JOURNAL OF CULTURE COLLECTIONS
Volume 6, 2008-2009, pp. 85-96
ASPOROGENIC MUTANTS OF ALTERNARIA CASSIAE GENERATED BY X-RAY IRRADIATION
Olubukola O. Babalola1
Department of Plant Sciences, Weizmann Institute of Science, Rehovot IL-76100, Israel
1On leave from the Department of Microbiology, Olabisi Onabanjo University, PMB 2002 Ago-Iwoye, Ogun State, Nigeria
*Corresponding author, e-mail: olubukola_babalola@yahoo.com
Summary
The prevention of sporulation is an important factor in precluding the spread of transgenic biocontrol agents beyond desired limits; asporogenic deletion mutants could prevent such spread. Alternaria cassiae is a biological control agent for controlling sicklepod (Cassia obtusifolia) and coffee senna (Cassia occidentalis). The NEP1 transformed fungus is more virulent than the parent. A. cassiae forms microcolonies on 0.9 g/l sodium deoxycholate plates. The spores have a D10 value of 50,000 rads when subjected to X-ray beams. Five putative mutants were achieved and 3 proved to revert. Mutants xAlt541 and xAlt524 are stable with no spore-forming capability. The xAlt541 mutant grew more slowly (4.63 cm) on yeast starch agar than xAlt524 (5.94 cm) and the parent (5.77 cm). The mutant xAlt524 lacks aerial hyphae, pigmentation, and spore production. The mycelia of the parent fungus have rosy brown to peach puff pigment after 5 days of growth on medium plus 1 g/l tyrosine, feldspar pigment on medium plus 1 g/l phenylalanine and appear slate gray in the absence of an amino acid supplement. The xAlt524 and xAlt541 mutants had cream and dark salmon color, respectively. At 2.5 x 106 propagules/ml, mutants’ xAlt541 (2.17a ± 0.31) and xAlt524 (2.0a ± 0.26) damage severity was not statistically different from that of the parent type AltNEP1 (2.5a ± 0.22) by 5 days post-inoculation.