Comparative genetic analysis of field resistance to downy mildew in the lettuce cultivars ‘Grand Rapids’ and ‘Iceberg’

Downy mildew on lettuce is currently controlled using host resistance genes (Dm genes) that confer race-specific resistance in seedlings. Field resistance (FR) that is active in adult plants but not seedlings was identified in the cvs. Grand Rapids and Iceberg. The goal of our study was to evaluate the utility of Grand Rapids as a source of novel Bremia resistance alleles, particularly in comparison with Iceberg. To measure FR, downy mildew symptoms were evaluated following natural infection in field experiments. The responses of Grand Rapids and Iceberg were similar in many respects. Although both cultivars had a small percentage of plants exhibiting disease symptoms, the average disease ratings were as low as for cultivars with effective Dm genes. We observed no evidence for race specificity. FR was effective over 3 years of our study, despite documented variation within pathogen populations. Both cultivars lacked all known seedling resistance genes except Dm13, which was not responsible for the resistance observed in field experiments. Similar segregation of FR was observed in F₂ populations for both Grand Rapids and Iceberg. The presence of highly susceptible families within Grand Rapids × Iceberg populations suggested the presence of at least one unique resistance allele in each cultivar. Preliminary genetic analysis of FR from Grand Rapids revealed a high estimate of narrow-sense heritability that suggested simple inheritance, but single gene models did not fit the observed data. Our results suggest that Grand Rapids may represent an underutilized resource for controlling downy mildew in lettuce.     

Inheritance of the resistant reaction of the lettuce cultivar `Grand Rapids' to the southern root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood

Resistance to the southern root-knot nematode Meloidogyne incognita Chitwood would be an important attribute of lettuce Lactuca sativa L. cultivars adapted to both protected and field cultivation in tropical regions. `Grand Rapids' and a few other cultivars are reported to be resistant to this nematode. In this paper, we studied the inheritance of the resistant reaction of `Grand Rapids' (P₂) in a cross with a standard nematode-susceptible cultivar Regma-71 (P₁). F₁(Regina-71 × Grand Rapids) and F₂ seed were obtained, and inoculated along with the parental cultivars with different races of M. incognita to evaluate nematode resistance. Broad sense heritability estimates for the number of galls and of egg masses per root system, gall size and gall index were generally in the order of 0.5 or higher. Class distributions of these variables over generations P₁, P₂, F₁ and F₂ were in agreement with simulated theoretical distributions based on monogenic inheritance models. F₃ families were obtained from randomly sampled F₂ plants and tested for reaction to the nematode. The frequency ratio of homozygous resistant, segregating and homozygous susceptible F₃ families did not differ from the 1:2:1 ratio expected from monogenic inheritance. M. incognita resistance appears to be under control of a single gene locus. The Grand Rapids allele (for which the symbol Me is proposed) is responsible for the resistant reaction, and shows high (though incomplete) penetrance, variable expressivity and predominantly additive gene action. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of alleles at two loci controlling resistance to Phomopsis stem blight in narrow-leafed lupin (Lupinus angustifolius L.)

