Effect of some isolates of Aspergillus niger on onion) Allium capa L. ( bulbs rot and its control by hot extract of ginger

Abstract

Pathogenicity test of 13 isolates of A.niger on onion bulbs revealed that all tested of onion cultivars, Texas Early Grano (TEG) , Early White Grano (EWG) and Red Baron (RB) , were susceptible to all tested isolates . However, the isolate 3 was the most distrutivars isolate that caused diagonal damage on bulbs that reached 4.29 cm . while the EWG was a highly effected cultivars by all isolates , the mean diagonal damage was 2.19 cm during of 4 weeks.Exudates of A.niger isolates also had the ability to rot bulbs and caused diagonal damage, the isolate 7 caused highly affected diagonal damage of 4.19 cm, while the cultivar RB was the most affected cultivar by all tested isolates,the diagonal damage mean of this cultivars was 2.17 cm . The isolate 3, among all tested isolates, was the most pathogenicity of all cultivars. Also the result of dipping of bulbs in a hot extract of ginger for 5 minutes showed decreasing in bulbs infection by blak rot rot . Isolate 3 had the ability to produce ochratoxin , aflatoxin B1 and aflatoxin B2 in the infected bulbs , the ochratoxin had the highest concentration in infected parts reaching to 1.129 mg.ml-1. The non-infected part of bulb, showed containing of ochratoxin, aflatoxin B1 and aflatoxin B2 at concentrations of 0.449 , 0.188 and 0.162 mg.ml-1 , respectively .