GENETICS OF AWN LENGTH OF DURUM WHEAT UNDER NORMAL- AND LATE-SOWN ENVIRONMENTS SUMMARY

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1 SABRAO Journal of Breeding and Genetics 36(1) 23-34, 2004 GENETICS OF AWN LENGTH OF DURUM WHEAT UNDER NORMAL- AND LATE-SOWN ENVIRONMENTS S. N. SHARMA 1 and R. S. SAIN SUMMARY Parental lines, namely: F 1, F 2, BC 1, BC 2, BC 11, BC 12, BC 21, BC 22, BC 1 selfed, and BC 2 selfed generations of three crosses involving six cultivars of durum wheat (Triticum durum Desf.) were studied for awn length under normal- and late-sown environments to analyze the nature of gene effects and components of heterosis (over the better parent). A sixparameter model in the cross Cocorit 71 x A in the normal-sown condition and a 10-parameter model in most of the cases were found adequate under both environments to explain the inheritance of this trait, indicating a greater role of epistatic interactions. Additive (d) gene effect was frequently observed to be more significant than the dominance (h) gene effect. Of the epistatic interactions, digenic and/or trigenic interactions played significant roles in controlling the inheritance of this trait. Nonfixable gene effects were higher than the fixable gene effects in all the crosses in both sowing environments, indicating the significant role of nonadditive gene effects in the inheritance of awn length. Significant positive heterosis (over the better parent) was observed in the cross Raj 911 x DWL 5002 under the normal-sowing environment. Significant heterobeltiosis in this cross is attributed to the major combined effects of additive x additive x dominance (x) and dominance x dominance (l) gene effects. Absence of significant heterosis in other cases could be due to the internal cancellation of heterosis components. Significant inbreeding depression was observed in the crosses HI 8062 x JNK-4W-128 and Raj 911 x DWL 5002 in the normalsowing environment. Duplicate type of epistasis at digenic level was observed in the cross Raj 911 x DWL 5002 in the normal sowing environment, hence, selection intensity should be mild in the earlier generations and intense in the later generations. Biparental mating in segregating generations and/or diallel selective mating in diverse parents, which exploits both fixable and non-fixable components, is suggested for the improvement of this trait in durum wheat. A restricted recurrent selection, by intermating the most desirable segregants, followed by selection might prove to be a useful breeding strategy for the amelioration of this trait in durum wheat. Key words: Durum wheat, awn length, epistatic interaction, gene effects, heterosis Durum wheat (Triticum durum Desf.) in India is grown in more than 2.5 million hectares, mostly in the central and the peninsular regions and, more recently, under the irrigated condition of the Northwestern plains zone. Despite its importance for human diet, 1 All India Coordinated Wheat and Barley Improvement Project, Rajasthan Agriculture University, Agricultural Research Station, Durgapura, Jaipur , Rajasthan (India). * Corresponding author: snsarsdgprjpr@yahoo.com 23

2 little progress has been made to improve the yield of this important wheat species. So far, durum wheat has received insufficient attention from plant breeders in India. Apart from its utility as a raw material for specific food products in the cooking industry, durum wheat has good potential as an export commodity; therefore, it is necessary to intensify efforts to improve durum wheat varieties (Nagarajan, 2001). Yield is a very complex character, direct selection for which is not effective. Selection for yield components has been suggested as a possible method for yield improvement (Adams, 1967; Grafius, 1969; Donald and Hamblin, 1976). Information on the genetic parameters associated with the inheritance of a character is a prerequisite for planning a sound-breeding programme. For a complex character like yield, information on the inheritance of morpho-physiological characters is also needed. Breeding on the basis of economic traits has received attention for a long time and has been fully exploited in wheat. In India, however, the yield level of wheat has almost reached a plateau. Further improvement in grain yield may be achieved by exploiting the genetic information of important physiological traits related to yield (Austin, 1980). Nasyrov (1978) also emphasized physiological components for increasing the yield potential of wheat. The presence of awns in wheat increases the surface area available both for light interception and CO 2 uptake, which may double the net photosynthetic rate of wheat ears (Evans and Rawson, 1970; Gautam et al., 1998). Atkins and Norris (1955) reported a 13% higher grain yield, particularly under drought stress condition, due to the transpiration rate of awns that is several times greater than that of the leaves and glumes (Blum, 1985; Blum, 1986). Acreman and Dixon (1986) reported awning to reduce the grain aphid (Sitobion avenae) population to the extent of 1/3 of that observed on awnless plants. Awned wheat mutants have also been reported to be useful in the development of truly isogenic lines (Zeven et al., 1983). Biffen (1905) first reported the awnless trait to be dominant over awned in wheat. Further, Watkins and Ellerton (1940) reported the most extensive genetic studies on the inheritance of awning. They suggested that five major genes, and possibly six, determine awn development in bread wheat. The contribution of the awns to wheat yield is 3-5 % and the increase in grain yield due to the awns can be ascribed to their assimilatory function (Vervelde, 1953). Earlier, authors (Schmid, 1898; Miller et al., 1944; Suneson et al., 1948) reported that bearded (awned) lines of wheat often have a higher kernel weight than the awnless lines and, on average, the bearded types were more productive than the awnless types. Vervelde (1953) reported that the better adaptation of bearded wheats to dry and warm climates could be ascribed to the fact that the awns have xeromorphous characteristics. The surface development of awns, which is usually high, can exceed that of the flagleaf in durum wheat (Mc Donough and Gauch, 1959), which is sufficient to double the photosynthetic rate of the spike (Apel, 1966). Furthermore, these organs have an extremely favorable position for intercepting light and CO 2. They also develop late and, as a consequence, will function longer than any other green part of the plant. This character makes them very useful in those environments where the plant has a short vegetative cycle and the other parts dry off rapidly. In fact, a long series of investigations reported in Grundbacher s review (1962), showed that the awned cultivars consistently outyielded the awnless ones. The breeder could assume that, with other conditions being equal, awned lines are to be preferred in arid climates (Mc Kenzie,1972). Hence, there is a need for genetic studies on the inheritance of awning for further enhancing this trait and, hence, the grain yield of durum wheat. 24

3 Previously, emphasis was put on the role of additive and dominance components in the inheritance of quantitative characters to decide the breeding programme for improving a trait. However, a number of authors (Jinks, 1955; Hayman, 1958; Brim and Cockerham, 1961; Gamble, 1962; Hill, 1966; Matinzinger, 1968; Stuber and Moll, 1974) noted the role of epistatic gene actions, besides additive and dominance types, in controlling the inheritance of a character. Hill (1966) concluded that epistatic interactions, even at the trigenic level, were also important in the inheritance of quantitative characters. Reports on these aspects are few in durum wheat. Very limited studies are reported on the inheritance of awn length, particularly in durum wheat. Since durum wheat is sown from mid-october to the last week of December in India, it was essential to investigate the effect of the sowing dates, which may affect the results of such genetic investigations. In the absence of such information, the breeding methods used may not result in an appreciable improvement in the desired trait. This study was, therefore, undertaken through generation means analysis in 12 generations of three crosses of durum wheat to provide information on: (a) the relative significance of different types of gene actions viz., main effects, digenic and trigenic epistatic interactions, and their components for awn length in normal- and latesown environments; (b) the role of heterosis and inbreeding depression for awn length in normal- and late-sown environments; and (c) the role of gene actions involved in the manifestation of these phenomena. With the results obtained, a breeding methodology was suggested for the improvement of awn length to further increase grain yield in durum wheat. MATERIALS AND METHODS The experimental material was generated from three crosses, namely: Cocorit 71 x A , HI 8062 x JNK-4W-128, and Raj 911 x DWL 5002, utilizing six diverse parents. In each cross combination, one of the parents had (A , JNK-4W-128, and Raj 911) long awns. Twelve basic generations viz., two parents, F 1 s and F 2 s, first backcross generations with both parents (BC 1 and BC 2 ), where BC 1 was the cross between F 1 x female parent and BC 2 