Specific Combining Ability Mean Squares Research Articles

Assessment of grain quality traits in rice under normal and water deficit condition

The main objective of this study was to assess the combining ability for rice grain quality to recognize the most desirable genotypes for rice breeding programs. A half diallel cross was made among eight rice genotypes. The obtained 28 F1 and their parents were evaluated in two separate irrigation experiments; the first experiment was irrigated every four days (normal condition). The second experiment was irrigated every ten days (a stress condition). The two experiments were designed in randomized complete block design with three replications. The results indicated that water deficit treatment significantly reduced all the studied traits except for amylose content % was increased under stressed treatments. General combining ability mean squares were highly significant for all the studied features except gelatinization temperature under drought irrigation. Specific combining ability mean squares were highly significant for grain elongation % under both conditions and amylose content % under water deficit; this indicates the importance of additive and non-additive genetic effects in the inheritance of these traits. Two crosses, Sakha106 × Sakha107 and Sakha106 × Sakha108 had the highest desirable mean values for hulling (%), milling (%), head rice, and gelatinization temperature, also lowest amylose content under both conditions. Three crosses, Giza 179 X Sakha 107, Giza 179 X Sakha 108, and Sakha 106 X Sakha 108, had the highest mean values of grain elongation % under both conditions. The cross Sakha107 × sakha108 showed highly significant positive desirable SCA effects for hulling (%) milling (%) gelatinization temperature and grain elongation. The varieties Sakha 107 and Sakha108 were the best general combiners and could be used in breeding programs for improving all the studied traits under both conditions.

Grain Fe and Zn content, heterosis, combining ability and its association with grain yield in irrigated and aerobic rice

Genetic improvement of rice for grain micronutrients, viz., iron (Fe) and zinc (Zn) content is one of the important breeding objectives, in addition to yield improvement under the irrigated and aerobic ecosystems. In view of developing genetic resources for aerobic conditions, line (L) × tester (T) analysis was conducted with four restorers, four CMS lines and 16 hybrids. Both hybrids and parental lines were evaluated in irrigated and aerobic field conditions for grain yield, grain Fe and Zn content. General Combining Ability (GCA) effects of parents and Specific Combining Ability (SCA) effects of hybrids were observed to be contrasting for the micronutrient content in both the growing environments. The grain Fe and Zn content for parental lines were negatively correlated with grain yield in both the contrasting growing conditions. However, hybrids exhibited positive correlation for grain Fe and Zn with grain yield under limited water conditions. The magnitude of SCA mean squares was much higher than GCA mean squares implying preponderance of dominance gene action and also role of complementary non-allelic gene(s) interaction of parents and suitability of hybrids to the aerobic system. The testers HHZ12-SAL8-Y1-SAL1 (T1) and HHZ17-Y16-Y3-Y2 (T2) were identified as good combiners for grain Zn content under irrigated and aerobic conditions respectively.

Efficiencies of Heterotic Grouping Methods for Classifying Early Maturing Maize Inbred Lines

The success of a hybrid breeding program is dependent on available heterotic patterns for exploitation of grain-yield heterosis. The efficiency of the assignment of germplasm lines into heterotic groups is a prerequisite for obtaining useful heterotic patterns among germplasm lines. A total of 256 maize hybrids, comprising 244 top crosses, six diallel cross hybrids, and six checks, were grown under Striga infestation, drought, and optimal conditions, from 2015 to 2017. The study determined the combining abilities of the parental inbreds, classified the inbreds into heterotic groups, and compared the efficiencies of the following four grouping methods for classifying the inbreds: specific combining ability (SCA) effect of grain yield; general combining ability (GCA) effects of multiple traits (HGCAMT); SCA and GCA (HSGCA) for yield; and single nucleotide polymorphism-based genetic distance (SNP-based genetic distance (GD)). Significant GCA and/or SCA mean squares were revealed for most measured traits in all test environments. Sums of squares (SS) due to GCA were higher than SCA SS for measured traits in all test environments. The HSGCA, SCA, and SNP-based GD methods identified four heterotic groups, whereas the HGCAMT identified three groups, in all environments. The additive gene effect was preponderant in the inheritance of most measured traits. The efficiencies of the grouping methods varied with the test environments. The HSGCA and SCA methods were the most efficient for grouping in all test conditions. For practical breeding purposes, the HGCAMT and HSGCA methods were recommended under Striga infestation and drought, respectively. The heterotic patterns, which were revealed in this study, were effective for planning hybridization schemes for developing high-yielding, Striga-tolerant/resistant, and drought-tolerant maize hybrids for stressful environments.

