The ghost mutant illustrated on the cover is one of the myriad monogenic variants known in the tomato. Although determined by a single gene (gh) of known chromosomal location, the homozygote is remarkably variable. It emerges with normal or slightly bleached cotyledons; the first true leaf is a mosaic of totally white and normal green areas; the subsequently developed leaves may have mostly green tissue, but are generally entirely white or light yellow phase; and either white or yellow phase can revert to patches or longitudinal stripes of the green phase. All selfed progeny from any of these phases are solely of gh phenotype. Although this mutant has elicited great interest as a possible example of transposable element activity, such activity has not been proven.
Attention here will be confined to those non-profit groups that serve to exchange information and materials related to genetics and breeding of specific horticultural crops. Being independent of the formal scientific societies and having arisen electively according to demand, they are highly heterogeneous in regard to functions, organization, support, and even titles. In most respects this heterogeneity is commendable since the needs of the various groups differ, and each group develops a distinctive character. It is beyond the scope of this article to present all the details of each cooperative, but they will be compared in respect to the most important aspects of their structure and functions. I hope to avoid an excessive slant toward the Tomato Genetics Cooperative, with which I have been associated since its inception. Excluded from major consideration in this article are groups devoted exclusively to line testing (ex. Southern Tomato Exchange Program, STEP), those covering an entire crop group (e.g. Vegetable Improvement Newsletter, VIN; Small Fruit Workers, SFW), or those which are restricted regionally.
The following is a brief review of our investigations on problems of germplasm acquisition, analysis, maintenance, evaluation, and use in the Lycopersicon spp. It is based entirely on our published research; hence, only a synopsis will be presented and appropriate citations made to direct readers to full presentation of results and analysis.