Nutritional Enhancement for Iron Content and Eombining Ability Studies in Newly Derived Inbred Lines of Okra (Abelmoschus esculentus Moench L.)  

Laxman Malakannavar1 , G. Shanthakumar2 , Thimmanna P. Ontagodi2 , Udaykumar Kage2 , Prakash Gangashetty2 , Sateesh Adiger2
1 Department of Genetics and Plant Breeding, GKVK, UAS Bangalore, India
2 Department of Genetics and Plant Breeding, college of agriculture, UAS Dharwad, India
Author    Correspondence author
Molecular Plant Breeding, 2013, Vol. 4, No. 3   doi: 10.5376/mpb.2013.04.0003
Received: 23 Nov., 2012    Accepted: 14 Dec., 2012    Published: 25 Dec., 2012
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Laxman M., et al., 2012, Nutritional Enhancement for Iron Content and Combining Ability Studies in Newly Derived Inbred Lines of Okra (Abelmoschus esculentus Moench L.), Molecular Plant Breeding, Vol.4, No.3 24-30 (doi: 10.5376/mpb.2013.04.0003)

Abstract

The study was undertaken to investigate the iron content and general combining ability (GCA) of parents, specific combining ability (SCA) of hybrids and the genetic behavior of characters in the hybrids obtained by 10x10 full diallel method involving ten double cross derived inbred lines of okra. The ninety F1s and their parents along with checks were planted in a Simple Lattice Design with two replications during kharif 2010. The general combining ability (GCA) of the parents and the specific combining ability (SCA) of the hybrids and the gene effects were estimated by using the full diallel analysis method 1, model 1, described by Griffing (1956). In the populations all the traits viz., days to first flowering, 50% flowering, plant height, number of branches, inter nodal length, fruit length, fruit diameter, number of seeds per fruit, 100 seed weight, number of fruits per plant, fruit weight, fruit yield per plant and fruit yield per hectare were influenced by both additive and non-additive gene effects. It was determined that Line 4 for fruit yield per hectare, Line 18 for fruit weight and fruit yield per plant, Line 37 for number of fruits, number of seeds per fruit and inter nodal length, Line 2 for fruit diameter and 100 seed weight, Line 13 for number of branches were the best genotypes having the highest general combining abilities. It was also determined that hybrid combinations 4x37 for fruit yield per hectare, 6x16 for fruit yield per plant, 5x18 for fruit weight, 4x5 for number of fruits per plant, 5x37 and 6x12 for 100 seed weight and 2x6 for fruit length were the most promising crosses with the highest specific combining ability. There is no reciprocal effects have been observed in these genotypes. Path of productivity analysis revealed that fruit weight and number of fruits per plant or hectare had the highest direct effect or contribution to fruit yield. Thus, in the present study, 5x37, 18x5 and 5x6 were identified as promising hybrids combining high fruit yield per plant with high fruit weight. These crosses can also be used to derive superior segregants in further generations. Iron content analysis indicated the parents involving in hybrid combination viz., 4x22 and 4x5 gave higher iron content compared to top parents Lines 37 and 22 genotypes by using AAS (Atomic Absorption Spectrophotometer).

Keywords
Okra (Abelmoschus esculentus (L.) Moench); Nutritional enhancement; Iron content; General combining ability; Path of productivity; Specific combining ability

Okra (Abelmoschus esculentus (L.) Moench) is an economically important vegetable crop grown in tropical and sub-tropical parts of the world. It is grown commercially in India, Turkey, Iran, Western Africa, Yugoslavia, Bangladesh, Afghanistan, Pakistan, Burma, Japan and the Southern United States. India ranks first in the world with 3.97 million tonnes (70% of the total world production) of okra produced from over 0.391 million ha land (Anon, 2009).

Okra is one of the important member of Malvaceae having higher chromosome number of 2n=8×=72 or 144 and polyploidy in nature. Being an often cross pollinated crop, okra is heterozygous in constitution in spite of its adoption for self-pollination. Out crossing ranging from 11.80% to 60.00% (Martin, 1979), which renders a considerable amount of genetic diversity. A short biological cycle, large and easy to manipulate flowers, autogamous and allogamous mode of reproduction, early and protracted flowering, fruit harvest just three days after flowering, a high added value in the offseason are all prior assets for breeding okra. Considering the potentiality of this crop there is a prime need for its improvement and to develop varieties and hybrids suitable for specific agro- climatic zones. The favorable characters of hybrids like production stability, suitability to high input agriculture, uniform growth and maturity shifted the focus towards heterosis breeding, leading to the release of the new potential hybrids.

