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 D
10 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 10
6 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 postinoculation.
