A Genetic Analysis of Yield and its Components of
Egyptian Cotton (Gossypium barbadense L.)
Under Divergent Environments
1Gamal I.A. Mohamed, 'S.H.M. Abd-El-Halem and'E.M.A. Ibrahim
1Faculty of Agriculture, Assiut University, Egypt
2Faculty of Agriculture, Al-Azhar University at Assiut, Egypt
Abstract: A half-diallel set of crosses was established among six local cotton varieties: Giza-88, Giza 90, Giza 87, Giza 89, Giza 91 and Giza 83 in order to estimate the genetic parameters of seed-cotton yield and its components under two divergent environments of clay-fertile and a sandy-calcareous infertile soils. The average reduction in seed-cotton yield/plant under drought stress were 42 and 37.4% and in lint yield/plant were 46.2 and 40.5% for the parent and it is F1 hybrids, respectively. The results revealed that the additive and non-additive gene effects were involved in the control of the studied traits in both environments. Most of the variation was attributed to the non-additive gene effects. For seed-cotton yield per plant and boll weight the additive gene effects were more important under favorable conditions but under stress, the non-additive effects of the genes were more important. The Wr/Vr analysis revealed that over-dominance was operating for the F1 generation and partial dominance was detected for the F2 generation under the two environments. The order of the dominance of the cultivars was reversed under drought. The genetic parameters indicated unequal distribution of dominant and recessive alleles among the six parents analyzed. Narrow-sense heritability values were much smaller relative to broad-sense heritability in the two environments indicating that the additive component was smaller than the other components of variance.
Key words: Egyptian cotton ~ Diallel analysis ~ Drought ~ Yield and its components
INTRODUCTION
Improving yield of cotton is the ultimate objective of many cotton breeding programs especially under adverse environmental conditions which prevail in the new land. Most of the newly reclaimed soils in Egypt are located in the desert where the availability of irrigation water is the most limiting factor. Drought stress is among the most important environmental factors influencing the yield components of cotton. Reduction in cotton yield is mainly due to moisture deficiency of the soils. Thus, breeding cotton for stress environments depends on their ability to resist drought [1]. Estimating the genetic parameters is an important step for identifying the best progenies to be used in the breeding program. Using information on the genetic structure of yield and its components as a quantification and selection criterion should be superior to use of yield under both normal and moisture deficiency [2,3,4]. The present investigation was conducted to study the effects of drought stress on the performance and genetic behaviour of some local cotton genotypes crossed in a half diallel and grown in stressed and non-stressed environments. Moreover, the genetic parameters and heritability were estimated for seed-cotton yield and yield components under both environments in order to determine the appropriate breeding strategy for yield improvement.
MATERIALS AND METHODS
Plant Materials: Six Egyptian cotton varieties: namely Giza-88 (P1), Giza-90 (P2), Giza-87 (P3), Giza-89 (P4), Giza-91 (P5) and Giza-83 (P6) were used in this study.: The seeds were grown in fertile clay-loam soil in Al-Azhar University Experimental Farm.
Field Experiment Conditions: In 2005 season, the six cotton varieties were sown into the field of Al-Azhar University Experimental Farm and crossed in all possible combinations, excluding reciprocals, in order to obtain a
total of 15 F1 crosses. In 2006 growing season, seeds of the six parental varieties and the 15 F1 hybrids were sown into the field and of Al-Azhar University Farm in order to produced the F2 seeds. Crosses were also made to produce more F1 seeds.
In 2007 season, seeds of the six parents, the 15 F1 s and the 15 F2 s of the six-parent half diallel cross were sown into the field at two experimental sites. The first experiment was conducted under the favourable conditions of the fertile clay-loam soil of Al-Azhar University Farm and was irrigated each three weeks after the planting irrigation.