In okra numbers of varieties have been released by hybridization and selection. There is a good scope for developing high yielding hybrids through hybridization. Several biometrical techniques have been used by the breeders for the selection of suitable parents in their breeding material. Of these, combining ability analysis proposed by Griffing (1956) provides inform- ation of genotypes in hybrid combinations and also on the nature and magnitude of gene action involved in controlling such metric traits. Diallel analysis is very efficient technique for evaluating inbreeds for their combining ability; besides, this technique also provides information on GCA and SCA, which are useful to study gene action controlling various characters to adopt appropriate breeding strategy.
Keeping these points in view, the study was undertaken to estimate general combin­ing ability of parents, specific combining ability of hy­brids and iron content analysis to develop high yielding hybrids using ten newly derived inbred lines of okra.
Results and Analysis
The analysis of variance carried out for the fruit yield and its component characters and was significant for all the traits. The variance due to parents was found highly significant for days to 50% flowering, inter nodal length, 100 seed weight, fruit weight and fruit yield per hectare. Hybrids showed highly significant variation for all characters viz., days to first flowering, days to 50% flowering, plant height, number of branches per plant, inter nodal length, fruit length, number of seeds per fruit, test weight, number of fruits per plant, fruit weight, fruit yield per plant and fruit yield per hectare. F1s recorded highly significant variation for all the characters studied except fruit length and days to 50 per cent flowering. Reciprocals exhibited highly significant variation for all the characters except days to first flowering, plant height and fruit length which showed significant only at 5% probability level. Parents Vs Hybrids exhibited significant variation for days to first flowering, number of branches, inter nodal length, number of seeds per fruit, 100 seed weight and number of fruits per plant and F1 Vs reciprocals exhibited significant variation for fruit yield per plot and fruit yield per hectare.  
The combining ability variances for the characters studied are presented below in Table 1. The mean sum of squares due to GCA were found highly significant for days to 50% flowering, plant height, inter nodal length, fruit length, number of branches per plant, fruit weight, fruit diameter, number of fruits per plant, fruit yield per plant, fruit yield per plot and fruit yield per hectare whereas, it was significant at 5% probability level for days to first flowering. The mean sum of squares for SCA was highly significant for number of branches, inter nodal length, fruit length, number of seeds per fruit, 100 seed weight, fruit yield per plant, fruit yield per plot and fruit yield per hectare whereas, days to 50% flowering and plant height found no significant variation. Similarly, reciprocals had shown significance for character viz. days to first flowering, days to 50% flowering, plant height, number of branches, inter nodal length, fruit yield per plot and fruit yield per hectare.  These results are in agreement with the previous studies of Vijay and Manohar,1986b, Ahmed et al., 1997, Sushmita Mitra and Das, 2003; and Srivastava et al., 2008.


Table 1 Top double cross derived lines for GCA effects with respect to fruit yield and its component traits

The estimate of general combining ability, specific combining ability effects and reciprocal effects for fruit yield per and its component traits are presented in Table 1 and Table 2, respectively. Range of GCA effect for fruit yield per hectare varies from
-3.44 (Line 2) to 2.15 (Line 4). The highest general combining ability effect for fruit yield per hectare recorded in Line 4 (2.15) followed by Line 5 (1.02), Line 16 (0.619), Line 12 (0.398), Line 18 (0.282) and Line 13 (0.07) but only two lines showed a significant positive GCA effect. Which means these lines can be used for pure line variety or for synthetic variety breeding. Range of GCA effect for fruit yield per plant varies from -68.53 (Line 2) to 27.92 (Line 18). The Line 18 (27.91) recorded the highest significant positive GCA effect followed by Line 16 (24.49) and Line 37 (19.89).


Table 2 Top three desirable hybrids with respect to SCA effects for thirteen characters in okra

