The effect of constant or various fluctuating temperature regimes and single or multiple tubers in rhizome chains on tuber sprouting of six purple nutsedge ecotypes was determined. After 24 d at constant 20 C, budbreak of tubers detached from the rhizome chain (single tubers) ranged from 11 to 85% among ecotypes. When dormant tubers were exposed to a single 0.5- to 12-h, 35 C pulse followed by constant 20 C, budbreak increased for all ecotypes; daily 0.5-h, 35 C pulses from a 20 C base temperature for three to seven cycles did not significantly increase budbreak more than these did for a single cycle. Shoot length increased linearly for all ecotypes as the number of 0.5-h, 35 C pulse cycles increased, although the magnitude of shoot elongation varied with ecotype. At a 20 and 30 C (12:12 h) daily alternating temperature regime, 98% of single tubers from a Kamuela, HI, ecotype produced actively growing shoots (active tubers), whereas only 32 to 60% of tubers in two- to six-tuber chains were active. The rhizome chain effect on budbreak was minor because ≥ 90% of the tubers in rhizome chains had budbreak. Using a range of constant and alternating temperatures on single tubers and four-tuber chains, similar results were observed for all six ecotypes as for the Kamuela ecotype. Although alternating temperature increased active tubers for both single tubers and tubers in chains, it did not overcome apical dominance among tubers in rhizome chains in suppressing active tubers. The budbreak and shoot elongation stimulation by alternating temperatures and high-temperature pulses appear to be common physiological responses to all purple nutsedge ecotypes examined in this study.

Nomenclature: Purple nutsedge, Cyperus rotundus L. CYPRO.