Genetic Analysis of Various Agronomic Traits in Some Intra and Inter-Specific Crosses of Wheat

Six wheat genotypes (4 hexaploid and 2 tetraploid) against plant height, days to heading, days to anthesis, days to maturity, grain filling period, grains per spike and 1000 grain weight characters were studiedfor combining ability and heterosis through 6 × 6 half diallel fashion. This experiment was conducted at Regional Agricultural Research Institute Bahawalpur during 2016-17. Results of mean square of general combing ability (GCA) and specific combing ability (SCA) was found significant for all studied characters except forplant height and grains per spike against SCA. Ratio of GCA/SCA showed the involvement of additive gene action in the inheritance of all under studied traits. Durum-1 was found best parent among all other parents against 1000 grain weight and days to heading. Miraj-08 was good general combiner as it reflected maximum grain yield per plant. Best specific combing ability and heterosis was exhibited by cross combination Ass-11× Chakwal-50, Glaxy-13 × Chakwal-50 and Chakwal-50 × Miraj-08 against plant height, grain per spike and yield character. Results indicated that selection of best general combiner would be helpful in increasing yield through hybridization and superior hybrids may develop by the selection of superior best specific combiners.


Introduction
Wheat is considered as important staple food and strategic crop worldwide with 27% contribution in world's cereal production. It is first ever plant grown by the human beings and due to its wider adaption and resistance to biotic and abiotic stresses it is now widely cultivated throughout the world [8].
Wheatis most important food grain crop of Pakistan. WorldwidePakistan ranked 6 th in wheat with production 25.4 million tonnes on area 9260 thousand hectares [3].
The contribution of wheat in agriculture and total GDP of Pakistan is about 9.9% and 2% (Anonymous, 2016-17). The average wheat production has increased in Pakistan but its yield is still low when compared to many other countries. Population of Pakistan is increasing geometrically which has been a great challenge for agriculture scientists. Yield potential of recent wheat varieties is not increasing in parallel to overcome demand of population in Pakistan. To meet the challenge of increasing population there is a dire need to develop high yielding varieties of wheat through different breeding methods which are adaptable to different climatic condition of the country. Breeder should develop few crosses, instead of maintaining many crosses, from parents having high genetic potential. Selection of best performing parents for hybridization is based on the production of desirable segregants when a specific line combine with other lines [7]. Heterosis play important role in combing ability of parents and can be included in breeding programme [14].
Combining ability analysis is important way to select parents with desirable characters along with information regarding nature and magnitude of controlling quantitative traits [9]. Better parents are selected on the basis of general combining ability while specific combining ability is associated with the selection of superior hybrids [1]. In GCA additive genetic effect is involved while SCA is due to nonadditive genetic effect i.e dominance or epistasis. Information related to mechanism of genetic controlling different plant characters in parents may help in improving the genetic makeup of plant to maintain and improve crop production.
Diallel approach is a powerful tool for evaluating combining abilityand heterosis in additiontoanalyse the genes nature involving in the inheritance of grainyield and itscontributingtraits [11]. Parental lines can be tested in all possible combinations through diallel crosses [6]. Selection of parents with desirable characteristics showing good GCAand SCA effects for yield and its trait components are essential [4].
The objectives of present study were to estimate the combining ability of some local bread and durum wheat genotypes and to assess the heterotic potential of intra and inter-specific crosses of wheat. Another important objective was to generate diversification in wheat germplasm to be used as base line fordevelopment of highly stable wheat verieties under changing climatic conditions.

Material and Methods
Six genotypes of Triticumaestivum were crossed in half diallel fashion at Regional Agricultural Research Institute Bahawalpur during 2015-16. Spikes of female were hand emasculated for crossing and covered by butter paper bag so that contamination of foreign pollen may not occur. Pollen of selected male parent was applied on the receptive ovaries of the emasculated spikes of the female parents. Sufficient number of spikes was emasculated for each of the 6 parents and pollinated to obtain maximum seed of 15 direct crosses which were to be planted in the following year. At harvesting F 0 seeds of each crosswere threshed separatelyand stored.
In the next year (2016-17) the F 0 seeds of 15 crosses with six parents were sown in the field in randomized complete block design (RCBD) with three repeats. Sowing was done with manual dibbler maintainingplant to plant distance 15cmand row to row distance30cm respectively. In each hole two seeds were sown and later thinned to one seedling per hole after 10-12 days of germination. Standard agronomic practices were performed from sowing to maturity of crop.
At reproductive stageten guarded plants were randomly selected from each experimental unit to record data for various traits including days to heading, days to anthesis, grain filling period, days to maturity, plant height (cm), grains per spike, 1000-grain weight (g) and grain yield per plant (g). Combining ability analysis and heterotic effect of F 1 hybrid was carried out by method given by Griffing [5].

