PRODUCTION OF SOLANAPYRONE A BY ALGERIAN ISOLATES OF ASCOCHYTA RABIEI AS THE CAUSE OF THE TOXICITY OF CULTURE FILTRATES TO CHICKPEA (CICER ARIETINUM) SEEDS AND SEEDLINGS

Abstract

Cultures, designated Ag1, Ag2 and Ag3, of a fungus resembling Ascochyta rabiei, Didymella rabiei (teleomorph), were isolated from blighted chickpea plants growing in three regions of Algeria. The isolates were shown to be the cause of the disease by fulfilling Koch’s postulates and were identified as A. rabiei by sequencing ribosomal DNA. When grown on a defined liquid medium, consisting of Czapek Dox nutrients and five cations, the filtrates inhibited germination of chickpea seed, and elongation of hypocotyls and radicles of seedlings. All three isolates produced the phytotoxin solanapyrone A in culture and maximal concentrations in the culture filtrates, recorded after incubation for 14 days were 15.1 ± 1.29 µg/ml, 8.4 ± 1.19 µg/ml and 7.4 ± 0.85 mg/ml for Ag 1 Ag2 and Ag3, respectively. ED50 values were 7.15 ± 1.77, 5.87 ± 1.40 and 3.60 ± 1.47 µg solanapyrone A/ml for inhibition of germination, hypocotyl elongation and radicle elongation, respectively. Concentrations of solanapyrone A in dilutions of culture filtrates that caused 50% inhibition of these three parameters were sufficient to explain their inhibitory effects in all cases except the inhibition of germination and hypocotyl elongation by filtrates of Ag2 and Ag3. Here they were only 65% and 58% of the amount required to cause the inhibition of germination, respectively and 60% and 63% of the amount required to inhibit hypocotyl elongation, respectively, suggesting that other factors may be involved.