Resistance tests and genetic resources for breeding fusarium root rot-resistant lettuce [Lactuca sativa]

Developing a method for testing the resistance of lettuce to the root rot of lettuce (RRL), we evaluated the resistance of genetic resources of lettuce gathered in Japan and from abroad to breed a new cultivar resistant to RRL. Seeds were sown in the mixture of nursery soil of pathogenic fungus-cultured bran and vermiculite (bran:vermiculite = 1 : 1.5, v/v) and commercial horticultural nursery soil (mixing ratio: 1/10 - 1/40, w/w), that included more than 10E8 cells of Fusarium oxysporum f. sp. lactucae per ml. The seeded plug trays were kept for 30 to 40 days at 15 deg C to 35 deg C (the mean of 25 deg C) in a glasshouse under natural daylength. After that, the seeding were indexed for resistance to RRL. Resistance tests were conducted on 78 breeds of genetic resources in Japan, and 77 breeds which were mainly crisp-type lettuce gathered from abroad between 1999 and 2000. There were large differences in disease severity among genetic resources. Among those in Japan, many of the 'Vanguard' type-cultivars (types) possessed resistance to isolate SB1-1 (Race 1) and 'V Lettuce' were highly resistance to isolate SB1-1, whereas 'Empire' types were highly susceptible. However, many 'Vanguard' types and 'V Lettuce' were highly susceptible to isolate F9501 (Race 2). 'Kikugawa 102' and 'Blizzard' possessed high resistance to isolate F9501, but they were susceptible to SB1-1. Compared to the genetic resources gathered in Japan, a larger number of those from abroad showed resistance. 'Batavia Tezier' and 'Batavia Blonde de Paris' had the resistance to both SB1-1 and F9501.