Bean Anthracnose 197 



practice will reduce the amount of affected seed planted, and if the seed 

 is picked over at least twice the chances of getting a clean crop will be 

 greatly improved as compared with the use of seed that has not been 

 carefully hand-picked. 



SUMMARY 



Bean anthracnose is a disease of beans, principally affecting varieties 

 of Phaseolus vulgaris L., which was first definitely reported and described 

 in 1878 although it probably existed at a much earlier date. It has since 

 been reported from every continent, and from nearly every country 

 where beans are grown. 



The disease has caused very large losses in years favorable for its 

 development. In the eastern part of the United States, epiphytotics 

 have occurred in the years 1906 to 1908 and 1914 to 1917. 



All parts of the plant, even the roots, are subject to the disease, but 

 it is most noticeable on the pods, where it forms dark, sunken cankers 

 which subsequently extend to the seed contained within. 



The spores germinate readily at room temperatures, within twenty- 

 four hours in nutrient culture media and in bean agar and more slowly 

 in water, the germ tube usually forming an appressorium on contact 

 with a hard substratum. 



A moderate growth of mycelium is produced in culture, which becomes 

 dark-colored and forms acervuli from which a flesh-colored mass of spores 

 is exuded. Under favorable conditions spores may be produced after 

 three days growth. Cultures lose their power to produce spores by age 

 or continued exposure to temperatures above the optimum. As the 

 culture dries, setae are produced within and around the acervuli. 



The minimum temperature for growth lies between 0° and 4° C, the 

 optimum near 22°, and the maximum between 34° and a few degrees 

 lower. 



The fungus after entering the host extends its hyphae horizontally 

 and diagonally into the cells. Browning of the cell contents occurs soon 

 after the attack. The walls collapse and a lesion may be observed, at 

 the earliest, four and one-half days after inoculation. 



A stroma is formed at about the time when the cells collapse, and from 

 it arise, in various places, a cluster of conidiophores which push up the 

 epidermis, forming pimples. Spores are produced at the extremity of 



