Dominance Gene Effects Research Articles

Inheritance of length and weight of mature larvae in six-parent diallel crosses of Mulberry Silkworm, Bombyx mori L.

Context: To gain a better understanding of the nature of gene action involved in the inheritance of quantitative characters can be obtained through the use of diallel cross analytical approach for the choice of desirable parents and the formulation of an effective breeding programme. Objectives: The aim was to study the nature and magnitude of gene action of inheritance for quantitative traits, length and weight of mature larvae in B. mori through six-parent diallel cross analysis in four rearing seasons Materials and Methods: Six inbred varieties of B. mori were used as parents for a diallel cross. The experiment was conducted in four rearing seasons. Mature larval length (cm) and weight (gm) were collected for statistical analysis. The data were analyzed following the biometrical techniques proposed by Jinks and Hayman (1953), Hayman (1954), Dickinson and Jinks (1956) and Jhonson and Aksel (1964). Results: In the Hayman’s analysis of variance for length and weight of mature larvae the items ‘a’ and ‘b’ were found to be significant against all the three tests of significance. The item ‘b2’ was significant for the seasons S-2 and S-3 and the ‘b3’ item was significant for all the seasons. The Items ‘c’ and ‘d’ were insignificant in all the seasons. The regressions of Wr on Vr for majority of the seasons were significant but did not deviate significantly from unit slope. The varieties Nistari, Nistari oval (G) and NanNung7B of S-1, S-2 and S-4, and Nistari of S-3 for length of larvae and Nistari and Nistari oval (G) of S-1, S-2 and S-3 and Nistari, Nistari oval (G) and Nan Nung 7B of S-4 for larval weight possessed an excess of recessive genes of negative effect. But Nistari oval (G) in S-3 for LL possessed excess of recessive genes with positive effects. On the other hand BSRI-95, BSRI-98 and BV (high) in S-1, S-2 and S-4, and Nan Nung 7B, BSRI-98 and BV(high) in S-3 for LL and BSRI-95, BSRI-98 and BV(high) in S-1, S-2 and S-3, and BSRI-95 and BV(high) in S-4 for LW possessed an excess of dominant genes, which was positive in nature. In S-3 only BSRI-95 for LL and NanNung7B in S-1, S-2 and S-3 and BSRI-98 in S-4 for LW possessed an excess of dominant genes of negative nature. At least one group of dominant genes was involved in controlling these characters. The broad sense heritability was high in all seasons for both the characters whereas the narrow sense heritability was moderate for majority of the seasons except S-3 and S-4 for LW. Conclusion: High heritability, dominant and recessive gene effects suggest that these parents could be used to develop better lines in respect of larval characters investigated in this study and selection programmes will be effective in early generations. DOI: http://dx.doi.org/10.3329/jbs.v21i0.22522 J. bio-sci. 21: 77-87, 2013

Why SR52 is such a great maize hybrid? I. Heterosis and generation mean analysis

SR52 is the first single cross maize hybrid to be commercialised in the world and forms the basis of maize breeding in Zimbabwe and Eastern and Southern Africa region. Although SR52 is such an exceptional hybrid, the genetic basis of its outstanding yield and heterosis has never been explained. Therefore genetic components of yield and associated traits in SR52 were studied using a generation mean analysis. Parents (P1 and P2), F1 and segregating F2 and backcross generations (BCP1 and BCP2) were evaluated. The experiment was laid out as a randomised complete block design with two replications across two sites in South Africa, during the 2012/2013 season. The study confirms high levels of heterosis exceeding 300 % for grain yield potential and revealed a significant lack of fit of the additive–dominance model for yield and most secondary traits. Consequently, the role of epistasis was investigated by partitioning it into additive × additive , additive × dominance and dominance × dominance gene effects. The full model confirmed presence of epistasis of highly significant (P ≤ 0.01) additive × additive nature for grain yield though negligible in magnitude (<10 %). Both dominance and additive gene effects were highly significant for yield and associated traits. However, dominance gene action contributed over 80 % to grain yield potential. Additive and additive × additive gene effects played a significant but minor role for grain yield potential (less than 20 %). We therefore concluded that dominance gene action is the basis for exceptional heterosis displayed by SR52.

Combining ability analysis of fruit yield and morphological traits in greenhouse cucumber (Cucumis sativusL.)

