The Verrall lecture 2015
The 2015 Verrall lecture was delivered by Prof Sue Hartley from the University of York. Dr
Chris Lyal welcomed the audience on behalf of the Natural History Museum and the Royal
Entomological Society and gave a warm overview of Sue's achievements, including her current
position as Director of the York Environmental Sustainability Institute (YESI).
Sue's lecture was on ‘Sustainable Crop Protection using Natural Plant Products’ and she
explained that she had once been introduced rather cheekily as “an expert on silicon but not
in a Pamela Anderson way”. Global agriculture is facing many problems: climate change, water
shortages and stagnating yields. Into this mix, pests and diseases remain recurrent problems.
Pests are becoming insecticide resistant and pesticides are being withdrawn from markets
following more stringent legislation. We also have a dangerous reliance on a few crops; for
example, half of the world's population relies on a single variety of rice, which has 10,000
fewer genes than its wild ancestor. Many of these genes may code for useful traits such as
resistance to drought or insect herbivores: modern crop varieties contain far fewer toxins
(secondary plant metabolites). This of course means that we can eat them but so can pests.
Essentially, we have disarmed our crops through domestication.
Most of our key crops are grasses and they have a secret defence - silicon. This is deposited as
solid granules known as phytoliths, which are sharp and abrasive so can act as mini razor
blades. Consequently, silicon deters feeding by leaf chewers (foliovores), though sap feeders
such as aphids seem less affected. Sue displayed SEM images showing mandibles worn down
by feeding on silica rich leaves. Silicon deters feeding and reduces N absorption due to
abrasion. Silicon is an inducible defence and is stimulated by repeated damage with actual
herbivore feeding; mechanical damage has less effect on silicon than herbivory. Relatively
little is known about how plants uptake silicon, but different plant species deposit it in
different ways, for example as spines or nodules, and the manner of deposition has
implications for defence against herbivores. To enhance crop protection, could plants be
engineered to uptake more silicon? Work comparing locally-adapted landrace varieties of
barley (Orkney Bere) with their modern counterparts showed that both varieties have silicon
defences, but in crops where they have been lost or reduced, it might be possible to breed
commercial varieties with improved silicon uptake.
The concluding part of Sue’s talk concerned root-feeding pests. The problem with root
feeders, she said, is that once the damage is seen in the plant, it is too late, the roots have
been eaten. Plants can be viewed as mediators of interactions between above- and belowground herbivores. For example, root nematode infection can increase aphid infestation. This
may be because the nematodes stimulated the salicylic acid defence pathway, but this did not
seem to be effective against the aphids and many compounds which deter herbivore feeding
were reduced in nematode infected plants. So in devoting resources to defend against one
pest the plant has made itself more vulnerable to another. Controlling root-feeding pests is
difficult and many methods have been tried. In the 15th Century, the Bishop of Lausanne even
tried to control chafers by ex-communicating them! Sue though spoke about another,
hopefully more effective, method. Brassicas are loaded with glucosinolates that when
damaged give rise to volatile compounds called isothiocyanates, which have pest control
properties. By ploughing brassicas into the soil, farmers can fumigate the soil with
isothiocyantes, thus providing an agronomic method of root pest control, just one way the
natural defences of plants can help us fight pests more sustainably in future.
Prof. John Pickett, President of the RES, thanked Sue for a humorous and informative lecture.
After chairing some questions from the audience, John presented Sue with a memento of her
lecture and looked forward to continuing discussion at the Verrall Supper.
By the Honorary Secretary
Photo captions:
The Verrall lecturer, Prof. Sue Hartley, with the RES President, Prof. John Pickett
Prof Hartley with Dr Chris Lyal of the Natural History Museum