Toward map-based cloning of fruit shape QTLs in tomato:fs8.1, a major QTL, sets the pattern of carpel shape well before anthesis; genetic characterization and high-resolution mapping ofovate

fs8.1 is a major fruit shape QTL differentiating fresh market and processing tomatoes. Fine mapping was undertaken to determine whether the effect is due to a single gene or several tightly linked. For the 1,212 gametes screened in F2 and F3 families, it was determined that fs8.1 behaves as a single locus and maps to a cluster of RAPD and RFLP markers thought to flank the centromere of chromosome 8.;A comparative developmental study of fs8.1 NILs revealed that fs8.1 alleles exert their effects on fruit shape early in carpel development at least six days before anthesis.;A major locus controlling pear-shaped fruit in tomato was mapped to chromosome 2 in crosses between L. esculentum c.v. yellow pear TA503, and the round fruited wild species L. pimpinellifolium LA1589 (PM), as well as a cross between TA503 and the round fruit near isogenic line IL2-5 (PN) carrying the distal portion of chromosome 2 from the L. pennellii genome. The locus discovered in their crosses is mostly likely the same as the locus called ovate in the classical literature (Lindstrom 1926, 1927). ovate exerts its effect by changing oblate (round) fruit to an oval shape, and it might be the same gene causing the constriction of pear-shaped fruit in tomato. However, this could also be due to tightly linked genes.;High resolution genetic and physical maps of the region of chromosome 2 containing the major fruit shape determining locus, ovate, have been constructed. A total of 3000 NIL F2/F3 lines derived from TA503 x L. pennellii were used to fine map ovate. ovate is adjacent to the marker TG645 and flanked by TG463 and TG169 (0.7 cM interval). The marker TG645 was used to screen a BIBAC (Binary Bacterial Artificial Chromosome) library from L. pennellii. Four BIBAC clones potentially containing ovate were isolated. The map-based cloning of ovate will open the door to a better understanding of the molecular basis of fruit development, and also facilitate the genetic engineering of fruit shape characteristics.