Inheritance of resistance to anthracnose caused by Colletotrichum capsici in Capsicum

Inheritance of resistance to anthracnose caused by Colletotrichum capsici (Syd.) Butler & Bisby was studied in interspecific Capsicum populations derived from a cross between a Thai elite cultivar Capsicum annuum L.‘Bangchang’ and a resistant line C. chinense Jacq.‘PBC932′. The resistance was assessed by measuring lesion area per fruit area (LFA) on detached chili fruits, using a laboratory‐based injection inoculation. Nil symptoms resembling the resistant parent ‘PBC932’ were also identified in the progeny F₂ and BC1 populations. Segregation of resistance (nil LFA) and susceptibility in the F₂ fitted a 1: 3 Mendelian ratio, indicating that resistance was responsible by a single recessive gene. The segregation of the trait in the testcrosses in both BC1s also confirmed the 1: 3 gene segregating model as found in the F₂.     

Differential resistances to anthracnose in Capsicum baccatum as responding to two Colletotrichum pathotypes and inoculation methods

Chili anthracnose, caused by Colletotrichum spp., is one of the major diseases to chili production in the tropics and subtropics worldwide. Breeding for durable anthracnose resistance requires a good understanding of the resistance mechanisms to different pathotypes and inoculation methods. This study aimed to investigate the inheritances of differential resistances as responding to two different Colletotrichum pathotypes, PCa2 and PCa3 and as by two different inoculation methods, microinjection (MI) and high pressure spray (HP). Detached ripe fruit of Capsicum baccatum ‘PBC80’ derived F₂ and BC₁s populations was assessed for anthracnose resistance. Two dominant genes were identified responsible for the differential resistance to anthracnose. One was responsible for the resistance to PCa2 and PCa3 by MI and the other was responsible for the resistance to PCa3 by HP. The two genes were linked with 16.7 cM distance.     

Resistance to Leveillula taurica in pepper (Capsicum annuum) is oligogenically controlled and stable in Mediterranean regions

The resistance to Leveillula taurica from an african pepper line H3 Capsicum annuum) was evaluated and analysed, using the androgenetic haplodiploid progeny from an F₁ hybrid between H3 and a susceptible line. Tests were performed in natural infection conditions in two locations (France and Sicily). Stable behaviour of the parental and haplodiploid lines was observed in both locations, confirming the high level and stability of this resistance source in Mediterranean countries. Heritability of resistance was high and genetic analysis suggested that it is under oligogenic control. However, the number of genetic factors involved in resistance depended on infection conditions: two or three genetic factors with additive and partial dominance effects appear sufficient to confer resistance at the beginning of the epidemic or in weak infection conditions. However, additional genes are necessary to slow down further disease progress and secondary infections and at least five genetic factors are necessary to confer resistance in severe infection. In this case, both additive and epistatic effects are significant. The transfer of this resistance into cultivars will require the use of artificial inoculation procedures to control the severity of the test.     

Selection for multiple disease resistance reduces cucumber yield potential

Summary Experiments were conducted in Wisconsin and Michigan to determine whether selection for multiple disease resistance adversely affects yielding ability of commercial cucumber (Cucumis sativus var. sativus L.; CS) lines. Inbred F₄ and F₅ lines were developed from C. sativus var. hardwickii (R.) Alef. (CH) x CS which had been either selected or not selected for resistance to the causal organisms of scab, anthracnose, and downy mildew. The exotic CH germplasms possesses a multiple fruiting habit with high yield potential and the CS genotypes include several disease resistance. In each comparison between selected and unselected progeny, the unselected families either significantly outyielded, or were not significantly different than their selected counterparts. In no case did the selected progeny outyield the unselected progeny. Since this was observed for both fruit number per plant and total fruit weight per plant, and it occurred despite differences in fruit size, we conclude that selection for disease resistance led to a reduction in yield potential in these populations.Received for publication-. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.     

