The construction of a Solanum habrochaites LYC4 introgression line population and the identification of QTLs for resistance to Botrytis cinerea

Abstract

Tomato (Solanum lycopersicum) is susceptible to grey mold (Botrytis cinerea). Partial resistance to this fungus has been identiWed in accessions of wild relatives of tomato such as Solanum habrochaites LYC4. In a previous F 2 mapping study, three QTLs conferring resistance to B. cinerea (Rbcq1, Rbcq2 and Rbcq4a) were identiWed. As it was probable that this study had not identiWed all QTLs involved in resistance we developed an introgression line (IL) population (n = 30), each containing a S. habrochaites introgression in the S. lycopersicum cv. Moneymaker genetic background. On average each IL contained 5.2% of the S. habrochaites genome and together the lines provide an estimated coverage of 95%. The level of susceptibility to B. cinerea for each of the ILs was assessed in a greenhouse trial and compared to the susceptible parent S. lycopersicum cv. Moneymaker. The eVect of the three previously identiWed loci could be conWrmed and seven additional loci were detected. Some ILs contains multiple QTLs and the increased resistance to B. cinerea in these ILs is in line with a completely additive model. We conclude that this set of QTLs oVers good perspectives for breeding of B. cinerea resistant cultivars and that screening an IL population is more sensitive for detection of QTLs conferring resistance to B. cinerea than the analysis in an F 2 population.

Quantitative resistance to Botrytis cinerea from Solanum neorickii

“…A correlation between DI and LG was observed in data of the F 3 families (r = 0.258; P < 0.01), but no significant correlation was observed in the SH F 2 population (r = 0.173; P > 0.05; Finkers et al 2007a). These correlations are lower than the correlation observed while testing the SH IL population (r = 0.65; P < 0.01; Finkers et al 2007b). The heterogeneous genetic background of F 2 and F 3 plants and/or the type of bioassay used may obscure the obvious relationship which was observed between DI and LG in the SH IL population (Finkers et al 2007b).…”

“…Two plants contained both pQTL4 and pQTL9 (group abb) and the additional reduction in DI of these lines suggests a fully additive model, showing the potential of pyramiding these two pQTLs. Figure 1 shows a comparison between (p)QTL positions identified in this study and previously mapped QTLs conferring resistance to B. cinerea (Finkers et al 2007b), mapped positions of resistance genes (R-genes), R-gene analogs mapped by Zhang et al (2002) and QTLs conferring resistance to other diseases (Tables 7, 8). The positions of B. cinerea QTLs may be homologous with the positions of R-genes or QTLs conferring resistance to Phytophtora infestans and Xanthomonas campestris (Chromosome 3); Ralstonia solanacearum, P. infestans, and O. neolycopersici (Chromosome 4); Alternaria solani, Fusarium oxysporum, and TMV (Chromosome 9).…”

“…1). CAPS analysis of the SH introgression lines (IL) containing Rbcq3 (Finkers et al 2007b) does not exclude the possibility that SN QTL3 is at a homologous position. We postulate that the three SN (p)QTLs identified in this study have QTLs at homologous positions in SH.…”

“…Previous analysis of the SH IL population, resulted in identification of two QTLs on Chromosome 9: Rbcq9a reducing LG and Rbcq9b reducing DI (Finkers et al 2007b). The region homologous to Rbcq9a is homozygous SL in this set of BC 3 S 2 plants and may explain why only a reduced DI was observed.…”

“…Disease tests, using the stem assay, resulted in identification of QTLs either reducing DI or reducing LG (Finkers et al 2007a). QTLs generally contributed to both a lower DI and LG in a greenhouse assay on mature plants (Finkers et al 2007b). QTL3 and pQTL4 might therefore be effective in reducing both DI and LG when used in commercial breeding programs.…”