Golabadi, M., Golkar, P. and Eghtedary, A.-R. 2015. Combining ability analysis of fruit yield and morphological traits in greenhouse cucumber (Cucumis sativus L.). Can. J. Plant Sci. 95: 377–385. Knowledge about the genetic control of the different quantitative characters related to fruit yield and its components is still insufficient in greenhouse cucumbers. This information is useful in planning breeding programs in this economically important crop. In this study, the genetics of morphological traits and fruit yield was investigated using a 9×9 full diallel population of cucumbers for the greenhouse market. Data were collected on internode length, leaf length, leaf width, fruit length, fruit diameter, number of fruits per plant, yield per fruit and yield per plant. Variance components showed that both the additive and the dominant gene effects played significant roles in the genetic control of the traits studied. Genetic control of internode length, leaf width and number of fruits per plant was accomplished by additive effects. The significant mean squares of reciprocal crosses for all of the studied traits suggested that maternal inheritance also played an important role in the inheritance of these traits. Significant general combining ability for fruit yield revealed that both selection and hybridization methods would lead to desirable genetic improvements in cucumber through accumulation of desirable alleles from parents in the target genotype, but that hybridization would be preferred.

Studies on heterotic parameters inPopulus deltoides

Exploitation of genetic variability of Populus deltoides Bartr. through control crossing involving Line x Tester mating design was attempted with the objective of selection of suitable clones as well as parents for hybridization in future and identification of best families and best individuals with in family for releasing first stage clones. Lines ST-72, D-121, G-48, exhibited the highest positive GCA effects for plant height, collar diameter, plant height at first branch and root length. In general G-48 also proved to be the best combiner for survival percentage, inter nodal length and leaf area. Among the testers ST-63 and ST-70 expressed highest GCA effects and excelled for a number of desirable characters. Full sib families (F1s) of D-121 x ST-70 and G-48 x ST-63 showed desirable SCA for plant height and collar diameter and therefore F1 hybrids of these crosses are recommended at first stage of selections. The percent contribution of line x tester interactions was higher than that of lines and testers except number of leaves per plant. 13 traits expressed higher SCA variance than GCA variance and dominant gene effect (σ2D) were found higher than additive gene effect (σ2A) except in root length. For recurrent selection based on GCA effects, parents G-48, ST-70, D-121 and ST-63 appeared more appropriate in crossing programme directed towards clonal improvement of Poplar in India.

Inheritance of fruit traits and generation mean analysis for estimation of horticultural traits in bitter gourd

Inheritance pattern of three fruit traits was studied using two diverse parents, namely, Sel-2 (∼25 cm long, non-prominent tubercles and curved) crossed with small fruited type Pusa Purvi (DBG-34) (∼4 cm long, prominent tubercles and straight). F1 generation obtained was intermediate (av. ∼10 cm) for fruit length and in F2 generation variation ranged from 2.5 to 25 cm. This continuous variation in fruit length of progeny by frequency distribution of nine classes with interval of 2.5 cm indicated its quantitative inheritance and more than 4 genes involved in controlling this trait. Distribution curve for fruit length in F2 generation skewed towards Pusa Purvi, which suggested that short fruit length is partially dominant over long fruit length. The broad sense heritability for this trait was reported to be 97.40% that is heritable variation and selection for fruit length will be useful for its improvement. The inheritance of tubercles and curviness of fruits in bitter gourd, governed by a single pair of nuclear gene and prominent tubercles was dominant over non tubercles. In cross Sel-2 × Pusa Purvi indicated that straight fruit is dominant over curved fruit and governed by a single pair of gene. Gene action for yield and its related traits in bitter gourd was studied using six basic generations (P1, P2, F1, F2, B1 and B2). The results revealed the presence of additive, dominance gene effects and epistatic interactions for all the characters studied in cross Sel-2 × Pusa Purvi indicating the importance of both additive and non-additive gene actions in the expression of the characters. Mean generation analysis for fruit length showed that dominance is the major contribution towards small fruits.

