The Anthracnose Disease of the Raspberry 177 



Again on April 15 fotir tender canes of a blackcap variety of raspberry- 

 were sprayed with a suspension of conidia as above. Bell glasses were 

 placed over them as in the previous experiments, and one check plant 

 was used. A sample of the conidia used was placed in a drop of water 

 on a slide, and about eight per cent of the spores germinated. After 

 about a v/eek, on April 21, a number of small purjDle spots had appeared 

 on the four canes and these later developed into typical anthracnose 

 lesions (fig. 21). The check plant remained normal. 



Cross-inoculations 



Although no cross-inoculation experiments were conducted to test the 

 ability of the pathogene isolated from one species of Rubus to infect 

 another species, some data regarding this are at hand. In the experi- 

 ments described above, the culture of the fungus from a single ascospore 

 was isolated from the hybrid known as Rubus neglectus. The pathogene 

 then produced infection on both Rubus occidentalis and Rubus idaeus 

 var. aculeatissimus. The cultural characters of the fungus isolated from 

 these three species, as well as from the blackberry (Rubus sp.), are 

 identical. 



THE EFFECT OF WEATHER CONDITIONS 



Practically nothing is known as to the exact effect the diseased canes 

 have on the yield of fruit. No experim.ents have been conducted to 

 determine the relationship and it is very difRcult to estimate. Obser- 

 vations show, however, that the decrease in yield due to the disease varies 

 considerably with weather conditions. This variation may be attributed 

 largely to the fact that both the pathogene and the canes are biennial. 

 The infection period of the fungus is during the early summer when the 

 canes are in their first year's growth, while fruit is not produced until 

 the second year. Therefore the weather conditions that prevail both 

 throughout the infection period and at fruiting time influence the yield. 

 If during the first year's growth of the canes there is an abundance of 

 rain and damp cloudy weather, the young shoots in a field where the 

 anthracnose exists become severely diseased. Such weather is effective 

 only the first part of the season, as practically no infection occurs after 

 July. Furthermore, if dry weather prevails the following year when the 

 canes produce fruit, the berries mature under very unfavorable conditions. 

 They are subject not only to the dry weather, but also to the diseased 

 condition of the canes where the conductive tissue is impaired. It is 

 during such combinations of seasons that the loss to the raspberry crop 

 is so noticeable, while in a season when there is plenty of moisture the 

 diseased canes may produce a good yield of berries. 



28y 



