The Future is No Clockwork Orange

By Nathan Smith

Imagine a life without citrus. No glass of orange juice in the morning. No slice of lemon for your iced tea. No having to segregate the green jelly babies because no one honestly likes them and you don’t understand why they continue to be produced. It would be a very different world indeed, but perhaps one we need to start considering.

Credit Father.Jack

Down with the green jelly babies… (Credit Father.Jack)

The threat to our favourite sources of Vitamin C comes from the double-pronged assault of the bacterial diseases citrus canker and huanglongbing (or citrus greening disease), which are currently having a massive impact on the citrus industry. To make matters worse there are few signs of resistance among the plants. This is mainly because the majority of citrus fruits aren’t natural species, they’re cultivars which are the result of varying inter-specific crosses. A few examples are the sweet orange, which is the result of a cross between a male mandarin and a female pomelo; and the grapefruit which is the result of a cross between a male sweet orange and a female pomelo.

800px-Fortunella

The invincible kumquat (Credit Acongagua)

A study by a group from Pakistan tested how various citrus cultivars responded to the citrus canker disease and found that some are more susceptible (like Valencia Oranges) than others (like Pigmented Oranges). While two cultivars were identified as highly resistant, Tahiti Lime and Kozan Sweet Oranges, all the cultivars showed some levels of disease. Unfortunately this indicates that all would eventually succumb to the ravages of citrus canker. That is, all except for the kumquats!  Both cultivars of kumquat tested (Meiwa and Naghmi) lacked the canker-caused lesions that unfairly graced the other plants. This may be because kumquats are only citrus fruits in the loosest sense. Unlike most of these other fruits, which belong to the Citrus genus or are products of genetic crosses within the genus, kumquats belong to the genus Fortunella. This makes them distinctly different to oranges and lemons genetically and means they may be a non-host for citrus canker and perhaps by extension for other diseases plaguing citrus; though reports of a huanglongbing-type disease in Kumquats in Taiwan suggests otherwise.

Even so resistance to citrus canker is promising. Humanity may learn to adapt and a future without oranges certainly seems brighter with the potential for Kumquat Flavoured Jelly Babies. At the very least they might taste better than the green ones.

 

 

Ash Dieback: What’s causing the rise in plant diseases?

by Nathan Smith

Ash Dieback is the latest craze sweeping the nation, and by ‘craze’ I of course mean ‘plant disease’. Like Dutch Elm disease before it, it threatens to destroy thousands of iconic trees and restructure the shape of British woodland.

Caused by the fungus Chalara Fraxinea, Ash Dieback was first noticed in Poland in 1992, though it is thought to have originated somewhere in Asia. It affects the crown of the tree (the bushy top bit) and causes it to die back, although it may not kill a mature tree for a number of years. Even then it is often the case that when a tree is killed it is through an opportunistic infection. C. Fraxinea may not kill, but it does significantly weaken the tree.

AshAttributedSo what’s to blame? Despite fears that the fungus may have come to the UK via infected plants in nurseries, the current view is that it came in the wind from Europe (at least in the majority of cases of the disease). Whilst this may seem good news (particularly for the people running the nurseries), it causes us to reach a depressing conclusionwe cannot ‘stop’ the disease. The reasoning behind this is that most plant diseases can be controlled in the early stages of an outbreak via selective removal of plants. These techniques will probably not work now: we are in the middle of a full blown Europe-wide pandemic and even if we could remove the disease from the UK, it could still come back on the wind from across the seas. This may all sound rather despairing, and work is being done to try and reduce the ecological damage, but the truth is the models still predict that in 10-20 years time the majority of ash trees will be infected, if not already dead.

In a world of increasing globalisation, ensuring plant security from biological threats is almost impossible. Whether from the soil on a backpacker’s shoe or on a tree imported from afar, new microbes will always be brought into environments they have not come across before. Ash Dieback is not the first major tree disease to affect the UK and it’s probably safe to say it will not be the last.

For all those interested in some light reading, please find the link for the Government’s plan on tackling Ash Dieback: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/69620/pb13843-chalara-control-plan-121206.pdf