Generation means analysis for fruit yield and its component traits in okra

Experimental material comprised of five generations (P1, P2, F1, F2 and F3) of Pusa Sawani × HBT-36, JNDOL-05 × HB-25-2 and HB-25-2 × HBT-36 okra crosses. Five generations of these crosses were raised in randomized block design with three replications in rainy season of 2011–12. The observation for fruit yield per plant and its five component traits, viz., plant height, fruit length, fruits per plant, inter-nodal length and weight per fruit in five generations were recorded. The mean values of the five generations were subjected to C-scaling test (l) and five parameter method to find out the gene effects and interactions. The C-scaling test showed the evidence of epistasis for all six characters in all three crosses. All three types of gene effects namely additive, dominance and epistasis were found involved in the inheritance of the characters studied. The additive gene effects were relatively more important than the dominance gene effects for fruits per plant and inter-nodal length however, for fruit yield the dominance gene effects were observed important. Out of 18 cases, 13 cases designated preponderance of complementary type of epistasis.

Generation Mean Analysis of Fibre Quality Characters in Upland Cotton (Gossypium hirsutum L.)

Generation mean analysis was carried out to estimate the nature and magnitude of gene effects for fibre quality traits in three crosses of upland cotton (Gossypium hirsutum L). The presence of epistasis was reflected by scaling tests and inadequacy of simple additive-dominance model for most of the characters studied. The results obtained revealed that the nature and magnitude of gene effects differed in different crosses and showed importance of additive as well as non-additive gene effects in the inheritance of different characters. In view of the parallel role of additive and non-additive gene effects in the inheritance of different characters, selection in the segregating generations should be delayed when dominance gene effects would have diminished or sophisticated selection procedures as recurrent selection and population improvement programmes may be followed. However, additive gene effects may be fixed with respect to some specific traits such as micronair value and fibre strength.

Gene effects and genetic analysis of indigenous land races and improved cultivars for yield and yield components in rice (Oryza sativaL.)

Rice is one of the crucial staple food crops and its unique grains assist to hold two third of world population. Generation mean analysis is commonly used in studies of inheritance of quantitative traits. Experimental material consisted of ten parents which included six high yielding varieties used as female parents and four traditional landraces used as male parents, F1, F2 and F3generation of six crosses viz., IR 72 x Veeradangan, ADT 39 x Kavuni, ADT 45 x Kavuni, ADT 43 x Navara, ASD 16 x Navara and TPS 4 x Kathanellu. Seven biometrical characters indicated that additive and dominance x dominance gene actions were predominant with duplicate type of gene action for five biometrical characters viz., plant height, number of productive tillers per plant, panicle length, number of filled grains per panicle and single plant yield. The epiststic effects, additive x additive [i] and dominance x dominance [h] were highly significant in most cases. The signs of (h) and (l) were opposite in all studied traits for most crosses. Non-allelic gene interaction was operating in the control of genetic variation in most studied traits. Also, the inheritance of all studied traits was controlled by additive and non-additive genetic effects, but dominance gene effects play the major role in controlling the genetic variation of the most studied traits. Present study indicated that early generation selection is effective and should be practiced for future breeding program.

Inheritance of kernel quality attributes in quality protein maize (Zea maysL.)

Nature and magnitude of gene actions were studied employing Hayman's component analysis, with 8 quality protein maize (QPM) inbred lines and their 56 diallel set of crosses including reciprocals. Kernels of each entry were subjected to analysis of endosperm modification (EM), endosperm protein content (EPR) and tryptophan content (TRP). Significant difference was observed among genotypes for the three traits. EM and TRP content exhibited importance of both additive and dominance components, whereas EPR exhibited prevalence of dominance gene effects. Average degree of dominance revealed partial to complete dominance for EM, whereas complete to overdominance was exhibited by TRP, over the seasons. EPR consistently showed over-dominance. The quality traits among QPM lines were observed to be controlled by 1–3 dominant genes/gene blocks. Heritability estimates ranged from 55–75.5% for EM, 32.2–51% for EPR and 35.3–60.6% for TRP over three seasons.

