Root infection of sugar beet by Cercospora beticola in a climate chamber and in the field

Abstract

Sugar beet root infection by Cercospora beticola, the causal agent of Cercospora leaf spot (CLS), was studied in a climate chamber and in the field. In the climate chamber, root incubation of susceptible seedlings with a conidial suspension resulted in disease incidences that were significantly different for two sugar beet cultivars (Auris: 0.8 ± 0.14 and A00170: 0.5 ± 0.18; P < 0.05) with regard to the control treatment 35 days after root incubation in a standard potting soil-fine river sand mixture. In a field trial with susceptible cv. Savannah with soil-incorporated CLS-infested leaf material, disease developed four weeks earlier in the infested plots than in the control plots. The probability that disease develops in the field was significantly higher for the infested than for the control plots (P < 0.05). Symptomless plants from infested field plots transferred to the glasshouse to induce leaf spot symptoms showed a significantly higher probability to induce symptom development (0.4 ± 0.08), than plants from control plots (0.02 ± 0.02) (P < 0.05) 14 days after transfer. This probability was significantly higher than for plants that remained in three of the infested field plots (0.2 ± 0.04; 0.2 ± 0.05 and 0.2 ± 0.04 respectively), except for one infested field plot (0.4 ± 0.05) on July 5. We conclude that C. beticola is able to infect sugar beet seedlings through their roots and that latent CLS infections in sugar beet lead to symptom development at high temperatures (>20°C) and high relative humidity (>95%) in our climate chamber or after canopy closure in the field. Quantification of root infection and long term survival in soil is necessary to assess its contribution to the epidemiology and life cycle of Cercospora beticola. Cultural methods such as a wider crop rotation, management of crop debris and ploughing systems may provide control strategies alternative to or reducing fungicide input.

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

“…For example, no common multilocus genotypes were detected in C. beticola populations sampled from the same fields between years [52]. This finding was also supported by the identification of only C. chenopodii from CLS lesions on a common The predominant, primary source of inoculum for CLS epidemics in New York table beet fields is largely unknown, but epidemics often begin as random foci [41,42]. Secondary spread resulting in foci expansion within a field begins when conidia are dispersed through windborne rain splash, reach the surface of the leaves, and penetrate the leaves through stomata [38].…”

“…In a red table beet cultivar CLS lesions have a red to purple margin, but in yellow and white cultivars the margin color is tan to brown (Figure 3a; [39,40]). Infection of roots [41,42] and crown lesions have been associated rarely with infection by C. beticola in sugar beet [43] but not reported on table beet [39]. The presence of pseudostromata (a thickened mycelial mass that gives rise to conidia) within the lesions that may be observed with a hand lens in the field is diagnostic [38].…”

“…The disease also causes significant losses to the sugar beet industry across the USA, estimated at approximately $45 million annually, due to reduced yield and fungicide application costs [44,45]. The predominant, primary source of inoculum for CLS epidemics in New York table beet fields is largely unknown, but epidemics often begin as random foci [41,42]. Secondary spread resulting in foci expansion within a field begins when conidia are dispersed through windborne rain splash, reach the surface of the leaves, and penetrate the leaves through stomata [38].…”

Spatial pattern of Cercospora leaf spot of sugar beet in fields in long- and recently-established areas

“…Pseudostromata of CLS surviving in the soil are capable of infecting sugar beet plants in later years (Nagel, 1938). First infections may occur on the lower leaves by splash dispersal of inoculum from the soil (Nagel, 1938), or through the roots (Vereijssen et al, 2004(Vereijssen et al, , 2005. Later, infections take place on higher (younger) leaves both by autoinfection, e.g.…”

Dynamics of spread and control of cercospora (Cercospora beticola Sacc.) and ramularia (Ramularia beticola Fautrey and F.Lamb.) leaf spot in sugar beet crops

“…The climate warming, shorter crop rotations, increasing soil compaction favour the occurrence of fungal diseases. To prevent the spread of fungal diseases it is of major importance to employ adequate crop and soil management practices such as optimal sugar beet share in a crop rotation, suitable pre-crops, good soil structure, timely and well-balanced fertilization, early sowing, choice of disease-resistant cultivars, destruction of disease causal agents and intermediate hosts (Vereijssen et al, 2005;Gaurilčikienė et al, 2006).…”