Exploiting heterosis is one method to increase cotton yield that has stagnated in recent years. One primarily to difficulty of producing F1 seed, use of heterosis in cotton (Gossypium hirsutum L.) has been limited. The objective of this study was to evaluate the potential of using F2 hybrids by comparing them with parents, commercial variety and F1,S for yield, yield components and fiber quality. The second objective of this study was to determine if parental research organization of origin was related to mid parent and useful heterosis. The genetic design was a half diallel consisting of six parent (evolved by different research organization), 15 F1,s and 15 F2,s. The 36 genotypes were grown in 2002-2003. Yield, yield components fiber length, strength and micronaire reading were determined. The highest yielding parent was FH-901 (3517 kg ha-1) with good yield components (recommended commercial variety for general cultivation), while the variety Reshmi had best quality traits among these parents. The cross combinations MNH439 X CIM-448, FH-901 X CIM-448 and NIAB-78 xX CIM-448 showed minimum inbreeding depression (-34.6, -20.0 and -21.8%, respectively) for seed cotton yield. These crosses also showed less inbreeding depression for yield components and fiber traits than expected inbreeding depression i.e 50.0%. General combining ability mean squares were significant for all traits and specific combining ability mean squares were also significant for all traits except boll weight and fiber strength. The GCA effects were higher than SCA effects for all traits, which indicated that additive gene action is prevailing with dominant for expression of these traits. The variety CIM448 was the best general combiner for the yield and yield components.
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Using heterosis to increase yield of cotton has been objective of breeders. Except in countries where a vast labour force was available to make emasculations and crosses by hand, no commercial use of heterosis currently exists in cotton (Chaudhry, 1997b). In India, at least 40% of cottons production is derived from intraspecific hybrids of G. hirsutum and 8% of its production is from G. hirsutum X G. barbadense L hybrids (Chaudhry, 1997b). The yield increase of hybrids over the better parent or best commercial variety due to sufficient magnitude of heterosis has been documented by Loden and Richmond (1951), Davis (1978), Meredith (1984), Baru (1995), Meyer (1975), Sheetz and Quisenberry (1986). A review using more recent data (Meredith, 1998) showed an average useful heterosis of 21.4% for F1 hybrids and 10.7% for F2,S, But heterosis for fiber properties was small averaging from 0 to 2.0% for most characteristics. These reviews conclusively showed that both F1 and F2 hybrids can produce significantly higher yields than the best yielding parents or the best yielding commercial cultivars. In Pakistan a hybrid of NIAB Krishma X CIM435 was given to growers for testing in the field which showed 10.5% increase in seed cotton yield over the best parent and best commercial variety, as NIAB Krishma was the best commercial variety during 1999-2000 by CCRI, Multan (Anonymous, 2000). Breeding research needs to address all possibilities to increase yield, including the use of heterosis. The average cotton yield for Pakistan and world has shown no increase since 1992 (Chaudhry, 1997a).
The major limiting factor for using heterosis in cotton is the lack of an efficient dependable crossing system. The discovery of male sterile cytoplasm (Olvery, 1986) and restorer factor (Weaver and Weaver, 1977) gave encouragement to breeders that hybrid cottons are obtainable. However, the complexities of developing good combiners with dependable fertility restoration present major problems for hybrid production. To avoid inconsistency of results from male sterile and restorer factors and cost of producing F1 seeds, the commercial use of F2 hybrids has been proposed (Olvery, 1986). One method of circumeting this inconsistency is to use male gametocides (Sheetz and Quisenberry, 1986); however, due to lack of a dependable and economic method of controlling the insect pollen carrier, it still has not been practical to produce F1 hybrid.
However, several well designed studies showed the potential for using F2 hybrids Tang et al. (1993), evaluated yield performance of 64 F2=S from four environments and reported 11.8% higher yields than that of commercial varieties. Weaver (1984), reported 13.2 and 7.1% heterosis over mid parents for F1 and F2, respectively. The advantage of use of F2=S is that it might have a broader range of adaptation that conventional varieties due to genetic variation. Reid (1995) reported that F2 superiority over their best parents was only detected under stress conditions. Baure and Green (1996) also reported F2=S greater superiority over their best parents was in lower yielding sites. The objective of this study was to compare the yield and fibre properties of F1, F2 and combining ability of the genotypes originated by different research organizations.