was F 1 x male parent, their selfed progenies (BC 1 F 2, BC 2 F 2 ) and second backcross generations (BC 11, BC 12, BC 21, BC 22 ), i.e. the BC 1 and BC 2 plants again crossed with both original parents (BC 1 x female parent; BC 1 x male parent and BC 2 x female parent; BC 2 x male parent), were used in this study. These 12 populations of each cross were evaluated in a randomized block design with three replications in two parallel experiments, one sown on 20 th November (normal-sown condition) and the other on 20 th December (late-sown condition) in the same cropping season. Each replicate was divided into three compact blocks. The crosses, each consisting of 12 populations, were randomly allotted to the blocks. All 12 populations were then randomly allotted to 12 plots within a block. The plots of various populations had different number of rows, i.e. each parent and F 1 plots consisted of two rows, while each backcross generation had four rows, and the F 2 and the second cycle of backcrosses had six rows. Each row was 5m, accommodating 33 plants spaced 15 cm apart, with a row to row distance of 30 cm. Border rows were provided at the beginning as well as at the end of the experimental rows in each block. The experiment was planted at the research farm of Rajasthan Agricultural University, Agricultural Research Station, Durgapura, Jaipur, Rajasthan, India. The awn length of the main spike of each selected plant was measured in centimeters. The data recorded were on 15 random plants in each parent and F 1 s, 30 plants in each backcross generation, and 60 plants in each F 2 and second backcross generation, in each replication under both sowing environments. 25

4 Standard statistical methods were used to calculate means and variances for each generation and each environment separately, as suggested by Snedecor and Cochran (1968). Replicate effect was eliminated from total variances to obtain within replicate variance. These variances were used to compute the standard error for each generation mean in each environment. The joint-scaling test proposed by Cavalli (1952) was used to estimate genetic parameters by the three-parameter non-epistatic model [m, (d), (h)], six-parameter model assuming digenic epistatic interaction [m, (d), (h), (i), (j), (l)], and 10-parameter model, which allowed specification of digenic and trigenic non-allelic interactions [m, (d), (h), (i), (j), (l), (w), (x), (y), (z)]. The estimates of gene effects were obtained by the weighted least squares technique. Initially, 12 equations were developed by equating observed generation means with their expectations in the presence of digenic and trigenic interactions as proposed by Hill (1966). Generation means and their expectations were weighted, appropriate weights being the reciprocals of the squared standard errors. The 12 simultaneous equations obtained were solved by way of matrix inversion as: M = J S 1, Where, M= column vector of the estimates of the parameters; S= matrix of score (right hand side); J= information matrix; and J -1 = inverse of information matrix J and is a variance covariance matrix. The adequacy of a model was tested by predicting the 12 generations mean from the estimates of each of the three-, six-, and 10-parameter models, by comparison of the weighted deviations of the observed and expected generation means in the form of chisquare test with n-p d.f., which provides a test of the goodness of fit of a model. In this situation, n is the number of statistics or generations and p is the number of parameters. The estimates of χ 2 (n-p) was obtained as: χ 2 (n-p) = (O i E i ) 2 W i, Where, O i = observed mean of the i th generation; E i = expected mean of i th generation; W i = weight of the i th generation, which is calculated as: W i = 1/V x = 1/SE 2 x. In the trigenic epistatic model, the parameters estimated were: m = mean of all possible homozygous lines; (d) = additive gene effects pooled over all loci; (h) = dominance gene effects pooled over all loci; (i) = overall additive x additive epistatic gene effects; (j) = overall additive x dominance epistatic gene effects; (l) = overall dominance x dominance epistatic gene effects; (w) = additive x additive x additive gene interaction effects; (x) = additive x additive x dominance gene interaction effects; (y) = additive x dominance x dominance gene interaction effects; and (z) = dominance x dominance x dominance gene interaction effects. The relative magnitude (in %) of various gene effects was also calculated by dividing the estimated value of each parameter by m and multiplying it by a hundred. The difference between the mean value of the F 1 generation and that of its betterparent was taken as a measure of heterosis. From the weighted least squares estimates of components of a generation mean, components of heterosis in the presence of digenic interaction were calculated as suggested by Jinks and Jones (1958) as follows: F 1 BP = [(h) (i)] [(d) ½ (j)] or [(h) (i) (d) + ½ (j)]. 26

