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.     

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.     

Analysis of mode of inheritance of Fusarium wilt resistance in castor (Ricinus communis L.)

Castor (Ricinus communis L.) is an important industrial oilseed crop grown worldwide. Wilt caused by Fusarium oxysporum f.sp. ricini is a devastating disease in castor. The inheritance mode of wilt resistance was investigated. The F₁, F₂ and backcross generations of four crosses involving four resistant and three susceptible parents were developed. The role of digenic (R¹ and R²) epistatic interactions on wilt resistance was confirmed. The 15 : 1, 9 : 7 and 13 : 3 ratios indicated duplicate dominant, duplicate recessive and dominant and recessive epistatic interactions, respectively. Castor parents used in the crosses exhibited varied inheritance modes. All generations of a cross exhibited similar inheritance mode when parents were comparable. However, generations varied in inheritance mode when parents were not comparable in inheritance mode. These results would have practical interest when decisions are required regarding the choice of parents and methodology in resistance and hybrid breeding. The results also provided a basis for investigating molecular genetics of wilt resistance mechanisms.     

偏凸-柱穗山羊草双二倍体与普通小麦不同杂种世代的染色体及性状分离特点

为探讨偏凸山羊草－柱穗山羊草双二倍体SDAU18在小麦遗传改良中的利用价值,以SDAU18和普通小麦品种烟农15及其9个杂种世代为材料,分析不同自交和回交世代染色体和性状分离的特点。结果表明,随自交和以烟农15为轮回亲本回交世代的增加,染色体数目逐渐减少,回交比自交能使后代的染色体数目更快趋近普通小麦的42条,至F₅和BC₃F₁代,染色体数目为42的植株已分别达93.9%和92.0%。与自交世代相比,回交后代减数第一分裂中期的花粉母细胞的染色体构型较为简单,回交次数过多不利于外源染色体与普通小麦染色体发生重组,一般应以回交2~3次为宜;随自交和回交世代的增进,杂种的育性提高,至F₃和BC₂F₁代育性基本稳定。在不同杂种世代可分离出具有矮秆、大穗、大粒、对白粉病、条锈病免疫或高抗及外观品质优良的变异类型,以F₃和BC₁F₁代的变异类型最丰富。     

Inheritance of very high linoleic acid content and its relationship with nuclear male sterility in safflower

Safflower (Carthamus tinctorius L.) possesses the highest amount of linoleic acid among the 10 major vegetable oil crops of the world. Very high linoleic acid content is controlled by recessive alleles at a single locus Li. However, deviated segregations from the expected monogenic inheritance have been observed in crosses involving nuclear male‐sterile (NMS) lines. The present research was undertaken to study the inheritance of very high linoleic acid content in safflower and its relationship with nuclear male sterility. F₁, F₂, F₃, BC₁F₁ and BC₁F₂ seed generations were evaluated in a cross between CR‐142 (a line with very high linoleic acid content, 88%) and CL1 (an NMS line with wild‐type linoleic acid content, 74%). The genetics of linoleic acid content in male‐sterile plants was determined by testcrossing with CR‐142. The results confirmed monogenic inheritance. The analysis of the F₃ and BC₁F₂ to CL1 seed generations demonstrated a repulsion‐phase linkage between Li and Ms loci, the latter conferring the NMS trait. The recombination rate between Li and Ms was estimated to be 0.09.     

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.     

Generation mean analysis of spring wheat (Triticum aestivum L.) seedlings tolerant to high levels of manganese

Effective utilisation of wheat (Triticum aestivum L.) germplasm tolerant to high manganese (Mn) in a breeding program requires an understanding of the genetics of Mn tolerance. Five wheat cultivars differing in their response to high Mn were crossed in a half diallel design with no reciprocals. Seedlings of parents and progeny generations were phenotyped in high Mn nutrient solutions. Total chlorophyll concentration, which was positively correlated with leaf elongation rate during recovery from Mn stress, was used for phenotyping Mn tolerance. Means of chlorophyll concentration of P₁, P₂, F₁, F₂, BC₁, and BC₂ generations, in all crosses which showed significant variation among generations, were subjected to line crosses analysis to estimate gene effects. The continuous frequency distribution of seedlings with differential Mn tolerance, the similarity of the F₁ and F₂ means, and the high and significant levels of additive gene action indicated quantitative inheritance for Mn tolerance at seedling stage. A preponderance of additive effects indicated that selection for Mn tolerance in early generations should be effective.     