Of the ten lines, Line 5 (
-0.38) recorded high significant negative GCA effect whereas, Line 13 (0.49) recorded high significant positive GCA effect for days to first flowering. The Line 22 (-1.06) recorded high significant negative GCA effect and Line 13 (1.345) recorded high significant positive GCA effect for 50% flowering. GCA effect for inter nodal length varied from -1.03 (Line 37) to 0.47 (Line 16). Out of 10 lines, one line recorded significant negative GCA effects. The negative GCA effects for days to first flowering, days to 50% flowering and inter nodal length were desirable for further breeding methods as earliness is desirable and due reduction in inter nodal length adds the more number of fruits bearing points in plant.
The significant positive GCA effect was observed in the lines Line 6 and Line 16 (0.46 and 0.47, respectively) for plant height whereas Line 37 (-6.53) exhibited maximum significant negative GCA effect followed by Line 2 (-6.40). The range of GCA effect for number of branches per plant was from -0.16 (Line 37) to 0.31 (Line 13) and the significant positive GCA effect was observed in the crosses Line 13 (0.307). The highest GCA effect was observed in Line 13 (0.31), these traits appear to be more desirable to get more fruit yield per plant. For fruit length higher significant GCA effect was observed in two lines Line 5 (0.92) followed by Line 37 (0.81) and remaining lines exhibited positive GCA effects but they were not significant that is better for increasing the fruit yield in desired direction plant breeding programme. The significant positive GCA effect was observed in the crosses Line 5 and Line 37. The GCA effects for fruit diameter ranged from –0.18 (Line 2) to 0.48 (Line 5). Among inbreds, Line 2 (–0.18) recorded the highest negative significant GCA effect followed by Line 12 (-0.13) and Line 37 (-0.05) it is better because consumer preference is of low girth. For test weight maximum significantly positive GCA effect in Line 2 (0.24) followed by Line 12 (0.12) which also adds to fruit yield parameter. In number of fruits per plant the highest significant GCA effect was expressed by Line 37 (1.18) followed by Line 5 (0.63).Similarly, for fruit weight Line 18 (0.98) exhibited maximum significant positive GCA effect followed by the Line 16 (0.61).
The estimates of GCA effects revealed that the Line 12 and Line 22 showed lesser days to first and to fifty per cent flowering, respectively, Line 6 for increased plant height, Line 16 for more number of branches per plant, Line 37 for lesser inter nodal length, for higher number of seeds per fruit and more number of fruits per plant, Line 4 for higher fruit length and higher fruit yield per hectare.Line 5 for reduced fruit diameter, and Line 2 for higher test weight, Line 18 for higher fruit weight and higher fruit yield per plant. Based on the total scoring values, it is observed that among the parents, Line 5 has higher GCA scores and is a good combiner for fruit diameter, fruit yield per plant, and fruit yield per hectare followed by Line 4, Line 37 and Line 22.

For direct crosses the SCA effect for fruit yield per hectare was ranged from -6.43 (18×22) to 5.56 (4×37). The highest significant positive SCA effect was observed in the cross 4×37 (5.56) followed by 13×18 (5.26), and 6×16 (4.21). Among 45 hybrids tested, 4 hybrids recorded significant positive SCA effects viz., 4×37 (5.56), 13×18 (5.26), 6×16 (4.21) and 5×6 (3.70). This trait indicates the non-additive gene action that exploit by heterosis breeding by testing these promising cross combinations at different locations. For fruit yield per plant the highest SCA effect was observed for the cross 6×16 (123.56) followed by 5× 18 (94.13) and 4×37 (93.40). Forty six hybrids exhibited positive SCA effects for fruit yield per plant, of which 7 crosses recorded significant positive SCA effects viz., crosses 6×7 (123.56), 5×18 (94.13), 4×37 (93.4), 16×22 (77.6), 12×13 (59.2), 5× 6 (57.2) and 18 ×37 (83.47).
For days to first flowering out of 45 hybrids, 24 hybrids exhibited SCA effects towards negative direction. Nevertheless, 3 hybrids recorded significant negative SCA effect which is considered to be desirable. In inter nodal length the highest significant negative SCA effect was found in 12×22 (-1.66). The range of SCA effect was from -1.66 (12×22) to 1.94 (4×37) but only one hybrid recorded significant negative SCA effect that can be used for further breeding programme.
For plant height, the significant positive SCA effect was observed in the crosses 4×18 (0.47), 4×12 (0.43). Similarly, 4×13 (0.32) for number of branches per plant showed the significant positive SCA effect which is desirable direction breeding programme. For fruit length the 24 recorded positive SCA effects, but only five were significant viz., 4×2 (3.24), 4×6 (2.57), 2×12 (2.39) and 5×18 (2.42). For fruit diameter high positive SCA effect was observed in 5×37 (1.72), whereas the hybrid 2×5 (-1.32) expressed the significantly negative SCA effect followed by 2×22 (-1.22). These combinations can utilize in further selection programme.
The highest significant positive SCA effect was observed number of fruits per plant that is desirable those will add to yield trait. The cross 4×5 (5.30) followed by 13×18 (2.57) and 12×37 (1.97) exhibited highest SCA effects. Among 45 hybrids tested for SCA effect, 8 hybrids recorded positive significant. The significant positive SCA effect was observed in the crosses 4×5 (5.3), 13×18 (4.57), 12×37 (1.97), 2×16 (1.89), 18×37 (1.85), 13×16 (1.72), 16×22 (1.71) and 5×22 (1.7). For fruit weight SCA effect ranged from -2.98 (16×18) to 3.57 (5×18). The highest significant positive SCA effect was observed in cross 3×18 (3.57) followed by 6×16 (3.314) and 4×16 (2.244).
Top three hybrids with respect to specific combining ability effects of the hybrids for fruit yield and its component traits are presented in Table 2. The estimates revealed that highest SCA effects in hybrids 4×37, 13×18 and 6×16 for fruit yield per hectare, 5×18, 4 ×16and 6×16 for fruit weight, 2×6, 5×13 and 4×16 for fruit length and 5×37, 6×12and 4×18 are top three cross combinations for test weight. Significant and positive SCA effects for number of fruits per plant were observed, among them top three crosses 4×5, 13×18 and 12×37. Significant and negative SCA effects for inter nodal length were observed in only one cross 12×22, 2×18 and 4×6 as these hybrid combination were found to be the best combinations for higher fruit yield.
For reciprocal crossescharacters like fruit length, fruit diameter, number of seeds per fruit, 100 seed weight, number of fruits per plant and fruit weight did not show any significant reciprocal effects. One cross, 16×13 (59.94) exhibited the reciprocal effects for fruit yield per plant. Out of 45 crosses one hybrid showed positive directions for reciprocal effects and only ten crosses had shown the positive significant reciprocal effects for the character, fruit yield per hectare showed the reciprocal effects for crosses like 37 ×5 (5.96) followed by 16×12 (5.11), 37×12 (3.87), 22×6 (3.72), 6×5 (3.01), 37×13 (2.99), 4×2 (2.72), 18×13 (2.64), 22×5 (2.59) and 37×22 (2.56) these can further tested for reciprocal effect as that is governed by maternal parent.
Total about 39 genotypes which include inbreds, selected top 25 hybrids and checks were tested for the iron content by using the instrument Automic Absorption Spectrophotometer (AAS) presented in Table 3. Among the ten parents Line 37 and 22 showed the highest iron content compared to other eight parents. Similarly, the crosses viz., 12×16, 4×22, 4×5 and 2×4 reported the highest iron content in the descending order of 1.60 mg, 1.50 mg, 1.44 mg and 1.36 mg per 100 gram. No much difference was seen in checks for iron content (Table 3).


