Gibberellin and auxin production by plant root-fungi and their biosynthesis under salinity-calcium interaction

Abstract

Rhizosphere and rhizoplane of fababean (Vicia faba), melochia (Corchorus olitorius), sesame (Sesamum indicum) and soyabean (Glycine max) plants are inhabited with fungi, mostly Aspergillus flavus, A. niger, Fusarium oxysporum, Penicillium corylophilum, P. cyclopium, P. funiculosum and Rhizopus stolonifer. All fungal species have the ability to produce gibberellin (GA) but F. oxysporum was found to produce both GA and indole-acetic acid (IAA). The optimum period for GA and IAA production by F. oxysporum was 10 days in the mycelium and 15 days in the filtrate at 28°C. The contents of GA and IAA were significantly increased at 0.5 and 1% NaCl after 5 days, but they were lowered at 4% (700 mM) NaCl. Cytochrome P-450 was significantly increased under salt stress at 0.5-7% NaCl. Calcium decreased NaCl stress on F. oxysporum by significant elevating GA biosynthesis at 40 mM Ca2+/700 mM Na+. GA at 10 µM and Ca2+ at 10 mM enhanced the germination of seeds under 175 mM Na+.