46 PROTECTION OF PLANTS — 1924-25 



The Yields in Bushels and Value of the Bean Crop. 



The disease under discussion, commonly called Anthracnose or Pod Spot 

 of Beans, is the most serious disease that attacks them. It has been 

 reported from as far north as Alaska, as far south as Australia, and has 

 also been reported as occurring in the tropics, though it cannot be so serious 

 there economically because of the fact that the disease thrives best in a tempera- 

 ture of 22.5 C. or 72.5 F. In the temperate zone, with a moderate climate and 

 plenty of rainfall, the disease becomes the most frequent limiting factor that the 

 farmer has to consider when planning his crop for the year. It attacks the 

 bean plant in all stages of growth; it kills the seedlings after they start to deve- 

 lop; causes the leaves to drop by necrosis of the petioles on the more mature 

 plants; spots the pods of both field and snap varieties; and disfigures the beans 

 with brownish lesions and discolorations on the seedcoat. The disease is car- 

 ried over winter in the beans themselves and it is spread in the field when mois- 

 ture frees the spores so that they can be carried by some agency such as man, or 

 splashed by falling rain drops. 



Anthracnose of beans is caused by CoUetotrichiim lindemuthianum (Sacc. 

 et Magn.) Bri. et. Cav. of the order Melanconiales of the Fungi Imperfecta A 

 perfect stage has been reported by Shear and Wood (8) as a Glomerella but it has 

 not been generally accepted. The disease is of great interest to plant patholo- 

 gists, not only because of its economic importance, but also because there are 

 certain physiological species or forms within this species that have no morpholo- 

 gical characters by which they may be distinguished but which have very diffe- 

 rent powers of infecting bean varieties. 



The hi tory of physiological specialization in Colletotrichum lindeinuthianum 

 dates back to 1911 when Barrus (11 made the announcement that he had disco- 

 vered two strains of this pathogen by means of their ability to infect different 

 varieties of beans. Since then several investigators have used this organism 

 for a study of the number of physiological species present and their bearing in the 

 breeding problem. 



Barrus (2) continued his investigations and classified all the cultures that he 

 had isolated. He found that they could be divided easily into two clear cut 

 groups based on the infection results on the bean varieties used and designates 

 them by the Greek letters alpha and beta. He also divided beans into 