Meanwhile, the second experiment was carried out under the stressed conditions of the infertile sandy-calcareous soil of the El-Ghoraieb Experimental Station which is located in the eastern desert 15 km south of Assiut and was irrigated each two weeks after the planting irrigation. The experimental layout in each site was a complete randomized block design with three replications. The parents and the F1 hybrids were represented by one row of plants per block, while four rows per block were used for each of the 15 F2 populations. Each row was 4.0 meter long, spaced 60 cm apart with plants spaced 25 cm within rows, on one side of the ridge with one seed per hill using the dry planting method. The agricultural practices recommended for cotton production were applied throughout the growing season. Measurements were recorded on a random sample of seven guarded plants for parents and the F1 hybrids and 20 guarded plants for each F2 populations in each replicate in the two experiments. The following characters were recorded for each plant: seed-cotton yield/plant, Lint yield/plant, Lint percentage and boll weight (gm).
Statistical Analysis: The collected data were analyzed using diallel analysis as developed by Hayman [2,5,6,7], Mather and Jinks [8] and Gomez and Gomez [9].
RESULTS AND DISCUSSION
The Means of the seed-cotton yield/plant, lint yield/plant, lint percentage and boll weight of the six parental cultivars, the 15 F1 hybrids and 15 F2 populations in the favourable (Al-Azhar) and stressed (El-Ghoraieb) environments are presented in Table 1. The parental means of seed cotton yield/plant under favourable conditions ranged from 27.64 (P1) to 54.27 (P2) grams with an average of 44.88 g. Under drought stress, the means were rather reduced to range from 14.02 (P1) to 46.72 (P6) with an average of 26.02 g indicating a 42% average reduction in seed-cotton yield/plant. The means of the F1 hybrids ranged from 48.45 to 63.21 g with an average of 54.64 g in the non-stress condition but in the stressed environment ranged from 14.53 to 49.11 g with an average of 34.21 g indicating 37.4% average reduction in seed-cotton yield/plant. Averaged over parents and F; s, seed-cotton yield/plant were reduced by 39.5% under stress conditions.
For lint yield/plant, the parental average reached 19.46 g in the favourable environment but was reduced to 10.53 g under the stressed sandy soil conditions indicating 46.2% reduction in lint yield/plant. The average of the F1 hybrids decreased from 23.21 g in the non-stress environment to 13.81 g under stress conditions indicating 40.5% reduction in lint yield/plant. In the two environments, the cultivar Giza 88 (P1) was the best in lint percentage trait (50.67 and 47.06) under favourable and stress conditions, respectively. Whereas, Giza 87 (P3) showed the lowest lint percentage (35.86 and 30.87, respectively).
The average lint percentage of the F1 hybrids decreased from 44.67 in the favourable environment to 38.26 in the stress environment. Giza 83 (P6) was the best for boll weight under favourable and stressed environments (2.89 and 2.44 g, respectively). The average boll weight of the F1 hybrids decreased from 2.98 g in the favourable environment down to 2.43 g in the stressed environment. Such reductions under stress are agreement with Hendawy [10], Kiani et al.[11], Mohamed et al. [12], Zerihun et al. [13] and Rokaya et al. [14].
The analysis of variance (Table 2) revealed highly significant differences among the genotypes for all characters studied in both the favourable and the stressed environments.
The Diallel Analysis of Variance: For seed-cotton yield/plant and its components, both "a" and "b" items measuring additive and non-additive gene effects, respectively were highly significant for both F1 and F2 generations in the two contrasting environments (Table 2). Directional dominance towards greater expression was operating for seed-cotton yield/plant, lintyield/plant and boll weight in the two contrasting environments as indicated by the significance of the "b1" item. However, dominance was ambidirectional for lint percentage in the favourable environment but was directional towards lower lint percentage under stress. The "b2" item was significant for all characters in the two contrasting environments indicating unequal distribution of dominant and recessive alleles among the parents. The significance of the "b3" item for all studied traits in the
two environments in the F1 and F2 generations indicated further dominance due to specific cross combinations and/or epistasis.
