Development of a PCR assay for detection of the thin, binucleate Rhizoctonia causing Eradu patch disease of lupin and barley

The field symptoms of Eradu patch are distinct, stunted patches in narrow-leaf lupin and ill-thrift patches in barley. The pathogen, a thin, binucleate Rhizoctonia (TBR), is difficult to isolate with standard methods. To develop an assay specific to TBR, the ribosomal RNA ITS region was amplified and a 610 bp section including the conserved 5.8S region was sequenced. This sequence did not match any published sequence. Primers specific to TBR were constructed. The specificity of the assay was confirmed using 104 isolates of TBR obtained from many sites in Western Australia. Tests against R. solani AG 8 and other fungi commonly isolated from lupin and barley roots were negative. TBR was detected in all roots from artificially infected lupin and barley, but detection of TBR in root samples collected from field patches in 1997 was low (0–15%). New methods for extracting the TBR DNA, including the use of soil immersion plates, enabled detection of TBR (80–100%) in field samples collected in 1999. The PCR assay developed is a reliable technique for the detection of TBR in field samples and will provide an effective tool for diagnostics and the conduct of field surveys

Rhizoctonia bare patch of cereals: An Australian perspective.

Rhizoctonia bare patch disease, caused by Rhizoctonia solani Kuhn AG-8, was first described in Australia in the late 1920s (11,53). Since then, it has been reported in England (7). Canada (1), Scotland (32), and the United States (61). R. solani AG-8 has been confirmed as the causal organism in all locations except Canada

RAPD-PCR used to confirm that four pectic isozyme (zymogram) groups within the AustralianRhizoctonia solaniAG 8 population are true intraspecific groups

RAPD-PCRs were used to study 79 isolates of Rhizoctonia solani AG 8 representing four pectic isozyme groups [zymogram (ZG)] (ZG1-1, 1-2, 1-4 and 1-5) from various locations in southern Australia. RAPD-PCR was performed on all isolates using six primers and the relatedness of the isolates determined by generating a neighbour joining tree. All isolates were also grouped according to vegetatively compatible populations (VCPs). Within each ZG there were four to nine VCPs. These studies show that the AG 8 population contains four distinct groups that matched the four ZGs and support the concept that ZGs are distinct intraspecific groups

The thin, binucleate Rhizoctonia causing Eradu patch is widespread in lupin and cereal crops in Western Australia

Eradu patch is a relatively newly discovered disease causing distinct patches in narrow-leaf lupin and ill-thrift patches in barley. Because the field symptoms are similar to Rhizoctonia bare patch and the pathogen, a thin, binucleate Rhizoctonia (TBR), is difficult to isolate, it has been impractical to conduct incidence surveys. The development of a PCR assay specific to TBR allowed field surveys to be conducted in the Western Australian cereal belt in 1999 and 2000. In 1999, 142 lupin crops were surveyed. Of these, 74 were classified visually as healthy and were not sampled. The remaining 68 showed various symptoms of poor growth. TBR was detected in 64 of the 68 crops. In 2000, 297 crops (including lupin, barley, wheat and oats) were surveyed. TBR was detected in 110 of these crops. These surveys demonstrated that the pathogen was widespread and could be detected in lupin, barley, wheat and oats. In contrast to barley, there was no evidence that TBR was causing clear symptoms of ill-thrift patches in wheat or oats

Transgenic tobacco plants show different resistance to Rhizoctonia solani AG 4 and AG 8

Transgenic tobacco plants expressing chitinase, ribosome-inhibiting protein or glucanase transgenes from barley, either singly or in combination, were tested for resistance to Rhizoctonia solani Kühn AG 4 and AG 8. With two exceptions out of 12 tests, the transgenic plants were resistant to AG 4 isolates, whereas only those plants showing high level expression of chitinase genes were resistant to AG 8 isolates. The level of resistance was markedly affected by the medium used to germinate the seeds and by the isolate used