Survival, Dispersal, and Primary Infection Site for Cercospora beticola in Sugar Beet

Abstract

Cercospora beticola survives as stromata in infected crop residue. Spores produced on these survival structures serve as primary inoculum during the next cropping season. This study was conducted to determine how long C. beticola can survive at different soil depths, the mechanism of inoculum dispersal, and the primary infection site in sugar beet. Longevity of C. beticola was studied over a 3-year period under field conditions at Fargo, ND. C. beticola-infected leaves were placed at depths of 0, 10, and 20 cm and retrieved after 10, 22, and 34 months. Survival of C. beticola inoculum declined with time and soil depth. Inoculum left on the soil surface, 0 cm in depth, survived the longest (22 months) compared with that buried at 10 cm (10 months) and 20 cm (10 months). C. beticola dispersal from the primary source of inoculum was studied in the field for three growing seasons. Sugar beet plants were surrounded with plastic cages with and without ground cover, or exposed with and without ground cover. Significantly higher disease severity was observed on exposed plants than caged plants with or without ground cover, suggesting that wind was the major dispersal factor for C. beticola inoculum. The primary infection site by C. beticola was determined in a greenhouse study. Leaves, roots, and stems of healthy sugar beet plants were inoculated with C. beticola. Cercospora leaf spot symptoms were observed only on plants that were leaf inoculated, suggesting that the leaf was the primary infection site for C. beticola.

Genetic structure of Cercospora beticola populations on Beta vulgaris in New York and Hawaii

“…Survival of C. beticola inoculum on plant debris within soil has been reported in many studies to be at least 10 months 35 to a maximum of three years 36 , depending on the climatic conditions. Planting sugar beet seed in infested soil was reported to result in infection of cotyledons and young seedlings 33 .…”

Challenges and Prospects for Building Resilient Disease Management Strategies and Tactics for the New York Table Beet Industry

“…In the mid-western USA, C. beticola survives as stromata and mycelia in infested sugar beet crop residue for up to 22 months when on the soil surface but survival time is significantly reduced to 10 months when buried at depths of 10 and 20 cm [60]. Therefore, for CLS management, the burial of crop residue after harvest and a rotation of at least three years between susceptible crops such as processing spinach (also grown in western New York) may be beneficial.…”

Cercospora Leaf Spot Disease of Sugar Beet

“…Although of minor importance, initial inocula can also originate from infested seed, conidia, or stromata from other host plants (Khan et al 2008;Franc 2010). Inoculum potential and weather conditions are determining factors in the initiation of cercospora leaf spot epidemic.…”