Unveiling superior cross combination in maize (Zea mays L.)

An experiment was conducted to find out the heterotic and heterobeliotic in maize during 2013-14 at Agricultural Research Institute, Dera Ismail Khan to get the superior cross combination expressing high hybrid vigour. The crosses were made in 2013 and F1 hybrids along with their parents were studied in 2014. Six maize inbred lines viz; Islamabad-white, Buffa Selection I, Sahiwal-2002, Sadaf, Islamabad Gold and Azam were used and full diallel approach was adopted to get the superior cross combination and to unveil best cross combination. Data were recorded on days to 50% pollen shed, days to 50% silking, plant height, number of ears plant , ear length, number of kernel rows ear , number of kernel row, 1000 kernel weight and grain yield kg ha. The analysis of variance revealed that means squares due to progenies and their parents were highly significant for all the traits except number of kernels ear and 1000 kernel weight which showed significant differences. Only number of kernels row ear depicted non-significant variation. The analysis of variance (Table 1) showed that mean squares due progenies and parents were highly significant for all the traits. Twenty two crosses had positive heterosis ranged from +0.84% (BS-1 x Sadaf) to 51.3 % (Islamabad-white x Sadaf) for grain yield kg ha. For days to 50% pollen shed, heterosis ranged from (-10.8 to +0.6%). The twenty seven hybrids showed negative heterosis, while the two hybrids showed positive heterosis for days to 50% silking. For plant height twenty seven crosses showed positive heterosis ranged from (0.0% to 15.5%). The heterosis and heterobeltiosis for number of ears palnt ranged from (-11.5% to 16.0 %), (-14.6 to +13.8 %) respectively. For ear length heterosis ranged from +0.12% (Islamabad-white x BS-1) to +26 % (BS-1 x Islamabad gold). Heterosis and heterobeltiosis ranged from +2.5 % (BS-1 x Islamabad-white) to 9.1 % (Sahiwal-2002 x Islamabad white) and 4.7 % (BS-1 x Azam) to 7.6 % (Sahiwal-2002 x Islamabad-white) for number of kernel rows ear. 1000 kernel weight showed heterosis and heterobeltiosis ranged from +1.5 (BS-1 x Azam) to +19.5 % (Islamabad white x Sadaf) and +0.2 % (Azam x Islamabad white) to 19.2 % (Islamabad white x Sadaf). Hence it is suggested that 3 parents viz; Islamabad Gold, Sahiwal 2002 and Sadaf can give promising yield if included in breeding experiments to unzip genetic configuration. Keyword: Maize; Inbred lines; Heterosis and heterobeltiosis Introduction Maize (Zea mays L.) is an important cereal and ranks 3 amongst other cereal. It is cultivated in Pakistan on about 1.096 million hectares with a total annual production of 38.05 million tons [1]. Despite of higher yield potential we are lagging far behind the world in average yield on per unit area basis. By producing high yielding hybrids, we may increase average yield. Increasing


Introduction
Maize (Zea mays L.) is an important cereal and ranks 3 rd amongst other cereal.It is cultivated in Pakistan on about 1.096 million hectares with a total annual production of 38.05 million tons [1].Despite of higher yield potential we are lagging far behind the world in average yield on per unit area basis.By producing high yielding hybrids, we may increase average yield.Increasing population has also raised the edible oil consumption.Hence billions of rupees are needed to meet the requirements of population.Maize plays an important role in the economy of Pakistan.Maize is a naturally cross-pollinated crop and a high degree of heterotic effect can be utilized by crossing the inbred lines.The success of any improvement programme for the production of high yield, early maturity and better quality maize hybrids or synthetic varieties depend upon the identification and selection of local and exotic elite parents to be utilized in a breeding programme.Heterosis breeding is the key tool for the production of high yielding hybrids and better response to fertilizers.The ultimate aim of most plant breeding programs is to increase yield and quality of crops.Thus to ascertain best cross combination present research was conducted at the Agricultural Research Institute, Ratta Kulachi, Dera Ismail Khan.

