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This study was carried out at the college of Agriculture field, University of Duhok, during 2013-2014 growing season. It involved half diallel crosses among five genotypes of pea.The seeds of genotypes (parents and F1 hybrids) were grown according to Randomized Complete Block Design with three replications, to estimate general combining ability effects of the parents and specific combining ability effects of hybrids, heterosis as deviation from mid and better parents for the following characters, Days to 50% flowering, plant-hieght (cm), numbers of branches plant-1, number of pods plant-1, pods weight plant-1 (g), number of seeds plant-1, numbers of seeds pod-1,100 seed weight (g), seed yield plant-1 (g), dry seed yield plant-1 (g), protein percentage and total chlorophyll percentage.The data was statistically analyzed according to Griffing (1956b) method 2 (fixed model). The results indicated that Parent (Petit provencal) showed the best general combination in the desirable direction for no. of pods plant-1, no. of seeds plant-1, no. of seeds pod-1, seed yield plant-1, dry seed yield plant-1 and total chlorophyll. Hybrid (Thomas laxton x Petit provencal) exhibited significant specific combining ability effect in a desirable direction for plant height, no. of branches plant-1, pods weight plant-1, no. of pods plant-1, no. of seeds plant-1, seed yield plant-1 and dry seed yield plant-1. The hybrids (Avola x Petit provencal) and (Thomas laxton x Petit provencal) gave the best heterosis in desirable direction measured as a deviation of F1 from mid-parents for days to 50% flowering, pods weight plant-1, no. of pods plant-1, no. of seeds plant-1, no. of seeds pod-1, seed yield plant-1, dry seed yield plant-1, total chlorophyll and also the same hybrids showed a high heterobeltiosis values for (5) characters for each hybrid which include (pods weight plant-1, no.of pods plant-1, no. of seeds plant-1, seed yield plant-1 and dry seed yield plant-1). Keyword: general and specific combining ability, heterosis in pea. Corresponding auther: Received:3/4/2018, Accepted:4/10/2018 INTRODUCTION Pea (Pisum sativum L.) is one of the annual herbaceous legume crop belongs to family fabaceae (leguminosae), diploid crop having 14 chromosome (2n=14, n=7) (sato et al. 2010). Pea originated in the Near East and Mediterranean regions. It is one of the world's oldest crops cultivated as early as 9,000 year ago for human food and animals feed (Pulse Canada, 2010). Pea is one of the four as most important cultivated legume and world's largest legume crop in production after soybean, peanuts and dry beans (Yoshida et al., 2007; Smykal et al., 2012). Pea is A part of M. Sc. thesis of the second author نــيدـفارــلا ةـــعارز ةـــلـجـم ( دلجملا 64 ( ددعلا ) 6 ) 8102 ISSN: 2224 9796 (Online) ISSN: 1815 316 X (Print) Mesopotamia J. of Agric. Vol. (64) No. (4) 8102 634 an economically valuable pulse crop grown around the globe for its high nutritive value, particularly proteins. Its seeds are rich in protein percent (20-25 %), 50% slowly digestible starch, 50% soluble sugars by mass and are also a source of fiber (Bastianelli et al., 1998). This crop are beneficial to human health, phytonutrients, vitamins, anti-oxidants and minerals (Pallavi et al., 2013). Pea is used for other soil restorative aim, because the pea crop through the formation of a symbiotic relationship with soil bacteria Rhizobium leguminosarum enhances soil fertility, which has the capability of fixing nitrogen from the atmosphere in to an available form for the plant uptake which can reduces the need to apply synthetic nitrogen fertilizers (McPhee, 2003). Pea genomics have been well-studied ever since the pioneering work of Gregor Mendel in nineteenth century (Samatadze et al., 2008). Hybridization is one of the plant breeding methods and the most successful approach in increasing the productivity in vegetable crops. Selection of superior genotypes genetically is the most important stage from the stand point of hybridization of vegetable crops in order to develop new genotypes which have desirable characters. Selecting of good parents and crosses one of the main important to vegetable breeders for developing high yielding varieties through either heterosis breeding or pedigree breeding (Inamullah et al., 2006).The combining ability analysis is very important and is an active tool in choosing the desirable parents for hybridization programs. The idea of combining ability