Perfect Syncarpy in Apple (Malus x domestica ‘Summerland McIntosh’) and its Implications for Pollination, Seed Distribution and Fruit Production (Rosaceae: Maloideae)
CORY S. SHEFFIELD1,2,*, ROBERT F. SMITH1 and PETER G. KEVAN2
1 Atlantic Food and Horticulture Research Centre, Agriculture and Agri-Food Canada, 32 Main Street, Kentville, Nova Scotia, Canada B4N 1J5 and 2 Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
* For correspondence. E-mail SheffieldC@agr.gc.ca
Received: 26 July 2004 Returned for revision: 22 September 2004 Accepted: 29 October 2004 Published electronically: 20 January 2005
• Background and Aims The gynoecium of the domestic apple, Malus x domestica, has been assumed to be imperfectly syncarpic, whereby pollination of each stigmatic surface can result in fertilization within only one of the five carpels. Despite its implied effect on fruit quantity and quality, the resulting influence of flower form on seed set and distribution within the apple fruit has seldom been investigated. Instead, poor fruit quality is usually attributed to problems with pollination, such as low bee numbers and/or ineffective pollinators within apple agro-ecosystems. The objective of this study was to determine the true nature of gynoecial structure and its influence on fruit production in the apple cultivar ‘Summerland McIntosh’.
• Methods A stigma-excision method was used to determine the effects of uneven pollination among the five stigmas on fruit quantity (as measured by fruit set), and quality (seed number and distribution). In addition, flowers were examined microscopically to determine pollen tube pathways.
• Key Results Fruit set, seed number, seed distribution, and the microscopic examination of flower gynoecial structure reported in this study indicated that the gynoecium of the cultivar Summerland McIntosh is perfectly syncarpic and not imperfectly syncarpic as previously thought.
• Conclusions Pollination levels among the five stigmas need not be uniform to obtain full seed development within Summerland McIntosh fruit; even if one stigmatic surface is adequately pollinated, a full complement of seeds is likely. The importance of perfect syncarpy in recognizing true causes of poor fruit quality in apple is discussed. Cory S. Sheffield, Robert F. Smith and Peter G. Kevan For the Department of Agriculture and Agri-Food, Government of Canada
Key words: Malus x domestica, apple, pollination, flower structure, pollen-tube pathway, perfect syncarpy, seed distribution, fruit quality
Annals of Botany 2005 95(4):583-591.