Cytological Study Of Teliospore Ontogeny And Development On The Alternate Host Oypucciniastriiformis

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most importantdiseases of wheat production in China and worldwide. Resently, it has demonstratedbarberries (Berberis spp.) not only serve as alternate hosts for stripe rust pathogen of wheat,but the pathogen of wheat stripe rust, P. striifromis f. sp. tritici, can also perform its sexualstage on Berberis spp. This finding will provide a more satisfactory interpretation for highlevel of genetic diversity and virulence variation, and a powerful support to improve strategiesfor a better control of wheat stripe rust in future studies in China. But the developmentprocess of wheat stripe rust on the alternate host and related cytological events have notreported. In addition, teliospore, usually germinate to form haploid basidiospores that theninfect alternate host, is the most essential phases in the life cycle of wheat stripe rust forsexual reproduction. As yet, However, little is known about ontogeny of teliospore. In thispaper, the cytology of teliospore formation and development on the alternate host of Pucciniastriiformis f. sp. tritici were examined by cryo-sectioning technique combined with light andelectron microscopies. It will privide a powerful information to elucidate the complete lifehistory of P. striiformis f. sp. tritici. The mainly results were as follows:(1) The observation showed that Pst teliospores generated from binucleate sporogenouscells lining the base of telia. At the early stage, spore-bud outgrew from one end ofsporogenous cells, expanding to form septum and related structures such as teliospore initial,pedicel and primary teliospore cell resulted from bud division. The primary teliospore celldifferentiated into two-celled teliospore with two nuclei in each cell after completion of thenuclear division and subsequent development of a septum. The matured teliospores werecharacterized with smooth surface, thickened cell wall, nuclear fusion, cytoplasmiccondensing and accumulation of lipid droplets and glycogen-like substances. Occassionally, aperidium structure in lotus shape was formed around a telia.(2) Teliospore geminated and give rise to basidiospore. Basidiospore, germinated witha germ tube, enters the Baberry by directly penetration into epidermal cells and formedmonokaryotic intercellular hypha. When intercellular hyphae contacted with host cells, penetration peg with papillar shape perforate the plant cell wall and formed monokaryotichaustoria in plant cell. The shapes of haustoria varied, such as rod, saccate,sickle,finger-shape and other irregular shapes.(3) Proliferation of the mononucleate hypha in the intercellular space of Berberis leavesresults in the establishment of a monokaryotic hyphal colony, from which the pycnia ariseunderneath of upper epidermis of leaves. The pycnium is in flask shape and made up of thepycniosporophores and sterile paraphyses, the pycniosporophores gives rise to pycniosporeand which is basically annellidic and with characateristics of phialidic development. A singlepyciniosporophore could produce in chain a number of picniospores successively. Eachsucceeding pycniospore was produced at fixed locus from pyciniosporophore, on which anannular scar is left after secession of pycniospores. The matured pycniospores aremononucleate and in long oval shape with smooth surface.(4) The aecia typicall arised from the flexuous hyphae on the undersides of the Berberisleaves shortly after pycnium development. The aecium was found to be cylinder or trumpet inshape, occupied by numerous prolonged with binuclei aeciosporophores which couldsuccessively give rise to a number of aeciospores from upper to lower. Division of theaeciosporophore formed an aeciospore initial, and from which an immature aeciospore and anintercalary cell arised by further division. The surface of mature aeciospore are covered withcoglike ornaments(5) Aeciospore, germinated with a germ tube, penetrates the wheat leaf through thestomatal opening and formed intercellular hypha. After proliferation of the intercellular hyphain the plant tissue, uredia and uredinispores are produce from sporogenous cells which arisedfrom intercellular hypha underneath epidermis of the leaves.(6) The stripe rust are macrocyclic heteroecious fungi, the life cycle of the pathogeninvolved five different stage and spore formation: basidial stage, pycnial stage, aecial stage,uredinial stage and telial stage.