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Extracts from 26 plant species representing 16 families, collected in the Free State Province of South Africa, were tested in vitro for their potential to inhibit the growth of eight plant pathogenic fungi and five plant pathogenic bacteria. None of the crude extracts showed any mycelial growth inhibition of the eight test fungi. All of the extracts inhibited the growth of one or more of the five plant pathogenic test bacteria, but to varying degrees. Crude extracts from Acacia karroo and Elephantorrhiza elephantina inhibited the growth of four bacteria, while that of Euclea crispa, Acacia erioloba, Senna italica and Buddleja saligna inhibited the growth of all five plant pathogenic bacteria. Of these, the crude extract of Euclea crispa was clearly superior to the rest as it compared more favourably to that of a commercial bactericide, Dimethyl Dodecyl Ammonium Chloride (DDAC). Subsequently, the Euclea crispa crude extract was fractionated by means of liquid-liquid extraction using four organic solvents, hexane, diethyl ether, chloroform and ethyl acetate, in order of increasing polarity. This was done in an attempt to assess the antimicrobial potential of the more concentrated fractions. Once again, none of the semi-purified fractions showed any antifungal activity. However, antibacterial activity was located in the more polar ethyl acetate fraction indicating that the substances involved were very similar in polarity and/or structure. From this it seems justified to further purify the ethyl acetate fraction of the Euclea crispa extract and attempt to identify the active substance(s) involved.

Sclerotium rolfsii , the causal organism of stem rot or southern blight of groundnut, is widely distributed and has been reported to cause disease in over 500 plant species throughout the world and at least 30 in South Africa. The disease is a problem in most groundnut producing areas in South Africa and no efficient control strategy has yet been developed in this country. Previous studies on the fungus have indicated that diversity within populations of S. rolfsii can be defined by placing isolates into mycelial compatibility groups (MCGs). A total of 121 S. rolfsii isolates were collected from 15 localities and seven plant species throughout South Africa and paired against each other. Thirteen MCGs were identified, some containing isolates from the same host plant or geographic area, suggesting a possible relationship between MCG and host plant or locality. Other MCGs, however, contained isolates from a variety of hosts from various localities. The population of the fungus in South Africa is diverse, with vague associations between MCG, host and geographical distribution.

Head blight, caused by certain species in the genus Fusarium, has become an economically important disease of wheat under centre pivot-irrigation along the Orange River region in South Africa. Isozyme analysis, by means of starch gel electrophoresis, was employed to compare 73 Fusarium isolates, obtained from three farms in this region, with isolates of Fusanum acuminatum, F. chlamydosporum, F. compactum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum Group I and Group II. F. moniliforme, F. oxysporum, F. solani, and F. subglutinans. For all 11 Fusarium species, nine loci were identified in eight enzyme systems and 19 electrophoretic phenotypes (EPs) were detected, each composed of isolates from one species only. The extent of isozyme polymorphisms found among these Fusarium spp. provides a potential method for delineating isolates at species level. Six EPs, of which the most common one comprised 36 isolates, were identified within isolates obtained from the three farms. These isolates clustered together with the F. graminearum Group II reference isolates. Based on perithecial production, their identity was confirmed as F. graminearum Group II.

Structural and cytochemical aspects of the stigma of Polygala virgata Thunb. var. virgata were studied. Flowers of an isolated group of plants were used. Indications are that the plants are autogamous. The stigma is of the wet papillate type with unicellular papillae forming the receptive surface of the stigma. Exudate production commenced at an early stage, more than six days before onset of anthesis and appeared alveolar or fibrillar. The papillar cell wall material became loosely arranged and the cytoplasm senescent. All stigmatic exudate is secreted by the papillar cells and is contained in the subcuticular space. The cuticle showed no signs of disruption, but exudate appeared on the papillar surface during middle anthesis. Cytochemical tests indicated the presence of lipids, pectins and some proteins in the exudate, while no polysaccharides were indicated. No protein pellicle was observed. The papillar cytoplasm showed signs of disruption during the middle anthesis stage of development and contained lobed plastids, endoplasmic reticulum plates and small vacuoles.