Nectria haematococca mating population. VI. Cultural parameters affecting growth, conidiation, and perithecial formation

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Abstract
Field and ascospore isolates of Nectria haematococca mating population VI were examined to determine the influence of culture conditions on growth of the sexual and asexual forms of the organism. A broad pH tolerance was noted for both mycelial growth and sexual fertility. Photoperiod did not affect mycelial growth, but strongly influenced the number and type of conidia and macroconidial size. The size, type, and number of conidia produced were also isolate and temperature dependent. The temperature optimum for mycelial radial growth was 27–30 °C for all of the isolates. Temperatures of 18–24 °C before and 21–24 °C after spermatization were most favorable for perithecium production and ascospore formation. A light requirement for perithecium and ascospore production could be satisfied by exposing the fungus to light either before or after spermatization. Light intensities from 120 to 3800 lx were sufficient to induce perithecium and ascospore formation, but at temperatures above or below the optimum for perithecia formation, a higher light intensity enhanced the fertility of the cross. Of the various media tested, a complex medium (V-8 agar medium) and a simple medium (Czapek–Dox) served best for production of the sexual stage.