Submitted to: Cereal Rusts and Mildews Conference European and Mediterranean Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/22/2004
Publication Date: 11/18/2004
Citation: Szabo, L.J., Markova, J., Anikster, Y., Eilam, T., Manisterski, J., Yehuda, P.B. 2004. In search of the correct name for leaf rust of cultivated wheat [abstract]. In: 11th International Cereal Rusts and Mildews Conference Proceedings, August 22-27, 2004, Norwich, England. Abstract 1.51. Available: http://www.crpmb.org/icrpmc11/abstracts.htm.
Technical Abstract: The taxonomic classification of leaf rust of cultivated wheat has been in flux for more than a century. In recent years the fungus has been referred to as Puccinia recondita f.sp. tritici, P. persistens f.sp. tritici and P. triticina. In 1857, Roberge described leaf rust on rye as P. recondita, which was later suggested by Cummins and Caldwell (1956) to be the valid name for leaf rusts of grasses including wheat. Plowright, in 1889, described leaf rust on Elytrigia (Agropyron) repens as P. persistens and demonstrated that the aecial host was Thalictrum flavum. In 1899, Eriksson described leaf rust on wheat as P. triticina and the aecial host was later shown to be Thalictrum species. From comparisons of host specificity, teliospore dimensions, amount of nuclear DNA and intercrossing ability, Anikster et al. (1997) concluded that leaf rust of wheat is a different species than leaf rusts of rye or several wild wheats. Consequently, 'P. recondita' was deemed inappropriate for leaf rust of cultivated wheat. We have extended this study by comparing leaf rusts collected from El. repens, El. intermedia and Th. minus (P. persistens) to leaf rust collected from cultivated wheat. Inoculation studies indicated that leaf rust collected from wheat ('wheat-type') and El. intermedia ('Elytrigia-type') have distinctly different host ranges. The 'wheat-type' leaf rust readily infected cultivated wheat (Triticum aestivum and Tr. durum) as well as Tr. boeoticum, Tr. urartu and Tr. dicoccoides. The 'Elytrigia-type' leaf rust did not infect Tr. aestivum, Tr. durum or Tr. dicoccoides, but gave infection type 3-CL on Tr. boeoticum and 1,1+2CL on T. urartu. Conversely, 'Elytrigia-type' leaf rust readily infected El. intermedia while the 'wheat-type' did not. Of eight species of Aegilops tested, three (Ae. longissima, Ae. ovata and Ae. sharonensis) were susceptible to both leaf rust types, three (Ae. bicornis, Ae. speltoides, and Ae. squarrosa) were susceptible to only the 'wheat-type', and the remaining two (Ae. cylindrica and Ae. variabilis) were not susceptible to either type. Inoculations with germinating telia of 'wheat-type' and 'Elytrigia-type' each infected Th. minus and Th. speciosissimum. Intercrossing between these leaf rust types resulted in the formation of aecia, however the aeciospores did not infect either of the original telial hosts (wheat or El. intermedia). Teliospore measurements were similar between the two types. Morphology of substomatal vesicles of the two types are distinctly different. Those of the 'wheat-type' are single-celled oval shaped, while those of the 'Elytrigia-type' are elongate often with a septum dividing the substomatal vesicle into two cells. DNA sequence analysis of the internal transcribed spacer region of the nuclear ribosomal RNA repeat indicated that the 'wheat-type' and 'Elytrigia-type' are distinct, but closely related. The 'wheat-type' sequences formed a single cluster (bootstrap value of 72%). The majority of the 'Elytrigia-type' sequences formed two, well supported clusters (bootstrap values >93%) divided primarily along host lines (El. intermedia and El. repens). Our results indicate that the leaf rusts of wheat and Elytrigia are separated by telial hosts, differ in some morphological traits and apparently have been genetically isolated in nature. It is likely that these two leaf rusts began to diverge with the domestication of wheat, approximately 10,000 years ago, and the 'wheat-type' has become adapted to an agricultural environment. For wheat leaf rust, the choice between P. triticina and P. persistens ssp. tritici appears to be a matter of judgment about how complete the process of speciation has been, as well as a practical consideration for plant pathologists dealing with the biology and control of leaf rust of wheat.