12 BULLETIN 828, U. S. DEPARTMENT OF AGRICULTURE. 



April 11, 1917. Not root pruned, but recently transplanted, and soil suspension 

 poured on base of stem as well as into soil around plant; 72 plants, 61 per cent wilted. 



April 13, 1917. Not root pruned, but recently transplanted; 114 plants, 25 per 

 cent wilted. 



May 27, 1917. Not root pruned, not transplanted; 20 plants, 2 plants to a pot, 

 none wilted. 



Averaging the percentages of infection for all these series of soil 

 inoculations to potted plants, it is found that 17 per cent of all the 

 nonroot-pruned plants became infected, as against 39 per cent of 

 infection among the root-pruned plants. But most of the cucumbers 

 had been recently transplanted, and where in these cases examina- 

 tions were made of nonroot-pruned wilting plants, root injuries of 

 some sort were usually found. In those cases where the plants had 

 neither been root pruned nor recently transplanted, infections even 

 in the presence of such enormous numbers of bacteria were rare. This 

 evidence, together with that given in other portions of this bulletin, 

 points to the conclusion that the wilt organism does not gain access 

 to the uninjured roots of cucurbits and that under field conditions 

 no infections at all come from the soil. 



VIABILITY OF THE WILT ORGANISM IN THE SOIL. 



In order to determine how long the wilt organism would remain 

 viable in ordinary garden soil, heavy tap-water suspensions of the 

 bacteria were poured on the soil in one corner of a greenhouse bed. 

 Then at intervals tap-water suspensions of the upper 2 to 4 inches 

 of this soil were made and sprinkled over the needle-punctured 

 leaves of young potted cucumber plants. In no case did any of 

 these plants contract wilt, although the control plants inoculated 

 by needle punctures with the original suspensions promptly suc- 

 cumbed to the disease. Details of these experiments follow: 



December 4, 1916. Eight plants were inoculated Arithin one-half hour after pouring 

 the bacterial suspension on the soil. Up to December 30 no wilt had occurred on 

 any of them, although all plants inoculated with the original suspension used in 

 inoculating the soil became infected. 



January 8, 1917. "Within one-half hour after pouring the bacterial suspension on the 

 soil the thin mud thus made was directly transferred to all the leaves of eight young 

 cucumber plants and numerous needle pricks made into each leaf. At the same time 

 the tips of two other young plants with several pricked leaves were inverted in some of 

 the water suspension of soil and bacteria, left in it for 24 hours, and then held for obser- 

 vation. Three days after the soil inoculation another thin-mud suspension from it in 

 tap water was made and sprinkled over the pricked leaves of 13 young cucumber 

 plants. All these plants were under observation for several weeks, but not a single 

 case of wilt occurred. The control plants inoculated with the original bacterial 

 suspension all wilted. 



January 18, 1917. Soil-suspension inoculations into the pricked leaves of eight 

 young cucumber plants, made one-half hour after inoculating the soil, all gave nega- 

 tive results. The control inoculations from the original suspension all gave positive 

 results. 



