Tomato entries reported as early blight resistant were collected and evaluated under severe early blight infection in the warm rainy summer months of 1982-1985 in Mayagüez, Puerto Rico to identify sources with useful resistance in Puerto Rico. Of the common tomato lines, 84B 510-4 was the closest in resistance to the best wild tomato species, which are less susceptible to early blight than common tomatoes. Useful field resistance was found in the minority of cases, but one or more entries of L. esculentum f. cerasiforme, L. pimpinellifolium, L. esculentum X L. pimpinellifolium, and L. hirsutum var. typicum showed useful early blight resistance. Lowest disease ratings were found in varieties of L. hirsutum, which also showed the lowest yield. Better fruiting was found in L. pimpinellifolium although resistance levels were slightly less. Crosses of L. pimpinellifolium and L. hirsutum with useful early blight resistance to susceptible L. esculentum were followed in F1, F2, and F3 generations. Resistance appeared partially dominant from F1 disease ratings, and segregation in F2 suggested that many modifying genes both dominant and recessive were probably involved in conditioning early blight resistance. Generally, common tomatoes appear much more susceptible to early blight than wild species. To enlarge the pool of early blight resistence genes, F2 selection and progressive back crosses are suggested. Susceptible tomatoes were defoliated by early blight within one month after first flower during the warm rainy months; whereas, entries with useful resistance defoliated from 6 weeks to 2 months after the same stage.
Greenhouse Disease Screen Facilitates Breeding Resistance to Tomato Early Blight
