The Origins and History of the

ISPP Committee on Taxonomy of Plant Pathogenic Bacteria

By John Young

 

 

In the early 70s, I had begun work with Doug Dye. Although my major research responsibilities were not taxonomic I became engaged with the nomenclatural conundrum generated by the development of the Code. The publication of the 1975 Code and the criteria for inclusion in 1980 Approved Lists meant that most identified plant pathogenic species, especially in Pseudomonas and Xanthomonas, would cease to be recognized for nomenclatural purposes. One response to this situation was to ignore the requirement of the Code and to propose all names of plant pathogens for inclusion in the Approved Lists, regardless of their satisfying the intention of the Code. Such an approach, while serving the utilitarian function of giving names to pathogens, would have subverted the intention of the Code to serve the wider taxonomic purpose of providing nomenclature that would reflect the natural relationships of bacteria. It seemed to us that the only alternative such subversion was to generate a system of nomenclature for pathogens at the infrasubspecific level that was sufficiently robust that it would be accepted and used by the community of bacterial pathologists. This would require a document analogous to the Code, providing guidelines for naming plant pathogenic bacteria as infrasubspecies. With Doug, I developed a proposal of the concept for publication (Young et al., 1978a). In the extensive correspondence during this process it became clear that there was little enthusiasm and some hostility to the concept, as is still the case. We attempted to enlist most known bacterial pathologists as co-authors, with little success. Final authorship comprised five colleagues. Our paper was duly published and I gave a presentation at the 4^th International Conference on Plant Pathogenic Bacteria at Angers in 1978 (Young et al. 1978b).

 

In parallel with these activities, and as a response to the draft manuscript of our paper, Arthur Kelman, as Chairman of the ISPP, convened an ad hoc meeting of interested scientists at Berkeley, in early 1978, at which the issues were discussed. At this meeting, chaired by Milt Schroth, the Committee on Taxonomy of Plant Pathogenic Bacteria of the ISPP was founded. Its membership comprised J.F. Bradbury, D.W. Dye, M. Goto, A.C. Hayward (Chairman), R.A. Lelliott and M.N. Schroth. Minutes of these deliberations were published (Committee on Taxonomy of Plant Pathogenic Bacteria of the ISPP 1978). At the meeting, it was agreed that lists of names of bacterial pathogens would be presented to the ICSP. These comprised names that met the criteria for inclusion in Approved Lists and names that did not meet these criteria but were important for plant pathologists. It was hoped that the ICSB would give some recognition to the latter by acceptance of pathovars as an infrasubspecific rank within the Code.

 

In the event, the ICSB did not agree although the authors to the Approved Lists did acknowledge the danger of reuse of names of plant pathogens in their introduction (Skerman et al., 1980). The CTPPB then set itself the task of propounding in detail the International Standards for Naming Pathovars (the Standards) under the aegis of the ISPP. Doug as secretary steered the development of the Standards (and in fact wrote them with the help of Rik Watson here), which were published as a proposal (Dye et al. 1980).

 

In the same way that the Code gave no guidance as to methods or criteria for the differentiation of taxa, the Standards gave little guidance either to methodology on pathogenicity testing, nor did it, nor could it, formally specify in any detailed way, what constituted a pathovar, by contrast with a race or pathogenic strain. Pathovars were derived directly from previously named species. This meant that they had relatively limited host ranges that were defined in their descriptions, although as has become increasingly clear, this did not necessarily mean restriction to related host plant taxa. It was expected that a pathovar concept would evolve in a way similar to the way the species concept has evolved. Our primary goal was to maintain continuity of the existing nomenclature of plant pathogens, leaving open how nomenclature would subsequently develop. It was obvious that many pathovars could probably be established as species if relevant data was found. It was equally obvious that it was highly unlikely that all pathogens would be recognized as species.

 

At this time, those engaged in systematics were expected to develop their understanding of formal nomenclature by reading the taxonomic literature, paying special attention to the Code. The formation of the Standards occurred in this climate.  The community of pathologists interested in taxonomy was very small. Development of a taxonomic project was a major undertaking, not just an afternoon�s sequencing, and those involved usually took the time to understand the fundamentals of the discipline.

