The dsRNA phenotype of 34 isolates representing 10 Australian pathotypes of Puccinia striiformis, 2 of P. recondita, and 1 each of P. graminis, P. sorghi, P. menthae, and Melampsora lini were examined. Each rust species had its own distinctive dsRNA pattern. Variation occurred in the dsRNA phenotype between the two isolates of P. recondita and among the 34 different isolates of P. striiformis but did not correlate with variation in pathotype. Single pustule isolates of P. graminis and P. recondita were examined to establish that all the dsRNAs were probably present in individual uredospores and were consistently transmitted asexually. The potential use of dsRNA phenotype as a cytoplasmic marker in rust population studies is discussed. Key words: dsRNA, Puccinia, rust.

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Double-stranded (ds) RNAs were found to be present in 33 of 38 collections of rust fungi, representing 15 species from four genera. This finding suggests that dsRNAs occur commonly in rust fungi. Tests were undertaken to determine the role or phenotype associated with the presence of dsRNAs. Comparisons were made between strains of Puccinia sorghi (maize rust) that had different dsRNAs and two fully isogenic strains of Melampsora lini (flax rust), one with no dsRNA and one with at least 13 dsRNAs. It was concluded that dsRNAs had no obvious effect on pathogen virulence or on growth rate as measured by rate of accumulation of leaf chitin or time to pustule eruption. Also it was demonstrated that the presence of dsRNAs had no effect on the interaction that exists between rusts over short distances in the leaf. Key words: dsRNA, rust, function, incidence.

A new set of loop-mediated isothermal amplification assays was developed for detection of phytoplasmas associated with plant diseases and optimised for rapid laboratory detection. This set of assays was designed based on the leucyl tRNA synthetase gene expressed in most of the phytoplasmas and showing a good level of sequence divergence among strains from different 16Sr groups. This makes it a good target for developing discrete assays that can detect specific phytoplasma 16Sr groups. In this study, unique sets of LAMP assays were designed and validated for seven phytoplasma ribosomal groups (16SrI, 16SrII, 16SrIII, 16SrV, 16SrVI, 16SrX, and 16SrXII). These assays are specific, rapid and as sensitive as the nested PCR assays and the results could be obtained in less than 30 minutes in real-time LAMP assays.