Estimation of Magnitude of Heterosis and Heritability in Sunflower in 8X8 Half Diallel Population

Selected eight inbreed line were used in crossing as half diallel fashion to find out different genetic parameter as well as targeting superior combination for hybrid vigour. Sunflower first introduce in Bangladesh 1980 by Bangladesh Agricultural Research Institute and Mennonite Central Committee. BARI Sunflower-1(Kironi) and BARI Sunflower-2 is only two released variety. But major obstacles for sunflower cultivation are both varieties are more than 1.50m height and require > 100 days for maturity. As this country is facing climate change unfavorable weather, sunflower cannot withstand in stormy weather. Specially at the time of prematurity stormy weather causes lodging due to over height, it is essential to develop dwarf stature plant.  Due to strong crop competition in winter it cannot fit in major cropping pattern T-Aman-Mustard-Boro due to it long duration. Bangladesh has accessible land of 0.85 million hectares in saline areas (Banik et al., 2011). These lands can be used for sunflower cultivation as it is moderately saline tolerant (Rahman et. al. 2018). On the other hand in different part of Bangladesh (e.g. Cumilla, Manikgonj, Sherpur, Jamalpur, Netrokina, Tangail, Dinajpur, etc.), a huge amount of lands are kept fellow after T. Aman harvest. These current fellow lands can be easily used by sunflower cultivation if short duration varieties are available. Both plant height and days to maturity were considered as favorable for negative heterosis to obtain dwarf plant stature and short duration plant to fit in existing cropping pattern in Bangladesh. Positive heterosis is considered desirable for other yield contributing traits. The hybrid HE15, HE17 and HE16 showed significant negative heterosis both for mid parent and better parent. Negative heterosis for plant height is desirable to adopt hybrid in unfavorable weather condition. The Hybrid HE15 showed both for significant negative mid parent and better parent heterosis. High heritability along with significant mid parent and better parent heterosis indicate scope of utilization of hybrid as commercial and further use in breeding programmes. Several outstanding cross combinations, HE17, HE16, HE14, HE15, and HE18 showed significant and desirable heterosis for seed yield per plant over mid parent and better parent. The hybrid combinations HE17, HE16 and HE14 could be utilized to exploit the heterosis as well as commercial multiplication of seed to get direct benefit by the farmers.

In Bangladesh sunflower has been introduced as an oilseed crop by Bangladesh Agricultural Research Institute and Mennonite Central Committee (MCC) in 1980 (Rahman, 2009). Its production was limited to very small areas and to the experimental field during 1980s. Now it is minor oilseed crop in Bangladesh. Sunflower covers 0.019 lac hectare of land in our country are producing 0.042 lac metric ton of seed during 2017-18 (Anon., 2019a. Major sunflower growing area in Bangladesh is Faridpur, Kushtia, Barisal, Rangpur, Tangail, Patuakhali, Rajshahi, Khulna and Satkhira region. Good scope for sunflower as an oil crop exists for some areas. The cultivated area of oilseed in Bangladesh is 7.24 lac hectares, from which 9.70 lac metric ton seed is produced and 3.38 lac metric ton oil is extracted (Anon., 2019a). On the other hand, annual demand of oil is 1.32 million tons oil [(22g/head/day, (Mallik, 2013) 164.60 million population (Anon., 2018)]. If we analyzed annual demand and production it is found deficit of oil is 75%. So Bangladesh is very deficit in vegetable oil supply. Domestic production can hardly meet 25% of the requirement. Oleiferous Brassica is the main source of domestic vegetable oil supply in Bangladesh (Mallik, 2013).
Over the past decades sunflower oil has become popular worldwide. Sunflower oil is light in taste and appearance and supplies more Vitamin E than any other vegetable oil. It is a combination of monounsaturated and polyunsaturated fats with low saturated fat levels. The oil is typically extracted by applying great pressure as like as mustard seeds and collecting the oil. The protein-rich cake remaining after the seeds have been processed for oil is used as a livestock feed.
For the development of hybrids, inbred lines are essential. The suitable inbred parents can be identified through combining ability test. The heterosis has also been recognized as one of the major land marks in crop improvement. Hence, there is a need to develop local hybrids to save the foreign exchange and also to increase the productivity. This is the need of time to produce sunflower hybrids which are well suited to local environment, have well yield potential for seed as well as oil contents. Estimation of combining abilities at both general and specific levels and manifestation of heterosis for yield components is an important criterion for obtaining productive hybrids. Sunflower is one of the important crop in which occurrence of heterosis is highly related with genetic distance between the parental lines.

