fs8.1, a major QTL, sets the pattern of tomato carpel shape well before anthesis

fs8.1 is a major fruit-shape QTL differentiating fresh-market and processin g tomatoes. Mature fruits from plants with the wild-type fresh-market allel es are round, whereas those with alleles from processing variety E6203 are elongated (sometimes referred to as blocky or square tomatoes). Fine mappin g was undertaken en to determine whether the effect is due to a single gene or several tightly linked genes. RAPD and RFLP linkage analysis, and subst itution mapping of nearly isogenic lines (NILs) segregating for the 22.8 cM -TG176-CT92 interval at the top of chromosome 8 in tomato were used for hig h-resolution mapping. For the 1212 gametes screened in F-2 and F-3 families , it was determined that fs8.1 maps as a single locus near the centromere o f chromosome 8. A comparative developmental study of fs8.1 NILs revealed th at fs8.1 alleles exert their effects on fruit shape early in carpel develop ment at least 6 days before anthesis. Field evaluations of the NILs indicat e that fs8.1 affects not only fruit shape, fruit length, and fruit weight b ut also the number of flowers and fruits per inflorescence, and the harvest index. The date of first flower and fruit diameter were not significantly affected.