The genetic studies in 10 x 10 diallel cross revealed a complementary type of non allelic interaction for plant height, number of tillers per plant, epiklets per panicle and grain yield per plant. Semidwarf mutants DM-24, DM38, DM-2, DM179-1 and DM-16-5-1 possess dominant genes for plantheight and DM15-4 and DM107-4 have recessive genes. For tillers per plant, DM-24; DM-38 and IR-6 possess dominant genes, and DM-15-11, DM-107-4 and DM-15-4 possess recessive genes. For spikelets per panicle, DM-16-5-1 and IR-6 possess dominant genes whereas DM-24 and DM-2 possessed recessive genes. For grain yield per lant DM-38 and DM-170-1 possess dominant genes and DM-15-11 and DM-15-4 possess recessive genes. The combining ability analysis show that variety IR-6 was best general combiner for plant height followed by the mutants DM-24, DM16-5-1, DM-38 and DM-2. For tillers per plant, DM-15-4, DM-15-11 and DM-38 were found good combiners. For apikelets per panicle, IR-6 was the best combiner followed by the mutants DM16-5-1DM-2, DM-38 and DM179-1. For grain yield per plant, DM-38, DM-179-1, DM-24, DM-2 and DM-15-11 were found good combiners. The study also revealed that none of the mutants/varieties possess all the genes having desirable effect for all the characters under study and that different varieties/mutants can be utilized as donor parent(s) for specific character(s) for which they possess positive effect rather than for all the characters. Heritability, estimates for plant height, culm length, peduncle length, internode 1,2 and 3 were highly suggestive of the variation observed being primarily of genetic origin and could be largely transmitted from parent to progeny moreover the cross combination DM-2 x DM-15-4 was observed as most appropriate fro selection of plant height as it exhibited maximum heritability. Cross combination DM-38 x DM107-4 proved useful for the transmission of culm length, internode No.2 (I2) and internode No.3 (I3); DM-24 x DM 107-4 for peduncle length; DM-24 x DM16-15-1 for internode No. 1 (I1) and internode No.4 (I4), and DM15-11 x DM-2 for internode 5 (I5).
The result with respect o amylase activity showed no noteable difference between the semidwrf nutants and the tall variety Basmati 370. However a clearcut difference was observed between the genotypes with respect to alpha and beta amylase activity. Alpha amylase activity was higher than beta amylase in Basmati 370, Ir-6, DM16-5-1, DM-15-4, DM15-11, DM-24 DM-38 and DM-179-1 whereas beta amylase activity was slightly higher in DM-2 and DM107-4. Nitrate reductase activity decreased from seedling stage with the progression of growth. Maximum activity of nitrate reductase was observed in DM-24 and minimum in DM-179-1. Semidwarf mutants DM-24, DM-2, DM-16-5-1 and DM-38 by virtue of their showing consistently high activity at all stages seem to be promising and could be used in the hybridization programme for breeding for nitrate reductase activity to desired level.
Results of the chlorophyll contents at different growth stages showed that maximum chlorophyll contents were observed at tillering stage whereas minimum chlorophyll was found in the leaf sample at maturity. At seedling stage maximum chlorophyll was found in semidwarf mutant DM-15-4 followed by than in variety IR-6. at tillering stage, the maximum chlorophyll contents were found in the mutant DM15-11 followed by DM-15-4. No consistent atturen of chlorophyll a and chlorophyll b, concentrations at different stages of all the genotypes was observed. The chlorophyll contents in all the genotypes showed decreasing trend beyond the tillering stages.
Results with respect to the frequency of stomata showed a higher number of stomata on the adaxial than on the abaxial surface of the leaf in all the genotypes. Variety IR-6 had the highest number of stomata on both the surfaces of leaf, and semidward mutant DM-107-4 showed the lowest number of stomata on adaxial surface whereas the lowest number of stomata on abaxial surface was found in the mutant DM-38. It was also observed that duration of stomata opening started with the sunrise and started closing with the fading sunlight. Also it was found that the stomata and abaxial surface closed one hour earlier in the morning and evening.