Identification of QTLs for resistance to anthracnose to two <Emphasis Type="Italic">Colletotrichum</Emphasis> species in pepper

Pepper (Capsicum spp.) anthracnose caused by Colletotrichum spp. is a serious disease damaging pepper production in Asian monsoon regions. For QTL mapping analyses of anthracnose resistance, an introgression BC₁F₂ population was made by interspecific crosses between Capsicum annuum ‘SP26’ (susceptible recurrent parent) and Capsicum baccatum ‘PBC81’ (resistant donor). Both green and red fruits were inoculated with C. acutatum ‘KSCa-1’ and C. capsici ‘ThSCc-1’ isolates and the disease reactions were evaluated by disease incidence, true lesion diameter, and overall lesion diameter. On the whole, distribution of anthracnose resistance was skewed toward the resistant parent. It might indicate that one or two major QTLs are present. The introgression map consisting of 13 linkage groups with a total of 218 markers (197 AFLP and 21 SSR), covering a total length of 325 cM was constructed. Composite interval mapping analysis revealed four QTLs for resistance to ‘KSCa-1’ and three QTLs for ‘ThSCc-1’ isolate, respectively. Interestingly, the major QTLs (CaR12.2 and CcR9) for resistance to C. acutatum and C. capsici, respectively, were differently positioned but there were close links between the minor QTL CcR12.2 for C. capsici and major QTL CaR12.2 as well as the minor QTL CaR9 for C. acutatum and major QTL CcR9. These results will be helpful for marker-assisted selection and pyramiding two different anthracnose-resistant genes in commercial pepper breeding.     

Genetic Relationships Among Four Pepper Genotypes Resistant to Phytophthora capsici

According to our previous investigations, resistance to Phytophthora capsid in Capsicum annuum genotypes, ‘Line 29’, ‘PI201232’, ‘PI201234’ and Serrano Criollo de Morelos 334 (‘SCM334’), seems to be controlled by three genes. In order to determine the genie relationships between these four sources of resistance, three experiments were conducted which included the four genotypes, their F₁s, F₂s, F3s and BC₁ generations together with the susceptible pepper genotype ‘Morron INI A 224’. Inoculations were made, when plants had 4—6 leaves, by irrigating the culture substrate with a zoospore suspension of P. capsici isolate ‘Bl’. Though the four genotypes showed percentages of resistance close to a 100%, none of them actually reached this level in the three experiments. ‘SCM334’ was the most resistant genotype, transmitting a high level of resistance to its F₁, F₂ and BQ generations. ‘Line 29’ was more resistant than ‘PI201232’ and ‘PI201234’. However, the F₁ F₂ and BQ generations of these three lines showed similar degrees of resistance. The four genotypes seem to have one of the three genes postulated for their resistance in common. All genes displayed a similar level of resistance, except the specific genes of ‘SCM334’, the effect of which was slightly higher. Several working procedures are suggested for breeding programmes.     

A Major Gene for Resistance to Anthracnose Leaf Blight in Maize

The inheritance of the reaction of maize (Zea mays L.) to anthracnose leaf blight caused by Colletotrichum graminicola was studied in eight generations derived from a cross between a hypersensitively resistant inbred. LB–58, and a susceptible inbred, A632. The generations consisted of the two parents, F₁, F₂ backcrosses and the backcrosses-selfed, Chisquare analysis of the data for individual locations as well as across locations indicated that resistance at both the seedling and mature plant stages of development is conditioned by a single dominant gene, designated CgL. A study of the reactions of LB-58 in several hybrid combinations indicated that resistance was expressed in ail cast-s even though the expression of CgL gene was modified somewhat in different hybrid combinations.     

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.     

