The kappa race of Colletotrichum lindemuthianum and sources of resistance to anthracnose in Phaseolus beans

Summary The utilization of American and European bean cultivars as host differentials for distinction of races of Colletotrichum lindemuthianum has been discussed. The new race occurring at Ebnet. Germany, since 1973 is named kappa. It broke down resistance derived from the Are gene originating from Cornell 49–242. Resistance to this kappa race appeared to be present in some European and Asiatic bean cultivars as well as in some American bean accessions.     

Inheritance of resistance to Acanthoscelides obtectus in a wild common bean accession crossed to commercial bean cultivars

Summary The bean weevil Acanthoscelides obtectus, is an important storage pest of common beans in Latin America and Africa. A few wild bean accessions from Mexico have been identified as highly resistant to the weevil. One accession, G 12952, was crossed to two susceptible bean cultivars differing in seed size. Reciprocal F1 and F2 individual seed were evaluated for days to adult emergence (DAE) and emerged adult weight. Maternally inherited seed size affected resistance measurements only in the F1 reciprocal crosses, however, the overall resistance level of the F1 was more similar to that of the susceptible cultivars. The F2 showed a continuous, but skewed distribution from low to high DAE. Very few F2 individuals had the resistance level of G 12952. When the frequency distributions were divided into discrete categories based on parental response, resistance was found to be inherited as two recessive complementary genes. The F3 generation showed an overall lowering of resistance levels compared to their original F2 evaluations. However, none of the lines classified as resistant (50 DAE) in the F2, fell into the susceptible category in the F3, indicating that the resistant genotypes were relatively stable as expected with recessively inherited traits. Modifying genes from the commercial parents may be responsible for general lowering of resistance. Seed size was negatively correlated with adult weight but not with DAE. The unique resistance of the wild bean accessions is discussed in relation to its inheritance. The results and obstacles encountered in the A. obtectus breeding program at CIAT are described.     

The exploration of genetic resources of Portuguese cabbage and kale for resistance to several Brassica diseases

Summary Twenty three accessions of nine Portuguese cabbage and kale land races from different geographic origins were tested at the seedling stage for resistance to several important brassica diseases. Resistance to downy mildew (Peronospora parasitica), expressed as necrosis of the cotyledon mesophyll, was found in all the accessions. Type A resistance to cabbage yellows (Fusarium oxysporum f. sp. conglutinans race 1) was present in most of the landraces. Resistance to clubroot (Plasmodiophora brassicae race 6) was found in one accession of the Portuguese tree kale. High resistance to blackleg (Leptosphaeria maculans) and white rust (Albuco candida) was not detected, although several accessions showed 20 to 30% of plants with intermediate expression of resistance. All Portuguese cole accessions were susceptible to blackrot (Xanthomonas campestris pv. campestris).     

Variation in virulence and resistance in the bean-bean rust pathosystem in Ecuador

Twenty two Uromyces appendiculatus isolates were tested on 20 differential and 25 Ecuadorian Phaseolus vulgaris cultivars in the seedling stage. Based on the infection types 20 races could be discerned. The Ecuadorian cultivars differed greatly in their reaction to the isolates, from resistant to only one isolate (`Red Small Garden') to resistant to all isolates (’G2333‘). The isolates showed a wide range of virulence to the Ecuadorian cultivars, from virulent to only two cultivars (isolate 13) to virulent to 21 cultivars (isolates 5 and 23). Seven cultivars with a basically susceptible infection type appeared to differ greatly in quantitative resistance when tested in three consecutive crop cycles. The disease severities in percentage leaf area affected averaged over the three cycles ranged between 83.9% for ‘Red Small Garden’ and 13.1% for ‘INIAP-414’. Race-specific resistance does not seem an advisable breeding strategy, but the quantitative resistance offers a good alternative.     

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.     

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.     

