Genetic diversity of Ustilago scitaminea (Syd.) Sudan isolates evaluated by differential sugarcane varieties under field conditions

Philip W. Marchelo-d’Raga, Yousif F. Mohamed, Gasim A. Dafalla

Abstract


Field experiments were conducted at the Sugarcane Research Centre, Guneid (lat. 15oN, long. 33oE), in seasons 2006/07 and 2008/09. The objectives were to biologically characterize six Sudan isolates of Ustilago scitaminea (Syd.) collected from different geographic locations; and, were designated as: GN1 (Guneid, NCO 376 isolate); GN2 (Guneid, CO 527 isolate); GN3 (Guneid, CO 6806 isolate); SN (Sennar, CO 527 isolate); AB (Abbasiya, isolate from mixed varieties); and NH (New-Halfa, CO 527/ CO 997 isolate) by a set of 25 differential sugarcane varieties. All inoculations were done artificially by Taiwanese pin prick method (TPPM) and dip method (DM). Results identified four pathotypes. The first and second groups; GN1, GN2 and GN3 occur in Guneid, while the third group; SN and  NH occur in Sennar and New Halfa and the fourth group AB in Abbasiya (Kenana/ Assalaya area). All four pathotypes were highly similar in pathogenicity and have relatedness percentages of 60 to 85%. Isolates GN1, NH and AB were slightly distinct and associated with virulence and, AB with avirulence, respectively. The other isolates were difficult to separate. Therefore, the absence of an isolate of high virulence indicates that the occurrence of smut in the current resistant variety CO 6806 is largely due to variety degradation/or resistance erosion and not due to a pathogenic entity of the smut pathogen. The study recommends an expanded screening program for smut resistance evaluation to make available a large number of resistant sugarcane varieties coupled with careful selection of seed cane.


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