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Samples of maize seed were obtained from countries in Central America, Africa and Asia and assessed for fungal infection. Fusarium spp. were the largest single group of fungi present, and from these Fusarium moniliforme was the species most frequently isolated. Other fungi, including Stenocarpella (Diplodia) maydis, S. macrospora and Acremonium strictum, were also present in significant numbers. Isolates of F. moniliforme were characterized for mating populations, using RAPDs, and a number of isolates, taken at random from those assigned to specific mating groups, were also confirmed by crossing. Isolates were also characterized for fusaric acid production and significant differences in fusaric acid production were detected between isolates from different countries and regions within countries. A detailed analysis of isolates from one country, Kenya, was undertaken. The importance of the pathogens is discussed in relation to human, animal and seed health and quarantine regulations, and plant breeding objectives.

The random amplified polymorphic DNA (RAPD) technique was used to determine the mating groups of several members of the Fusarium section Liseola recovered from maize, rice and sorghum collected from different locations in Ghana. Three mating groups were identified, A, D and F, of which all A and F isolates were confirmed by mating studies. Fertile crosses were also obtained in crosses involving two of the isolates identified as belonging to the D population. Variability within the A population isolated from seeds and stem-bases of maize was investigated to determine whether the sub-structuring of this population was related to the host tissue from which the isolates were obtained. The relative merits of the RAPD procedure, compared to the mating procedure, for determining the mating affiliations of isolates and for more detailed analyses of isolates within a population, as well as its possible advantages over established RFLP methodologies are discussed.

Fusarium moniliforme, the imperfect stage of the ascomycete Gibberella fujikuroi, is an economically important pathogen with a very wide host range. The genetic characteristics of isolates of the fungus collected from different regions of Ghana from maize, rice and sorghum were determined using the random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) techniques. The pathogenicity of the isolates was also compared on maize and rice. DNA fingerprints detected as RFLPs of ribosomal DNA and RAPDs separated the isolates into discrete groups which were generally host-related. The possibility of a sub-structuring of the maize population of the fungus into tissue-related subgroups was suggested by the results. A dendrogram of the relatedness of the isolates is presented. However, the pathogenicity of the isolates on rice, measured by their ability to cause ‘bakanae’ symptoms, did not resolve the isolates into the clearly defined groups suggested by the genetic studies, and maize isolates of the fungus could cause ‘bakanae’ symptoms to the same extent as rice isolates. Similarly, some isolates identified as rice-type isolates caused as much shoot stunting in maize as maize isolates. However, the effects of the isolates on root growth of maize seedlings showed a broad correlation with the defined genetic groups, with maize isolates of the fungus showing the greatest tendency to cause root stunting

The relative pathogenicity of isolates of Macrophomina phaseolina was comparable both on sunflower tissue cultures and on mature plants and seedlings. The relative susceptibility of the different sunflower lines in vitro showed a similar pattern for cotyledon callus cultures, but not for immature embryo cultures. Although these protocols appear to be unsuitable for the selection of novel disease resistance, they do offer the potential for a rapid, non-destructive screen for resistant material.

Sixty nine samples of maize were collected from pre-harvest standing crops and on-farm storage facilities from 52 smallholder farms located within 4 regions of Honduras during October 1992 and November 1993. Samples were visually assessed for insect damage and fungal spoilage, and the mycoflora quantified on artificial media. The major components of the ear rot complex were: Fusarium moniliforme, F. moniliforme var. subglutinans, Penicillium species, Stenocarpella maydis, S. macrospora and Acremonium spp. Representative samples were also assayed for mycotoxin content. Fumonisin B1 was detected in all 24 samples tested at levels of between 68-6,555 (micrograms/kg), and aflatoxin was detected in 2 samples heavily contaminated with Aspergillus flavus. Moniliformin and tenuazonic acid were not detected in the samples tested. The implications of these findings for human and livestock health risk are discussed, together with possible strategies for controlling these pathogens.

The effect of ultra violet (UV) irradiation on cultured isolated microspores of rapid cycling Brassica napus was investigated. The microspores were highly sensitive to UV, with the calculated LD 50 being an exposure of 20 s. Viability tests suggested that death of the microspores was not immediate, but occurred during subsequent incubation (7d). None of the embryos produced following UV-irradiation of microspores showed gross morphological variation. A large number of regenerants was established from embryoids and grown to flowering(.)