MATERIALS AND METHODS

The experiment was conducted at soil salinity research institute, Pindi Bhattian. The experimental material comprised of 8 X 8 complete diallel cross seed. The F₁ along with eight parents were grown in salinized soil. The following cultivars/lines were as parents: Bas- 370, Bas- 385, Super Bas, F-9, NR- 1, IR- 6, NIAB - 6, Jhona- 349.

A soil of the required salinity-sodicity level (EC_e 7.75 d S / mG), SAR 28 (m mol lG¹)^½, pH 9.0) was selected from a salt-affected field. The soil was filled into the salinity blocks. The leaching in the blocks was stopped by lining the bed of the blocks by a polythene sheet; a uniform saline soil column of ten inches depth was maintained in the blocks. Three such blocks were built each serving as one replication. Forty days old nursery was transplanted into the blocks. Single plant was transplanted per hill. Twelve plants/replication with plant to plant distance 23 cm were maintained for each of the eight parents and F₁. The data were recorded on ten plants in each of the entries of the parents and F₁. The characters included in the data were plant height, panicle length, panicle fertility, productive tillers, primary branches/panicle, days to maturity, shoot dry weight, paddy yield; Na, Ca and K content of the shoot and K/Na ratio of the shoot. The plant samples were analyzed using nitric acid and per chloric acid method (Staff, 1968). The data obtained for different traits were subjected to ordinary analyses of variance technique (Steel and Torrie, 1980), inorder to determine the significance of genotype differences. Further analyses for combining ability effects were performed by using Griffings (1956) Method I, Model II.

RESULTS AND DISCUSSION

Combining ability analyses: Hybridization breeding for desirable genotypes always demands the parental genotypes having efficacy to combine and give rise to improved genotypic combinations. From breeding viewpoint only those parental cultivars/genotypes are considered to be superior which prove to be good donor and better combiner for desirable traits. Breeding for salinity/sodicity stress, due to its urgency, particularly in Pakistan, needs the best combiners and desirable donors, which could be helpful in evolving desirable genotypes for salinity/sodicity stress conditions. The significant differences among genotypes allowed the data for further analysis. The total genetic variability observed in the analysis for each character was partitioned into its components i.e., general, specific combining ability and reciprocal effects as defined by Griffing (1956). The components of variances are shown in Table 1. The estimates of general combining ablitiy (G. C. A. ) for different parental genotypes are presented in Table 2 and estimates of specific comninind ablitiy (S. C. A.) For different cross combinations are given in Table 3. The components of variation for all the characters were computed to have numerical estimates of heritable for plant heigh, panicle length, productive tillers, primary branches/panicle and paddy yield. This unfurled a high percentage of additive variation out of the total genetic variation for these characters. Additive variation (in % age) foe the above characters was 90.01, 74.63, 86.87,100.01 and 42.87, respectively. As for as S. C. A. Is concerned , high values were obtained for panicle fertility days to maturity, a hot dry weight, paddy yield, Na, Ca and K content of the shoot along with K/Na, ratio of the shoot. High S. C. A. value indicated high non-additive effect for these characters. The non-additive variation (in %age ) foe these characters was 73.80, 88.52, 113.35, 57.13, 91.66, 86.76, 108.11 and 115.41, respectively.

General combining ability effects: The general combining ability effects for different parental genotypes and critical differences (CD) for each trait are given in Table 2. Highest positive G.C.A. effects for plant height were observed in Bas-370 whereas the lowest negative G.C.A. effects were found for NIAB-6. For panicle length the greatest G.C.A. effects were exhibited by Bas-385 and lowest G.C.A. effects were shown by NIAB-6. In case of panicle fertility, the highest G.C.A. effects were exhibited by Jhona-349 whereas the lowest negative G.C.A. effects were exhibited by NIAB 6.

Table 1:	Estimates of components of various characters/traits of rice (Oryza sativa L.) In a 8 X 8 diallel cross experiment (F1 generation).
*Values given in parenthesis are the percentage of the total genetic variance.

Table 2:	Estimates of general combining ability (G.C.A.) effects for various characters of rice (Oryza sativa L.) in a 8 X 8 diallel cross experiment (F1 generation).

Table 3:	Estimates of specific combining ability (S.C.A.) effects for various characters of rice (Oryza sativa L.) in a 8 X 8 diallel cross experiment (F1 generation).

