Production of Ascochyta rabiei lacking solanapyrone A toxin production.

Ascochyta rabiei, agent of Ascochyta blight of chickpea produces three toxins, Solanapyrones A, B and C of which solanapyrone A is the most toxic. All isolates of the fungus so far examined produce at least one of the Solanapyrone toxins, usually Solanapyrone A. The universality of solanapyrone production argues strongly for the importance of the toxins in virulence or pathogenicity. However, further evidence for this awaits the development of mutants lacking toxin production. Generation and isolation of fungal mutants defective in pathogenicity has been very useful for understanding the genetic and enzymatic processes responsible for infectivity in a number of pathosystems. Numerous tools have been used to transform plants and micro-organisms but the most widely micro-organism employed is Agrobacterium tumefaciens. In the present experiments, two strains of A. tumefaciens, AGL1 and LBA1126, harbouring two different plasmids, both encoding a gene for hygromycin resistance in the T-DNA region were used to transform isolate Tk21 of A. rabiei. The transformation of Ascochyta rabiei, gave rise to 498 colonies which grew on media supplemented with the selective agent; hygromycin B. The 30 sporulated transformants produced solanapyrone A on the specific medium at different rates. Solanapyrone A production, as demonstrated by the absorption of light at 327 nm, varied from 2.11 microg/ml to 4.32 microg/ml, representing a reduction of 74.11% to 46.99% in comparison with the wild type (8.15 microg/ml).