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.     

Genetics of Resistance in Vicia sativa L. to Orobanche crenata Forsk.

The genetics of resistance of common vetch (Vicia sativa L.) to broomrape (Orobanche crenata Forsk.) was studied for two years by using the P₁, P₂, F₁, BC¹, BC₂, F₂ F₃, and F₄ generations obtained from crosses between resistant and susceptible lines. Resistant lines were selected by screening a world collection m a naturally infested plot. Resistance was tested both under field and greenhouse conditions. The best index to measure resistance was the number of emerged broomrapes per host plant. The results fit the additive-dominance model. The main component of the variation was additivity; dominance and interaction effects seemed to depend on the environment. When dominance is expressed, a low number is dominant over a high number of broomrapes per host plant.     

Inheritance of drought resistance related traits in two crosses of groundnut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

Groundnut (Arachis hypogaea L.) is an important oilseed crop grown in more than 100 countries across wide range of environments. Frequent occurrence of drought is one of the limiting factors adversely affecting groundnut productivity, especially in rainfed areas, and hence genotypes having high water use efficiency (WUE) under limited available water need to be developed. In groundnut, WUE is correlated with SPAD chlorophyll meter reading (SCMR) and specific leaf area (SLA). These two traits, SCMR and SLA, can be used as surrogate traits for selecting for WUE. In order to improve SCMR and SLA, and in turn WUE in groundnut, a good knowledge of the genetic system controlling the expressions of these traits is essential for the selection of the most appropriate and efficient breeding procedure. The present investigation was conducted to determine the gene action controlling the inheritance of SCMR and SLA in two crosses, ICG 7243 × ICG 9418 and ICG 6766 × Chico, and their reciprocals. Six generations of each cross (P₁, P₂, F₁, F₂, BC₁P₁, and BC₁P₂) were evaluated for SCMR and SLA at two stages of the crop growth viz., 60 and 80 days after sowing (DAS). For SCMR at 80 DAS, additive effects were important in both the crosses whereas predominance of dominance effects with duplicate epistasis was observed for SCMR at 60 DAS and SLA at both stages in both the crosses. Predominance of additive effect for SCMR at 80 DAS suggested effective selection could be practiced even in early generations whereas for SCMR at 60 DAS and SLA at both stages in both crosses, it would be better to defer selection to later generations. Further, recording of SCMR and SLA should be done between 60 and 80 DAS for screening the germplasm lines for drought tolerance.     

Inheritance of resistance to broomrape (Orobanche cumana Wallr.) race F in a sunflower line derived from wild sunflower species

Genetic resistance to broomrape (Orobanche cumana Wallr.) race F in sunflower line J1, derived from the wild perennial species Helianthusgrosseserratus Martens and Helianthus divaricatus L., has been reported to be controlled by dominant alleles at a single locus, Or6. However, deviations from this monogenic inheritance have been observed. The objective of the present study was to gain insight into the inheritance of resistance to broomrape race F in the sunflower line J1. F₁, F₂, F₃ and BC generations from crosses between J1 and three susceptible lines, P21, NR5 and HA821 were evaluated. F₁ hybrids showed both resistant (R) and moderately resistant (MR) plants, the latter having a maximum of five broomrape stalks per plant compared with >10 in the susceptible parents. This indicated incomplete dominance of the Or6 alleles. F₂ plants were classified as R, MR or susceptible (more than five broomrape stalks per plant). Three different segregation ratios were observed: 3 : 1, 13 : 3 and 15 : 1 (R + MR : S), suggesting the presence of a second gene, Or7, whose expression was influenced by the environment. A digenic model was confirmed, based on the evaluation of F_2:3 families.     

