| The cultivated tomato (Lycopersicon esculentum Mill.) is a chilling-sensitive species, suffering injury at temperatures below 10°C. Regions of the genome associated with responses to low temperature were studied using a quantitative trait loci (QTL) approach. A backcross recombinant inbred fine (BCRIL) population derived from L. esculentum cv. E6203 (recurrent parent) and L. hirsutum accession LA1777 (chilling-tolerant, donor parent) was used. Chilling at 9/4°C (day/night temperature) was imposed in short-term (48 hours) growth chamber experiments, and a long-term (20 days of chilling) greenhouse experiment. Chlorophyll fluorescence parameters as well as plant growth and development were monitored.; QTLs for prevention of photoinhibition were not always mapped to the same regions of the genome as QTLs for faster growth and development under low temperatures. Both parents contributed alleles that improved chilling tolerance. The physiology behind these QTLs is discussed, particularly those involved in growth and prevention of photoinhibition under suboptimal temperatures.; In a second series of experiments, QTLs mapped in the BCRIL population were verified using near isogenic lines (NILs) and segregating populations. Effects on prevention of photoinhibition, increase in quantum efficiency of photosystem II, increase in anthocyanin production, increase in dry mass accumulation, and faster leaf and flower development under chilling were confirmed in QTLs on chromosomes 2, 3, 4, 6, 7, 9 and 10. Segregation of leaf development under chilling stress indicated that a recessive gene (or gene cluster) is responsible for this trait on chromosome 2. Similarly, two recessive genes (or gene clusters) on chromosome 10 induce increased anthocyanin production under chilling stress. The implications of these findings in tomato variety improvement are discussed.; In a third study, the role of anthocyanins in the overall responses to low temperature stress was examined in a NIL containing an introgression on chromosome 10 and the recurrent parent. Plants with high anthocyanins showed less photoinhibition than green (control) plants in some cases, suggesting that these pigments can act as a neutal absorber, reducing excess light absorption during chilling without negatively affecting the capacity for carbon assimilation. Ecophysiological implications of the transient increase in anthocyanins during chilling stress are discussed. |