 

The ISPP had no policy of defining the activities of its Sub-Committees, nor, as far as I am aware of any reporting policy. The CTPPB did take steps to give regulation to itself. The 5th International Conference on Plant Pathogenic Bacteria was held in Cali, Colombia, in 1981. Dye did not attend. At the Bacteriology Section Meeting the organization of the CTPPB was discussed (Vidaver, 1982). It was resolved that, in future, the Committee on Taxonomy would be the responsibility of the Bacteriology Section Committee. Meetings would be held under the auspices of the Section Committee at the regular international conferences on plant pathogenic. Resignations from the CTPPB were to be filled by consensus of the CTPPB or by the Section Committee. The Committee elected was J.F. Bradbury, D.W. Dye (Chairman), R.S. Dickey, M. Goto, A.C. Hayward and A.K. Vidaver.

 

A public meeting of the Committee was held at the ISPP Conference, Melbourne, 1983. Dye did not attend and Anne Vidaver chaired the meeting. The International Standards for Naming Pathovars (Dye et al. 1980) were adopted by resolution of a meeting. I was elected that the meeting. I have contacted Vidaver to see if there is a record of business, without reply so far.

 

The 6th International Conference on Plant Pathogenic Bacteria was held in Maryland, in 1984. There is no public record of the meeting. I do not know who initiated or chaired this meeting. Neither Doug Dye nor I attended. The Committee after this conference was J.F. Bradbury, R.E. Davis, R.S. Dickey, G.L. Ercolani, A.C. Hayward, A.K. Vidaver (Chair), J.M. Young. Following this, I initiated the first revisions of the Standards and the development of the first annotated list of names of pathogens. In this publication, the Committee modified details of the Standards and provided a supplementary list of names as an addendum to that of the 1980 paper (Young et al. 1991a). 

                       

The 7th International Conference on Plant Pathogenic Bacteria was held in Budapest, Hungary, in 1989. At that meeting, the elected committee comprised J.F. Bradbury, L. Gardan, R.I. Gvozdyak, D.E. Stead, Y. Takikawa, and J.M. Young (Convener)[1].

The revisions to the Standards were proposed at the Budapest meeting. The conference was held immediately following the publication of Gabriel et al. (1989). Publication of new species based on RFLP was disquieting as a precedent because of the obvious taxonomic ambiguities inherent in the method. At this meeting, the question of a discussion paper to caution against the use of RFLP as a general method for proposing species was discussed. My correspondence with R.G. E. Murray, then Editor of IJSB,  brought home to me the dangers inherent in our committee becoming engaged in commentary on aspects of classification, whether of theory or of method. Our Committee both makes and arbitrates the Standards. To engage in debate on classification would almost inevitably result in becoming partisan and to lose the claim to being an independent arbiter of nomenclature. The publication of Young et al. (1991b), although by the membership of the CTPPB was not in the name of the Committee. I confess that although I had forgotten this distinction in recent discussions, I think it is very important. I hope that when the Guidelines for the Committee are developed, this point will be made explicit. My remark at the Edinburgh conference should be forgotten.

 

The 8th International Conference on Plant Pathogenic Bacteria was held in Versailles, France, in 1992. The revision of the Standards (Young et al. 1991) was adopted by resolution of a meeting held at the ISPP Conference on Plant Pathogenic Bacteria, Versailles, 1992. The committee elected was J.F. Bradbury, S.H. De Boer, L. Gardan, R.I. Gvozdyak, G. Saddler, D.E. Stead, Y. Takikawa, L. Vauterin and J.M. Young (Convener). At that meeting, Gerry Saddler proposed that the Committee publish a full list of species and pathovars of plant pathogenic bacteria. This was developed and published as Young et al. (1996).

 

Until this time all correspondence and manuscript development was in hard copy. Correspondence turn-around was between 14 days and a month. At some point, the ISPP decided that we were a Sub-committee under the Bacteriology Section and then that we were a Subject Matter Committee, their President stating that we were one of the more active subject matter committees.

 

The 9th International Conference on Plant Pathogenic Bacteria was held in Bangalore, India, in 1996. At that time, all N.Z. science positions were under threat and I did not have travel funds. A meeting of the Committee was run (I think) by Solke, Gerry and Louis Gardan, at which the taxonomic proposals of Vauterin et al. (1995) on Xanthomonas were discussed. (One of you would like to produce some retrospective minutes to complete the record).

