Negative General Combining Ability Effects Research Articles

Agronomic Performance and Resistance to Maize Lethal Necrosis in Maize Hybrids Derived from Doubled Haploid Lines

Maize (Zea mays L.) is one of the most widely cultivated grain crops globally. In sub-Saharan Africa (SSA), it plays an important role in ensuring both food and income security for smallholder farmers. This study was conducted to (i) assess the performances of testcross hybrids constituted from maize lethal necrosis (MLN) tolerant doubled haploid (DH) lines under various management conditions; (ii) estimate the combining ability effects and determine the nature of gene action in the DH lines; and (iii) identify DH lines and testcross hybrids for resistance to MLN, high grain yield, and other important traits. Eleven DH lines were crossed with 11 single-cross testers using the line-by-tester mating design, and 115 successful testcross hybrids were generated. These hybrids, along with five commercial check hybrids, were evaluated across four optimum management conditions, two MLN artificial inoculations, and one managed drought environment in Kenya. Under each management condition, the effects of genotypes, environments, and genotype-by-environment interactions were significant for grain yield (GY) and most other traits. Hybrids T1/L3, T10/L3, and T11/L3 exhibited higher grain yields under at least two management conditions. A combining ability analysis revealed that additive gene effects were more important than non-additive effects for GY and most other traits, except for leaf senescence (SEN) and MLN disease severity score. DH line L3 exhibited a desirable general combining ability (GCA) effect for GY, while L5 was the best general combiner for anthesis date (AD) and plant height (PH) across all management conditions. DH lines L2, L6, and L7 showed negative GCA effects for MLN disease severity. Single-cross testers T11 and T10 were good general combiners for GY under all management conditions. Hybrids T2/L11, T9/L10, and T2/L10 demonstrated high specific combining ability (SCA) effects for GY under all conditions. This study identified DH lines and testers with favorable GCA effects for grain yield, MLN resistance, and other agronomic traits that can be used in breeding programs to develop high-yielding and MLN-resistant maize varieties. Better-performing testcross hybrids identified in the current study could be verified through on-farm testing and released for commercial production to replace MLN-susceptible, low-yield hybrids grown in the target ecologies.

Genetic analysis of late blight (Phytophthora infestans (mont.) de Bary) resistance in tomato

ABSTRACT Diallel analysis provides basic genetic information that is critically important to identify parents involved in hybridization breeding programs. This study was initiated to estimate combining ability effects and determine the type of gene action involved in inheritance of late blight resistance. Five tomato lines and 10F1 progenies produced by crossing of parents in a 5 × 5 half-diallel fashion were assessed for late blight resistance in field conditions. The combining ability ratio was greater than unity for all traits considered in this stud. At the same time, the degree of dominance was less than unity for all the traits, indicating a greater importance of additive gene effects for the inheritance of late blight resistance. The parents ’Eshete’ and ’Roma VF’ were general combiners, exhibiting significantadverse general combining ability effects for all studied traits. Specific combining ability effects of ’Roma VF × Eshete’ and ’Melkashola × Eshete’ were significantly negative for disease incidence, with all the lines exhibiting significant negative general combining ability effects for the trait, indicating transgressive segregants that are late blight resistant could be produced from crossing of these parental lines. These results, accordingly, indicated that the parents could be utilized in the crossing programme to develop late blight resistant transgressive segregant varieties.

Combining Ability Analysis of Yield-Related Traits of Two Elite Rice Restorer Lines in Chinese Hybrid Rice.

