The Role of Water Content in the Casing Layer for Mushroom Crop Production and the Occurrence of Fungal Diseases

Mushroom cultivation requires effective control of environmental cues to obtain the best yield and high quality. The impact of water content in the casing layer on mushroom yield and the incidence of two of the most important diseases in the mushroom growing farms, dry bubble and cobweb diseases, was evaluated. Different initial water content in the casing and two alternative irrigation programs applied (light or moderate irrigation) were the agronomic parameters under study during five separate button mushroom crop trials. Higher initial humidity content in the casing layer reported a larger yield, with a fewer number of basidiomes but heavier, while no correlation to the dry matter content or the colour of the basidiomes was noted. The incidence of dry bubble disease was not conditioned by the water content of the casing layer, at the high moisture levels established in the study. In the case of Cladobotryum mycophilum, the lower moisture level of the casing layer reported more incidence of cobweb disease, and subsequently harmful yield losses. According to the results obtained, the right management of the moisture level in the casing materials could promote crop yield and preclude the significant impact of dry bubble and cobweb diseases.

Revisiting the casing layer: Casing materials and management in Agaricus mushroom cultivation

ABSTRACT The cultivation of button mushroom has reached a high technological level in developed countries and is associated with high productivity indices. This technological level involves not only compost production and crop management but also the casing layer. Peat has been established as one of the most appropriate casing materials for the cultivation of button mushroom due to its excellent properties. However, good-quality peat is not available in all countries, and peat is not renewable, which reinforces the need for alternative materials. Therefore, studies on the casing layer should include its response to the induction of fruiting since this stage is where the main changes that lead to the formation of primordia occur. This review addresses the different aspects of fruiting induction of Agaricus mushrooms and the influence of the characteristics of the casing layer on mushroom production.

Bioaccumulation of insecticide in Agaricus subrufescens

Agaricus subrufescens, known as Sun Mushroom, is a high-value mushroom because of its medicinal properties, used as nutraceutical food to stimulate the immune system and to prevent some diseases, including cancer. Mushrooms are generally characterized by their great ability to bioaccumulate heavy metals and other toxic substances from the mushroom compost. Sugarcane bagasse is a common raw material used in mushroom compost production for Agaricus subrufescenscultivation, whereas insecticides, such as fipronil, can be applied to combat several pests in sugarcane crops. For this reason, we aimed to assess mushroom yield and fipronil bioaccumulation in Sun Mushroom, regarding different concentrations added to the mushroom compost (0, 8, 16 and 32 mg kg-1) and casing layer (0, 2, 4 and 8 mg kg-1). Each experiment was arranged in a completely randomized design with four replicates. Regression analysis from mushroom production data was applied using SISVAR 5.1 program. Fipronil was quantified using gas-liquid chromatography (HP 6890) with thermionic detector (NPD). Mushroom yield was affected when fipronil was added, decreasing from 12% (compost with 0 mg kg-1 of fipronil) to 4.8% (compost with 32 mg kg-1). However, bioaccumulation was not detected. In contrast, insecticide bioaccumulation was detected when adding fipronil to casing layer, increasing from <0.01 mg kg-1 (casing layer with 2 mg kg-1) to 0.26 mg kg-1 (casing layer with 8 mg kg-1), however, mushroom yield was not affected.

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.