Investigation of genomic organization in switchgrass (Panicum virgatum L.) using DNA markers.

We report an early investigation into genomic organization and chromosomal transmission in switchgrass based on restriction fragment length polymorphism (RFLP) markers. The segregation of 224 single dose restriction fragments (SDRF) in 85 full-sib progeny of a cross between the genotypes Alamo (AP13) and Summer (VS16) was used to determine linkage associations in each parent. In the seed parent AP13, 11 cosegregation groups were identified by 45 SDRF markers with a cumulative recombination length of 412.4 cM. In the pollen parent VS16, 57 SDRF markers were assigned to 16 cosegregation groups covering a length of 466.5 cM. SDRF markers identified by the same probes and mapping to different cosegregation groups were used to combine the two maps and identify homology groups. Eight homology groups were identified among the nine haploid linkage groups expected in switchgrass. The high incidence of repulsion phase associations indicates that preferential pairing between homologous chromosomes is predominant in switchgrass. Based on marker distribution in the paternal map (VS16), we estimated the recombinational length of switchgrass genome to be 4,617 cM. In order to link 95% of the genome to a marker at a 15-cM distance, a minimum of 459 markers will be required. Using information from the ratio of repulsion to coupling linkages, we infer that switchgrass is an autotetraploid with a high degree of preferential pairing. The information presented in this study establishes a foundation for extending genetic mapping in this crop and constitutes a framework for basic and applied genetic studies.

Tuberculosis of the sternoclavicular joint. Report of two cases.

The sternoclavicular joint accounts for only 1 to 2% of all cases of peripheral tuberculous arthritis and is more often infected by pyogenic organisms than by the tubercle bacillus. We report two cases of sternoclavicular joint tuberculosis, in a 38-year-old man and a 46-year-old woman without risk factors for immune deficiency. Swelling of the joint was the presenting manifestation. Laboratory tests indicated inflammation in only one of the patients. The intradermal tuberculin test was strongly positive in both patients, whereas smears and cultures of sputum and urine samples were negative for the tubercle bacillus. Serologic tests for the human immunodeficiency virus were negative. Erosions of the affected joint were seen by computed tomography. Histological studies of a surgical biopsy specimen confirmed the diagnosis. Cultures of the biopsy specimens were negative. The outcome was favorable after treatment with rifampin, isoniazid and pyrazinamide for six months in the man and nine in the woman. Follow-ups were eight and six months, respectively, at the time of this writing. Tuberculosis of the sternoclavicular joint is extraordinarily rare and can raise diagnostic problems. The diagnosis should be considered in every patient with arthritis in a sternoclavicular joint or unexplained pain in a shoulder. Possible complications include compression or erosion of the large blood vessels at the base of the neck and migration of tuberculous abscesses to the mediastinum.