Transformation of Botrytis cinerea with the nitrate reductase gene (niaD) shows a high frequency of homologous recombination.

The nitrate reductase (niaD) gene was isolated from the phytopathogenic ascomycete Botrytis cinerea using a probe obtained by a polymerase chain reaction (PCR) with degenerate oligonucleotides corresponding to domains conserved among three fungal nitrate reductases. The B. cinerea niaD gene encodes a predicted protein of 907 amino acids and contains no intron. Nitrate reductase-deficient mutants of B. cinerea have been isolated. One of them was transformed with the niaD genes of Fusarium oxysporum f.sp. melonis and B. cinerea. The transformation was always ectopic when the donor DNA originated from F. oxysporum, but there was 80% gene replacement when the donor DNA originated from B. cinerea.