The significance of temperature during sporulation on the biology of pycnidiospores of Mycosphaerella ligiilicola

The germination, infectivity and survival of pycnidiospores obtained from cultures of Mycosphaerella ligulicola grown at 15 and 26 °C were compared. Spores formed at 26° (‘26° spores’) were less able to germinate at low relative humidities and showed a narrower temperature range for maximum germination after 6 h. At high spore densities 26° spores showed self-inhibition of germination and, over a range of lower densities, growth of their germ tubes was checked, which resulted in lower infection of leaf discs compared with 15° spores in which this phenomenon did not occur. The fungus could be recovered from un-sterile compost over a longer period after inoculation with 15° spores. Only after storage at a temperature well below zero was there a difference in viability between 15° and 26° spores. It is thought that the potential advantage of producing larger numbers of spores at 26° would be realized only under optimum conditions for dispersal and infection. The smaller number of spores produced at 15° are likely to be successful under natural conditions.