Genetic Introgression And QTL Analysis For Cold Tolerance In Wild Tomato (S.pimpinellifolium)

Tomato (Solanum lycopersicum L.) is an important thermophilic crop. Cold injury is one of the main abiotic constrains in tomato production, especially in north solar greenhouse during winter and spring period.Therefor, breeding for cold-tolerant tomato is highly desirable. Introgression of genes controlling cold tolerance from wild congeners into S. lycopersicum has potential to improve resistance to chilling temperature. Molecular marker technology will be contributed to exploring the useful information in effects to develop cold-tolerant germplasm efficiently through location the QTL, which could be significant to improve the quality and yield in tomato production.In this study, the Solanum pimpinellifolium LA722 (cold tolerance) and Solanum lycopersicum 9706 (cold sensitive) were used to construct advanced backcross population. The objective was to map cold-tolerant QTL and then obtain some cold-tolerant germplasm by highly screening under cold stress during germination stage and AB-QTL analysis. The main results were as followed:1. A total of 408 SSR markers and 573 CAPS markers were used to screen polymorphism among two parents 9706, LA722 and their F1 progeny, which resulted in 160 polymorphic SSR markers and 97 polymorphic CAPS markers. The 257 markers were used to amplify the three types of gene pools - BC₂, BC₃ and F₄, in which 61 SSR markers and 35 CAPS markers were used for map constrction finally.2. For highly screening under cold stress during germination stage, a total of 273 BC3S1 individuals were genotyped for CAPS and SSR markers. A molecular linkage map consisted of 11 chromosomes was constructed with the mapping software Joinmap4.0. It covered approximately 616.78 cM of tomato genome with an average genetic distance of 9.07 cM, mapping up of 22 CAPS markers and 46 SSR markers. The number of markers on each chromosome varies form 4 to 9, with the length form 38.30 cM to 72.47 cM.3. The performance for cold tolerance during seed germination and seedling stages of 273 BC3S2 families were identified and analyzed. Results indicated that the frequence distribution of germination rate at 10℃, relative germination index and chilling index at the seedling stage in the BC3S2 population were all nomal distribution and the effect met the requirement to perform the mapping of QTLs. Cold tolerance during seed germination had correlation with cold tolerance during vegetable growth (r=0.15).4. Based on MQM mapping method (using MapQTL4.0), 13 QTLs were identified during seed germination and seedling stages. 6 QTLs for germination rate of 25 days (GR25) under cold stress (10℃) were mapped to chromosome 1, 2, 8, 9, 11 and 12. The contribution of individual QTL to phenotypic variation varied from 2.1% to 12.1%, and the positive alleles were contribution by the cold-tolerant parent LA722. 5 QTLs for relative germination index (RGI) were mapped to chromosome 1, 2, 5 and 11. The contribution of individual QTL to phenotypic variation varied from 3.2% to 32.9%. The positive alleles of qRGI-11-1 was contribution by 9706, and other four were contribution by LA722. 2 QTLs for chilling index (CI) at the seedling stage were mapped to chromosome 2 and 8. The contribution of individual QTL to phenotypic variation were 3.3% and 4.9%, and the positive alleles were both contribution by LA722.5. 23 QTLs controlled the characteristics of 4-ear plant height (PH), maximum leaf length (MLL), maximum leaf width (MLW), fruit weight (FW), fruit pericarp thickness (FPT), locule number (LN), soluble solids content (SSC) and 100-seed weight (SW) were mapped to chromosome 2, 5, 6, 8, 9, 11 and 12. In this study, QTLs co-location among different traits was commom.6. Six families'self-pollinated progeny, which named 162-4, 164-2, 164-4, 169-2 169-6 and 171-2, had better cold-tolerance performance than LA722 both at seed germination and seedling stages. These plants also had excellent agricultural performance. 164-2 and 164-4 contained both qRGI-2-1 and qRGI-5-1, whith could be used as good breedling germplasm.