First Report of Syzygites megalocarpus (Mucorales) Web Mold on the Commercial Portabella Button Mushroom Agaricus bisporus in North America.

Agaricus bisporus (Lange) Imbach mushrooms, which are cultivated commercially under environmentally controlled conditions, are the most valuable crop in Pennsylvania. In August 2011, we first observed a mucoraceous mold colonizing primordia and mature basidiocarps of a new brown portabella strain of A. bisporus at two commercial mushroom farms in Chester County, PA. This strain is a hybrid between a commercial strain producing white basidiocarps and a brown wild type isolate of A. bisporus. Mushrooms mature in weekly "flushes". By third flush, 25% of the production surface at both farms was colonized by a fast growing mycelium that was initially white, subsequently yellow to golden brown, and finally grayish. Mushrooms colonized by the mold showed pitting, discoloration, and necrosis. Two pure cultures of the mold were obtained by the hyphal tip method from mature, necrotic basidiocarps at each farm. These isolates were accessioned in the ARS Culture Collection (NRRL, Peoria, IL) as NRRL 54814 to 54815 and 54818 to 54819. The cultures produced abundant aerial sporangiophores that branched dichotomously on potato dextrose agar. Light microscopic examination revealed that each branch terminated in a globose, multispored sporangium with a conspicuous columella. Individual cultures of NRRL 54818 and 54819 produced large (175 to 250 × 200 to 250 µm), barrel-shaped, dark brown to black zygosporangia between opposed suspensors, indicating they were homothallic. Morphological and cultural characteristics of the mold matched the description of Syzygites megalocarpus (3), a member of the Mucorales reported to colonize diverse, mostly fleshy basidiomycetes (2), including cultivated matsutake (Tricholoma matsutake) in Korea (1). Molecular phylogenetic confirmation of the morphological identification was obtained by PCR amplifying and sequencing domains D1 and D2 at the 5' end of the nuclear ribosomal large subunit (LSU rDNA). The four isolates shared an identical LSU rDNA allele. A search of the NCBI nucleotide database, using a partial LSU rDNA sequence from NRRL 54814 as the BLAST query, revealed that it shared 99.5% identity with AF157216.1, a reference isolate of S. megalocarpus NRRL 6288 (3). To assess whether cultures of S. megalocarpus could induce the disease, caps of portabella and white button mushrooms were inoculated with 3.7 × 106 sporangiospores. When incubated in moist chambers at 21 to 22°C with a 12-h photoperiod, disease symptoms developed in 2 to 3 days on portabella that included discoloration and pitting at the site of inoculation. S. megalocarpus was reisolated from the symptomatic mushrooms and produced a colony identical to the original. By comparison, white button mushrooms inoculated with S. megalocarpus, using the same method, only showed minor pitting and discoloration. Disease symptoms were not observed on mushrooms inoculated with water as a negative control. Although development of new commercial varieties derived using "wild" genetically diverse stocks is an effective way to introduce desirable traits into cultivated mushrooms, it carries the risk of introducing new diseases into the industry. References: (1) K.-H. Ka et al. Korean J. Mycology 27:345, 1999. (2) R. L. Kovacs and W. J. Sundberg. Trans. Il. State Acad. Sci. 92:181, 1999. (3) K. O'Donnell. Zygomycetes in culture. Palfrey Contributions in Botany. No. 2. Department of Botany, University of Georgia, Athens, 1979.

The relation between sunscreen layer thickness and vitamin D production after ultraviolet B exposure: a randomized clinical trial.

BACKGROUND: Sunscreens absorb ultraviolet B (UVB) and it is a major concern that sunscreen use may lead to vitamin D deficiency. OBJECTIVES: To investigate the relation between the amount of sunscreen applied and the vitamin D serum level in humans after UVB exposure under controlled conditions. METHODS: Thirty-seven healthy volunteers with fair skin types were randomized to receive an inorganic sunscreen with sun protection factor (SPF) 8 of 0 mg cm(-2) , 0.5 mg cm(-2) , 1 mg cm(-2) , 1.5 mg cm(-2) , or 2 mg cm(-2) thickness on the upper body, approximately 25% of the body area. Participants were irradiated with a fixed UVB dose of 3 standard erythema doses 20 min after sunscreen application. This procedure was repeated four times with a 2- to 3-day interval. Blood samples were drawn before the first irradiation and 3 days after the last to determine the serum vitamin D level expressed as 25-hydroxyvitamin D(3) [25(OH)D]. RESULTS: The vitamin D serum level increased in an exponential manner with decreasing thickness of sunscreen layer in response to UVB exposure. For all thicknesses of sunscreen, the level of 25(OH)D increased significantly after irradiation (P<0.05), except for the group treated with 2 mg cm(-2) , in which the increase in 25(OH)D was not statistically significant (P=0.16). CONCLUSIONS: Vitamin D production increases exponentially when thinner sunscreen layers than recommended are applied (<2 mg cm(-2) ). When the amount of sunscreen and SPF advised by the World Health Organization are used, vitamin D production may be abolished. Re-evaluation of sun-protection strategies could be warranted.

Clothing reduces the sun protection factor of sunscreens.

