BROWN ROT OF SOLANACEAE. 



201 



milk (compare pi. 23, figs, i, ia, 3, 5 with fig. 7); or grow in closed end of fermentation 

 tubes in peptone-water with common sugars. There are other differences, e. g. t behavior 

 on cooked potato (compare pi. 23, figs. 6, 6a with pi. 41, fig. 4); appearance of colonies in 

 thin-sown gelatin plates; and, finally, behavior in the plant. 



TREATMENT. 



Fields on which this disease has appeared should be planted for some years to crops 

 which are not subject to it. Inasmuch as the organism appears to be a wound-parasite often 

 disseminated by insects, etc., prompt attention should be given to the destruction of these 

 pests. Land subject to nematodes should not be planted to Solanaceae if this bacterial 

 organism also occurs in the soil. When transplanting to such soil is necessary, it should be 

 done early and with great care not to injure the roots. Plants with broken roots should not 

 be set on such land. In the transplanting of large plants many roots are certain to be broken. 

 The prompt removal of diseased plants is also recommended in early stages of the disease. 



Such a course reduces to a minimum 

 the amount of infectious material sub- 

 ject to insect depredations and liable to 

 contaminate the soil further, a precau- 

 tion which must always be an important 

 matter in all diseases disseminated in 

 this way. It is probable that the dis- 

 ease is sometimes spread from field to 

 field in "seed" potatoes. For this rea- 

 son potatoes designed for planting 

 should be sorted over several times 

 at intervals of some weeks with the 

 greatest care, all suspicious tubers being 

 rejected. There should also be a final 

 inspection at planting time. It would 

 be still better to secure tubers for plant- 

 ing from fields known to be free from 

 this disease. The tubers from infected 

 localities should be cut across the stem- 

 end at planting time and a further re- 

 jection made of all suspicious ones. 

 The sound ones should now be exposed 

 before planting to dry air for a day or 

 two, i. e., long enough for the develop- 

 ment of a protective cork-layer on the 



cut surface. By following this method of careful selection and by a rotation of crops, being 

 very careful never to plant potatoes immediately after potatoes, a certain Portsmouth, Vir- 

 ginia, planter, who is a very successful potato-grower and who was formerly much troubled 

 by this disease, believes he has overcome it. At least it is not now troublesome in his 

 fields. In 1905, the writer searched for it in vain on this farm in a large field planted from 

 such carefully selected tubers, but found it readily on the same farm in another (rented) field 

 planted with a variety of unselected tubers on land which was in potatoes the preceding 

 year. In case of fields of potatoes attacked by this disease, the crop should be harvested 

 as soon as fit to dig, should be stored in a cold, dry place, and should be marketed and con- 

 sumed as early as possible. In no case should the crop be allowed to remain in the ground 



*Fic. 1 13. Colonies of Bacterium solanacearum on + 15 standard nutrient agar, grown for 7 days at 30 C. Plate 

 poured June 10, 1902, from the interior of a diseased tomato stem received from Porto Rico. Natural size. These 

 colonies became brown and stained the agar. 



Fig. 113.* 



