Determination of photoperiod response characteristics using a greenhouse

The photoperiod response characteristics of two cultivars of seven long-day species of crop plants were determined by seeding at 33 biweekly intervals in a greenhouse at 49? 43′ N Latitude. Parameters of a segmented linear regression were estimated using a non-linear computer program. This gave good estimates of the length of the basic vegetative and reproductive phases, the photoperiod sensitivity and minimum optimal photoperiods. It was apparent that the photoperiod of importance was that of the day of floral initiation. If the plant is old enough and the photoperiod of the day is not inhibitory, initiation will occur. At certain times of the year, the photoperiod changes so rapidly that flower initiation is prevented. Using this method of analysis, comparisons of large numbers of genotypes can be made.