Classification of Eustoina grandiflorum (Raf.) Shinn. Cultivars on Rosette Characteristics Based on the Bolting Ratios after a High Temperature Treatment

Abstract

Seedlings of Eustoma grandiflorum (Raf.) Shinn. form rosettes and do not bolt (elongation of internodes) when they are grown at a high temperature. The rosetted plants will bolt after being subjected to a certain period of cool temperature. To explain the rosette characteristics of cultivars, we examined weekly the bolting ratios of every cultivar after high temperature treatments at four experiments, and classified 125 cultivars from the data.
When exposed to a cool temperature after a high temperature treatment, the rapidity of bolting was very different among seedlings or cultivars. We considered that the seedlings which bolted early were insensitive to high temperature, conversely, the seedlings bolted late were sensitive and needed longer period of cool temperature for bolting.
The species is propagated by seeds and occasionally maintains hybrid vigor by out-breeding. So, individuals in a cultivar are not uniform in their response to a high temperature treatment, and the degree of uniformity differs among cultivars. Therefore, it was 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 ascertaining when the bolting ratio of a cultivar reached 20%, 50%, and 80% (a-value, b-value, and c-value), respectively. The b-value is considered to represent the average rapidity; whereas, the difference between a- and c-value represents the degree of variation within the cultivar. Using this method, the cultivars were classified into 5 grades, "A" to "E" based on their b-values, and into 5 categories, "1" to "5" based on theire c- minus a-values. Hence, cultivars classified as being in group "A" would have seedlings most insensitive to high temperature and which would bolt readily upon exposure to cool temperature; whereas, 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. Cultivars classified as being in category "1" respond uniformly to the temperature treatment, whereas those in category "5" do not. The data obtained in this study with 125 cultivars will be useful for selecting or breeding cultivars which will raise seedling in summer and flower in winter.