2019 ASHS Annual Conference

Prior to the 1980’s, apple cultivars were planted in mixed blocks to ensure cross-pollination. A commonly used planting system during this time was a mixed block design consisting of four rows of ‘Red Delicious’ and two rows of ‘Golden Delicious’. This system allocated a lot of space to the pollinizing cultivar and required orchard management techniques that considered both cultivars at the same time. Since the 1980s, the use of solid blocks with a single cultivar has become more popular because this design saved space and simplified orchard management techniques, such as spraying and harvesting. However, because apples express a gametophytic self-incompatibility system, a compatible pollinizer to replace ‘Golden Delicious’ was needed. The Manchurian crabapple was a suitable candidate during this time, since it flowered early, bloomed annually, produced viable pollen and was compatible with other main cultivars like 'Red Delicious', 'Fuji' and 'Granny Smith'. Since then, the Manchurian crabapple has become one of the most commonly used pollinizers in the Pacific Northwest. However, during the past decades, new requirements for pollinizers have arisen that were not considered during the crabapple screening in the early 1980s. These new requirements include low disease susceptibility to various quarantine pathogens to avoid trade issues, an upright growth habit to fit in high density plantings, and a long and profuse bloom period that overlaps with new cultivars used in the PWN to achieve cross-pollination. The goal of this research was to identify new crabapples that can potentially be used as pollinizers in modern apple orchards. The candidate crabapples were screened for their bloom intensity and duration, pollen production and viability, return bloom, disease susceptibility, as well as several traits related to growth habit, like internode distance, tree height and width, and total shoot length. Important horticultural traits of some of the genotypes in the trial will be discussed.