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.     

Genetic basis of pod borer (Helicoverpa armigera) resistance and grain yield in desi and Kabuli Chickpea (Cicer arietinum L.) under unprotected conditions

A series of half-diallel crosses involving early, medium and late maturity desi and kabuli type chickpea (Cicer arietinum L.) genotypes with stable resistance to Helicoverpa pod borer, along with the parents, were evaluated at two locations in India to understand the inheritance of pod borer resistance and grain yield. Inheritance of resistance to pod borer and grain yield was different in desi and kabuli types. In desi type chickpea, the additive component of genetic variance was important in early maturity and dominance component was predominant in medium maturity group, while in the late maturity group, additive as well as dominance components were equally important in the inheritance of pod borer resistance. Both dominant and recessive genes conferring pod borer resistance seemed equally frequent in the desi type parental lines of medium maturity group. However, dominant genes were in overall excess in the parents of early and late maturity groups. In the kabuli medium maturity group, parents appeared to be genetically similar, possibly due to dispersion of genes conferring pod borer resistance and susceptibility, while their F₁s were significantly different for pod borer damage. The association of genes conferring pod borer resistance and susceptibility in the parents could be attributed to the similarity of parents as well as their F₁s for pod borer damage in kabuli early and late maturity groups. Grain yield was predominantly under the control of dominant gene action irrespective of the maturity groups in desi chickpea. In all the maturity groups, dominant and recessive genes were in equal frequency among the desi parental lines. Dominant genes, which tend to increase or decrease grain yield are more or less present in equal frequency in parents of the early maturity group, while in medium and late maturity groups, they were comparatively in unequal frequency in desi type. Unlike in desi chickpea, differential patterns of genetic components were observed in kabuli chickpea. While the dominant genetic component was important in early and late maturity group, additive gene action was involved in the inheritance of grain yield in medium duration group in kabuli chickpea. The dominant and recessive genes controlling grain yield are asymmetrically distributed in early and medium maturity groups in kabuli chickpea. The implications of the inheritance pattern of pod borer resistance and grain yield are discussed in the context of strategies to enhance pod borer resistance and grain yield in desi and kabuli chickpea cultivars.     

Genetics of resistance to ascochyta blight in chickpea (Cicer arietinum L.)

Summary Six chickpea lines resistant to Ascochyta rabiei (Pass.) Lab. were crossed to four susceptible cultivars. The hybrids were resistant in all the crosses except the crosses where resistant line BRG 8 was involved. Segregation pattern for diseases reaction in F₂, BCP₁, BCP₂ and F₃ generations in field and glasshouse conditions revealed that resistance to Ascochyta blight is under the control of a single dominant gene in EC 26446, PG 82-1, P 919, P 1252-1 and NEC 2451 while a recessive gene is responsible in BRG 8. Allelic tests indicated the presence of three independently segregating genes for resistance; one dominant gene in P 1215-1 and one in EC 26446 and PG 82-1, and a recessive one in BRG 8.Research paper No. 3600     

Identification of segregation-distortion-neutral alleles to improve pollen fertility of indica-japonica hybrids in rice (Oryza sativa L.)

The genetics of resistance to Ascochyta blight (Ascochyta fabae f. sp. fabae) was studied in two populations of faba bean (Vicia faba). Plants of a resistant population, ILB 752, and a susceptible one, NEB 463, were screened for their reaction to the pathogen and the results were quantified on a scale of 0–5. Crosses were made between plants both within and between accessions and the F₁ and F₂ generations assessed in a field trial 21 and 45 days after inoculation. Disease scores were greater at 45 days than at 21 days and they were not significantly affected by the presence of susceptible spreader rows in part of the trial. ILB 752 carried a major dominant gene conferring resistance while NEB 463 carried the recessive allele for susceptibility. Furthermore, a minority of plants of NEB 463 appeared to carry at least one pair of complementary recessive genes, also conferring resistance. Most of the plants of ILB 752 were homozygous for the dominant resistance gene and a few were heterozygous. Reciprocal crosses behaved identically, indicating the absence of maternal effects in the expression of Ascochyta blight resistance in faba beans. The results show that it is important to confirm the level of heterozygosity for the resistance genes in this partially outbreeding species before crossing is commenced. The major dominant gene for resistance, identified in ILB 752, has clear potential for use in breeding for Ascochyta blight resistance. The minor genes identified in NEB 463 also show the potential for accumulating resistance through mass selection. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Detection and inheritance of leaf rust resistance in common wheat lines Agra Local and IWP94

