Rapd

In a modified technique called random amplified polymorphic DNA (RAPD), synthetic 10-base long primers are used to amplify random sequences of genomic DNA from the test strains by the polymerase chain reaction. Variation is detected as the presence or absence of amplified DNA sequences. RAPD polymorphisms were detected in 10 random isolates of Erysiphe graminis f.sp. Hordei, which causes the powdery mildew of barley, sampled from a single field. The DNA fingerprints (Figure 13.4) were different, suggesting that these isolates were clonal lineages. In a study of the ectomycorrhizal fungus Suillus granulatus, Jacobson et al. (1993) demonstrated the high resolution of RAPD marker

Figure 13.2 RFLPs of 28 Mycosphaerella graminicola isolates from a single infected wheat field. The DNA extracted from isolates was separated by gel electrophoresis and hybridized to a cloned radiolabelled DNA fragment (probe) segment and X-ray film was exposed to the gel. Arrows indicate isolates having the same DNA fingerprints are products of asexual reproduction. (From McDonald and McDermott (1993). With permission of the publisher.)

Figure 13.2 RFLPs of 28 Mycosphaerella graminicola isolates from a single infected wheat field. The DNA extracted from isolates was separated by gel electrophoresis and hybridized to a cloned radiolabelled DNA fragment (probe) segment and X-ray film was exposed to the gel. Arrows indicate isolates having the same DNA fingerprints are products of asexual reproduction. (From McDonald and McDermott (1993). With permission of the publisher.)

analysis. Some of the isolates of the fungus, earlier reported as similar based on vegetative compatibility reaction and considered to belong to same genotype, were found to be genetically dissimilar by RAPD analysis. This method resolved 17 collected strains of Aspergillus niger into 15 subgroups (Megnegneau et al., 1993). The RAPD method has a finer resolution than either RFLP or isozymes.

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