5 The formula given by Hill (1966) was used to calculate the components of heterosis when trigenic interactions were also present as follows: F 1 BP = [(h) + ¼ (l) + 1/8 (z)] [(d) + (i) ½ (j) + ¼ (l) + (w) ½ (x) + ¼ (y) 1/8(z)], which equals- [(h) (i) + ½ (x) + ¼ (z)] [(d) ½ (j) + (w) + ¼ (y)] or [(h) (i) + ½ (x) + ¼ (z) (d) + ½ (j) (w) ¼ (y)]. Percent heterosis over the better parent and inbreeding depression were calculated as follows: Heterosis (over better-parent) = [F 1 -BP / BP] x 100; S.E. (F 1 -BP) = (2 EMS / r) 1/2, and Inbreeding depression = [F 1 -F 2 / F 1 ] x 100; S.E. (F 1 -F 2 ) = (2 EMS / r) 1/2, where BP = Better-parent; S.E. = Standard error; and EMS = Error mean sum of squares. Parameters (h), (l), and (z) were not affected by the degree of association r ; therefore, interpretation of the different interactions in this study was based on the magnitude and relative signs of these parameters (Hill, 1966). RESULTS AND DISCUSSION The results of generation means and standard errors analysis for awn length in the three inter-varietal crosses of durum wheat under normal- and late-sown environments revealed significant differences among all 12 generation means, indicating the presence of genetic variability for this trait in the materials studied (Table 1). The joint-scaling tests showed that in the cross Cocorit 71 x A , all three models (three-, six-, and 10- parameter) showed non-significant chi-square values. However, the six-parameter model showed a perfect fit, with the probability of as high as in the normal-sown condition (Table 2). Under late-sown condition, the three-parameter model was significant, whereas the other two models were non-significant. The 10-parameter model gave a chisquare value of 0.32 and a probability between , and was, therefore, considered as appropriate to explain the genetic variation in the generations of this cross. In the cross HI 8062 x JNK-4W-128, the three- and six-parameter models showed significant chi-square values; however, subsequent fitting of the 10-parameter model gave a chi-square value of 8.08 and a probability between , considered appropriate in the normal-sown environment. Under late sowing, the chi-square probabilities in all three models were less than 0.001; therefore, the joint tests indicated that more than trigenic interactions or linkages accounted for the genetic variation in the generation means. In the cross Raj 911 x DWL 5002, none of the models showed a chi-square probability of more than in the normal-sown environment indicating that the 10-parameter model is not sufficient to explain the genetic inheritance of this trait. In late planting condition, the chi-square values were significant for the three- and six-parameter models. The subsequent fitting of the 10- parameter model gave a chi-square value of 1.87 and a probability between that was considered adequate (Table 2). In the crosses and the environments where the 10- parameter model was not fitted in the data, the various gene effects were, however, estimated following the trigenic interaction model, in view of the fact that the chi-square value for this model was the lowest and no model was available to calculate more complex interactions in the present study. These results indicated that epistatic interactions had a significant role to play in governing the inheritance of awn length in durum wheat. 27

6 Table 1. Generation means and standard errors for awn length in the three crosses of durum wheat in normal- and late-sown conditions. Gen Cocorit 71 x A HI 8062 x JNK-4W-128 Raj 911 x DWL 5002 Normal Late Normal Late Normal Late P ± ± ± ± ± ±0.02 P ± ± ± ± ± ±0.05 F ± ± ± ± ± ±0.01 F ± ± ± ± ± ±0.00 BC ± ± ± ± ± ±0.06 BC ± ± ± ± ± ±0.00 BC ± ± ± ± ± ±0.12 BC ± ± ± ± ± ±0.04 BC ± ± ± ± ± ±0.02 BC ± ± ± ± ± ±0.01 BC 1s 12.60± ± ± ± ± ±0.01 BC 2 s 13.27± ± ± ± ± ±0.01 * Upper line- means; Lower line- Standard errors. Table 2. Joint-scaling test for awn length in three crosses of durum wheat in normal- and late-sown conditions. Model No. of Chi-square value d.f. Probability parameters Normal Late Normal Late Cocorit 71 x A Additive-dominance < Digenic interaction Trigenic interaction HI 8062 x JNK-4W-128 Additive-dominance < < Digenic interaction < < Trigenic interaction < Raj 911 x DWL 5002 Additive-dominance < < Digenic interaction < < Trigenic interaction <

