Genetic analysis of grain mould resistance in coloured sorghum genotypes

Grain moulds are a major constraint to sorghum production and to adoption of improved cultivars in many tropical areas. Information on the inheritance of grain mould reaction is required to facilitate breeding of resistant cultivars. The genetic control of grain mould reaction was studied in 7 crosses of 2 resistant sorghum genotypes. P₁, P₂, F₁, F₂, BC₁ and BC₂ families of each cross were evaluated under sprinkler irrigation for field grade and threshed grade scores and subjected to generation mean analysis. Frequency distributions for grain mould reaction were derived and F₂ and BC₁ segregation ratios were calculated. Grain mould reaction in crosses of coloured grain sorghum was generally controlled by two or three major genes. Resistance to grain moulds was dominant. Significant additive gene effects were also found in all cross/season combinations. Significant dominance effects of similar magnitude to additive effects were also observed in five out of ten cross/season combinations. Gene interactions varied according to the parents with both resistant and susceptible parents contributing major genes. Choice of parents with complementary resistance genes and mechanisms of resistance will be critical to the success of resistance breeding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of resistance to head bugs and its interaction with grain molds in Sorghum bicolor

Sorghum head bug, Calocoris angustatus Lethiery is one of the most important pests of grain sorghum in India. Head bug damage increases the severity of grain molds, which renders the grain unfit for human consumption. Therefore, we studied the gene action for resistance to head bugs and grain molds in a diverse array of male-sterile lines and testers in a line × tester mating design under natural infestation. Mean squares for parents, parents vs crosses, lines, testers, and lines × testers were significant for head bug damage and grain mold severity. General combining ability (GCA) effects were significant and negative for ICSA 88019 for head bug damage, and ICSA 88019 and ICSA 88020 for grain molds (except for ICSA 88020 in 1993). General combining ability effects were positive for ICSA 42 and 296 A. GCA effects of lines and testers for head bug damage and grain mold severity were in the same direction (+ve or −ve). Head bug damage in the grain was significantly correlated with grain mold severity. Testers IS 8891, IS 15107, and TAM 2566 (with colored grain and less susceptibility to molds) produced mold-resistant hybrids in combination with all the male-sterile lines, while the reverse was true in the case of Swarna and ICSV 112. Resistance to head bugs showed dominance to partial dominance type of gene action, while in the case of grain molds, it showed dominance to over dominance. Resistance to these pests is governed by both additive and nonadditive types of gene action. The implications of these results are discussed in relation to need for crop improvement in sorghum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Estimation of additive, dominance and digenic epistatic interaction effects for certain yield characters in Vigna sesquipedalis Fruw

Inheritance of yield and yield contributing characters were investigated using generation mean analysis, utilising the means of six basic populations viz., P₁, P₂, F₁, F₂, BC₁P₁ and BC₁P₂ in four crosses of Vigna sesquipedalis. The analysis reiterated that the importance of dominance (h) gene effects for pod yield/plant and pods/plant as compared to additive (d) gene effects. However, significant and positive additive effects were noticed for pod yield/plant, pods/plant, pod weight and seed weight in different crosses. The three types of gene interactions (additive, dominance and epistasis) were significantly involved for pods/plant in cross KU 7 ×KU 8. Among the digenic epistatic interactions, both additive ×additive (i) and dominance × dominance (l) contributed more for pod yield/plant and pods/plant, however, it varied among the crosses. Populations having earliness can be developed as indicated by reducing dominance effects. Pedigree selection and heterosis breeding is suggested to exploit the fixable and non fixable components of variation respectively in Vigna sesquipedalis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pattern of genetic inheritance of morphological and agronomic traits of sorghum associated with resistance to sorghum shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis>

