Rumen methanogens in sheep from Venezuela were examined using 16S rRNA gene libraries and denaturing gradient gel electrophoresis (DGGE) profiles prepared from pooled and individual PCR products from the rumen contents from 10 animals. A total of 104 clones were examined, revealing 14 different 16S rRNA gene sequences or phylotypes. Of the 14 phylotypes, 13 (99 of 104 clones) belonged to the genus Methanobrevibacter, indicating that the genus Methanobrevibacter is the most dominant component of methanogen populations in sheep in Venezuela. The largest group of clones (41 clones) was 97.9-98.5% similar to Methanobrevibacter gottschalkii. Two sequences were identified as possible new species, one belonging to the genus Methanobrevibacter and the other belonging to the genus Methanobacterium. DGGE analysis of the rumen contents from individual animals also revealed 14 different bands with a range of 4-9 bands per animal.

Screening for root traits has been one of the most difficult areas to practise over large number of genotypes. Hydroponic systems enable easy access to roots while high-molecular weight polyethylene glycol (PEG) is used to induce water stress. A total of 838 genotypes were evaluated for root length in a hydroponic trial under PEG-induced stress and non-stress growing conditions. Augmented complete block design with seven blocks and six standard control varieties was used. Root length differences were highly significant (P < 0.01) under both stress and non-stress growing conditions among genotypes. Osmotic stress has caused an average reduction of 54 % in root length. Among the genotypes, root length ranged from 1.4 to 13.3 cm under stress, and 4.4 to 23.3 cm under non-stress conditions, respectively. The best control variety for drought resistance was significantly (P < 0.05) outperformed by four new entries namely Colotana 296-52, Compare, Santa Elena and Tammarin Rock, while the shortest roots were measured on genotypes Aus 16356, Elia, Camm, Portugal 3, and Sentinel. Differences among ploidy levels, domesticated and wild forms were also significant (P < 0.05). Hexaploid wheat showed significantly longer roots in both growing conditions while wild tetraploids showed the shortest roots under stress. There was a change in the ranking of genotypes under the two water regimes, which indicates the difficulty of selecting drought resistant varieties under optimum environments.

Subterranean clover (Trifolium subterraneum) is grown extensively as a pasture legume in agronomic regions with Mediterranean-type climates in parts of Africa, Asia, Australia, Europe, North America and South America. Root diseases of subterranean clover, especially those caused by oomycete pathogens including Aphanomyces, Phytophthora and Pythium, greatly reduce productivity by significantly decreasing germination, seedling establishment, plant survival and seed set. For this reason, experiments were conducted to determine the species of Aphanomyces causing root disease on subterranean clover in the high-rainfall areas of south-west Western Australia. The effects of flooding, temperature and inoculum concentration on the development of root disease on subterranean clover caused by this Aphanomyces sp. were also investigated as was its host range. Morphological and molecular characteristics were used to identify the pathogen as a new species Aphanomyces trifolii sp. nov. (O’Rourke et al.), which forms a distinct clade with its nearest relative being A. cladogamus. A. trifolii caused significant lateral root pruning as well as hypocotyl collapse and tap root disease of subterranean clover. The level of disease was greater in treatments where soil was flooded for 24 h rather than for 6 h or in unflooded treatments. The pathogen caused more disease at 18/13oC than at lower (10/5oC) or higher (25/20oC) temperatures. The pathogen caused more disease at 1% inoculum than at 0.5 or 0.2% (% inoculum : dry weight of soil). In greenhouse trials, A. trifolii also caused root disease on annual medic (M. polymorpha and M. truncatula), dwarf beans (Phaseolus vulgaris) and tomatoes (Solanum lycopersicum). However, the pathogen did not cause disease on peas (Pisum sativum), chickpea (Cicer arietinum), wheat (Triticum aestivum), annual ryegrass (Lolium rigidium) or capsicum (Capsicum annuum). A. trifolii is a serious pathogen in the high-rainfall areas of south-west Western Australia and is likely a significant cause of root disease and subsequent decline in subterranean clover pastures across southern Australia.

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