The Interpretation of the Wr/Vr Graph: The Wr, Vr, (Wr+Vr) and (Wr-Vr) values were calculated for each array in each block separately from the F1 and F2 diallel tables in both environments. The results of the analysis of the variance of the (Wr+Vr) and (Wr-Vr) values (Table 2) revealed significant array differences in the (Wr+Vr) value for F1 generations in most cases confirming the presence of non-additive genetic variation for most characters
studied, except boll weight under favourable environment. The differences in the magnitude of the (Wr-Vr) values over arrays were significant in most cases indicating the presence of either non-allelic gene interaction or epistatic effects. The Wr/Vr relationship is graphically illustrated in Fig. 1. The slope of the Wr/Vr regression line was significantly different from zero but not from unity (b = 0.76±0.23) for the F1's of seed cotton yield/plant under favourable conditions indicating the adequacy of additive-dominance model. The regression line intercepted the Wr axis near the origin point indicating almost complete dominance. However, for the F2
generation, the regression line was not significantly deviating from zero indicating non-allelic interaction. Under stress conditions, the slope of F1 regression line was not significantly deviating from zero (b = 0.12±0.77). However, the F2 regression line was significantly deviating from both zero and unity (b = 0.596±0.156) indicating that non-allelic interaction was operating. For lint yield per plant, the slope of the Wr/Vr regression line was significantly different from zero but not from unity (b = 0.81±0.36) for the F1 under favourable conditions indicating the adequacy of additive-dominance model. The regression line intercepted the Wr axis below the origin point indicating over-dominance. However, for F2 generation, the regression line was not significantly deviating from zero indicating non-allelic interaction. Under stress conditions, the slope of the F1 regression line was not significantly deviating from zero (b = 0.13±0.65). However, the F2 regression line was significantly deviating from zero (b = 0.89±0.17) indicating the adequacy of additive-dominance model. For lint percentage, the slope of the regression lines were not significantly deviating from zero for the F1 (b = 0.33±0.46) and the F2 (b = 0.13±0.26) under favourable conditions, as well as the F1 (b = 0.29±0.32) and the F2 (b = 0.39±0.27) under stress conditions indicating non-allelic interaction was operating. The regression line of the F1 generation under favourable condition intercepted the Wr axis near the origin point indicating almost complete dominance. For boll weight, the slope of the regression line were not significantly deviating from zero for the F1 (b = 0.35±0.41) and the F2 (b = 0.297±0.15) under favourable conditions indicating non-allelic interaction. However, under stress conditions the slope of the regression lines were significantly different from zero but not from unity for both the F1 (b = 0.85±0.12) and the F2 (b = 1.28±0.31) indicating the adequacy of additive-dominance model. The regression line intercepted the Wr axis below the origin point indicating over-dominance for both the F1 and F2 generations under stress conditions.
Genetic Parameters: The estimates of various components of genetic variation are given in Table 3. For seed-cotton yield/plant, the "D" parameter estimating the additive effect was much smaller than the dominance parameter "H1" for both the F1 and the F2 in the two environments except that of the F1 in the favourable environment where the "D" parameter was quite larger. These results confirmed those revealed by the Wr/Vr graph regarding the non-allelic interaction operating. The average degree of dominance as measured by the (H1/D)1/2
ratio reached (0.999) for the F1 in the favourable environment indicating complete dominance. Meanwhile, the (H1/D)1/2 were (2.396) for the F2 in the favourable environment and for F1 and F2 were 2.417 and 1.215, respectively in the stressed condition indicating over-dominance. Similar results were obtained by Talaat [15] and Iqbal et al. [16], however the results are on the contrary with those obtained by Ahmed [17]. The "F" parameter is positive for both the F1 and the F2 in the two soil types indicating that there were more dominant than recessive alleles. Similar results were obtained by Abdel-Hafez et al. [18] and Afiah and Ghoneim [19]. The HJ4H1 value indicated that the UV value was not equal to 0.25 indicating non-equal distribution of the dominant and recessive alleles among the six parents analyzed, which was indicated before from the significance of the "b2" item. Broad-sense heritability values were 0.32 and 0.83 for the F1 and F2 in the favourable environment, whereas under stress, the values were 0.78 and 0.87, respectively. The narrow-sense heritability values were 0.09 and 0.13 under favourable conditions and 0.07 and 0.42 under stressed for F1 and F2, respectively. These results indicated that the additive component was much smaller than the other components of variance. Such moderate estimates were also reported by Basal and Turgut [20] and Costa et al. [21].
