Base temperature for florets opening and anthochron in gladiolus
ABSTRACT Gladiolus is an important cut flower in national and international markets. The floral stem, a kind of spike, is composed of florets that have acropetal opening. Knowledge on the opening speed of florets, represented by the anthochron, can assist in planning harvesting and marketing activities. The objectives of this study were to estimate the base temperature for floret opening in gladiolus and to determine the anthochron, with the time unit represented by the thermal time. Two field experiments were conducted in Santa Maria, RS, Brazil, for two years (2011-2013), each experiment composed of 12 planting dates and three cultivars. The daily thermal time (STd) was calculated as the difference between the daily mean temperature and the base temperature (Tb) and the accumulated thermal time was obtained by the sum of STd. To estimate the Tb for floret opening, we used the number of open florets (NFA) collected in the experiments. We concluded that the Tb for floret opening in gladiolus is 6 °C and for the anthochron is, on average, 14.7 ºC day per floret, but the anthochron Tb varies according to solar radiation during spike flowering period.