Evaluation of quantitative resistance to yellow rust (Puccinia striiformis f. sp. hordei) in the ICARDA/CIMMYT barley breeding programme

The resistance to yellow rust (Puccinia striiformis f. sp. hordei) of 500 advanced barley lines from the ICARDA/CIMMYT breeding programme in Mexico was evaluated on seedlings in the greenhouse and on adult plants in the field. A high frequency of advanced lines (85.8%) showed a susceptible reaction (infection type ≥ 7) on seedlings after inoculation with isolate Mex-1, representing a Mexican variant of race 24. This indicates the absence of effective hypersensitive resistance. In addition, the same advanced lines showed a large variation in disease severity in the field, ranging from 0 to 95%. More than 76% of the advanced lines with a susceptible reaction in the seedling stage demonstrated low disease severity (10% or less in the adult plant). Consequently, these advanced lines possess high levels of quantitative resistance. Two aspects in the ICARDA/CIMMYT barley breeding programme may explain the large number of advanced lines with high levels of quantitative resistance. First, a recurrent selection approach is applied when advanced (F₅) lines reaching homozygosity are intercrossed. Second, low levels of disease are accepted in the selection process instead of selecting the ultimate green plant. Both aspects combined allow the accumulation of quantitative resistance. Certain cultivars released from South-American national programmes in the late 1970s and early 1980s in Peru (UNA-80), Bolivia (IBTA 80) and Ecuador (Teran) are still resistant, demonstrating the durable nature of quantitative resistance to yellow rust.     

Identification and characterization of RAPD and SCAR markers linked to anthracnose resistance gene in sorghum [Sorghum bicolor (L.) Moench]

Anthracnose, one of the destructive foliar diseases of sorghum growing in warm humid regions, is incited by the fungus Colletotrichum graminicola.The inheritance of anthracnose resistance was studied using the parental cultivars of Sorghum bicolor (L.) Moench, HC 136 (susceptible to anthracnose) and G 73 (anthracnose resistant). The F₁ and F₂ plants were inoculated with the local isolates of C. graminicola cultures. The F₂ plants showed a segregation ratio of 3 (susceptible): 1(resistant) indicating that the locus for resistance to anthracnose in sorghum accession G 73 segregates as a recessive trait in a cross to susceptible cultivar HC 136. RAPD (random amplified polymorphic DNA) marker OPJ 01₁₄₃₇ was identified as marker closely linked to anthracnose resistance gene in sorghum by bulked segregant analysis of HC 136 × G73 derived recombinant inbred lines (RILs) of sorghum. A total of 84 random decamer primers were used to screen polymorphism among the parental genotypes. Among these, only 24 primers were polymorphic. On bulked segregant analysis, primer OPJ 01 amplified a 1437 bp fragment only in resistant parent G 73 and resistant bulk. The marker OPJ 01₁₄₃₇ was cloned and sequenced. The sequence of RAPD marker OPJ 01₁₄₃₇ was used to generate specific markers called sequence characterized amplified regions (SCARs). A pair of SCAR markers SCJ 01-1 and SCJ 01-2 was developed using Mac Vector program. SCAR amplification of resistant and susceptible parents along with their respective bulks and RILs confirmed that SCAR marker SCJ 01 is at the same loci as that of RAPD marker OPJ 01₁₄₃₇ and hence, is linked to anthracnose resistance gene. Resistant parent G 73 and resistant bulk amplified single specific band on PCR amplification using SCAR primer pairs. The RAPD marker OPJ 01₁₄₃₇ was mapped at a distance of 3.26 cM apart from the locus governing anthracnose resistance on the sorghum genetic map by the segregation analysis of the RILs. Using BLAST program, it was found that the marker showed 100 per cent alignment with the contig{_}3966 located on the longer arm of chromosome 8 of sorghum genome. Therefore, these identified RAPD and SCAR markers can be used in the resistance-breeding program of sorghum anthracnose by marker-assisted selection.An erratum to this article can be found at     

Inheritance of resistance to fruit rot (Phytophthora capsici Leon.) and induction of resistance in bell pepper (Capsicum annuum L.)

