BACTERIAL DISEASE OF PISUM SATIVUM. 



By DOROTHY M. CAYLEY 



Minor Studeyit, John Innes Horticultural Institution, Merton, Surrey. 



A SHORT preliminary note on this disease was published Nov. 1912(4), 

 and since that date further investigations have been carried out into 

 the life-history of the organism, and its effect on the host plant. As 1 

 there showed the disease is caused by a bacterium for which I propose 

 the name Pseadomonas setniniun. 



As stated in the above mentioned preliminary note, the disease in 

 this district, at all events, is a serious one, and now further details have 

 come to hand showing that it occurs in other parts of the south of 

 England. The disease causes considerable damage at this Institution 

 where peas are grown fairly extensively for experimental purposes. 



In the case of peas grown thickly in rows for cuhnary purposes, the 

 diseased plants, unless they occur in large numbers, are either not 

 noticed, or ignored, or their condition is attributed to one or more of 

 the many diseases or insect pests to which eating peas are liable. 



The most remarkable characteristic of this disease is that the 

 organism is actually present in large numbers in the tissues of the 

 cotyledon, and sometimes in the young embryo itself. Samples of 

 diseased peas from Sleaford in Lincolnshire, sent to the Board of 

 Agriculture in 1915 and forwarded to me for examination, proved to 

 be infected with Ps. seminum, and showed the typical discoloration 

 in the centre of the cotyledons. Other samples from various retail 

 seedsmen have been examined from time to time, some of which have 

 been absolutely healthy, others slightly diseased. The conclusion 

 arrived at from the examination of these samples is that the disease 

 is becoming more generally distributed. Whereas in 1913 and 1914 

 it was comparatively easy to find samples without disease, this year, 

 1916, considerable difficulty was experienced in procuring sterile seeds 

 for experimental purposes, free from blemish inside or on the seed-coat. 



