The allelic relationship between A IP(internal pigmentation) and A RC (red cabbage) in Brassica oleracea var. capitata L.

Summary Internal anthocyanin pigmentation (IP), previously reported to be controlled by a single gene dominant to aa of normal green cabbage, was studied further to determine its relationship to A ^RC A ^RC of red cabbage. When IP line R52 was crossed with an early red cabbage line. F₁ heads were pigmented throughout, but pigment intensity was intermediate. Subjective classification of F₂ plants by pigmentation intensity and distribution scores gave a ratio of 1 intense red throughout (red cabbage):2 medium red throughout:1 medium to light red, restricted to the central portion of the head (IP). The genotypes A ^RC A ^RC: A ^RC A ^IP: A ^IP A ^IP. respectively, are proposed to explain these 3 phenotypic classes. F₂ progenies contained no normal green plants, supporting the conclusion that A ^IP and A ^RC are alleles.Technical Paper 7052, Oregon Agricultural Experiment Station.     

Inheritance of internode length,plant form,and annual habit in a cross of cabbage and broccoli (Brassica oleracea var. capitata L. and var. italica Plenck.)

Summary When an inbred line of cabbage, Brassica oleracea L. var. capitata L., was crossed with an inbred line of broccoli B. oleraceae var. italica, the F₁ progeny were vigorous late annuals. All F₁ × broccoli backcross plants and 92% of the 3260 F₂ plants were annuals, while 40% of the F₁ × cabbage backcross plants were biennials. Annual habit is thus dominant and controlled by more than a single gene. Number of days to bud appearance in annuals varied continuously, and was primarily additive in inheritance. F₁ data suggested partial dominance for lateness but this was not supported by the F₂. Internode length was also continuous in distribution and primarily additive in inheritance, but with some dominance for short internodes in the F₁. Cabbage head forming ability was recessive and multigenic, with 2% of the F₂ plants forming heads, of which none were of commercial type and about half bolted as annuals. There was a significant chi square association between biennial habit and tendency for cabbage head formation. Clasping habit of terminal leaves was recessive to open leaves, multigenic, and associated with both cabbage heading and biennial habit.Technical Paper 4836, Oregon Agricultural Experiment Station; from an M.S. thesis by the senior author.     

Inheritance of black testa colour in lentil (Lens culinaris Medik.)

The inheritance of testa (seed coat) colour and interaction of cotyledon and testa colours were studied in seven crosses of lentil (Lens culinaris Medik.) involving parents with black, brown, tan or green testa and with orange, yellow or dark green cotyledons. Analysis of F₂ and F₃ seed harvested from F₁ and F₂ plants, respectively, revealed that although black testa is dominant over nonblack testa, its penetrance is not complete since both F₁ plants and heterozygous F₂ plants produced varying proportions of seeds with either black or nonblack testa. The F₂ populations of the crosses between parents with brown and tan, as well as brown and green, testa segregated in the ratio of 3 brown : 1 tan and 3 brown : 1 green, respectively, indicating monogenic dominance of brown testa colour over tan or green. The expression of testa colour was influenced by cotyledon colour when parents with brown or green testa are crossed with those having orange or green cotyledons. Thus F₂ seeds from these crosses with a green testa always had green cotyledons and never orange cotyledons. F₂ seeds from these crosses with a brown testa always had orange cotyledons and never green cotyledons. These results suggest diffusion of a soluble pigment from the cotyledons to the testa. This revised version was published online in July 2006 with corrections to the Cover Date.     

RAPD markers linked to microspore embryogenic ability in Brassica crops

In order to identify the markers linked to microspore embryogenic ability in Brassica crops, RAPD segregation analyses were performed in a microspore-derived (MD) population and a F₂ population derived from F₁between ‘Ho Mei’ (high responsive parent in microspore embryogenesis) and ‘269’ (low responsive parent) in Chinese cabbage, and between ‘Lisandra’ (high responsive parent) and ‘Kamikita’ (low responsive parent) in oil seed rape. After 230 and 143 primers were screened, a total of 148 and 52markers were detected to be polymorphic between the parents in Chinese cabbage and oilseed rape, respectively. Twenty-seven percent of the markers in the MD population showed a significant segregation distortion in both crops. Of the markers showing segregation distortion in the MD population, 71–75% of the markers followed the expected Mendelian segregation ratio in the F₂ population. When the relationships between such distorted markers and microspore embryogenesis of the F₂ population were examined, 7 and 3 markers were identified to be associated with embryogenic ability in Chinese cabbage and oilseed rape, respectively. These markers showed additive effects on embryo yields, and the plants having more alleles of the high responsive parent produced higher embryo yields. These markers maybe useful in marker-assisted selection for improving microspore responsiveness straits in Brassica crops. This revised version was published online in July 2006 with corrections to the Cover Date.     