NARROW SENSE HERITABILITY AND GENE EFFECTS FOR LATE LEAF SPOT RESISTANCE IN VALENCIA GROUNDNUTS

Late leaf spot (LLS), Phaeoisariopsis personata (Berk. and Curtis) Deighton, is one of the most important foliar diseases of groundnut (Arachis hypogaea L.) worldwide. Effective chemical control is heavily reliant upon multiple fungicide applications which are costly for resource poor farmers in Sub-Saharan Africa. The deployment of resistant cultivars is a better option to control this disease in groundnut. A study was conducted to determine narrow sense heritability and gene action controlling LLS resistance in Valencia groundnut materials. The materials used included six generations; F 1 , F 2 , F 1 backcrosses to the susceptible BC 1 P 1 and resistant BC 1 P 2 parents, and their respective parental lines of crosses between NuMex-M 3 × ICGV -SM 02501, Valencia C × ICGV-SM 02501and Redbeauty × ICGV -SM 03590. All the test materials were evaluated at the National Semi-Arid Resources Research Institute (NaSARRI) at Serere in Uganda. Narrow-sense heritability estimates were 12, 27 and 36%, for Redbeauty × ICGV-SM 03590, Valencia C × ICGV-SM 02501 and NuMex-M 3 × ICGV-SM 02501 crosses, respectively. Both additive and dominance gene effects contributed significantly to the inheritance of LLS resistance in all the crosses, except in Redbeauty × ICGV-SM 02501 where the effects of dominance were not significant.

INHERITANCE OF RESISTANCE AGAINST PHYTOPHTHORA INFESTANS Inlycopersicon pimpenellifolium L3708

In Egypt, no commercial tomato (Lycopersicon esculentum Mill.) varieties are available which are resistant to the late blight, one of the most important tomato diseases, caused by the phytopathogenic oomycete Phytophthora infestans. The wild tomato (Lycopersicon pimpenellifolium) shows resistance to P. infestans. So, in this investigation an interspecific cross between L.esculentum cv. Castle Rock and L. pimpenellifolium accession L3708 from the AVRDC were made. The genitors, F1, F2, BC1 and BC2 were used to study the inheritance of resistance to P. infestans and to estimate the genetic parameters associated with resistance. The resistance to P. infestans is controlled polygenic ally. The analysis of variances and genetic parameters suggested that this type of resistance was inherited quantitatively, and dominance was predominant over susceptibility, and not for resistance, that would be more interesting. The data supported the hypothesis that race-non-specific resistance in L. pimpenellifoliumL3708 is controlled by partially-dominant and dominant epistatic effects. The heritability in broad (Hb.s%) and narrow sense (Hn.s %) estimates were 73.28 and 26.86% for severity revealed the magnitude of the environmental factors on the total variation. The dominance gene effects were quire important in the inheritance of resistance to P. infestans. Estimates of additive gene effects were of low, magnitude. Epistatic gene effects were considered to be more important than the additive gene effects in the inheritance of resistance to P. infestans in the cross under study. The additive x additive, additive x dominance and dominance x dominance gene effects were highly significant. The reciprocal recurrent selection breeding is the best method to improve the resistance to P. infestans.

Inheritance of Some Important Characters to Improve Sweet Melon (Cucumis melo L.) Fruits

The present investigation was carried out during three years of 2012, 2013 and 2014. These experiments were done at Sabaheya Horticultural Research Station, Alexandria, and Fowa area, Kafer El- Sheikh, Egypt. Type of gene action, correlation coefficient and path analysis among all combinations of some important characteristics of sweet melon were studied. A 5X5 half-diallel cross was performed among five pure lines of sweet melon. Additive gene effects were found to be significant for plant length, number of branches / plant, flowering date, maturity date and flesh thickness indicating that the additive gene action played the main role in the inheritance of these traits. The evaluated characteristics of fruit netting, fruit shape index, total soluble solids % and moisture content exhibited insignificant values for the additive gene action. The dominant gene effect was found to be significant for plant length, number of branches per plant, maturity date, fruit netting degree, Total soluble solids % and moisture content indicating the importance of dominant gene effect in the inheritance of this characters. Total yield per plant, phenotypically, correlated with plant length, average fruit number and average fruit weight. Hence, a lot of attention for such relationships in the improvement program of such characters of sweet melon through selection.

Estimation of genetic parameters for heat stress, including dominance gene effects, on milk yield in Thai Holstein dairy cattle.