Hybrid rice breeding is an important strategy for enhancing grain yield. Breeding high-performance parental lines and identifying combining abilities is a top priority for hybrid breeding. Yuenongsimiao (YNSM) and its derivative variety Yuehesimiao (YHSM) are elite restorer lines with a high ability of fertility restoration, from which 67 derived hybrid combinations have been authorized to different degrees in more than 110 instances in China. In this study, we found that YNSM and YHSM contained three candidate restorer-of-fertility (Rf) genes, Rf3, Rf4, and Rf5/Rf1a, that might confer their restoration ability. Subsequently, we investigated heterosis and combining ability of YNSM and YHSM using 50 F1 hybrids from a 5 × 10 incomplete diallelic mating design. Our results indicated that hybrid combinations exhibited significant genetic differences, and the additive effects of the parental genes played a preponderant role in the inheritance of observed traits. The metrics of plant height (PH), 1000-grain weight (TGW), panicle length (PL), and the number of spikelets per panicle (NSP) were mainly affected by genetic inheritance with higher heritability. Notably, the general combining ability (GCA) of YHSM exhibited the largest positive effect on the number of grains per panicle (NGP), NSP, PL, and TGW. Thus, YHSM had the largest GCA effect on yield per plant (YPP). In addition, the GCA of YNSM exhibited a positive impact on YPP, mainly due to the critical contribution of seed setting percentage (SSP). Moreover, YNSM and YHSM exhibited negative GCA effects on PH, implying that YNSM and YHSM could effectively enhance plant lodging resistance by reducing the plant height of the derived hybrids. Remarkably, among the hybrids, Yuanxiang A/YNSM (YXA/YNSM), Shen 08S/Yuemeizhan (S08S/YMZ), and Quan 9311A/YHSM (Q9311A/YHSM) represent promising new combinations with a higher specific combining ability (SCA) effect value on YPP with a value more than 3.50. Our research thus highlights the promising application for the rational utilization of YNSM and YHSM in hybrid rice breeding.

Performance of testers with contrasting provitamin A content to evaluate provitamin A maize for resistance to Aspergillus flavus infection and aflatoxin production.

In sub-Saharan Africa (SSA), millions of people depend on maize as a primary staple. However, maize consumers in SSA may be exposed to malnutrition due to vitamin A deficiency (VAD) and unsafe aflatoxin levels, which can lead to serious economic and public health problems. Provitamin A (PVA) biofortified maize has been developed to alleviate VAD and may have additional benefits such as reduced aflatoxin contamination. In this study, maize inbred testers with contrasting PVA content in grain were used to identify inbred lines with desirable combining ability for breeding to enhance their level of resistance to aflatoxin. Kernels of 120 PVA hybrids generated by crossing 60 PVA inbreds with varying levels of PVA (5.4 to 51.7 µg/g) and two testers (low and high PVA, 14.4 and 25.0 µg/g, respectively) were inoculated with a highly toxigenic strain of Aspergillus flavus. Aflatoxin had a negative genetic correlation with β-carotene (r= -0.29, p < 0.0001) and PVA (r = -0.23, p < 0.0001), indicating that hybrids with high PVA content accumulated less aflatoxin than those with low to medium PVA. Both general combining ability (GCA) and specific combining ability (SCA) effects of lines and testers were significant for aflatoxin accumulation, number of spores, PVA, and other carotenoids, with additive gene actions playing a prominent role in regulating the mode of inheritance (GCA/SCA ratio >0.5). Eight inbreds had combined significant negative GCA effects for aflatoxin accumulation and spore count with significant positive GCA effects for PVA. Five testcrosses had combined significant negative SCA effects for aflatoxin with significant positive SCA effects for PVA. The high PVA tester had significant negative GCA effects for aflatoxin, lutein, β-carotene, and PVA. The study identified lines that can be used as parents to develop superior hybrids with high PVA and reduced aflatoxin accumulation. Overall, the results point out the importance of testers in maize breeding programs to develop materials that can contribute to controlling aflatoxin contamination and reducing VAD.

Identification of Heat Tolerant Cotton Lines Showing Genetic Variation in Cell Membrane Thermostability, Stomata, and Trichome Size and Its Effect on Yield and Fiber Quality Traits.