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.     

Inheritance of Striga hermonthica adaptive traits in an early‐maturing white maize inbred line containing resistance genes from Zea diploperennis

Striga hermonthica can cause as high as 100% yield loss in maize depending on soil fertility level, type of genotype, severity of infestation and climatic conditions. Understanding the mode of inheritance of Striga resistance in maize is crucial for introgression of resistance genes into tropical germplasm and deployment of resistant varieties. This study examined the mode of inheritance of resistance to Striga in early‐maturing inbred line, TZdEI 352 containing resistance genes from Zea diploperennis. Six generations, P₁, P₂, F₁, F₂, BC₁P₁ and BC₁P₂ derived from a cross between resistant line, TZdEI 352 and susceptible line, TZdEI 425 were screened under artificial Striga infestation at Mokwa and Abuja, Nigeria, 2015. Additive‐dominance model was adequate in describing observed variations in the number of emerged Striga plants among the population; hence, digenic epistatic model was adopted for Striga damage. Dominance effects were higher than the additive effects for the number of emerged Striga plants at both locations signifying that non‐additive gene action conditioned inheritance of Striga resistance. Inbred TZdEI 352 could serve as invaluable parent for hybrid development in Striga endemic agro‐ecologies of sub‐Saharan Africa.     

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.     

Backcross variability for grain yield in oat species crosses (Avena sativa L. x A. sterilis L.)

Summary Avena sterilis introductions from the Middle East were useful sources of genes for improving the grain yield of adapted A. sativa cultivars for midwestern US. Introgression of genes from A. sterilis materials into A. sativa oat breeding populations was readily accomplished through a backcrossing procedure. Backcrossing successfully accomplished the recombination required to introgress complexly inherited traits. The BC₁F₂, BC₂F₂, BC₃F₂, and BC₄F₂ generations appeared to be best for selecting high-yielding transgressive segregates from the A. sativa x A. sterilis crosses.Journal Paper No. J-7919 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50010. Project No. 1752.     

Inheritance of insensitivity to culture filtrate of Pyrenophora tritici-repentis, race 2, in wheat (Triticum aestivum L.)

Tan spot of wheat is caused by the fungus Pyrenophora tritici‐repentis. On susceptible hosts, P. tritici‐repentis induces two phenotypically distinct symptoms, tan necrosis and chlorosis. This fungus produces several toxins that induce tan necrosis and chlorosis symptoms in susceptible cultivars. The objectives of this study were to determine the inheritance of insensitivity to necrosis‐inducing culture filtrate of P. tritici‐repentis, race 2, and to establish the relationship between the host reaction to culture filtrate and spore inoculation with respect to the necrosis component. The F₁, F₂, and BC₁F₁ plants and F_2:8 lines of five crosses involving resistant wheat genotypes ‘Erik’, ‘Red Chief’, and line 86ISMN 2137 with susceptible cultivars ‘Glenlea’ and ‘Kenyon’ were studied. Plants were spore‐inoculated at the two‐leaf stage. Four days later, the newly emerged uninoculated third leaf was infiltrated with a culture filtrate of isolate Ptr 92–164 (race 2). Reactions to the spore inoculation and the culture filtrate were recorded 8 days after spore inoculation. The segregation observed in the F₂ and BC₁F₁ generations and the F_2:8 lines of all crosses indicated that a single recessive gene controlled insensitivity to necrosis caused by culture filtrate. This gene also controlled resistance to necrosis induced by spore inoculation.     

