Isolation, Purification, and Biological Activity of a Phytotoxin Produced by Stemphylium solani

Abstract

Stemphylium solani, the causal agent of leaf blight of garlic (Allium sativum), produced phytotoxic metabolites in culture. A non-host-specific phytotoxin from culture filtrate of S. solani isolate DY-5, named SS-toxin, was extracted by ethyl acetate, isolated by bioassay-guided thin layer chromatography on silica gel, and purified by preparative liquid chromatography. SS-toxin produced necrotic lesions on detached garlic leaves, similar to that caused by S. solani. When wounded leaves were each treated with a 10-μl droplet of toxin, Changbanpo, a garlic cultivar susceptible to leaf blight, showed necrotic lesions at 11 μg/ml toxin, while a resistant cultivar, Qingganruanye, showed symptoms at 44 μg/ml. The effective doses causing 50% inhibition (EC50 values) of root growth and shoot elongation of the susceptible cultivar were 64.9 and 178.5 μg/ml, respectively. The SS-toxin significantly inhibited mitotic activity of root tip cells of the susceptible cultivar from 22 μg/ml and higher causing an abnormally high frequency of cells in interphase. Concentrations over 50 μg/ml of SS-toxin were found to be significantly toxic to total chlorophyll, both chlorophyll a and b, of the susceptible cultivar. The plasma membrane–cell wall interface, nuclear membranes, mitochondria, and chloroplasts were affected by SS-toxin in susceptible leaf cells. This is the first report of the purification and testing of a phytotoxin produced by S. solani.

Partial Resistance of Carrot to Alternaria dauci Correlates with In Vitro Cultured Carrot Cell Resistance to Fungal Exudates

“…The introduction of a wheat oxalate oxidase gene in tomato reduced disease symptoms in plants infected by Botrytis cinerea or Sclerotinia sclerotiorum , two necrotrophic fungi producing oxalic acid, a toxin that is considered to be an important factor determining pathogenicity. In the same line of thought, a correlation between partial resistance and toxin resistance has been found in two other plant-necrotrophic fungal pathogen interactions: Allium sativum - Stemphylium solani [22] and Hevea brasiliensis - Corynespora cassiicola (V. Pujade-Renaud, personnal communication). To our knowledge, the discovery of partial resistance mechanisms based on QRLs and linked to a pathogen-produced toxin has never been published.…”

“…Conversely, fungal toxins from Rhizoctonia solani and Sarocladium oryzae were shown to inhibit defense-related compounds in rice cell suspensions [51] . A link between plant pathogen partial resistance and toxin resistance has been suggested in the Allium sativum – Stemphylium solani pathosystem [22] but, to our knowledge, the present study is the first example where in vitro cell viability and embryogenic ability were used as an indicator of fungal toxin plant resistance. In our study, we adapted cell viability measurement methods based on measuring esterase activity using FDA as a substrate to carrot cell suspension cultures.…”

“…This bias seems to be absent in papers investigating the activity of other phytotoxins. For example, in the Stemphylium solani - Allium sativum pathosystem [22] , necrotic lesions were observed on leaves of a susceptible garlic genotype using a purified toxin (SS-toxin) at 11 µg mL −1 concentration from a 21 day fungal culture filtrate. In the present study, no phytotoxic reactions were observed using 10 µM zinniol (3 µg mL −1 ).…”

Toxins Produced by Valsa mali var. mali and Their Relationship with Pathogenicity

“…Given defined host-pathogen interactions, specific toxins were employed to promote symptoms [20,21,22]. Therefore, it is of great significance to elucidate the toxin arsenal and its bioactivities, as well as the relationship between toxins and fungal pathogenicity.…”

“…Previous research indicated that the enzymes and toxins produced by fungal pathogens during infection contributed largely to disease development [ 9 , 11 ]. Given defined host-pathogen interactions, specific toxins were employed to promote symptoms [ 20 , 21 , 22 ]. Therefore, it is of great significance to elucidate the toxin arsenal and its bioactivities, as well as the relationship between toxins and fungal pathogenicity.…”