Heat stress in cotton reduces its productivity. The development of heat-tolerant cotton varieties having resilience against changing climate is feasible. The purpose of this study was to probe the genetic variability in upland cotton for heat tolerance, the association of cell membrane thermostability (CMT), stomata, and trichome size with cotton adaptation to high temperature and effective breeding strategy to advance the valued traits. Relative cell injury percentage (RCI%) in studied genotypes ranged from 39 to 86%. Seventeen genotypes were found heat tolerant on the basis of low RCI%, heat susceptibility index (HSI<1), higher number of boll/plant, and seed cotton yield (SCY). Scanning electron microscopy (SEM) of heat-tolerant genotypes revealed the presence of different size of stomata (21.57 to 105.04 μm2) and trichomes (177 to 782.6 μm) on leaves of selected genotypes. The regression analysis showed a strong and negative association of RCI% and stomata size with SCY. However, no association was observed between the trichome size, yield, and fiber traits. On the overall location basis, a significant genotype × environment interaction was observed. All selected genotypes produced a higher SCY as compared with check varieties. But the stability analysis showed that the high yielding genotypes NIA-M-30, NIA-80, NIA-83, and CRIS-342 were also wide adaptive with unit regression (bi∼1) and non-significant deviation from the regression line (S2d∼0). The ability for the combination of some heat-tolerant genotypes was estimated by using the line × tester method among nine hybrids along with their 3 testers (i.e., male) and 3 lines (i.e., females). Genotypes, CRIS-342 and NIA-Perkh, were observed as best general combiners for SCY with a negative general combining ability effects for RCI%. Five hybrids showed a positive specific combining ability and heterotic effects for studied traits and also found lowest for HSI. RCI% and SCY/plant displayed higher estimates of heritability and genetic advance, indicating the heritability due to additive gene effects and chances of effective selection. The identified heat-tolerant and wide adaptive germplasm can be further advanced and utilized in cotton breeding programs for developing heat-tolerant cultivars. Selection criteria involving CMT and stomata size concluded to be an effective strategy for the screening of heat-tolerant cotton.

STUDY ON COMBINING ABILITY FOR YIELD AND YIELD CONTRIBUTING TRAITS IN WATER STRESS TOLERANT GENOTYPES OF TOMATO (SOLANUM LYCOPERSICUM L.)

The experiment was conducted to develop tomato hybrids by identifying parental lines with estimation of good combining ability effects and their variances through line x tester analysis of 44 genotypes including 32 F1 cross combinations using 12 parents after selfing (8 lines and 4 testers). The genotypes were evaluated for the yield and contributing traits. The analysis of variance (ANOVA) showed highly significant difference for all the characters suggesting the presence of genetic variability among the studied materials. The variance values of general combining ability (GCA) were lower than the specific combining ability (SCA) for all the traits except plant height. This indicates that these traits were under the control of non-additive (non-fixable) gene effects and could be exploited by heterosis breeding. The lines L1, L2, L3, L5, and testers T2, and T4 showed a desirable significant negative GCA effect for days to first flowering and days to maturity. The line L5 showed a positive significant GCA effect for most of the traits except fruit per cluster and L4 for plant height, cluster per plant, fruit per cluster, fruit per plant, fruit diameter, and yield per plant. Based on GCA effects across ten traits L4 and L5 were identified as the most promising parental lines for inclusion in hybridization programs. Outstanding crosses based on SCA effects across ten traits were L6XT1, L2XT3, L7XT2, and L4XT4. These crosses could be considered the most promising specific combiner for most traits which can be used to develop elite tomato varieties.

Genetics of dual resistance to african stem borer, busseola fusca and spotted stem borer, Chilo partellus in sorghum

