1) International Rice Research Institute, PO Box 933, Manila, Philippines
2) Present address: Tropical Agriculture Research Center, 1-2 Ohwashi, Tsukuba, Ibarakiken, 305 Japan
A single dominant gene for resistance to bacterial blight was identified in
Semora Mangga by Librojo et al. (1976). When the allele test between this gene
and Sz-4 was made, no susceptible plants were obtained. Thus this gene was
considered allelic to Xa-4. However, cultivars with Xa-4 are resistant at
maximum tillering and later stages but Semora Mangga shows resistance at
booting stage. Therefore the dominant gene of Semora Mangga was designated as
Xa-4b. The segregating populations were inoculated with race 1 of bacterial
blight only. However, we now have 4 races of bacterial blight in the
Philippines. We reevaluated the resistance of Semora Mangga with 4 Philippine
races of bacterial blight and found it to be resistant to the four races. The
cultivars with Xa-4 are resistant to race 1 only. We also crossed Semora Mangga
with Java 14 which has Xa-3 for resistance. No susceptible plants were observed
in the F\2\ of this cross. On the basis of this new data it was concluded that
Semora Mangga has Xa-3 gene for resistance to bacterial blight - not Xa-4b
(Ogawa et al. 1986). We have now analyzed many crosses between cultivars having
Xa-3 on one hand and Xa-4 on the other and susceptible plants were rarely
observed in the F\2\ populations. Thus Xa-3 and Xa-4 are closely linked.
Therefore, non appearance of susceptible plants in the F\2\ of IR22 which has
Xa-4 for resistance and Semora Mangga was due to very close linkage between Xa-
3 and Xa-4.
Sidhu et al. (1978, 1979) analyzed several rice cultivars genetically for resistance to bacterial blight using Philippine Race 1 only. The conclusion was that some cultivars had Xa-4 and others Xa-4b. We re-examined these cultivars by inoculating them with four Philippine races of bacterial blight. Most of the cultivars which were earlier supposed to have Xa-4b turned out to have Xa-3 for resistance (Table 1). Thus, like Semora Mangga, their genes were mistakenly designated as Xa-4b. Our recent investigations show that there are no cultivars with Xa-4b. Thus this gene symbol is redundant.
Table 1. Reaction of cultivars studied by Sidhu et al. (1979) to four
Philippine races of bacterial blight
===============================================================================
Cultivar IRRI Reaction to Races Estimated
Acc. ============================== gene
No. 1 2 3 4
===============================================================================
Ketan Gondo puro 17859 41.4 33.0 39.4 32.5 None
Sintawati 18863 9.4 33.8 34.6 14.9 Xa-4
Bandja Ili 17216 5.1 32.4 34.4 21.4 Xa-4
Ketan Gondel 17857 1.3 0.5 0.5 0.7 Xa-3
Padi Tomat 18408 0.8 0.5 0.4 0.5 Xa-3
Plampeyan 18494 1.7 0.7 0.7 0.6 Xa-3
Rante 18608 8.6 9.3 6.9 13.9 Xa-3*
Remadja Bulu 18620 2.1 1.5 0.9 1.3 Xa-3
Rengesi 18628 4.9 1.3 8.1 1.3 Xa-3
Seksrek 18740 2.6 1.1 1.5 3.0 Xa-3
Slendoran 18902 0.9 4.0 5.0 12.5 Xa-5
