CLASSIFICATION OF EUSTOMA-GRANDIFLORUM (R AF) SHINN CULTIVARS ON ROSETTE CHARACTERISTICS BASED ON THE BOLTING RATIOS AFTER A HIGH-TEMPERATURE TREATMENT

Seedlings of Eustoma grandiflorum (Raf) Shinn. form rosettes and do no t bolt (elongation of internodes) when they are grown at a high temper ature. The rosetted plants will bolt after being subjected to a certai n period of cool temperature. To explain the rosette characteristics o f cultivars, we examined weekly the bolting ratios of every cultivar a fter high temperature treatments at four experiments, and classified 1 25 cultivars from the data. When exposed to a cool temperature after a high temperature treatment, the rapidity of bolting was very differen t among seedlings or cultivars. We considered that the seedlings which bolted early were insensitive to high temperature, conversely, the se edlings bolted late were sensitive and needed longer period of cool te mperature for bolting. The species is propagated by seeds and occasion ally maintains hybrid vigor by outbreeding. So, individuals in a culti var are not uniform in their response to a high temperature treatment, and the degree of uniformity differs among cultivars. Therefore, it w as necessary to consider not only the rapidity but also the uniformity for classification. Using the data (weekly cumulative bolting ratios) , the rapidity and uniformity of bolting were arrived at by ascertaini ng when the bolting ratio of a cultivar reached 20%, 50%, and 80% (a-v alue, b-value, and c-value), respectively. The b-value is considered t o represent the average rapidity; whereas, the difference between a- a nd c-value represents the degree of variation within the cultivar. Usi ng this method, the cultivars were classified into 5 grades, ''A'' to ''E'' based on their b-values, and into 5 categories, ''1'' to ''5'' b ased on theire c- minus a-values. Hence, cultivars classified as being in group ''A'' would have seedlings most insensitive to high temperat ure and which would bolt readily upon exposure to cool temperature; wh ereas, cultivars in group ''E'' would have seedlings most sensitive to high temperature and which tend to remain in the rosette stage for an extended period after being transferred to a cool environment. Cultiv ars classified as being in category ''1'' respond uniformly to the tem perature treatment, whereas those in category ''5'' do not. The data o btained in this study with 125 cultivars will be useful for selecting or breeding cultivars which will raise seedling in summer and flower i n winter.