462 Bacterial Disease of Pisum sativum 



Besides bacteria, Sclerotinia is very frequently present in the seed-coat, 

 even after seed-sterilisation for 15 to 20 minutes in 1 per cent, corrosive 

 sublimate. This treatment does not prevent germination in normal 

 healthy seeds, but seeds attacked by Sclerotinia in many cases fail to 

 germinate at all, or if they do germinate only make weak growth. 



Such samples grown for culinary purposes under ordinary conditions 

 in the open would give a good average crop, but so little is as yet known 

 as to the external conditions controlling this disease, that a bad outbreak 

 in any one year is not beyond the limits of possibility. 



The disease occurs on both heavy and light soils. The earher tall 

 varieties of peas are much freer from disease than the later more succulent 

 varieties. External temperature together with succulent growth greatly 

 influences the development and spread of the organism in the plant. 



The disease was especially bad during the first two or three summers 

 after this Institution was opened, namely, 1910, 1911, and 1912. The 

 land, which had previously been used as a market garden, is a heavy 

 clay with an impervious subsoil of blue London clay. When the land 

 was first taken over the drainage was quite inadequate and parts were 

 liable to be under water in wet weather in the winter. Latterly, as 

 the tilth has been improved by drainage, etc., the effects of the disease 

 have not been so marked. In the case of a light soil, the previous 

 history of which was known, the disease occurred on freshly broken 

 poor grass-land, which had not carried a crop of peas for many years, 

 if ever. This soil was somewhat deficient in lime. 



In order to detect the presence of bacteria in the tissues, the young 

 fresh succulent growth should be examined, where large numbers of 

 the organism can be seen in the motile stage, in the cells of the cortical 

 tissue near the phloem. As far as can be judged the organism pene- 

 trates and travels up through the plant in the motile stage, but it only 

 remains motile if there is a considerable amount of moisture present. 



Several instances of seeds with foreign organisms in their interior, 

 both symbiotic and parasitic, have been recorded of recent years. The 

 only strictly analogous case to this pea disease, in which however the 

 parasite is a fungus instead of a bacterium, is that of Barley Smut 

 {Ustilago hordei nuda), described by Broili and Schikorra in 1913(3). 

 These authors found the mycelium of the Smut both in the endosperm and 

 the embryo of the resting seed. Another interesting point of similarity 

 is that the fungus, during the earlier stages of the growth of the host 

 plant, grows up with it in a state of serai-symbiosis without causing 

 any very marked disturbance until the flower spike begins to develop. 



