Gibberella avenacea (Fusarium blight)

Many varieties and cultivars of wheat, rye, barley and triticale have shown resistance to species of Fusarium in several screening and breeding programmes. Resistant varieties and cultivars have effectively served as a means of controlling fusarial diseases in different cereal crops. Triticale lines were more susceptible than wheat to Fusarium injury but were more resistant than rye. Winter and spring wheat appeared to be the most susceptible to infection (Arseniuk et al., 1993). In general, the octoploid accessions were more resistant than hexaploids. Some of the hybrids were more resistant than varieties in winter rye (Komenda et al., 1982). Potato cultivars like Provita and Stina exhibited vertical resistance to G. avenacea (Seppanen, 1983a), while Sabina, Saturna and Jaakko possessed some horizontal resistance (Seppanen, 1981). Best resistance to fusariosis in flax was achieved by crosses of resistant genotypes with a maximum proportion of dominant alleles and subsequent selection of hybrids under moderately severe infection (Pavelek, 1983). Hybrid lupins are available of the type Vada, Apva and Laf-RP1 with resistance inherited from Frost and also the bitter (alkaloid) types BSKhA 890, BSKhA 892 and N56-23 (Debelyi et al., 1991). In red clover, Coulman and Lambert (1995) suggested that more than one virulent isolate or species of the fungus should be used in screening programmes for effective selection of resistance to root rot. Cell lines with stable resistance to species of Fusarium were obtained with embryonic cell suspension cultures of Medicago sativa in vitro which showed better tolerance to filtrates of the pathogen (Binarova et al., 1990). Electrophoretic analysis of pea seeds showed that anode globulins and cathode albumins of aleurone grains, and cathode globulins and albumins of the embryo, were indicators of resistance (Volodin and Timofeev, 1984).

The incidence and severity of disease appears to be more directly related to the level of additional nitrogen (N) applied than to cropping practice. Increased rates of applied N not only increased the recovery of the pathogen but also the incidence and severity of symptoms of attack by G. avenacea. Disease was more severe in high input monocrop and bicrop treatments. Levels of the pathogen on wheat within cereal legume bicrop was higher and root rot was far more severe in the continuous wheat-soybean rotation. Lupins grown after cereals showed less infection by G. avenacea, due to build-up of antagonistic microbes in the rhizosphere of cereals (Kiselev and Dukhanina, 1973). Superior plant growth and improved grain yield in the non-cereal rotation have been attributed to the lower destructive potential of fungal complexes formed during root regeneration in spring (Sturz and Bernier, 1989). Sowing in October-November instead of September lowered the injury by species of Fusarium. Irrigation at sowing to shoot formation protects spring wheat from early infection (Dorovskaya, 1978).

Pseudomonas fluorescens, antagonistic to pathogenic and saprophytic fungi on rape and flax, protected germinating plants against infection by G. avenacea. Isolates of Penicillium cyclopium, Bacillus sp., Agrobacterium radiobacter and Trichoderma viride inhibited the growth of G. avenacea in vitro. T. viride showed promise in the control of root pathogens of winter wheat. Nigrospora oryzae isolated from the culm base of rye with take-all symptoms offers protection against species of Fusarium, provided it establishes an early contact with rye roots (Truszkowska et al., 1986). Take-all decline could be prevented by the presence of other root and foot rot pathogens (Zogg and Amiet, 1980). Seed dressing treatment of Streptomyces griseoviridis on barley and spring wheat in field experiments increased yields slightly (Tahvonen et al., 1995). A combination of the bacterium Bacillus subtilis and the fungicide Vitaflo R-280 (Carbathiin + Thiram) was the most effective method for reducing disease severity in lentil.Certain strains of nodule bacteria, Streptomyces griseus, Trichurus spiralis and nonpathogenic Fusarium roseum 'Gibbosum' were also used in the biocontrol of G. avenacea.G. avenacea appears to be a candidate for the biocontrol of spotted knapweed (Centaurea maculosa). Topical application of ice nucleating active bacteria or fungi decreases the cold tolerance of freeze-intolerant insects by raising their supercooling points (Steigerwald et al., 1995). Ice nuclei from G. avenacea raised the supercooling point of Cryptolestes ferrugineus, a stored grain pest, from -17 to 9°C and increased the mortality at -9°C for 24 h from 10 to 33% (Fields et al., 1995). Enniatins from G. avenacea isolated from the foliage of balsam fir were found to be toxic to spruce budworm (Choristoneura fumiferana) larvae when incorporated into insect diet (Strongman et al., 1988).

Various fungicides are in use against Fusarium diseases in different crops. The most effective fungicides in the control of G. avenacea include carbendazim, benlate, mancozeb, UK 204, prochloraz, carbendazim and thiophanate-methyl. Fungicides UK 264 (tebuconazole + triadimenol) and prochloraz are most effective as sprays when applied to wheat ears for controlling subsequent ear diseases (Hutcheon and Jordan, 1992). Triadimenol and tebuconazole in combination with imazalil gave best control of stem diseases in spring barley (Lacicowa and Pieta, 1994). Thiram, thiabendazole (TBZ), prochloraz and thiophanate-methyl were the most effective fungicides as seed dressers in controlling seedborne G. avenacea and other pathogens of winter wheat, medics, linseed and other crops. Seed treatment with antibiotics like nimphimycin and griseofulvin reduced root rot by over 60% (Mladenov and Tsvetkov, 1979). Thiabendazole is the most frequently used fungicide in the control of dry rot of potatoes during storage besides thiram. Most of the pathogenic isolates of G. avenacea were sensitive to fungicides like TBZ and benomyl, except for a few isolates (Hanson et al., 1996; Satyaprasad et al., 1997). Incorporation of the fungicide metalaxyl into soil effectively controlled G. avenacea and other fungi in glasshouse studies (Bretag and Kollmorgen, 1986).