African stem borer, Busseola fusca Fuller (Noctuidae) and spotted stem borer, Chilo partellus Swinhoe (Crambidae) cause more than 40 % of grain yield loss in cereals and bothpests co-exist in mid-altitudes in Kenya. Development of sorghum with dual resistance to B. fusca and C. partellus has been difficult due to the inadequate understanding of inheritance of resistance traits to the two species. The objective of this study was to investigate the genetics of dual resistance to the two insect species in sorghum. Thirty sorghum populations derived from crossing sorghum lines with varying levels of resistance to the two insect species were studied. The experiments were conducted in two separate sites at Embu and Kiboko in Kenya with two replications per site. North Calorina Design II mating design was used. Artificial infestation with first instar neonates of each pest species was done at 30 days after planting in both sites. Data collected included sorghum damage due to the two borer species and agro-morphological traits. Genetic analyses were performed using line x tester method using Genstat statistical software. Data analyses revealed that general combining ability (GCA) and specific combining ability (SCA) effects were significant for foliar and stem damage traits, indicating that additive and non-additive gene effects conditioned resistance to B. fusca and C. partellus. Sorghum lines ICSA 464, ICSB 474, ICSB 464 and ICSA 472 and ICSB 473 exhibited desirable high negative GCA effects to B. fusca and C. partellus. These parents could be used in development of sorghum with dual resistance to B. fusca and C. partellus thus contributing to sustainable integrated management of these two stem borer species in sorghum via host plant resistance management.

Combining ability study for yield and quality traits in cucumber (Cucumis sativus L.)

Seven cucumber (Cucumissativus L.) genotypes (3 lines and 4 testers) were crossed in a line × tester mating design. The resultant 12 hybrids and their parents were evaluated using Randomised Block Design with two replications during Kharif 2018. Sufficient genetic variability was observed for all the characters under study. In this study, the parents L2 (Koradacherry local), T2 (Orathanadu local) and T3 (Aipatti local) exhibited high positive GCA (General Combining Ability) effects for yield related traits and high negative GCA effects for earliness characters. The parent T2 identified in this study may be used in multiple crossing programme to isolate high yielding varieties. Among the hybrid combinations, L2xT3, L1xT2 and L3xT4 expressed the maximum positive significant SCA (Specific Combining Ability) effects for yield and yield associated characters. In the above cross combinations one parent was a good combiner and the other was an average/poor combiner; hence the hybrids can be exploited for transgressive selection.

English

A diallel cross was produced using diverse maize (Zea mays L.) germplasm of saline tolerant and saline susceptible maize lines as parents. Agronomic performance of the offspring of the diallel cross was examined. Eight germplasm lines bearing diversified agronomic traits of five known tolerant and susceptible lines were involved as parents of the diallel cross that was evaluated at three different ecological areas viz. Gazipur, Benerpota, and Kaliganj. CZ-29 and CZ-26 had positive and significant general combining ability (GCA) effects for yield in both the saline environments, where CZ-12 possessed negative and significant GCA effects for yield in the same areas but none of the parents exhibited either significantly positive or negative GCA in Gazipur location. Of the saline tolerant lines evaluated, CZ-29 was a good source for increased yield with significant and positive GCA values in both the saline environments that was also responsible for dwarfness and earliness in all locations. CZ-26×CZ-24 yielded well except at Benerpota with an additional benefit of shorter plant type across all environments. Hybrid CZ-29×BIL-65, however, was consistent and promising over the environments for bold seed and higher yield that ranked 2nd at Benerpota (4.81 t ha-1) and Kaliganj (6.73 t ha-1) and 3rd at Gazipur (7.40 t ha-1) location for yield having significant positive specific combining ability (SCA) effects at Gazipur and Kaliganj. Moreover, six hybrids either significantly or not consistently decreased yield over the locations with negative SCA. However, considering the overall performance of the hybrids, the involvement of saline susceptible or tolerant parents was not consistent in the present study. Crosses between saline tolerant lines did not produce any tolerant hybrids or dwarf parents did not produce dwarf hybrids except CZ-29×CZ-36 that was able to produce shorter hybrid for all the locations. Therefore, among the lines evaluated in this diallel cross having a distinct different genetic background, CZ-28 and CZ-29 contributed to earliness; CZ-29 and BIL-65 reduced plant height; CZ-12 increased seed size; CZ-26 and CZ-29 improved yield. Thus, these lines should be useful sources of alleles for pyramiding, earlier maturity, shorter plant heights, increased seed size and improved yield into desired breeding lines. Key words: Diallel, maize, saline, environments, general combining ability, specific combining ability.