Genetic studies were undertaken to determine the number and identities of leaf rust resistance genes in common wheat lines Agra Local and IWP94. The infection type arrays of the two lines with eight pathotypes (pt.) of P. triticina were different from those of lines possessing known leaf rust resistance (Lr) genes. Agra Local possessed two recessive resistance genes, one conditioning resistance to pathotype 4R9-7, and the other, a temperature-sensitive factor, gave resistance to pt. 121R127 at high temperature (27°C). IWP94 was previously demonstrated to carry Lr23. From the present study IWP94 was determined to have at least four leaf rust resistance genes. The first of these was the same recessive gene conferring resistance to pathotype 4R9-7 which was found in Agra Local. A second partially dominant gene conferred resistance to pathotype 121R127 at high temperature and two additional recessive genes governed resistance to pathotype 93R15. When present together, these two recessive genes complemented each other and provided resistance to pathotype 69R13 as well. One of the two recessive genes conferring resistance to pathotypes 93R15 and 69R13 was Lr23.     

Inheritance of resistance and genetic relationships among soybean plant introductions to races of soybean cyst nematode

Summary The objectives of this study were to determine if genes for resistance to soybean cyst nematode (SCN) in soybean PI 437654 were identical or different from the genes in Peking, and PI 90763. The F₂ plants and F₃ families were studied from crosses between PI 437654, Peking, and PI 90763. The cross PI 437654 × susceptible Essex was included to determine inheritance of resistance to SCN. For Race 3, PI 437654 was found to have genes in common with Peking and PI 90763. The segregation in PI 437654 × Essex indicated the presence of one dominant and two recessive genes. For Race 5, PI 437654 indicated the presence of similar genes as those in PI 90763 and Peking whereas, PI 437654 × Essex indicated the action of the segregation ratios of two dominant and two recessive genes. For Race 14, the data from the cross PI 437654 × PI 90763 indicated monogenic inheritance with resistance being dominant; whereas PI 437654 × Peking showed a recessive gene controlling resistance. The segregation in PI 437654(R) × Essex(S) suggested one dominant and two recessive genes for Race 14 reaction.     

An analysis of genes for resistance against Indian stem rust races in two bread wheat cultivars

Summary The genetic constitution of two bread wheat accessions from the International Spring Wheat Rust Nurseries (E 5883 and E 6032) has been studied for reaction to four Indian races of stem rust. Analysis of E 5883 has revealed that for each of the races 15C, 21 and 40 a single dominant gene operates for resistance. The dominant gene against race 15C was identified as Sr6. The dominant genes for resistance against races 21 and 40 were found to be different from the genes described so far. Resistance against race 122 is controlled by a single recessive gene producing characteristically a 2 type of reaction. This gene was identified as Sr8.The resistance of E 6032 against each of the races 15C, 21 and 40 is controlled by two genes, one dominant and one recessive, which act independently. Dominant genes effective against 15C, 21 and 40 were conclusively identified as Sr6, Sr5 and Sr9b, respectively. From the correlated behaviour against races 15C and 40 as well as from the phenotypes of the resistance reactions rhe same recessive gene, undescribed so far, operates against the two races. The second recessive gene operating against race 21 was also observed to be different from those so far designated. E 6032 was, however, found to be susceptible to races 122.The presence of Sr6 both in E 5883 and E 6032 against race 15C was further confirmed through F₂ and F₃ segregation data.     

Genetics of resistance to cotton jassid,Amrasca biguttula biguttula (Ishida) in okra

Summary The resistance to cotton jassid in okra was found controlled by dominant genes. Both additive and dominance gene effects were significant but both additive gene effects and dominance x dominance type of interactions appear to be more important than other effects. The former could be exploited for developing genotypes resistant to jassids in okra.     

Inheritance of resistance to Fusarium wilt in Indian lentil germplasm (Lens culinaris Medik.)

Summary Three lentil genotypes resistant to Fusarium oxysporum f.sp. lentis viz. Pant L 234, JL 446 and LP 286 were crossed with two susceptible ones. The hybrid plants were all resistant in the eight crosses evaluated. Segregation pattern for wilt reaction in F₂, BC(P₁), BC(P₂) and F₃ generations in field and glasshouse conditions indicated that resistance to Fusarium wilt is under the control of two dominant duplicate genes in Pant L 234 and two independent dominant genes with complementary effects in JL 446 and LP 286. A third dominant gene complementary to the dominant genes in JL 446 and LP 286 is present in two susceptible lines. Allelic tests suggest the presence of five independently segregating genes for resistance. Duplicate dominant genes in Pant L 234 are non-allelic to two dominant genes with complementary effects in LP 286 and JL 446 and the third gene complementary to the two genes in JL 446 and LP 286 in susceptible lines JL 641 and L 9–12. Gene symbols among parental genotypes have been designated.     