7 The results of joint-scaling tests in the cross Cocorit 71 x A in late planting condition further revealed that the environment played a role in the expression of different non-allelic interactions, in such a way that a significant contribution for the trait changed drastically by changing the environment. When sowing was delayed, genotypic expression was affected, leading to the possibility that true phenotypic differences were not resolved resulting in non-significant differences among the genetic parameters estimated in the normal- and late-sowing environments. In such situations, the estimates made in the latesown environment are found to be less or non-significant compared to the normal environment, unless the parents involved are specially selected for the target environment (Table 3). Table 3. Joint scaling test and gene effects for awn length in durum wheat under normaland late-sown conditions. Eff. Cocorit 71 x A HI 8062 x JNK-4W-128 Raj 911 x DWL 5002 Normal Late Normal Late Normal Late m 12.93**± **± **± **± **± **±0.19 (d) -1.40**± **± ± * ± ± * ±0.17 (h) ± ± **± **± ± **±0.36 (i) ± **± **± ± ± ±0.44 (j) -2.31**± ± ± ± ± ±0.91 (l) 3.45 ± * ± ± ± *± * ±1.81 (w) ± ± ± ± ±0.78 (x) **± **± ± *± * ±1.84 (y) ± ± ** ± ± ±2.83 (z) * ± ± ± ± ±3.64 *, ** Significant at 5% and 1% probability levels, respectively. In the analysis of gene effects, the additive (d) gene effect was frequently observed to be significant in all three crosses under both planting dates, whereas, the dominance (h) gene effect was not observed so frequently but its relative magnitude was higher than the additive (d) effect in all the cases where it was significant. The relative magnitude and direction of both gene effects changed with the cross as well as the sowing environment (Table 3). The digenic epistatic interactions [(i), (j), and (l)] analysis revealed that the dominance x dominance (l) effect was significant in all crosses, in both the sowing dates. However, additive x additive (i) effects in two cases and additive x dominance (j) effects in one case, were also significant. The results of trigenic interactions analysis showed that additive x additive x dominance (x) interaction was significant in almost all the crosses in both normal- and late-sowing environments. However, other trigenic interactions did not significantly contribute to the genetic control of the inheritance of this trait except additive x dominance x dominance (y) in the cross HI 8062 x JNK-4W-128, and dominance x dominance x dominance (z) in the cross Cocorit 71 x A under the late sown condition (Table 3). These results confirmed that non-allelic interactions played a greater 29

8 role than the additive (d) and dominance (h) gene effects in the genetic control of the inheritance of awn length in durum wheat. The gene effects of greatest magnitude (%) in the cross Cocorit 71 x A were additive x dominance (j) followed by additive (d) in the normal-sowing condition and dominance x dominance x dominance (z) followed by additive x additive x dominance (x), dominance x dominance (l), additive x additive (i), and additive (d) in the late-sowing conditions (Table 4). In the cross HI 8062 x JNK-4W-128, additive x additive x dominance (x) followed by additive x additive (i) and dominance (h) in the normal planting and additive x dominance x dominance (y) followed by dominance (h) and additive (d) in the late-planting condition contributed the most to the inheritance of awn length. Additive x additive x dominance (x) followed by dominance x dominance (l) contributed the most in the cross Raj 911 x DWL 5002 in both the sowing dates; however, both additive (d) and dominance (h) effects also contributed significantly in the late-sowing environment (Table 4). Table 4. Relative magnitude (in %) of gene effects for awn length in the three crosses of durum wheat in normal- and late-sown conditions. Effects Cocorit 71 x A HI 8062 x JNK-4W-128 Raj 911 x DWL 5002 Normal Late Normal Late Normal Late m (d) (h) (i) (j) (l) (w) (x) (y) (z) Note: Only the underlined components were significant. Generation mean analysis further showed that the absolute totals (ignoring signs) of second order interactions [(w) + (x) + (y) + (z)] were much higher than the main effects and first order interactions [(i) + (j) + (l)] in all the crosses under both planting dates, except in the cross Cocorit 71 x A under normal planting (Table 5). In this cross, first order interactions contributed more than the main effects. These results confirmed the greater role of non-allelic interactions in the genetic control of the inheritance of the awn length. Watkins and Ellerton (1940) also