Nuclear behavior in the life cycle of Melampsora larici-populina Kleb

Melampsora larici-populina is one of macro-cyclic fungi, but differs a lot from other macro-cyclic rust fungi, with monokaryotic, dikaryotic and multikaryotic co-existing in its life cycle. The basidiospores are uniformly dikaryotic, containing two nuclei instead of one, and they germinate secondary spore with a single haploid nucleus, which can infect larch and produce dikaryotic aeciospores. After aeciospores landing on poplar leaves for 7-8 days, urediospores are produced repeatedly. Urediospores are uniformly dikaryotic with two nuclei, as well as their germtubes. The most important finding in this paper is that germtubes on the poplar leaves often fused together, in which, tetra-nucleate and tri-nucleate can be found. The new and often temporary association of nuclei may provide another means, aside from the usual sexual process, of gene recombination, which leads to pathogenesis variation and population division oil the stage of uredinial. At the end of this paper, we summarized the nuclear behavior of Melampsora larici-populina in the life cycle.