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1) Faculty of Agriculture, Hokkaido University, Sapporo, 060, Japan
2) USDA-ARS, Department of Agronomy and Range Science, University of California, Davis, CA 95616, USA
3) Du Pont Agriculture Products, Stine-Haskell Building 200, P. O. Box 30, Newark, DE 19714, USA
4) International Rice Research Institute, P.O. Box 933, Manila, Philippines
Pi-2(t) is a completely dominant gene conferring true resistance to rice blast (Pyricularia oryzae Cav.) in C101A51, one of the near-isogenic lines developed by Mackill and Bonman (1992). The donor and recurrent parents were resistant indica cultivar 5173 and highly susceptible indica cultivar C039, respectively. This gene was introduced into C039 by six backcrosses using Philippine isolate IK81-3 as test isolate. RFLP analysis revealed that Pi-2(t) was linked to a single-copy
Table 1. Reaction of parents and F2 populations to isolate IK81-3.
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Reaction to IK81-3 Goodness of fit
=========================== ======================
Parents and F2 populations R S Total Ratio X2
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Fukunishiki 10 0 10
Aichi asahi 0 10 10
F2 (FukunishikixAichi asahi) 83 17 100 3:1 3.4ns
C101A51 32 0 32
Fukunishiki 47 0 47
F2 (C101A51 X Fukunishiki) 876 0 876 1:0
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ns=Non-significant.
R = Resistant, S=Susceptible.
DNA clone RG 64 on chromosome 6 with a map distance of 2.8+/- 1.4cM (Yu et al.
1991). The Pi-z locus has also been mapped on chromosome 6 (Fukuyama et al.
1970). The Pi-2(t) and Pi-z loci were found to be tightly linked to the Se-1
locus with a map distance of 2.8+/-1.4cM and a recombination value of
3.5+/-0.5%, respectively (Mackill et al. 1990; Yokoo et al. 1971).
Therefore, it appears that the Pi-2(t) locus is tightly linked or allelic to
the Pi-z locus. Because the japonica cultivar Fukunishiki with Pi-z, one of
Kiyosawa's differentials, was resistant to isolate IK81-3 (Table 1), we
investigated allelism between the Pi-2(t) and Pi-z loci using the isolate
IK81-3.
Fukunishiki was crossed with the japonica cultivar Aichi asahi, which is susceptible to isolate IK81-3. The resulting F2 population was inoculated with isolate IK81-3 to estimate the number of genes in Fukunishiki conferring resistance to the isolate. The results indicated that Fukunishiki had a single dominant gene conferring resistance to isolate IK81-3 (Table 1). Fukunishiki was then crossed with C101A51 and the resulting F2 population was inoculated with the same isolate to investigate allelism between resistance genes in each cultivar. All F2 derivatives of Fukunishiki and C101A51 were resistant to isolate IK81-3 (Table 1).
These results indicate that the gene in Fukunishiki conferring resistance to isolate IK81-3 may be allelic to Pi-2(t) in C101A51. However, genetic analysis involving a much larger F2population from the cross of Fukunishiki and C101A51 is necessary to resolve the question of allelism between these two genes.
References
Fukuyama, T., M.E. Takahashi, T. Kinoshita and S. Saito, 1970. Linkage relationships between marker genes and blast-resistance genes in rice, IV. Jpn. J. Breed. 20 (Suppl. 1): 95-96 (in Japanese).
Mackill, D.J. and J.M. Bonman, 1992. Inheritance of blast resistance in nearisogenic lines of rice. Phytopathology 82: 746-749.
Mackill, D.J., Z.Y. Wang and S.D. Tanksley, 1990. Linkage between a RFLP probe and photoperiod sensitivity. RGN 7: 145-147.
Yokoo, M. and H. Fujimaki, 1971. Tight linkage of blast-resistance with late maturity observed in different Indica varieties of rice. Jpn. J. Breed. 21: 35-39.
Yu, Z.H., D.J. Mackill, J.M. Bonman and S.D. Tanksley, 1991. Tagging genes for blast resistance in rice via linkage to RFLP markers. Theor Appl Genet 81: 471-476.
