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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-3(t) is a completely dominant gene conferring true resistance to rice blast (Pyricularia orjlzae Cav.) in the near-isogenic line C104PKT (Mackill and Bonnian 1992). This near-isogenic line was developed by six backcrosses using the resistant japonica cultivar Pai-kan-tao and the highly susceptible indica cultivar C039 as donor and recurrent parents, respectively. IRRI isolate P03-82-51 collected in the Philippines was used as the pathogen. In this study, we investigated allelism between Pi-3(t) in C104PKT and resistance genes in Kiyosawa's differentials to isolate P03-82-51.
The reaction of each of Kiyosawa's differentials to isolate P03-82-51 was observed and the nine cultivars that were resistant to the isolate were crossed with C104PKT. The resulting F2 populations were inoculated with the same isolate to investigate allelism between resistance genes in each cultivar. Only the cross between C104PKT and Fujisaka 5 did not give susceptible recombinants (Table 1). C104RKT and Fujisaka 5 were crossed with the japonica cultivars K59 and Aichi asahi, respectively, that were susceptible to isolate P03-82-51. The resulting F2'S
Table 1. Reaction of F2 Populations to isolate P03-82-51
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Reaction to P03-82-51 Goodness of fit
Cross of F2 populations ============================= =====================
R S Total Ratio X2
===============================================================================
C104PKTxShin 2(Pi-ks) 173 22 195 15:1 8.4**
Fujisaka 5(Pi-i)xC104PKT 155 0 155 1:0
Kusabue (Pi-k)xC104PKT 422 8 430 63:1 0.2ns
Tsuyuake (Pi-km)xC104PKT 189 14 203 15:1 0.1ns
C104PKTxFukunishiki (Pi-z) 211 12 223 15:1 0.3ns
Pi No.4(Pi-ta2)xC104PKT 208 14 222 15:1 O.Ons
Toride 1(Pi-zt)xC104PKT 211 14 225 15:1 O.Ons
BL 1(Pi-b)xC104PKT 211 9 220 15:1 1.8ns
C104PKTxK 60(Pi-kp) 201 9 210 15:1 1.4ns
C104PKTxK59 153 66 219 3:1 3.1ns
Fujisaka 5xAichi asahi 173 49 222 3:1 1.0ns
===============================================================================
**=Significant at 1% level.
ns=Non-significant.
R=Resistant,S=Susceptible,
Table 2. Reaction of F3 Segregating lines from the cross Fujisaka 5 X C104PKT
to isolate P03-82-51
===============================================================================
Reaction to P03-82-51 Goodness of fit
F3 lines ======================== ===============================
R S Total Ratio X2
===============================================================================
Line-14 17 3 20 3:1 1.1
32 16 3 19 3:1 0.9
38 14 4 18 3:1 0.1
90 5 1 6 3:1 0.2
104 6 2 8 3:1 0.0
===============================================================================
All chi-square values are non-significant.
R=Resistant,S=Susceptible.
were inoculated to estimate the number of resistance genes in both cultivars
to that isolate (Table 1). Both C104PKT and Fujisaka 5 had a single
resistance gene to the isolate.
Pi-3(t) in C104PKT is allelic or tightly linked to a resistance gene in Fujisaka 5. However, the size of the F2 population of C104PKT and Fujisaka 5 was not large enough to determine the linkage relationship between the resistance genes in C104PKT and Fujisaka 5, so F3 lines were inoculated with isolate P03-82-51. Due to severe hybrid sterility, only 125 F2 plants out of 155 were advanced to the F3 generation. About 20 plants per F3 line were tested to detect the segregation of a single gene. Five out of 125 lines showed segregation within a line with respect to resistance to isolate P03-82-51 (Table 2). This indicated that Pi-3(t) was not allelic but linked to the resistance gene in Fujisaka 5.
These results indicate that Pi-3(t) in C104PKT is not identical to any of the resistance genes in Kiyosawa's differentials.
References
Mackill, D.J. and J.M. Bonman, 1992. Inheritance of blast resistance in nearisogenic lines of rice. Phytopathology 83: 746-749.