Sorghum shoot fly, Atherigona soccata is an important pest of sorghum during the seedling stage, which influences both fodder and grain yield. To understand the nature of inheritance of shoot fly resistance in sorghum, we performed generation mean analysis using two crosses IS 18551 × Swarna and M 35-1 × ICSV 700 during the 2013–2014 cropping seasons. The F₁, F₂, BC₁ and BC₂ progenies, along with the parental lines were evaluated for agronomic and morphological traits associated with resistance/susceptibility to sorghum shoot fly, A. soccata. The cross IS 18551 × Swarna exhibited significant differences between the parents for shoot fly deadhearts (%) in the postrainy season. The progenies of this cross exhibited lower shoot fly damage, suggesting that at least one of the parents should have genes for resistance to develop shoot fly-resistant hybrids. Leaf glossiness, leafsheath pigmentation and plant vigor score during the seedling stage exhibited non-allelic gene interactions with dominant gene action, whereas 100 seed weight showed both additive and dominant gene interactions. Presence of awns showed recessive nature of the awned gene. Generation mean analysis suggested that both additive and dominance gene effects were important for most of the traits evaluated in this study, but dominance had a more pronounced effect.     

Genetics of spike length in durum wheat

Gene effects were analyzed using mean spike length of 12 populations, viz., both parents, F₁, F₂, first back cross generation, BC₁ and BC₂, second backcross generations, BC₁₁,BC₁₂, BC₂₁ and BC₂₂ along with BC₁ self and BC₂ self derived by selfing BC₁ and BC₂populations of three crosses involving six diverse cultivars of Triticum durumto determine the nature of gene actions governing spike length through generation mean analysis under normal and late sown environments. The six-parameter model was adequate in most of the cases to explain genetic variation among the generation means under both the sowing environments. Additive (d) gene effect was significant in all the cases, whereas dominance (h) gene effect was not so frequently observed significant. Epistatic effects, particularly digenic types were predominant over additive and dominance effects in most of the cases under both normal and late sown environments except in the cross Cocorit 71 × A-9-30-1 (normal sown).Additive × dominance × dominance (y), trigenic interaction played significant role in controlling the inheritance of this trait in the cross HI 8062 × JNK-4W-128under late sown condition. Duplicate epistasis was observed in the cross HI 8062× JNK-4W-128 (normal sown). Non-fixable gene effects were of higher magnitude than fixable gene effects in almost all cases, confirmed the major role of non-additive gene effects to control the inheritance of spike length in durum wheat. Significant heterosis over better parent was not observed. Similarly, inbreeding depression was not commonly observed. Favourable and suitable environment must be considered before finalizing breeding programme for its simple inheritance to get desirable improvement for high grain yield. Hybridization systems, such as biparental mating and / or diallel selective mating, which exploit both additive and non-additive gene effects, simultaneously, could be useful in the improvement of spike length in durum wheat. This revised version was published online in July 2006 with corrections to the Cover Date.     

Generation means analysis of resistance to peanut bud necrosis caused by peanut bud necrosis tospovirus in peanut

This study was conducted to evaluate the types of gene action governing the inheritance of resistance to peanut bud necrosis disease (PBND) in populations derived from three crosses involving two resistant (ICGV 86388 and IC 10) and one susceptible (KK 60–1) peanut lines. Populations were composed of P₁ P₂, F₁ F₂, BC₁₁, BC₁₂, BC₁₁S and BC₁₂S. These populations were evaluated for PBND incidence in a farmer's field in Kalasin province in north‐east Thailand, where PBND is a recurring problem. Results showed variations between crosses in the relative contributions of different types of gene effect. The results indicate that multiple genes control the PBND resistance trait, and that the two resistant lines differ in some of these genes. As non‐additive gene effects are important in all three crosses, selection for low PBND incidence in these crosses would be more effective in later generations.     

Involvement of higher order interactions addressing complex polygenetically controlled inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot] resistance in pearl millet [Pennisetum glaucum (L.) R.Br.]

Inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot]resistance was studied using generation mean analysis in pearl millet [Pennisetum glaucum (L.) R.Br.]. Eleven basic generations, namely, P₁, P₂, F₁, F₂, B₁, B₂, B₁F₂, B₂F₂, L₁, L₂ and L₃ of three crosses involving six diverse lines for downy mildew incidence were evaluated under artificial epiphytotic conditions over two environments. The downy mildew incidence was best fitting for digenic, trigenic and tetragenic ratios when fitted into classical Mendelian ratios demonstrating involvement of two or more genes. Digenic and trigenic interaction models were adequate in the case of crosses I and III respectively, to account for the total variability in generation means. Unlike severity, comparative estimates of gene effects over two environments were mostly consistent in all crosses for prevalence. Most of the epistatic and major gene effects were found significant in all crosses for both the disease traits. Non-allelic interactions particularly at three-gene loci viz., w (additive × additive × additive) and y (additive × dominance × dominance) in cross II and all trigenic interactions in cross III were predominant. Duplicate dominance (cross I) and complementary epistasis (crosses II and III) were observed for both the traits revealing inconsistency of gene effects over crosses. The gd₁ (interaction of additive gene effect with e₁) and gh₁(interaction of dominant gene effect with e₁) were significant in crosses I and II, indicating interaction of additive and dominance gene effects with environments. Thus a breeding method that can mop up the resistant genes to form superior gene constellations interacting in a favorable manner against pathotype I would be more suitable to accelerate the pace of resistance improvement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Resistance to the cabbage root fly, Delia radicum, within Brassica fruticulosa

Two transgenic Bt rice lines, KMD1 and KMD2, both containing a synthetic cry1Ab gene from Bt, were crossed with conventional rice varieties. The inheritance of resistance to SSB of KMD1 and KMD2was investigated through LSB and field examination of their progenies, e.g. F₁, BC₁ and F₂ populations. In LSBs, 100.0% of newly hatched SSB larvae died on the second day after feeding on leaf tissues of F₁ and GUS positive BC₁ plants, of which the area of leaf tissues consumed by SSB is also similar to that of transgenic parents. These results imply that the resistance of Bt rice to SSB is dominantly controlled and could be easily exploited in hybrid rice production. Field evaluation showed that segregation ratios for SSB resistance to susceptibility in BC₁ populations fit the ratio of 1:1, which was also confirmed by LSBs. However, in F₂ populations, the ratio was significantly smaller than 3:1 for resistant to susceptible plants in all 6 indica × japonica (KMD1 and KMD2) crosses, though it fitted 3:1 in all 4 japonica × japonica crosses. The results implied that the resistance of Bt rice to SSB was controlled by a dominant gene which was present in a homozygous condition in both KMD1 and KMD2, but the inheritance could be affected by other factors. Assays for Cry1Ab protein showed that, in most crosses, the content of Cry1Ab is significantly higher in leaves of GUS positive F₁, BC₁ and F₂ plants than that in transgenic Bt parent plants, which accounts for the high resistance observed in these plants to SSB. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance and allelic relationship among gene(s) for blast resistance in pearl millet [Pennisetum glaucum (L.) R. Br.]

Six blast‐resistant pearl millet genotypes, ICMB 93333, ICMB 97222, ICMR 06444, ICMR 06222, ICMR 11003 and IP 21187‐P1, were crossed with two susceptible genotypes, ICMB 95444 and ICMB 89111 to generate F₁s, F₂s and backcrosses, BC₁P₁ (susceptible parent × F₁) and BC₁P₂ (resistant parent × F₁) for inheritance study. The resistant genotypes were crossed among themselves in half diallel to generate F₁s and F₂s for test of allelism. The F₁, F₂ and backcross generations, and their parents were screened in a glasshouse against Magnaporthe grisea isolates Pg 45 and Pg 53. The reaction of the F₁s, segregation pattern of F₂s and BC₁P₁ derived from crosses involving two susceptible parents and six resistant parents revealed the presence of single dominant gene governing resistance in the resistant genotypes. No segregation for blast reaction was observed in the F₂s derived from the crosses of resistant × resistant parents. The resistance reaction of these F₂s indicated that single dominant gene conferring resistance in the six genotypes is allelic, that is same gene imparts blast resistance in these genotypes to M. grisea isolates.     