 

The 10th International Conference on Plant Pathogenic Bacteria was held in Charlottetown, Canada, in 2000. The conference was held following the publication of Schaad et al. (2000). The nomenclatural defects of this paper were canvassed and a rebuttal was subsequently published in the name of the Committee (Young et al. 2001). Following the discussion there, the ISPP was approached with a view to activating a website, which was done.

 

In 2001, as you know, I became ill and Gerry Saddler agreed to be convener. I do not have any notes. The Committee met at the ISPP Congress in Christchurch, New Zealand in 2002, with Gerry in the chair. The main issue discussed was whether the committee could act as an advocate for any particular nomenclature. I believe the committee agreed that to advocate a particular nomenclature was to advocate a particular classification, which was outside its scope. (In my view, the neutrality of the committee can only be maintained by restricting itself to noting the implications of adopting any particular nomenclature.) In 2003, I became well again and Gerry and the committee agreed that I become convener again. The List was updated and placed on the Website (Young et al. 2004.

 

The 11th International Conference on Plant Pathogenic Bacteria was held in Edinburgh, Scotland, in 2006. The rest you know.

 

The ISPP website

 In 2000, we gained access to the ISPP website and various documents were placed on it. Since its inception, managing the information on the website has been a source of constant frustration. The ISPP site was/is run through grace and favour by CABI and had a low priority. Making changes to the site was slow, sometimes impossible; changes agreed to were not made. It was almost a year from the time that the updated List was submitted to its appearance on the website. A general discussion site could not be got rid of. Very recently, I discovered that there are separate entry points to our site and that information available depended on the point of entry (Marion�s complaint that she could not find the 2004 Lists was a mystery to me then out now explained).  At that stage there was no obvious alternative for long-term management to the site. Recently, the ISPP Executive agreed that we would have control of our web pages.

 

Lists on the Web

 

The 1996 List

The 1996 List was posted on the web in 2001. It contains all validly published pathogenic species and all pathovars. As the introduction to the List explains, this List contains all names of pathogens published since 1980, listed according to the most recent publication, without commitment to any particular taxonomic interpretation. It is not a �validation� list of species, which is a matter for the ICSP, and in my view, it does not �validate� pathovar names. All it can is point out which names do not conform to the Standards, leaving it to others to decide which names they will use. Annotations are made against species names where the Code may not have been conformed with, and comment has been made where, in the opinion of the Committee, the Standards have not been complied with. I proposed a number of additional annotations, mainly connected with the publication of names in which the descriptions do not allow differentiation of taxa except using reassociation or sequencing methods. I did this so that pathologists would not read description expecting to be enlightened about methods of identification.

 

New Names

At least as an interim measure, the Committee prepared annual lists on new names. Each year, I asked for names for the year and updated the lists of New Names. In retrospect I wish I had produced a new list for each year. The question of upgrading the 1996 lists whether by editing them on the web or of publishing a further hard copy version, was in abeyance.

 

The 2004 List

This is an integrated list comprising the above lists.

 

Committee Membership

 

Election date

1980 D.W. Dye, J.F. Bradbury, M. Goto, A.C. Hayward (Convener), R.A. Lelliott and M.N Schroth.

 

1981 D.W. Dye (Convener), J.F. Bradbury, M. Goto, A.C. Hayward, R.A. Lelliott and M.N Schroth.

 

1983 J.F. Bradbury, R. Davis, R.S. Dickey, M. Goto, G.L. Ercolani, A.C. Hayward, A.K. Vidaver, (Convener), J.M. Young

 

1984 J.F. Bradbury, R. Davis, R.S. Dickey, M. Goto, G.L. Ercolani, A.C. Hayward, A.K. Vidaver (Convener), J.M. Young

 

1989 J.F. Bradbury, R. Davis, R.S. Dickey, L. Gardan, R.I. Gvozdyak, G.L. Ercolani, A.C. Hayward, A.K. Vidaver, (Convener), J.M. Young

 

1992 L. Gardan, R.I. Gvozdyak, Y. Takikawa, G.E. Saddler, D.E. Stead, L. Vauterin, J.M. Young (Convener)

 

