Comparative studies on Phytophthora megasperma isolates from chickpea collected in Australia and Spain

The relationships between isolates of the complex species Phytophthora megasperma from chickpea in Spain and from chickpea and lucerne in Australia were investigated. In the isolates from Spain > 90% of the sporangia had flattened apices, whereas in the Australian isolates only 5·6% of sporangia had conspicuously flattened apices, the remainder being convex. No differences were found between the sex organs of the two groups, except that oospore walls were thinner in the Spanish isolates (&- x = 2·2 ± 0·6 μm) than in the Australian collection (&- x = 3·4 ± 1·0 μm). The isolates from Spain had an optimum temperature for growth of ca 24°C and a maximum temperature range of 30–33°, whereas the Australian isolates had a higher optimum growth temperature (26°) and a higher maximum temperature range (33–35°). RAPD analysis of total DNA revealed a genetic dissimilarity of ca 80% between the two groups of isolates. The study therefore differentiated two genetically distinct groups among isolates causing chickpea root and stem rot in Spain and Australia. However, it is suggested that designation of a new taxon for the Spanish isolates should be deferred until all extant representatives of the P. megasperma complex have been fully molecularly and phylogenetically analysed.