Inheritance of White Rust Resistance in Brassica juncea

Inheritance of white rust resistance was studied in two crosses between resistant (R) and sensitive (S) types of Brassica juncea, namely EC 12749 בParkash’ (R × S) and EC 12749 בVaruna’ (R × S) under conditions of normal and late sowing. Analysis of six generations revealed the importance of additive, dominant and epistatic effects. Disease was more prevalent under late sowing due to favourable environment. Reciprocal recurrent selection is advocated for exploiting the additive and non-additive gene effects for resistance to white rust.     

Inheritance of black leaf mold resistance in tomato

Summary Inheritance of black leaf mold (BLM) (caused by Pseudocercospora fuligena) resistance was studied in four crosses involving two resistant Lycopersicon accessions (PI134417, L. hirsutum and PI254655, L. esculentum) and four susceptible Asian Vegetable Research and Development Center tomato lines (CLN657BC₁F₂-267-0-3-12-7, CL143-0-10-3-0-1-10, CLN698BC₁F₂-358-4-13 and CL5915-93D₄-1-0-3). For each cross, six generations, i.e. P₁, P₂, F₁, F₂, BC₁F₁ and BC₁F₂ were evaluated following inoculations with isolate Pf-2 of P. fuligena. Chi-square analyses of the data based on the ratio of resistant to susceptible plants in the F₂ in three of four crosses gave a good fit to a segregation ratio of 1 R : 15 S, and BC₁F₂ data in three of four crosses gave an acceptable fit to the segregation ratio of 1 R : 63 S. The results indicate that resistance to BLM may be conditioned by two recessive genes acting epistatically in both PI134417 and PI254655.     

Genetics of grain yield and other agronomic characters in t'ef (Eragrostis tef Zucc. Trotter). I. Generation means and variances analysis

Quantitative genetics of grain yield and other agronomic characters of t'ef (Eragrostis tef) were studied using the F₁, F₂, BC₁, and BC₂ of the cross Fesho × Kay Murri. The study was carried out to estimate gene effects controlling the inheritance of grain yield and related agronomic characters. Significant additive [d] and dominance × dominance [l] interaction effects were detected for grain yield. The variations of yield per panicle and panicle weight were explained in terms of [d], dominance [h], and additive × additive [i] interactions. Non-allelic gene interactions were also detected for kernel weight, harvest index, tiller number, plant height, days to heading and days to maturity. The simple additive-dominance model explained the variation for panicle length, culm diameter and plant weight, allowing unbiased estimates of additive (D) and dominance (H) variance components. Large dominance variances (H) were estimated for grain yield, yield per panicle, and panicle weight. The additive variances for plant height, panicle length, days to heading and days to maturity were higher than the respective dominance variances. High narrow-sense heritability (h²) values (> 0.50) were estimated for plant height, panicle length, days to heading and days to maturity. The lowest h² (0.09) was obtained for kernel weight for which there was little variability. Since grain yield and several important agronomic characters of t'ef are influenced by non-allelic gene interaction, it is advisable to delay selection for yield to later generations with increased homozygosity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of resistance to two races of sunflower downy mildew (Plasmopara halstedii) in two Helianthus annuus L. lines