Allelic relationships of genes controlling number of flowers per axis in chickpea

Genetic variation for number of flowers per axis in chickpea (Cicer arietinum L.) includes single-flower, double-flower, triple-flower and multi-flower traits. A double-flowered (DF) line ICC 4929, a triple-flowered (TF) line IPC 99-18 and a multi-flowered (MF) line JGM 7 were intercrossed in all possible combinations and flowering behavior of parents, F₁s and F₂s was studied to establish allelic relationships, penetrance and expressivity of genes controlling number of flowers per axis in chickpea. The F₁ from ICC 4929 (DF) × IPC 99-18 (TF) cross were double-flowered, whereas F₁ from ICC 4929 (DF) × JGM 7 (MF) and IPC 99-18 (TF) × JGM 7 (MF) crosses were single-flowered. The F₂ from ICC 4929 (DF) × IPC 99-18 (TF) cross gave a good fit to a 3:1 ratio for double-flowered and triple-flowered plants. The F₂ from ICC 4929 (DF) × JGM 7 (MF) cross segregated in a ratio of 9:3:3:1 for single-flowered, double-flowered, multi-flowered and double-multi-flowered plants. The F₂ from IPC 99-18 (TF) × JGM 7 (MF) cross segregated in a ratio of 9:3:4 for single-flowered, triple-flowered and multi-flowered plants. The results clearly established that two loci control number of flowers per axis in chickpea. The double-flower and triple-flower traits are controlled by a single-locus (Sfl) and the allele for double-flowered trait (sfl ^d ) is dominant over the allele for triple-flower trait (sfl ^t ). The three alleles at the Sfl locus has the dominance relationship Sfl > sfl ^d > sfl ^t . The multi-flower trait is controlled by a different gene (cym). Single-flowered plants have dominant alleles at both the loci (Sfl_ Cym_). The double-flower, the triple-flower and the multi-flower traits showed complete penetrance, but variable expressivity. The expressivity was 96.3% for double-flower and 76.4% for double-pod in ICC 4929, 81.2% for triple-flower and 0.0% for triple-pod in IPC 99-18, and 51.3% for multi-flower and 24.7% for multi-pod in JGM 7. Average number of flowers per axis and average number of pods per axis were higher in JGM 7 than double-flowered line ICC 4929 and triple-flowered line IPC 99-18. The results of this study will help in development of breeding strategies for exploitation of these flowering and podding traits in chickpea improvement.     

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.     

Development and characterisation of a <Emphasis Type="Italic">Brassica carinata</Emphasis> inbred line incorporating genes for low glucosinolate content from <Emphasis Type="Italic">B. juncea</Emphasis>

The presence of high levels of sinigrin in the seeds represents a serious constraint for the commercial utilisation of Ethiopian mustard (Brassica carinata A. Braun) meal. The objective of this research was the introgression of genes for low glucosinolate content from B. juncea into B. carinata. BC₁F₁ seed from crosses between double zero B. juncea line Heera and B. carinata line N2-142 was produced. Simultaneous selection for B. carinata phenotype and low glucosinolate content was conducted from BC₁F₂ to BC₁F₄ plant generations. Forty-three BC₁F₄ derived lines were selected and subject to a detailed phenotypic and molecular evaluation to identify lines with low glucosinolate content and genetic proximity to B. carinata. Sixteen phenotypic traits and 80 SSR markers were used. Eight BC₁F₄ derived lines were very close to N2-142 both at the phenotypic and molecular level. Three of them, with average glucosinolate contents from 52 to 61 micromoles g⁻¹, compared to 35 micromoles g⁻¹ for Heera and 86 micromoles g⁻¹ for N2-142, were selected and evaluated in two additional environments, resulting in average glucosinolate contents from 43 to 56 micromoles g⁻¹, compared to 29 micromoles g⁻¹ for Heera and 84 micromoles g⁻¹ for N2-142. The best line (BCH-1773), with a glucosinolate profile made up of sinigrin (>95%) and a chromosome number of 2n = 34, was further evaluated in two environments (field and pots in open-air conditions). Average glucosinolate contents over the four environments included in this research were 42, 31 and 74 micromoles g⁻¹ for BCH-1773, Heera and N2-142, respectively. These are the lowest stable levels of glucosinolates reported so far in B. carinata.     

Variation in pigment content of flour color in bread wheat (Triticum aestivum L.)