BACKGROUND: Individuals are recommended to wait for 20 min following sunscreen application before dressing. However, this is probably seldom done in daily life, and therefore we investigated how dressing earlier than 20 min after application affected the sun protection factor (SPF). OBJECTIVES: To determine the SPF of a sunscreen applied at different amounts at 4, 8 and 20 min before dressing. METHODS: An organic sunscreen was used on the backs of 22 healthy volunteers. Before SPF testing, participants wore a cotton T-shirt for 60 min after the test areas had been uncovered for 4, 8 or 20 min after sunscreen application. The SPF was also tested on unclothed skin. RESULTS: The median SPF was 11.7 (2 mg cm(-2)), 5.7 (1 mg cm(-2)) and 3.3 (0.5 mg cm(-2)) for unclothed skin, and 8.1 (2 mg cm(-2)), 4.8 (1 mg cm(-2)) and 2.2 (0.5 mg cm(-2)) following an interval of 8 min before dressing. The SPF was similar for time intervals of 20 and 8 min when the amount was 1 mg cm(-2) (P = 0.48) and 2 mg cm(-2) (P = 0.56). For 0.5 mg cm(-2) there was no difference between skin clothed after 20 min and unclothed skin (P = 0.19), nor between skin clothed after 4 min and after 8 min (P = 0.28). CONCLUSIONS: When sunscreens are applied at amounts of 1 and 2 mg cm(-2) the time between sunscreen application and dressing can be as little as 8 min. When less sunscreen is used the SPF is insensitive to the length of time between application and dressing.

Yield Comparison of Hybrid Agaricus Mushroom Strains as a Measure of Resistance to Trichoderma Green Mold.

Commercially available strains of hybrid white, hybrid off-white, and brown Agaricus bisporus mushrooms were compared for resistance to green mold caused by Trichoderma harzianum biotype 4 (Th4). Seven mushroom spawn strains were assessed for total weight of mushrooms (grams per 0.1 m2) with or without the addition of an aqueous Th4 spore suspension added at spawning time. Cropping studies were conducted at the Mushroom Research Center (Pennsylvania State University) to emulate commercial growing operations. Excessive spawn handling had no significant effect on development of green mold. Severity of green mold was related to time between infestation and green mold appearance, with more significant yield losses occurring when green sporulation was detected early in production. Significant differences in yield were measured among mushroom strains in response to Th4 infestation. Hybrid white strains were extremely susceptible, with a mean yield loss of 96%. Hybrid off-white strains exhibited intermediate susceptibility, with mean yield losses of 56 to 73%. Brown strains were highly resistant, with mean yield losses of 9 to 16%. From these findings, we report the existence of green mold resistance, with a continuum of resistance among spawn strains. The findings suggest use of brown strains to manage green mold outbreaks, particularly where benomyl resistance in Trichoderma spp. is a threat.

First Report of Trichoderma harzianum Biotype Th4, on Commercial Button Mushrooms in California.

Button mushrooms of Agaricus bisporus (Lange) Imbach are commercially cultivated under environmentally controlled conditions. In California they are the most economically important agricultural crop in Santa Clara and San Mateo counties, and also an important crop in 10 other counties. Trichoderma harzianum Rifai, biotype Th4, can reduce production by preventing formation of fruiting bodies. Biotype Th4 was previously detected and described in Canada (2), Pennsylvania, and Delaware. Unofficial reports suggest its presence in San Mateo County since 1995. Disease incidence and severity on the mushroom farms varied; some mushrooms became severely infected. Green epigeous mycelia and conidia were present on the casing layer resulting in empty patches. On some farms 30% of the production surface was infected during the peak of the epidemic. Initial identification of the species was made by isolating the fungus from the substrate and casing layer. Potato dextrose agar (PDA) cultures coincided with the cultural description of T. harzianum (1,3). Biotype assessments with standard procedures were conducted at Penn State, with polymerase chain reaction (PCR) amplification of total genomic DNA to screen the California isolates of T. harzianum. Random amplified polymorphic DNA (RAPD)-PCR analysis with 14 different primers indicated that they were the same RAPD haplotype as biotype Th4. The Horticultural Research Institute of Ontario relies on morphological observations from cultures grown on 2% MEA (malt extra agar) at 24°C under diffuse daylight to identify biotypes of T. harzianum (2), and microscopic characters of biotype Th4 were also positively confirmed on the California isolates. More than a parasite or pathogen, T. harzianum biotype Th4 is considered a weed mold of mushroom cultivation. The precise interaction is yet unknown. Modified Koch's postulates were confirmed with bags of commercial mushroom substrate (45 kg) inoculated by spraying 100 ml of a spore suspension (3.0 × 106 spores per ml) at filling, to give final concentrations of 103 to 108 spores per kg of compost. Treatments were T. harzianum biotype Th4, strain Th1, an unidentified isolate, control (distilled water only), and noninoculated. Eight replications per treatment were laid out in a randomized block design. Bags were subjected to standard mushroom cultivation practices. Biotype Th4 was reisolated from empty patches on the casing of all Th4 repetitions. Mean percent cover of the mold (therefore mushroom empty patches) was 30% for crops (flushes) 1 and 2, but individual bags varied from 15 to 90%. The mean percent cover in the other two treatments and in the controls was 0% for crops 1 to 4, therefore significantly different. Green mold was covering the total surface on all Th4 repetitions at third crop. No yields were recorded, but serious losses were obvious for the Th4 treatments. Green mold was not observed in the controls. References: (1) H. M. Grogan et al. Mushroom News 45:29, 1997. (2) D. L. Rinker et al. Mushroom World 8:71, 1997. (3) D. A. Seaby. Plant Pathol. 45:905, 1996.