Sunflower downy mildew caused by Plasmopara halstedii is an important disease of sunflower capable of causing losses of more than 80% of production. Races 100, 300, 310, 330, 710, 703, 730 and770 of the fungus have been identified in Spain. Race 703, of high virulence, has been identified frequently in the northeast, while race 310 seems to occur over the south, the main sunflower growing region of the country. Oil sunflower lines RHA-274 and DM4 were studied for their resistance to races 310(RHA-274 and DM4) and 703 (DM4). In each cross, only one plant of the resistant parent was crossed to the inbred susceptible line HA-89 (or cmsHA-89).Plants from F₂ and backcross(BC₁F₁ to susceptible parent)generations were evaluated for fungal sporulation on true leaves and/or cotyledons. The resistant-to-susceptible ratios obtained in the F₂ and BC₁F₁ progenies from the crosses cmsHA-89 × RHA-274 and HA-89 × DM4suggested that one major gene in each line is responsible for resistance to race 703.The segregations of the progenies of the cross HA-89 × DM4 inoculated with race 703also fitted the ratios 1:1 and 3:1 (for BC₁F₁ and F₂, respectively)corresponding to control of resistance by a single dominant gene. In RHA-274, the gene for resistance to race 310 was designated Pl ₉, whereas Pl _v is tentatively proposed to designate the gene in DM4 responsible for resistance to races310 and 703. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to race F of broomrape in sunflower lines of different origins

A new race F of broomrape overcomes all known resistance genes in cultivated sunflower, but recently, sources of resistance against race F have been developed. The objective of the present research was to study the inheritance of resistance to race F in crosses between 12 resistant sunflower breeding lines, derived from three different sources of resistance, and the susceptible male‐sterile line P‐21. Parental lines and F₁, F₂, F₃ and BC₁ generations were evaluated for broomrape resistance. Segregations in the F₂ and BC₁ to resistant parent approached resistant to susceptible ratios of 1: 15 and 1: 3, respectively, in most of the crosses, suggesting a double dominant epistasis. However, segregations of 3: 13 and 1: 1 for F₂ and BC₁, respectively, indicating a dominant‐recessive epistasis, were also found. The F₃ data confirmed these results. Owing to the recessive nature of this resistance, it must be incorporated into both parental lines for developing resistant hybrid cultivars.     

Genetics of resistance to early blight (Alternaria solani Sorauer) in tomato (Lycopersicon esculentum L.)

The genetic nature of early blight resistance in tomato was studied in three crosses at seedling and adult plant stages. A six generation mean analysis of the cross Arka Saurabh (susceptible) × IHR1939 (resistance) and its reciprocal cross revealed that the resistance to early blight was conferred by recessive polygenes at both seedling and adult plant stages. This polygenic early blight resistance revealed the importance of additive and additive × additive gene effects at seedling stage and higher magnitude of dominance and dominance× dominance gene effects at adult plant stage. Evaluation of parents, F₁, F₂ and backcross generations of IHR1816 (resistance) × IHR1939 (resistance) revealed that the early blight resistance genes in IHR1816 (Lycopersicon esculentum NCEBR-1) and IHR1939 (Lycopersicon pimpinellifolium L4394) are independent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Introgression of resistance to Columbia and Northern root-knot nematodes fromSolanum bulbocastanum into cultivated potato

Summary Resistance toMeliodogyne chitwoodi races 1 (MC1) and 2 (MC2) andM. hapla (MH) derived fromSolanum bulbocastanum was introduced into the cultivated potato gene pool through somatic fusion. The initial F₁ hybrids showed resistance to the three nematodes. Resistance to reproduction on roots by MC1 was accompanied by resistance to tuber damage in F₁ clones. Tuber damage sometimes occurred, however, in hybrids of BC₁ progeny resistant to reproduction on roots when MC2 and MH were the challenging nematodes. Resistance to reproduction was transferred into BC₁ individuals, but a greater proportion of BC₁ progeny was resistant to MC1 than to MC2 or MH. Resistance to MC1 appears to be dominant and discretely inherited. F₁ and BC₁ progeny were pollen sterile, but seed were produced from crosses using cultivated tetraploid pollen sources. Approximately 11 and 33 per cent of pollinations produced berries on F₁ and BC₁ pistillate parents, respectively. Seed yield increased fourfold overall in crosses with F₁ compared to BC₁ individuals.Abbreviations MC1 Meloidogyne chitwoodi race 1 - MC2 Meloidogyne chitwoodi race 2 - MH Meloidogyne hapla - Rf Reproductive factor     

Genetic Analysis of Resistance to Phytophthora Root Rot in Tomato (Lycopersicon esculentum Mill.)