reported that five major genes, possibly six genes, determine awn development in bread wheat. Results showed that the parameters (h) and (l) were significant in the cross Raj 911 x DWL 5002 in late planting. The relative signs of both these parameters differed in direction, indicating duplicate type of epistasis at digenic level (Table 3). Conclusion regarding any type of epistasis could not be drawn in other cases because among (h), (l), and (z), one or the other parameter was found non-significant. The absolute total of fixable [(d) + (i) + (w)] and non-fixable [(h) + (j) + (l) + (x) + (y) + (z)] gene effects showed that, in all the crosses, non-fixable (non-additive) gene effects were many times higher than the fixable (additive) gene effects, indicating the need for a complicated breeding procedure for their further exploitation (Table 5). Jain and Singh (1976), Bariga (1979), Prabhu and Sharma (1984), and Sood and Dawa (1999) also 30

9 reported the greater role of non-additive gene effects in the inheritance of morphophysiological traits in wheat. Table 5. Absolute totals of epistatic effects, fixable and non-fixable gene effects for awn length in durum wheat under normal- and late-sown conditions. Cross Env t Main effects Epistatic effects Total gene effects (d) (h) I order II order Fixable Non-fixable Cocorit 71 x Normal A Late HI 8062 x Normal JNK-4W-128 Late Raj 911 x Normal DWL 5002 Late First order interactions: [(i), (j), (l)]; Second order interactions: [(w), (x), (y), (z)]; Fixable components: [(d), (i), (w)]; Non-fixable components: [(h), (j), (l), (x), (y), (z)]. Knowledge of the degree of heterosis and inbreeding depression plays a decisive role towards the choice of breeding methodology. Exploitation of heterosis is considered to be one of the outstanding achievements of plant breeding. In a self-pollinated crop like wheat, the scope for utilization of heterosis depends mainly upon its direction and magnitude. Estimation of heterosis over the better-parent (heterobeltiosis) is useful in identifying truly heterotic cross combinations (Singh and Kandola, 1969; Sindhu and Singh, 1975). Analysis of heterosis (over the better-parent) showed that heterobeltiosis was significant in the cross Raj 911 x DWL 5002 in the normal-planting condition (Table 6). Significant positive heterobeltiosis is desirable in durum wheat because the F 1 hybrid showed longer awn length than the better parent. Estimation of components of heterosis showed that additive x additive x dominance (x) and dominance x dominance (l) interactions contributed the most towards significant positive heterosis. Absence of significant heterosis in the remaining cases could be explained by the internal cancellation of heterosis components. Significant inbreeding depression was recorded in the crosses HI 8062 x JNK-4W-128 and Raj 911 x DWL 5002 in normal sowing, which is not desirable because the F 2 had shorter awns than the F 1 (Table 6). The inbreeding depression in the study could be due to the dissipation of non-additive dominance effects or epistatic effects involving dominance in the F 2 generation. The inbreeding depression is indirectly the manifestation of the non-additive gene action controlling the character, which may require a complicated breeding methodology for its exploitation. Results of the present investigation showed that epistasis was an integral component of the genetic architecture of awn length in durum wheat and, hence, detection, estimation, and consideration of this component are important for the formulation of a breeding programme. As a consequence of the higher magnitude of interactions, particularly of the trigenic type, the non-fixable gene effects were higher than the fixable effects, indicating the major role of non-additive gene effects. The successful breeding methods will be those that accumulate the genes to form superior gene constellations interacting in a favorable manner. Some form of recurrent selection, such as diallel selective mating (Jensen, 1970) or bi-parental mating in early segregating generations (Joshi and Dhawan, 1966), might prove to be effective approaches. Restricted recurrent selection by intermating the most desirable segregants followed by selection (Joshi, 1979) might also be a useful breeding strategy for the exploitation of both additive and nonadditive types of gene action. These breeding approaches could be helpful in developing 31