Diallel Analysis of Barley Resistance to Blumeria graminis

Powdery mildew, caused by Blumeria graminis f. sp. hordei (Bgh) is a common foliar disease of barley worldwide. The creation of new cultivars with durable resistance to Bgh is highly desirable. This work was undertaken to examine the resistance to Bgh in 10 genetically diverse barley parents, and to evaluate their general combining ability (GCA) and specific combining ability (SCA) effects toward determining the genetic basis of disease resistance. Two experiments, in a growth chamber on seedling and in the field on adult plant stages, were conducted using a randomized complete block design with three replicates. The parents expressing differences in their reactions to Bgh were crossed in a half-diallel mating design to generate 45 full-sib families. Genetic component analysis showed significant effects for both GCA and SCA under both experiments suggesting that additive as well as non-additive genetic mechanisms were involved in the expression of resistance in these parents. The estimate of narrow-sense heritability was 0.63 and broad-sense heritability was 98% indicating that selection for the disease resistance should be effective in these crosses. Resistant parents ‘Banteng, PK 30-136 and ‘Igri’ had significantly negative GCA effects, suggesting their prime suitability for use in barley breeding programs to improve resistance to Bgh.

Combining ability and heterosis of selected sweetpotato (Ipomoea batatas L.) clones for storage root yield, yield-related traits and resistance to sweetpotato virus disease

Designed crosses using genetically diverse and complementary genotypes is useful to develop sweetpotato clones with improved agronomic traits. The objective of this study was to determine combining ability and heterosis among selected sweetpotato clones for number of storage roots per plant (NRPP), storage root yield (SRY), dry matter content (DMC) and resistance to sweetpotato virus disease (SPVD) for breeding. Eight selected genotypes were crossed using an 8 × 8 half diallel mating design to generate 28 families which were evaluated along their parents under field condition at three sites using a 6 × 6 lattice design with three replications. General combining ability (GCA) and specific combining ability (SCA) effects were highly significant (P < 0.001) among families. Significant GCA × sites and SCA × sites effects indicated environmental effect on gene action and expression. Parental genotypes Simama and Gairo had positive and significant GCA effects for NRPP. The parents 03-03, Ukerewe and Simama had significant and positive GCA effects for SRY and DMC, respectively. Further, Ex-Msimbu-1 and Gairo displayed negative and significant (P ≤ 0.01) GCA effect for SPVD resistance. The genotypes Gairo, 03-03, Ukerewe, Simama and Ex-Msimbu-1 are promising parents for sweetpotato breeding to improve NRPP, SRY, DMC and resistance to SPVD. Further, the study selected best performing families namely: 03-03 × Simama, 03-03 × Resisto and Simama × Ex-Msimbu-1 which recorded the highest mean storage root yields of 16.1, 16.6 and 17.2 tons/ha combined with high DMC and resistant to SPVD for genetic advancement.

Genetics of Resistance in F2 Soybean Populations for Adzuki Bean Bruchid (Callosobruchus chinensis)

Adzuki bean bruchid (Callosobruchus chinensis) is a significant pest of soybean in Uganda. To sustainably manage this pest, utilization of resistant soybean varieties is the key solution. Development of resistant varieties needs knowledge on modes of inheritance which is crucial in selection of parent materials. To identify parents, a study was initiated to determine the gene action and mode of inheritance of resistance to bruchids in soybean. Nine parental lines were crossed in a full-diallel at Makerere University Agricultural Institute, Uganda. The generated F1s were advanced to F2 and seeds were evaluated for response to bruchid infestation in a randomised complete block design. Ten seeds were infested with 10 randomly selected unsexed 1-3 day old bruchids. Genotypes showed significant differences in seed weight loss (swl), adult bruchid emergence (ABE) and Dobie susceptibility index (DSI) indicating that these parameters could be used to screen genotypes in genetic analysis. Mean squares of general combining ability (GCA) were significant (P &amp;lt; 0.05) for swl, DSI and number of ABE from the F2 seeds indicating additive gene action. Susceptibility parameters ABE and DSI showed significant specific combining ability (SCA) indicating non-additive gene action. Resistance was influenced by maternal effects indicating that direction of the cross was important. Genotypes S-Line 9.2 and S-Line 13.2A showed negative significant GCA effects for at least two of the susceptibility parameters indicating that they were the best parents for bruchid resistance breeding. The study established that additive, non additive and maternal effects governed the gene expression in soybean resistance to bruchids.

