Gr. Smith et al., EVIDENCE FOR THE INVOLVEMENT OF ASCOCHITINE IN PHOMA LEAFSPOT-WILT DISEASE OF CLEMATIS, Physiological and molecular plant pathology, 45(5), 1994, pp. 333-348
Ascochitine, a phytotoxic metabolite, was purified from cultures of Ph
oma clematidina and identified by H-1 and C-13 nuclear magnetic resona
nce spectroscopy and electron impact and chemical ionization mass spec
troscopy. This toxin-induced electrolyte leakage from leaf discs of Cl
ematis cultivars that were susceptible to fungal infection: while ther
e was no significant electrolyte leakage from leaf discs of the cultiv
ar most resistant to fungal infection. The level of ascochitine produc
tion in vitro by P. clematidina isolates was related to isolate virule
nce. The Fungal isolates could be characterized into two groups: (1) h
igh virulence, high ascochitine production, and (2) low virulence, low
ascochitine production. Ascochitine was isolated from P. clematidina-
infected leaf discs, indicating the toxin is produced in vivo. Leaf ti
ssues exposed to ascochitine solutions showed black flecking in propor
tion to the concentration of ascochitine. Scanning electron and light
microscopy of infected leaves indicated that the fungal hyphae were we
ll behind the necrotic zone in leaf spots, while transmission electron
and light microscopy suggested that mitochondria and chloroplasts wer
e the major organelles affected by ascochitine, although extensive cel
lular damage was evident. These observations suggest that ascochitine
may be involved in the pathogenesis of P. clematidina against Clematis
, by killing plant cells prior to hyphae ramification through the necr
otic tissue.