Carbon and nitrogen requirements for macroconidial germination of Fusarium solani: dependence on conidial density.

Abstract

Washed, PGA-grown macroconidia of F. solani did not require exogenous carbon or nitrogen for rapid (within 7 h), complete germination in a phosphate-buffered inorganic salts medium (pH 5.7) when the density of conidia was 3 × 103/ml or 3 × 102/ml. Rapid germination of macroconidia was fully dependent on exogenous carbon at 3 × 105 conidia/ml. Full dependence on both exogenous carbon and nitrogen was observed near 1 × 106 conidia/ml. Incomplete and slow germination of macroconidia was observed over 978 h at 6.4 × 105 and 3.2 × 105 conidia/ml in the absence of exogenous carbon and nitrogen.When glucose and NH4Cl were supplied at 4.0 μg C plus 0.26 μg N/ml or 40 μg C plus 2.6 μg N/ml, percentage germination of macroconidia, number of germ tubes/macroconidium, and mean germ tube length increased as the density of conidia decreased between 6.4 × 105 and 6.4 × 104 conidia/ml. Percentage germination increased as conidial density decreased between 3.1 × 106 and 3.1 × 104 conidia/ml when glucose and NH4Cl were supplied at each density at constant low amounts/conidium. Chlamydo–spore morphogenesis on germ tubes closely followed macroconidial germination in media initially containing low or no glucose and NH4Cl. The possible relation of these findings to macroconidial germination and chlamydospore morphogenesis in soil is discussed.