Mean Performance
Means of parents and their cross combination were given in table 1. Broad range of expression was shown by parents for various plant characters especially for plant height ranging 88 cm to 102 cm. Among six parents, minimum plant height (88cm) was observed in parent Durum-2 followed by Durum-1 (90cm). Genotype Ass-11 exhibited maximum plant height 102 cm. Minimum days (94) against days to heading were recorded in Duram-2 while Chakwal-50 showed maximum days in heading i.e 102. Genotype Duram-2 took 100 days to anthesis while maximum days were recorded in glaxy-13 (109). Early maturity (139 days) was observed in Miraj-08 followed by Duram-1 in which 142 days were recorded for maturity. Glaxy-13 showed maximum days i.e 148 to mature. Genotype Miraj-08 exhibited minimum days (36) against grain filling character and maximum days (43) for grain filling was recorded in Duram-2. Maximum no of grain per spike shown by Ass-11 which was 54 followed by Chakwal-50 in which 50 grain/spike was recorded. Ass-11 and Duram-1 showed maximum weight (42g) against 1000 grain weight and minimum weight was observed in Chakwal-50 which was 39g. Highest grain yield/plant (35g) was observed in variety Glaxy-13 followed by Miraj-08 which exhibited 34g yield/plant while Duram-1 and Duram-2 showed minimum yield/ plant 31g among all parents.
Mean values of 15 crosses were presented in table 1. Cross combination Durum-1 x Durum-2 performed better against plant height trait with minimum value 90cm followed by cross Miraj-08 x Durum-1 having plant height 92cm. Better performance with minimumvalue (94) for days to heading was performed by cross Ass-11 x Miraj-08 and maximum value was recorded for Ass-11 x Chakwal-50. Glaxy-13 x Durum-2 took 99 days for anthesis while maximum days i.e 109 was recorded for Glaxy-13 x Ass-1. Early maturity (140 days) was recorded in cross Miraj-08 x Durum-1and cross combination Miraj-08 x Durum-2 took minimum days (32) for grain filling while maximum days was exhibited by Glaxy-13 x Durum-2 which was 45 days. Highest grains (50) in a spike was found in cross Ass-11 x Durum-2 followed by Chakwal-50 x Durum-2 (49). Weight of 1000-grain is a vital yield component and is more or less stable character of wheat. Cross combination Durum-1 x Durum-2 and Chakwal-50 x Miraj-09 exhibited maximum 1000 grain weight 44g and yield per plant 37g.

Analysis of Variance (ANOVA)
Plant breeders rely on the availability of genetic diversityfor the improvement of any plant trait. Significant differences ( Table 2) of wheat varieties and their hybrids indicated the presence of genetic variation between genotypes and crosses. Highly significant or significant mean squares due to male, female and their interaction showed the involvement ofboth additive and non-additive i.e dominance and epistasis gene action in the expression of studied triats. [2] also found significant differences among wheat varieties against days to heading, weight of 1000 grain and grain yield per plant. General combing ability (GCA) of parents was observed higher than specific combing ability (SCA) of crosses for all traits like plant height, days to heading, days to anthesis, days to maturity, grain filling period, grains per spike, 1000 grain weight and grain yield per plant. High GCA reflected the prominent role of additive type of gene action in the inheritance of studied traits although significant mean squares for specific combing ability of crosses werealso observed against characters except plant height and grains per spike. Similar findings have also been observed in wheat by [12].

General Combing Ability
The general combing ability gives information about better performing parents based on their hybrid performance to exploit heterosis breeding. Among parents, genotype Durum-2 was best general combiner against plant height and days to anthesis with minimum negative value 2.93 and 1.74. Durum-1 exhibited maximum 1000 grain weight (1.14). Minimum days to heading (1.38), days to maturity (2.38) and maximum grain yield per plant (1.06) was shown by Miraj-08. Ass-11 showedbest performance against grain filling period character with minimum negative value 1.22 and exhibited maximum no of grains per spike 2.61. Parents with maximum GCA effects were the best general combiners as valuable genes were present in them for the improvement of traits and such parents may be preferred for selection and hybrid development [10].

Specific Combing Ability
Among fifteen hybrids, best specific combing ability against plant height was exhibited by cross combination Ass-11 x Chakwal-50 with minimum negative value 1.91cm.
Minimum days to heading (4.14) and days to anthesis (4.68) was recorded in Ass-11 x Miraj-08. The hybrid Glaxy-13 x Chakwal-50 was find to be best specific combiner against days to maturity and grains per spike with minimum negative value 1.61 and maximum positive value 0.58. Minimum days in grain filling period was recorded in cross Miraj-08 x Durum-2 as it showed minimum negative SCA value 7.10. High yield per plant (2.26g) was observed in cross combination Chakwal-50 x Miraj-08 (Table 3). Selection of such crosses with high specific combing abilitiy would be fruitful in the development of superior hybrid through heterosis breeding. It is not a rule that hybrid should be produced by parents with best general combiners sometimes hybrid may be developed by the combination of either parent showing poor GCA (Patel et al., 1997)e.g Ass-11 x Chakwal-50 for plant height, Ass-11 x Miraj-08 for days to anthesis, Glaxy-13 x Chakwal-50 for days to maturity and Durum-1 x Durum-2 for 1000 grain weight respectively in this study.

Heterosis
Means of eight characters of fifteen F 1 hybrids were compared with values of mid parent (relative heterosis), better parent (heterobeltosis) and over standard parent (table 4).

Conclusion
Our results indicated the presence of both additive and non additive (dominant or epistasis) gene action in the inheritance of studied traits. General combing ability (GCA) of parents was observed higher than specific combing ability (SCA) of crosses for all traits like plant height, days to heading, days to anthesis, days to maturity, grain filling period, grains per spike, 1000 grain weight and grain yield per plant. Durum-1 was found best parent among all other parents against 1000 grain weight and days to heading. Miraj-08 was good general combiner as it reflected maximum grain yield per plant. These parents contain valuable genes for improvement of characters and may be preffered for selection and hybridization program. Best specific combing ability and heterosis was exhibited by cross combination Ass-11× Chakwal-50, Glaxy-13 × Chakwal-50 and Chakwal-50 × Miraj-08 against plant height, grain per spike and yield character. Selection of such crosses would be beneficial for the development of superior hybrids through heterosis breeding.