GROWTH-INHIBITION OF CALADIUM BY HIGH-TEMPERATURE

Nonplanted Caladium xhortulanum Birdsey 'Candidum' tubers were exposed to 26 (control), 38, 43, or 48C for 1, 2, or 3 days. Then tubers were planted and forced in a glasshouse for 4 weeks at 18 to 33C (air). Le af emergence from tubers exposed to 48C for 1 or 2 days required 3-12 days longer than leaf emergence from control tubers. No leaves emerged from tubers treated at 48C for 3 days. Exposing tubers to 38C for 3 d ays or 43C for 1 day did not affect subsequent plant growth. Exposing tubers to 43C for 2 or 3 days or 48C for 1 or 2 days resulted in plant s with reduced shoot fresh weights and fewer leaves greater than or eq ual to 15 cm. In a second experiment, planted tubers were forced for 1 0 days at 26C so that roots had developed to the edge of the pot and s hoots had emerged to the soil surface. These planted (sprouting) tuber s were exposed to 43C for 0, 4, 8, 12, 16, 20, or 24 hours/day for 1, 3, or 5 days and then forced for 7 weeks in a glasshouse. With 3- or 5 -day treatments, days to leaf emergence increased as the hours of expo sure to 43C increased. Only 33% of planted tubers exposed to 43C for 2 4 hours/day for 5 days sprouted. Tubers exposed to 43C for less than o r equal to 12 hours/day for 3 days produced plants of similar or great er height, numbers of leaves greater than or equal to 15 cm wide, and shoot fresh weights, but additional hours of daily exposure decreased these plant characteristics. At 5 days, plant height, number of greate r than or equal to 15-cm-wide leaves, and shoot fresh weight decreased linearly with increased hours of exposure of tubers to high temperatu re.