AbstractsBiology & Animal Science

ix, 110 leaves, bound ill. (some col.) 29 cm Overall, control efforts are focused on breaking the disease cycle. The disease cycle is initiated when spores disperse from a contaminated source to a healthy host. For Fusarium species, two types of asexual spores, macroconidia and microconidia, are often the primary means of dispersal, although sexual spores (ascospores) can also playa role (21). In nurseries, ascospore dispersal is by wind (45), and conidia can spread by both wind and water splash, primarily from overhead watering (21, 45). Vectors, such as insects and tools which contact infected material, also contribute to spread (2). Once in contact with the host, the spore germinates, penetrates the tissue, and enters the host. The pathogen infects the tissue, feeding on cellular material, growing, and producing spores that are then dispersed, perpetuating the disease cycle. If a host is absent, thick walled survival spores, called chlamydospores, can develop from cells in the hyphae and/or the macroconidia (87). Chlamydospores can allow for survival in plant parts (such as root matter) or in the soil for many years (87). Spread of Fusarium in greenhouse or field grown orchids can be reduced by various cultural practices, including removal of infected material (2, 28, 34), regulation of watering and wind (when possible) (21,45,56), and management of vectors (96), among other sanitary practices. Fusarium infection and reproduction can also be prevented through the use of resistant cultivars (2, 77). Fusarium germination growth and infection can also be inhibited by anti-fungal compounds, including chemical fungicides and biological controls (2). Some of the most successful practices in controlling fusarial diseases on nursery crops have involved the use of anti-fungal compounds, and the various types are reviewed below, together with examples of efficacy in controlling Fusarium in nursery systems. Chemical Fungicides: Chemical fungicides are toxic compounds which inhibit fungal germination, infection, growth, and reproduction. Compounds are either broad spectrum, with efficacy against many fungi, or are specific to certain fungi. Most fungicides are preventative, protecting the surface tissues on which they are applied, and inhibiting fungal germination (2). However, some fungicides are systemic, and enter the plants vascular system, reducing fungal growth and reproduction within the host, and curing very early stages of infection. Most systemic fungicides function either by releasing antifungal toxins into host's vascular system, or by inducing a systemic resistance response in the plant. Many of these fungicides are "traditional" compounds, which persist in the environment, and have higher mammalian toxicity than newer compounds. As an alternative to traditional fungicides, there are several compounds available, characterized as reduced risk, which have low mammalian toxicity and degrade quickly in the environment. Although many of these reduced risk compounds can be effective, they are often expensive and…