Heat stress in tropical regions is a major cause that strongly negatively affects to milk production in dairy cattle. Genetic selection for dairy heat tolerance is powerful technique to improve genetic performance. Therefore, the current study aimed to estimate genetic parameters and investigate the threshold point of heat stress for milk yield. Data included 52 701 test-day milk yield records for the first parity from 6247 Thai Holstein dairy cattle, covering the period 1990 to 2007. The random regression test day model with EM-REML was used to estimate variance components, genetic parameters and milk production loss. A decline in milk production was found when temperature and humidity index (THI) exceeded a threshold of 74, also it was associated with the high percentage of Holstein genetics. All variance component estimates increased with THI. The estimate of heritability of test-day milk yield was 0.231. Dominance variance as a proportion to additive variance (0.035) indicated that non-additive effects might not be of concern for milk genetics studies in Thai Holstein cattle. Correlations between genetic and permanent environmental effects, for regular conditions and due to heat stress, were - 0.223 and - 0.521, respectively. The heritability and genetic correlations from this study show that simultaneous selection for milk production and heat tolerance is possible.

Inheritance Analysis of Linoleic Acid Content in Half Diallel Maize Populations

In the last few years, the analysis of fatty acids has gained importance because of their nutritional and health implications. This increased attention led to a half dialell crossing design study during 2006 and 2007 seasons in Edirne -Turkey conditions. In this study, 28 F1 maize hybrids were obtained by 8x8 half diallel crossing. In half – diallel maize population, inheritance of linoleic acid content in grains and combining ability were investigated. Mean squares of inbred lines and hybrids were highly significant for all studies traits, indicating the genetic variance among lines. This study examined inheritance of linoleic acid which is an important unsaturated fatty acid for potential health benefits. Therefore, linoleic acid content and inheritance in maize oil was investigated in this research. The linoleic acid content in grain was under the dominance gene effect. Also linoleic acid content was affected by additive gene effects.

Generation Means Analysis for Fiber Elongation in Upland Cotton

ABSTRACTEach bale (218 kg) of upland cotton (Gossypium hirsutum L.) produced in the United States is graded on the basis of several fiber quality traits, namely, strength, upper‐half mean length, micronaire, uniformity index, color, and trash content. To promote production of high‐quality cotton, producers are given monetary incentives to meet and exceed market standards. Quantitative inheritance of these quality traits have been the primary research focus of many cotton researchers worldwide in an effort to better understand the genetics governing these traits. Increased fiber bundle elongation (ability to stretch without breaking) has not been considered because of its weak but negative correlation with fiber bundle strength. However, current literature suggests that elongation, along with fiber strength, contributes to yarn tenacity. To better understand the genetics of fiber elongation, six distinctive upland families derived from four parental genotypes representative of elongation variation within modern cotton germplasm pools were analyzed using generation means analysis (GMA). Additive gene effects were predominant over dominance gene effects, and nonallelic gene interactions were minimal for elongation. The large numbers of effective factors identified suggests that parents used in the GMA are carrying different genetic materials or loci for elongation. Considerable gains in elongation may be achieved by selectively crossing some of these materials in a pure‐line breeding scheme while holding other important fiber traits constant.

Genetics of seed yield and related traits in biparental crosses of okra, Abelmoschus esculentus (L.) Moench

Gene action and interaction are very important in formulating the appropriate breeding technique to produce new varieties in okra. The objective of the study was to investigate gene action controlling yield and 12 related traits in okra. Sixteen bi-parental progenies of okra were evaluated in October, 2013 and May, 2014 at the Federal University of Agriculture, Abeokuta (Lat 7°29 N, Long 3°30 E), Nigeria. Seeds were sown in single-row plots laid out in randomized complete block design with three replicates. Mean squares were obtained for the thirteen characters according to North Carolina Design II. Heritable variances were partitioned into additive and dominance components. General (GCA) and specific combining abilities (SCA) of both parental and progenies respectively were estimated with a view to identifying high combiners among genotypes. Results suggested both additive and dominant gene effects for most characters with dominant gene effects for number of leaves per plant and weight of 100 seeds. The study concluded that both additive and dominant gene actions controlled the expression of characters in okra. NHGB/09/009A and FUNAAB-11-8 are high combiners for number of days to 50% flowering and number of pods/plant and they are recommended as high-yielding, early-maturing okra variety. FUNAAB-11-4 x LD 88 and UI4-30 x FUNAAB-11-8 can be further improved to develop high-yielding hybrid okra varieties due to their high SCA. Number of days to 50% flowering, plant height, number of branches per plant, pod weight and number of ridges per pod will respond to selection because of the preponderance of additive gene action.

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.

