Abstract
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.
Highlights
The knowledge of the stage of ovule maturity at anthesis time, when, generally, the flower stigmata can receive the pollen, is very illustrative of the possibilities of a flower to become a fruit
In order to facilitate the evaluation of results, a value was assigned to the six ovule development stages established (1: no megaspore; 2: megaspore to tetrad; 3: embryo sac with two nuclei; 4: embryo sac with four nuclei; 5: embryo sac with eight nuclei; 6: embryo sac with eight organised nuclei), and the ovule development stage of each cultivar was expressed as the average value of the ovules studied in the sample
In 2002, flowering time for all cultivars occurred during the second fortnight of February, while in 2003 flowering time occurred in the first fortnight of March (Table 1)
Summary
The knowledge of the stage of ovule maturity at anthesis time, when, generally, the flower stigmata can receive the pollen, is very illustrative of the possibilities of a flower to become a fruit. Hülskamp et al (1995) showed that none of the ovules with arrested growth during megasporogenesis or early stages of embryo sac development were associated with a pollen tube. Ovule development at anthesis has a genetic determination, differences related to climate have been found (Egea and Burgos, 1994, 2000) This knowledge could be an index of the possibilities of adaptation of cultivars to different areas, mainly in relation with the effect of post-anthesis temperatures on fruit set, with those varieties with advanced ovules at anthesis showing poor adaptation to cold areas (Thompson and Liu, 1973; Keulemans and Van Laer, 1987). The present work deals with the establishment of the stage of ovule development at anthesis during two consecutive years of unequally cold winter temperatures for seven major plum cultivars. Variability among plum cultivars and year-by-year variation has been evaluated
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