Association between advanced generations and genealogy in inbred lines of snap bean by the Ward-Modified Location Model

Genetics of resistance to ascochyta blight was studied using different generations of fifteen crosses of chickpea (Cicer arietinum L.). Six parents comprising two susceptible varieties GL 769, C 214 and four resistant lines GG 1267, GL 90168, GL 96010 and GL 98010 were used to develop one S × S, eight S × R and six R × R crosses and some of the back crosses and F₃ generations were developed. Field screening technique was used to evaluate the different generations for disease reaction using mixture of ten prevalent isolates (ab₁–ab₁₀) of ascochyta blight (Ascochyta rabiei). Inheritance study showed digenic recessive control of resistance in the cross GL 769 × C 214, whereas monogenic recessive control of resistance was found in the crosses GL 769 × GL 98010 and C 214 × GL 98010. Digenic dominant and recessive control of resistance was found in the crosses GL 769 × GG 1267 and C 214 × GG 1267 while the crosses GL 769 × GL 90168 and C 214 × GL 96010 showed the monogenic dominant control of resistance. Trigenic dominant and recessive control of resistance was observed in the crosses GL 769 × GL 96010 and C 214 × GL 90168. Allelic relationship studies showed that three resistant parents viz., GG 1267, GL 96010 and GL 90168 possessed allelic single dominant gene for resistance. Besides, GG 1267 possessed two minor recessive genes for resistance, one of them was allelic to the minor recessive gene possessed by GL 90168 and other with GL 96010. The resistant parents GL 90168 and GL 96010 possessed non-allelic minor gene for resistance. The resistant parent GL 98010 possessed two minor recessive genes for resistance which were allelic to respective single recessive gene for resistance possessed by the susceptible parents GL 769 and C 214. The susceptible parents GL 769 and C 214 also possessed single independent inhibitory dominant susceptibility gene. The inhibitory gene was epistatic to the corresponding recessive gene for resistance.     

Genetics of resistance to 3 isolates of Ascochyta fabae on Faba bean (Vicia faba L.) in controlled conditions

Summary Genetics of resistance to Ascochyta fabae Speg. in Vicia faba L. was studied with a final objective to develop resistant faba bean varieties to Ascochyta blight. The study was conducted separately on 3 single spore isolates (AF10-2 and AF13-2 from Tunisia and AF4-3 from France) and belonging to different groups of virulence (GV1 and GV2). Important general combining ability (GCA) effects were found especially with isolates AF10-2 and AF4-3. Specific combining ability (SCA), although significant for the 3 isolates, was important only with AF13 -2, but less important than GCA. Additive gene effects were predominant to non-additive effects. Lines 29H and A8817 transmitted to their progenies resistance to the 3 isolates, whereas 14–12 and 19TB conferred resistance to their progenies only with isolates AF13-2 and AF4-3, respectively. In the material studied, resistance was generally controlled by dominant genes but also could be attributed to recessive genes although less frequent. Analysis of segregation in the F2 of 2 crosses between the resistant lines (A8817 and 29H) and the susceptible line (14–12) with isolate AF4-3 revealed dominant monogenic control at the level of leaves in the 2 resistant lines and, in addition, a recessive gene controlling resistance of stems. Non-allelic interactions were occasionally manifested and their origin appeared to be due to line 19TB. A recurrent selection scheme was proposed with the objective to develop improved open-pollination populations and synthetic varieties responding to the objective of the national Tunisian research programme on faba bean.     

Genetic analysis of broad spectrum resistance to potyviruses using doubled haploid lines of pepper (Capsicum annuum L.)

Summary Genetic analysis of resistance to PVY in androgenetic doubled haploid lines, F1, F2 and backcross progenies of the Mexican pepper line, CM 334 (Capsicum annuum L.), was performed. Three reaction types were observed when seedlings were inoculated with several PVY strains of different pathotypes and with an American PeMV strain. Resistant genotypes never showed systemic symptoms although some individuals sporadically developed necrotic local lesions on inoculated cotyledons. Susceptible genotypes exhibited either a typical systemic mosaic or a systemic necrosis that caused the death of the inoculated seedlings. Segregation analyses indicated that resistance to pepper potyviruses in CM 334 is conferred by two genes. The first one, tentatively named Pr4, is dominant and confers the resistance to all now known pathotypes of PVY and to PeMV. The second one, tentatively named pr5, is recessive; it confers only the resistance to common strains of PVY. The systemic necrotic response is conferred by an independent dominant gene, tentatively named Pn1.     

