Dept. of Plant Breeding, Himachal Pradesh Agricultural University, Palampur, 176062 India
Seven diverse genotypes, viz. Himalaya 1, HPU 8020, China 988 (CH 988),
Himdhan, Madhu Malti (MM), Phul Patas 72 (PP 72) and R 575, were crossed in
all possible combinations, excluding reciprocals. Himalaya 1 and HPU 8020 are
two high yielding semidwarf indica varieties, all others are local tall
indicas, except himadhan, which is an improved tall indica. Madhu Malti is a
highly scented Basmai variety and R575 is a purple leaved variety. Twenty one
F\1\'s and the seven parents, were grown at Palampur in a randomized block
design with three replications during Kharif, 1982. A uniform fertilizer dose
of 100 kg N, 50 kg P and 50 kg K/ha was applied in the field. Two fully
expanded leaves (excluding flag leaf) from five random plants of each entry in
each replication were taken for chlorophyll analysis. Chlorophyll content was
analyzed as per procedure described in the Laboratory Manual for physiological
studies in rice (IRRI, 1976). Data were analyzed statistically using Method II
Model I of Griffing (1956) and component analysis approach of Hayman (1954).
All entries flowered between August 18 and September 30, 1982, when the mean
maximum and minimum temperatures ranged from 25.2-27.8 and 13.9-19.9degreesC,
respectively. However, no significant correlation was observed between the
mean minimum temperature (during the week preceding the day of chlorophyll
estimation) and the total chlorophyll content (r=0.07), and chlorophyll
a/chlorophyll b (ca/cb) ratio (r=0.345).
Two semidwarf varieties Himalaya 1 and HPU8020 had the highest chlorophyll content of 1.713 and 1.240 mg/g fresh weight, respectively. All other strains had chlorophyll content below one, the lowest being 0.518 in MM and 0.563 mg/g in PP 72. Among crosses, Himalaya 1/CH 988 had the highest chlorophyll content of 1.472, followed by HPU 8020/MM (1.371), HPU 8020/R 575 (1.265), CH 988/PP 72 (1.218), HPU 8020/PP 72 (1.206) and Himalaya 1/HPU 8020 (1.028). Lowest chlorophyll content was recorded in cross Himdhan/PP 72 (0.499). Himalaya 1 had the highest ca/cb ratio of 1.237, followed by Himdhan (0.857) and China 988 (0.830). R 575 had the lowest ca/cb ratio of 0.653. Among the crosses, only one cross Himalaya 1/CH 988 had a ca/cb ratio (1.131) of more than one. Chlorophyll content had significant negative correlation with plant height, panicle length, 1000-grain weight and grain length, whereas ca/cb ratio had significant negative correlation with days to flower, leaf area index and plant height.
Combining ability analysis
Mean squares due to gca and sca were highly significant for both the characters, indicating the importance of both additive and non-additive components. However, non-additive component was predominant for chlorophyll content. Semidwarfs, HPU 8020 and Himalaya 1 were the best general combiners for chlorophyll content, whereas Himdhan and PP 72 were the poorest combiners. CH 988/PP 72, PU 8020/MM and Himalaya 1 were the best general combiners for chlorophyll content, whereas Himdhan and PP 72 were the poorest combiners. CH 988/PP 72, HPU 8020/MM and Himalaya 1/CH 988 were the best specific crosses, as they displayed highly significant positive sca effects. Himalaya 1/HPU 8020, was a poor specific cross, even though its parents were best general combiners. Himalaya 1, was the best general combiner for ca/cb ratio, whereas R 575, MM and PP 72 were poor combiners. Himalaya 1/CH 988, was the only cross exhibiting highly significant positive sca effects for ca/cb ratio.
Genetic component analysis
Homogeneity of Wr-Vr, as tested by t2 test and regression of Wr on Vr, indicated the fulfilment of basic assumptions for chlorophyll content. However, for ca/cb ratio the tests indicated failure of some assumptions and the probable presence of complementary type of interacton. Both additive (D) and non-additive (H\1\) genetic components contributed to the genetic expression of both chlorophyll content and ca/cb ratio with predominance of non-additive component for chlorophyll content. The value of (H\1\/D)1/2 indiciated that the mean degree of dominance for chlorophyll content was in the overdominance range, whereas for ca/cb ratio complete dominance was observed. Significant h2 value for ca/cb ratio showed that it was unidirectional. Since progeny mean was less than the parental mean (h being negative) for ca/cb ratio, the dominance was in the direction of low ca/cb ratio. Significant influence of environmental component on variance components for chlorophyll content was observed. Positive and negative alleles at loci exhibiting dominance were symmetrically distributed in the parents for ca/cb ratio (H\2\/4H\1\=0.25 and non-significant value of H\2\-H\1\). For chlorophyll content, H\2\/4H\1\=0.25 indicated unequal proportion of negative and positive genes in parents. Significant value of F for chlorophyll content indicated asymmetrical distribution of dominant and recessive genes in parents, while for ca/cb ratio symmetrical distribution was observed. K\D\/K\R\ also indicated that the proportion of dominant genes for chlorophyll content was more in parents. Data on the number of effective factors (h2/H\2\) indicated the presence of at least two groups of the genes exhibiting dominance for ca/cb ratio. Significant positive correlation between (Wr+Vr) and Yr indicated that for ca/cb ratio, the higher parent (Himalaya 1) had greater frequency of dominant genes with positive effect.
Both analyses indicated the predominance of non-additive gene action for chlorophyll content and importance of both additive and non-additive components for ca/cb ratio. However, in wheat, Ellison et al. (1983) reported the preponderance of significant gca variance for flag leaf chlorophyll levels, suggesting the importance of additive gene action in the inheritance of this trait.
References
Ellison, F., N.F. Denera, and D.G. Pederson, 1983. Inheritance of physiological characters associated with yield variation in bread wheat. Euphytica 32:241-255.
Griffing, B. 1956. Concept of general and specific combining ability in relation to diallel crossing system. Aust. J. Biol. Sci. 9:463-493.
Hayman, B.I. 1954. The theory and analysis of diallel cross. Genet. 39: 789- 809.