pathogens within the Fusarium oxysporum species complex.

We constructed a two-locus database, comprising partial translation elongation factor (EF-1alpha) gene sequences and nearly full-length sequences of the nuclear ribosomal intergenic spacer region (IGS rDNA) for 850 isolates spanning the phylogenetic breadth of the Fusarium oxysporum species complex (FOSC). Of the 850 isolates typed, 101 EF-1alpha, 203 IGS rDNA, and 256 two-locus sequence types (STs) were differentiated. Analysis of the combined dataset suggests that two-thirds of the STs might be associated with a single host plant. This analysis also revealed that the 26 STs associated with human mycoses were genetically diverse, including several which appear to be nosocomial in origin. A congruence analysis, comparing partial EF-1alpha and IGS rDNA bootstrap consensus, identified a significant number of conflicting relationships dispersed throughout the bipartitions, suggesting that some of the IGS rDNA sequences may be non-orthologous. We also evaluated enniatin, fumonisin and moniliformin mycotoxin production in vitro within a phylogenetic framework.

Modeling long-term effects of hairy vetch cultivation on cotton production in Northwest Louisiana.

The use of hairy vetch as a winter cover crop for cotton production in Northwest Louisiana has contributed to sustaining cotton production as well as improving soil quality. To test the efficacy of hairy vetch (HV) cultivation as a natural N supplement for cotton production, a long-term field experiment lasting 27years was evaluated using the Denitrification-Decomposition (DNDC) model. Different N fertilization practices, including 0kgNha-1 (PL_1), HV alone (PL_2), 44.8kgNha-1 (PL_3), and 67.3kgNha-1 (PL_4), were compared to evaluate nitrogen (N) response to cotton yield. Measured crop yield from each treatment was used to calibrate and validate the model. The DNDC model was employed to test the effects of N application scenarios on cotton yields and HV incorporation on N balance under irrigated and non-irrigated conditions. In model calibration, statistical indices for the model performance on cotton seed yield showed that PL_1 had a normalized root mean square error (NRMSE) value of 24.5%, a model efficiency (ME) value of 0.51, and a correlation coefficient (r) of 0.87 (P<0.01). The DNDC model was validated with PL_2, PL_3, and PL_4. PL_2, PL_3 and PL_4 had a NRMSE of 18.6%, 16.4% and 15.8% respectively, ME value of 0.19, 0.47 and 0.52 respectively, and an r of 0.75, 0.83 and 0.85 (P<0.05) respectively. Estimates of soil organic carbon (SOC) for HV treatment showed double the SOC content during a 27-year long-term experiment, while both treatments of 44.8kgNha-1 and 67.3kgNha-1 showed similar levels of SOC of a 25% increase compared to the control. Based on the scenario analysis, sustainable cotton yields do not require N fertilizer application under HV cultivated fields, and no yield differences were observed between irrigated and non-irrigated conditions.