Agriculture Reference
In-Depth Information
CHAPTER 15
WIND-DISPERSED DISEASES
B. HAU AND C. DE VALLAVIEILLE-POPE
15.1 INTRODUCTION
Dispersal by wind is important in many plant pathosystems but this chapter is
restricted to two groups of important wind-dispersed diseases: the powdery mildews
and the rusts. Both groups are of special interest in epidemiology because they are
highly sensitive to the environment and their presence can vary from season to
season. The fungal pathogens causing these diseases are biotrophic obligate
parasites creating well known diseases on many crop plants. Here, the discussion
concentrates on cereals, which can be seriously affected by powdery mildew and
rust fungi, and particularly on the powdery mildews of wheat and barley and the
rusts of wheat.
Powdery mildew of cereals is caused by
Blumeria graminis
(syn.
Erysiphe
graminis
) which is specialized into
formae speciales
on cereals in temperate
climates, i.e. on wheat, barley, oats, rye and their hybrids. According to Oerke
et al.
(1994), mildew on wheat is an important disease world-wide but more serious in
Europe. The biology and epidemiology of cereal powdery mildews have been
discussed by Jenkyn and Bainbridge (1978), Aust and von Hoyningen-Huene
(1986), Jørgensen (1988) and Wolfe and McDermott (1994), the latter two with
emphasis on genetics.
Cereal rusts are divided into five main species, which are also specialized into
formae speciales
(i.e. on wheat, barley, rye, oats), but the separations between the
formae speciales
are not always strict. The three wheat rust species are adapted to
particular environmental niches, that correspond to their specific requirements
during the infection stages. Stem (black) rust, caused by
Puccinia graminis
f.sp.
tritici
is adapted to the warmest conditions; stripe (yellow) rust caused by
Puccinia
striiformis
is adapted to the coolest conditions, while leaf (brown) rust caused by
Puccinia triticina
=
P. recondita
f.sp.
tritici
(Anikster
et al.,
1997) is intermediate.
Stripe rust is well adapted to cool maritime or high altitude climates or where wheat
is grown in winter seasons in countries that have warm summers, such as north
India, Australia and the US Pacific northwest (Johnson, 1992). Severe stripe rust
epidemics are sporadic although they have recently occurred in Australia in 2003, in
the United States in 2000 (Chen
et al.,
2002), and in China in 2002 (Wan
et al
.,
2004). Leaf rust occurs almost annually in most areas and is considered to be the
most widely distributed of the three rusts. Cereal rust losses in Europe are primarily
associated with stripe and leaf rusts. The importance of stem rust declined due to
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