Environmental control of phenological development in two Lesquerella species

Development rate for both species varied with sowing date with plant cycles shorter in spring sown plants, even if measured in thermal time. L. mendocina plants sown in late spring displayed a biennial cycle. These results are consistent with those obtained under controlled conditions. However, cycle shortening in thermal time with delays in sowing date suggested that factors other than temperature also influenced phenology of these two species. Further studies under controlled conditions showed that phenological development of L. fendleri plants was also altered by photoperiod, with plants displaying a typical long-day response. At the highest temperatures used in these studies L. mendocina plants did not respond to photoperiod. The possibility that incident radiation is involved in L. mendocina response to sowing date is discussed.