Reproductive behaviour and broomrape resistance in interspecific hybrids of sunflower

Interspecific hybrids and backcross generations between the wild perennial species Helianthus resinosus, Helianthus paucifiorus, Helianthus laevigatus, Helianthus nuttallii ssp. nuttallii T. & G. and Helianthus giganteus, resistant to broomrape (Orobanche cernua) and susceptible inbred lines were obtained to study crossability to cultivated sunflower and the transmission and expression of resistance to this parasitic weed. Conventional crosses with all the species tested were successful except for the crosses with diploid H. giganteus, for which embryo rescue techniques were needed to overcome hybrid incompatibility. Pollen viability and seed set were highest for F₁ hybrids with hexaploid species and lowest for those with the diploid H. giganteus. We evaluated F₁, BC₁F₁, some BC₂F₁ plants and the wild and cultivated parents. The wild species and interspecific hybrids were resistant to broomrape infection except for H. nuttallii, which showed segregation, indicating that the resistance is dominant. The crossability and resistance of F₁, and back-cross generations of species with different ploidy levels indicate that the transfer of broomrape resistance to cultivated sunflower is feasible.     

Genetic analysis of grain mold resistance in white seed sorghum genotypes

Grain molds in rainy season sorghums can cause poor grain quality resulting in economic losses. Grain molds are a major constraint to the sorghum production and for adoption of the improved cultivars. A complex of fungi causes grain mold. Information on genetics of grain mold resistance and mechanisms is required to facilitate the breeding of durable resistant cultivars. A genetic study was conducted using one white susceptible, three white resistant/tolerant sources, and one colored resistant source in the crossing programme to obtain four crosses. P₁, P₂, F₁, BC₁, and BC₂, and F₂ families of each cross were evaluated for the field grade and threshed grade scores, under sprinkler irrigation. Generation mean analyses and frequency distribution studies were carried out. The frequency distribution studies showed that grain mold resistance in the white-grained resistance sources was polygenic. The additive gene action and additive × additive gene interaction were significant in all the crosses. Simple recurrent selection or backcrossing should accumulate the genes for resistance. Epistasis gene interactions were observed in colored resistance × white resistance cross. Gene interaction was influenced by pronounced G × E. Pooled analysis showed that environment × additive gene interaction and environment × dominant gene interaction were significant. The complex genetics of mold resistance is due to the presence of different mechanisms of inheritance from various sources. Evaluation of segregating population for resistance and selection for stable derivatives in advanced generations in different environments will be effective.     

Inheritance of siliqua orientation and seed coat colour in Brassica tournefortii

The inheritance of siliqua orientation and seed coat colour in Brassica tournefortii was investigated using four genotypes varying in these two characters. The F₁, F₂ and backcross generations of two crosses were used for studying the segregation pattern of the traits. The plants were classified for seed colour as having brown or yellow seeds and for siliqua orientation as having upright, semi‐spread or spread siliqua. Seed colour was found to be under monogenic control with brown being dominant over yellow. Siliqua orientation was under digenic polymeric gene action: upright siliqua was produced by the presence of two dominant genes and spread siliqua by two recessive genes. The absence of even a single dominant gene resulted in a third type of siliqua orientation, semi‐spread siliqua.     

Generation mean analysis of horticultural traits in mid‐late cauliflower (Brassica oleracea L. var. botrytis) under sub temperate conditions of Western Himalayas

Suitable breeding procedure for crop improvement mainly depends on the type and relative amount of genetic components and presence of non‐allelic interactions. Therefore, the study was carried out during three successive rabi seasons 2013‐14, 2014‐15 and 2015‐16 in mid hill zone of North‐western Himalayas, India with objective to estimate the main genetic effects including digenic non‐allelic interactions controlling horticultural traits in cauliflower. The generation mean analysis was carried out on six generations (P₁, P₂, F₁, F₂, B₁ and B₂) of six crosses involving four diverse parents of cauliflower. The results obtained revealed that the nature and magnitude of gene effects differed in different crosses and showed importance of duplicate epistasis in the inheritance of curd diameter and curd size index, whose effect can be wiped out by following sophisticated selection procedure such as reciprocal recurrent selection and/or biparental mating in early segregating generation. Complementary type of epistasis was recorded in most of the cross combinations for the important yield traits, which indicates the importance of heterosis breeding for the development of high yielding varieties.