The Royal Society Report - Push-Pull

Table 2.2. Examples of diseases affecting a selection of crops.
Crop Pathogen, disease, bacteria or virus Effect
Apples and
pears
Banana
Fireblight disease (Erwina amylovora)
Black Sigatoka disease
(Mycosphaerella fijiensis)
Panama disease (Fusarium)
Xanthomonas wilt (Xanthomonas
campestris)
Destructive bacterial disease that kills blossoms, shoots, limbs
and sometimes entire trees.
Necessitates weekly sprays with fungicides in major banana
producing areas. Since the major worldwide commercial cultivar
(Cavendish) is susceptible, there is concern that security of
supply may be undermined.
As the disease progresses, younger and younger leaves collapse
until the entire canopy consists of dead or dying leaves.
Pathogen enters the vascular system of the plant, destroying the
fruit bunches and eventually killing the entire plant.
Barley Powdery mildew (Blumeria graminis) Fast evolving and severe constraint on barley production
necessitating regular fungicide applications in northern Europe.
Beans Bacterial blight (several species) Losses occur from death of plants, partial loss of leaves, and
pod-spotting quality factors.
Brassicas Black-rot (Xanthomonas campestris) Seed-borne vascular disease that can cause affected leaves
to drop prematurely and distortion of leaves, dwarfing and
plant death.
Cassava
Citrus fruit
Potato
Rice
Cassava mosaic virus (Geminiviridae
family)
Citrus canker (Xanthomonas
axonopodis)
Potato late blight (Phytophthora
infestans)
Bacterial wilt (Ralstonia solanacearum)
Many fungal diseases (particularly
Magnaporthe grisea)
Plant pathogenic virus that may cause either a mosaic
appearance to plant leaves, or chlorosis, a loss of chlorophyll.
Infection causes lesions on the leaves, stems and fruit of citrus
trees, including lime, oranges and grapefruit. A fruit infected
with canker is safe to eat but too unsightly to be sold.
Causes devastating losses necessitating widespread fungicide
applications.
Very destructive, especially during hot and wet seasons. Plants
wilt and die suddenly.
Despite intensive breeding for resistance, losses are still
considerable in Africa and Asia.
Soya bean Soya bean rust (Phakopsora pakirhizi) Causes a major reduction in yields in Brazil.
Tomato
Wheat
Bacterial speck disease
(Pseudomonas syringae)
Ug99: a race of stem rust caused by
Puccinia graminis (see Case study 3.5)
Cool, moist environmental conditions contribute to the
development of the disease, which has now established itself as
a major production problem in northern USA.
Overcomes previously effective disease resistance genes;
currently affecting yields in Africa.
work, they need food. In developing countries, where
mechanisation may be limited, the energy inputs required
to grow food (from human and animal labour) represent a
significant part of the constraint on production. In the
UK, agriculture uses about 1.5% of UK total energy and
accounts for 0.8% of total carbon emissions (Warwick
HRI 2007).
In addition to CO 2 , the other significant greenhouse gas
associated with crop production is N 2 O, as discussed in
Section 2.6.1. Agriculture accounts for the majority of the
N 2 O emissions in the UK (DEFRA 2009a).
2.9 Maintenance of genetic resources and
germplasm availability
Genetic variation in crops and their relatives is vital for
agricultural development. Many modern varieties have
incorporated traits, for example disease resistance, that
were transferred by conventional breeding using different
varieties, landraces and relatives. However, genetic
uniformity and a narrowing genetic base may lead to
decreased resilience in the face of environmental stress
(as discussed further in Chapter 4) and the potential for
continued novelty and improvements in the future
18 I October 2009 I Reaping the Benefits The Royal Society