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 Cercospora Leaf Spot Resistance in Mung Bean, Vigna radiata (L.) Wilczek

Inheritance of Cercospora leaf spot resistance in mungbean was studied in 20 crosses involving crosses of resistant × susceptible, resistant × resistant, susceptible × susceptible lines. 3:1 ratio was observed in all 14 F₂s involving resistant × susceptible parents. The inheritance of Cercospora leaf spot resistance is thus controlled by a single recessive gene. Our results are contradictory to observations of Thaklk et al. (1977 a, b) who found monogenic dominant inheritance of Cercospora leaf spot resistance in mungbean.     

Diallel analyses reveal the genetic control of resistance to ascochyta blight in diverse chickpea and wild Cicer species

Ascochyta blight is a major fungal disease affecting chickpea production worldwide. The genetics of ascochyta blight resistance was studied in five 5 × 5 half-diallel cross sets involving seven genotypes of chickpea (ICC 3996, Almaz, Lasseter, Kaniva, 24B-Isoline, IG 9337 and Kimberley Large), three accessions of Cicer reticulatum (ILWC 118, ILWC 139 and ILWC 184) and one accession of C. echinospermum (ILWC 181) under field conditions. Both F₁ and F₂ generations were used in the diallel analysis. The disease was rated in the field using a 1–9 scale. Almaz, ICC 3996 and ILWC 118 were the most resistant (rated 3–4) and all other genotypes were susceptible (rated 6–9) to ascochyta blight. Estimates of genetic parameters, following Hayman’s method, showed significant additive and dominant gene actions. The analysis also revealed the involvement of both major and minor genes. Susceptibility was dominant over resistance to ascochyta blight. The recessive alleles were concentrated in the two resistant chickpea parents ICC 3996 and Almaz, and one C. reticulatum genotype ILWC 118. The wild Cicer accessions may have different major or minor resistant genes compared to the cultivated chickpea. High narrow-sense heritability (ranging from 82% to 86% for F₁ generations, and 43% to 63% for F₂ generations) indicates that additive gene effects were more important than non-additive gene effects in the inheritance of the trait and greater genetic gain can be achieved in the breeding of resistant chickpea cultivars by using carefully selected parental genotypes.     

Inheritance of resistance to Fusarium wilt (race 2) in chickpea

The inheritance of resistance to Fusarium wilt (race 2) of chickpea was studied in a set of three crosses, i.e. ‘WR315’בC104’ (resistant × susceptible), ‘WR315’בK850’ (resistant × tolerant) and ‘K850’בGW5/7’ (tolerant × tolerant) in order to investigate the number of genes involved, their complementation and to find out whether resistant segregants are possible in a cross between two tolerant cultivars. Tests of F₁, F₂ and F₃ generations of these crosses under controlled conditions at ICRISAT, Patancheru, India, indicated involvement of three loci (two recessive and one dominant alleles). The homozygous recessive form at the first two loci conferred resistance whereas susceptibility occurred when the first two loci were in the dominant form. A dominant allele at the third locus can complement the dominant alleles at the other two loci to confer tolerance. Occurrence of resistant segregants in a cross between two tolerant cultivars was observed.     

Resistance to Ascochyta blight in chickpea - Genetic basis

Summary Genetic regulation of host resistance in chickpea-Ascochyta rabiei interaction system is governed by two dominant complementary genes each in the genotypes GLG 84038 and GL 84099, whereas the resistance in a black seeded genotype ICC 1468 was controlled by one dominant and one recessive independent gene. In all the genotypes, resistance is operated by inter-allelic interactions. The genes conferring resistance in GLG 84038 were found to be different to those operating in GL 84099 and ICC 1468. Among the five dominant genes dispersed in 3 genotypes under study, at least one has been reported for the first time, as to date, only three dominant genes have been reported in the literature.The four identified dominant genes in GLG 84038 and GL 84099 have been named as Arc₁, Arc₂ (in GLG 84038) and Arc₃, Arc₄ (in GL 84099). The undistinguished dominant gene in ICC 1468 has been named as Arc_5(3,4) as it could not be equated or differentiated from Arc₃ or Arc₄. The recessive gene in ICC 1468 has been named as Arc₁.Generation mean analysis of the 6 resistant × susceptible crosses involving the same genotypes, revealed that the genes conferring resistance in any of the 3 genotypes did not follow simple Mendelian inheritance but were influenced by inter allelic interactions. Additive gene effect along with dominance were operative in all the 3 genotypes under study in conferring resistance. However, the mechanism of resistance in GLG 84038 and GL 84099 were primarily additive in nature while that in ICC 1468, dominance as well as dominance × dominance interactions were more important than additive gene action.     