MATERIALS AND METHODS
A half diallel genetic design consisting of six varieties and 15 F1 and F2 hybrids were grown in three replications at Cotton Research Station, Multan during 2001-2002. The F1 seeds were produced by hand crosses, F2 seeds were produced by selfing the F1 hybrids during 2002-2003.
The parents were Reshmi, MNH439, NIAB-78, CRIS-9, CIM446 and FH-901. The detail of research organizations which developed these varieties is given below:-
These six genotypes originated from six major cotton Research Organization in Pakistan. The experimental design was randomized complete block design with three replication. Standard cultural methods for Multan region were used. The parents and F1 were grown in four rows plot of 30 ft long, while; each genotypes of F2 was grown in ten rows plot of 30 ft long. Fifty bolls samples were hand harvested from each replication of all generations. These samples were used to determine the boll weight, lint percentage and fiber quality traits. The seed cotton yield per acre was determined from the total plot weight, combining ability analysis were made using the method given by Griffing, 1956 (Method-2 and model-2).
RESULTS AND DISCUSSION
The objective of this study was to compare consistency of performance of parents, F1=S and F2=S crosses.
Mean Yield, Yield Components and Fibre Properties of Four Parents
Mean yield, yield components and fibre properties for the six parents, are given in Table 1, significant differences were detected for all characters under study among parents. The yield superiority of F1 hybrids over the F2 and their parents is evident (Table 2). Usually the heterosis denote mid parent heterosis (Comparison of F1 or F2 Vs parent mean) but the major interest in the present study was the yield comparison of F2 hybrids with established varieties, (Table 3). The highest yielding variety, FH-901 averaged 3517 kg ha1. Maximum heterosis was observed in NIAB-78 X CIM448 (% increase over best commercial variety is 36.8). It is evident from Table-2 that several F2 hybrids were superior in yield to well established varieties (FH901 and CIM448). The highest yielding F2 hybrids, MNH439 X CIM448, FH901 X CIM448 and NIAB-78 X CIM448, averaged 3546, 3739 and 3761 kg ha1respectively.
Assuming that dominance gene action causes the heterosis, the F2 yield was expected to loose 50% of the heterosis expected by F1. However, for total yield, the F2 produced significantly more than the expected. The maximum hybrid vigour loss for yield was observed B47.4% in cross Reshmi X CIM448, whereas minimum hybrid vigour loss for yield was recorded B1.9 and B1.6% for Reshmi X NIAB-78 and MNH439 X FH-901 respectively. The highest yielding F2 hybrids MNH439 X CIM448, FH-901 X CIM448 and NIAB-78 X CIM448 loosed B36.6, -20.0 and B12.8% hybrid vigour over F1 but the yield was quite significantly higher than best commercial variety FH901. The inbreeding depression of highest yielding F1 hybrids was about what was expected on a 50% decrease in dominance from the F1 to F2. Several crosses, however showed little inbreeding depression (Table 2). Other authors (Meyer, 1975; and Sheetz and Quisenbery, 1986 have reported higher yielding F2 hybrids that produced greater yields than expected on the basis of their F1 and parental performance. Significant deviation of the F2 from expected could be done to non-additive gene action other than dominance, or plant competition within the F2 population. These results showed that for total yield and yield components, F2 hybrids could be competitive with established commercial variety. The percent increase for yield component and fiber quality traits over best commercial variety of F1 and F2 population is presented in Table 3.
