Ovule development at anthesis in Japanese plum (Prunus salicina Lindl.) cultivars

The stage of ovule development at anthesis has been studied in two consecutive years in seven major cultivated plum cultivars: "Red Beaut", "Fortune", "Angeleno", "Santa Rosa", "Larry Ann", "Son Gold" and "Golden Japan". Ovules examined were in general delayed. In much of them mature embryo sacs were not found at time of anthesis. Differences among cultivars were found and these differences were consistent during both years, indicating a genetic determination. In addition, a high heterogeneity of the developmental stage of the ovules examined in each cultivar was observed. The year influenced the developmental stages of ovules at anthesis, and ovules were more delayed in 2002 than in 2003. Cultivars which showed a more advanced ovule development were those that flowered later, in spite of the fact that chilling requirements for breaking of rest were adequately fulfilled during both years. This work gives interesting information regarding the stage of ovule maturity at anthesis in Japanese plum cultivars, which is closely related to their fruit set viability.