Determination of vernalization requirement and cold tolerance in two bread wheat cultivars

This study was conducted to determine the relationship between vernalization requirement and phenological development with expression of low-temperature (LT) tolerance in two bread wheat cultivars acclimated under both controlled and field conditions in cold and temperate climates of Iran. Two bread wheat cultivars (MV17and Shahryar) with different vernalization response and phenological developments were planted under field conditions at Zanjan Agricultural Research Station in cold region and Karaj Agricultural Research Station، Seed and Plant Improvement Institute in temperate zone of Iran in the autumns of 2009. LT tolerance، as measured by LT50، stage of phenological development، as estimated by final leaf number and shoot apex developmental morphology were determined during the autumn and winter seasons. Second set of experiments were conducted under controlled conditions. Norstar (winter wheat) and Azar2 (facultative wheat) cultivars were subjected to cold acclimating temperature (2°C) over a period of 0-89 days and LT tolerance and vernalization fulfillment were measured at various acclimation periods. Results of field experiments showed that winter habit ‘cv. MV17’ and facultative ‘cv. Shahryar reached their maximum LT tolerance at LT50= -19ºC and LT5 = -16ºC، respectively، at the point of vernalization fulfillment in Zanjan. While، maximum LT50 of MV17 and Shahryar cultivars were -12 and -8ºC in Karaj temperate region، respectively. The level and trends of LT tolerance were different for two cultivars in two different regions. Double ridge was formed very late in plants acclimated in Zanjan cold region. Delay in the vegetative to the reproductive transition in winter wheat cv. MV17 grown in cold region maintained plants for a longer time in the vegetative stage and caused increased level of LT (LT50= - 19oC). While plant development to advanced stage reduced the ability of cv. MV17 in Karaj temperate region to acclimate to LT with LT50 of about -16oC. Similar results were observed for LT50 of cv. Shahryar (facultative wheat). with LT50 of about -16oC in Zanjan as compared to LT50 of about -12oC in Karaj supporting the regulatory role of developmental traits in the expression of LT. Results of experiments conducted under controlled conditions showed that cv. Norstar (winter wheat) had a longer vernalization requirement (between 35-42 days) than Azar2 (facultative wheat). Maximum level of LT was achieved about the same time as vernalization fulfillment occurred in both cultivars. It is concluded that both the acclimation conditions of regions and plant development had major influence on controlling of LT in bread wheat cultivars.