Physiological race of soybean rust fungus, Phakopsora pachyrhizi H. & P. Syd., and inheritance of the resistance in soybean
1997
Srisuk Poonpolgul
Physiological races of soybean rust fungus, Phakopsora pachyrhizi, and inheritance of the resistance in 4 soybean cultivars was determined at Kasetsart University, Kamphaeng Saen, Nakhon Pathom during 1994-1996. Ten soybean cultivars Ankur, CM60, PI200492, PI230971, PI459024, PI459025, TKno.5, TNno.4, and Wayne, were used to differentiate physiological races by observing the symptoms of reddish brown (RB) and tan (TAN) type reaction. Sixty nine isolates from 6 districts in 5 provinces were grouped into 59 races. Interaction between hosts and pathogens, RB type and Tan type, gave different uredospore per uredium on hosts. There was no significant difference in uredospore production of 4 representing rust isolates on 10 soybean cultivars. TKno.5 produced the highest number of uredospore in 2 weeks from race LOI-4 (2626 uredospore/uredium) while LOI-4 on PI459024 produced the least (195 uredospore/uredium). Fifteen physiological races of Phakopsora pachyrhizi were further analyzed by random amplified polymorphic DNA (RAPD). Reaction types on 10 differential cultivars were compared with the RAPD patterns. The amplification pattern obtained from 57 primers have no correlation with reaction types on soybean hosts. The inheritance of RB and Tan type reaction of 4 soybean crosses indicated interrelationship between specific resistance genes in cultivars CM60, PI230970, PI459025 and Wayne. Each cultivar carried a different single dominant gene for resistance and these genes were located at different loci. PI230970 and Wayne have the same resistance gene for rust reaction at the same locus. The genes for rust reaction were assigned to the four soybean parental types as followed; CM60: Rpp1Rpp1 rpp2rpp2 rpp3rpp3; PI230970 and Wayne: rpp1rpp1 Rpp2Rpp2 rpp3rpp3; and PI459025: rpp1rpp1 rpp2rpp2 Rpp3Rpp3.
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