10 durum wheat populations with long awns as well as high economic yield under different sowing environments. Furthermore, the duplicate type of epistasis observed in the cross Raj 911 x DWL 5002 under normally-sown environments, indicate that selection intensity should be mild in the earlier generations and intense in the later generations to achieve desired improvement in this trait in durum wheat. The study also showed that inheritance of awn length is highly affected by environment; hence, an appropriate choice of the environment should be made to improve this trait in durum wheat. Table 6. Percent heterosis (over better-parent) and inbreeding depression and components of heterosis for awn length in the three crosses of durum wheat in normal- and late- sown conditions. Components Cocorit 71 x A HI 8062 x JNK-4W-128 Raj 911 x DWL 5002 Normal Late Normal Late Normal Late (h) (i) ½ (x) ¼ (z) (d) ½ (j) (w) /4 (y) F 1 -BP S.E. ± Heterosis (%) * F 1 -F S.E. ± Inbreeding depression (%) ** * 0.53 *, ** Significant at 5% and 1% probability levels, respectively. REFERENCES Adams, W.M Basis of yield components compensation in crop plants. Crop Sci. 7: Apel, P Die Bedeutung der Grannen fur die Kornentwicklung. III. Photosynthese intensitat der Ahren verschiedener Gersten und Weizensorten. Kulturpflanze 14: Austin, R.B., J. Bingham, R.D. Blackwell, L.T. Evans, M.A. Ford, C.L. Morgan, and M. Taylor Genetic improvement in winter wheat yields since 1900 and associated physiological changes. J. Agric. Sci. 94: Bariga, P Inheritance of photosynthetic areas above the flagleaf node in spring wheat. Revista Brasileira de Genetica 2: Biffen, R.H Mendel s laws of inheritance and wheat breeding. J. Agric. Sci. 1: Brim, A.C., and C.C. Cockerham Inheritance of quantitative characters in soybean. Crop Sci. 1: Cavalli, L.L Quantitative Inheritance. Reeves, Waddington, London, UK. pp Donald, C.M., and J. Hamblin The biological yield and harvest index of cereals as agronomic and plant breeding criteria. Adv. Agron. 78: Gamble, E.E Gene effects in corn (Zea mays L.) I. Separation and relative 32

11 importance of gene effects for yield. Can. J. Plant Sci. 42: Grafius, T.E Components of yield in oats: geometrical interpretation. Agron. J. 48: Grundbacher, F.J The physiological function of cereal awn. Bot. Rev. 29: Hill, J Recurrent backcrossing in the study of quantitative inheritance. Heredity 21: Hayman, B.I The separation of epistatic from additive and dominance variation in generation means. Heredity 12: Jain, F.P., and R.B. Singh Study of combining ability and genetic parameters for physio-morphological characters in bread wheat (Triticum aestivum L.). Egyptian J. Genet. Cytol. 5: Jensen, N.F A diallel selective mating system for cereal breeding. Crop Sci. 10: Jinks, J.L A survey of the genetical basis of heterosis in a variety of diallel crosses. Heredity 9: Jinks, J.L., and R.M. Jones Estimation of components of heterosis. Genetics 43: Joshi, A.B., and N.L. Dhawan Genetic improvement in yield with special reference to self-fertilizing crops. Indian J. Genet. 26(a): Joshi, A.B Breeding methodology for autogamous crops. Indian J. Genet. 39: Mc Donough, W.T., and H.G. Gauch The contribution of the awns to the development of the kernel of bearded wheat. Md. Agric. Exp. Stn. Bull. A. 103: Mc Kenzie, H Adverse influence of awns on yield of wheat. Can. J. Plant Sci. 52: Matinzinger, D.F Genetic variability in the cured varieties of Nicotiana tabacum L. III Sc. 58 x Dixie Bright, 244. Crop Sci. 14: Miller, E.C., H.G. Gauch, and G.A. Gries A study of the morphological nature and physiological function of the awns in winter wheat. Kansas Agric. Exp. Stn. Bull. p. 57. Nagarajan, S Annual Report Directorate of Wheat Research, Karnal, Haryana, India. Nasyrov, Y.S Genetic control of photosynthesis and improving of crop productivity. Annu. Rev. Plant Physiol. 29: Prabhu K.V., and G.S. Sharma Combining ability for physiological traits in spring wheat. Indian J. Genet. 44(1): Schmid, B Bau und Funktionen der Grannen unserer Geyreideearten. Bot. Centralbl. 76: 1-9, 36-41, 70-76, , , , , , Sindhu, J.S., and R.P. Singh Heterosis in wheat. Indian J. Genet. 35: Singh, K.B., and H.S. Kandola Heterosis in wheat. Indian J. Genet. 29: Snedecor, G.W., and W.G. Cochran Statistical Methods. The Iowa State Univ. Press, Ames, Iowa, USA. Sood, V.K., and T. Dawa Genetic architecture of some physiological traits in wheat. Indian J. Genet. 59(2): Stuber, C.W., and R.H. Moll Epistasis in maize (Zea mays L.) IV. Crosses among lines selected for superior inter-variety single cross performance. Crop Sci. 14: Suneson, C.A., B.B. Bayles, and C.C. Fifield Effects of awns on yield and market qualities of wheat. USDA Cir Vervelde, G.J The agricultural value of awns in cereals. Neth. J. Agr. Sci. 1:2. Watkins, A.E., and S. Ellerton Variation and genetics of the awn in Triticum. J. Genetics