Combining ability and heterosis for some canola characteristics sown on recommended and late planting dates using biplot

Canola (Brassica napus L.) is one of the most efficient oil-producing crops in arid and semi-arid regions of the world. In the current study, ten winter canola genotypes [seven genotypes as lines (Zarfam (L1), Talaye (L2), SLM046 (L3), Geronimo (L4), Modena (L5), Opera (L6) and Symbol (L7)] and three genotypes as testers [Okapi (T1), Licord (T2) and Orient (T3)] and their F1 hybrids (21 hybrids) were evaluated to determine the genetic parameters for grain yield, oil content, meal and seed glucosinolate contents under two different planting date [recommended (late September) and late planting (late October)]. According to combined analysis of variance there were significant differences among the genotypes for most studied traits. The genotype main effect and genotype × environment interaction (GGE) biplot method was used for analyzing line × tester design data. Among the lines, L5 showed high negative general combining ability (GCA) effect for meal glucosinolate content in both conditions whereas L1, L5 and L6 revealed high negative GCA effects for seed glucosinolate content in both planting date. From the results, it could be concluded that, hybridization between T1×L1, T1×L6 or T3×L5 is an efficient approach to release genotypes with low seed and meal glucosinolate content. Furthermore, to develop canola cultivars with higher seed and oil yield, hybridization between T1×L7 or T2×L7 is highly recommended. Improved oil content will be achieved if T1×L5, T2×L5 or T3×L6 hybrids are implemented into the breeding programs.

Heterotic affinity and combining ability of exotic maize inbred lines for resistance to aflatoxin accumulation

Aflatoxin accumulation in maize (Zea mays L.) kernels is a serious economic and health problem that reduces grain quality and nutritional values and causes death to livestock and humans. Understanding the genetic parameters and heterotic responses of exotic maize inbred lines can facilitate their use for developing aflatoxin resistant parents of hybrids in Africa. This study was designed to (1) determine the heterotic affinities of aflatoxin resistant exotic lines, (2) identify exotic inbreds with good combining ability, and (3) determine the mode of inheritance of resistance to aflatoxin contamination in these lines. A line × tester mating design was used to determine combining ability of 12 yellow and 13 white inbreds and classify them into heterotic groups. The inbreds were crossed to two adapted testers representing two African heterotic groups and the resulting testcrosses along with hybrid checks were evaluated in separate trials at two locations for 2 years in Nigeria. General combining ability (GCA) effects were more important than specific combining ability effects for aflatoxin and grain yield. Among 15 exotic inbred lines having negative GCA effects for aflatoxin and 13 with positive GCA effects for grain yield, six combined the two desired traits. Five white and six yellow endosperm testcrosses were found to be good specific combiners for the two desired traits. The exotic lines with negative GCA effects for aflatoxin accumulation will be used as donor parents to develop backcross populations for generating new inbred lines with much higher levels of resistance to aflatoxin accumulation.

