Do I need to worry about senescence?

[notplants]

this is a question I had a week ago, which @glyph helped answer for me, which I will write here as I understand it for any future mushroom growers who have the same question as me

at first, my plan was to just do grain-to-grain transfers indefinitely, until I saw senescence start to happen. I thought once I saw senescence, like a batch that wouldn’t fruit, I would just get some new spawn from a supplier and restart the process.

@glyph helped me realize this is probably not a good approach, because senescence can come on slowly. Its like the mycelium getting old, and just getting less vigorous – so it could lead to less fruiting, easier contaminations, slower growth – and I wouldn’t necessarily be able to know when it was “starting”. In my initial plan of just doing grain to grain transfers indefinitely, senescence might appear just as the slow chtulian shadow creep of things slowly working progressively less well.

In practice, I was actually able to do grain to grain transfers for many months, and we are still seeing fruits. In fact some of the mushrooms fruiting in our chamber now came from an oyster mushroom I cloned last spring, and expanded via grain to grain transfers tens of times since then. so I’m curious what the practical limits are of after how many generations of g2g transfers you could expect to see senescence with oyster mushrooms,
but in practice, to avoid unknowable shadow creep,
I’m going to go back to the standard of having master cultures in agar and in liquid,
and a limited known number of generations each time from master culture to bulk inoculation.

Since I had good results with many g2g transfers, I might still experiment with doing a couple generations of g2g transfers, but I won’t do it indefinitely.

to close this post, here is a relevant thought experiment from the shroomery forum which makes me laugh,

source: Can Grain-to-Grain Transfers Be Done Indefinetly? - Mushroom Cultivation - Shroomery Message Board

[Tim]

Super interesting, thanks for sharing!

[glyph]

@notplants

I’m sharing some paper links and research notes here to help us better understand senescence. I lack a detailed understanding of the underlying processes, and have mostly just followed best-practices I’ve read in cultivation books. Would be great to develop our understanding together.

Here’s an older paper which is nonetheless quite illuminating:

Gramss G (1991). “Definitive senescence” in stock cultures of basidiomycetous wood‐decay fungi. Journal of Basic Microbiology, 31(2): 107–112. https://doi.org/10.1002/jobm.3620310207

For 7 cultures of basidiomycetous wood‐decay fungi the decline of the following vitality marks were recorded over a 6‐year period: (i) Consumption of sterilized beech wood substrate within a time unit as an indicator of the overall vigorousness of the fungus, (ii) decline of the competitive saprophytic ability (kratovirulence), which enables the fungus to colonize natural nonsterile substrates, (iii) capacity for sexual reproduction, (iv) several morphological features of the fungal colony.

The substrains maintained on liquid still cultures at 23°C lost their vitality marks after a period of continuous decline rather abruptly. With the loss of kratovirulence and fruiting capacity the strains were no longer viable under field conditions, and with the drop of the sterile wood‐decay capacity to less than 3% by dry weight the formation of aerial mycelium and melanin pigments virtually ceased. In several fungal species the colonies segregated into coexisting sectors of extreme senescence and comparative juvenility, and a spread of senescence to the juvenile sectors did not occur. It is concluded that stock cultures of wood‐decay fungi are subject to progressive senescence even under optimum conditions of strain preservation.

It looks like they transferred the liquid culture strains to new batches every 6 months over the 6 year period. I imagine the process of senescence is accelerated when expansion events are more frequent, but I’m not yet sure about that.

In strains of the commercial mushroom, Agaricus bisporus (LGE.) IMBACH, a reduced fruiting capacity can occur (FRITSCHE 1969) which has no pathogenic roots. In other fungal species the capacity for both sexual and asexual reproduction terminate after several years of propagation in monoxenic culture (ASCHAN-ABERG 1960, ESSER 1973). In addition, the microbial cell can abate in its capacity to form antibiotics (PRAEVE 1959), enzymes (MASSOW and SCHMIDT 1973) and fungal cell pigments (ASCHAN-ABERG 1960, MOSER 1958). Plant associated microorganisms show losses in pathogenicity, virulence (HELTON 1970, AWUAH and LORBEER 1988) and host specificity (WILSON et al. 1975) as well as in the potential to form mycorrhizas with plant roots (MOSER 1958, MARX and DANIEL 1976, KROPP et al. 1987). Surprisingly, a common root of these effects of debilitation has never been established. Moreover, the mere possibility of the presence of debilitation symptoms in strains obtained from stock culture collections or in strains employed in pathogenicity and other interaction studies with host plants is widely ignored. This means that expected properties of microbial strains that have been lost during long-term preservation can become confused with basic physiological incompetences. The present paper tries to interpret the gradual debilitation in the physiology of long-lived strains of basidiomycetous wood-decay fungi as a kind of ageing that is different from that in certain well-known models of fungal senescence (FULBRIGHT 1984, HAMMAR et al. 1989, OSIEWACZ 1990).

I’ll continue sharing papers and findings as I go. I can only take so much senescence-talk at one time