Figure 1. Frequency distribution of the F2 plants according to plant length. The arrows indicate the mean values for the parents and F1.
Center for Plant Breeding and Reproduction Research, Droevendaalsesteeg 1, P.O. Box 16, NL-6700 AA Wageningen, the Netherlands
An F2 between Lycopersicon esculentum cv Allround and L. pennellii LA 716 was made to obtain a segregating population. This population will be used to map new molecular markers and to confirm already mapped markers where needed. The F2 population consisted of 377 plants on which 15 phenotypic characteristics were observed (e.g. plant vigor, plant length, earliness, number of leaves, resistance to a spontaneous infestation of the greenhouse whitefly (Trialeurodes vaporariorum) and caterpillars, etc). For all characteristics a large variation was observed that frequently outranked the parents (Figure. 1). In a separate experiment part of the F2 population (77 plants) was tested for resistance to the greenhouse whitefly after artificial inoculation and for glandular trichome density. F3 lines of the plants of the core population will be used in further studies on resistance to the greenhouse whitefly in correspondence to trichome density and for studies on growth and development.
Figure 1. Frequency distribution of the F2 plants according to plant length.
The arrows indicate the mean values for the parents and F1.
Based on the variation of phenotypic characteristics, 100 plants of the F2 population were chosen as the core population. The DNA from the plants of the core population have been analyzed for RFLPs, equally distributed over all chromosomes (digestions were done with Eco RI, Eco RV and Hae III). Based on the RFLP segregation data a genetic map was made. In general our tomato RFLP map was similar to the RFLP map obtained by Tanksley et al.(1990). Only in the upper part of chromosome 1 some differences were observed (Figure 2). Some of the probes used (TG 59, TG66 and TG178) gave two RFLPs, which could be scored individually. These two RFLP loci mapped on the same chromosome and approximately 5-10 cM apart.
All plants were selfed by hand pollination and 261 F2 plants produced F3 seeds. By repetitive selfing recombinant inbred lines (RILs) of the plants of the core population will be made via single seed descent, with the final aim to obtain about 100 homozygous lines. These will be used to explore the genetic variation of Lycopersicon pennellii (LA 716) and map quantitative trait loci present in this species.
Figure 2. Chromosome 1 of the tomato L. esculentum cv Allround and L.
pennellii LA 716. a. chromosome according to Tanksley et al. (1990) b.
chromosome 1 according to the present study
References:
Tanksley, S.D., M.A. Mutschler 1990. Linkage map of the tomato (Lycopersicon esculentum)(2N=24). In: O'Brian, S.J. (ed) Genetic maps; locus maps of complex genomes. Cold Spring Harbor, Laboratory Press, Cold Spring Harbor, NY. p6.3-6.15.