Identification and mapping of new tomato late blight resistance genes in an accession of the wild tomato species, Solanum pimpinellifolium
Open Access
- Author:
- Merk, Heather Lynn
- Graduate Program:
- Genetics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 24, 2010
- Committee Members:
- Majid R Foolad, Dissertation Advisor/Co-Advisor
Majid R Foolad, Committee Member
Mark Guiltinan, Committee Chair/Co-Chair
Surinder Chopra, Committee Member
Beth Krueger Gugino, Committee Member
David Robert Huff, Committee Member
Seogchan Kang, Committee Member - Keywords:
- Phytophthora infestans
late blight
tomato
plant breeding - Abstract:
- Late blight (LB), caused by the oomycete Phytophthora infestans (Mont.) de Bary, is one of the most potentially destructive and devastating diseases of tomato. Previously, LB was relatively well-controlled through heavy fungicide application, cultural practices, and growing semi-resistant potato cultivars. However, there have never been tomato cultivars with adequate levels of resistance and newer, more aggressive isolates of P. infestans have been reported. To regain adequate control of LB, new sources of genetic resistance in wild species are being identified and characterized. An LB outbreak in summer 2004 in the northeastern U.S. with considerable impact on The Pennsylvania State University’s tomato breeding program prompted research to identify new sources of LB resistance with the intent of transferring the resistance to breeding material to provide adequate protection against future infections. Previous field, high tunnel, greenhouse and growth chamber evaluations of approximately 70 S. pimpinellifolium accessions led to identification of several with LB resistance. One of these highly resistant accessions, PSLP153, was selected for further evaluation and genetic characterization as described in this Ph.D. thesis. PSLP153 was hybridized with NCEBR-2, a S. lycopersicum breeding line and F1 and F2 populations were previously developed. As an initial step in genetic characterization of the LB resistance, a large F2 population (n=986) was grown and evaluated for LB resistance. Heritability (h2) for LB resistance conferred by PSLP153 was estimated to be 0.68 and 0.76 based on disease severity scores of selected resistant and susceptible F2 individuals and their self (F3) progeny using the parent-progeny method in two replicated experiments. The moderately-high h2 values indicate that reasonable selection progress for increasing LB resistance can be achieved. As a result, breeding efforts have been undertaken to introduce the LB resistance conferred by PSLP153 to material in The Pennsylvania State University tomato breeding program. Selected resistant and susceptible F2 individuals were genotyped with 153 molecular markers to develop a genetic map and for trait-based analysis (TBA) to identify regions of the tomato genome associated with LB resistance. Employing TBA, a 23.0 cM region on the long arm of chromosome 1 and a region at the distal end of chromosome 10 were identified as associated with LB resistance. This was the first research to identify LB resistance on chromosome 1. The LB resistance region on chromosome 10 may coincide with a previously identified tomato LB resistance gene, Ph-2. Two further filial populations (F3 and F4), four backcross populations (F4BC1, F4BC2, F4BC3, F4BC4) and an F4BC3S1 population were developed with objectives of confirming the resistance regions, estimating LB resistance gene effects, and making progress toward developing near isogenic lines to delineate and fine map the LB resistance genes. The chromosome 10 region was confirmed in F4BC4, and F4BC3S1 populations. QTL analysis in the F4BC3S1 generation indicated that the region on chromosome 10 explained 50.7% of the phenotypic variation of LB response. In addition, this region had additive genetic effects of 35.7% and dominant genetic effects of 5.2%. The large effect of this region suggests that it can be extremely useful for breeding purposes. To fully exploit the utility of this LB resistance for use in marker-assisted selection, the region must be further delineated in a large population containing additional DNA markers. Unfortunately, the region on chromosome 1 associated with LB resistance could not be confirmed. Further experiments need to be conducted to recover the resistance. The eventual fine-mapping and possible cloning of these LB resistance genes will be useful to plant breeders for developing commercial cultivars with improved levels of LB resistance. Efforts to pyramid these genes with other LB resistance genes may provide more durable resistance against LB, which is a continual threat to the tomato industry worldwide.