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ARS Home » Southeast Area » Miami, Florida » Subtropical Horticulture Research » Research » Publications at this Location » Publication #210735
Title: An estimation of outcrossing in Florida avocado (Persea americana Mill.) using microsatellite markers

Author
item Borrone, James
item Tondo, Cecile
item Kuhn, David
item Brown, James
item VIOLI, HELEN - VOLUNTEER
item PLOETZ, R - UNIV. FLORIDA TREC
item Schnell Ii, Raymond

Submitted to: Botanical Society of America Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/16/2007
Publication Date: 7/16/2007
Citation: Borrone, J.W., Olano, C.T., Kuhn, D.N., Brown, J.S., Violi, H., Ploetz, R., Schnell Ii, R.J. 2007. An estimation of outcrossing in Florida avocado (Persea americana Mill.) using microsatellite markers. Botanical Society of America Proceedings.

Interpretive Summary: Avocado has a unique floral mechanism in which flowers are functionally male or functionally female at different times. Cultivars are classified based upon their flowering type. Type A cultivars are functionally female in the morning, close, and are functionally male the following afternoon. The reverse occurs in Type B cultivars. This mechanism is believed to promote outcrossing among individual trees, and commercial growers plant Type A and B cultivars in close proximity to ensure cross-pollination. A hypothesis, based upon direct observation of flowers, suggests that self-fertilization occurs in 95% of the flowers in Florida avocados. However, it does not address whether harvested fruit result from self-pollination or cross-pollination. We characterized 1,430 progeny purchased from a commercial grove consisting of two cultivars. 'Simmonds' (Type A) and 'Tonnage' (Type B) in Florida using microsatellite markers. From the 'Simmonds' progeny, 38% were a result of a cross between 'Simmonds' and 'Tonnage', 26% were judged as self-pollinations, and 38% were off-types. From the 'Tonnage', 5% were judged as self-pollinations, and 10% were off-types. The majority of harvested fruit was a result of cross-pollination ('Simmonds' and 'Tonnage' hybrids and off-type hybrids), and suggests that interplanting cultivars increases the yield of commercially harvestable fruit. Additionally, seedlings derived from cross-pollinations between 'Simmonds' and 'Tonnage' will be maintained at the USDA-ARS as an F1 population, and evaluated for important agronomic traits.

Technical Abstract: Persea americana Mill. exhibits a unique flowering mechanism, synchronous dichogamy, in which the male and female parts of the perfect flower are functional at different times. Cultivars are classified based upon their flowering type. Type A cultivars open in the morning as functionally female flowers, close, then reopen in the afternoon the following day as functionally male flowers. The reverse occurs with Type B cultivars. This mechanism is believed to promote outcorssing, thus many commercial growers plant Type A and B cultivars in close proximity to maximize cross-pollination events. A hypothesis, based upon direct observation of floral pollination events, suggests that self-fertilization occurs in 95% of the flowers in Florida avocados. However, a significant number of fruits are aborted before maturation, and the hypothesis does not address whether mature fruit results from self- or cross-pollination events. To address this, 1,926 avocado fruit were purchased from a commercial grove consisting of three rows of one cultivar Simmonds (Type A) and a pollinator row of cultivar Tonnage (Type B) and germinated. Progeny of 'Simmonds' (729) and progeny of 'Tonnage' (701) were genotyped using microsatellite markers to determine the amount of outcrossing between the two cultivars. From the 'Simmonds' progeny, 38% were a result of a cross between 'Simmonds' and 'Tonnage', 25% were judged as self-pollinations, and 38% were off-types. From the 'Tonnage' progeny, 85% were a result of a cross between 'Simonds' and 'Tonnage", 5% were judged as self-pollinations, and 10% were off-types. Therefore, the majority of harvested fruit was a result of cross-pollination events ('Simmonds and 'Tonnage" hybrids and off-type hybrids), and suggests that interplanting cultivars increases the yield of commercially harvestable fruit. Additionally, seedlings derived from cross-pollinations between 'Simmonds' and 'Tonnage' will be maintained at the USDA-ARS as an F1 population, and evaluated for important agronomic traits.