RELATIVE EFFECTS OF PHOTOPERIOD AND IRRADIANCE ON PREANTHESIS DEVELOPMENT IN SPRING BARLEY (HORDEUM-VULGARE L)

This study examined the effects of changes in irradiance level and pho toperiod on the duration of pre-anthesis development in three barley c ultivars. The duration of the pre-anthesis period of development was c ompared at two photoperiods (10 and 18 h) with similar levels of daily radiation and at 18 h under differing irradiance levels. The duration of this period of two photoperiod-sensitive barley cultivars, Clipper and Galleon, was reduced by a factor of ca. 2.6 and 2.7 by the 18 h p hotoperiod relative in comparison to 10 h. The maximum number of spike let primordia at the apex of the main culm was higher by a factor of 1 .7 under the 10 h than the 18 h photoperiod in Clipper and Galleon. Si milarly the final number of leaves on the main culm (increased by 1.6 times) and the length of the main culm (increased by a factor of 1.2) were greater under 10 h than 18 h at the same level of irradiance for Clipper and Galleon. The photoperiod-insensitive cultivar, Finlay, exh ibited little response to photoperiod for both of the abovementioned c haracters. Under a 10 h photoperiod anthesis was delayed in all three cultivars. Further effects of irradiance and photoperiod on the durati ons of pre-anthesis development and plant characters are discussed.