Summary Variation in pigment content of the flour of bread wheats (Triticum aestivum L.) was studied in the progenies of F₁ and F₂ of three crosses and their reciprocals. Reciprocal differences in pigment content were observed in the F₁ and F₂ means. Low pigment content was found to be partially dominant or over dominant in the crosses studied. There was evidence of substantial mid-parent F₁ heterosis in all crosses and betterparent F₁ heterosis in three crosses. In the F₂, heritability estimates were moderate to high. The F₂ frequency distributions were not normal. Estimation of effective factor pairs indicated the presence of one or two major gene pairs involved in the expression of pigment content in the flour. Action of modifiers was also assumed in one cross and its reciprocal. A factorial approach to metrical character suggested that the F₂ segregation ratios of low pigment content to high pigment content were 3:1, 15:1, 13:3 and 9:7 for the different crosses. Utilization of the findings in a wheat breeding program is briefly discussed.     

High-performance liquid chromatographic analysis of anthocyanins in induced amphidiploids of Iris laevigata Fisch. × I. ensata Thunb.

Summary Anthocyanins of colchicine-induced amphidiploids of I. laevigata × I. ensata were analyzed by the HPLC procedure and compared with those of parental species and F₁ hybrids of I. laevigata × I. ensata. The amphidiploids were characterized by seventeen anthocyanins, and exhibited all anthocyanins of the parental species and the F₁ hybrids. Malvidin 3RGac5G and petunidin 3RGac5G in anthocyanins detected were major pigments in the amphidiploids, which exhibited strongly the malvidin 3RGac5G-petunidin 3RGac5G type of I. ensata rather than the petunidin 3RGac5G-malvidin 3RGac5G type of I. laevigata. Moreover, a higher degree of anthocyanin content was observed in the amphidiploids and the F₁ hybrids. Namely, the anthocyanin content of the amphidiploids and the F₁ hybrids were 2.81 and 2.45 times as much as that of the mid-parent. This implies that there is a complementary effect on anthocyanin synthesis of parental genes in them. Finally, the utility of the amphidiploids was discussed.Contribution from the Laboratory of Plant Breeding, Faculty of Agriculture, Miyazaki Univ., No. 64.     

紫色不结球白菜花色苷合酶基因BrcANS的克隆与表达分析

以不结球白菜紫色品系NJZX1-3和其绿色突变体NJZX1-0及其后代F₂的2个株系NJZX2-1和NJZX2-2为材料,研究花色苷合酶基因在紫色不结球白菜叶片花色苷合成途径中的作用。利用同源克隆的方法,分别在NJZX1-3及NJZX1-0中克隆到花色苷合酶基因;经序列比对发现,花色苷合酶基因的核苷酸和氨基酸序列在2种材料和大白菜中完全一致,长度为1077 bp,编码358个残基,第211~307肽段具有2OG-Fe (II)双加氧酶家族基因的结构域,被命名为BrcANS。BrcANS蛋白与同科芥菜的同源性高达99%,进化关系亦与其最相近。在全部4种材料鲜叶中,总花色苷的含量(TAC)与叶片紫色程度是一致的,其中,NJZX1-3叶片中总花色苷含量最高,达到80.15±5.74 mg 100 g^–1 FW;BrcANS表达量为NJZX1-0 < NJZX2-1 < NJZX2-2< NJZX1-3,与其总花色苷含量呈正相关。BrcANS的mRNA在NJZX1-3和NJZX1-0两种材料的不同组织中特异性表达：在叶片中高度表达,而在其他组织中表达较弱;另外,在两种材料间的表达亦存在显著差异,在NJZX1-3叶片中的表达丰度显著高于NJZX1-0。随着叶龄的增大,紫色不接球白菜叶片紫色变浅,BrcANS的表达量下降,但在NJZX1-3和NJZX1-0间的表达差异亦明显减小。以上结果表明,BrcANS基因是紫色不结球白菜中花色苷合成的关键基因之一,其mRNA表达量与叶片紫色直接相关,可能在其转录水平上调控叶片中紫色的形成。     

