Assessing the Role of the Pistil in Sweet Cherry Fruit Set, Poster Board #298

Several sweet cherry (Prunus avium L.) cultivars have compelling quality attributes but are beset with poor productivity (e.g., ‘Benton’, ‘Tieton’, and ‘Regina’).  The causes of this poor performance are being investigated so that remedial programs may be developed. Previous work in our lab has implicated maternal factors in poor fruit set. Our current research is investigating therefore the role of stigma receptivity and ovule viability on fertilization in sweet cherry. In addition, the role of temperature on these key elements of crop fertility was investigated. We studied four cultivars, ‘Sweetheart’ (self-fertile, high productivity), ‘Benton’ (self-fertile, low productivity), ‘Rainier’ (self-sterile, high productivity), and ‘Tieton’ (self-sterile, low productivity) in field and growth chamber studies.  Sections of two-year-old branches were collected prior to anthesis and distributed randomly among growth chambers set to either a high, moderate, or low temperature profile. Flowers were emasculated at full white (i.e., within 12–24 hr of anthesis) to avoid self-pollination. Hand pollinations were made in the chambers to replicate sets of flower using previously collected compatible pollen. Single applications of pollen were made manually to stigmatic surfaces at 24 hr intervals up to 6 days after anthesis. Pistils were collected at 3 intervals (8 hr, 24 hr, 48 hr) post pollination for microscopic assessment of stigma receptivity and ovule activity. To assess stigmatic receptivity we evaluated the rate of pollen hydration and germination. Pollen hydration rate was affected by cultivar more than temperature. Pollen germination on the stigmatic surface was related positively with temperature. The highest recorded rate of pollen germination was ca. 35%, and ‘Rainier’ and ‘Sweetheart’ had higher germination rates than ‘Benton’ and ‘Tieton’ under cold temperature. The rate of pollen tube growth increased with pollination timing, peaking on 4 days after anthesis. By the same time we observed significant senescence of the primary ovule. We also observed a positive relation between temperature and ovule senescence, irrespective of cultivar. Primary ovule viability of ‘Rainier’ was greater than other cultivars though this difference among varieties was negligible for the second ovule. With further analyses, and integrating all results, we will revisit models for effective pollination period in sweet cherry.