Race differentiation and search for sources of resistance to Rhynchosporium secalis in barley in Italy

Summary Barley in Italy has recently been seriously affected by Rhynchosporium secalis. The pathogenic variation of the fungus was studied and 17 races were differentiated on 13 barley cultivars carrying most of the currently known genes for resistance. RC 1, the most virulent and most frequent race, was virulent on 10 out of the 13 differentials and the remaining races proved to be less virulent variants of RC 1. Atlas (C.I. 4118), Atlas 46 (C.I. 7323) and Osiris (C.I. 1622) were the only three differentials resistant to all the analyzed single-spore isolates.Differential cultivars previously assumed to have identical resistance factors did not react in the same way to all the Italian races, thereby revealing either undisclosed differences in the genes described or the presence of additional unidentified ones.Our findings were compared with previous data about virulence of scald populations from different countries, on the basis of tests with common differentials: fundamental differences were found between the Italian population and those of other countries with regard to virulence patterns.The susceptible reactions to race RC 1 of most barley cultivars grown in Italy indicate the urgent need for resistance genes to be incorporated in the cultivated material. Seventy-one barley accessions, known as sources of resistance in different parts of the world, were screened for their behaviour to races RC 1 and RC 13. Twenty-two appeared resistant to both of them.     

New sources of resistance of cowpea (Vigna unguiculata) toStriga gesnerioides,a parasitic angiosperm

Summary Thirty-seven accessions of cowpea and yard-long bean were assessed for resistance toStriga gesnerioides. Cowpea plants were grown using anin vitro method, then inoculated with young seedlings ofS. gesnerioides produced from seed from three West African countries. Resistance was assessed by comparing the number and size ofS. gesnerioides tubercles on these accessions with those on a known susceptible cowpea, cv. Blackeye. Two cowpea landraces, APL-1 and 87-2, were completely resistant toS. gesnerioides from Burkina Faso, Mali and Cameroon and partially resistant toS. gesnerioides from Niger. Complete resistance was expressed either as a hypersensitive response of infected root tissues or as a severely retarded development of successful infections. All other accessions, including three samples of yard-long bean were susceptible toS. gesnerioides. The original 87-2 plants segregated for resistance and susceptibility. However, uniformly resistant progeny were obtained by producing seed from vegetatively propagated clones of single resistant 87-2 plants. Resistance of APL-1 and 87-2 toS. gesnerioides was confirmed in pot and field trials. Neither of these cowpeas were resistant toAlectra vogelii. Varieties APL-1 and 87-2 provide additional sources of resistance to most races ofS. gesnerioides, including a newly discovered virulent race from Benin.Abbreviations ICRISAT International Crops Research Institute for the Semi-Arid Tropics - IITA International Institute of Tropical Agriculture - SAFGRAD Semi-Arid Food Grain Research and Development     

Assessment of Gossypium sturtianum and G. australe as potential sources of Fusarium wilt resistance to cotton

When challenged with Fusarium oxysporum f. sp. vasinfectum (Fov) from vegetative compatibility groups (VCGs) 01111 and 01112 in glasshouse tests, Gossypium australe Mueller and Gossypium sturtianum Willis accessions showed a variety of disease responses ranging from highly resistant to highly susceptible. Under high disease pressure G. sturtianum accession Gos-5275 was significantly more resistant than the commercial G. hirsutum cultivars that are designated standards for Fusarium resistance by Australian cotton breeders. Under low disease pressure G. sturtianum accession Gos-5250 was more susceptible than a highly susceptible commercial cultivar. A series of glasshouse tests was performed at two locations (Indooroopilly, QLD. and Canberra, ACT), and under low and high disease pressure. In these tests, a hexaploid cross (Gos-5271) generated from a Fusarium-resistant G. sturtianum (Gos-5275) and a Fusarium-susceptible G. hirsutum L. (CPI-138969) was significantly more resistant to Fusarium wilt than its G. hirsutum parent. Thus G. sturtianum, with a diploid genome and a range of responses to Fov challenge, has the potential to provide the basis for the elucidation of the genetic basis of resistance to Fusarium wilt in cotton species. In addition, resistant accessions of G. sturtianum are identified as a potential source of Fusarium wilt resistance genes for cotton breeding. In the glasshouse tests used to assess the resistance of various Gossypium accessions to Fusarium wilt disease, the scoring of vascular browning was found to give a more reliable indication of disease severity than the scoring of foliar symptoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