|Table 2:|| |
Mean Yield, Yield Components and Fibre Properties Of, 15 F1, 15 F2 Population and Comprison of F1 and F2
These crosses showed heterosis for almost for all traits under consideration except staple length and GOT. Meredith,s (1984) summery of 18 states research on heterosis in cotton reported on an average total yield heterosis of 18.5%. The hybrid vigor loss in F2 for cross MNH-439 x CIM-448 was B11.7, -4.2, -3.4, -4.8, -4.4 and -2.23 %for number of boll per plant, boll weight, GOT%, staple length, fineness and fiber strength respectively. The hybrid vigor loss in F2 for cross combination FH-901 x CIM-448over F1 was B20.7, -9.5, -1.3, -0.6, -2.9 and B0.63% for number of bolls per plant, boll weight, GOT%, staple length, fineness and fiber strength, respectively (Table 2). Similarly inbreeding depression in F2 for cross NIAB-78 x CIM-448 was B20.0, -12.4, -1.3, -0.3, -11.3 and -1.1% for number of bolls per plant, boll weight, GOT%, staple length, fineness and fiber strength respectively (Table 4). These results indicated that inbreeding depression for these three crosses is less than 50.0% for all traits under study. It is also concluded from these results that F2 generation can also be cultivated in field for use of hetrotic vigor and cost of seed production can be decreased. These results are also in according to the previous findings of Meyer (1975) and Sheetz and Quisenbery (1986). The significant deviation of F2 in hybrid vigour ( in breeding depression) from expected (50%) could be due to non-additive gene action other than dominance. From these results it can also be concluded that F2S can produce better combinations of yield and fiber quality than their parents. On the basis of genetic variation within F2, it might have a broader range of adaptation than conventional variety and F1.
Comparison of Seed Cotton Yield of F1 and F2 with Best Parent (Fh-901)
So the question concerning the stability across environments of parents, F1 and F2 remain open, as it will require a greater range of climates, soils, pests and management environments to determine whether F2 hybrids are more adaptable than their parents in F1 hybrids. In general the interactions of yield components with environments were of lesser magnitude this for total yield.
From Table 5, it is evident that general combining ability (GCA) variances were significant for all the traits and specific combining ability (SCA) variances were also significant at P=0.05 except for boll weight and fibre strength. The variety MNH448 is the best general combiner for number of bolls per plant, boll weight and seed cotton yield per plant. Reshmi is good general combiner for fiber quality traits (Table 6). The crosses combinations NIAB-78 X CIM448, FH901 X CIM448, Reshmi X CIM448 are valuable for seed cotton yield and its components as these crosses had high SCA effect for seed cotton yield and its components (Table 7).
These results suggest that at least one percent should be well adapted for developing hybrid having high yield. The three crosses MNH439 X CIM448, FH901 X CIM448 and NIAB-78 X CIM448, which showed low inbreeding depression had also low Specific Combining Ability effects for all traits under study. As SCA effects are due to dominant gene action, if dominant gene action will be present the expected inbreeding depression in F2 will 50%. As in these three crosses the value of SCA effects is low indicating that other than dominance gene action is prevailing due to the reason, inbreeding depression for these three crosses is less than 50%. In these three crosses the common parent is CIM448, which has high GCA effect for seed cotton yield and its components (Table 5) indicating that CIM448 is good general combiner for yield and yield components. For hybrid vigour choosing of second parent is bit more difficult. No pattern of variety related to research organizations for the selection of second parent was evident. An expectation exist when fibre quality is a major breeding objective then, one must choose at last one parent that has above average fiber properties.
|Table 4:||Mean squares for various plant characters of cotton in F1 generation of 6 x 6 half diallel cross|
|Table 5:||Mean squares for combining ability analysis in 6x6 half diallel cross of cotton|
|*: P # 0.05 ; ** : P # 0.01, G.C.A = General combining ability affect, S.C.A = Specific combining ability affect, R.C.A = Reciprocal affect|
|Table 6:|| |
Estimates of general combing ability effects for yield, yield components and fiber traits in a set of half diallel cross among six cotton varieties
|Table 7:|| |
Estimates of specific combing ability effects for yield, yield components and fiber traits in a set of half diallel cross among six cotton varieties
The genetic differences among potential parents are required to detain high heterosis, it is no assurance that diverse parents will produce high heterosis.
The crosses Reshmi X CIM448 is valuable not only for seed cotton yield but also for fiber quality traits (having staple length 34.29 mm, fiber fineness 4.42 micronaire and fiber 95.1 tppsi of F1 hybrid) to meet the international market requirement. The progenies of this cross should be used for three way cross or modified back cross method or reciprocal recurrent selection method to incorporate the yield components of CIM448 from the advance early progenies of cross Reshmi X CIM448 having desirable fiber quality traits.
- Griffing, B., 1956. Concept of general and specific combining ability in relation to diallel crossing systems. Aust. J. Biol. Sci., 9: 463-493.