Influence of nitrogen sources on growth and mycotoxin production by isolates of Pyrenophora tritici-repentis from wheat

The fungus Pyrenophora tritici-repentis (Died.) Drechs. infects the leaves and kernels of wheat, causing tan spot and red smudge, respectively. Isolates of P. tritici-repentis have been reported to be both phytopathogenic and mycotoxigenic. This research investigates the influence of nitrogen sources on growth and production of mycotoxins by eight different isolates of P. tritici-repentis. A synthetic agar medium (SAM) was used with different nitrogen sources, both inorganic [(NH4Cl, NH4NO3 and (NH4)2SO4)] and organic (l-alanine, l-histidine, and l-lysine), at a concentration of 37.5 mmol L− 1. Individual isolates exhibited different growth rates that varied according to the nitrogen source added to the medium. The choice of nitrogen source also had a major effect on production of the mycotoxins emodin, catenarin and islandicin. The highest concentrations of emodin, 54.40 ± 4.46 μg g− 1, 43.07 ± 23.39 μg g− 1 and 28.91 ± 4.64 μg g− 1 of growth medium, were produced on the complex medium (V8-potato dextrose agar) by the isolates Alg-H2, 331-2 and TS93-71B, respectively. A relatively high concentration of emodin also was produced by isolates Az35-5 (28.29 ± 4.71 μg g− 1 of medium) and TS93-71B (27.03 ± 4.09 μg g− 1 of medium) on synthetic medium supplemented with l-alanine. The highest concentrations of catenarin (174.54 ± 14.46 μg g− 1 and 104.87 ± 6.13 μg g− 1 of medium) were recorded for isolates TS93-71B and Alg-H2 on synthetic medium supplemented with l-alanine and NH4Cl, respectively. The highest concentration of islandicin (4.64 ± 0.36 μg g− 1 medium) was observed for isolate 331-2 in the presence of l-lysine. There was not a close relationship between mycelial growth and mycotoxin production by the fungal isolates. This is the first report on the influence of nitrogen sources on the production of mycotoxins by P. tritici-repentis.