BREEDING FOR SOME QUANTITATIVE TRAITS IN COMMON WHEAT (TRITICUM AESTIVUM L) USING MOLECULAR MARKER TECHNIQUE

A diallel cross set was carried out among six parents of common wheat Varieties without reciprocal crosses to study the inheritance of yield and its components. - Griffing method :- Genotypes, parents and the resultant crosses mean squares were found to be highly significant for most traits studied at the two different nitrogen levels and their combined data. General combining ability (GCA) and specific combining ability (SCA) mean squares were found to be highly significant for most characters under examination. The interaction of the two different nitrogen fertilizer levels with general and specific combining ability mean squares were found to highly significant for some traits . Concerning grain yield per plant, five hybrid combinations showed significant specific combining ability effects . - The graphical analysis:- Partial dominance was found in the inheritance of days to heading and grain yield per plant. Complete dominance was found in the inheritance of days to maturity, plant height no. of spikes per plant. Over dominance was detected to be involved in the genetics of some traits. - Hayman method:- The additive genetic variance () was found to be highly significant for all traits studied except number of grains per spike and grain yield per plant . The dominance genetic variation and were found to be highly significant for all traits studied . The average degree of dominance (/)1/2 was found to be greater than unity for all traits under investigations. Moderate heritability values were detected for heading date, plant height and spike length . - Jones method: The additive genetic variance (a) was found to be highly significant for all characters studied. The dominance genetic variation (b) was highly significant for all characters studied . Assessing genetic diversity using SCoT markers: The total of 137 alleles were detected by twelve SCoT markers on the six wheat genotypes. The lowest genetic distance was between Gemmeiza11 and Line3 and the highest genetic distance was between Gemmiza11 and Line2.

Combining ability analysis of yield and yield components in selected rice (Oryza sativa L.) genotypes

This study was conducted to analyze the combining ability for yield and yield contributing traits of selected rice genotypes. Eighteen F2 populations developed by half-diallel mating design and seven parental lines were planted in randomized complete block design in three replications. Analysis of variance indicated that genotypes, general combining ability and specific combining ability mean square values were highly significant (p ≤ 0.001) for all measured traits which indicated the genetic diversity of the parents and the importance of both additive and nonadditive gene effects in the inheritance of the measured traits respectively. Parent P2 (WAC 18-WAT 15-3-1) followed by parent P1(WAB 1573-22-B-B-FKR 4-2-WAC 1-TGR 3-WAT9-1) were the best general combiners for days to flowering, number of effective tillers per hill, panicle length, flag leaf length and width, plant height, and grain yield per plant. Hybrid combinations with good mean performance, desirable SCA estimates and involving at least one of the parents with high GCA would be considered for favorable allele combinations. As a result cross combinations involving parent with good GCA (P2), WAC 18-WAT 15-3-1 x SR33701-HB3330-78 (2.54) had the high desirable grain yield followed by crosses, SR33701-HB3330-78 x SR33859-HB3324-93 (2.34), SR33701-HB3330-78 x SR33859-HB3324-133(2.43), and SR33859-HB3324-93 x SR33859-HB3324-133(1.48) which gave high SCA value in the required direction for grain yield. In general, the crosses showing significant and desirable combining ability effects were associated with better per se performance of their respective parents.

