No abstract

Production of fumonisins by Fusarium moniliforme on naturally infected maize ears is an important food safety concern due to the toxic nature of this class of mycotoxins. Assessing the potential risk of fumonisin production in developing maize ears prior to harvest requires an understanding of the regulation of toxin biosynthesis during kernel maturation. We investigated the developmental-stage-dependent relationship between maize kernels and fumonisin B1 production by using kernels collected at the blister (R2), milk (R3), dough (R4), and dent (R5) stages following inoculation in culture at their respective field moisture contents with F. moniliforme. Highly significant differences (P ≤ 0.001) in fumonisin B1production were found among kernels at the different developmental stages. The highest levels of fumonisin B1 were produced on the dent stage kernels, and the lowest levels were produced on the blister stage kernels. The differences in fumonisin B1production among kernels at the different developmental stages remained significant (P ≤ 0.001) when the moisture contents of the kernels were adjusted to the same level prior to inoculation. We concluded that toxin production is affected by substrate composition as well as by moisture content. Our study also demonstrated that fumonisin B1 biosynthesis on maize kernels is influenced by factors which vary with the developmental age of the tissue. The risk of fumonisin contamination may begin early in maize ear development and increases as the kernels reach physiological maturity.

A survey of 14 nurseries growing hybrid rhododendron, Pieris spp., or Viburnum spp. was conducted as part of the 2003 Sudden Oak Death Pilot National Survey to determine if Phytophthora ramorum, the causal agent of sudden oak death, had been introduced to nurseries in North Carolina. Over 220,000 hybrid rhododendrons, 1,700 plants of Pieris spp., and 2,800 plants of Viburnum spp. were surveyed. Across nurseries, blight and dieback incidence averaged 2.4% for Pieris spp. and 10% for rhododendron. P. ramorum was not recovered by isolation or detected by polymerase chain reaction in the 347 plant samples collected. Three species of Phytophthora were isolated from hybrid rhododendron and Pieris spp., but no Phytophthora isolates were recovered from Viburnum spp. P. citricola and P. cambivora were isolated most frequently (61 and 39 isolates, respectively), while 2 isolates of P. cactorum were recovered. Occasionally, two Phytophthora spp. were found in the same block of rhododendrons within a nursery, but only one species was recovered from an individual plant. Most cultivars of rhododendron surveyed, including ‘English Roseum,’ ‘Nova Zembla,’ and ‘Roseum Elegans,’ had less than 0.5% incidence of Phytophthora blight and dieback, whereas ‘Lee's Dark Purple’ had 3.8% disease incidence across all nurseries surveyed.

Impatiens downy mildew (IDM) of cultivated Impatiens walleriana has had a significant economic impact on the ornamental horticulture industry in the United States and globally. Although recent IDM outbreaks started in 2003, downy mildews on noncultivated Impatiens species have been documented since the 1880s. To understand the relationship between the pathogen causing recent epidemics and the pathogen historically present in the United States, this work characterized genetic variation among a collection of 1,000 samples on 18 plant hosts. Samples included collections during recent IDM epidemics and historical herbarium specimens. Ten major genotypes were identified from cloned rDNA amplicon sequencing and endpoint SNP genotyping. Three genotypes accounted for >95% of the samples, with only one of these three genotypes found on samples predating recent IDM outbreaks. Based on phylogenetic analysis integrating data from three markers and the presence of individual genotypes on multiple Impatiens species, there was some evidence of pathogen-specific infection of I. noli-tangere, but the distinction between genotypes infecting I. walleriana and I. balsamina was not upheld. Overall, this work provides evidence that the majority of rDNA genotypes recovered from recent IDM epidemics are different from historical U.S. genotypes, and that these genotypes can infect Impatiens spp. other than I. walleriana.

A friable and fast-growing type of callus was isolated from a long term shoot-competent cell culture of wheat. The suspension cultures established from this callus consisted of small, densely cytoplasmic cells which divided more rapidly but with a lower plant regeneration frequency than the original culture. A high yield of protoplasts was released from suspension cells (2 to 3×10(7) protoplasts per ml packed cell volume) when treated with enzyme mixtures. The isolated protoplasts divided at a relatively high frequency (20% to 50%) in both liquid and agarose-solidified KM8p medium. Up to 0.21% of the dividing protoplasts continued to divide and form micro-calli. Sixty-eight plants were regenerated from micro-calli, and among the 30 plants which were transplanted to the greenhouse, 3 have survived.