GERMINATION OF SEEDS AND DAMPING-OFF AND 



GROWTH OF SEEDLINGS OF ORNAMENTAL 



PLANTS AS AFFECTED BY SOIL 



TREATMENTS 



By William L. Doran, Research Professor of Botany 



INTRODUCTION AND METHODS 



The production of ornamental plants is an important industry in Massachu- 

 setts, receipts from their sales comparing favorably with receipts from such other 

 leading crops as apples, tobacco, potatoes, and onions; and there are, of course, 

 many amateur gardeners in the State for whom gardening is a recreation. 



As is well known both to professional plantsmen and to those who find in 

 gardening an avocation, a principal problem in the propagation of plants from 

 seed is the damping-off disease by which germination is injured and seedlings 

 weakened or killed. This disease, too generally recognized to need description 

 here, is controllable by known methods of soil disinfection; but it is doubtful 

 whether any of them are sufficiently effective against fungi, during a long enough 

 period, and at the same time sufficiently safe to plants and low in cost, to be 

 altogether satisfactory in more than a limited way. Thus, according to Newhall 

 (69)^ the cost of soil sterilization by formaldehyde is more than $400 per acre. 

 The search for better, safer, and less expensive soil fungicides continues and this 

 bulletin, which includes also some reference to the work of earlier investigators, 

 is a summary of the results of some of the writer's investigations in this field. 



Damping-off of seedlings may be caused by species of at least eight genera 

 of fungi (38), but those most common here and the only ones involved in this 

 work are Rhizoctonia solani Kiihn and species of Pythium. They were isolated 

 from infected seedlings and several strains of them, in culture, were also obtained 

 from other investigators^. Although at least two species of Pythium were used, 

 no distinction is made between them, for a control measure effective against one 

 was equally- so against another. The strain of Rhizoctonia solani used most often 

 was isolated from thyme, the mats of which are often severely injured by this 

 fungus in rainy summers. 



Soil was autoclaved several days before inoculation, and the inoculum, the 

 fungus in culture, was well worked into the soil three or four days before it was 

 used. It many cases naturally contaminated soil was also used, in a supplementary 

 way, for the artificial inoculation of an autoclaved soil may mean an unreasonably 

 drastic test of soil fungicides. Fungi were not reisolated from inoculated soil, 

 but they were isolated from damped-off seedlings in such soil. 



Seeds (or, in a few cases, cuttings) of the species of ornamental plants listed 

 in the appendix were used. These species are referred to in the text in more 

 abbreviated ways. Use was also made of a number of vegetables — beet, cress 

 {Lepidium sativum L.), cucumber, pepper, etc. 



Frequent reference is here made to the effect of soil treatments on growth, 

 and the evidence supports the conclusion of Delafon (27) that a soil disinfectant 

 which is good for use with some species of plants may not be at all good with some 



'Reference is made by number to "Literature Cited". 



'G. P. Clinton, Annie P. Gravatt, C. E. F. Guterman, L. \V. R. Jackson, and George L. Peltier. 