Genetics of host reactions to three races of the bacterial pustule pathogen in cowpea

Summary Inheritance of the brown hypersensitive resistant (BHR), non-hypersensitive resistant (R) and susceptible (S) host reactions produced by three races of the bacterial pustule pathogen (Xanthomonas campestris pv. vignaeunguiculatae) was studied in 45 F₁, F₂ and testcross progenies, using the infiltration inoculation method BHR reaction was dominant over R and S reactions, and R was recessive to S reaction. Two genes appeared to be involved in BHR reaction; one governing BHR reaction to race 1 and the other to races 1 and 2. Both were ineffective against race 3. R reaction, effective against all the races, appeared to be controlled by one, two or three recessive genes. One cowpea line had one BHR gene and two duplicate recessive R genes. Reaction expression in the segregants was clear and as expected with races 2 and 3 but was modified with race 1, possibly due to interactions between dominant or recessive alleles of the BHR genes and the homozygous recessive allele of the R genes. Gene symbols Bp-1 and Bp-2 are proposed for the BHR genes and bp-3, bp-4 and bp-5 for the recessive R genes. The genes present in each of the differential cowpea line are suggested.Contribution from the International Institute of Tropical Agriculture, Ibadan, Nigeria and Crop Development Division, Ministry of Agriculture, P.O. Box 9071, Dar es Salaam Tanzania.     

Inheritance studies with nine characters in Capsicum annuum L.

Summary Information obtained from breeding work with relatively small F₂ populations suggests independent segregation in 12 pairs of characters. Anthocyanin pigmentation in the cotyledon is either recessive or dominant, showing either single gene or polygenic inheritance, depending on parental genotypes. When single gene inheritance was observed, pigmentation was independent of resistance to potato virus-y, of the male sterile-1 (ms1) gene and of male sterile-2 (ms2) gene. However, additional observation suggests that one of the genes involved in pigmentation is linked with the male sterile-1 gene.     

An induced brachytic mutant of chickpea and its possible use in ideotype breeding

Mutations were induced in chickpea (Cicer arietinum L.) cultivar ‘JG 315’ through treatment of seeds with ethyl methane sulphonate (EMS). One of the mutants, named JGM 1, had brachytic growth (compact growth), characterized by erect growth habit, thick and sturdy stem, short internodal and interleaflet distances and few tertiary and later order branches. It was isolated from M₂ derived from seeds treated with 0.6% EMS for 6 h. Segregation analyses in F₂ progenies of its crosses with normal chickpea genotypes (JG 315, ICC 4929, and ICC 10301) suggested that a single recessive gene controlled brachytic growth in JGM 1. This gene was not allelic to the br gene for brachytic growth in spontaneous brachytic mutant E100YM. Thus, the gene for brachytic growth in JGM 1 was designated br2 and the br gene of E100YM was redesignated br1. Efforts are being made to use JGM 1 in development of a plant type with short internodes and erect growth habit. Such plant type may resist excessive vegetative growth in high input (irrigation and fertility) conditions and accommodate more plants per unit area.     

An allelic series at the Co-1 locus conditioning resistance to anthracnose in common bean of Andean origin

In this study, we characterized the genetic resistance of the Andean bean cultivars Kaboon and Perry Marrow and their relation to other sources of anthracnose resistance in common bean. Based on the segregation ratio (3R:1S) observed in two F₂ populations we demonstrated that Kaboon carries one major dominant gene conferring resistance to races 7 and 73 of Colletotrichum lindemuthianum. This gene in Kaboon is independent from the Co-2 gene and is an allele of the Co-1 gene present in Michigan Dark Red Kidney (MDRK) cultivar. Therefore, we propose the symbol CO-1 ² for the major dominant gene in Kaboon. The Co-1 is the only gene of Andean origin among the Co anthracnose resistance genes characterized in common bean. When inoculated with the less virulent Andean race 5, the segregation ratio in the F₂ progeny of Cardinal and Kaboon was 57R:7S (p = 0.38). These data indicate that Kaboon must possess other weaker dominant resistance genes with a complementary mode of action, since Cardinal is not known to possess genes for anthracnose resistance. Perry Marrow, a second Andean cultivar with resistance to a different group of races, was shown to possess another resistant allele at the Co-1 locus and the gene symbol Co-1 ³ was assigned. In R × R crosses between Perry Marrow and MDRK or Kaboon, no susceptible F₂ plants were found when inoculated with race 73. These findings support the presence of a multiple allelic series at the Andean Co-1 locus, and have major implications in breeding for durable anthracnose resistance in common bean. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of siliqua characters in Indian colza I. Locule number and siliqua position

