| Chinese chestnut (Castanea mollissima Bl.) is one of the important fruit native resources in China, its yield is limited because of lots of male flowers and a few female flowers, then one aim in chestnut breeding is to select few male flowers and the high ratio of female flowers to male inflorescence. In this paper, the shorter male inflorescence sport was obtained and studied by biological observation, paraffin slices, scanning electron microscopy, biochemical analysis and pollination test. Main results as below: 1. The male inflorescence of sport was shorter, its average length was 2.2 cm and diameter was 0.122 cm, filament length was 0.522 mm, the average anther diameter was 299.47 μm, each part of them was 15.5%, 64.7%, 118.1% and 87.6% of contrast. Besides filament length was longer than contrast, the others were all significantly shorter than contrast. 2. The main characteristic of shorter male inflorescence sport could be kept after its coins were grafted on both juvenile tree and adult tree. 3. The sport and contrast differed in morphology and biochemistry of leaves, male inflorescence and nut. The average leave size of sport was 15.4×7.0 cm, the content of chlorophyll was 2.14mg/g·FW; inflorescence contained energy substance just as sugar and protein, its nutrition level was higher than contrast, because of these, we could conclude that the reason of inflorescence changing short was not lack of nutrition. Nut was similar with contrast in size and quality. The activity of POD, PPO, and Mg2+-ATPase in sport male inflorescence were lower than contrast, but the difference was not clear. 4. The scanning electron microscopy and paraffin slices methods were applied in observation on pollen, male inflorescence and male flower, the results were showed: sport's pollen was similar with contrast, pollen grain was long ellipse with tricolporate, polar plane 3-lobed circular, with 3 long and narrow grooves and without film, no bore on film; the equatorial plane was slippy with 1～2 grooves that were deep to equatorial axes, surface clear besides a few feebleness and abnormal veins. The markedly difference was the length of equatorial axes, sports was 12.2 μm obviously shorter than contrast (15.3 μm), P/E was 0.64 and 0.51. Through observing in pollen colony we couldn't find the aberrant pollen. There was no difference in the form of anther, the development of pollen and the blossom of flower between sports and contrast. But the cambium thin cell greatly focused on the middle part of inflorescence axes in sport, they were not obvious distinct in single cytological characteristic. According to the promeristem theory the mutant might be taken place in L-III. 5. Sport's pollen viability(31.0%) were significantly lower than contrast(37.7%). Its self-pollination rate was 90.3%, but fruited rate was only 64.5%, lower than contrast(73.1%); but in sport♂×yanhong♀, the fruited rate was 89.1%. It showed sport was part male sterility. The metaxenia was clear in number and weight of nuts, the effect of metaxenia on nut quality was not found from this research.
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