FUSARIUM HEAD BLIGHT AND DON CONTAMINATION MANAGEMENT IN SOFT AND DURUM WHEAT CULTIVATION - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 133

3. E COLOGY AND E PIDEMIOLOGY OF F USARIUM H EAD B LIGHT IN
W HEAT AND S YNTHESIS OF D EOXYNIVALENOL
In order to understand how Fusarium head blight invades wheat grain and synthesizes
DON, it is important to consider the Fusarium spp. life cycle on small grain cereals
Many papers have dealt with the epidemiology of Fusarium head blight, or more
specifically of F. graminearum , which has always been considered the most important FHB
pathogen.
Atanasoff, in 1920, first described the development of FHB, and in particular of
Gibberella saubinetii (= Gibberella zeae ). The first attempt to describe the complete life cycle
of F. graminearum on cereals was, however, made by Sutton (1982) who described the
disease cycle of the fungus in relation to the pathosystem formed by maize, wheat and the
fungus itself in which the fungus survives, spreads, develops and invades the cereal tissues,
producing mycotoxin in grain. The study by Sutton, was followed by others (Snijders, 1990;
Parry et al., 1995; Gilchrist and Dubin, 2002; Logrieco et al., 2003; Gilbert and Fernando,
2004; Xu and Berrie, 2005; Wagacha and Muthomi, 2007) which described the epidemiology
of head blight Fusaria, and other which updated the description of the pathosystem with new
knowledge about (i) the influence of the environmental and climatic conditions on the fungi
development (Doohan et al., 2003; Xu, 2003), (ii) the competitive relationships between
different Fusarium spp (Xu et al., 2007), (iii) the inoculum dispersal dynamics (Horberg,
2002; Rossi et al., 2002a; Paul et al., 2004; Maldonado-Ramirez et al., 2005), and so on. One
of the most recent descriptions of the epidemiology of FHB was given by Osborne and Stein
in 2007.
A brief description of the epidemiology of FHB in wheat is given in this section, through
a review of the main literature.
3.1. Inoculum Sources and Inoculum Structures
The principal Fusarium spp. sources of inoculum are crop debris like maize stalks, grain,
ear pieces and cob, and the stubble and straw of barley, wheat, and other cereals. Soil itself
and contaminated seeds can be also sources of inoculum, but their role is marginal compared
to the former sources. The fungi are present and survive in colonized crop residues as
mycelium, and may develop saprophytically on residues on the soil surface for 2 or 3 years
(Sutton, 1982; Osborne and Stein, 2007). Moreover, Fusarium spp can survive parasitically
and saprohytically on leaves throughout the wheat growing season, which means that these
leaves may contribute additional inoculum to the FHB development (Ali and Francl, 2001). In
some locations, the leaves have also shown large macroconidial concentrations, suggesting
that the fungus can also grow epiphytically, resulting in a higher inoculum level within the
canopy (Gilbert and Fernando, 2004). In addition, noncereal residues such as soybeans,
sunflower, pasture, and many gramineous weed species have been reported to be important
sources of inoculum for Fusarium spp. (Jenkinson and Parry, 1994; Inch and Gilbert, 2003;
Pereyra and Dill-Macky, 2008).
In general, the inoculum structures are spores (ascospores, macroconidia,
chlamidospores) and fungal mycelia (Sutton, 1982), but macroconidia and ascospores have