In vitro and in vivo selection for Myrothecium roridum resistance in melon using the phytotoxin roridin E
Mackay, Wayne Archibald.
Thesis of PhD, Deparment of Horticulture, Maryland University, College Park (USA). 1990. 136 p.
1991
บทคัดย่อ
The fungus Myrothecium roridum Tode ex. Fries is pathogenic to melon (Cucumis melo L.) causing both preharvest and postharvest losses. There is currently no identified source of natural genetic resistance. The potential to identify and develop disease resistant melon germplasm through tissue culture was investigated.
Regeneration protocols were developed for three melon cultigens. The cultigens Hales Best, Perlita, and Iroquois developed morphogenic callus when cultured on a variety of different media. Morphogenic response of the cultigens varied depending on the type and concentration of cytokinin. Morphogenic callus was maintained for over two years for 'Hales Best' and 'Perlita' with shoots and plants recovered throughout this period.
Studies indicated that the phytotoxin roridin E was a good candidate for use as an in vitro selection agent. Incubation of callus or cotyledons in the toxin solution was the only successful selection method at the concentrations tested. Primary callus was not sensitive to roridin A or E at the concentrations used. Secondary callus exhibited a differential response to roridins A and E similar to that of detached leaf assays. Electrolyte leakage studies provided further evidence that callus morphology was important in the sensitivity of the cells to roridin E. Repeated exposure of secondary callus did not result in uniformly resistant cell populations.
Regenerants of 'Hales Best' and 'Iroquois' from unselected callus cultures had host reactions similar to seed derived plants, indicating no change in resistance in the population screened. Screening studies using parental, F1, F2, and backcross populations of plants at the four to five true leaf stage indicated that this stage of plant development was not useful in determining the genetics of the disease reaction as there was little difference in host reaction of the different populations.
Somaclonal variants were observed for fruit characters of shape, ground color, and netting characteristics. Segregation of these traits in the R1, R2, and R3 open pollinated generations varied between regenerant lines.