Balacong 19232 4.8 1.2 3.6 4.3 Xa-3
Ketan Lumbu 16461 1.1 0.4 0.2 0.6 Xa-3
Ketan Gundel 17865 1.5 0.4 0.3 0.7 Xa-3
Ketan Temon 17967 0.6 0.6 2.5 0.4 Xa-3
Lenggang Genuk Bulu18119 1.4 0.8 0.4 0.4 Xa-3
Sampangan Perak 19677 5.5 1.5 1.1 1.9 Xa-3
Sampangan Kunig 18678 3.9 1.4 1.9 2.5 Xa-3
Pulu banra kaja 20073 0.7 0.8 0.4 0.5 Xa-3
Pulut Bongo 28397 1.0 0.5 0.3 0.2 Xa-3
Bulu Maggali 17348 1.9 0.4 1.4 0.9 Xa-3
Bulu Putih 17350 17.5 13.7 11.4 14.3 Xa-3
Camor 17366 0.8 0.5 0.5 0.3 Xa-3
Gaja Baru 17586 4.6 21.1 20.9 11.8 Xa-4
Gendjah Urang 17639 0.7 0.3 0.7 0.4 Xa-3
Gewal Bangaran 17651 2.7 0.8 0.8 1.0 Xa-3
Hegar Manah 17733 5.4 26.9 - 11.9 Xa-4*
Hegar Manah-2 17733 2.9 1.5 28.4 - Xa-4+Xa-10
Ketan Gadjih 13512 19.7 12.6 16.6 20.0 ?*
Benong 13520 8.6 2.5 2.4 - Xa-3
Walen 16685 4.5 1.4 1.6 2.6 Xa-3
Ketan Bendu 17838 3.4 0.9 1.0 0.7 Xa-3
Ketan Gobel 17851 6.8 3.8 4.2 2.3 Xa-3
Ketan Laler 17897 1.8 0.7 0.8 0.8 Xa-3
Ketan Pandan 17932 0.5 0.7 0.3 0.6 Xa-3
Ketan Saponjono 17959 0.5 0.5 0.4 0.5 Xa-3
Ketan Tjendoni 17970 2.9 0.7 1.0 1.0 Xa-3
Palotan Melati 18426 0.8 0.8 1.3 0.9 Xa-3
Parew Buwun 18456 2.3 1.0 0.7 1.6 Xa-3
Pare Djerah 18458 19.3 13.4 17.2 14.9 Xa-3
Keian Gundil 24568 0.4 0.6 0.5 0.6 Xa-3
Pulut Kemandi 24621 0.2 0.2 0.3 0.4 Xa-3
Remadja 6793 7.7 28.6 31.8 15.5 Xa-4*
Sidjangguk 18826 0.6 0.8 0.6 0.5 Xa-3
Item 14652 8.8 12.4 8.1 14.5 Xa-3
Andel 17153 1.0 1.0 0.7 0.7 Xa-3
Bajang 17183 7.4 40.7 39.8 15.7 Xa-4
Beak Ganggas 17253 2.0 1.1 0.8 1.0 Xa-3*
Bulu Djambu 17343 2.2 1.3 1.3 1.2 Xa-3
Djawalara 17471 1.8 1.0 1.1 1.9 Xa-3*
Djrabang 17543 1.5 0.9 0.8 1.2 Xa-3
Boder 17315 1.4 1.2 0.9 1.0 Xa-3
Bujtak Tuwunbatu 17356 3.8 1.8 1.4 1.8 Xa-3
Bulu Sampang 17352 1.4 1.9 1.2 1.4 Xa-3
Balik Semah 17201 2.7 2.5 1.4 2.2 Xa-3
Bulu Baselijan 17341 4.3 1.8 1.8 1.3 Xa-3
Indel 17748 4.5 21.9 28.0 7.6 Xa-3
===============================================================================
*segregation was observed
===============================================================================
1. The expression of lesion length is affected by sunshine and temperature
during disease development, the genetic background of the cultivar,
concentration of inoculation, and virulence.
2. Genetic analysis by inoculation at maximum tillering is less reliable as compared to the inoculation at booting stage.
3. It is desirable to evaluate the resistance by inoculating with several races.
References
Librojo, V., H.E. Kauffman and G.S. Khush, 1976. Genetic analysis of bacterial blight resistance in four varieties of rice. SABRAO J. 8: 105-110.
Ogawa, T., R.E. Tabien, G.A. Busto, G.S. Khush and T.W. Mew, 1986. The relationship of Xa-3, Xa-4 and Xa-4b for resistance to rice bacterial blight. RGN 3: 83-84.
Sidhu, G.S., G.S. Khush and T.W. Mew, 1978. Genetic analysis of bacterial blight resistance in seventy-four cultivars of rice, Oryza sativa L. Theor. Appl. Genet. 53: 105-111.
Sidhu, G.S., G.S. Khush and T.W. Mew, 1979. Genetic analysis of resistance to bacterial blight in seventy cultivar of rice, Oryza sativa L. from Indonesia. Crop Improv. 6: 19-25.