PERFORMANCE AND COMBINING ABILITY FOR STRAW YIELD AND RELATED CHARACTERS IN A DIALLEL CROSS OF FLAX (Linum usitatissmum, L.) UNDER DIFFERENT SOWING DATES

Thirty six entries of flax (Linum usitatissmum, L.) involving eight parental genotypes and their twenty eight hybrids were evaluated for straw yield and its related traits in the F1 during (2015/2016) and F2 populations during (2016/2017) under early (F2D1) and late (F2D2) sowing dates (two environments) in the Agricultural Research Station, Faculty of Agriculture, Ain Shams University at Shalakan, Kalubia Governorate. Mean squares due to genotypes, parents and crosses were highly significant for straw yield, plant height, technical stem length, fiber yield/plant, fiber percentage, fiber length and fiber fineness in the F1 and F2 generations (at early and late sowing dates), indicating that parental genotypes as well as their F1 and F2 generations exhibited reasonable degree of variability for all studied traits. Highly significant variations mean performance were found for parental genotypes and hybrids for straw yield/plant and its related traits in the F1, F2D1and F2D2, indicating presence of wide genetic variability among studied genotypes. The highest mean values were recorded under all studied environments, for straw yield/plant, fiber yield/plant and fiber fineness were found by S. 402/1 genotype, while Sakha 5 gave the highest mean values for plant height, technical stem length and fiber length. General and specific combining ability mean squares were highly significant for all studied traits in F1, F2D1 and F2D2 with the exception of a few cases, indicating the importance of both additive and non-additive gene effects in the expression of straw yield and its components. The additive effects were more important than non-additive effects under all studied environments for straw yield/plant (except at F2D2), plant height (except at F1), fiber percentage and fineness. On the other hand, the non- additive effects were more effective than additive effects for technical stem length, fiber yield/plant and fiber length. Results showed that the parents; Giza 11and Giza 12 for straw yield/plant, Sakha 5 for plant height and fiber length, Sakha 6 for fiber yield/plant, Jowhar for fiber percentage and S. 402/1, Sakha 2, Giza 12 and Sakha 5 for fiber fineness, these parents appeared to be the best general combiners for these traits. Some of the crosses exhibited highly significant and positive SCA effects included high x high and high x low general combiner parents, suggesting that the breeding procedure which utilize both additive and non-additive genetic variances would be more useful for improvement of straw yield and its components of flax.

Inheritance and combining ability of grain yield in half diallel barley population

Studies on the genetic control of grain yield are of great importance for devising effective breeding programmes for yield gain in barley. Hence, inheritance of grain yield, heterosis and combining ability was investigated in barley population obtained from half-diallel crossing among 7 parental lines. The analysis of variance revealed that mean squares due to genotypes were highly significant for grain yield indicating wide diversity among the parental materials usedin the study. Mean squares of general combining ability (GCA) and specific combining ability (SCA), the ratio of GCA to SCA mean squares and portion of additive and dominance variances showed, the importance of both additive and non-additive gene effects for grain yield. The non-significant ratio of GCA to SCA mean square highlighted that non-additive gene effects were more important than additive effects. Distribution of dominant and recessive alleles in parentswas asymmetrical and parents possess the majority of recessive alleles. Since an average degree of dominance has values greater than 1, which indicated the over-dominance type of gene action in the inheritance of the grain yield. The parent BHS400 was considered suitable according to its yield capacities and general combining ability effects. Only 2 crosses viz., BHS400 X RD2660 and BHS400 X RD2552 had significantly higher grain yield than that of the check variety (BHS400), high significant SCA values and high significant useful heterosis values. Considering average narrow-sense heritability and over-dominant effects in the genetic control of grain yield it is better to postpone selection for this trait until advanced breeding generations. Doi.org/ 10.25174/2249-4065/2018/83278

