QTL Mapping for Cold Tolerance and Flower Type in a Reciprocal F1 Florida Avocado Mapping Population

Avocado (Persea americana Mill.) farmers in South Florida have traditionally grown West Indian and Guatemalan x West Indian hybrid cultivars because they are more suitable to prevalent growing conditions.  Currently, there is a growing interest in expanding the avocado production to other areas of the state as an alternative crop to citrus.  However, the West Indian and Guatemalan x West Indian hybrids are sensitive to cold damage.  The objectives of this research were to a) evaluate cold tolerance in a F₁ avocado mapping population of the reciprocal cross of two Florida cultivars 'Simmonds' and 'Tonnage' b) identify DNA markers associated with cold tolerance and flower type, and place them in their respective linkage groups.  A total of 800 trees were used to collect phenotypic data for traits of horticultural interest during three years.  A single QTL has been identified for cold tolerance using composite interval mapping.  The cold tolerance QTL is located on LG1 and accounts for more than 25% of the total phenotypic variation for this trait.  A marker-trait association analysis for flower type (type A vs. type B) identified four markers associated with flower type located on two different linkage groups (LG 10 and LG4).  This is the first QTL identified for avocado and these are the first marker trait associations identified for flower type.  This mapping population, as well as a second population developed from a reciprocal cross of ‘Hass’ and ‘Bacon’, will continue to be evaluated for the next 5–10 years and additional QTL will be identified.