The interactions among IBA concentrations and durations of treatment and propagation medium temperatures on the rooting of stem cuttings were compared for cultivars of Hibiscus rosa-sinensk L. Cultivar rooting was rapid with extensive root development for `Pink Versicolor', average for `Jim Hendry', and slow with few roots per cutting for `Silver Anniversary'. The IBA concentration and duration of treatment that cuttings required to reach maximum rooting declined with increase in medium temperature (from 18 to 34C). `Pink Versicolor' stem cuttings receiving 4- to 6-minute basal dips required 8000 ppm IBA with the medium at 18C, 6000 ppm at 26C, and 2500 ppm at 34C, to achieve 100% rooting of the cuttings. `Pink Versicolor' stem cuttings had the most roots at 10,000 ppm IBA, with 10-min stem dips best at 18C, 4 to 8 min at 26C, and 7 to 8 min at 34C. Maximum dry weights per root were achieved at 6000 ppm IBA, with longer basal stem dip durations needed at 18C than 26 or 34C. Lower IBA levels were required for 100% rooting of `Pink Versicolor' than for `Jim Hendry', with highest levels needed for `Silver Anniversary'. The results indicated that the benefits in rooting achieved from higher IBA levels greatly exceeded those that could be achieved by increased medium temperature. Chemical name used: indole-3-butyric acid (IBA).
W.J. Carpenter and J.A. Cornell
W.J. Carpenter, G.J. Wilfret, and J.A. Cornell
Gladiolus (G. grandiflorus) seed germination was light-independent, but temperature influenced the germination rate. Constant 20C promoted higher total germination (97%), fewer days (4.3) to 50% of final germination, and shorter span of days (4.8) between 10% and 90% germination than other constant temperatures, although similar results were achieved by alternating 12-h cycles of 20 to 25C. Total germination was unchanged after seed treatment for 7 days at 10 to -20C, but longer germination periods were required after treatments below -10C. Reducing seed moisture contents from 11.8% to 4.2% caused no reduction in total germination, but moisture contents below 6.6% delayed achieving 50% of final germination and extended the periods from 10% to 90% of germination. Temperature and relative humidity (RH) during storage were important in retaining seed viability, with RH having a larger effect. Smallest declines in total germination during 12 months of storage occurred at 11% and 33% RH at 15C. The statistical analysis estimated the optimum seed storage at 14C and 26% RH.
W.J. Carpenter, E.R. Ostmark, and J.A. Cornell
Phlox drummondii Hook seed germinated well over a wide range of constant or alternating temperatures. Germination percentages at constant temperatures of 10 to 25C ranged from 94% to 98% for `Light Salmon' and from 83% to 88% for `Deep Salmon'. No seeds germinated at constant 30C. Total germination percentages at alternating temperatures ranged from 93% to 99% for `Light Salmon' and 67% to 82% for `Deep Salmon'. For both cultivars, the number of days to 50% of final germination (T50) and between 10% and 90% germination (T90-T10) decreased as constant temperatures or the median for alternating temperatures rose from 10 to 20C. The seeds had only limited desiccation tolerance. Reducing the moisture content of stored seed from 9 % to 5 % did not reduce total germination significantly, but 5% to 6% seed moisture levels increased the days to T50 and T90-T10 compared with higher moisture contents. The relative humidity and temperature that phlox seed received during long-term storage influenced germination. After seed was stored at 5C, germination generally was higher, earlier, and more uniform than after storage at 15 or 25C. The highest total germination percentages and shortest T50 and T90-T10 occurred following storage for 12 months at 5C and 20% to 40% relative humidity.