Hypervariable spacer regions are good sites for developing specific PCR-RFLP markers and PCR primers for screening actinorhizal symbionts.

While the ribosomal RNA like highly conserved genes are good molecular chronometers for establishing phylogenetic relationships, they can also be useful in securing the amplification of adjoining hyper-variable regions. These regions can then be used for developing specific PCR primers or PCR-RFL profiles to be used as molecular markers. We report here the use of ITS region of rrn operon of Frankia for developing PCR-RFL profiles capable of discriminating between closely related frankiae. We have also made use of the ITS1 region of the nuclear rrn operon of Alnus nepalensis (D Don) for designing a PCR primer for specific amplification of nuclear DNA of this tree.

RAPD based DNA markers linked to anthracnose disease resistance in Sorghum bicolor ( L.) Moench.

Anthracnose caused by Colletotrichum graminicola is one of the major diseases of sorghum. The locus for disease resistance in sorghum [Sorghum biocolor (L.) Moench] accession G73 was found to segregate as a simple recessive trait in a cross to susceptible cultivar HC136. In order to identify molecular markers linked to the locus for disease resistance, random amplified polymorphic DNA (RAPD) analysis was coupled with bulk segregant analysis. DNA from the parental cultivars and the bulks were, screened by PCR amplification with 114 RAPD primers. Three RAPD primers amplified a sequence that consegregated with the recessive resistance allele, while another three amplified a band linked to the susceptible allele. The six disease linked markers were screened with individual resistant and susceptible genotypes to observe degree of linkage of identified RAPD markers with the gene for resistance. Two primer sequences (OPI 16 and OPD 12) were found to be closely linked to the locus for disease resistance.