School of Agriculture, Food and Ecosystem Sciences - Theses

Permanent URI for this collection

http://hdl.handle.net/11343/427

Filters

2005 - 2007 2
1 1
Reset filters

Settings
Statistics
Citations
Start date: 2000 × End date: 2019 × Type: Masters Research thesis × Subject: Australia × Subject: Diseases and pests ×

Search Results

Now showing 1 - 2 of 2
  • Item
    Thumbnail Image
    Studies of Ascochyta rabiei in Australia
    Pradhan, Prashanti ( 2005)
    Ascochyta rabiei (teleomorph: Didymella rabiei) which causes ascochyta blight is the most serious disease of chickpea (Cicer arietinum) in Australia as it causes significant losses in crop yield and quality. Although A. rabiei is heterothallic and genetically diverse elsewhere in the world, a study carried out on Australian isolates collected between 1995 and 2000 identified only one mating type and a low level of genetic diversity within the Australian A. rabiei population. In 2002, ascospores of Didymella rabiei, the sexual state of A. rabiei, were trapped in a discharge chamber, from chickpea stubble naturally infected with ascochyta blight in Western Australia. Examination of the stubble revealed pseudothecia typical of Didymella rabiei. The reported presence of the teleomorph in Western Australia indicated that the second mating type had been introduced into Australia or that the pathogen was capable of a low level of homothallic compatibility, previously undetected. The aims of this research were, to undertake a new survey of Australian A. rabiei isolates, to test for the presence of the second mating type, to determine if there has been a change in the diversity of the Australian population and to investigate if pathogenic variability was displayed among isolates. Sixty-seven isolates collected from chickpea fields in South Australia, New South Wales, Queensland, Victoria and Western Australia during the 2003 cropping season were single spored and confirmed as A. rabiei using a PCR test. The isolates were typed for mating type using MAT gene specific PCR primers and compared with tester isolates from USA. This test revealed that all the 67 isolates belonged to mating type 2 (MAT 1-2), thus, the presence of mating type 1 (MAT 1-1) in Australia could not be confirmed. Sequence Tagged Micro Satellite (STMS) markers were used to examine the genetic diversity of the A. rabiei isolates. The isolates were assessed for allelic variation at 19 microsatellite loci, each of which amplified a single locus. Seven of the loci were polymorphic across all the 67 isolates, while the remaining twelve were monomorphic. Based on the allele profiles at the seven polymorphic loci, 19 distinct A. rabiei haplotypes were identified with a total of 33 alleles. One haplotype constituted 35.8 % of the population and was found in the collections from South Australia, New South Wales, Queensland and Victoria. Cluster analysis did not show a clear distinction between isolates based on the state from which they were collected. Polymorphism across the 19 microsatellite loci revealed a slight elevation in diversity in the 2003-2004 population (Ht = 0.07; compared to 0.02 in the 1995 to 2000 collection) and an increase in the number of haplotypes compared with that detected in the previous study of Australian isolates. To examine the pathogenic variability of the Australian population of A. rabiei, nine isolates were inoculated on five chickpea differentials, ranging from highly susceptible to resistant, under controlled conditions optimal for A. rabiei growth and infection. Eight of the isolates were virulent on the susceptible and intermediate chickpea cultivars but not the resistant cultivar and one isolate was only virulent on the susceptible cultivar. Based on these results the isolates were classified into two pathotype groups. The results obtained from the study of the population structure and the pathogenic variability of A. rabiei in Australia will enable the Australian chickpea breeders to understand the A. rabiei population better for formulating management and breeding strategies.
  • Item