28. 
A RAPD marker for the gene conferring resistance to Indian biotype of BPH 
K.K. JENA’, I.C. PASALU2, K. Krishniah2 and G.S. KHUSH3
1) 
Biotechnology Centre, Mahyco Research Foundation, 245-11 Kamalapun Colony, Hyderabad 500073, 
India
2) 
Directorate of Rice Research, Rajendranagar, Hyderabad 500 030, India
3) 
International Rice Research Institute, P.O. Box 933, Manila, Philippines
Brown planthopper (BPH) is one of the most destructive insect pests of rice. Indian biotype of BPH is different from all other biotypes and is designated as biotype 4 (Khush and Brar 1991). Three genes such as bph-5, Bph-6 and bph-7 confer resistance to biotype 4 only. We report here the identification of a DNA marker linked to a BPH resistance gene present in an introgression line derived from the cross of 0. sativa and 0. officinalis.
The introgression line, IR54741-3-21-22 has inherited BPH resistance gene from the wild species 0. officinalis (Jena and Khush 1992). One F2 population of 95 plants was developed from a single F, plant of a cross between the resistant parent 1R54741-3-21-22 and the susceptible parent 1R31917-45-3-2. Reaction of F3 progeny rows of 95 F2 plants against Indian biotype of BPH was determined in a glass house test by infesting 2nd or
instar nymphs on plants at 3 leaf stage. Individual F2 plants were assessed for a phenotypic cut off (to distinguish resistant from susceptible individuals) based on their F3 reaction to BPH. Chi-square goodness of fit tests showed that segregation ratios of both F2 and F3 populations agreed with a single dominant gene control of resistance (Table 1). 267 decamer primers obtained from Operon were used to amplify genomic DNA of the parents in a PCR-based RAPD reaction. Twenty-seven primers detected polymorphism between the parents. Of the 27 polymorphic primers surveyed on F2 population, only one primer (OPA!6) showed co-segregation with BPH resistance gene. The primer OPAq6 amplified a RAPD fragment of 938 bp in the resistant parent and the resistant F2 individuals but was absent in susceptible F2 individuals as well as the susceptible parent. Only one recombinant F2 plant was detected which had resistant phenotype without resistance specific band (Fig. 1). Bulked segregant analysis of F2 individuals showed that the RAPD marker 0PA938 co-segregated in resistant bulk but was absent in the susceptible bulk. These results indicated that the putative RAPD marker OPA 16938 is closely linked to the gene conferring resistance to BPH biotype of India.
This study showed that resistance specific RAPD marker OPA 16938 could be used for marker-aided selection (MAS) of resistance gene against Indian biotype of BPH for rice improvement.

 
Table 1. 
Chi-square test for segregation of the gene for BPH resistance in F2 and F3 
population
     
Observed
  
Chi-square
Probability
Population
Expected ratio
R
frequency
(No.)
RJS
S
x2)
3:1/1:2:1
(P)
F2
3:1
76
—
19
1.26
0.50—0.25
F3
1:2:1
17
59
19
5.64
0.10—0.05
R = resistant, RJS = segregating, S = Susceptible.

 
References
Jena, K.K. and OS. Khush, 1992. Introgression of genes from Oryza officinalis Well ex Watt to cultivated rice,
0. 
sativa L. Theor. Appl. Genet. 80: 737-745.
Khush, G.S. and D.S. Brar, 1991. Genetics of resistance to insects in crop plants. Adv. Agron. 45: 223-273.