English

The genetic potentials of resistance to turcicum leaf blight (TLB), grey leaf spot (GLS), and common rust (CR) disease, grain yield and selected agronomic trait were studied in 45 F1 hybrids from a half diallel following Griffing’s Model 1, Method 4. The 45 hybrids excluding parents were evaluated in 5 × 9 alpha lattice designs with three replications. The study was carried out at Jimma Agricultural Research Center during 2015 cropping season with the objective to evaluate combining ability for turcicum leaf blight, grey leaf spot, common rust disease, grain yield and selected agronomic trait in maize inbred lines. For analysis of variance, days to 50% anthesis, days to 50% silking, turcicum leaf blight, grey leaf spot, common rust disease severity index, days to maturity and grain yield data were collected. Mean square due to general combining ability (GCA) was highly significant (P ≤ 0.01) for all traits, while specific combining ability (SCA) mean square was non-significant except for grain yield, days to 50% tasseling, days to 50% of silking, and days to maturity. This study showed the importance of additive types of gene action in controlling the inheritance of the traits. Among ten inbred lines, L7 and L10 were best combiners for GLS tolerance with the highest negative value of GCA effects and inbred line L7 was the best combiner for TLB and CR tolerance with the highest negative value of GCA effect. Inbred lines L2 and L9 were best combiner for grain yield with the highest positive GCA effect value. Therefore, maize breeding program can engage in hybridization and synthetic variety formation based on the information of inbred lines with high negative value GCA effect for diseases tolerant and high GCA for grain yield. Key words: Combining ability, general combining ability (GCA), inbred lines, specific combining ability (SCA).

Combining Ability Analysis of RILs Developed from a YML32 × Q11 Cross for Grain Yield and Resistance to Gray Leaf Spot

The development of resistant lines and hybrids is an economical way to control disease and improve yield stability. The objectives of this study were (i) to investigate if differences in resistance to gray leaf spot (GLS, caused by Cercospora zeina) exist among recombinant inbred lines (RILs) with and without the quantitative trait locus encompassing the resistance‐carrying GZ204/IDP5 DNA segment (RDNAS) and to determine its effect on grain yield, and (ii) to determine general combining ability and specific combining ability effects for grain yield and GLS scores (GLSS). Four RILs (three with RDNAS [RL1_1, RL1_2, and RL2_1] and one without RDNAS [RL2_2]) were developed via marker‐assisted selection from a cross between YML32 and Q11—an elite line susceptible to GLS. The four RILs and the susceptible parent (Q11) were crossed as testers with 13 maize (Zea mays L.) lines of known heterotic groups (Suwan1, Reid, and non‐Reid). The three RDNAS‐carrying RILs showed reduced GLSS and improved grain yield stability, but grain yield itself was not significantly increased. These three RILs also showed negative general combining ability effects for GLSS. RL2_1 was the best line for improving GLS resistance. The RILs possessing the RDNAS in crosses with lines from the Suwan1 heterotic group had lower GLSS than those from Reid and non‐Reid heterotic groups, suggesting that resistance genes or quantitative trait loci, in addition to RDNAS, might be present in Suwan1.

Investigation on genetic control for yield and yield contributing traits in advanced generation of maize (Zea mays L.)

Twenty five cross progeny of maize developed by Plant Breeding Division of BARI were evaluated by determining general combining ability (GCA) and specific combining ability (SCA) effects following line × tester design involving five female lines and five testers for grain yield and other yield contributing traits. Highly significant genotypic variances specified inclusive inconsistency existed among the genotypes. None of the lines showed significant GCA effects for all the characters, but the line Pac-60/S4-3 and Pac-60/S4-9 showed negative GCA effect for days to 50% tasseling and silking which is desirable to develop early variety. Additionally, the line Pac-60/S4-9, Pac-60/S4-18 and Pac-60/S4-21 showed negative GCA effect for plant and ear height which is also desirable to develop dwarf variety. Nevertheless, none of the cross showed significant SCA effect for any character studied, but crosses Pac-60/S4-21×BIL-113, Pac-60/S4-21×Utn/S4-15, Pac-60/S4-18×Utn/S4-8, Pac-60/S4-3×BIL-113, Pac-60/S4-3×Utn/S4-18, Pac-60/S4-9×Utn/S4-15, Pac-60/S4-9×BIL-113 and Pac-60/S4-21×Utn/S4-10 had higher yield with positive SCA effects. However, considering yield data along with lodging percentage, five crosses namely Pac-60/S4-21×BIL-113, Pac-60/S4-21×Utn/S4-15, Pac-60/S4-21×Utn/S4-10 Pac-60/S4-9×Utn/S4-15 and Pac-60/S4-3×BIL-113 showed better performance.Bangladesh J. Agril. Res. 42(4): 715-724, December 2017