EVALUATION OF SOME CROSSES FOR ECONOMIC TRAITS IN COTTON (GOSSYPIUM BARBADENSE L.)

This investigation was carried out to evaluate heterosis, combining ability, gene action and heritability of yield component traits for three commercial cotton varieties G90, G85 and G92 as female and three genotypes as male (G83x “G75x5844”), (G77xG70) and (G89xPima S6) using line x tester analysis. Results indicated that mean squares due to all 15 genotypes including parents and crosses were highly significant for all studied traits indicating the presence of sufficient genetic variability in this population. It was also found that parents vs. crosses mean squares as expressed to average heterosis over all crosses were highly significant for lint percentage and seed index. The mean performance of parents and their F1’s hybrids gave a wide range of variation for all studied traits. Heterotic values over the mid- and the better-parent varied between positive or negative significance and highly significant for most of the studied traits. The estimates of variance due to SCA were positive and higher in magnitude than the variance of GCA for all studied traits indicating that the non-additive genetic effect played a major role in the genetic expression of these traits. While, additive effects had a minor role in the inheritance of these traits indicating that the hybridization program would be effective in improving yield and its components traits. Comparing the GCA effects of individual parent revealed that G83xG75x5844 was the best combiner for all studied traits. Dominance estimates were higher than the additive estimates for all studied traits indicating more importance for dominant gene effect in the inheritance of these traits. Estimates of heritability in both broad and narrow senses for yield and its components showed high heritability values in broad sense were detected for all traits under investigation.

Genetic analysis of resistance to six virus diseases in a multiple virus-resistant maize inbred line

Novel and previously known resistance loci for six phylogenetically diverse viruses were tightly clustered on chromosomes 2, 3, 6 and 10 in the multiply virus-resistant maize inbred line, Oh1VI. Virus diseases in maize can cause severe yield reductions that threaten crop production and food supplies in some regions of the world. Genetic resistance to different viruses has been characterized in maize populations in diverse environments using different screening techniques, and resistance loci have been mapped to all maize chromosomes. The maize inbred line, Oh1VI, is resistant to at least ten viruses, including viruses in five different families. To determine the genes and inheritance mechanisms responsible for the multiple virus resistance in this line, F1 hybrids, F2 progeny and a recombinant inbred line (RIL) population derived from a cross of Oh1VI and the virus-susceptible inbred line Oh28 were evaluated. Progeny were screened for their responses to Maize dwarf mosaic virus, Sugarcane mosaic virus, Wheat streak mosaic virus, Maize chlorotic dwarf virus, Maize fine streak virus, and Maize mosaic virus. Depending on the virus, dominant, recessive, or additive gene effects were responsible for the resistance observed in F1 plants. One to three gene models explained the observed segregation of resistance in the F2 generation for all six viruses. Composite interval mapping in the RIL population identified 17 resistance QTLs associated with the six viruses. Of these, 15 were clustered in specific regions of chr. 2, 3, 6, and 10. It is unknown whether these QTL clusters contain single or multiple virus resistance genes, but the coupling phase linkage of genes conferring resistance to multiple virus diseases in this population could facilitate breeding efforts to develop multi-virus resistant crops.

Gene Effects for Sugar Content, Green Cane Yield and its Component Traits in Sweet Sorghum [Sorghum bicolor (L.) Moench

Generation mean analysis was carried out to estimate the nature and magnitude of gene effects for sugar content, green cane yield and its component traits in sweet sorghum [Sorghum bicolor (L.) Moench]. Six generations viz., P1 , P2 , F1 , F2 , BC1 and BC 2 of a cross derived from two parents viz., 27 B and NSSV 13, which are contrasting for the trait of interest i.e., grain quality and yield traits of grain sorghum and juiciness of sweet sorghum were evaluated in summer 2012. The scaling tests as well as chi square test from joint scaling test were highly significant for all the fourteen quantitative characters, indicating inadequacy of simple additive - dominance model and justifying the use of six parameter model for the detection of gene interactions. Both additive and dominance gene effects were highly significant for all the traits barring stem girth, grain yield, total biomass and fresh stalk yield where only dominance component is predominant in first two traits, while additive in later two traits. Among non allelic interactions, dominance × dominance (l) gene interaction was of greater magnitude than main gene effects for all the characters under study indicating the importance of heterosis breeding to utilize non additive gene effects.