Materials and methods
The present study was conducted to unveil superior cross combinations amongst thirty direct and reciprocal crosses, evolved from six parental inbred lines i.e. have also report ed negati ve het erosis for the param eter discuss ed.The dat a observed for 50 % silking ranged from 0.7 to -9.6 % and 0.0 to -9.8 % against MP, BP heterosis as (Table 2) have also shown negative heterosis.The cross BS-1 x Sahiwal-2002 had the highest negative heterosis, MP and BP -9.7 and -9.8.Crosses involving Azam and BS-1 generally showed higher negative heterotic effect.Table .2 showed that the highest value of 55.0 days to 50 % silking for parental line for Sadaf and the minimum value 48.0 for Azam.On the other hand crosses showed variability ranging from 48.0 to 52.0 days.These results of [7-9] described useful crosses for 50% silking.Hence heterosis studies for 50% silking is not advisable The estimation of heterosis and heterobeltiosis are presented in Table 2, indicating for plant height of 30 crosses, 28, and 21 crosses showed positive heterosis over their mid and better parental values, respectively.The magnitude of heterotic effect appeared to vary from -8.2 to 15.5% and -10.7, 10.3% against the mid and better parental values, so for as the plant height is concerned.The cross of Sadaf x Islamabadwhite had the highest value 15.5% for mid parent heterosis, and Islamabad-gold x Sadaf, 10.3% for better parent heterosis.As regards parental lines, the highest value of plant height, 195.1cm and the lowest value of 161.0cm were recorded in Sahiwal-2002 and Islamabad-white, respectively.While the crosses, Sadaf x BS-1, 210.0cm and Sahiwal-2002 x BS-1, 204.0cm resulted the tallest plant while shortest plants of 174.3cm and 177.7cm was shown by Sadaf x Sahiwal-2002, Islamabad-gold x Azam, respectively.In case of plant height tall x tall produced tall hybrids.However, the tallness parameter may or may not be beneficial.Because tallness may lead to lodging and consequently may declines the yield.However sometimes dwarf plant may produce prominent yield.In present studies mixed trend was noted, which is also supported by Ali et 2).Out of 30 crosses, 18 showed positive heterosis over mid parent.Better parent heterosis estimates revealed the presence of such effect in 14 crosses, out of 30 crosses.The range of heterosis in crosses -11.5 to 16.0 % and -14.6 to 13.8 % against their mid and better parental values, respectively.The highest value for ears per plant was recorded in crosses, 1.2 and 1.0 for Azam x Islamabadgold and Islamabad-gold x Azam, respectively.[13, 14] was also of same opinion for this character.The variation in estimated values of heterosis might be due to differences in cytoplasmic effects of the corresponding fertile hybrids The degree of heterosis varied from cross to cross for ear length.For number of kernels ear -1 , the magnitude of the highest values of heterosis was 22.8% and 21.4% BS-1 x Islamabad-gold over their mid and better parental values respectively.And closely followed by Sahiwal-2002 x Azam and Sahiwal-2002 x Islamabad-gold, 22.7, 22.1% and 13.1, 18.6% over their mid and better parental heterosis.The degree of heterotic effect appeared to range from, -7.0 to 22.8% and -9.9 to 21.4% against the mid and better parental values so for as grains ear -1 concerned.

Conclusion
It is concluded from the present research work that the magnitude of heterosis and heterobeltiosis in all the studied traits showed that these inbred lines are fruitful for further breeding purpose in maize hybrids production.

[5] and Dickers and Tracy [6]
Data for the trait under study showed heterosis of 16.0% and 13.8% in cross of Azam x Islamabad-gold for mid and better parent, respectively (Table al. [10], Ali et al. [11] and Iqbal et al. [12].

Table 2
revealeds that the cross of BS-1 x Islamabad-gold had the highest values of heterosis 26.2% and heterobeltiosis 19.2% over their mid and better parental values, respectively, and closely followed by cross Islamabad-gold x Islamabad-white, 24.8, 20.8% heterosis MP, BP.The range of magnitude of heterotic effect among the crosses appeared to be from -12.6 to 26.2% and -17.5 to 20.8% against their mid and better parental values, respectively.Table2showed that the highest values 15.2cm and 14.3cm were observed in parental lines BS-1 and Sahiwal-2002.In case of crosses the highest ear length was recorded in cross BS-1 x Islamabad-gold and Islamabad-gold x Islamabad-white, 18.1, 16.3cm, respectively.And the minimum ear length was recorded in cross Islamabad-white x Azam and Islamabad-white x Islamabad-gold 11.8 11.5cm.These finding are in agreement with work quoted by Iqbal et al. [15] and Guimaraes and Souza [16].