Modulation of Sporulation of Alternaria Tagetica by Carbon Dioxide1

A mutant ofAlternaria tagetica with altered regulation of sporulation was obtained. Wildtype strains require light to sporulate whereas the mutant sporulated in the absence of light. Sporulation of the mutant was unaffected by culture plate sealing which inhibited the wildtype 99-100%. Absorption of CO2 from the atmosphere within the plates via KOH counteracted wildtype inhibition by plate sealing and induced light-independent sporulation in wildtype strains of A. tagetica, as well as in A. carthami, A. macrospora, A. porri, and A. cucumerina, species which typically require light for sporulation. Continuous fluorescent light inhibited sporulation for all wildtype Alternaria species tested at both 28 C and 20 C, but sporulation was induced under the same light regime when fungi were grown 3 days at 28 C followed by 3 days at 20 C. The identical temperature drop induced sporulation in the dark in A. tagetica, A. cucumerina, A. macrospora, and A. carthami. Both mutant and wildtype strains of A. tagetica produced 7-8 times more CO2 on potato dextrose agar (PDA) than on V-8 agar. However, the mutant produced more conidia on PDA than on V-8 whereas the wildtype produced fewer conidia on PDA. Many aspects of in vitro sporulation may be attributable to the influence of CO2.