ISHS Acta Horticulturae 695: I International Symposium on Tomato Diseases
BREEDING TOMATOES FOR RESISTANCE TO BACTERIAL WILT, A GLOBAL VIEW |
| Authors: | J.W. Scott, J.F. Wang, P.M. Hanson |
| Keywords: | fruit size, Lycopersicon esculentum, Ralstonia solanacearum, inheritance |
| Abstract:
Developing horticulturally acceptable tomato varieties with resistance to bacterial wilt (BW) has been difficult as evidenced by the lack of such varieties in many growing regions where the disease is a major constraint. The pathogen harbors tremendous genetic diversity and attacks a wide range of plant families, often an indicator of a pathogen that is difficult to control genetically. Resistance is complex being controlled quantitatively and strongly influenced by environmental conditions such as soil temperature, pH, and moisture. Environmental effects also hinder effective selection in segregating populations as there are sometimes symptomatic plants in resistant entries and symptomless plants in susceptible entries. BW resistance originated from wild tomato, particularly L. esculentum var. cerasiforme and L. pimpinellifolium and most tomato resistance sources tend to be small-fruited. Incorporation of resistance into large-fruited varieties has been a major challenge to breeders for many years, suggesting linkage between small fruit size and resistance. Recently, the linkage between small fruit and BW resistance may have been broken in the senior author’s laboratory. A worldwide evaluation of 31 genotypes derived from at least 14 resistance sources in 11 countries identified seven genotypes that had over 90% overall survival. Three sources were from Hawaii, three were from the Philippines, and the other was apparently from North Carolina but it had a Hawaiian-like phenotype. These may be useful in developing varieties with broad adaptation, but other more specific sources of resistance may prove useful for specific regions. Some molecular marker studies have identified genomic regions associated with resistance from some resistance sources, including Hawaii 7996, the most resistant genotype in the worldwide study. Different results obtained from several inheritance and molecular mapping studies indicated the possibility of a single major gene and several minor genes conditioning the overall resistance. Marker assisted selection may improve breeding efficiency in the future. | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
