Abstract
To determine the optimum pollination time in Japanese chestnut (Castanea crenata Sieb.et Zucc.) 'Yamato-Wase', female flowers were pollinated with 'Ginyose' 11 times at intervals of 34 days on and after 19 June when styles of the central female flower emerged from the involucre. The relation among the optimum pollination time, style elongation, and ovule development was investigated.
1. Early bur abscission until late July was rather severe after pollination on 19 June, although it became less severe after later pollinations. Preharvest bur abscission began after 25 August and was severe from 28 August to 1 September regardless of pollination time, although it decreased to 20, 35, and 50% after pollinations on 17, 21, and 24 July, respectively.
2. Percentage of burs with nut (s) set at harvest on 11 September attained a maximum of 80% after pollination on 17 July, which was succeeded by 65 and 35% after pollinations on 21 and 24 July, respectively. Most burs resulting from pollinations on and before 14 July contained only one nut. After pollinations on 17 and 21 July, burs with 3 nuts appeared and those with 2 nuts increased, but no burs with 3 nuts appeared after pollination on 24 July. Consequently, the period between 17 to 21 July was considered to be optimum for pollination.
3. Styles of central and lateral female flowers appeared on involucres on 19 and 23 June, respectively. They both began to spread out on 7 July, and on 14 July they ceased to elongate, attaining a length of about 4 mm. Thus, the optimum pollination time seems to be between 3 to 7 days after styles ceased to elongate, when scales of the involucre began to spread out.
4. In the ovary of the lateral female flower, outer and inner integuments and nucellus were differentiated in all ovules on 28 July. In the largest ovule in each ovary, the embryo sac was found on 4 August and the nucellus was gone after 11 August.