New sources of major gene resistance in Lactuca to Bremia lactucae

Summary A total of 1789 accessions of several lettuce collections was screened to find new major gene resistance to the downy mildew fungus Bremia lactucae Regel. The accessions belonged to the species Lactuca sativa (N=1288), L. serriola (N=399), L. saligna (N=52) and L. virosa (N=50). A total of 20 races of B. lactucae were used, 14 of which were NL-races, isolated from cultivated lettuce in the Netherlands. The other six races were isolated from wild L. serriola in Czechoslovakia. The accessions were initially screened with two races: NL1 and NL3. Accessions with resistance to one or both of these races were tested with the other races. Phenotypes with new resistance were found in accessions of all four Lactuca species. Of L. sativa, four accessions were found with resistance phenotypes that could not be explained by combinations of known major genes. Many accessions of L. serriola had resistance phenotypes that indicated the presence of unknown resistance genes. All interactions between accessions of L. saligna and races of B. lactucae were incompatible in leaf disc tests, except for four accessions, which showed some sporulation with race NL6. Several accessions of L. virosa were resistant to all races used. Other accessions of L. virosa gave a race-specific interaction with B. lactucae.     

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.     

Andean beans (Phaseolus vulgaris L.) with resistance to the angular leaf spot pathogen (Phaeoisariopsis griseola) in southern and eastern Africa

Common beans (Phaseolus vulgaris) are separated into two distinct groups: Andean and Middle American. We identified CAL 143 as the first Andean bean with resistance to angular leaf spot disease caused by Phaeoisariopsis griseola. Angular leaf spot is the most widespread and economically important bean disease in southern and eastern Africa, and it is especially severe on the extensively grown Andean beans. Cal 143 was resistant in Malawi, South Africa, Tanzania, and Zambia, but it was susceptible in Uganda. This was attributed to the presence of races of P. griseola in Uganda not present in the other countries. We identified two additional Andean bean lines, AND 277 and AND 279, with resistance to angular leaf spot in Malawi. We also characterized the virulence diversity of 15 isolates of P. griseola from southern and eastern Africa into nine different races. Five of six isolates from Malawi and two of seven from Uganda, obtained from large-seeded Andean beans, were characterized into four different races considered Andean. These were compatible only or mostly with large-seeded Andean cultivars. The other eight isolates from Uganda, Malawi, and the Democratic Republic of Congo, obtained from a small- or medium-seeded Middle American beans, were characterized into five different Middle American races. These were compatible with Middle American and Andean cultivars. CAL 143 was resistant or intermediate under greenhouse conditions to all but one of the same 15 isolates from southern and eastern Africa, but it was susceptible to an isolate from Uganda obtained from a medium-seeded Middle American bean. This revised version was published online in July 2006 with corrections to the Cover Date.     

Morphological and molecular characterization of melon accessions resistant to Fusarium wilts

Fusarium wilt incited by Fusarium oxysporum f. sp. melonis (F.o.m) is one of the most widespread and devastating melon diseases. While resistance to physiological races 0, 1, and 2 is relatively frequent in different botanical varieties, sources of resistance to race 1,2 are restricted to a few Far-Eastern accessions. In this work, the results of a screening for resistance to F.o.m. race 1,2 among 32 accessions are presented. Three Japanese accessions (‘Kogane Nashi Makuwa’, ‘C-211’, and ‘C-40’) showed the highest resistance levels, but useful levels of resistance were also detected in one Russian ‘C-160’ and two Spanish (‘C-300’ and ‘Mollerusa-7’) accessions. These resistant materials, together with other accessions previously described as resistant to F.o.m. races 0, 1, and/or 2 have been morphologically and molecularly characterized. Based on cluster analysis, these accessions have been grouped according to the botanical subspecies they belong to. Assessment of genetic diversity indicated that the resistant accessions to races 0, 1 and 2, are scattered along the established clusters. On the other hand, high levels of resistance to the race 1,2 could be found only among accessions belonging to Cucumis melo subsp. agrestis, nevertheless, a certain degree of resistance to this race could also be found within some accessions belonging to subsp. melo. As far as we know, this is the first report of resistance to F.o.m race 1,2 found out from the Far-Eastern melon material. Based on fruits characteristics, it appears that several inodurus and cantalupensis accessions could be exploited in breeding programs as resistance sources to F.o.m races 0, 1 and/or 2 for the improvement of these melon types. The accessions with the highest levels of resistance to the race 1,2 appeared to be very distant both molecularly and morphologically from the commercial types. Nevertheless ‘C-160’, ‘C-300’, and ‘Mollerusa-7’ classified as var. inodorus are morphologically very similar to the Spanish commercial types and might be used as resistant sources in breeding these melon types.     