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.     

Genetic analysis of resistance to watermelon bud necrosis orthotospovirus in watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai]

An experiment was conducted to study the genetics and nature of gene action of resistance to watermelon bud necrosis orthotospovirus (WBNV) in watermelon. The experimental materials comprised of two resistant (BIL‐53 and IIHR‐19) and one susceptible (IIHR‐140) parents. Each of the resistant parents was crossed with the susceptible parent to develop six generations (P1, P2, F₁, F₂, BC1 and BC2) to study genetics. The results of segregation in F₂ and backcross progenies suggested that resistance is governed by a major dominant gene along with other background minor genes in both the crosses. BIL‐53 was found to possess higher degree of resistance with simple inheritance and hence may be of interest to breeders. Simple selection can be effective for improving the trait in the cross BIL‐53 × IIHR‐140 as additive gene action is prevalent.     

Inheritance of Dry Root Rot (Rhizoctonia bataticola) Resistance in Chickpea (Cicer arietinum)

The inheritance of resistance to dry root rot of chickpea caused by Rhizoctonia bataticola was studied. Parental F₁ and F₂ populations of two resistant and two susceptible parents, along with 49 F₁ progenies of one of the resistant × susceptible crosses were rested for their reaction to dry root rot using the blotting-paper technique. All F, plants of the resistant × susceptible crosses were resistant; the F₂ generation fitted a 3 resistant: 1 susceptible ratio indicating monogenic inheritance, with resistance dominant over susceptibility. F³ family segregation data confirmed the results. No segregation occurred among the progeny of resistant × resistant and susceptible × susceptible crosses.     

Genetic analysis of resistance to <Emphasis Type="Italic">Fusarium</Emphasis> root rot in common bean

Fusarium root rot (FRR) is a major disease of common bean worldwide. Knowledge of the inheritance of resistance to FRR would be important in devising strategies to breed resistant varieties. Therefore, a 12 × 12 full diallel mating scheme with reciprocal crosses was performed to generate 132 F₁ progenies, which were then advanced to the F₃. The progenies were evaluated for resistance to FRR under green house conditions in Uganda. General combining ability (GCA) effects were highly significant (P ≤ 0.01) for disease scores. Specific combining ability effects were not significant (P > 0.05) in the F₁, but were highly significant (P < 0.01) in the F₃ generation. These results indicate that resistance to FRR was governed by genes with additive effects in combination with genes with non-additive effects. Reciprocal differences were also significant (P = 0.01) at F₁ and F₃, primarily reflecting a large influence of maternal effects in both these generations. In fact, susceptible parents did not differ significantly (P > 0.05) for disease scores when used as paternal parents in the F₃, but differed strongly as maternal parents (P = 0.0002). Generally, the progenies were distinctly more resistant when the resistant parent was used as the female in crosses, especially as observed in the F₃. The maternal effects were strong in the F₃ generation, suggesting a complex form of cytoplasmic–genetic interaction. The non-maternal reciprocal effects in the F₃ were significant (P < 0.05) in both the resistant × resistant diallel, and in the resistant × susceptible crosses. Mid-parent heterosis (MPH) occurred in most crosses, with average heterosis approximately equal in each of the three generations, indicating that epistasis was probably more influential than dominance of individual genes. Gene-number formulas indicated that several genes were involved in resistant × susceptible crosses. Among resistant × resistant crosses, many produced continuous distributions of F₁ progeny scores, suggesting polygenic inheritance, while bi-modal distributions were characteristic of the F₃ distributions, and fit expected ratios for two or three loci segregating in each cross. Dominant forms of epistasis favoring resistance were strongly indicated. Parent–offspring heritability estimates were moderate. Overall, the results indicate that resistant parents contain a number of different resistance genes that can be combined with the expectation of producing strong and durable resistance. The lines MLB-49-89A, MLB-48-89, RWR719 and Vuninkingi, with large and negative GCA effects, contributed high levels of resistance in crosses and would be recommended for use in breeding programs.     

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.     

Leaf type is not associated with ascochyta blight disease in chickpea (Cicer arietinum L.)