Combining Ability of Plant Height and Yield components in Indian Mustard (Brassica junceaL.Czern &amp; Coss.) under Salt affected Soil using Line×Tester Analysis

Line × tester analysis of twenty lines and three testers of Indian mustard (Brassica juncea L. Czern &amp; Coss.) cultivars were used to estimate general combining ability (GCA), specific combining ability (SCA) effects, high parent heterosis and narrow-sense heritability estimate for plant height, yield components and seed yield. Significant variance of line x tester for the traits like pods per plant and seed yield indicating non additive genetic effects have important role for controlling these traits. Significant mean squares of parents v/s crosses which are indicating significant average heterosis were also significant for all the traits except seeds per pod. High narrow-sense heritability estimates for all the traits except seeds per pod exhibited the prime importance of additive genetic effects for these traits except seeds per pod. Most of the crosses with negative SCA effect for plant height had at least one parent with significant negative or negative GCA effect for this trait. For most of the traits except pods per plant, the efficiency of high parent heterosis effect was more than SCA effect for determining superior cross combinations.

Combining ability for yield and oil quality traits in Indian mustard [Brassica juncea (L.) Czern &amp; Coss] using line × tester analysis

ABSTRACT : Ten lines and four testers of Indian mustard [Brassica juncea (L.) Czern & Coss.] genotypes were used to estimate general combining ability (GCA) and specific combining ability (SCA) effects estimate for yield and oil quality traits. For all the quantitative and quality traits, the mean sum of squares due to line/tester was highly significant, proving that the parental lines used in present investigation are comprising the diverse genetic background. Among the lines and testers, good general combiner RH-30, RAURD 214, EC 401574 and Rajendra Sufalam have exhibited desirable negative and significant GCA effect for days to 50 per cent flowering and days to maturity, whereas positive and significant GCA effect for number of primary and secondary branches per plant, siliqua per plant, siliqua length, 1000 seed weight, biological yield per plant, oleic acid, oil content and seed yield per plant, indicating the presence of additive gene action or additive x additive interaction effects. On the basis of desirable SCA effects for yield, oil and its component traits were found best cross combinations RAURD 153/ JD-6, EC 401574/Rajendra Sufalam, RAURD 170/JD-6 and RAURD 214/Rajendra Sufalam. The cross combinations EC 401574/Rajendra Sufalam, RAURD 214/Pusa Bold and RAURD 172/ Pusa Bold with highly significant economic heterosis and SCA effects, reflected presence of both additive and non-additive gene effects responsible for increase in grain yield over economic parents.

Genetic analysis of resistance to Alternaria leaf petiole and stem blight of sweetpotato in Uganda

Alternaria blight (Alternaria spp.) is an important sweetpotato disease in Uganda causing yield losses of over 50 % in susceptible genotypes. In Uganda, Alternaria bataticola and Alternaria alternata are the major species with A. bataticola the more aggressive of the two. The most effective control measure for this disease is the use of resistant genotypes. This study was conducted to determine the inheritance of resistance to Alternaria blight and the general and specific combining abilities of the available germplasm. Sixteen parental clones varying in reaction to Alternaria blight were crossed using the North Carolina II mating scheme. Due to incompatibility of some parents, two sets of compatible parents were formed. Differences among the families for Alternaria blight severity were significant while general combining ability (GCA) and specific combining ability (SCA) mean squares were highly significant (P < 0.001) for the disease with GCA sum of squares (SS) being more predominant at 67.4 % of the treatment SS for Set 1 and the SCA SS predominant at 54.0 % of the treatment SS for Set 2. This indicated that both additive and non-additive effects are important in controlling this trait. Some parents with high, negative GCA effects produced families with undesirable SCA effects and the reverse was also true. This implies that the best parents should not be chosen on GCA alone but also on SCA of their best crosses. The wide range in the area under disease progress curve for the families indicated that it was possible to select for highly resistant genotypes.