72 James G. Horsfall 



ones are resistant may be correlated with this. It is also of interest that 

 the Danish strain, Hersnap, was the most resistant in Ware's trials (1923) 

 in England and that the Tennessee-anthracnose-resistant strain was not 

 resistant to this disease in Kentucky (Haskell, 1928:347). If we postu- 

 late that this disease is a northern one, then the clovers grown constantly 

 in its presence are more likely to be resistant, whereas clovers not nor- 

 mally subjected to it should be more highly susceptible. A possible 

 explanation for the northern distribution is set forth by Monteith who 

 shows that the causal organism has a relatively low optimum temperature 

 (20° C) for growth, while the minimum temperature is 4° C. (1926:71). 



Economic importance 



In the three seasons, 1926, 1927, 1928, Kabatiella anthracnose un- 

 doubtedly has been the most destructive disease of red clover in New 

 York. 



The anthracnose disease is unlike leaf spots in the character of its effects 

 on the suscept. The disease not only kills the tissues actually invade:!, 

 but also affects the tissue beyond the infected area as well and frequently 

 kills it. A lesion of a given size on the stem or the petiole will be respon- 

 sible for much more injury than a lesion of the same unit size on the lamina 

 of a leaf. For this reason the index of infection for this disease obtained 

 in the survey of first-cutting clover in 1928 indicated the disease to be of 

 less importance than either Pseudopeziza leaf spot or Macrosporium leaf 

 spot, whereas it probably is more important than either. 



™ • i ft,- ■ at v i • i iooq (1) (9) (33) (15) (42) 

 1 he index of infection m New Y ork in June 1928 was _ _, 



119 

 which means that 7.92 per cent of the stems and petioles of red 

 clover in the State were affected at that time. Inasmuch as the effect 

 of this amount of necrosis on the general economy of the plant is unknown, 

 no estimate of absolute loss can be given. It may be less than 7.92 per 

 cent or more — probably the latter. Estimates in the literature con- 

 cerning losses are frequent, but they probably mean little except by way 

 of indicating the relative significance of the disease. 



Some workers have claimed that the reduction in yield is very large. 

 Lobik (1915), for example, in his study of the effect of fungi upon clover 

 yields reports a reduction of about 50 per cent because of this anthracnose. 



Symptomatology 



The most diagnostic characteristic of this disease, as pointed out by 

 Kirchner (1902) in his original description of it, is the occurrence of 

 elongated or somewhat stripe-like, sunken, light- to dark-brown spots 

 surrounded by a broad black zone. Sometimes the latter is not prominent, 

 however. These spots are at first small and somewhat watersoaked, 