was enunciated by Sprague and Tatum (1942). Dixit (2003) from a study of combining ability analysis reported that some crosses showed a significant and desirable SCA effects for number of pods plant-1, plant height and pod yield plant-1 in pea. Nassef and AL-Rawy (2013) observed hight significant GCA and SCA for plant height, number of branches plant-1, number of green pods plant-1, green pods weight plant1 and seeds pod-1, but GCA was not significant for plant height in pea. AlHamdany (2014) reported that GCA was significant for plant height, seed yield, 100 seed weight, and pods weight but not significant for seeds pod-1, while SCA for most characters was significant in pea. Heterosis is genetically a complex phenomenon depending on the equilibrium of the additive, dominance and their interaction. Heterosis point out to the phenomenon that offspring of different varieties of a species or crosses among species which show speed of development, fertility than both parents and greater biomass. The phenomenon has clearly been recognized in one form or another for centuries by various civilization (Chen, 2010). Patil et al. (2011) studied heterosis in pea and they found significant and desirable heterosis in crosses for green pod yield, number of seeds pod-1, plant height, pods plant-1 over better and mid parents. Some researchers in their studies on heterosis as deviation from mid and better parents found positive heterosis for grain yield, green pods plant-1 and negative heterosis for days to 50% flowering (Dagla et al., 2013; Sharma and Bora, 2013; Esposito et al., 2013). Kosev (2014) conducted a field study on breeding and genetic assessment of some quantitative traits in pea and showed a highest positive values of heterosis for number of seeds pod-1, plant height, and Tawfiq and Abdulla (2014) obtained negative heterosis for number of days to 50% flowering, when study the genetic analysis of pea. The main objectives of the present study is to estimate the effects of general combining ability of parents, and specific combining ability of hybrids and to نــيدـفارــلا ةـــعارز ةـــلـجـم ( دلجملا 64 ( ددعلا ) 6 ) 8102 ISSN: 2224 9796 (Online) ISSN: 1815 316 X (Print) Mesopotamia J. of Agric. Vol. (64) No. (4) 8102 634 determine the heterosis as compared with mid and best parents, by using half diallel crossing programme. MATERIALS AND METHODS This investigation was carried out at the Research farm, College of Agriculture, University of Duhok during 2013-2014 seasons, by using five different cultivars of pea ((1)Avola (2)Thomas laxton (3)Petit provencal (4)Jof and (5)Local cultivar). The cultivars were sown to obtain 10 hybrids through half diallel cross during growing season 2013. In the next season on 20th of November 2014, the F1 hybrids with parents were arranged in Randomized Complete Block Design with three replications in experimental field, each block was consisted of 15 genotypes (5 parents + 10 hybrids). Each genotype planted in three rows of 2.5m long and 75cm between rows (1 row for dry seed yield and 2 other rows for vegetative measurement). One seed per hole was sown with spacing 25cm between plant to plant in rows. Application of fertilizer was done according to the recommendations, weed control and other cultural practices were performed according to requirements. The data were collected from 6 plants for vegetative measurements except dry seed yield from 3 plants in each experimental unit on the following characters: Days to 50% flowering of plants, plant height (cm), number of branches plant-1, number of pods plant-1, pods weight plant-1 (g), number of seeds plant-1, number of seeds pod-1,100 seed weight (g), seed yield plant-1 (g), dry seed yield plant-1 (g), protein percentage and total chlorophyll percentage. Statistical analysis was done for collecting data using Griffing (1956b) method 2, model 1, using the liner model for the analysis which takes the formula of: Yijk= μ +gi + gj +sij +rk +eijk i, j = 1, 2 n k= 1, 2r Where: Yijk: observed value (ij) of the experimental unit (k). μ: population mean. gi: general combining ability (GCA) effect for the (i) parent. gj: general combining ability for the (j) parent. sij: specific combining ability effect (SCA) for the cross involving parent (i) and (j). rk: replication (block) effect. eijk: experimental error effect for observation (ij) in block (k). General and specific combining ability effects estimated as follows:

HETEROSIS AND COMBINING ABILITY EFFECTS FOR SOME TRAITS OF PEA (Pisum sativum L.)