Multiple studies of the domestication process have been conducted on
grain crops where above-ground traits (increasing yield quantity/size and
prolonging fruiting season) are typically favoured over below-ground traits. Less is known about domestication in crops which require a mutualistic
relationship with below-ground mycorrhizal fungi.
Fruit crops (which constitute to a large part of the human diet) are enhanced
by these root symbionts by allowing the plant to access
nutrients as well as increasing disease resistance and adding protection from pathogens.
Mycorrhizal fungi are beneficial and can potentially influence plant fitness,
community structure, biodiversity, ecosystem productivity and variability (Fig 1).
An important staple food crop across the Tropics and
Oceania is breadfruit (Artocarpus
altils). Over 2000-3000
years domestication has changed breadfruit significantly from
its ancestor, breadnut (A. camansi) by extending fruiting season, creating fleshier fruit with fewer
seeds and increasing fruiting loads (Fig 2). To be considered domesticated, it must be
wholly dependent upon human intervention for dispersal, growth and reproduction,
which can be seen in all cultivated seedless breadfruit species.
A study by Xing
et al., (2012) followed the domestication process of breadfruit species (Artocarpus
sp.) across
a strong geographical gradient from west to east across the Melanesian and Polynesian
islands with a focus on its mutualistic partner - arbuscular mycorrhizas (AM
fungi). It was found that modern breadfruit species are less able to support AM
fungi than wild ancestors. This is supported by a decrease in quantity and
colonization rate across the domestication gradient from wild ancestors to
modern species.
It is possible that a trade-off in resource allocation has occurred.
Fruits are considered a strong sink for photosynthate, where sugar and other
chemicals created from photosynthesis are primarily allocated for fruit
production. As selection for high fruit yield in
breadfruit has occurred, the amount of photosynthate may have been limited with
fewer resources available for below ground root colonization and the maintenance
of the mutualistic AM fungi relationship.
The consequences of reduced AM fungi colonisation could
result in higher disease vulnerability/reduced resistance to pathogens as well
as less efficiency in accessing nutrients and water under stressful conditions. Breadfruit has the potential to be propagated at an industrial crop scale
internationally in new environments using a single cultivated genotype. However there is much uncertainty in its success - especially in places that have nutrient limitations or
drought stress. This study suggests that human-driven selection, as seen in
cultivated breadfruit, can have unintended effects on below-ground mutualists,
with potential impacts on the stress tolerance of crops and overall long-term
food security.
Incredible! It’s not often that we think to look at the interactions with other organisms during the domestication process. Can you suggest a way that humans could potentially counteract the negative effects of reduced mutualists, without adding non-natural products (e.g. fertilizers and pesticides) to the crops? Very cool!
ReplyDeleteHey Tasmin, I believe biological controls (resistant plant varieties, pheromones etc) are being looked into to suppress plant pathogens and diseases for certain species. Also reverting back to natural farming methods such as mulching/manure addition, co-planting and crop production on smaller scales to provide and retain nutrients in the soil without the addition of fertilisers. In regards to mutualistic species I have read that there are such processes as microbial inoculants, where microbes are introduced to target crops as 'biofertilisers' which form a symbiotic relationship with the crop species and bring back/support the current mutualists and provide greater plant nutrition and growth where required.
ReplyDelete