M13 DNA fingerprinting was used to determine evolutionary changes that occurred in Latin American germ plasm and USA cultivars of commonbean (Phaseolus vulgaris L.) during domestication. Linkage mapping experiments showed that M13-related sequences in the common-bean genome were either located at the distal ends of linkage groups or that they were unlinked to each other or to any previously mapped markers. Levels of polymorphism observed by hybridization with M13 (1 probe-enzyme combination) were comparable to those observed by hybridization with single-copy random PstI genomic probes (36 enzyme-probe combinations) but were higher than those observed for isozymes (10 loci). Results indicated that the wild ancestor had diverged into two taxa, one distributed in Middle America (Mexico, Central America, and Colombia) and the other in the Andes (Peru and Argentina); they also suggested separate domestications in the two areas leading to two cultivated gene pools. Domestication in both areas led to pronounced reductions in diversity in cultivated descendants in Middle America and the Andes. The marked lack of polymorphism within commercial classes of USA cultivars suggests that the dispersal of cultivars from the centers of origin and subsequent breeding of improved cultivars led to high levels of genetic uniformity. To our knowledge, this is the first crop for which this reduction in diversity has been documented with a single type of marker in lineages that span the evolution between wild ancestor and advanced cultivars.

We report the use of the bacteriophage Pi Cre-lox system for generating conservative site-specific recombinaton between tobacco chromosomes. Two constructs, one contaning a promoterless hygromycin-resistance gene preceded by a lox site (lox-hpt) and the other containing a caulilower mosaic vfirus 35 promoter linked to a lox sequence and the cre coding region (35S-lox-cre), were introduced separately into tobacco plants. Crosses Wi38 was mediated by infection of leaf explants with Agrobacterium tumefaciens GV3111(pTiB6S3S3) carrying pCB11 or pCB36 (19). Independent kanamycin-resistant (KanR) primary transformants hemizygous for the constructs pCB11 (Ph plants) and pCB36 (Pc plants) were cross-pollinated (Pc as pollen donor) and self-pollinated. Plants whose selfed progenies segregated --3:1 for resistance to kanamycin were considered to have a single transgenic locus. Southern blot analysis using Xho I, which cuts outside the transgenes, was used to determine whether there was a single band. Four Ph (11.1, 11.4, 11.5, and 11.6) and four Pc (36.3, 36.4, 36.9, and 36.10)

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Analyses of genetic diversity within populations could be of great benefit to plant genetic resources conservation . In order to identify genetic markers that are variable within populations, the genome of Phaseolus vulgaris was screened with several DNA sequences in order to identify hypervariable sequences . Polymorphisms were observed between Middle American and Andean cultivars using the protein III tandem repeat of the M13 phase and the 33 .15 human minisatellite . Extensive differences were observed when the DNA of two divergent lines -BAT93 and Jalo EEP558, of Middle American and Andean origin, respectively -were digested with Hinfl, Tagl, HaeI11 and hybridized with the 33 .15 human minisatellite. Similarly, numerous polymorphisms were observed when the M13 protein III tandem repeat region was hybridized with Tagl digests of these cultivars . Polymorphism was also detected among sister lines of two F6 backcross materials involving Middle American and Andean lines when genomic DNA was digested with TaqI and hybridized with M13 tandem repeat region . In addition, polymorphism was observed among Porrillo cultivars that resulted from selection within a single landrace population. Whereas only one isozyme difference had been observed previously among the Porrillo cultivars, eleven restriction fragments detected by the M13 protein III tandem repeat sequence differentiated these cultivars .'Ribosomal DNA also hybridized to several polymorphic bands on TaqI and EcoRI genomic Southern blots of the F6 backcross material . Only one polymorphism was observed with EcoRI-digested genomic DNA of BAT93 and Jalo EEP558 was hybridized with microsatellite (GACA)4 . This probe might be useful in ascertaining relationships at the species and subspecies level, and as a marker in mapping studies . Our results show that both the human 33 .15 minisatellite and M13 should be useful probes to detect within-population variability in common bean . 177