Evaluation of the virulence of races 1, 2 and 4 of Fusarium oxysporum f.sp. dianthi in carnation

Summary A simultaneous analysis of the virulence of races 1, 2 and 4 of Fusarium oxysporum f.sp. dianthi to a series of nine carnation cultivars revealed the presence of different interactions between races and cultivars, as well as differences in pathogenesis between race 1 on the one hand and race 2 and 4 on the other.The most common race 2 induced typical symptoms of Fusarium wilt in all susceptible cultivars. The cultivars showed considerable variation in resistance to race 2. Only Novada remained free of external symptoms throughout the experiment. In diseased plants of all cultivars studied, infected vascular tissue was white with dark brown margins, and heavy degradation of the cell walls and xylem parenchyma cells had occurred. All Dutch isolates corresponded with race 2.Race 4 induced wilt symptoms similar to those induced by race 2, and there was a similar variation in resistance to race 2 and 4 in the cultivars. On average, the race 4 isolates were less aggressive than those of race 2. Compared with race 2, there was evidence of some genotype × race interactions: Pallas proved to be considerably more susceptible, and Lena more resistant to race 4 than to race 2. The isolates of race 4 induced a nistopathology similar to that induced by race 2, but with less vascular browning.Race 1 induced atypical but severe wilt symptoms and unusual vascular discoloration in Elsy, Niky and Sam's Pride only. The vascular tissue in these cultivars turned pale brown; in spite of heavy colonization of these tissues virtually no degradation of cell walls was observed. All other cultivars tested proved virtually resistant to race 1, providing further evidence for genotype × race interactions.Within races, limited but statistically significant genotype × isolate interactions were found as well, in particular within race 4. These are tentatively attributed to independent variation of two (or more) resistance components.     

Inheritance of anthracnose resistance in the common bean cultivar Widusa

Snap bean (Phaseolus vulgaris L.) cultivar, Widusa, was crossed to Michigan Dark Red Kidney (MDRK), Michelite, BAT 93, Mexico 222, Cornell 49–242, and TO cultivars to study the inheritance of resistance to anthracnose in Widusa. The segregation patterns observed in six F₂ populations supported an expected 3R:1S ratio suggesting that Widusa carries a single dominant gene conditioning resistance to races 7, 65, 73, and 453 of Colletotrichum lindemuthianum, the causal organism of bean anthracnose. Allelism tests conducted with F₂ populations derived from crosses between Widusa and Cornell 49–242 (Co-2), Mexico 222 (Co-3), TO (Co-4), TU (Co-5), AB 136 (Co-6), BAT 93 (Co-9), and Ouro Negro (Co-10), inoculated with races 7, 9, 65 and 73, showed a segregation ratio of 15R:1S. These results suggest that the anthracnose resistance gene in Widusa is independent from the Co-2, Co-3, Co-4,Co-5, Co-6, Co-9, and Co-10 genes. A lack of segregation was observed among 200 F₂ individuals from the cross Widusa/MDRK, and among 138 F₂ individuals from the cross Widusa/Kaboon inoculated with race 65, suggesting that Widusa carries an allele at the Co-1 locus. We propose that the anthracnose resistance allele in Widusa be named Co-1 ⁵ as Widusa exhibits a unique reaction to race 89 compared to other alleles at the Co-1 locus. RAPD marker A18₁₅₀₀ co-segregated in repulsion-phase linkage with the Co-1 ⁵ gene at a distance of 1.2 cM and will provide bean breeders with a ready tool to enhance the use of the Co-1 ⁵ gene in future bean cultivars.     