Summary F₁, F₂, BC₁ and BC₂ generations, involving bilocular and tetralocular siliquae and with upright and pendent siliqua position, were studied with their parents. The segregation pattern in these generations indicated that number of locules is monogenically governed with the allel for bilocular type (VV-two valved pods) showing complete dominance over tetralocular (vv). Upright siliqua position is governed by two dominant genes (Up₁ Up₁ Up₂ Up₂) and pendent by two recessive genes (up₁ up₁ up₂ up₂). However, in absence of even a single dominant gene it give rise to a third type of siliqua position i.e. parallel.     

Localisation and combination of resistance genes against soil-borne viruses of barley (BaMMV,BaYMV) using doubled haploids and molecular markers

Barley yellow mosaic virus disease caused by different strains of BaYMV and BaMMV is a major threat to winter barley cultivation in Europe. Different resistance genes against these viruses have been mapped and suitable PCR-based markers have been developed. In this respect doubled haploid (DH) populations proved to be advantageous as they facilitate a repeated test for resistance against all agents of the barley yellow mosaic virus complex and besides this, dominant marker systems are as informative as co-dominant ones in DHs due to the lack of heterozygous genotypes. Using DH populations resistance genes rym4, rym5, rym11, rym13, rym15 and the BaYMV/BaYMV-2 resistance of the barley cultivar ‘Chikurin Ibaraki 1’ have been mapped. DHs are also well suited to pyramiding resistance genes against BaMMV and BaYMV. Since homozygous recessive genotypes are more frequent in DHs than in segregating F₂ populations, DHs can be efficiently used to create broad-spectrum resistance and to extend the usability of partly overcome resistance genes. Results from employing two different strategies for pyramiding, based on one and two DH-steps, respectively, combining three recessive resistance genes, i.e. rym4/rym5, rym9 and rym11, are presented. The faster strategy based on one haploidy step resulted in the identification of all three and two-way combinations of the respective resistance genes.     

Genetics of Cyst Nematode Resistance in Soybean PIs 467312 and 507354

Soybean Cyst nematode (SCN) Heterodera glycines Ichinohe is the most serious pest of soybean [Glycine max (L.) Merr.] in the world and genetic resistance in soybean cultivars have been the most effective means of control. Nematode populations, however, are variable and have adapted to reproduce on resistant cultivars over time due mainly to the narrow genetic base of SCN resistance in G. max. The majority of the resistant cultivars trace to two soybean accessions. It is hoped that new sources of resistance might provide durable resistance. Soybean plant introductions PI 467312 and PI 507354, are unique because they provide resistance to several nematode populations, i.e. SCN HG types 0, 2.7, and 1.3.6.7 (corresponding to races 3, 5, and 14) and HG types 2.5.7, 0, and 2.7 (corresponding to races 1, 3, and 5), respectively. The genetic basis of SCN resistance in these PIs is not yet known. We have investigated the inheritance of resistance to SCN HG types 0, 2.7, and 1.3.6.7 (races 3, 5, and14) in PI467312 and the SCN resistance to SCN HG types 2.5.7 and 2.7 (races 1 and 5) in PI 507354. PI 467312 was crossed to ‘Marcus’, a susceptible cultivar to generate F₁ hybrids, 196 random F₂ individuals, and 196 F_2:3 families (designated as Pop 467). PI 507354 and the cultivar Hutcheson, susceptible to all known SCN races, were crossed to generate F₁ hybrids, 225 random F₂ individuals and 225 F_2:3 families (designated as Pop 507). The F_2:3 families from each cross were evaluated for responses to the specific SCN HG types in the greenhouse. Chi-square (χ²) analyses showed resistance from PI 467312 to HG types 2.7, and 1.3.6.7 (races 5 and 14) in Pop 467 were conditioned by one dominant and two recessive genes (Rhg rhg rhg) and resistance to HG type 0 (race 3) was controlled by three recessive genes (rhg rhg rhg). The 225 F_2:3 progenies in Pop 507 showed a segregation of 2:223 (R:S) for response to both HG types 2.5.7 and 2.7 (corresponding to races 1 and 5). The Chi-square analysis showed SCN resistance from PI 507354 fit a one dominant and 3 recessive gene model (Rhg rhg rhg rhg). This information will be useful to soybean breeders who use these sources to develop SCN resistant cultivars. The complex inheritance patterns determined for the two PIs are similar to the three and four gene models for other SCN resistance sources known to date.