Responses of Spring Wheats to Vernalization and Photoperiod1

Spring wheat (Triticum aestivum L. em. Thell.) cultivars from various sources and different maturity classes were analyzed for responses to vernalization and photoperiod. Response measurements were days to heading, number of leaves on the main culm, and number of tillers at time of heading. Seven of 13 spring cultivars responded to vernalization as measured by reduced leaf number at heading, although differences were small. All 13 spring cultivars, plus a semi‐winter and a winter cultivar, headed sooner if vernalized, although the reductions (2 or 3 days) in some of them can probably attributed to slow development during vernalization. Tiller number at heading was reduced in cultivars responding to vernalization. Response to vernalization of spring types appeared unrelated to earliness of maturity under field conditions. All cultivars tested headed earlier with increasing photoperiods in a series of treatments from 9 to 17 hours. Early maturing cultivars responded least to lengthened photoperiods, and late‐maturing cultivars responded most. A highly significant interaction was obtained between the vernalization and photoperiod responses in one cultivar showing small responses to these individual treatments. However, photoperiod alone rather than vernalization appeared to be the primary factor controlling maturity in spring wheats.