Coming or Going? Short of Phytoalexins?

With the shortening days and weakening light of late autumn, plants want to shut shut down and have a good long sleep till spring. Then they can awake refreshed about early February when things are picking up. Just like us, as tiredness sets in and they become weaker they are extremely susceptible to disease, since they have no vigour with which to resist it. Resist it? How do they do that?

Whereas humans produce antibodies with which to attack disease, plants have other methods:

• Firstly, they can restrict entry by quickly forming calluses (the plants' equivalent of scabs) over wounds.
• Secondly, they can produce toxins; woody plants, for example, often produce resins, which act as poisons. However, they can also react more actively.
  

ACTIVE DEFENCE
In the 1940s, scientists discovered that infected plants could react actively in response to fungal attack by producing substances which they called 'Phytoalexins'. Since that time about twenty phytoalexins have been discovered, of which each plant species uses one or two. Unlike antibodies, they are not species specific, so just like a contact fungicide they can be used against a wide range of fungal infections.

Now back to the fuchsias. It is hard to know whether the suddenly-yellowing leaves are caused by the plants trying to shut down, or whether it is our old friend botrytis gaining the upper hand as the plants lose vigour. Just a couple of weeks ago I noted how the healthy fuchsias grown in soil outside had resisted this disease. Could this be evidence of phytoalexin use by fuchsias?