Stem cells in epithelial tissues

Most, if not all, epithelial tissues contain stem cells. They are responsible for normal tissue renewal or for regeneration following damage. Our present knowledge of their properties is limited and is mainly derived from studies of cell kinetics and from clonal analysis.     

Use of the virus strain group concept to characterize the resistance to PVX and PVYo in the potato cv Allegany

Resistance to the potato viruses X (PVX), Y (PVY) and A (PVA) was examined in the potato cv Allegany released by Cornell University in 1990. Standard potato cultivars from North America and Europe were included for characterization of the resistance response. Allegany was extremely resistant to a strain group 3 isolate of PVX and reacted with hypersensitivity to an ordinary strain isolate of PVY (PVY^o). However, Allegany was susceptible to an isolate of PVY causing necrosis in tobacco (PVY^N), and to an isolate of PVA. No symptoms appeared following infection with PVY^N and PVA. Identification of existing virus strain groups in a geographic area is an important aspect of predicting cultivar response to inoculation in the field.     

Detection of potato spindle tuber viroid in true potato seed by bioassay on Rutgers tomato

Various methods of preparing inoculum from single and composite samples of true potato (TP) seeds and TP seedlings were evaluated by bioassay on Rutgers tomato. An inhibitor of infection was found in concentrated plant sap prepared from composite TP seedlings that could be sequestered with RNasin or purified bentonite. Sap extracts from TP seedlings prepared in buffer containing bentonite were more infectious than nucleic acid extracts from an equivalent fresh weight of tissue. PSTV was detected in single seeds when sap preparations were inoculated on tomato and amplified to levels detectable by polyacrylamide gel electrophoresis.     

Comparison of some diagnostic assays for bacterial ring rot of potato: A case study

The results of testing 48 stems and tuber samples, representing 15 seed lots from several different growers, for the presence of the causal organism of bacterial ring rot,Clavibacter michiganensis subsp.sepedonicus with the gram stain, latex agglutination (LAT), enzyme-linked immunosorbent assay (ELISA), and a DNA hybridization assay (DHA) were compared. The frequency with which positive tests were obtained varied significantly among assays and was associated with symptom expression in samples. Detection was highest with the serological assays and lowest for DHA. Use of the gram stain, in conjunction with either LAT, ELISA, or DHA reduced the number of positive diagnoses, but increased the agreement between results for different assay combinations. Based on a comparison of results for both individual samples and seed lots, the performance of LAT and ELISA for diagnostic purposes were equivalent. DHA was found to be less useful due to limitations in test sensitivity forC. m. sepedonicus, but it does give unequivocal diagnoses of samples where bacterial populations are sufficient to allow detection.