(Jul. 2006) The development and impact of Verticillium wilt on post-harvest quality in commercial lettuce fields naturally infested with V. dahliae.

The development and impact of Verticillium wilt on post-harvest quality in commercial lettuce fields naturally infested with V. dahliae.

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Jul. 2006

Vallad, G., Qin, Q., Hayes, R., and Subbarao, K.

Phytopathology

Verticillium wilt of lettuce, caused by the soilborne pathogen V. dahliae, poses a serious threat to California¿s $1.5 billion lettuce industry, as the acreage affected by the disease increases steadily in coastal production areas. Knowledge of disease development and its impact on post-harvest (PH) quality would help growers better manage afflicted fields. Trials were established in commercial lettuce fields in 2004 and 2005. Periodic sampling to monitor disease in several crisphead varieties found that root symptoms developed quickly at the latter stage of heading, followed by the onset of foliar symptoms as the crop reached harvest maturity. The impact of V. dahliae on PH quality was based on the proportion of marketable lettuce heads per case that retained marketability following 1, 2 and 3 weeks of refrigerated storage at a commercial facility. Across three field trials, the average disease incidence and PH quality ranged from 0.0 to 95.0% and 70.8 to 100.0% across all lettuce types and varieties. Regression analysis detected no significant relationship between disease incidence and PH quality across all varieties tested (R² = 0.0016, P (0.05 = 0.6989), or within horticultural lettuce types; even though V. dahliae was recovered from 34% of the plants harvested. These findings suggest that growers can harvest lettuce from an infested field before foliar symptoms develop with negligible impact on PH quality by V. dahliae.