11 Allelism test among high locule number tomato mutants and genetic mapping of the loci involved Barrero, L . S . and Tanksley, S . D . Cornell University, Plant Breeding and Plant Biology Departments, Ithaca, NY 14853, USA Lycopersicon esculentum fasciated stocks were assembled from TGRC ( http://tgrc . ucdavis . edu/ ) in 1999 . The stocks were characterized based on their average locule number (ALN) at anthesis and fruit maturity stages under field and greenhouse conditions . Based on a t - test ( p <0 . 05) and a multiple comparison procedure that indicates which accession (s) carries the largest number of locules, accessions were classified into three groups . The first group (I) comprised accessions with the largest ALN (>10) . The second group (II) comprised the accession LA2352 whose phenotype was variable depending on the environmental conditions: In 1999 greenhouse conditions the ALN for this accession was < 4 and in 1999 and 2000 field conditions ALN was >4 . The third group (III) comprised accessions with an ALN > 4 but not > 10 (Table 1) . Under greenhouse conditions, all F1 progenies obtained from crosses among accessions had a mutant phenotype except for F1s derived from crosses between LA2352 (group II) with LA0020, LA2349, and LA2595 (group III), whose ALN was <4 . Under 2000 field conditions, F2 progenies derived from crosses with LA2352 showed wild type segregation (Table 2) indicating that at least two different complementation groups (genes) were present .   These loci probably correspond to fasciated and locule number described by early tomato geneticists (MacArthur, 1934; Yeager, 1937), which have recently been localized on the tomato molecular map on chromosomes 11 and 2 respectively (Lippman and Tanksley, 2001) . The stocks LA2371 and LA2352 were chosen for mapping of these loci . The mutation in LA2371 maps at fasciated on the bottom of chromosome 11 and has a recessive gene action as expected . Mapping of the mutation carried by LA2352 will be performed in the 2001 field in Ithaca, NY .   The existence of allelic series for fasciated was also observed . A good example is the stock LA0767 of group I, first described by Rick (1965), which was semi - dominant with regard to non - fused (separated) carpels . An F2 population developed from a cross between introgression lines suitable for mapping at chromosome 11, (Eshed and Zamir, 1995) and LA0767 showed a reduction of > 96% in recombination frequency compared to crosses made with LA2371, which suggests that the mutation in LA0767 could be an inversion or a deletion . Different alleles of the same locus will be valuable for future cloning of the gene . Map - based cloning of fasciated is being performed as a prerequisite for the understanding of the molecular biology of the trait .