Phenology of sunflower cultivars. II. Controlled-environment studies of temperature and photoperiod effects

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Abstract
The effects of photoperiod and temperature on the phenology of the open-pollinated sunflower cultivar, Sunfola 68-2, the hybrid, Hysun 30, and its parents, were studied in five experiments using the CSIRO Canberra phytotron. Photoperiod and temperature influenced the number of days to first anthesis (FA) mainly during the emergence (E) to head-visible (HV) stage of growth. Leaf counts and plant height measurements supported this finding. There were major differences in the responses of the two cultivars to short photoperiods and low temperatures. The differences were removed by increasing temperature to a regimen of 27/22¦C (day/night) or by increasing the photoperiod to 14 h. At low temperature, Sunfola 68-2 showed little response to photoperiods of between 10 and 14 h, whereas Hysun 30 showed a marked increase in duration of the E-HV stage for photoperiods shorter than 14 h. At photoperiods of 10 and 12 h there was a general decline in all measured attributes with increases in temperature, except the number of leaves on Sunfola 68-2 which remained relatively constant. Hysun 30 was similar to its male parent ('R' line) in response to photoperiod and temperature. The experiments suggest that the effects of radiation levels on sunflower phenology and photoperiod x temperature interactions in the 14-18 h photoperiod range require further investigation.

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