Study of the leaf architecture showed that all the semidwarf mutants possessed narrower leaf angle than the parent variety. Basmati 370. Maximum leaf area and leaf area index was exhibited by the mutant DM15-4. crop growth rate study at different growth stage indicated that semidward mutants DM-38, DM-16-5-1, DM-15-4, DM-15-11 exhibited a high crop growth rate (CGR) at tillering and flowering stages whereas DM16-5-1 exhibited highest CGR at maturity stage. The results of the study with respect to harvest index showed a significant variation among the genotypes with semidwarf mutants DM-24 exhibiting the maximum value of harvest index followed by DM-24, DM-2 and DM-38. It was also noticed that high harvest index is not related with high biological yield and grain yield.
A significant difference among all the rice mutants/varieties was observed at all growth stages with respect to nitrogen contents. The nitrogen contents at maturity stage were higher in grain than in straw in all the genotype suggesting the efficient translocation of photsynthates from leaves to the grains. Semidwarf mutants DM-15-4, DM-15-11 DM-24 and DM-38 were found better converter of photosynthats to grains. Potassium contents showed significant difference in all the rice mutants/varieties at all the growth stages. Maximum values of potassium contents were observed in the mutant DM-107-4 at seedling stage. Generally the potassium contents showed a decreasing trend from seedling to maturity stage. The zinc contents in various rice genotypes differed significantly at all the growth stages. Maximum zinc contents were observed in the straw of mutant DM16-5-1 at maturity stage. The variation in the concentration of zic in rice genotypes provide a clue for selection extracting nutrients from soil.
The copper contents at all the growth stages in the ten rice maximum copper contents were found in DM-107-4 and DM-15-11 at seedling stage. Generally, the copper contents showed a decreasing trend from seedling stage to maturity. The copper contents in IR-6, DM-2, DM-107-4, DM-15-4 and DM-38 were higher in straw as compared to grain where as in DM-16-5-1, DM-15-11 and DM-179-1, the contents were higher in grain than in straw. Of the ten genotypes, DM-107-4, DM-15-11 and DM-24 seems to be very efficient in extracting copper from the soil.
Studies on the trace elements and mineral contents in rice plant in the ten rice genotypes revealed varietal difference. The concentration of zinc, manganese, iron and calcium was higher in straw as compared to grain in all the genotypes whereas the concentration of copper and phosphorus did not show any particular trend. Differences in the mineral contents in the straw and grain of fine grain tall variety Basmati 370 and its semidwarf mutants indicate the differential nature of fine grain types in absorbing nutrients from the soil as well as their translocation to the grain during the growth period.
Results of the study with respect to protein, carbohydrate, fat and ash contents in the rice genotypes showed significant differences among the rice genotypes. Protein contents ranged from 1.6 to 2.1% in straw and 6.4 to 7.5% in grain. Basmati 370, IR-6, and semidwarf mutants DM-15-4 and DM-15-11 showed higher protein contents.
The carbohydrate contents ranged from 46.4 to 56.7% in the straw and 82.0 to 85.7% in the grain. In the straw, highest value of carbohydrate was found in DM-24 whereas the grain of DM-15-11 contained highest carbohydrate. The variation in carbohydrate contents could be exploited toward selecting rice varieties with desirable amylase contents.
Fat contents in the straw of rice genotype ranged from 0.56 to 0.64%, highest being in DM-24. The fat contents in grain ranged from 1.27 to 1.55%. Highest value of fat contents were found in the grain of DM-38. A significant variation in the fat contents of rice mutants provides a clued for selecting rice varieties with relatively higher fat contents so as to get rice diet with high energy density.
The total ash content in the straw of rice mutants/ varieties ranged from 11.5 to 17.0%. IR-6 contained highest quantity of ash. In case of grain the ash contents ranged from 1.00 to 1.35% with DM-2 containing highest ash contents. Varietal differences in ash contents of rice mutants/varieties show that ash contents may be a genetically controlled trait.
The correlation studies showed that rain yield was positively and significantly correlated with harvest index and nitrate reductase activity. On the other hand grain yield showed a negative and significant correlation with flag leaf area.
Investigation regarding path coefficient showed that chlorophyll content and nitrate reductase had maximum direct positive effect. The indirect effects were mostly contributed via flag leaf angle, leaf area, nitrogen content and harvest index.