Reproduction
Members of the genus Phytophthora may reproduce by both sexual and asexual methods. P. alni is homothallic meaning that both structures for sexual reproduction (antheridia and oogonia) appear in a single culture. The antheridia are amphigynous, except in some cultures of P. alni. multiformis where paragynous antheridia may occur. Unlike most species of Phytophthora, which are diploid, P. alni alni is near tetraploid and unable to complete meiosis beyond metaphase I. In culture, many oogonia prematurely abort or appear abnormal and only one third of the oospores that appear normal are reported to be viable. As a result it is believed to spread predominantly via asexual means, namely zoospores which are produced in a specialised structure known as the sporangium. Water temperature has been shown to affect sporulation, with warmer water increasing sporangia production. Temperatures of 8°C and below prevent production of sporangia.
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