HEAT TOLERANCE IN SOME BREAD WHEAT GENOTYPES UNDER TWO SOWING DATES

A 7x7 half diallel cross along with their parental wheat cultivars were evaluated under two sowing dates (19th Nov. and 17th Dec.).The results revealed that mean squares due to sowing dates, genotypes and genotypes x sowing dates interaction were significant for most of the studied traits. Delaying sowing date to Dec. reduced all studied characters compared to the normal sowing date except electrolyte leakage which increased by delaying sowing date. Heterosis over better parents showed that, the best hybrids under stress condition were Misr 2 X Giza 168 and Sids 1 X Giza 168 for grain yield / plant and some of other studied traits. General and specific combining ability mean squares indicated the importance of both additive and non-additive gene effects in the inheritance of the studied traits with few exceptions. However, the additive effect was more important than the non-additive effects in the inheritance of days to 50% heading, plant height, No. of spikes/ plant,No. of kernels / spike and 1000-kernel weight while, the non-additive effects were more important than the additive effects in the inheritance of electrolyte leakage and flag leaf area. The best general combiner parents for grain yield / plant and some of other studied traits were Gemmeiza 11 and Giza 168under stress condition. The best hybrids for SCA effects were Sakha 93 X Sids 1, Gemmeiza 11 X Giza 168, Misr 2 X Giza 168 and Sids 1 X Giza 168 under stress condition for grain yield / plant and some of other studied traits. The crosses Gemmeiza 11 X Giza 168 (HSI 0.36), Gemmeiza 7 X Giza 168 (HSI 0.58) and Sakha 93 X Giza 168 (HSI 0.60) have recorded the lowest values of heat susceptibility index (HSI), indicating their tolerance to heat stress (late sowing date).

Combining ability and performance of extra-early maturing yellow maize inbreds in hybrid combinations under drought and rain-fed conditions.

Maize (Zea mays L.) is a major staple food and cash crop in sub-Saharan Africa (SSA). However, its production and productivity are severely constrained by drought. A total of 120 single-cross hybrids and an open-pollinated control variety were evaluated for 2 years at two locations under managed drought and rain-fed conditions in Nigeria. The objective of the present study was to assess their performance, classify them into distinct heterotic groups and identify promising hybrids for commercialization in the West and Central Africa sub-region. General combining ability and specific combining ability mean squares were highly significant for grain yield and other traits under the research environments. However, there was a preponderance of additive gene action over non-additive. Only six out of 39 inbreds were classified into distinct heterotic groups by the testers. The highest-yielding drought-tolerant hybrid, TZEEI 102 × TZEEI 95, out-yielded the open-pollinated control variety by 43·70%. The average yield reduction under drought was 54·90% of the yield under rain-fed conditions. The hybrids TZEEI 81 × TZEE1 79, TZEEI 100 × TZEEI 63 and TZEEI 64 × TZEEI 79 were the highest-yielding and most stable across environments. These outstanding drought-tolerant hybrids, which are also resistant to Striga, have the potential to contribute to food security and increased incomes in SSA and should be tested extensively on-farm and commercialized.

Combining ability analysis of cassava (Manihot esculenta Crantz) genotypes for cassava mosaic disease in Zambia

Despite the importance of cassava as a staple crop in Luapula province and other regions of Zambia, there is a lack of information on the resistance to diseases and associated combining ability of the locally cultivated cassava cultivars. Therefore, this study was carried out in 2010/2011 to: identify progeny with resistance to cassava mosaic disease (CMD); evaluate the performance of F1 progeny for agronomic traits and determine general combining ability and specific combining ability for resistance to CMD. A total of 809 genotypes comprising of parents and progeny were developed through controlled crossing and evaluated using α-lattice design. The general combining ability (GCA) and SCA mean squares (MS) were highly significant (P<0.001) for CMD. The total sum of squares (SS) for CMD was mainly accounted for by specific combining ability (SCA) effects (67.9%). Bangweulu a local highly susceptible cultivar had the most negative, significant (P<0.001) GCA effect among the landraces. In summary, the results indicated that the local landraces (Bangweulu and Kampolombo) used as parents can be sources of CMD resistance.

