Alternatives to Peat Moss for Casing Layer Materials and Their Influence on Agaricus bisporus Yield, Quality, and Disease Susceptibility

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Restricted (Penn State Only)
Author:
Vozzella, Tony
Graduate Program:
Plant Pathology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 01, 2026
Committee Members:
David Meigs Beyer, Thesis Advisor/Co-Advisor
Jasna Kovac, Committee Member
Maria Del Mar Jimenez Gasco, Program Head/Chair
Gretchen Anna Kuldau, Thesis Advisor/Co-Advisor
Kevin Loren Hockett, Committee Member
Kari Anne Peter, Committee Member
Keywords:
Sphagnum peat moss
Agaricus bisporus
Alternative casing materials
Bacterial Blotch Disease
Abstract:
In 2025, Pennsylvania accounted for ~69% of all US Agaricus bisporus pounds produced, valued at ~535 million USD. Agaricus bisporus relies on an intricate microbial ecological succession throughout its cultivation. A necessary step in A. bisporus production is the addition of a casing layer on top of mycelium-colonized compost to induce fruitification. The industry standard casing material, sphagnum peat moss, is a non-renewable resource that is set to be banned in some countries. The mushroom industry needs alternatives to peat. Alternative casing materials were evaluated for their effect on white button mushroom yield, postharvest quality, and susceptibility to bacterial blotch disease (BBD). The casing treatments include a control of 100% sphagnum peat, and three ratios of peat mixed with recycled mushroom compost (RMC) and wood fiber (WF). Three replicate mushroom crops were conducted at the PSU Mushroom Research Center (MRC) to assess the impact of the casing treatments on yield and average mushroom size. Statistical comparisons of the effect on yield did not indicate a significant difference (p<0.05) for all three replicate crops combined where the overall yield of alternative casing treatments were numerically lower compared to the 100% peat casing. Individually, only one crop of three showed statistically significant difference (p<0.05) where the 100% peat casing had the highest yield. The effect on average mushroom size was not found to be significant (p>0.05) for any of the three replicate crops. A post-harvest shelf-life study was conducted on these same crops. Mushrooms were picked and stored at 4 °C for a post-harvest shelf-life study. Mushrooms were sampled fresh (day 0; pick day) and then from cold storage on days 3, 6, and 10 and tested for whiteness, firmness, and moisture content/dry weight. Across all three crops as the proportion of alternative casing materials increased between casing treatments when mixed with peat, results were statistically significant (p>0.05) as whiteness increased, firmness increased, moisture content increased, and dry weight decreased. These outcomes are most likely due to decreases in casing moisture and increases casing salt content as the proportion of alternative casing materials increased when mixed with peat, suggesting that the mushroom moisture content influences yield and fresh quality. Three additional crops were conducted to assess the impact of the casing treatments on BBD, caused by Pseudomonas tolaasii (strain BP1006). Using numerical sums of asymptomatic and symptomatic mushrooms harvested between non-inoculated and inoculated casing treatments, data were fitted to a binomial generalized linear mixed model to compare BBD incidence between casing treatments. Only one crop of three indicated the 100% peat casing treatment had a higher incidence of BBD than alternative casing treatments. The decrease in disease incidence of alternative casing treatments compared to the 100% peat casing upon inoculation was most likely due to decreases in casing moisture content and increases casing salt content as the proportion of alternative casing materials increased when mixed with peat, reflecting the influence of the mushroom moisture content on BBD onset. The other two crops did not result in an increase in BBD due to inadequate humidity control in the growing room they were conducted in. However, regardless of the casing material, proper crop management is required to prevent BBD from causing yield loss. While yield and mushroom size were not significantly influenced, the increase in mushroom quality and decrease in susceptibility to BBD should encourage the usage of alternative casing materials as the mushroom industry reduces the use sphagnum peat moss as a primary casing material. By increasing the usage of alternative casing materials, A. bisporus farmers may be able to lower input costs and increase earnings because yield will not be affected, while mushroom quality increases and susceptibility to BBD decreases to potentially allow the sale of white button mushrooms at higher prices.