In vivo control of Mycosphaerella pinodes on pea leaves by a crude bulb extract of Eucomis autumnalis

We previously reported on the in vitro antifungal activity of a crude whole plant extract from Eucomis autumnalis against seven economically important plant pathogenic fungi. A crude extract of the bulb showed similar in vitro mycelial growth inhibition of the same plant pathogenic fungi as well as that of an eighth fungus, Mycosphaerella pinodes, the cause of black spot or Ascochyta blight, in peas. Subsequently, fourth internode leaves were removed from 4 wk old pea plants, placed on moist filter paper in Petri dishes and inoculated with an M. pinodes spore suspension before and after treatment with the extract. The control of Ascochyta blight by different concentrations of the crude E. autumnalis extract was followed in vivo by leaf symptoms over a 6 day period at 20°C in a growth cabinet. The crude extract prevented M. pinodes spore infection of the leaves when the leaves were inoculated with spores both before or after treatment with the extract, confirming complete inhibition of spore germination. The crude E. autumnalis extract showed no phytotoxic reaction on the leaves even at the highest concentration applied.     

Geometric morphometries and the analysis of higher taxa: a case study based on the metendosternite of the Scarabaeoidea (Coleoptera)

A geometric morphometric analysis of families belonging to the Scarabaeoidea, using landmarks from three two-dimensional views (frontal, dorsal and lateral) of an internally situated rigid structure, the metendosternite, was carried out. Procrustes distances matrices were obtained to produce phenograms from the three analyses. Relative warp analyses were also performed and the first two relative warps for the three data sets plotted against each other. The metendosternite is an internally situated anatomical structure that has largely been neglected in past studies. However, it proved to be useful in geometric morphometric studies, because it is rigid and landmarks can be easily identified. Geometric morphometries is shown to be a powerful tool to identify phenetic relationships between higher level taxa, and the metendosternite is a new structure available for beetle systematisists.     

Genetic comparison of Ug99 with selected South African races of Puccinia graminis f.sp. tritici

Using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) marker analyses, the genetic structure of selected South African wheat stem rust races was compared with Ug99. SSR analysis divided the population into two distinct groups with 24.5% similarity between them. A local race, UVPgt55 (North American race notation TTKSF), grouped with Ug99 (TTKSK) with a 100% similarity. When AFLP data were included, the same groups were found, but with an increased similarity of 66.7%. Although the SSR data were unable to distinguish between all individual isolates, the AFLP data alone and in combination with the SSR data discriminated between the isolates. The grouping of individual isolates resembled the pathogenicity profile of the different races. On the basis of its similarity with Ug99, it was concluded that UVPgt55 was most probably an exotic introduction into South Africa, whereas the other races specialized locally through mutational adaptation.     

Mycelial growth inhibition of plant pathogenic fungi by extracts of South African plant species

Eleven plant species were collected from the Blyde River Canyon area, Mpumalanga, South Africa. Methanolic crude extracts of the plant samples were concentrated to dryness, dissolved in sterile distilled water and bioassayed in the laboratory for their fungicidal potential against seven plant fungal pathogens, namely Botrytis cinerea, Fusarium oxysporum, Sclerotium rolfsii, Rhizoctonia solani, Verticillium dahliae, Botryosphaeria dothidea and Pythium ultimum, at equal concentrations. A modified agar dilution method was used to determine the inhibitory effect of the plant extracts on the mycelial radial growth of the plant pathogens. Antifungal activity was confirmed in all the plants, but not in all plant parts and also not against all the test organisms. The crude extract of Eucomis autumnalis performed best of all the plant extracts tested, as it showed significant antifungal activity against all seven of the plant pathogenic test organisms and compared favourably to the inhibition of the mycelial growth by a broad spectrum synthetic fungicide (carbendazim/ difenoconazole). The crude extract of Schrebera alata came out second best, in the sense that at least one plant part inhibited the mycelial radial growth of four of the seven test organisms by at least 50%.     

Fungitoxic properties of selected South African plant species against plant pathogens of economic importance in agriculture

Thirty‐nine plant species, representing 20 families from the subclasses Rosidae, Asteridae, Commelinidae and Liliidae, were collected from the Blyde River Canyon Nature Reserve, Mpumalanga, South Africa. Crude extracts were prepared and bioassayed, at equal concentrations, for their antifungal potential by determining the inhibitory effects on the mycelial growth of seven economically important plant pathogenic fungi. Statistically significant differences between plants and plant parts were observed as well as the resistance of different fungi to treatment with different plant extracts. The most significant mycelial growth inhibition was obtained with extracts from two species of the subclass Liliidae, namely Aristea ecklonii and Agapanthus inapertus. The crude extract of A. ecklonii performed best of all extracts as it totally inhibited the mycelial growth of all seven of the plant pathogenic test organisms and outperformed the inhibition by a broad spectrum synthetic fungicide (carbendazim/difenoconazole). Crude extracts of A. inapertus showed complete inhibition of four and strong inhibition of the remaining three plant pathogenic fungi. Although not as efficient as the previous two species, the extract of Anisopappus junodii, from the subclass Asteridae, also showed promising antifungal activity by completely inhibiting mycelial radial growth of two and strongly inhibiting that of the remaining five fungi.     

Evidence for an Ethylene Requirement to Reduce Soaking Injury in Bean Seeds and the Beneficial Effect of Heavy Metals

In addition to CO₂, low concentrations, in decreasing orderof effectiveness, of Ag, Ni, Hg, Zn, Co, Pb, and Cu salts tendedto reduce soaking injury in bean seeds. Their effects did notappear to be due to ethylene antagonism. The CO₂ effect wasnot related to it lowering the pH of the soaking solution. Soakinginjury was aggravated by L-a-(2-aminoethoxyvinyl) glycinehydrochloride(AVG) and 2,5-norbornadiene (NBD) and this effect was reversedby ethrel. Soaking in the presence of an ethylene absorbantHg(CIO₄)2 increased injury. The beneficial effect of CO₂ wasdiminished by NBD and this was reversed by ethrel. Ethrel andethylene tended to decrease soaking injury. Injurious treatmentsresulted in less ethylene release by soaked seeds than beneficialtreatments. It is concluded that ethylene does not cause soakinginjury but appears to be partially required for its prevention. Key words: Phaseolus vulgaris, soaking injury, ethylene, ethylene antagonists, heavy metals