The genetics of resistance to Phomopsis stem blight caused by Diaporthe toxica Will., Highet, Gams & Sivasith. in narrow-leafed lupin (Lupinus angustifolius L.) was studied in crosses between resistant cv. Merrit, very resistant breeding line 75A:258 and susceptible cv. Unicrop. A non-destructive glasshouse infection test was developed to assess resistance in the F₁, F₂, selected F₂-derived F₃ (F_2:3) families, and in selfed parent plants. The F₁ of Unicrop × 75A:258 (and reciprocal cross) was very resistant, and the F₂ segregated in a ratio of 3:1 (resistant: susceptible), which suggested the presence of a single dominant allele for resistance in 75A:258. In Merrit × Unicrop (and reciprocal), the F₁ was moderately resistant, and the F₂ segregated in a ratio of 3:1 (resistant: susceptible). Thus Merrit appeared to carry an incompletely dominant resistance allele for resistance. The F₁ of Merrit × 75A:258 (and reciprocal) was very resistant and the F₂ segregated in a ratio of 15:1 (resistant: susceptible), which supported the existence of independently segregating resistance alleles for resistance in 75A:258 and Merrit. Alleles at loci for early flowering (Ku) and speckled seeds (for which we propose the symbol Spk) segregated normally and independently of the resistance alleles. Resistant F₂ plants gave rise to uniformly resistant or segregating F_2:3 families, whereas susceptible F₂ plants gave rise only to susceptible F_2:3 families. However, the variation in resistance in the F₂ and some F_2:3 families of crosses involving 75A:258, from moderately to extremely resistant, was greater than that expected by chance or environmental variation. We propose the symbols Phr1 to describe the dominant resistance allele in 75A:258, and Phr2 for the incompletely dominant resistance allele in Merrit. Phr1 appears to be epistatic to Phr2, and expression of Phr1 may be altered by independently segregating modifier allele(s). This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of disease resistance in urdbean (Vigna mungo (L.) Hepper) to the leaf spots caused by Colletotrichum truncatum (Schw.) Andrus & Moore

Summary The resistance sources among various test cultivars of urdbean to Colletotrichum truncatum, a leaf spotting pathogen, were identified and genetics of resistance was worked out by studying F₁, F₂ and F₃ generations of crosses between resistant cultivars and the susceptible cv. Kulu 4 and of those among the resistant parents. The resistance was found to be controlled by single dominant genes and the resistance genes were non-allelic.     

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.     

Parent-offspring correlation estimate of heritability for early blight resistance in tomato, Lycopersicon esculentum Mill.

This study estimated the heritability (h ²) of early blight (EB) resistance in filial progeny of a cross between a susceptible (`NC84173';mid-season maturity) and a resistant (`NC39E'; late-season maturity)tomato breeding lines. It addition, it examined the potential of identifying progeny with mid-season maturity and EB resistance. A total of 162F₂ plants were grown under field conditions in 1998 and evaluated for disease symptoms three times during the season, and the area under the disease progress curve (AUDPC) and final percent defoliation (disease severity) were determined. The F₂ plants were self-pollinated and F₃ seeds produced. The 162 F₃ progeny families, consisting of 20 plants per family, were grown in a replicated field trial in 1999 and evaluated for EB resistance (final percent defoliation) and plant maturity(days to 50% ripe fruit). The distributions of the final percent defoliation values in the F₂ and F₃ generations indicated that resistance from `NC39E' was quantitative in nature. Estimates of h <sup>2</sup> for EB resistance, computed as the correlation coefficients between F<sub>3</sub>progeny family means and F<sub>2</sub> individual plant values, ranged from0.65 to 0.71, indicating that EB resistance of `NC39E' was heritable. Across F₃ families, a negative correlation (r = –0.46, p< 0.01) was observed between disease severity and earliness in maturity, indicating that plant maturity affected disease severity. However, several F₃ families were identified with considerable EB resistance and mid-season maturity, indicating that resistance from `NC39E' might be useful for the development of commercially acceptable EB resistant tomato cultivars. This revised version was published online in August 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.     

Genetic analysis of grain mould resistance in coloured sorghum genotypes

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

Evidence for the production of unreduced gametes by tetraploid Rosa hybrida L.

The objective of this study was to determine the mode of inheritance of field resistance to downy mildew (Peronospora parasitica (Pers. ex Fr.) Fr.) in broccoli (Brassica oleracea var.italica) at the adult plant stage. The F₁, F₂ and F₃ progeny of resistant and susceptible plants of broccoli were tested in the field under natural infection, in central Portugal, from August to December in two successive years. The plants were evaluated for resistance to downy mildew at maturity using a five-class scale of increasing susceptibility to the disease, which took into account the number of infected leaves and the size of the sporulating lesions. The F₁ was completely resistant, the F₂ segregated a clear 3 resistant: 1susceptible and the F₃ confirmed the F₂ segregation, which suggests a dominant character controlled by a single locus. This resistance has good potencial for direct use in commercial broccoli breeding or for transfer to other Brassica vegetables. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Resistance to <Emphasis Type="Italic">Meloidogyne incognita</Emphasis> race 1 in the lettuce cultivars Grand Rapids and Salinas-88