Material and Methods
Twenty eight F1's were developed through crossing between eight parents following 8 x 8 half diallel fashion (Table 1). Seeds of 28 hybrids along with parents were sown during Rabi season of 2017-18 using RCBD design with three replications. The unit plot size was 4m x 4m with spacing 50cm X 25 cm. ISSN 2166-0379 2021  Staggered sowing of selected inbreed lines was carried out three times at an interval of two days to ensure synchronization of all inbreeds. In order to prevent undesirable pollination, heads of inbreed lines were covered with cloth bags a day prior to opening of first ray floret. Cloth bags were only open when hand pollination was done. Pollen from the inbred lines was collected in petridis from which using A4 paper applied to the flowers of female lines using camel hairbrush during morning hours usually 9.30 am-11.30 am. The pollination was repeated for five to six days in each of the combination to ensure sufficient seed set and simultaneously, parental lines were maintained by self-pollination. The heads of all the resultant 28 hybrids and 8 parents were harvested, dried and threshed separately.

Estimation of Heterosis
Heterosis expressed as percent increase or decrease in hybrid vigour over its better parent (BP), mid parent (MP) values in the desirable direction estimated in terms of different parameters.
(i) Mid parent heterosis (MP)/Relative heterosis (RH) expressed as percent deviation of mean performance of F1 from mid parents value, i.e. average value of female and male parents involved. It was estimated as formula suggested by Turner (1953).
Mid parent heterosis/Relative heterosis (RH) = MP= Mean value of the parents for respective hybrid F1= Mean performance of the hybrid (F1).
(ii) Better parent (BP)/Heterobeltiosis (HB) expressed as percent deviation of mean performance of F1 towards better parent in respect to desired direction. It was estimated as formula suggested by Fonseca and Patterson (1968).

Heterosis
Negative heterosisis considered beneficial for days to maturity and plant height and positive heterosis is considered desirable for other yield contributing traits. Heterosis estimated over mid parent and better parent are presented in Table 3 and 4, respectively. The salient features of heterosis for different characters are described below:

Days to Maturity
Mid parent and better parent heterosis ranged from -95 (HE18) to 658 (HE3) and -97 (HE22) to 290 (HE3), respectively. Among the 28 cross combinations, significant positive heterosis for mid parent was observed in 12 crosses and eight crosses showed better parent heterosis. Both significant negative heterosis over mid parent (-95%) and better parent (-97%) were observed in four crosses. For days to maturity negative heterosis is desirable to get early maturing hybrid. The crosses HE18, HE15, HE17and HE16 showed significant negative heterosis over mid parent and the crosses HE15, HE17, HE16 and HE14 showed significant negative heterosis over better parent. The presence of negative heterosis for days to maturity was reported by Bharathi et al. (2007), Chavan (2013), Reddy and Nadaf (2013).

Seed Yield per Plant
Positive heterosis for seed yield per plot is an important aspect for the improvement of seed yield in sunflower. Table 3. Heterosis over mid parent and better parent for number of seed per head, seed weight per head, 100 seed weight and seed yield per plot in sunflower Sl. No.

Heritability
Significant difference was observed among the inbreds which used for crossing in half diallel fashion for the character days to maturity, plant height, head diameter, number of seed per head and for seed yield/plant. Genotypic coefficient of variation and phenotypic coefficient of variation were close to each other for the character days to maturity, plant height, stem diameter and for seed yield per plant which indicate additive gene action. High heritability found for the characters days to maturity, plant height, stem diameter and for seed yield/plant. NS= Number of seed per head, SW= Seed weight per head, rg= Genotypic correlation, rp= Phenotypic correlation, ** = Significant at 1% level, * = Significant at 5% level.

Conclusion
High heritability along with significant mid parent and better parent heterosis indicate scope of utilization of hybrid as commercial and further use in breeding programmes. Several outstanding cross combinations, HE17(P3 x P7), HE16 (P3 x P6), HE14 (P3 x P4), HE15 (P3 x P5), and HE18 (P3 x P8) showed significant and desirable heterosis for seed yield per plant over mid parent and better parent. The hybrid combinations HE17, HE16 and HE14 could be utilized to exploit the heterosis as well as commercial multiplication of seed to get direct benefit by the farmers.