The three major leaf types in chickpea are normal compound leaf, simple leaf and multipinnate. Simple leaf types are less commonly cultivated worldwide and are often reputed to be susceptible to ascochyta blight disease, whereas other leaf types range from resistant to susceptible. This study determined the association between host plant resistance to ascochyta blight and different leaf types in segregating populations derived from crosses between disease resistant and susceptible chickpea genotypes. In addition, the inheritance of disease resistance and leaf type was investigated in intraspecific progeny derived from crosses between two resistant genotypes with normal leaf type (ICC 3996 and Almaz), one susceptible simple leaf type (Kimberley Large) and one susceptible multipinnate leaf type (24 B-Isoline). Our results showed that, in these segregating populations, susceptibility to ascochyta blight was not linked to multipinnate or simple leaf types; resistance to ascochyta blight depended more on genetic background than leaf shape; leaf type was controlled by two genes with a dihybrid supplementary gene action; normal leaf type was dominant over other leaf types; and inheritance of ascochyta blight resistance was controlled by two major genes, one dominant and one recessive. Since there was no linkage between ascochyta blight susceptibility and leaf type, breeding various leaf types with ascochyta blight resistance is a clear possibility. These results have significant implications for chickpea improvement, as most current extra large seeded kabuli varieties have a simple leaf type.     

Genetics of resistance to P3 isolate of Phytophthora blight in pigeonpea

Seedlings from six crosses between susceptible × resistant and two between susceptible parents were screened against P₃ isolate of Phytophthora drechsleri f. sp. cajani in the glasshouses. Disease reaction was scored on a rating scale of 1–5. Resistance was found to be controlled by one dominant gene and some minor genes and is affected by ontogeny. The resistance gene appeared to be different from the one reported earlier (Pd₁) and is designated here as Pd₃. 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 resistance to Aphis craccivora in cowpea

Summary Inheritance of aphid resistance and allelic relationships among sources of resistance was studied in the parents, F₁, F₂, F₃, and backcross populations of cowpea crosses. Each 4-day old seedling was infested with five fourthinstar aphids. Seedling reaction was recorded 14–16 days after infestation when the susceptible check was killed. The segregation data from eight crosses between resistant and susceptible cowpea cultivars indicated that aphid resistance was inherited as a monogenic dominant trait. Segregation data from crosses among eight resistant cultivars indicated that one or two loci and modifier(s) were involved in the expression of resistance to aphids. It was suggested that further studies on allelism among sources of resistance needed to be conducted in order to resolve this.     

Inheritance of resistance to <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">melonis</Emphasis> races 0 and 2 in melon accession Tortuga

The inheritance of the resistance to Fusarium oxysporum f. sp. melonis (F.o.m.) races 0 and 2 in ‘Tortuga’, a Spanish cantalupensis accession, was studied from crosses of ‘Tortuga’ by the susceptible line ‘Piel de Sapo’ and the resistant one ‘Charentais-Fom1’ that carries the resistance gene Fom-1. The segregation patterns observed in the F₂ (‘Tortuga’ × ‘Piel de Sapo’) and the backcross (‘Piel de Sapo’ × (‘Tortuga’ × ‘Piel de Sapo’) populations, suggest that resistance of ‘Tortuga’ to races 0 and 2 of F.o.m. is conferred by two independent genes: one dominant and the other recessive. In the F2 derived from the cross between accessions ‘Tortuga’ and ‘Charentais-Fom1’, the lack of susceptible plants indicated that the two accessions are carrying the same resistance gene (Fom-1). The analysis of 158 F₂ plants (‘Tortuga’ × ‘Piel de Sapo’) with a Cleaved Amplified Polymorphic Sequence marker 618-CAPS, tightly linked to Fom-1 (0.9 cM), confirmed that ‘Tortuga’ also carries a recessive gene, that we propose to symbolize by fom-4.     

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.     

