Impact of Continuous Cropping of Lettuce on the Disease Dynamics of Bottom Rot and Genotypic Diversity of Rhizoctonia solani AG 1-IB

Abstract

The impact of continuous cropping of lettuce on the disease dynamics of bottom rot and genotypic diversity of the causal pathogen Rhizoctonia solani AG 1-IB was studied over 3 years with two crops per year within a field naturally infested with R. solani the pathogen. This field had not had lettuce cultivated in it for 7 years. The disease incidence (DI) and disease severity (DS) were assessed at each harvest and mapped. Surprisingly, a high DI was already observed in the first crop of year one of this field study. In addition, the pathogen was also found to be evenly distributed. Severely infected plants occurred mainly in patches, and the position varied between crops. A significant increase in DS was already observed in the second year, and both temperature conditions and continuous cropping influenced the DS on average over time. Rhizoctonia isolates were randomly collected from the first crop in 1999 and the sixth crop in 2001. The genotypic diversity within the subgroup of R. solani AG 1-IB was analysed by BOX-PCR genomic fingerprinting and the aggressiveness of isolates by bioassay. The fingerprints revealed a high level of genotypic diversity within the AG 1-IB field population. However, continuous cropping was found not to have an impact on genotypic diversity and aggressiveness.

Rhizoctonia solani and Bacterial Inoculants Stimulate Root Exudation of Antifungal Compounds in Lettuce in a Soil-Type Specific Manner

“…The use of resistant cultivars, application of chemical pesticides, as well as crop rotation [2] represent approaches aimed to reduce the incidence and severity of pathogen attacks [1,3]. However, particularly for soil-borne pathogenic fungi with a wide host spectrum, such as Rhizoctonia, Fusarium, or Pythium, the development of efficient control strategies remains a highly challenging task.…”

Assessing genetic diversity in the web blight pathogen Thanatephorus cucumeris (anamorph = Rhizoctonia solani) subgroups AG-1-IE and AG-1-IF with molecular markers

“…However, no attempts have been made to determine the extent of intra-population variability in R. solani AG-1-IE and AG-1-IF. DNA fingerprints generated by dominant neutral molecular markers have been employed for initial assessment of genetic diversity and population structure for AG-2, AG-3, AG-4, AG-8, AG-9 and AG-1-IB (Ceresini et al 2002;Duncan et al 1993;Grosch et al 2011;Justesen et al 2003;Meinhardt et al 2002;Yang et al 1995). A comprehensive review of molecular methods used for characterization and classification of Rhizoctonia spp.…”

Control of lettuce bottom rot by isolates of Trichoderma spp

“…Na primeira fase dos experimentos in vivo, foram avaliados o número e a massa seca de plântulas de alface da cultivar White Boston. Na segunda fase, 12 foram avaliados com relação à sua capacidade de controlar a queima da saia em dois experimentos repetidos, e também tiveram suas espécies identificadas. A maioria dos isolados de Trichoderma spp.…”

“…Losses of up to 70% have been reported for cultures produced on infested soils under conditions of high humidity and temperatures between 25 and 27 o C during the cycle of the lettuce crop (23). The incidence of this disease is related to the amount of pathogen inocula present on the soil (12), and the control of R. solani is difficult because it can survive for a long time on the soil associated with organic matter or as micro-sclerotia (1).…”