E. J. Welsford 



39 



showed the characteristic symptoms of the disease under investigation, 

 namely, precocious growth, an abnormally well-developed root system, 

 blotches on the leaves and, above all, discoloured and rotting bulb 

 scales. No Fusarium was observed. Another set of bulbs treated in 

 a similar way, but planted in unsterilised soil, also developed bulb rot. 

 Healthy bulbs, some of which were cut and the rest uninjured, were 

 planted in both sterilised and unsterilised soil as a control; all these 

 bulbs remained healthy and showed no symptoms of disease. 



When these results are considered in relation to the invariable 

 presence of eel worm in naturally diseased bulbs and to the fact that 

 organisms, such as Fusarium and bacteria, which may be found associ- 

 ated with these nematodes, are unable to cause bulb rot, it becomes cleai' 

 that the eelworm, Tylenchus devastatrix, is the sole cause of the disease. 



Course of Disease. 



Healthy bulbs may become infected at any time of the year pro- 

 vided the ground is sufficiently warm for the eelworm to be active. 

 When the tissue in which eelworms are living becomes decayed they 

 forsake it and pass into the ground. In a short 

 time they infect another bulb, entering it either by 

 the bases of the old leaves, which, as is the case 

 with Monocotyledons, are unprotected by a callus, 

 or by young leaves which have been injured and 

 are just pushing up through the soil (Fig. 1). The 

 first noticeable sign of disease in the young leaves 

 is the appearance of pale green areas; these areas 

 become yellow, and, then spreading downwards, 

 produce discoloured "stripes" on the bulb scales. 

 If such an affected portion of leaf is examined, 

 eelworms will be found in the tissue ; they lie 

 parallel to the course of the vascular bundles and 

 pass downwards between the cells (Fig. 2). In a 

 few weeks after infection the tissue will contain 

 a large number of eelworms and probably also 

 numerous eggs. It is sometimes difficult to be 

 certain of the presence or absence of eelworms 

 and especially of their eggs, but both can be 

 demonstrated easily by the following method. The 

 material to be examined is fixed in 25 % acetic-alcohol and hand- 

 sections are stained in Ziehl's carbol fuchsin for about an hour, the stain 



'/m\^^' 



Fig. 1. Infection at 

 crown on bases of 

 old leaves and 

 young leaves. 



on 



