Bur Abscission in Japanese Chestnut (Castanea crenata Sieb. et Zucc.) as Relatedto Degeneration of Ovules

Abstract

Bur abscission in Japanese chestnut (Castanea crenata Sieb. et Zucc.) 'Yamato-Wase' was investigated in relation to development and degeneration of ovules.
1. In bagged burs with non-pollinated flowers and unbagged burs with open-pollinated flowers, the first bur abscission ceased before mid- and late July, and cumulatively reached 40% and 15%, respectively. Moreover, it occurred prior to fertilization, which seemed to occur early in August.
2. The second bur abscission occurred with a peak at the end of August both in bagged and unbagged burs, and the percent abscission in this period reached 60 and 16, respectively. Thus, all of the bagged burs abscised by early September.
3. Both bagged and unbagged burs increased in weight rapidly after 31 July, but after 7 August bagged burs were a little inferior in the increase and after 21 August became unmeasurable due to abscission.
4. Each of three ovaries in a bur produced 16 18 ovules, which grew equally until early August both in bagged and unbagged burs. In and after mid-August, however, only one ovule per ovary in unbagged burs enlarged rapidly and the rest degenerated gradually. On the other hand, in burs which had been bagged during the pollination period, no enlarged ovule was found and all ovules degenerated.
5. The weight of ovaries, each with an enlarged ovule, increased rapidly from mid-August, and at the peak of the second bur abscission it was twice that of ovaries without an enlarged ovule in unbagged burs. Weight increase of ovaries in bagged burs was equal to or slightly less than that of ovaries without an enlarged ovule in unbagged burs.
6. The second bur abscission seemed to be due to the failure of fertilization. It occurred about 3 weeks after fertilization, about 2 weeks after the recognition of an enlarged ovule in each ovary and at the time of rapid growth of the ovule and ovary in unbagged burs.