Abstract
Rhizoctonia solani is one of the most destructive pathogens causing foot rot disease on tomato. In this study, the molecular and cellular changes of a partially resistant (Sunny 6066) and a susceptible (Rio Grande) tomato cultivar after infection with necrotrophic soil-borne fungus R. solani were compared. The expression of defense-related genes such as chitinase (LOC544149) and peroxidase (CEVI-1) in infected tomato cultivars was investigated using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). This method revealed elevated levels of expression for both genes in the partially resistant cultivar compared to the susceptible cultivar. One of the most prominent facets of basal plant defense responses is the formation of physical barriers at sites of attempted fungal penetration. These structures are produced around the sites of potential pathogen ingress to prevent pathogen progress in plant tissues. We investigated formation of lignin, as one of the most important structural barriers affecting plant resistance, using thioglycolic acid assay. A correlation was found between lignification and higher level of resistance in Sunny 6066 compared to Rio Grande cultivar. These findings suggest the involvement of chitinase, peroxidase, and lignin formation in defense responses of tomato plants against R. solani as a destructive pathogen.
Highlights
Tomato (Lycopersicon esculentum) is one of the most important vegetables in the world which suffers from various fungal diseases [1, 2]
The level of lignin detected in partially resistant sunny plants (Figure 1) using thioglycoli acid (TGA) assay was significantly higher than that of susceptible Rio Grande plants at all time points after challenge inoculation with R. solani (Figure 2)
We demonstrated that basal resistance to R. solani in Sunny cultivar was correlated with higher levels of lignin formation in this cultivar compared to Rio Grande as a susceptible tomato cultivar (Figures 1 and 2)
Summary
Tomato (Lycopersicon esculentum) is one of the most important vegetables in the world which suffers from various fungal diseases [1, 2]. Rhizoctonia solani is a species complex composed of several anastomosis groups (AGs). This pathogen can survive in soil within diseased plant material as mycelia or sclerotia during unfavorable environmental conditions for several years. The pathogen is transported in infested soil or through movement of diseased plant tissues. Usually R. solani has asexual reproduction and exists primarily as vegetative mycelium and/or sclerotia. Formation of basidiospores on diseased host plants in nature is rarely observed. In favorable environmental conditions, following infection of the host plant by R. solani, sexual spores are formed on specialized structures called basidia. The hyphae produced by germinating spores will fuse or anastamose with each other to form new hyphae with a mixture of different types of nuclei [3]
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