|Strik, Bernadine - OREGON STATE UNIVERSITY|
|Peacock, Derek - OREGON STATE UNIVERSITY|
|Clark, John - UNIVERSITY OF ARKANSAS|
Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 5, 2002
Publication Date: April 28, 2002
Citation: Takeda, F., Strik, B.C., Peacock, D., Clark, J.R. 2002. Cultivar differences and the effect of winter temperature on flower bud development in blackberry. Journal of the American Society for Horticultural Science. 127:495-501 Interpretive Summary: In this study, we investigated the time of transition to reproductive development in blackberries and the development of floral primordai in four varieties ('Cherokee', 'Chester Thornless', 'Boysen', and 'Marion') growing in Arkansas, Oregon, and W. Virginia, in order to better understand the relationship between temperature and reproductive bud development and determine when flower bud development occurs in currently important blackberry varieties in Oregon. We also examined the pattern of flower bud development within the long canes of trailing 'Boysen' and 'Marion' blackberries. The average daily mean temperatures in Oregon were generally well above 32 degrees F from October to March, but were below 32 degrees F on most days from mid-December to early February in Arkansas and from November to March in West Virginia. Flower bud development in varieties that were developed in Oregon and Arkansas occurred in winter, with increasing complexity in the floral organs. Much of the bud development di not occur until spring in 'Chester Thornless', an eastern variety that is better adapted for areas with more severe winter.The results suggested that reproductive bud development in blackberry proceeds at temperataures much lower than the temperature threshold for standard growing degree models. This study has contributed to a better understanding of relationships between flower bud development, heat unit accumulation, and the temperature threshold needed for flower bud development. Winter temperature influences the uniformity of budbreak and bloom and the time and duration of fruiting season. Also, better understanding of physiological processes to overcome uneven and poor budbreak will lead to more efficient and economical blackberry production in areas with mild winter conditions.
Technical Abstract: Transition to reproductive development & subsequent development of floral primordia (e.g. sepals, petals, stamens, & pistils) were determined in sev- eral blackberry cultivars ('Boysen', 'Cherokee', 'Chester Thornless', 'Marion', & 'Thornless Evergreen') growing at one or more locations (Clarksville, AR, Aurora and Hillsboro, OR, and Kearneysville, WV). Also, daily max-min temperatures for each location were recorded to determine cumulative daily mean temperature hours above 0 degrees C for the September to April sampling period. In buds of 'Boysen' and 'Marion' from Oregon, sepal primordia were first observed in September & November, respectively. Further floral bud development continued into January. Sepal development in 'Cherokee' buds occurred in November in Oregon and in December in Arkansas. At all three sites, the buds of 'Chester Thornless' blackberry remained undifferentiated until spring. The average mean temperatures in Oregon were egenerally well above 0 degrees C during the bud sampling period, but were close to 0 degrees C on most days from mid-December to early February in Arkansas and from November to late February in West Virginia. The phenology of flower bud differentiation varied among the cultivars and was affected by prevailing winter temperatures. In the trailing types ('Boysen' and 'Marion') from Oregon, buds located in the middle one-third section of canes were at a more advanced stage of flower bud differentiation than in those buds sampled from the top one-third section of canes. In the erect types ('Cherokee' and 'Chester Thornless') there was little evidence of any trend in bud differentiation. The results suggest that floral bud development in blackberry, once initiated, is continuous. However, periods of low temperature (<0 degrees C)can arrest development.