The objective of this work was to check the possible allelism between two sources of resistance to the root-knot nematode Meloidogyne incognita race 1 in lettuce (‘Grand Rapids’ and ‘Salinas-88’). The experiments were carried out in greenhouses, in expanded 128-cell polystyrene trays filled with commercial substrate. Lettuce cultivars ‘Salinas 88’ and ‘Grand Rapids’ were tested along with the populations F₁ (‘Grand Rapids’ × ‘Salinas-88’), F₂ (‘Grand Rapids’ × ‘Salinas-88’), F₃ (‘Grand Rapids’ × ‘Salinas-88’), and with F₄ families derived from the latter population. Seedlings were inoculated 15 days after sowing with a nematode egg suspension equivalent to 30 eggs ml⁻¹ of substrate. Plants were evaluated for apparent gall incidence, gall scores, egg mass scores and extracted egg numbers 45 days after the inoculation date. There was evidence that two different genes are involved in control of resistance to M. incognita race 1 in lettuce cultivars Grand Rapids and Salinas-88. Lines with higher levels of nematode resistance than either Grand Rapids or Salinas-88 could be selected in the F4 generation of the cross between these resistant parental lines.     

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

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

Resistance of lettuce (Lactuca) to the leaf aphid Nasonovia ribis nigri. 2. Inheritance of the resistance

Summary The inheritance of resistance to Nasonovia ribis nigri in L. sativa was investigated. Parents and F₁ and F₂ populations from crosses between the susceptible cultivar Ravel and two resistant breeding lines were tested. In both breeding lines one dominant gene appeared responsible for resistance.     

Inheritance of resistance to Soybean mosaic virus in FT-10 soybean

The occurrence of a new isolate from the G5 strain of Soybean mosaic virus (SMV), which broke the resistance of soybean cultivar FT-10, was first reported in Brazil in 1995. Cultivar Davis is an ancestor of ‘FT-10’ and the likely source of resistance to the virus. Diallel crosses among resistant cultivars Epps (PI 96983), Ogden and FT-10, and susceptible cultivar Hill were made to investigate the inheritance of SMV resistance in FT-10. The experiments for genetic studies were performed undergreen house conditions. Plants of the F₂ population and F₃ families from each cross and the parents were inoculated with SMV G1 and G5 strains. Plants were classified as: symptom less (R), susceptible with typical symptoms of mosaic (S), and systemic necrosis (N). Plants showing necrosis or no symptoms were classified as resistant. Each F₃ family was classified as resistant (homozygous),susceptible (homozygous), or segregating (heterozygous). The results of both F₂ and F₃ were analyzed by Chi-square tests. The results suggested that FT-10 carries an allele at the Rsv ₁ locus for resistance to SMV. However, the allele is different from those in Epps and Ogden. The symbol Rsv ₁ ^d is a tentatively named for the newly detected allele in FT-10. This allele probably originated from Davis cultivar. This revised version was published online in July 2006 with corrections to the Cover Date.     

The inheritance of resistance to beet necrotic yellow vein virus (BNYVV) in B. vulgaris subsp. maritima, accession WB42: Statistical comparisons with Holly-1-4

In this study, the inheritance of resistance to Beet necrotic yellow vein virus (BNYVV) in accessions Holly-1-4and WB42 was investigated. Crosses between both resistant sources and susceptible parents were carried out and F₁F₂ and BC₁ populations were obtained. Virus concentrations in WB42and its F₁ populations were lower than in Holly-1-4. Observed ratios of susceptible and resistant plants in segregating populations of Holly-1-4 as well as WB42 were in agreement with hypothesis of one dominant major gene. Segregation of plants in F₂ populations obtained from crosses betweenHolly-1-4 and WB42 revealed that the resistance genes in Holly-1-4 and WB42 were nonallelic and linked loci. This revised version was published online in July 2006 with corrections to the Cover Date.     

