Which of the following plants requires light exposure less than the critical period to initiate flowering?

Step-by-step solution

The critical photoperiod is the light period required for floral induction, which must not be exceeded in short-day plants and should always be exceeded in long day plants in order to bring them to flower. Tobacco is a short-day plant (SDP). When the photoperiod is less than the critical period plant will flower. Wheat, Spinach and oat are all long-day plants (LDP), which flower when they receive photoperiod or light hours above the critical photoperiod.