Serenomyces associated with palms in southeastern USA: isolation, culture storage and genetic variation.

Serenomyces is a genus belonging to the family Phaeochoraceae, which is known to occur only in association with the plant family Arecaceae (palms). It is presumed to be one of the causes of a leaf disease referred to as either rachis blight or petiole blight, depending on the palm species affected. The fungus is not readily observed, with few reports in the literature; it cannot be readily isolated from tissue, with only one known instance of it being cultured on artificial media and has no DNA sequences deposited in GenBank. Over an 8 y period, leaves symptomatic for rachis or petiole blight were obtained from Florida and South Carolina, USA. The fungus was induced to produce ascospores, and single-spore isolates were obtained in culture and, in some instances, induced to produce ascospores in culture. Based on ascospores size and ITS sequencing, Serenomyces from Phoenix canariensis and P. dactylifera form one group, Serenomyces from Thrinax radiata form a second group and Serenomyces from Sabal palmetto form a third. All three groups are most similar morphologically to Serenomyces phoenicis. Due to the observed instability of Serenomyces in culture, we have suggestions regarding the storage of this fungus.

Fusarium oxysporum f. sp. palmarum, a Novel Forma Specialis Causing a Lethal Disease of Syagrus romanzoffiana and Washingtonia robusta in Florida.

A new disease of Syagrus romanzoffiana (queen palm) and Washingtonia robusta (Mexican fan palm) has spread across the southern half of Florida during the past 5 years. The initial foliar symptom is a one-sided chlorosis or necrosis of older leaf blades, with a distinct reddish-brown stripe along the petiole and rachis and an associated discoloration of internal tissue. Within 2 to 3 months after onset of symptoms, the entire canopy becomes desiccated and necrotic but the leaves do not droop or hang down around the trunk. Based on pathogenicity and morphological and molecular characterization, the etiological agent has been identified as a new forma specialis of Fusarium oxysporum, designated f. sp. palmarum. Sequence analysis of a portion of the translation elongation factor 1-α gene (EF-1α) separated 27 representative isolates into two EF-1α groups, which differed by two transition mutations. Members of both EF-1α groups are pathogenic on both species of palm. A phylogenetic analysis inferred from partial EF-1α sequences from a genetically diverse set of F. oxysporum isolates, including three other formae speciales pathogenic on palm (i.e., f. sp. albedinis, f. sp. canariensis, and f. sp. elaeidis), suggested that f. sp. palmarum and f. sp. albedinis may be more closely related to one another than either is to the two other palm pathogens.

Viability and stability of biological control agents on cotton and snap bean seeds.

Cotton and snap bean were selected for a multi-year, multi-state regional (south-eastern USA) research project to evaluate the efficacy of both commercial and experimental bacterial and fungal biological control agents for the management of damping-off diseases. The goal for this portion of the project was to determine the viability and stability of biological agents after application to seed. The biological seed treatments used included: (1) Bacillaceae bacteria, (2) non-Bacillaceae bacteria, (3) the fungus Trichoderma and (4) the fungus Beauveria bassiana. Seed assays were conducted to evaluate the following application factors: short-term (< or = 3 months) stability after seed treatment; quality (i.e. isolate purity); compatibility with chemical pesticides and other biocontrol agents; application uniformity between years and plant species. For the bacterial treatments, the Bacillaceae genera (Bacillus and Paenibacillus) maintained the greatest population of bacteria per seed, the best viability over time and the best application uniformity across years and seed type. The non-Bacillaceae genera Burkholderia and Pseudomonas had the least viability and uniformity. Although Beauveria bassiana was only evaluated one year, the seed fungal populations were high and uniform. The seed fungal populations and uniformity for the Trichoderma isolates were more variable, except for the commercial product T-22. However, this product was contaminated with a Streptomyces isolate in both the years that it was evaluated. The study demonstrated that Bacillaceae can be mixed with Trichoderma isolates or with numerous pesticides to provide an integrated pest control/growth enhancement package.

Detection of an arbuscular mycorrhizal fungus in roots of different plant species with the PCR.

PCR was used with the primer pair VANS1-NS21 to detect the arbuscular mycorrhizal fungus Glomus intraradices (commercial inoculum source) on roots of lettuce, zinnia, leek, pepper, and endive plants. The appropriate amplification product was obtained directly from roots without DNA extraction and purification.

Selective medium for isolation of Xanthomonas maltophilia from soil and rhizosphere environments.

A selective medium (XMSM) was developed for isolation of Xanthomonas maltophilia from bulk soil and plant rhizosphere environments. The XMSM basal medium contained maltose, tryptone, bromthymol blue, and agar. Antibiotics added to select for X. maltophilia were cycloheximide, nystatin, cephalexin, bacitracin, penicillin G, novobiocin, neomycin sulfate, and tobramycin. A comparison was made between XMSM and 1/10-strength tryptic soy broth agar for recovery of X. maltophilia from sterile and nonsterile soil infested with known X. maltophilia isolates. A recovery rate of 97% or greater for XMSM was demonstrated. XMSM was used to isolate X. maltophilia from a variety of soil and rhizosphere environments.