Heterotic Patterns of IITA and CIMMYT Early‐Maturing Yellow Maize Inbreds under Contrasting Environments

Drought and low soil nitrogen (low‐N) constitute major constraints to maize (Zea mays L.) production in West Africa (WA). The International Institute of Tropical Agriculture (IITA) and International Center for Maize and Wheat Improvement (CIMMYT) have developed drought and low‐N tolerant inbreds for Africa. Combinations between selected IITA and CIMMYT inbreds could produce outstanding hybrids. Diallel crosses of 12 IITA and five CIMMYT early yellow inbreds plus four checks were evaluated under drought, low‐N and optimal conditions at four locations in Nigeria for 2 yr. The objectives were to examine the combining ability of the inbreds for grain yield and other traits, classify the lines into heterotic groups, identify best testers under the contrasting environments, assess genotype × environment interactions and evaluate the yield performance and stability of single‐cross hybrids. Grouping of the inbred lines was done with heterotic group's specific combining ability (SCA) and general combining ability (GCA) (HSGCA), single nucleotide polymorphism based genetic distance (SNP‐GD) and GCA effects of multiple traits (HGCAMT) methods. The GCA mean squares for all traits were greater than SCA mean squares in all environments. The inbreds were classified into four heterotic groups each across environments by HSGCA and SNP‐GD while HGCAMT method placed them into three groups. HGCAMT was the most efficient followed by HSGCA and then SNP‐GD method. The HGCAMT identified inbreds ENT 17, ENT 15, and ENT 8 as best testers for heterotic Groups 1, 2, and 3. Hybrids TZEI 17 × ENT 15, and TZEI 149 × ENT 15 were outstanding across environments.Core Ideas Seventeen inbreds from CIMMYT and IITA were classified into four heterotic groups each across environments by HSGCA and SNP‐GD while HGCAMT method placed them into three groups. The HGCAMT is the most efficient heterotic grouping method and offers a great opportunity for grouping IITA inbreds that are yet to be grouped. The HGCAMT identified inbreds ENT 17, ENT 15, and ENT 8 as best testers for heterotic Groups 1, 2, and 3, across environments. ENT13, TZEI 17, and TZEI 16 may provide genes for drought and low‐N tolerance for broadening and diversifying genetic base of germplasm and to develop hybrids adapted to sub‐Saharan Africa. Planned crosses involving IITA and CIMMYT inbreds could produce outstanding hybrids for commercialization in SSA.

Combining Ability Analysis of Storage Root Yield and Related Traits in Cassava at the Seedling Evaluation Stage of Breeding

Selection of genotypes at the seedling evaluation stage of cassava breeding for advancement is largely based on high heritability traits. Moreover, combining ability and family data at this stage are rarely analyzed, leading to a loss of potential genetic information. This study was conducted to estimate the general combining ability (GCA) of nine cassava parents and specific combining ability (SCA) of their crosses for storage root yield (SRY) and related traits, as well as to determine the gene action controlling these traits. Thirty-six full-sib cassava families were developed from a 9 x 9 half-diallel mating design and evaluated in a 6 x 6 triple lattice design. The family mean squares (MS) were significantly different for all traits assessed, suggesting significant differences among families for all traits. The GCA MS were significant for all traits, whereas SCA MS were significant for only storage root number (SRN). Percentage sum of squares attributable to GCA accounted for >50.0% of variability expressed by families in five of the seven traits studied, indicating predominance of additive gene effects in controlling expression of most traits. Parent CT4 was the best general combiner for SRY, SRN, and resistance to cassava brown streak and mosaic diseases, while crosses NASE3 x CT2, CT5 x CT3, and NASE3 x CT4 had desirable SCA effects for SRY. Correlation analysis indicated a possibility of selecting for SRY and quality traits simultaneously. Simultaneous selection of these traits at the seedling generational stage of cassava breeding could reduce the cassava breeding cycle.

