Development and diffusion of stable production methods of high quality fruit of tankan (Citrus tankan Hayata) grown in the area from Southern Kyushu to Amami Islands under anathermal climate

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(1) Mixed planting of tankan on devigorated rootstocks of trifoliate orange and vigorating rootstocks of citrange or citrumelo is recommended in the area from Southern Kyushu to Amami Islands. For trifoliateorange rootstocks, it is better to promote vegetative growth and to suppress flowering as well as fruit setting in early stage after planting. On the other hand, it is important to cultivate reproductive growth with flower and fruit set in early stage for citrange orcitrumelo rootstocks(2) It is possible to achieve the stable production of high qualityfruits for long years by setting the fruitlets with 3 to 4 peduncle leaves and avoiding heavy crops by thinning. And it is shown that starch content in the middle roots of about 5mm diameter can be used as the index of the optimum fruit setting.3) In Amami Islands,the climate of which is subtropical, the thinning of tankan must be performed in the middle to late October for annual bearing of high quality. It was found that thinning doneearlier than that could yield excessively large and low quality fruit. Delayed thinningcould result in low flower bearing in the next year.