Breeding for Late Blight Resistance and High Fruit Lycopene Content In Tomato

A goal of the Penn State Tomato Breeding Program is to develop breeding lines and cultivars of tomato with desirable horticultural characteristics, including early blight (EB) and late blight (LB) resistance and high fruit lycopene (LYC) content. Here our recent findings in genetics and breeding of LB resistance and high fruit lycopene content are presented. LB, caused by Phytophthora infestans, is one of the most devastating foliar diseases of tomato (Solanum lycopersicum) worldwide. Previously, 3 major resistance genes (Ph-1, Ph-2 and Ph-3) and a few resistance QTLs were identified, and recently a few resistant breeding lines and commercial hybrid cultivars have been developed. At Penn State, we screened a large collection of S. pimpinellifolium accessions and identified a few with strong LB resistance. One accession has been used for genetic and breeding studies. A trait-based marker analysis resulted in the identification of two locations on chromosomes 1 and 10 with strong effects on LB resistance. Based on a combination of graphical genotypes and plant phenotypes, an F₄ individual containing both resistance regions but with least genomic background from S. pimpinellifolium was used in a marker-assisted backcross program, which led to the development of NILs containing the two resistance regions in the cultivated tomato genetic background. Research is underway to verify, fine-map and characterize the resistance genes on chromosomes 1 and 10. We also are developing fresh-market and processing tomato lines with this new source of resistance. Furthermore, we have developed tomato lines with LB resistance conferred by Ph-3 and Ph-2, and efforts are underway to pyramid Ph-3 and Ph-2 with the new resistance genes. Regarding fruit LYC content, previously we identified a new source of high fruit LYC content in S. pimpinellifolium, which has been used to develop various filial (including RILs) and backcross populations (including NILs). These populations were used to identify and map QTLs contributing to high fruit LYC content. Specifically, we have focused on two major QTLs on chromosomes 12 (lyc12) and 7 (lyc7), which have been fine-mapped. For example, lyc12 has been located within 1-2 cM, and NILs containing this QTL has been developed. Simultaneously, the high LYC trait has been incorporated into Penn State tomato breeding germplasm and have developed fresh market and processing tomato breeding lines with exceptionally high fruit LYC content. A summary of the breeding lines developed at Penn State, which are available for commercial hybrid production, is presented.