Summary Fruit rot in bell pepper caused by Phytopthora capsici Leon. is a limiting factor in its commercial production. Crosses were made between Waxy Globe, a small fruited hot type, resistant to fruit rot and four highly susceptible bell pepper commercial cultivars (Chinese Giant, California Wonder, Osh, Kosh and Yolo Wonder). Studies of the F₁'s, F₂'s and backcrosses indicated that Waxy Globe carries a dominant gene imparting resistance to fruit rot. After three backcrosses with California Wonder, lines were obtained combining the resistance gene of Waxy Globe with the large fruit size and low capsaicin of California Wonder.     

Penetrance of gene I for Fusarium resistance in the tomato

Tomato seedlings were inoculated, from one to ten days after emergence, with the tomato Fusarium wilt fungus race 1. The penetrance of gene I for Fusarium resistance in the homozygous resistant variety Homestead 24 was almost complete. In the F₁ (Ii) between Homestead 24 and the susceptible Marmande penetrance was incomplete and ranged between 66.3% and 100% in different experiments. The age of seedlings at time of inoculation did not affect the final percentage of diseased plants while it influenced the nature and the time of appearance of disease symptoms. Possible consequences of incomplete penetrance for the resistance of F₁ hybrids are discussed.     

Cytogenetic studies on the interspecific hybrid Capsicum baccatum L.× C. frutescens L. and its progeny

Summary Morphological and cytogenetical studies were carried out on the F₁ and F₂ hybrids and backcross derivatives of the interspecific cross Capsicum baccatum L. x C. frutescens L. The F₁ and F₂ hybrids displayed irregular meiosis with a maximum association of eight chromosomes in the former and one quadrivalent in the latter with the appropriate number of bivalents and univalents. It is inferred that C. baccatum differs from C. frutescens (yellow) by at least tow or three interchanges and from the white cultivar by a single interchange. Structural repatterning of chromosomes, erratic meiotic behaviour, genes for pollen sterility, segregational imbalances following intergenomic recombination are believed to be major factors causing sterility in the hybrids. The two species are sympatric and natural hybrids have not been realised.     

The Inheritance of Resistance to Septoria Glume Blotch:

The inheritance of resistance in common wheat (Triticum aestivum, L.) to Septoria glume blotch, caused by the pathogen Septoria nodorum Berk., was studied. Four quantitative parameters of resistance were measured: infection efficiency (IE) and disease severity (DS) on intact young plants together with legion size (LS) and length of latent period (LP) on detached leaves. The method of testing the disease reaction of wheat to S. nodorum on detached leaves was refined and standardised to minimize the non-pathological sources of variation. Four wheat cultivars were tested for their reaction to 11 Septoria nodorum isolates. Two of the cultivars were crossed for studies on the genetics for host resistance, using a single S. nodorum isolate for inoculation; parental, F₁, F₂ and F₃ populations were analysed. Interaction between wheat cultivars and S. nodorum isolates was significant, but its variance component was quite small compared with the main effects of cultivars and isolates, The inheritance of resistance was mainly additive, with low to moderate heritability, apparently controlled by 3 to 4 quantitative genes, with indications of gene interactions. LS and LP were highly correlated, suggesting pleiotrapy for these two parameters of resistance. IE and DS (on intact plants) were moderately correlated to LS and LP (on detached leaves), apparently due to a partial pleiotropy or linkage.     

Potential for Incorporation of Early and Late Leafspot Resistance in Peanut*

A detached leaf technique was used to evaluate components of resistance to both early and late leafspot caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk, and Curt.) Deighton, respectively, for F₂ plants of two peanut (Arachis hypogaea L.) crosses (FESR 5-P2-B1 /PI 269685 and PI 35068Q/GP-NC 343), No negative correlations were obtained when comparing components of resistance to early leafspot with components of resistance to late leafspot, indicating that the resistances are inherited independently. A small number of F₂ plants had greater partial resistance to both leafspots than their parents when evaluated by an index including percent necrotic area, latent period and sporulation. Broad sense heritabilities of resistance components were moderate to high (0.4 to 0.8) for the F₂ populations. A visual sporulation rating scale was significantly correlated (0.8 to 0.9) with conidia per lesion and conidia per necrotic area. The data suggest that peanut cultivars resistant to both leafspots can be developed.     

