Grandillo et al. (1999) summarized the results of QTL mapping for fruit weight obtained in 17 studies based on progeny of various types and involving seven wild species. According to the studies, three to more than 18 QTLs were detected. Six QTLs explained more than 20% of the phenotypic variation. A common set of 28 QTLs could be identified that frequently segregated in at least two populations. Nevertheless only QTL cloning and complementation permits determination of whether each consensus QTL location corresponds to a single gene. Lippman and Tanksley (2001) studied progeny based on a cross between two genotypes of extreme fruit size. None of the detected six QTLs mapped to a novel location, but this was the first time that these six QTLs were detected together.
For fruit shape, Grandillo et al. (1999) identified a common set of 11 QTLs from the six studies where the fruit length:diameter ratio was segregating. In another study, three major QTLs were identified, ovate on chromosome 2, sun on chromosome 7 and fs8.1 on chromosome 8 (van der Knapp et al. 2002). Locule number is another major component of fruit size. Several QTLs have been mapped for this trait (Lipp-man and Tanksley 2001; van der Knaap and Tanksley 2003; Barrero and Tanksley 2004) the major two corresponding to the mutations fasciated on chromosome 11 and lc on chromosome 2. A strong epistatic interaction between these two genes was shown, with locule number considerably increasing when both loci were homozygous for the alleles increasing locule number (Lippman and Tanksley 2001).
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