A single dominant gene for downy mildew resistance in broccoli

Downy mildew, incited by Peronospora parasitica (Pers.: Fr.) Fr., is a destructive disease of broccoli (Brassica oleraceaL., Italica Group). Resistant cultivars represent a desirable control method to provide a practical, environmentally benign, and long-term means of limiting damage from this disease. Doubled-haploid (DH) lines developed by us exhibit a high level of downy mildew resistance at the cotyledon stage. To determine the mode of inheritance for this resistance, a resistant DH line was crossed to a susceptible DH line to make an F₁, from which F₂ and backcross (BC) populations were developed. All populations were evaluated for response to artificial inoculation with P. parasitica at the cotyledon stage. All F₁ plants (including reciprocals) were as resistant as the resistant parent, indicating no maternal effect for this trait. F₂ populations segregated approximately 3resistant to 1 susceptible, BC populations using the resistant parent as the recurrent parent contained all resistant plants, and the BC to the susceptible parent segregated 1 resistant to 1 susceptible. These results indicate that resistance is controlled by a single dominant gene. This gene should be easily incorporated into F₁ hybrids and used commercially to prevent downy mildew at the cotyledon stage. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quantitative resistance to Botrytis cinerea from Solanum neorickii

Tomato (Solanum lycopersicum) is susceptible to gray mold (Botrytis cinerea). Quantitative resistance to B. cinerea was previously identified in a wild relative, S. neorickii G1.1601. The 122 F₃ families derived from a cross between the susceptible S. lycopersicum cv. Moneymaker and the partially resistant S. neorickii G1.1601 were tested for susceptibility to B. cinerea using a stem bioassay. Three putative quantitative trait loci (pQTL) were detected: pQTL3 and pQTL9 reducing lesion growth (LG) and pQTL4 reducing disease incidence (DI). For each pQTL, a putative homologous locus was identified recently in another wild tomato relative, S. habrochaites LYC4. pQTL3 was confirmed by assessing disease resistance in BC₃S₁ and BC₃S₂ progenies of S. neorickii G1.1601. pQTL4 was not statistically confirmed but the presence of the S. neorickii resistance allele reduced DI in all three tested populations. The reduction in LG of pQTL9 was not confirmed but rather, this locus conferred a reduced DI, similar to observations in the QTL study using S. habrochaites. The results are discussed in relation to other disease resistance loci identified in studies with other wild tomato relatives.     

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 trichomes and resistance to pod borer (Helicoverpa armigera) and their association in interspecific crosses between cultivated pigeonpea (Cajanus cajan) and its wild relative C. scarabaeoides

The legume pod borer, Helicoverpa armigera, is one of the most devastating pests of pigeonpea. High levels of resistance to pod borer have been reported in the wild relative of pigeonpea, Cajanus scarabaeoides. Trichomes (their type, orientation, density and length) and their exudates on pod wall surface play an important role in the ovipositional behavior and host selection process of insect herbivores. They have been widely exploited as an insect defense mechanism in number of crops. In the present investigation, inheritance of resistance to pod borer and different types of trichomes (A, B, C and D) on the pod wall surface in the parents (C. cajan and C. scarabaeoides) and their F₁, F₂, BC₁ (C. cajan × F₁), and F₃ generations has been studied. Trichomes of the wild parents (high density of the non-glandular trichomes C and D, and glandular trichome B and low density of glandular trichome A) were dominant over the trichome features of C. cajan. A single dominant gene as indicated by the segregation patterns individually will govern each trait in the F₂ and backcross generation. Segregation ratio of 3 (resistant): 1 (susceptible) for resistance to pod borer in the F₂ generation under field conditions was corroborated with a ratio of 1:1 in the backcross generation, and the ratio of 1 non-segregating (resistant): 2 segregating (3 resistant: 1 susceptible): 1 non-segregating (susceptible) in F₃ generation. Similar results were obtained for pod borer resistance under no-choice conditions. Resistance to pod borer and trichomes associated with it (low density of type A trichome and high density of type C) are governed individually by a dominant allele of a single gene in C. scarabaeoides. Following backcrossing, these traits can be transferred from C. scarabaeoides into the cultivated background.     

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.