Nov. i5, 1914) Pecan Rosette 1 5 7 



Out of 22 pieces of tissue taken at the juncture of dead and living 

 wood on badly resetted twigs, all developed fungous colonies. 



Of 40 bits of inner bark taken from dying twigs, 27 were sterile, 6 devel- 

 oped fungous colonies, and 7 grew bacterial colonies. 



Of 32 pieces of the inner bark taken from partly dying roots, 25 re- 

 mained sterile, while 7 developed colonies of bacteria. 



Since no constant form appeared in the cases where organisms did 

 develop, it was thought highly improbable that the disease could be 

 attributed to any of them, especially since a majority of the cultures 

 remained sterile. Nevertheless, for the sake of completeness, greenhouse 

 inoculations were made with all the different strains isolated, including 

 15 types of fungus and 17 types of bacteria. In each case needle-puncture 

 inoculations were made in the tender growing tip and in the older bark 

 of one or more pecan seedlings, and the latter were left under bell 

 jars for several days. Check trees were similarly punctured with a 

 sterile needle. Daily observations were made, and at the end of a week 

 the needle punctures in the checks, and with two exceptions in all the 

 inoculated trees, were healing over. The tips of these two inoculated 

 trees were beginning to wither, but since their tissues were much broken 

 up in the process of inoculation, this was thought to be due to mechanical 

 injury. However, for further certainty several other trees were inocu- 

 lated with these two bacterial strains, care being taken to injure the 

 succulent tissues as little as possible. These all healed over without signs 

 of infection. 



Several examinations of healthy and rosetted roots showed a whitish, 

 fungous weft on the young roots of healthy trees which was at first not 

 found on those with rosette. It was thought possible that the pecan 

 might be dependent on some mycorrhizal relation for its well-being and 

 that the absence of the fungous syrabiont gave rise to the diseased con- 

 dition. However, diseased and healthy trees have been dug up in Texas, 

 Georgia, Florida, and South Carolina, and in some cases the sterile, fun- 

 gous weft has been found on healthy roots, sometimes on rosetted roots, 

 but more frequently, so far as could be detected, it was absent. More- 

 over, of 300 healthy trees grown from seed in the Department greenhouses 

 at Washington, D. C, those with and without fungous weft on the roots 

 were about equal in number. Twelve isolations were made from speci- 

 mens with this fungous growth, and all, when grown on corn-meal agar, 

 developed typical Fusarium spores. 



It is by no means demonstrated that rosette has no mycorrhizal rela- 

 tions, but the preponderance of evidence lies strongly on the positive side 

 of the question. The apparent absence of fungi and bacteria from still 

 living rosetted material, as shown by cultural tests, and the negative 

 results of inoculations with organisms obtained from partly dead rosetted 

 material strongly support the view that the disease is not of parasitic 

 nature. 



