171 



A Preliminary Note on a New Bacterial Disease of Pisum 



sativum. 



By Doeothy M. Cayley, Eesearch Student, John Innes Horticultural 

 Institution, Merton, Surrey. 



(Communicated by W. Bateson, F.B.S. Beceived November 19, 1912, — Bead 



January 23, 1913.) 



Investigations have been carried out this year at the John Innes 

 Horticultural Institution to elucidate the nature of a disease which affects 

 culinary peas {Pisum sativum). 



The disease, in this district at all events, is a serious one, killing a large 

 proportion Of the crop, but I have no information as to its prevalence in 

 other parts of the country. I have succeeded in proving that the disease in 

 culinary peas is caused by a large bacillus which exhibits a peculiar feature, 

 inasmuch as it is transmitted in the interior of the seeds of the plant. As 

 far as I am aware no analogous instances are known. Owing to the work of 

 Chamberland (1879), Lehmann (1889), Laurent (1891), and others, it has 

 been definitely proved that not only is the interior of a normal seed sterile, 

 but also beans and peas taken under sterile conditions from healthy pods are 

 free from bacteria. 



A very large rod-shaped bacillus has been isolated from the stem of the 

 living pea plant and from the centre of the cotyledons of the pea. The life 

 history of the organism is complicated by involution-forms and a zooglceal 

 stage. In the rod stage the bacillus is Gram-positive, non-acid-fast, very 

 motile when young but enveloped in a capsule when at rest. It varies 

 considerably in size according to the amount of water, food material, and 

 other conditions. It grows well on acid (1 per cent, normal HC1), alkaline 

 (1 per cent, normal NaOH), and neutral pea agar agar, forming small 

 circular, pale buff, translucent, watery colonies on the surface of the 

 medium, and when submerged the colonies are deeper in colour, opaque and 

 lens-shaped. The colour of the colonies varies according to the medium 

 used. Under certain conditions the colonies may have a decided orange tint. 

 This was especially noticeable in an impure culture into which a spore of 

 Penicillium had been introduced. The bacterial colonies immediately round 

 the Penicillium were both larger and of a deeper tint than in other parts of 

 the Petri dish where no fungoid growth occurred. 



This orange tint has also been observed in badly diseased cotyledons after 

 vol. lxxxvi. — b. o 



