Blackberry Pollen Sterility Associated with Merton Thornless Germplasm

Abstract

Merton Thornless is the most important source of genetic thornlessness for tetraploid blackberry breeding programs. As a source of thornless ness, however, it has several drawbacks, including an ability to transmit sterility to a high percentage of its progeny (4). Although Merton Thornless is fully self-fertile, it was derived from a backcross of John Innes to a partially fertile thornless seedling of John Innes (4). Sterility associated with crosses involving Merton Thornless was one of the major problems encountered early in the USDA thornless blackberry breeding program (3, 4). Many backcross, F ₁, and F ₂progeny of Merton Thornless failed to blossom, and a high incidence of partial sterility existed in those that did blossom (4). Selection of fully fertile thornless progeny was accomplished, however, and 5 cultivars have been originated by the USDA (1, 2, 3). Several of the USDA thornless cultivars and selections have been used as a source of thornlessness in the Arkansas blackberry breeding program.