Resistance to Sunflower Rust and its Inheritance in Wild Sunflower Species

Resistance to the prevailing races of sunflower rust, Puccinia hehanthi Schw., is lacking in the commercial hybrids (Helianthus annuus L.). The objective of this study was to identify new sources of resistance to the four North American rust races in wild Helianthus species, and to determine their mode of inheritance. Seventy-eight accessions of H. annuus L., H. argophyllus Torrey and Gray, and H. petiolans Nutt. were evaluated in the greenhouse. Resistance to races 1, 2, 3, and 4 was observed in 25, 28, 15, and 26% of the plants, respectively, and 10% of the plants were resistant to all four races. Seven accessions that had a high percentage of resistant plants to all the four races were selected and one resistant plant from each accession was crossed with susceptible inbred line HA89. Three to four F₁ plants resistant to all four races from each cross were backcrossed with HA89. F₁ plants from PI-413118 × HA89 and PI 413175 × HA89 were resistant to all four races. The PI 413023 × HA89 F₁ plants were 100 % resistant to races 3 and 4 and segregated in a 3: 1 resistant (R) to susceptible (S) ratio to races 1 and 2. The other four F₁ combinations segregated 3R: IS ratios to all four races. Bc₁F₁ progenies revealed that plants from PI 413048, PI 413037, PI 413038, and PI 413171 used in the crosses possessed two dominant genes in heterozygous condition for resistance to each of the four races, whereas plants from PI 413023 possessed two dominant genes in heterozygous condition for resistance to each of races 1 and 2, and one dominant resistance gene in homozygous condition for each of races 3 and 4. Plants from PI 413118 and PI 413175 carried a single dominant gene in homozygous condition for resistance against each of the four races.     

大豆抗胞囊线虫4号生理小种新品系SSR标记分析

培育抗病品种是大豆胞囊线虫(Soybean Cyst Nematode, SCN)病经济、有效的防治方法。利用130个SSR标记对26份抗SCN 4号生理小种(SCN 4)新品系和15份感病品系进行基因型分析, 旨在明确抗病品系与SCN 4抗性相关联的SSR标记, 提出抗性基因分子标记鉴定方法, 以提高抗病品系在育种中的利用效率。研究表明, Hartwig与晋品系亲本具有不同的SCN 4抗病基因, 其遗传相似系数为0.362。与抗性显著关联的22个SSR位点分布在11个连锁群(LG), 推测LG D1b上分布的SSR标记附近存在1个新的SCN 4抗病基因; 而Satt684、Sat_230、Sat_222、Satt615和Satt231位点, 来自亲本Hartwig等位基因与抗病相关联, 而来自晋品系的等位基因与感病相关联, 在Sat_400、Satt329和Satt557等其他17个SSR位点, 来自Hartwig等位基因与感病相关联, 来自晋品系亲本的等位基因与抗病相关联。利用非连锁不平衡SSR标记Satt684和Sat_400可对供试品系进行有效的抗性辅助选择。     

Inheritance and allelism of wheat streak mosaic virus resistance in two Iranian wheat lines

Wheat streak mosaic (WSM) caused by wheat streak mosaic virus (WSMV) is a serious disease of wheat and many plants in the grass family. In previous studies genotypes collected from different parts of Iran, were screened for WSM resistance. Two resistant genotypes, “Adl Cross” and “4004” were crossed to one susceptible genotype “Marvdasht.” Reciprocal crosses were also made. Seedlings of parents, F₁, F₂, backcrosses to susceptible (BCS) and resistant (BCR) were evaluated for WSMV reaction based on scales 0–7, by artificial infection under greenhouse conditions. Allelism was studied by evaluating the F₁ and F₂ seedlings of the resistant × resistant cross. Inheritance of resistance to WSMV in Adl Cross and 4004 was controlled by one dominant gene. No allelism was observed between resistance genes. Among the F₂ seedlings of the resistant × resistant cross relatively more resistant genotypes with a zero score were observed. These two genes, therefore, can be incorporated into an adapted wheat cultivar to produce a more durable resistance.     

Quantitative resistance to Cercospora leaf spot disease caused by Pseudocercospora cruenta in cowpea

Six populations (Parent 1, Parent 2, F1, F2, BC1 and BC2) generated from each of four crosses involving four resistant and two susceptible varieties of cowpea (Vigna unguiculata L. Walp) were evaluated for resistance to Cercospora leaf spot (CLS) disease caused by Pseudocercospora cruenta under induced epiphytotic conditions, in four separate field experiments. Climatic conditions determined the onset of CLS disease in the susceptible cultivar and varied in the four experiments from 35 to 48 days after planting (DAP). Genetic analysis revealed that the mode of inheritance of resistance to P. cruenta can be oligogenic or polygenic depending upon the cross. This is the first report of polygenic inheritance of CLS resistance. Number of nodes infected fitted a simple additive dominance model with predominance of additive effects based on generation mean analysis. Oligogenic resistance was observed for the other three crosses, with the most plausible models being: a single gene model with incomplete dominance in CB27 × IT87D-939-1; a single gene model with complete dominance in CB27 × VRB-10; and a triger model in Los Banos Bush Sitao × IT86D-792, based on segregation analysis of symptomatic : non-symptomatic plants. The role of minor genes was also indicated in the above crosses. Suggested approaches to breeding for resistance to CLS are discussed.