By Dr. Helen Grogan, Teagasc, Ireland (
Helen.grogan@
teagasc.ie), Mr. Eoin O’Connor and Dr. David Fitzpatrick, Maynooth University, Ireland
New MVX Research VIRUS X
With Coronavirus causing havoc around the world and researchers frantically looking for solutions, it is timely to discuss some recent research on increasing our understanding of how Mushroom Virus (MVX) viruses interact with the host, Agaricus bisporus, identifying potential opportunities for breeders to develop a virus-resistant strain.
T The lack of
genetic diversity makes
mushrooms
susceptible to the same pathogens
he commercial mushroom, Agaricus bisporus, is susceptible to a disease caused by a complex of at least 18 viruses known collectively as
Mushroom Virus X (MVX). Symptoms include poor quality mushrooms and mushroom cap discolouration (browning), which have been correlated with the A. bisporus Virus 16 or ‘AbV16’ while another virus, the AbV6 virus, is also associated with virus outbreaks. AbV6 has not been directly correlated with distinct symp- toms although it was one of the viruses regularly detected in virus-infected crops in the early 2000’s in the UK. Most modern-day commer- cial varieties of A. bisporus are ‘mid-range hybrids’ and are almost identical genetically, having been derived from a hybrid cross bet- ween two strains in the 1980s.
One major disadvantage of this lack of genetic diversity is the universal susceptibility of mushroom crops worldwide to the same patho- gens, including viruses. Furthermore, the increased internationalisation of mushroom businesses means that the transmission and spread of viruses is facilitated by the trans- portation of substrates and mushrooms, not only across land and sea borders but also across continents.
‘Virus-breaker’ strain
In the past when La France virus was a problem, the ‘virus-breaker’ strain ‘Agaricus bitorquis’ was often grown as it was incompatible with A. bisporus and so virus transmission on an infec- ted farm was halted when this ‘virus-breaker’ strain was grown. This species is no longer commercially acceptable but it would be very desirable to have an A. bisporus variety that could function as a virus-breaker strain. It would have to be commercially acceptable as well as being vegetatively incompatible with the current dominant commercial strains. This is a
32 MUSHROOM BUSINESS
tall order and challenge for mushroom bree- ders, who will have to look outside the very narrow gene pool of the current commercial strains if they are to succeed. Mushroom bree- ders and geneticists now have a large collection of wild Agaricus bisporus strains from all over the world available to them in the form of the ‘Agaricus Resource Program’ (ARP), and this great resource will underpin the development of new exciting mushroom strains for the future. It has already been used in the produc- tion of the brown ‘Heirloom’ strain from Amycel, although this, and other brown strains can also become infected with MVX. Hopefully some new strains will be bred for being resistant or more tolerant to the common diseases, including viruses.
Infection and genomics
Growers know when there is something wrong with their crop because they see outward symp- toms, such as off-coloured mushrooms, poor quality or poor crops. However, there is a lack of knowledge on how these symptoms are pro- duced – what is the mushroom doing differently to cause such abnormal symptoms? Resear- chers need to know more about how A. bisporus strains respond to virus infection within the mushroom mycelium itself. How does it defend and protect itself from these unwanted infecti- ons? These responses are encoded within the mushroom’s genome. An infection will usually trigger a response that may result in proteins being produced or supressed, and it is these ‘proteomic’ responses that can upset the nor- mal functioning of the mycelium, causing the mushroom to be stressed and to develop the symptoms that we see. Sometimes the res- ponse may be to attack and destroy the virus itself and such ‘anti-viral’ traits would be highly desirable in new strains. The main aim of this research project was to
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