Monogenic resistance in tomato to Fusarium oxysporum f. sp. lycopersici race 3

Summary Resistance to fusarium wilt, incited by Fusarium oxysporum (Schlecht.) f. sp. lycopersici (Sacc.) Snyder & Hansen race 3 in tomato (Lycopersicon esculentum Mill.) was discovered in LA 716, a L. pennellii accession. A resistant BC₁F₃ breeding line, E427, was developed from LA 716. E427 was crossed with the susceptible cv. Suncoast and F₁, BCP₁, BCP₂ (to Fla 7155, a susceptible parent) F₂, F₃, and BCP₂S₁ seeds were obtained. Segregation for resistance following root dip inoculation over three experiments indicated a single dominant gene controlled resistance. Five of the 12 BCP₁S₁'s segregated more susceptible plants, whereas one of the 12 segregated more resistant plants than expected (P<0.05). Three of 23 F₃ lines segregated more susceptible plants than expected while 1 of the 23 had more resistant plants than expected (P<0.05). Segregation in all other lines fit expected ratios. Five of the 23 F₃'s were homozygous resistant which was an acceptable fit to expectations (P=0.1–0.5). The gene symbol I ₃ is proposed for resistance to race 3 of the wilt pathogen. Deviations from expected ratios in data reported here and for other breeding lines indicate an effect of modifier genes and/or incomplete penetrance. Plant age at inoculation and seed dormancy did not affect results.Florida Agricultural Experiment Station Journal Series No. 8101.     

Inheritance of adult-plant resistance to Phytophthora capsici in pepper

Summary Inheritance studies were conducted to determine the genetic basis of adult-plant resistance in pepper (Capsicum annuum L.) to Phytophthora capsici. F₁, backcrosses and F₂ populations were developed using the resistant parent Criollo de Morellos 334 and susceptible parents Agronômico 10-G and Yolo Wonder. Pepper plants, at 36 days post-emergence, were inoculated near the base of the stem with an inoculum suspension of 5×10⁴ zoospores/ml. Segregation ratios in the F₂ generation of 13 resistant to 3 susceptible plants fit a 2-gene model for resistance with dominant and recessive epistasis.     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. Oleracea spp. Capitata). IV. A resistant 18-chromosome B1 plant and its B2 progenies

Summary The somatic karyotype and meiotic chromosome behavior were studied in an 18-chromosome B₁ plant derived from backcrossing a triploid (Brassica napus x B. oleracea ssp. capitata) F₁ hybrid to cabbage. It is considered that cabbage chromosomes no. 1 and no. 7 were substituted by two shorter B. napus chromosomes. Meiotic disturbances were more apparent during the late stages of second division. Seed fertility of this plant was largely restored in the second backcrosses with both cabbage and broccoli. 18-chromosome B₂ plants resistant to race 2 of Plasmodiophora brassicae were recovered among the progenies.Contribution no. J. 725 from the Research Station, Research Branch, Agriculture Canada, St-Jean, Québec J3B 6Z8.     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. oleracea ssp. capitata). III. First backcross and F2 progenies from interspecific hybrids between B. napus and B. oleracea ssp. capitata

Summary The first backcross and F₂ progenies from triploid F₁ and tetraploid F₁ hybrids between B. napus and 2x and 4x B. oleracea ssp. capitata (cabbage) were studied for their general morphology, resistance to race 2 of the clubroot pathogen, chromosome number and meiotic chromosome behavior. No linkage was apparent between resistance and the major morphological characters. Unreduced gametes played a large part in the successful formation of seed of the B₁ and F₂ progeny. B₁ plants with low chromosome numbers were selected for use in recurrent backcrosses. The potential use of anther culture to extract gametic progenies from resistant B₁ and F₂ plants with higher chromosome numbers was suggested. The presence of homoeologous pairing observed in all the plants is considered advantageous for selecting suitable progeny in later generations.     

Genetical analysis of resistance to Mycosphaerella pinodes in pea seedlings

Summary In studies of the inheritance of resistance, pea seedlings of seven lines in which stems and leaves were both resistant to Mycosphaerella pinodes were crossed with a line in which they were both susceptible. With seven of the crosses resistance was dominant to susceptibility. When F₂ progenies of five crosses were inoculated on either stems or leaves independently, phenotypes segregated in a ratio of 3 resistant: 1 susceptible indicating that a single dominant gene controlled resistance. F₂ progenies of one other cross gave ratios with a better fit to 9 resistant: 7 susceptible indicating that two co-dominant genes controlled resistance. The F₂ progeny of another cross segregated in complex ratios indicating multigene resistance.When resistant lines JI 97 and JI 1089 were crossed with a susceptible line and leaves and stems of each F₂ plant were inoculated, resistance phenotypes segregated independently demonstrating that leaf and stem resistance were controlled by different genes. In two experiments where the F₂ progeny of the cross JI 97×JI 1089 were tested for stem and leaf resistance separately, both characters segregated in a ratio of 15 resistant:1 susceptible indicating that these two resistant lines contain two non-allelic genes for stem resistance (designated Rmp1 and Rmp2) and two for leaf resistance (designated Rmp3 and Rmp4). Evidence that the gene for leaf resistance in JI 1089 is located in linkage group 4 of Pisum sativum is presented.     

