One aim of our experiments is to identify specific nutrients that are depleted during the production cycle and that limit mushroom yield. We have evaluated several amino acids that play central roles both as building blocks of proteins and as intermediates in metabolism. Of the 15 or so amino acids examined to date, L-isoleucine has proven the most effective in stimulating mushroom yield in a second crop (Royse and Sanchez 2008a, Royse 2008). Yield increases of greater than 50 percent have been observed when 3.6 percent (dry wt) L-isoleucine is added to fragmented 1st or 2nd break compost compared to fragmented, non-supplemented compost. L-isoleucine is found as a free amino acid in mushrooms but in much lower concentrations than several other amino acids. Thus, its role in stimulating mushroom yield remains unknown but may be related to vegetative mycelial growth and development.

Other nutrients that stimulate mushroom yield for a second crop include hydrolyzed proteins and commercial supplements. Hydrolyzed soy protein, Remo's commercial supplement and egg white protein, added at 3.6 percent (dry wt) to 1st break compost, stimulated mushroom yield by 61 percent, 54 percent and 51 percent, respectively, compared to the fragmented, non-supplemented control (Royse and Sanchez 2008b).

We are also exploring the effects of adding phase II compost to 2nd break mushroom compost on mushroom yield and quality. The addition of 20-25 percent phase II compost to 2nd break compost replaces dry matter lost during production of the first crop. This would allow growers to maintain compost dry wt/[m.sup.2] at the same level as the first crop. In our experiments, we have been able to obtain yields (kg/[m.sup.2]) and biological efficiencies (percent BE) in the second mushroom crop that were equivalent to the first crop.

Another objective of our research on double cropping is to determine the optimum time of re-casing for the second crop. For example, is it more advantageous to re-case immediately after re-supplementing or are greater yields and better mushroom quality achieved when casing is delayed for 4-7 days? This work is underway at the mushroom research facilities.

Finally, we are exploring the possibility of applying this work on a commercial scale. Through a grant from the American Mushroom Institute and the Pennsylvania Department of Agriculture, we are working with growers to identify and overcome obstacles that arise on commercial farms when attempting to practice double cropping. Growers at two bed farms and one tray farm in Pennsylvania are cooperating in this effort by conducting experiments at their facilities to determine the feasibility of double cropping.

Re-supplementing and re-casing 2nd break compost represents a potential opportunity for growers to increase revenues and reduce costs associated with preparation and disposal of compost. Double cropping would ultimately lower the cost of mushroom production by reducing labor, raw materials and time required to prepare fresh phase II compost.

Production of A bisporus on minimally composted substrate

The development of non-composted or minimally composted substrates has become more attractive in recent years because these substrates promise to eliminate or sharply curtail problems associated with traditional compost preparation. Preparation of traditional compost has some disadvantages, including cost of composting equipment, and sometimes the costs of forced aeration bunkers, and phases II and III tunnels. In addition, there is a loss of substrate dry matter due to microbial activity during the composting process, and odors and effluents may become a problem for the surrounding community.

Our most recent efforts have focused on the development of a simplified method to cultivate A. bisporus with relatively low energy input. Our initial results demonstrated the advantage of pre-colonizing a milled substrate with Scytalidium thermophilum (St), a thermophylic fungus readily found in phase II compost, for only 3-4 days before spawning with A. bisporus (Sanchez, Mejia, Royse 2008). With this process, phase I composting is not required, thus eliminating a potential source of odors and runoff. We have continued to work to improve the yield capacity of substrates pre-colonized by St by evaluating various cereal grains, sawdust, cotton seed hulls and chopped straw and corn stover and then supplementing these substrates at spawning and at casing with commercial delayed release nutrients. To date, maximum BE (99 percent) and yield (21.6 kg/[m.sup.2]) were obtained on St-colonized milled wheat straw + 2 percent hydrated lime supplemented with 9 percent commercial supplement added both at spawning and at casing (Sanchez, Royse 2009). We anticipate further improvements in mushroom yield through evaluation of additional substrates and their method of preparation.

References

Royse, D. J., J. E. Sanchez, R. B. Beelman and J. Davidson. 2008. Re-supplementing and re-casing mushroom (Agaricus bisporus) compost for a second crop. World J. Microbiol. Biotechnol. 24:319-325.

Royse, D. J. and J. E. Sanchez. 2008a. Supplementation of 2nd break mushroom compost with isoleucine, leucine, valine, phenylalanine, Fermenten and SoyPlus. World J. Microbiol. Biotechnol. 24:2011-2017.

Royse, D. J. and J. E. Sanchez. 2008b. Supplementation of first break mushroom compost with hydrolyzed protein, commercial supplements and crystalline amino acids. World J. Microbiol. Biotechnol. 24:1333-1339.

Royse, D. J. 2008. Double cropping Agaricus bisporus by re-supplementing and re-casing compost. Pp 48-53. In: Lelley, J.I. and Buswell, J.A. (eds.) Proceedings of the 6th International Conference on Mushroom Biology and Mushroom Products, 29 Sept--3 Oct, Bonn, Germany.

Sanchez, J. E., L. Mejia and D. J. Royse. 2008. Pangola grass colonized with Schytalidium thermophilum for the production of Agaricus bisporus. BioresourceTechnol. 99:655-662.

Sanchez, J. E. and D. J. Royse. 2009. Scytalidium thermophilum-colonized grain, corncobs and chopped wheat straw substrates for the production of Agaricus bisporus. Bioresource Technol. 100:1670-1674.

PDF files of the references are available from the author via email (djr4@psu.edu)

Daniel J. Royse

[ILLUSTRATION OMITTED]

Professor Dept. of Plant Pathology

316 Buckhout Lab

Pertn State

University Park, PA 16802

djr4@psu.edu