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 resistance to early blight (Alternaria solani Sorauer) in tomato (Lycopersicon esculentum L.)

The genetic nature of early blight resistance in tomato was studied in three crosses at seedling and adult plant stages. A six generation mean analysis of the cross Arka Saurabh (susceptible) × IHR1939 (resistance) and its reciprocal cross revealed that the resistance to early blight was conferred by recessive polygenes at both seedling and adult plant stages. This polygenic early blight resistance revealed the importance of additive and additive × additive gene effects at seedling stage and higher magnitude of dominance and dominance× dominance gene effects at adult plant stage. Evaluation of parents, F₁, F₂ and backcross generations of IHR1816 (resistance) × IHR1939 (resistance) revealed that the early blight resistance genes in IHR1816 (Lycopersicon esculentum NCEBR-1) and IHR1939 (Lycopersicon pimpinellifolium L4394) are independent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of a novel recessive gene for resistance to powdery mildew (Blumeria graminis f. sp. hordei) in barley (Hordeum vulgare)

One of the most important diseases of barley (Hordeum vulgare) is powdery mildew, caused by Blumeria graminis f. sp. hordei. Spring barley line 173-1-2 was selected from a Moroccan landrace and revealed broad-spectrum resistance to powdery mildew. The objective of this study was to map and characterize the gene for seedling powdery mildew resistance in this line. After crossing with the susceptible cultivar ‘Manchuria’, genetic analysis of F₂ and F₃ families at the seedling stage revealed powdery mildew resistance in line 173-1-2 conditioned by a single recessive gene. Molecular analysis of non-segregating homozygous resistant and homozygous susceptible F₂ plants conducted on the DArTseq platform (Diversity Arrays Technology Pty Ltd) identified significant markers which were converted to allele-specific PCR markers and tested among 94 F₂ individuals. The new resistance gene was mapped on the long arm of chromosome 6H. No other powdery mildew recessive resistance gene has been located on 6H so far. Therefore, we concluded that the 173-1-2 barley line carries a novel recessive resistance gene designated as mlmr.     

Inheritance of closed flower in pepper

Summary Progenies of pepper (Capsicum annuum L.) crosses between the closed flower pepper line UFBG 8209-1 and cultivars Permagreen and Early Calwonder representing the normal, open flower type, were evaluated in a field experiment. The F₁ generation was open flowered. Backcrosses and F₂ generations indicated that the closed flower trait was controlled by a single recessive gene.Florida Agricultural Experiment Stations Journal Series No. 4918.     

Effectiveness of quantitative resistance conferred by the genetic background of pepper in the control of root‐knot nematodes and influence onto durability of Me1‐ and Me3‐resistant genes in greenhouse conditions

In pepper (Capsicum annuum), the major genes (R‐genes) Me1 and Me3 confer resistance against root‐knot nematodes (Meloidogyne spp.). The combination of R‐genes and quantitative resistance factors in the same genotype is considered a good breeding strategy for increasing the durability of R‐genes. To ascertain this hypothesis, five pepper inbred lines, differing in their quantitative resistance level, were combined with Me1 or Me3 genes in F₁ hybrids. The resistance of inbred lines and F₁ hybrids was evaluated in a greenhouse with soil naturally infected by M. incognita in two successive growing years. In both years, lines carrying Me3 were less infected by the nematode when combined with quantitative resistance. An increase in nematode infection was observed in the second growing year in lines carrying Me1 or Me3, independently of quantitative resistance. The infection level recorded in inbred lines without R‐genes was similar in both years. The effectiveness of quantitative resistance controlling M. incognita is confirmed in greenhouse conditions, although the durability of Me1 and Me3 when combined with quantitative resistance factors was not seen to increase.