Identification of QTLs associated with commercial postharvest quality traits and disorders using a collection of near isogenic lines of melon

The external and internal appearance and other nutritious compounds of the inodorus melon cultivar 'Piel de Sapo' are very important quality traits for the Spanish market. This cultivar is much appreciated for its aroma and sweetness and shows a very low browning potential for fresh-cut processing. Our objective was to identify polygenes in the near isogenic lines (NILs) showing positive or negative effects on quality traits such as commercial visual appearance, skin and flesh color evaluated by using tristimulus colorimeter, pulp area and absence of disorders. The analysis was performed on a collection of NILs of melon fruit containing a single introgression of the exotic alleles from the Korean accession PI161375 and using the genetic map of melon (Gonzalo et al., 2005). Three NILs showed better commercial appearance than the parental line (PS), while skin netting was increased in seven lines compared to the PS. Five NILs showed greener skin (higher hue angle values) compared to the PS. Nine NILs showed pulp with different degrees of greener flesh color (higher h ^* values) compared to the parental line PS and one, particularly, showed development of light orange flesh colors as a result of carotenoid biosynthesis. Fruit calcium forms increased in at least one NIL compared to the PS. Several NILs with lightness or chroma significantly different from the PS were also found. Just five NILs developed a higher percentage of pulp area than the PS. Only lines SC 2-3 and SC 9-2 presented some degree of necrosis of fruit placental tissue, a disorder found in the PI161375 donor. Line SC 3-5 was particularly hypersensitive to chilling injury. These results proved the genetic inheritance of commercial qualities. Melon appearance can be modified in order to design more attractive varieties of PS melons using NILs as an effective tool to find the candidate genes responsible for raising the quality traits demanded by consumers. Additionally, NILs were useful to study undesirable side effects such as postharvest disorders.