Table 3 Iron content analysis in okra genotypes

Human body has not only required the building blocks like carbohydrates, lipids, fats and proteins but also needs the micro nutrients like iron (Fe) which is important and acts as antibody for many of anaemic diseases, hence iron content in food supplement is most important. However, present investigation indicated that some of genotypes or hybrids had the higher amount of iron content on okra genotypes. The parents viz., Line 37 and 22 can use for improving iron content. Similarly hybrids which reported more than parents of iron content are 12×16, 4×22, 4×5 and 2×4 similar results also in barn yard millet and horse gram by Kadwe et al.(1974), Vanita Nadagouda (1992) and Kulkarni (1992).
From this study significant additive and non-additive genetic effects were observed for days to first and 50% flowering, plant height, number of branches, inter nodal length, fruit length, fruit diameter, number of seeds per fruit, 100 seed weight, number of fruits, fruit weight, fruit yield per plant and fruit yield per hectare. Therefore, selection in advanced generations may be more appropri­ate for characters under non-additive genetic effects, but early generation selection may be more appropriate for characters under additive genetic effects, because effective selection in early generations of segregating material can be achieved when additive genetic effects are substantial and environmental effects are low. And also the selection of traits which were more contributing to yield. Coming to iron content analysis indicated the lot variability which can be used in further breeding.
Calculation
Total (Zn, Cu, Fe and Mn ppm)=Volume made after digestion/ Weight of fruit sample used×ppm from the instrument
Materials and Methods
The materials for the present study consisted of ten newly developed inbred lines and were crossed in a full diallel mating design during rabi 2009 to develop ninety hybrids. The parents and their F1shy­brids along with checks were planted in a Simple Lattice Design with two replications at the Main Agricultural Research Station (MARS), UAS, Dharwad during kharif 2010. All recommended package of practices are followed for uniform crop stand. Observations were taken on days to first flowering, days to 50% flowering, plant height, number of branches, inter nodal length, fruit length, fruit diameter, number of seeds per fruit, 100 seed weight, number of fruits per plant, fruit weight, fruit yield per plant and fruit yield hectare. The general combining ability effects of the parents and the specific combining ability effects of the hybrids were estimated using the full diallel analysis method described by Griffing (1956) based on method 1, model 1.
For Fe content, the di acid or tri acid digest of oven dried fruit is directly fed to Atomic Absorption Spectrophotometer (AAS) with respective cathode lamps (Zn, Cu, Fe and Mn) with suitable dilutions if necessary and concentrations of these elements is recorded in ppm by referring to standard curve. The following formula was used for calculation of Fe content.
Authors' contributions
The author conducted the major part of this study including experimental design, data analysis and manuscript preparation. Laxman Malakannavar and G shanthakumar participated in experimental design and preliminary analysis of data. Thimanna Ontagodi, Sateesh Adiger and Udaykumar Kage carried out stastical analysis. Prakash Gangashetty did final data analysis, tables and manuscript preparation. All authors read and approved the final manuscript.
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