Predicting transgressive segregants in early generation using single seed descent method-derived <Emphasis Type="Italic">micro-macrosperma</Emphasis> genepool of lentil (<Emphasis Type="Italic">Lens culinaris</Emphasis> Medikus)

In a self-fertilised crop like lentil, the identification of transgressive segregants for economically important trait such as seed yield is an important aspect of any practical breeding programme. The prediction of expected transgressive segregants in F₁ generation obtained as a ratio of additive genic effect [d] and additive variance (D) i.e. [d]/√D was studied in 28 crosses of lentil generated in a diallel fashion involving four parents each of macrosperma (exotic) and microsperma (Indian) types, respectively, resulting in three hybridization groups. The seed material advanced to F₂, F₃ and F₄ generations through single seed descent method was evaluated to determine the observed transgressive segregants for seed yield/plant. The observed frequency of crosses showing more than 20% transgressive segregants in F₂ to F₄ generations were exhibited in 9(32%) crosses, of which 7(77%) crosses were of macrosperma × microsperma type. Genotypes Precoz and HPL-5 of the exotic group (macrosperma) produced maximum number of transgressive segregants with the genotypes L-259, L-4145 and PL-406 of the Indian origin (microsperma). Goodness of fit (non-significant χ² value) in F₂ generation was observed for 19(68%) crosses of the total genepool, out of which 9(56%) crosses each in F₃ and F₄ generation belonged to the macrosperma × microsperma group, depicting it as the gene pool of paramount importance to obtain maximum transgressive segregants, therefore establishing the efficacy of the method used.     

Inheritance of the virgata pattern of partly colored seed coats in ‘Early Giant’ common bean

The inheritance of the virgata pattern of partly colored seed coats found in common bean (Phaseolus vulgaris L.) Early Giant (EG) was studied by a series of test crosses with line 5-593 and genetic stocks developed by backcrossing selected genes into the recurrent parent 5-593, a Florida dry bean breeding line with a self-colored, black seed coat with genotype T Z Bip P [C r] J G B V Rk. Analysis of the F₂ from the cross EG × 5-593 led to the hypothesis that the virgata pattern of EG has genotype t z bip^vgt, where vgt stands for virgata. The test cross EG × t z virgarcus BC₃ 5-593 confirmed the hypothesis that EG carries t z from data recorded in F₁, F₂, and 27 F₃ progenies from randomly selected F₂ plants. The F₃ segregation was also consistent with the hypothesis that a single recessive gene converts virgarcus into virgata. The test cross EG × t z bip bipunctata BC₃ 5-593 failed to show genetic complementation in F₁ progeny, and the F₂ segregated 3:1 for the parental phenotypes virgata and bipunctata, respectively. Including previously published data, all possible crosses were made among bipunctata, virgata, and virgarcus parents, supporting a multiple allelic series at Bip. We propose the gene symbol bip^vgt for the new allele at Bip, where the allelic series has the order of gene dominance Bip > bip^vgt > bip. Based on test crosses, the complete seed-coat color and pattern genotype of EG is tz bip^vgt P [C r] J G B v^lae rk^d.     

Molecular mapping of S-c, an F1 pollen sterility gene in cultivated rice

Hybrids between indica and japonica rice varieties usually show partial sterility, and are a major limiting factor in the utilization of heterosis at subspecific level. When studying male-gamete (pollen) abortion, a possibly important cause for sterility, six loci (S-a, S-b, S-c, S-d, S-e and S-f) for F₁ pollen sterility were identified. Here we report genetic and linkage analysis of S-c locus using molecular markers in a cross between Taichung 65, a japonica variety carrying allele S-c ^j, and its isogenic line TISL5, carrying alleleS-c ^j. Our results show that pollen sterility occurring in the hybrids is controlled by one locus. We used 208 RFLP markers, as well as 500 RAPD primers, to survey the polymorphism between Taichung 65 and TISL5. Six RFLP markers located on a small region of chromosome 3, detected different RFLP patterns. Co-segregation analysis of fertility and RFLP patterns with 123 F₂ plants confirmed that the markers RG227, RG391, R1420 were completely linked with the S-c locus. The genetic distances between the markers C730, RG166 and RG369 and the S-c locus were 0.5 cM, 3.4 cM, and 3.4 cM respectively. Distorted F₂ ratios were also observed for these 4 RFLP markers in the cross. This result suggests that the `one locus sporo-gametophytic' model could explain F₁ hybrid pollen sterility in cultivated rice. RG227, the completely linked marker, has been converted to STS marker for marker-assisted selection. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

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.