17. Inheritance of resistance to gallmidge in rice

1) Department of Plant Breeding, Indira Gandhi, Agric. University, Raipur, 492 012, India

2) Department of Plant Breeding, Jawaharlal Nehru Agric. University, Jabalpur, 482 004, India

Gall midge (Orseolia oryzae Wood-Mason) is one of the major pests of rice, Oryza sativa L. It is known to occur extensively in several South and Southeast Asian and African countries.

Host plant resistance has been suggested to be most economical and logical approach to control this pest since chemicals have not been found very effective (Khush 1977; Heinrichs and Pathak 1981). Occurence of more than one biotype has added a new dimension to the problem necessitating the identification of as many

Ten resistant parents were studied (Table 1). Two of these, viz, Samridhi and Surekha are semi-dwarfs having already defined genes, Gm-1 and GM-2 respectively (Choudhary et al. 1986). Shakti and Cult. 245 are also semi-dwarfs. The remaining six parents are tall and were obtained from the germplasm collection maintained at Indira Gandhi Agricultural University, Raipur. All resistant parents, except Shakti and Bahawar kanak have shown high resistance under field conditions. Shakti and Bahawar kanak continued to show a few silver shoots even after purification on single plant basis and thus were classified as moderately resistant. The crosses were made between resistant and susceptible parents as well as between resistant parents. The susceptible parents used were Ranikajar, TNl and R2270.

The F1 and F2 populations of crosses listed in Tables 2 and 3 were screened during wet season of 1986 under field conditions. All efforts were made to develop adequate pest pressure. The sowing of test material was delayed to third week of August to coincide with active tillering phase of the crop with peak population period of the pest. Two rows of highly susceptible purple leaf cultivar, R259-WR37-2 were planted all around the screening plots and also between F1 and F2 populations. The live silver shoots and infected plants were brought from farmers

Table 2. Segregation for resistance to gall midge in crosses between resistant and susceptible varieties (wet season 1986)

As the data of Table 2 show, the resistance of Samridhi and Surekha was found to be under the control of a single dominant gene. This is in conformity with the results reported earlier (Choudhary et al. 1986). The F2 population from the cross ARC 6632/R2270 segregated in a ratio of 3 resistant to 1 susceptible thereby showing that a single dominant gene confers resistance in ARC 6632. On the other hand F2 populations from the crosses TN1/Shakti, ARC 5984/R2270 and Kalimoonch 64/R2270 segregated in a ration of 1 resistant to 3 susceptible plants thereby showing that single recessive genes confer resistance in Shakti, ARC 5984 and Kalimoonch 64.

Four resistant varieties, e.g., Kodakuri, Jalpa, Bhawar kanak and Cult. 245 were found to have Gm-2 as there was no segregation for susceptibility in the F2 populations of their crosses with Surekha (Table 3). The F2 populations froin the crosses of ARC5984 with Samridhi and Surekha segregated in a ratio of 13R: 3S thereby showing that the recessive gene of ARC 5984 segregates independently of Gm-1 and Gm-2. This gene is designated as gm-3. The allelic relationships of the recessive genes of Shakti and Kalimoonch 64 with gm-3 need to be investigated. Similarly, the allelic relationships of the dominant gene of ARC 6632 with Gm-1 and Gm-2 should be investigated.

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