For productive tillers/plant, the maximal positive G.C.A. effects were displayed by Jhona-349 and lowest negative G.C.A. effects were shown by NR-1. As far as primary branches/panicle are concerned, the paramount positive G.C.A. effects were observed for Bas-385 and the lowest negative G.C.A. effects were exhibited by NIAB-6. As regards the days to maturity, the highest positive G.C.A. effects were divulged by NIAB-6 and the smallest negative effects were exhibited by Jhona-349. For shoot dry weight the greatest positive G.C.A. effects were unfurled by Jhona-349 and lowest negative G.C.A. effects were exhibited by Super Bas.

As far as paddy yield is concerned, the highest G.C.A. effects were divulged by Jhona-349 and the lowest negative effects were exhibited by NIAB-6. For Na content of the shoot, the highest positive G.C.A. effects were observed for Jhona-349 and the lowest negative G.C.A. effects were shown by IR-6. As regard to Ca content of the shoot, highest positive G.C.A. effects were shown by Bas-385 and the lowest negative G.C.A. effects were exhibited by Jhona-349 and F-9. As for as K content of the shoot is concerned, the paramount positive G.C.A. effects were shown by Jhona-349 and smallest negative G.C.A. effects were flaunted by Bas-385. In case of K/Na ratio of the shoot, the highest positive G.C.A. effects were exhibited by F-9 and the be used as donor parents in hybridization. Mosina (1986) and Jones (1985) also reported similar results. Narayanan and Rangasamy (1990) also reported the results of six parent diallel cross experiments they found significant additive and dominance gene effects for plant height, tiller number, panicle length, number of spikelets/panicle, thousand grain weight and dry matter accumulation under both normal and salinized conditions. Cations like Na, Ca, K and K/Na as salt tolerance parameters have been studied by many workers like Yeo and Flowers (1984), Yamanouchi et al. (1987) and Bui and Do (1988).

Specific combining ability effects: The estimates of S. C. A. are given in Table 3. As far as plant height is concerned the cross combination Super Bas X Jhona-349 performed the best and have the greatest S.C.A. effect. The lowest estimate of S.C.A. was found for NR-1 X Jhona-349. In case of panicle length, the highest S.C.A. effect was flaunted by cross combination Bas-385 X Jhona-349 while the lowest effect was shown by Bas-385 X IR-6. For panicle fertility, the maximal S.C.A. effect was divulged by the cross combination NIAB-6 X IR-6 and the lowest was shown by the combination Super Bas X IR-6.

As to productive tillers/plant, the highest S.C.A. effect was shown by the cross combination Super Bas X NR-1 while the lowest was exhibited by the cross combination NIAB-6 X Jhona-349. As far as primary branches/panicle are concerned, the highest estimate of S.C.A. was exhibited by Super Bas X Jhona-349 whereas the lowest by Super Bas X NIAB-6. For days to maturity, the maximal S.C.A. effect was shown by Super Bas X IR-6 and the lowest was divulged by NIAB-6 X IR-6. As far as shoot dry weight is concerned the highest S.C.A. effects were flaunted by Bas-370 X NIAB-6 and the minimal were exhibited by NIAB-6 X IR-6. For paddy yield, the highest S.C.A. effects were exhibited by the cross combination NIAB-6 X IR-6 and the lowest was shown by Super Bas X IR-6. In case of Na content of shoot, the highest S.C.A. effects were shown by the cross combination Super Bas X Jhona-349. As for as Ca content of the shoot is concerned the greatest S.C.A. effect was exhibited by the cross combination of NR-1 X IR-6 whereas, the lowest S.C.A. effect was shown by Bas-370 X NIAB-6. For K content of the shoot, the paramount S.C.A. effects were exhibited by Bas-370 X NR-1 and the lowest were shown by Bas-370 X Bas-385. In case of K/Na ratio of the shoot the highest S.C.A. effect was revealed by Bas-370 X NIAB-6 and the lowest S.C.A. effect was exhibited by the cross combination F-9 X Bas-370. With the assumptions that differences in general combining ability resulted primarily from differences in the additive gene effects, and that in specific combining ability effects were due to differences in non-additive gene effects, it was conspicuous from the material under the traits like height of the plant, panicle length, productive tillers and primary branches/panicle were controlled by additive genes and these characters could easily by manipulated for genetic improvement. The panicle fertility, shoot dry weight, paddy yield; Na, Ca and K content of the shoot and K/Na ratio were found to be controlled by non-additive effects indicating that their genetic improvement under salt stress environment was a tedious exercise. Similar findings were reported by Mishra (1990).