Sources of resistance to angular leaf spot (Phaeoisariopsis griseola) in common bean core collection, wild Phaseolus vulgaris and secondary gene pool

Angular leaf spot (ALS) is one of the most devastating diseases of common bean (Phaseolus vulgaris L.) in tropical and subtropical countries. The causal fungus, Phaeoisariopsis griseola(Sacc.) Ferr. is highly variable and a diverse source of resistance genes is required to manage this disease. We evaluated a common bean core collection,primary and secondary gene pools and lines derived from inter-specific crosses of P. vulgaris and P. coccineus or P. polyanthus (secondary gene pool) for resistance to angular leaf spot. Of the 1441 accessiones in the core collection, only 2.2% were resistant to both Andean and Mesoamerican races of P. griseola, 28% were resistant only to Andean and 9% to Mesoamerican races. Of the 32 resistant accessions, 68%originated from Bolivia, Colombia,Guatemala and Mexico. More accessions from these countries should be examined for P. griseola reaction. Very few wild P. vulgaris accessions (4%), were resistant to ALS. In contrast, high levels of resistance (62%) were found in the secondary gene pool. Among the 1010 lines from inter-specific crosses, 109 lines were highly resistant. These genotypes from the primary and secondary common bean gene pools resistant to Andean and Mesoamerican races of P. griseola offer a potential for developing broad and durable ALS resistance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Screening for resistance in wild Lycopersicon species to Fusarium oxysporum f.sp. lycopersici race 1 and race 2

Wild Lycopersicon accessions were screened for resistance to the Fusarium wilt disease caused by Fusarium oxysporum f.sp. lycopersici (Fol) race 1 and race 2. In total, four isolates of each race were used. Among 17 accessions of six Lycopersicon species tested, a wide genetic variation for wilt resistance was observed. Most accessions were highly susceptible, some showed intermediate resistance, but one accession of L. cheesmanii (G1.1615 = PI 266375) and two accessions of L. chilense (G1.1556 and G1.1558) were highly resistant to Fol races 1 and 2. The resistance in the latter three accessions equalled or was higher than the resistance determined by the known I-genes, that have been widely used in breeding programmes. These newly found resistant accessions provide breeders with more opportunities for Fusarium disease resistance and may contribute to our understanding of Fusarium disease resistance gene organisation and evolution.     

New sources of resistance to anthracnose and angular leaf spot of beans (Phaseolus vulgaris L.)

Summary over 13000 CIAT bean accessions were evaluated for their reactions to the anthracnose (Colletotrichum lindemuthianum) and angular leaf spot (Isariopsis griseola) pathogens over a 3 yr period. Among these accessions, 156 were resistant to all races of the anthracnose pathogen collected from Popayán, Colombia. Thirty were resistant to numerous races obtained from other parts of the world, including Europe. Although many of these new resistant sources originated in Mexico and Central America, they are quite diverse for geographic origin, plant type, seed color and seed size. In addition, more than 50 of the 156 lines were also resistant to isolates of I. griseola with diverse sources of origin throughout Colombia.     

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 variation in Zantedeschia spp. (Araceae) for resistance to soft rot caused by Erwinia carotovora subsp. carotovora

Bacterial soft rot caused by Erwiniacarotovora subsp. carotovora is amajor disease in Zantedeschia spp.,particularly in cultivars from the sectionAestivae. The disease can partiallybe controlled by cultivation measures, so acombination with resistant cultivars couldeffectively protect the crop. However,resistant commercial Aestivaecultivars are not available yet. By meansof a recently developed non-destructiveresistance test, variation inaggressiveness was observed among fiveisolates of Erwinia carotovora subsp.carotovora without interactionsbetween the isolates and three Zantedeschia accessions. Within elevenaccessions of Z. aethiopica,variation was observed from almost completeto moderate resistance, while theZ. odorata accession was susceptible.All 21 Aestivae cultivars weresusceptible. Within the Aestivaespecies, Z. elliotiana and Z.pentlandii were also susceptible, butwithin twelve accessions of Z.albomaculata, as well as in six accessionsof Z. rehmannii, variation was foundfrom susceptible to moderately resistant.Hence, new sources of resistance wereidentified that show good potentials forresistance breeding.