Fundamental studies for cross breeding in taro

本研究的目的是为芋的杂交育种提供基础研究结果。主要研究结果如下：所调查的孟加拉野生二倍体芋花粉母细胞减数分裂相对正常，花粉育性较高。这些野生芋头开花结果很好。人工杂交获得的种子容易萌发。这些结果表明，这些野生芋具有较高的种子繁殖能力。在这些试验中，获得了大量的自交和杂交苗木。自交和杂交苗除含有二倍体外，还含有频率较低的三倍体。这说明三倍体香芋起源于二倍体香芋的自交和杂交。对三倍体杂交种的同工酶分析表明，形成三倍体芋的途径有两种。这两种方式是：1)未还原雌雄配子之间的合子；2)还原雌配子与未还原雄配子之间的合子。通过对日本和国外的芋品种/材料进行同工酶分析，为阐明日本侧块茎品种(三倍体品种)的起源提供了线索。茎尖培养有助于芋植株的体外长期保存。结果表明，简易冷冻法适合于芋的超低温保存。

The purpose of the present study was to obtain the fundamental findings for cross breeding in taro. The main findings obtained are shown as follows.Meiosis of pollen mother cells was relatively normal and pollen fertility was high in wild diploid taros from Bangladesh investigated. These wild taros flowered and fruited well. The seeds obtained by artificial crossings germinated easily. These results indicated that these wild taros have high ability to perform seed propagation. In these experiments, a large amount of selfed and crossed seedlings were obtained. Both the selfed and crossed seedlings contained triploid ones with low frequency in addition to diploid ones. This proved that triploid taros originated in selfing and crossing between diploid ones. Through isozyme analysis of the triploid hybrids, it was indicated that there are two ways of forming triploid taros. These two ways are 1)zygosis between unreduced female gamate and reduced male gamate and 2)zygosis between reduced female gamate and unreduced male gamate.The data obtained by isozyme analysis using Japanese and foreign varieties/accessions of taro gave some clues to clarify the origin of the Japanese lateral tuber varieties(triploid varieties).Shoot apex culture was revealed to be useful for long term preservation of taro plants in vitro. The simple freezing method was suggested to be suitable for cryopreservation of taro.