Sunflower (Helianthus annuus L.) is cultivated over a wide range of photoperiod and temperature conditions. The objective of this research was to determine the response of 16 diverse sunflower genotypes to varying photoperiod and temperature. Field research sites were at five locations including Argentina, Alaska, and Hawaii. The photoperiod (daylength + twilight hours) at vegetative emergence (VE) for most sites, except Hawaii and Alaska, ranged from 14.5 to 16.2 h. Within this range there was no evidence that photoperiod affected the time from VEto bud visible stage (R1). Instead, differences in temperature at various sites were responsible for differing rates of development. However, the short photoperiods at VE at Hawaii (11.2 h) decreased development rate and long photoperiods at Alaska (24 h) increased development rate dramatically. A nonparametric method was applied to rank the genotypes into temperature response groups. Four distinct groups resulted for the VE to R1 growth stage intervals, which were classed as very quick, quick, medium, and slow with respect to the time taken to reach RI from VE. Four groups also resulted for the R1 to anthesis (R5.1) time period. The groups for R1 to R5.1 differed from those for VE to Rl. Genotypes within these groups were dissimilar to those for VE to Rl. It was concluded that models used to predict phenological development in sunflower could be based on temperature alone provided photoperiod was within the 14.5 to 16.2 h range. To predict development outside this photoperiod range would require photoperiod be included in the model.

Synchronization of anthesis of male and female inbred sunflower (Helianthus annuus L.) lines to be crossed in either breeding nurseries or seed production fields is important. Research was conducted to determine the influence of photoperiod on phenological development in a diverse group of sunflower genotypes. An understanding of this response would allow the development of a model to predict sunflower anthesis. Sixteen sunflower genotypes, including hybrid and inbred lines, were classified for photoperiod response in greenhouse plantings carried out over a 2-yr period at Fargo, ND (latitude 46°54'N, elevation 183 m). Plantings were made so that emergence occurted each time natural photoperiod changed by about 1 h. Although some genotypes displayed long-day, short-day, or insensitive photoperiodic reactions for the period from emergence to floral bud development, many of the genotypes appeared to be ambiphotoperiodic, with 11 through 13 h at emergence being the photoperiods delaying time to flower bud development. This delay could be of consequence to breeding programs in those latitudes where planting dates may result in emergence and early growth of the sunflower coinciding with these intermediate photoperiods.

The synchronization of anthesis of sunflower (Helianthus annuus L.) genotypes to be crossed is important for seed production. Little information is available concerning the interaction of temperature with photoperiod on the phenological development of sunflower. Research was conducted in growth chambers to determine the influence of variations in temperature, photoperiod, and light quantity on the phenological development of 16 sunflower genotypes. The sunflower genotypes were subjected to light treatments of: (i) 12‐h fluorescent and incandescent light, (ii) 14‐h fluorescent and incandescent light, and (iii) 12‐h fluorescent and incandescent light followed by 2‐h exposure to incandescent lights only. The fluorescent‐incandescent light combination provided a photosynthetic photon flux density (PPFD) of about 430 μmol m−2 s−1 in the chambers, whereas that for the incandescent lights alone was 5 μmol m−2 s−1. All light treatments were imposed under day/night temperature regimes of 18/15 and 28/22°C. The light X temperature X genotype interaction was not significant. Light X genotype and temperature X genotype interactions were highly significant for number of days from emergence (VE) to bud visible (R1) and number of leaves at R1. Other significant interactions were temperature X genotype for number of leaves and plant height at R1, and light X genotype for plant height. Some of the genotypes exhibited substantial delay in reaching R1 under the 12‐h light treatment, confirming prior observations in greenhouse plantings. Differences in light energy levels had little influence on genotype photoperiodic behavior.

Synchronization of anthesis of male and female sunflower (Helianthus annuus L.) inbreds to be crossed is important for successful hybrid seed production. The use of weather‐related models, which predict anthesis dates in scheduling planting times could assist in this synchronization. The field plantings of 16 sunflower genotypes in locations from 32°51' S to 64°50' N lat. during 1982 and 1983 were used to develop an anthesis predictive model. This model which related mean daily screen temperature to daily rate of development accounted for genotypes classified into developmental response groups as very quick, quick, medium and slow. The model had satisfactory predictive ability when validated on independent data. The model requires refinement to account for temperature by photoperiod interactions when additional data are available.