Combining Ability of Certain Agronomic Traits in Quality Protein Maize under Stress and Nonstress Environments in Eastern and Southern Africa

ABSTRACTGrowing maize (Zea mays L.) hybrids tolerant to drought and low‐nitrogen (N) stress would significantly reduce yield losses occurring in Africa. This study evaluated the performance of quality protein maize (QPM) F1 hybrids, and general (GCA) and specific combining ability (SCA) of QPM inbred lines for grain yield and other agronomic traits under stress and nonstress environments. A diallel cross of 15 QPM inbred lines was evaluated under drought and low‐N stresses and optimal conditions in a total of 17 environments in Eastern and Southern Africa. Significant variations were observed among the hybrids for all measured traits. TZMI703 × (6207QB/6207QA), GQL5 × (6207QB/6207QA), and CML511 × (6207QB/6207QA) were identified as the best single crosses across environments. The GCA and SCA mean squares were significant for all measured traits, indicating that additive and nonadditive genetic effects were important in this set of genotypes under all test environments. The GCA effects were more important under drought stress, and SCA effects were more important under low‐N and optimal conditions for grain yield. There was preponderance of GCA effects for most agronomic traits tested in all environmental conditions. Inbred lines CML159SR, GQL5, CML159, and CML312SRQ exhibited favorable GCA effects for grain yield under stress and optimal conditions, indicating that the genetic systems controlling a given trait under different conditions are at least partially similar. Cross combinations with favorable SCA effects for grain yield and other traits were also identified. Generally, this study provided evidence that good performance can be achieved under stress and nonstress conditions in QPM germplasm.

Combining ability of maize (Zea mays) inbred lines resistant to Striga hermonthica (Del.) Benth evaluated under artificial Striga infestation

The parasitic weed Striga affects maize on an estimated 20 million ha in Africa, making it a major cause of maize yield reduction from near world average of 4.2 t/ha few decades ago to the present 1.5 t/ha. The objectives of this study were to examine the combining ability of 20 inbred lines and identify single crosses which can be used to develop other hybrids resistant to Striga hermonthica (Del.) Benth. Fourteen female lines were mated using North Carolina Design II with all six males. The resulting 84 F1s along with six commercial checks were evaluated in four separate trials for two rainy seasons during 2010. The trials were conducted on station under both artificial Striga infestation and Striga free environments using standard procedures at the Kibos and Alupe sites, both in the Kenya’s Lake Victoria Basin. Data were recorded on Striga counts, Striga damage rating (SDR), grain yield and other agronomic traits. General combining ability (GCA) and specific combining ability (SCA) effects were computed using SAS. The new F1 hybrids outperformed the commercial checks in grain yield and reaction to Striga. Single crosses JI-30-3/TESTR 151, JI-30-18/TESTR 151, CML206//56/44-6-3-7-1/TESTR 149 and JI-30-18/TESTR 156 gave the highest yield while single cross JI10-28-#/TESTR 136 gave the lowest yield. The ratio of GCA: SCA mean squares exhibited a predominance of additive gene effects in the inheritance of Striga resistance traits as opposed to dominance gene effects. Inbred lines with good GCA for yield and Striga resistance traits were identified as TESTR 151, TESTR 156 and OSU231//56/44-6-4-17-3. The high GCA inbred lines and the superior single crosses will provide a basis for future use perse and also development of three-way and double cross hybrids to be grown in Striga prone areas of the Lake Victoria Basin in eastern Africa. Key words: Maize, Striga hermonthica, general combining ability (GCA), specific combining ability (SCA), host plant resistance, sub-Saharan Africa.

