Yield Losses to Iceberg Lettuce Due to Corky Root Caused byRhizomonas suberifaciens

Effect of temperature on corky root disease of lettuce and growth of the pathogenRhizomonas suberifaciens

“…Four micropiot experiments were conducted in the spring of 1989 and 1990 and in the fall of 1988 and 1989 as described previously (11). Microplots were either infested with R. suberifaciens strain CA1 (5 X 108 cfu/m 2 ) or left uninfested (11).…”

“…As described previously (11) five plants per plot were uprooted every 8 days starting from 15 or 30 days after planting in the fall and spring, respectively. The microplots were sampled 10 times in each experiment.…”

“…However, average seasonal temperatures were not well correlated with disease (11). In vitro, the bacterium appears to grow most rapidly at relatively high temperatures (17).…”

“…The disease is generally more severe in areas with subtropical or mediterranean climates, such as Florida (3), California (14), Italy (4), and Queensland (16) than in cooler regions such as Northern Europe (15) and the northern states of the U.S.A (13). Within the same geographical region, corky root is generally more severe in summer and fall crops than in spring crops (11,12) with the exception of New York, where corky root was more common in spring and fall than in the summer (5). However, the symptoms seen may have been confused with those of excessive ammonia (12) which is prevalent in cool, wet springs.…”

“…Losses due to corky root ranged from 34 to 92% in both California and Florida, depending on the season (3,11), with more severe disease in warmer seasons.…”