| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 89 === The purpose of this research was to investigate the pollen development, pollen vaiability, fruit set, and seed germination of Oncidium and allied genera. The capsule set ratio of Oncidium and allied genera was low. In total 143 pollination combinations, 28 formed capsules were obtained. Among the capsules, there were 3 self-pollinated, 14 Oncidium interspecific cross, and 11 intergeneric cross formed capsules. There were 14 cross combinations which showed unilateral cross incompatibility.
Capsules were obtained by crossing Mtdm. Pupukea Sunset ‘H&R’ with Onc. Gower Ramsey as male parent only. Some pollinia in Onc. Gower Ramsey were empty and deficient in pollen grains at anthesis. It was suggested that Onc. Gower Ramsey was a triploid or aneuploid, which resulted in abnormal meiosis of pollen mother cells. Abnormal meiosis resulted in forming of some pollen grains as monad, dyad, and tetrad with micronucleus. The tapetum of Onc. Gower Ramsey had already started to disintegrate before tetrad formed. Comparing with Onc. Gower Ramsey, the disintegration of the tapetum of Onc. Sharry Baby ‘Sweet Fragrance’ and Onc. Sweet Sugar ‘Angel’ which could as male parent, occurred after formation of tetrad. The in vitro pollen germiantion percentage of Onc. Sharry Baby ‘Sweet Fragrance’ and Onc. Sweet Sugar ‘Angel’ was 20-30 %, and Onc. Golden Fish was higher, up to 93.4 %. Little pollens of Onc. Gower Ramsey germinated, and the pollen germination in vivo was not high. Onc. Gower Ramsey appeared to be partially male sterile.
The pollens did not germinate and the growth of pollen tubes from self-incompatible pollination was inhibited at stigma or style. Some pollen tubes screwed or accumulated callose inside. The self-incompatibility of Oncidium and allied genera might be of gametophytic type. Limited fruit set from crossing Oncidium with allied genera was largely due to cross incompatibility. The pollen tubes of incompatible intespecific and intergeneic cross were inhibited at stigma, style, or ovary. The pedicles turned yellow and withered approximately 7 to 43 days after incompatible pollination. Pollen tube growth existed differences when reciprocal cross of Oncidium and allied genera. No capsule was obtained when Onc. Gower Ramsey, Onc. Sharry Baby ‘Sweet Fragrance’ and Onc. Sweet Sugar ‘Angel’ self- or cross-pollinated at different day/ night temperatures. At lower temperatures (20/15 ℃ and 15/13 ℃), the yellowing and withering of pedicle was delayed, pollen germination was lower , and the growth rate of pollen tubes was slower. And pollen tubes swollen or screwed abnormally, as compared with those at temperatures >20 ℃.
The capsule development increased soon after pollination in most Oncidium interspecific cross. Maximum length and width of capsule were recorded at 55-70 days after pollination. Maturation to harvest of the capsule was approximately 80-100 days after pollination. Mature seeds of Oncidium were easy to germinate, 2-3 weeks after sowing, and the germination percentage was 50-70 %. There was no significant effect between 2 g·l-1 and 3 g·l-1 of Hyponex (No.1) on seed germination and seedling development. Addition of 1 g·l-1 of activated charcoal had minor improvement on early seed germination. In Onc. Sweet Sugar ‘Angel’ × Onc. Java ‘Augie’, there were 98 days after sowing to seedling with three leaves appeared. Seed quantity and germination was almost zero in Colm. Wildcat × Onc. Sweet Sugar ‘Angel’, the abortion of embryos might be due to the interspecific cross incompatibility.
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