1996 L. Gardan, R.I. Gvozdyak, L. Gardan, G.E. Saddler, D.E. Stead, Y. Takikawa, L. Vauterin, J.M. Young (Convener)

 

2000 C.T. Bull, S.H. De Boer, G. Firrao, L. Gardan, G.E. Saddler, D.E. Stead and Y. Takikawa, J.M. Young (Convener)

 

2006 C.T. Bull, S.H. De Boer, T. Denny, M. Fischer-Le Saux, G. Firrao, G.E. Saddler, D.E. M. Scortichini, Stead and Y. Takikawa, J.M. Young (Convener)

 

2006 C.T. Bull, (convener starting August 2006). S.H. De Boer, T. Denny, M. Fischer-Le Saux, G. Firrao, G.E. Saddler, D.E. M. Scortichini, Stead and Y. Takikawa, J.M. Young

2007 C.T. Bull (Convener). S.H. De Boer, T. Denny, M. Fischer-Le Saux, G. Firrao, G.E. Saddler, M. Scortichini, D.E. Stead and Y. Takikawa

 

Publications

 

Committee on Taxonomy of Plant Pathogenic Bacteria of the ISPP, 1978. I.S.P.P. Lists of names of phytopathogenic bacteria in relation to the Approved Lists of Bacterial Names 1980. Proceeding of the 4th International Conference on Plant Pathogenic Bacteria � Angers, France, 1978, 395�399.

Gabriel, D.W.; Kingsley, M.T.; Hunter, J.E.; Gottwald, T. (1989) Reinstatement of Xanthomonas citri (ex Hasse) and X. phaseoli (ex Smith) to species and reclassification of all X. campestris pv. citri strains. International Journal of Systematic Bacteriology 39, 14�22.

Schaad, N.W.; Vidaver, A.K.; Lacy G.H.; Rudolph, K.; Jones, J. B. 2000. Evaluation of proposed amended names of several pseudomonads and xanthomonads and recommendations. Phytopathology 90, 208-213.

Vidaver, A.K.1982. General Meeting Report. Proceedings of the 5th International Conference on Plant Pathogenic Bacteria � Cali, Colombia, 1981. 620-622.

Young, J.M.; Bradbury, J.F.; Davis, R.E.; Dickey, R.S.; Ercolani, G.L.; Hayward, A.C.; Vidaver, A.K. 1991. Nomenclatural revisions of plant pathogenic bacteria and list of names 1980�1988. Review of Plant Pathology 70, 211�221.

Young, J.M., Bradbury, J.F.; Gardan, L.; Gvozdyak, R.I.; Stead, D.E.; Takikawa, Y.; Vidaver, A.K.; 1991. Comment on the reinstatement of Xanthomonas phaseoli (ex Hasse 1915) Gabriel et al. 1989 and X. phaseoli (ex Smith 1897) Gabriel et al. 1989; an indication of the need for Minimal Standards for the genus Xanthomonas. International Journal of Systematic Bacteriology 41, 172�177.

Young JM, Bull CT, De Boer SH, Firrao G, Gardan L, Saddler GE, Stead DE, Takikawa Y, 2001. Classification, nomenclature and plant pathogenic bacteria � a clarification. Phytopathology 91, 617�620.

Young JM, Bull CT, De Boer SH, Firrao G, Gardan L, Saddler GE, Stead DE, Takikawa Y, 2005. Names of plant pathogenic bacteria, 1864�2004. (http://www.isppweb.org/names_bacterial.asp).

Young JM, Dye DW, Bradbury JF, Panagopoulos CG, Robbs CF, 1978a. A proposed nomenclature and classification for plant pathogenic bacteria. New Zealand Journal of Agricultural Research 21, 153�177.

Young JM, Dye DW, Bradbury JF, Panagopoulos CG, Robbs CF, 1978b. The use of the term "pathovar" in the classification of plant pathogenic bacteria. Proceeding of the 4th International Conference on Plant Pathogenic Bacteria � Angers, France, 1978, 359�363.

Young, J.M.; Saddler, G.; Takikawa, Y.; De Boer, S.H.; Vauterin, L.; Gardan, L.; Gvozdyak, R.I.; Stead, D.E. (1996) Names of plant pathogenic bacteria 1864�1995. Review of Plant Pathology 75, 721�763.