ROOT KNOT NEMATODE INFESTATION 5 



to be more or less arbitrary in determining what plants should be in- 

 cluded in this compilation and also what reports should be cited about 

 the plants listed. 



The following kinds of material are included: 



1. Every known report of resistance in any plant species or variety, provided 

 that the report was based on first-hand experience or observation. Where contra- 

 dictory statements were made by one author, his earlier statements have some- 

 times been omitted, but the latest statement, based on broader experience, is 

 always given; the change is usually in the direction of reporting greater suscepti- 

 bility than had been found previously. When revisions of a publication make no 

 changes, the original edition is cited. 



Reports that infestation, though present, is usually light cannot always be 

 ignored, because they may indicate partial resistance or at least a vigorous root 

 system. Plants rated "c" in Bessey's (16) list, meaning "nematodes not abundant 

 and no injury observed," are included, except some weeds and two crop plants, 

 parsley and parsnip, for which all other reports indicate more severe infestation. 

 Bessey cautioned that his ratings should not be depended on altogether, but that 

 they indicated the most severe infestation he had observed on each plant, fre- 

 quently under uncontrolled conditions. 



2. The majority of the reports of tolerance for all plants except weeds, some of 

 which are omitted for reasons explained later. The known hosts should be re- 

 considered in this connection, because certain plants have a definite capacity for 

 enduring infestation even though they show conspicuous gall development. There 

 are, unfortunately, no experimental measurements of the degree of injury or lack 

 of injury to heavily infested plants, whereas data from mere observation are subject 

 to individual evaluation as well as to external influences. What material is avail- 

 able is given as a starting point for further contributions. 



3. The most informative reports on every plant listed, however contradictory. 

 The reason for this is to give a perspective on the present knowledge concerning 

 each plant discussed. 



4. Reports from growers considered observant and dependable. Although such 

 data are commonly ignored as unscientific, it is felt that growers have opportuni- 

 ties for making practical observations that are fully as accurate as the majority of 

 the unstandardized experiments and opinions that have been reported in the 

 literature. 



5. A few reports included merely for the academic purpose of correcting errone- 

 ous published citations of otherwise unfamiliar papers. For example, many errors 

 have been caused by a lack of information concerning the several genera and 

 species of nematodes that parasitize plants. It is easy to lose sight of the fact 

 that the root knot nematode is not the only nematode. 



6. Citations of early publications, valuable not only for their historical interest 

 but also because they show the sources of many statements that are still repeated 

 in current bulletins. On the subject of resistance many writers have culled from 

 previously published lists until requotations have become so involved that their 

 origins are frequently not recognized even by the writers who use the material. 



7. Unpublished data on recent investigations, by special permission. Breeding 

 and testing projects with beans, cowpeas, and stone fruits are now advancing 

 rapidly enough to change the status of certain recently tested varieties, even dis- 

 carding some in favor of others more newly discovered or developed. 



No attempt is made to include the following kinds of material in 

 entirety, although occasional citations from them are given where 

 additional information is needed on particular plants: 



1. Host lists unaccompanied by ratings on susceptibility. 



2. Lists or data taken by a writer from other sources, whether or "not acknowl- 

 edged, if there is no reason to believe that original observations are included. 

 Familiarity with many lists and comparison of statements on the less common 

 plants have helped in tracing the sources of compilations. This has not been 

 possible in the case of all popular bulletins, whose authors frequently have con- 

 siderable practical experience on this subject, although they may also legitimately 

 make use of data from other sources. 



3. Reports of plants found "not infested," where there is no good evidence that 

 the plants were exposed to infestation. 



4. Reports on plants found "not infested" in one case only, when the same pub- 

 lication reports another case of infestation on the same kind of plant. 



