ISHS Acta Horticulturae 695: I International Symposium on Tomato Diseases
PERSPECTIVES ON TOMATO DISEASE RESISTANCE BREEDING: PAST, PRESENT, AND FUTURE |
| Author: | J.W. Scott |
| Keywords: | Lycopersicon esculentum, vertical genes, horizontal genes, linkage, quantitative trait loci, variety, hybrid, molecular markers |
| Abstract:
Multiple-disease-resistant varieties have become prevalent as a result of disease resistance breeding that began about 70 years ago. Most of the resistances are conferred by single dominant, vertical genes that fit well with hybrid breeding that is common in today’s world. Varietal progress has been most evident with soil-borne fungal diseases such as; Fusarium wilt (races 1, 2, and more recently 3), Verticillium wilt (race 1), Alternaria stem canker, and to some degree with Fusarium crown rot. Varieties with major gene resistance to foliar fungal pathogens such as gray leafspot and Cladosporium leaf mold (two genes usually used) are common, while a few varieties have resistance to some races of late blight. Single dominant viral resistance genes are used in varieties resistant to tomato mosaic virus (ToMV) and more recently spotted wilt virus. Tomato yellow leaf curl virus (TYLCV) resistant varieties have recently emerged with one or more sometimes undescribed major genes conferring resistance. Varieties with bacterial resistance are rare with the exception of those with resistance to bacterial speck (Pto gene). Breeders have had much less success with quantitative or horizontal genetic resistances. Varieties with such resistances are rare, although successful varieties often have less susceptibility to various diseases than other varieties. Much work in the last couple of decades has focused on developing molecular markers linked to resistance genes and these are most useful where disease screening is cumbersome. Marker assisted selection will play a larger role in the future and will be an asset in working with quantitative resistance systems. Many disease resistance genes are clustered in the genome. As more resistance genes are added to single varieties, future issues for resistance breeding will involve unfavorable repulsion linkages between clustered resistance loci and unforeseen actions of the resistance genes themselves. An example of the latter between tomato mottle virus infection and ToMV resistance is described. | |
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