8 THE RICE WORM (tYLENCHUS ANGUSTUS) AND ITS CONTROL 



is also attacked, and these attacks have been found as late as the middle of 

 February in Noakhali. Between February and June no case of ufra has been 

 seen under natural conditions, though, as will be described below, it is possible 

 to secure successful inoculations in the laboratory during this period. 



It is not easy to detect the early attacks, as the symptoms are not well 

 marked on seedlings or even up to the time the young ear begins to form within 

 the bud. There is little change except a somewhat stunted growth and a pallid 

 appearance of the upper leaves. The most recently expanded leaves are either 

 chlorosed as a whole or are marked by pale longitudinal streaks. They are 

 also somewhat thinner and more flaccid than the normal. But it is only 

 later, when brown marks appear on the leaf sheaths and the ears become altered 

 as described in the previous paper, that recognition is easy. 



The length of time after infection has occurred before symptoms can be 

 detected varies greatly according to the age of the plant and to other condi- 

 tions connected partly with the season of the year. On very young seedlings 

 symptoms of chlorosis have been detected within a week of inoculation. On 

 larger plants it may take from ten days to six weeks before the symptoms 

 are definite. When natural infection re.iults from the stubble left from the 

 previous crop it may take two to four months before the disease becomes 

 evident, and this is the m^st usual expOiience in field outbreaks in the infected 

 area. It wall be seen below that it is possible to offer an explanation of these 

 variations. 



The cause of ufra. 



The cause of ufra was ascertained in 1912 to be a hitherto undescribed 

 nematode worm (" eelworm "), which was named Tylenchus angustus and 

 described at length in the previous paper. When recorded no other parasitic 

 Tylenchus was known which resembled it in its life-history or biology. 

 Recently, however, a serious black-currant disease has been found near 

 Cambridge, England, caused by another previously unknown species, Tylenchus 

 ribes Taylor,^ which has many points of similarity in habits to the rice worm, 

 though morphologically quite distinct. It is evident, therefore, that there 

 are more than one species of this well-known genus of nematodes which are 

 characterized by an ectoparasitic life on the above-ground parts of plants, 

 the individuals remaining on the surface of the parts attacked (without 

 actually entering the tissues as most of the parasites of this group do) and 



i Taylor, Miss A. M. " Black currant eelworm." Journ. Agric. Science, VIII, 1917, 

 p. 246. 



