Pflanzenkrankheiten. 279 



Die Gallen der Pflanzen, 1911, nicht mehr berücksichtigt werden 

 konnten, und eigene, bisher unpublizierte Beobachtungen. 



Matouschek (Wien). 



Orton, W. A. and F. V. Rand. Pecan rosette. (Journ. agr. 

 Res. Washington. III. p. 149—174. 1914.) 



The summary, given b}^ the writers, runs as follows: 



Pecan rosette has been rather generali}'- recognized b)'^ growers 

 of pecan {Carya illinoensis) as a serious disease almost from the 

 inception of pecan orcharding. It does not appear to be limited to 

 any particular soil type, topography or season. The disease first 

 makes itself evident through the putting out of undersized, more 

 or less crinkled, and yellow-mottled leaves. The veins tend to stand 

 out prominently, giving a roughened appearance to the leaf blade 

 and the lighter areas between the veins are usually not fully de- 

 veloped. The axes of growth are usualh' shortened, so that the 

 leaves are clustered together into a sort of rosette. In well-marked 

 cases the branches usually die back from the tip and other shoots 

 are developed from normal or adventitious buds, only in their turn 

 to pass through the same series of Symptoms. 



The nonparasitism of the disease seems rather definitely esta- 

 blished experimentally from the nontransmission by seed, the nega- 

 tive results of isolation cultures and inoculation tests, the varying 

 presence and nonpresence of mycorrhiza on both healthy and 

 rosetted trees, the budding and grafting tests. and the transplan- 

 ting experiments. 



It appears from the results of experiments in pruning and cut- 

 ting back, transplanting tests, fertilizer experiments, results of 

 subsoil dynamiting, and orchard records that the disease is directly 

 or indirectly caused bj^ some soil relation. On account of their 

 variable character the ash analyses have shed but little light on 

 the Problem. 



Leaf hopper injury has been observed on pecans, but is distinct 

 from rosette and has occurred both in the presence and the absence 

 of the latter disease. Sun scald, or "winterkill" manifests itself in 

 the death of the cambium at the base of the trunk and is not likeh' 

 to be confused with rosette. Frost injury may simulate rosette in 

 the killing back of the terminals, but the other rosette Symptoms 

 are lacking. Rosette and j^ellows of peach in a general way sug- 

 gest pecan rosette, but though some s5'-mptoms may be common to 

 all three diseases the complete clinical picture is distinct in each 

 case. A striking resemblance is to be observed between pecan rosette 

 and ordinary chlorosis of various trees, where all gradations occur 

 from mere yellowing of the leaves to cases where the Symptoms 

 closely simulate rosette of pecans. The spike disease of pine-apples 

 also bears some general resemblance to the rosette of pecans, both 

 as to effect and apparent cause. 



Observations and experimental evidence point to the conclusion 

 that pecan rosette belongs among the chlorotic diseases of plants 

 grouped by Sorauer into two main classes: 1. Noninheritable and 

 noninfectious diseases, due mostly to improper nutritive supply or 

 to injurious physical conditions and 2. inheritable and infectious 

 diseases, due probably to enz\^matic disturbances. It seems to the 

 writers legitimate to conclude from the data outlined in this paper 

 that pecan rosette belongs to the first group. The evidence strongly 