The resistant accession, LA1312, and the susceptible cultivar ‘Peto 343′, were crossed to develop F₁, F₂ and BC₁ populations for genetic analysis of resistance in tomatoes to Phytophthora parasitica Dastur, the causal agent of Phytophthora root rot. There was no maternal effect on resistance. Generation means analysis indicated that tolerance to Phytophthora root rot was under genetic control with both simple (additive and dominance) and digenic interaction (additive × additive and additive × dominance) effects contributing to the total genetic variation among generation means. Weighted least square regression analysis indicated that the majority (ca. 96 %) of the genetic variation could be explained by simple additive effects alone. Narrow sense heritability was estimated as 0.22. Based on effective factor formulae, at least five effective factors controlled the resistance. Implications for breeding procedures are discussed.     

Inheritance of resistance to the chlorosis component of tan spot of wheat caused by Pyrenophora tritici-repentis, races 1 and 3

The fungus Pyrenophora tritici-repentis, causal agent of tan spot of wheat, produces two phenotypically distinct symptoms, tan necrosis and extensive chlorosis. The inheritance of resistance to chlorosis induced by P. tritici-repentis races 1 and 3 was studied in crosses between common wheat resistant genotypes Erik, Hadden, Red Chief, Glenlea, and 86ISMN 2137 and susceptible genotype 6B-365. Plants were inoculated under controlled environmental conditions at the two-leaf stage and disease rating was based on presence or absence of chlorosis. In all the resistant × susceptible crosses, F₁ plants were resistant and the segregation of the F₂ generation and F₃ families indicated that a single dominant gene controlled resistance. Lack of segregation in a partial diallel series of crosses among the resistant genotypes tested with race 3␣indicated that the resistant genotypes possessed␣the same resistance gene. This resistance gene was effective against chlorosis induced by P.␣tritici-repentis races 1 and 3.     

Generation mean analysis of phosphorus‐use efficiency in freely nodulating soybean crosses grown in low‐phosphorus soil

Freely nodulating soybean genotypes vary in their phosphorus (P) uptake and P‐use efficiency (PUE) in low‐P soils. Understanding the genetic basis of these genotypes’ performance is essential for effective breeding. To study the inheritance of PUE, we conducted crosses using two high‐PUE genotypes, two moderate‐PUE genotypes and two inefficient‐PUE genotypes, and obtained F₁, F_2, BC₁ and BC₂ populations. The inheritance of PUE was evaluated using a randomized complete block design. A generation mean analysis of phenotypic data showed that PUE was heritable, with complex inheritance patterns and the presence of additive, dominance and epistatic gene effects. Seed P, shoot P, root P, P‐incorporation efficiency and PUE were largely quantitatively inherited traits. There were dominance, additive × additive and dominance × dominance gene effects on PUE, grain yield, shoot dry weight, 100‐seed weight, root dry weight and shoot dry matter per unit P for populations grown under low‐P conditions. Dominance effects were generally greater than additive effects on PUE‐related indices. These PUE indices can be used to select P‐efficient soybean genotypes from segregating populations.     

Diallel analysis of Fusarium head blight resistance in genetically diverse winter wheat germplasm

New sources of partial resistance to Fusarium head blight (FHB) in wheat have been identified over the past decade; however, little is known of their breeding value. A 20 parent partial diallel that included resistant genotypes from the U.S., Europe, China and South America was used to evaluate the potential of these sources of resistance as parents in wheat breeding programs. Eight plants replication⁻¹ of each of 190 crosses and 20 parents were point-inoculated with Fusarium graminearum under greenhouse conditions in two replicated experiments. Both general (GCA) and specific combining ability (SCA) were significant. Most of the variance for FHB severity was associated with additive genes; however, estimates for SCA ranged from highly negative to highly positive in both resistant × resistant and resistant × susceptible crosses which suggest that improving FHB resistance through gene pyramiding strategies based on additive genetic variation may be complicated by interaction effects that condition FHB resistance.