H. Hayden

Genetic-Relationships as Assessed by Molecular Markers and Cross-Infection Among Strains of Colletotrichum gloeosporioides

Morphological characterisation allows isolates of Colletotrichum gloeosporioides, Colletotrichum musae and Colletotrichum acutatum to be identified only to species level. Pathogenicity tests and random amplified polymorphic DNA (RAPD) markers distinguished a mango biotype of C. gloeosporioides from eight other isolates of C gloeosporioides obtained from five different fruit species. Using these procedures, it was also possible to distinguish C. acutatum and C. musae both from each other, and from the C. gloeosporioides isolates. In cross-infectivity studies, isolates of C. gloeosporioides displayed a wide host range with the exception of isolates from mango, which were highly virulent on mango only. Teleomorphic isolates of C gloeosporioides were clustered together by RAPD analysis. This work has demonstrated the existence of a biotype of C. gloeosporioides which shows specialisation to mango.

Population structure of Sclerotinia sclerotiorum on sunflower in Australia

Sunflower (Helianthus annuus) is host to infections by Sclerotinia sclerotiorum originating from either homothallic sexually-derived ascospores (stem and head rots) or asexually-derived sclerotia (root rot). While sunflower can be infected by either ascospores or sclerotia this study found no association between the genotypes found in lesions and the type of infection (stem, head or root rot). Multicopy Restriction Fragment Length Polymorphisms (RFLPs) showed individual sclerotia comprised of only one genotype, and that all eight ascospores within an ascus also had only one genotype. Mycelial Compatibility Groups (MCGs), Random Amplified Polymorphic DNAs (RAPDs), single and multicopy RFLP analyses all showed the majority of sunflower plants were infected by only one genotype. A sample of 250 isolates collected hierarchically from sunflowers in Queensland and New South Wales were shown to belong to one large genetic population of S. sclerotiorum. Temporal studies revealed genetic uniformity was maintained across years, further confirming one genetic population. A range of molecular markers were used to genotype 120 isolates, resulting in differing levels of resolution of a genotype. Between 13 and 24 genotypes were identified with similarities and differences in the assemblages of isolates within each genotype depending on the marker used.

The Genetic Structure of Australian Populations of Mycosphaerella musicola Suggests Restricted Gene Flow at the Continental Scale.

ABSTRACT Mycosphaerella musicola causes Sigatoka disease of banana and is endemic to Australia. The population genetic structure of M. musicola in Australia was examined by applying single-copy restriction fragment length polymorphism probes to hierarchically sampled populations collected along the Australian east coast. The 363 isolates studied were from 16 plantations at 12 sites in four different regions, and comprised 11 populations. These populations displayed moderate levels of gene diversity (H = 0.142 to 0.369) and similar levels of genotypic richness and evenness. Populations were dominated by unique genotypes, but isolates sharing the same genotype (putative clones) were detected. Genotype distribution was highly localized within each population, and the majority of putative clones were detected for isolates sampled from different sporodochia in the same lesion or different lesions on a plant. Multilocus gametic disequilibrium tests provided further evidence of a degree of clonality within the populations at the plant scale. A complex pattern of population differentiation was detected for M. musicola in Australia. Populations sampled from plantations outside the two major production areas were genetically very different to all other populations. Differentiation was much lower between populations of the two major production areas, despite their geographic separation of over 1,000 km. These results suggest low gene flow at the continental scale due to limited spore dispersal and the movement of infected plant material.