English

Thirty six (36) genotypes (eight parents and 28 F1 diallel crosses) were grown in randomized complete block design with two replicates during 2006 at Mandura, North western Ethiopia. The experiment was executed to study the inheritance of two primary yield component traits: number of seeds per pod and 1000 seed weight. Statistical significant difference was observed between genotypes, parents and crosses for the traits considered. The mean square due to general combining ability was significant for the two traits. However, specific combining ability mean square was significant only for number of seeds per pod. Thus, both additive and non-additive types of gene actions were important in the inheritance of number of seeds per pod. Significant b1 component was obtained for number of seeds per pod. The b2 and b3 components however, were insignificant, suggesting the absence of gene asymmetry. From Wr/Vr graph, inheritance of seeds per pod was governed by partial dominance with additive gene action. Key words: Diallel crosses, general combining ability, Phaseolus vulgaris L., specific combining ability.

Combining ability and genetic components for pod and seed traits in cowpea lines

The identification of suitable parental genotypes potentially generating superior lines with traits contributing to the overall yield of cowpea is an important step in the development of improved varieties. Eight parents and their 28 hybrids obtained through diallel crossing design were evaluated in a randomized complete block design with three replications. Highly significant differences among the parents and their hybrids for different traits were observed. General combining ability (GCA) mean squares were larger than the specific combining ability mean squares for all the traits analysed. The ratio h 2 /H 2 revealed different number of genes controlling the traits, pointing out their polygenic inherited control. The estimated low narrow sense heritability recorded in this study indicated that recurrent selection procedure could be effective to improve the analysed traits in the genotypes included in this study. Kananado with large, positive and significant GCA effects was identified as the parent with desirable genes for the genetic improvement of the considered yield component in cowpea. In addition, IT03K-316-1 x Cowpea-2 and IT99K-316-2 x Kananado seemed to be the best hybrids for number of pods/plant and 100-seed weight, respectively.

General and Specific Combining Ability for Quantitative Characters in Sunflower

Seven sunflower (Helianthus annuus L.) inbred lines were crossed in 7´7 half diallel to obtain 21 F1 hybrids which further used to estimate general combining ability (GCA) and specific combining ability (SCA) effects for yield, head diameter, 1,000-seed weight, plant height and oil content of sunflower. The 7 inbred lines and 21 hybrids were planted in a randomized complete block design with three replications at Nakhon Ratchasima, Thailand during 2008-2009. General combining ability and specific combining ability were estimated for seed yield, head diameter, 1,000-seed weight, plant height and oil content. The results revealed that mean squares for GCA were highly significant for head diameter and significant for yield and oil content. Mean squares for SCA were highly significant for 1,000-seed weight and plant height, while those of yield, head diameter and oil content were non-significant. Components of variance showed that the GCA variance was higher than the SCA variance for yield, head diameter and oil content. These results indicated that additive gene action was more important than non-additive gene action for these traits. Inbred line 5A exhibited the highest GCA effects for yield and oil content, followed by the line 2A. Among all the crosses, 2A´5A showed the greatest positive SCA effects for 1,000-seed weight and oil content. Thus, the two inbred lines (2A and 5A) revealed good potential to be used as parents for hybrid.

COMBINING ABILITY ANALYSIS IN DIALLEL CROSSESِ OF TOMATO ( Lycopersicon Spp.)

An experiment was conducted by using four tomato genotypes vs. (1)the wild species (L.pimpinellifolium) and three varieties of cultivated tomato (Lycopersicon esculentum Mill.) namely (2) Pearson (3) Early Parson (4) mahaly (karmless).The objectives of this experiment was to enter the wild specie(L.pimpinellifolium) in programme of full diallel crosses and to estimate of several genetic parameters. Analysis of variance revealed highly significant differences among genotypes ,parents and hybrids for all the characters of General combining ability mean square was significant for plant height, No. of branches/plant, No. of total leaves/ plant, average leaf area, No. of leaf lets, flowering earliness, No. of flowers/in florescence, No. of in florescence/ plant, early picking, No. fruits/ plant, mean fruits weight, mean total yield/ plant, average fruit diameter, No. of locules / fruit and vitamin C content, while the specific combining ability mean squares were significant for plant height , early picking, mean fruits weight, mean total yield/ plant, average fruit diameter and No.of locules/fruit.The results showed that wild tomato species (L.pimpinellifolium) was the best combiner for the favorable characters while specific combining ability results for each hybrids indicated that the hybrid(Early Parson X L.pimpinellifolium) have a good S. C. A. for the most favorable characters.

