稻線蟲心枯病に關する研究

第2報 稻體上の線蟲數と分布

抄録

(1) Number and distribution of the nematode (Aphelenchoides or yzae YOKOO) were examined in relation to white tip of rice plants. On germinating the nematode fewer in number is found remaining in the seeds, but it could not be found any on the part of buds. On the seedlings just to be transplanted (6 to 7 leaf stages), the nematode could not be detected. In the tillering stage in the paddy field, the nematode exists in the cavity above the growing tip of the rudimentary culm, or on the young leaf surrounded by the innermost leaf_sheath (Fig. 1). In accompany with the growth of rice plant, distribution of the nematode shifts towards the upper part of the larger rolled leaf which is still enclosed completely in the sheath. At the latest part of the tillering stage and thereafter, the nematode becomes to increase rapidly in number.
(2) When the young ear develops to 5-6.cm in length, the nematode shows a tendency to assemble on the ear. At the stage of booting, this tendency becomes more apparent. The nematode distributes mostly sticking on the ear, and a certain percent of it enters into the pre-flowering glumes (Fig. 2). At earing the majority of the nematode comes to outside of the leaf sheath in accompany with the ear. At this stage and a while thereafter before flowering, the nematode exists mostly outside the glumes sticking on the surface, though the percentage in the glumes slightly increasing. The ratio of the outside nematode decreases suddenly during the period of flowering (about 6 days). This suggests the entering of the outside nematode into the glumes. However, detailed comparison of the number of the nematode between pre-and post-flowering stages reveals that a rapid increase in the glumes is a more important factor. Soon after the earing, a small number of the nematode is found remained inside the flag-leaf sheath, but thereafter it is confirmed rarely outside the unhulled grain.
(3) As a rule the more the white-tipped leaves per stem the more is the nematode detected. The nematode can also be detected frequently on apparently healthy stems (carrying stems) in affected fields. Its number is markedly less (about 1/8-1/10) as compared with that of the stems bearing white-tipped leaves. On the basis of detailed observations, the number of the "carrying stems" reaches to about 1.4 times of the stems bearing with white-tipped leaves.
(4) The main (seminal) stem is invaded more frequently than the tillers. The number of the nematode is numerous on the former, even when the white tip symptom was equal in grade. As regards-the position of grains on an ear, the nematode distributes slightly dense at the middle, followed by the lower part, and the terminal part is slightly sparse. In regard to the size of a grain, the larger one contains usually more of the nematode. It is remarkably decreased in empty unhulled grains.
(5) The rice plants developed from nematodecarrying seed grains grow up sometimes as carrying or no-nematode stems. (Tokai-Kinki National Agr. Exp. Station. Ishinden, Pref. Mie)