For lint yield/plant, the "D" parameter was much smaller than the dominance parameter "H1" for both the F1 and the F2 in the two environments. Thus, over-dominance was operating which confirm the results revealed by the Wr/Vr graph. The "F" parameter is positive for both the F1 and F2 in the two environments indicating that there were more dominant alleles than recessive ones. Similar results were obtained by El-Ameen [22]; Esmail and Abdel-Hamid [23] and El-Zahab et al. [24]. The (H1/D)1/2 ratio were 1.58 and 2.19 for the F1 and the F2 , respectively, in the favourable environment and were 2.95 and 1.35 for the F1 and the F2, respectively, in the stressed environment indicating over dominance. Similar results were obtained by Kar et al. [25]. The value of UV was not equal to 0.25 indicating non-equal distribution of the dominant and recessive alleles among the six parents analyzed, which has been indicated before from the "b2" item. Broad-sense heritability values were 0.69 and 0.88 in the favourable environment, but were 0.82 and 0.88 under stress for both F1 and F2, respectively. Meanwhile, narrow-sense heritability values were 0.11 and 0.14 in the favourable environment and were 0.18 and 0.39 under stress for F1 and F2, respectively. These results indicated that the additive component was much smaller
than the other components of variance. Similar results were also reported by Lyanar et al. [26].
For lint percentage, the "D" parameter was much smaller than the dominance parameter "H1" for both the F1 and the F2 in the two environments, confirming that over-dominance since the (H1/D)1/2 were 2.29 and 9.69 in the favourable environment and 2.896 and 1.83 under stress for the F1 and the F2, respectively. These results confirming the results of the Wr/Vr graph. Similar results were also reported by Zerihun et al. [13]. The "F" parameter is positive for both the F1 and F2 in the two environments indicating that there were more dominant than recessive alleles. Similar results were obtained by Zerihun et al. [13] and Rajeswari [27]. The value (H2/4H1) that measures UV was not equal to 0.25 indicating non-equal distribution of the dominant and recessive alleles among the six parents analyzed, which was indicated before from the "b2" item. Broad-sense heritability values under favourable conditions were 0.26 and 0.71, whereas under stress, the values were 0.69 and 0.59 for the F1 and F2, respectively. The narrow-sense heritability reached -0.11 and 0.13 under favourable conditions and 0.08 and 0.15 under stress for the F1 and F2, respectively. Similar results were obtained by El-Ameen [22] and Nadeem et al. [28].
For boll weight, the "D" parameter estimating the additive effect was much smaller than the dominance parameter "H1" for both the F1 and the F2 generations in
the two environments, indicating over-dominance since the average degree of dominance as measured by the (H1/D)1/2 were 1.55 and 1.48 in the favourable conditions and were 1.49 and 1.17 for the F1 and the F2, respectively, under stress. The "F" parameter is positive for both the F1 and the F2 in the stressed environment indicating that there were more dominant than recessive alleles. However, for the favourable environment the "F" value was negative for both the F1 and the F2 indicating an excess of recessive over dominant alleles. The UV value was not equal to 0.25 indicating non-equal distribution of dominant and recessive alleles among the six parents analyzed. Broad-sense heritability values under favourable conditions were 0.19 and 0.21 and under stress, the values were 0.82 and 0.47 for the F1 and F2, respectively. These results indicating that the major proportion of the total phenotypic variation was non-genetic variation, except for the F1 generation under stress. The narrow-sense heritability values indicated that the additive component was much smaller than the other components of variance. Similar results were obtained by Iqbal et al. [16], Esmail and Abdel-Hamid [23] and Gerik et al. [29].