HETEROSIS AND COMBINING ABILITY IN MAIZE (Zea mays L.) DIALLEL CROSSES

A half diallel cross among developed eight yellow maize inbred lines and made at Gemmeiza Agricultural Research Station, Agricultural Research center (ARC), Egypt during 2007 growing season . Parents , F1 crosses plus two checks ( SC 166 and SC 3084) were evaluated at Gemmeiza and Sids Agricultural Research Stations in 2008 growing season. Data were recorded on grain yield, resistance to late wilt ,days to 50% silking , plant height and ear height. Data were genetically analyzed according to the procedures developed by Griffing (1956) method-4 model-1.The obtained results indicated that, mean squares associated with locations were highly significant for all studied traits except resistance to late wilt . Also, mean squares due to genotypes and their partitions : crosses, parents and parents vs. crosses showed highly significant differences. General and specific combining ability mean squares and their interaction with locations were highly significant for all studied traits. Also, the ratio of GCA /SCA revealed that additive and additive x additive type of gene action were more important in expression of all traits under two locations and their combined. Inbred lines Gm.701 and Gm.705 have significant GCA effects for grain yield and resistance to late wilt, while inbred line Gm.709 considered the best combiner for earliness and plant height under combined data. The eight crosses Gm.701 x Gm.705 (10.65 %), Gm.701 x Gm.712 (8.40 %) , Gm.705 x Gm.710 (8.40 %), Gm.701 x Gm.709 ( 8.07 %) , Gm.701 x Gm. 710 (7.10 %), Gm.715 x Gm.718 (6.13%) , Gm.705 x Gm.706 (3.55%) and Gm.712 x Gm.715 (2.86 %) had significantly positive heterotic effects relative to the highest commercial hybrid S.C. 166 in the combined over locations. These crosses are considered as promising genotypes for grain yield and could be used in maize breeding program.

Combining ability of maize inbred lines containing genes from Zea diploperennis for resistance to Striga hermonthica (Del.) Benth

AbstractMaize (Zea mays) is a staple food crop in sub‐Saharan Africa, but its production is threatened by Striga hermonthica (Del.) Benth. Transfer of resistance genes from wild relatives may increase resistance to S. hermonthica in tropical maize. The objective of this study was to determine the combining ability of resistance to S. hermonthica among lines containing Zea diploperennis and tropical germplasm. Forty‐five diallel crosses of 10 inbred lines were evaluated in an alpha‐lattice design with and without artificial Striga infestation at two locations each in the Republic of Benin and Nigeria for 3 years. Results of analyses showed that only general combining ability (GCA) mean square was significant (P = 0.01) for number of emerged Striga plants (NESPP), while both GCA and specific combining ability (SCA) mean squares were significant for host damage score (HDS) and grain yield under Striga infestation. The ratio of GCA to SCA mean squares for the three traits varied from 3.5 to 57.5. Although GCA × environment interaction was significant for the three traits, two inbred lines containing Z. diploperennis (ZD 551) and tropical (TZL TC 87) germplasm had negative and significant GCA effects for NESPP and HDS and positive GCA effects for grain yield under Striga infestation in the two countries. Correlation between NESPP and HDS was strong and significant (r = 0.87, P = 0.01). Our results highlight the importance of harnessing useful genes from wild relatives to improve resistance to S. hermonthica in adapted maize germplasm.