Genetic resistance of common bean cultivar Beija Flor to Colletotrichum lindemuthianum

Anthracnose, which is caused by the fungus Colletotrichum lindemuthianum, is one of the most widespread and important diseases of the common bean (Phaseolus vulgaris L.) in the world. The objective of the present study was to characterize the genetic resistance of the Beija Flor cultivar by inheritance and to conduct allelism tests. The inheritance test was conducted in the F2 population derived from the Beija Flor (resistant) x TU (susceptible) cross inoculated with race 2047 of C. lindemuthianum. Furthermore, allelism tests exhibited a fitted segregation ratio of 15R:1S, thereby indicating the independence of the Beija Flor gene from the following previously characterized genes: Co-1, Co-2, Co-4, Co-42, Co-6, Co-12, Co-14, Co-15, and Co-Pe. Based on the aforementioned results, we are proposing the symbol Co-Bf to designate the new anthracnose resistance gene in the Brazilian Andean common bean cultivar Beija Flor. This cultivar is an important source of resistance to C. lindemuthianum that should provide a valuable contribution to the common bean breeding program for anthracnose resistance.

Pairing and Exchanging between Daypyrum villosum Chromosomes 6V#2 and 6V#4 in the Hybrids of Two Different Wheat Alien Substitution Lines

Normal pairing and exchanging is an important basis to evaluate the genetic relationship between homologous chromosomes in a wheat background. The pairing behavior between 6V#2 and 6V#4, two chromosomes from different Dasypyrum villosum accessions, is still not clear. In this study, two wheat alien substitution lines, 6V#2 (6A) and 6V#4 (6D), were crossed to obtain the F1 hybrids and F2 segregating populations, and the testcross populations were obtained by using the F1 as a parent crossed with wheat variety Wan7107. The chromosomal behavior at meiosis in pollen mother cells (PMCs) of the F1 hybrids was observed using a genomic in situ hybridization (GISH) technique. Exchange events of two alien chromosomes were investigated in the F2 populations using nine polymerase chain reaction (PCR) markers located on the 6V short arm. The results showed that the two alien chromosomes could pair with each other to form ring- or rod-shaped bivalent chromosomes in 79.76% of the total PMCs, and most were pulled to two poles evenly at anaphase I. Investigation of the F2 populations showed that the segregation ratios of seven markers were consistent with the theoretical values 3:1 or 1:2:1, and recombinants among markers were detected. A genetic linkage map of nine PCR markers for 6VS was accordingly constructed based on the exchange frequencies and compared with the physical maps of wheat and barley based on homologous sequences of the markers, which showed that conservation of sequence order compared to 6V was 6H and 6B > 6A > 6D. In the testcross populations with 482 plants, seven showed susceptibility to powdery mildew (PM) and lacked amplification of alien chromosomal bands. Six other plants had amplification of specific bands of both the alien chromosomes at multiple sites, which suggested that the alien chromosomes had abnormal separation behavior in about 1.5% of the PMCs in F1, which resulted in some gametes containing two alien chromosomes. In addition, three new types of chromosome substitution were developed. This study lays a foundation for alien allelism tests and further assessment of the genetic relationship among 6V#2, 6V#4, and their wheat homoeologous chromosomes.

Identification of a New Powdery Mildew Resistance Gene pmDHT at or Closely Linked to the Pm5 Locus in the Chinese Wheat Landrace Dahongtou

Chinese wheat landrace Dahongtou was resistant to 35 of 38 tested Chinese isolates of Blumeria graminis f. sp. tritici at the seedling stage. Genetic analysis of the F2 populations and their derived F2:3 families of crosses of Dahongtou with the susceptible varieties Mingxian 169 and Huixianhong indicated that the resistance of Dahongtou to B. graminis f. sp. tritici isolate E09 was conferred by a single recessive gene, tentatively designated as pmDHT. The gene was mapped to chromosome arm 7BL and flanked by markers Xwmc526/XBE443877 and Xgwm611/Xwmc511 at genetic distances of 0.8 and 0.3 cM, respectively. The chromosomal position of pmDHT was similar to the multi-allelic Pm5 locus on 7BL. Allelism tests with crosses of Dahongtou with Fuzhuang 30 (Pm5e) and Xiaobaidong (mlxbd) indicated that pmDHT was allelic to both Pm5e and mlxbd. However, pmDHT showed a different pattern of resistance to the 38 B. graminis f. sp. tritici isolates compared with wheat lines with Pm5a, Pm5b, Pm5e, mlxbd, and PmHYM and also differed from PmSGA. Thus, pmDHT was identified most likely as a new allele or at least a closely linked gene of the Pm5 locus. This gene can be transferred into susceptible wheat cultivars/lines and pyramided with other resistance genes through marker-assisted selection to improve powdery mildew resistance.

The multi-allelic APRR2 gene is associated with fruit pigment accumulation in melon and watermelon

Color and pigment contents are important aspects of fruit quality and consumer acceptance of cucurbit crops. Here, we describe the independent mapping and cloning of a common causative APRR2 gene regulating pigment accumulation in melon and watermelon. We initially show that the APRR2 transcription factor is causative for the qualitative difference between dark and light green rind in both crops. Further analyses establish the link between sequence or expression level variations in the CmAPRR2 gene and pigment content in the rind and flesh of mature melon fruits. A genome-wide association study (GWAS) of young fruit rind color in a panel composed of 177 diverse melon accessions did not result in any significant association, leading to an earlier assumption that multiple genes are involved in shaping the overall phenotypic variation in this trait. Through resequencing of 25 representative accessions and allelism tests between light rind accessions, we show that multiple independent single nucleotide polymorphisms in the CmAPRR2 gene are causative of the light rind phenotype. The multi-haplotypic nature of this gene explains the lack of detection power obtained through genotyping by sequencing-based GWAS and confirms the pivotal role of this gene in shaping fruit color variation in melon. This study demonstrates the power of combining bi- and multi-allelic designs with deep sequencing, to resolve lack of power due to high haplotypic diversity and low allele frequencies. Due to its central role and broad effect on pigment accumulation in fruits, the APRR2 gene is an attractive target for carotenoid bio-fortification of cucurbit crops.

Multi-allelic APRR2 Gene is Associated with Fruit Pigment Accumulation in Melon and Watermelon

Color and pigment content are important aspects of fruit quality and consumer acceptance of cucurbit crops. Here, we describe the independent mapping and cloning of a common causative APRR2 gene regulating pigment accumulation in melon and watermelon. We initially show that the APRR2 transcription factor is causative for the qualitative difference between dark and light green rind in both crops. Further analyses establish the link between sequence or expression level variations in the CmAPRR2 gene and pigments content in the rind and flesh of mature melon fruits. GWAS of young fruit rind color in a panel composed of 177 diverse melon accessions did not result in any significant association, leading to an earlier assumption that multiple genes are involved in shaping the overall phenotypic variation at this trait. Through resequencing of 25 representative accessions and allelism tests between light rind accessions, we show that multiple independent SNPs in the CmAPRR2 gene are causative for the light rind phenotype. The multi-haplotypic nature of this gene explain the lack of detection power obtained through GBS-based GWAS and confirm the pivotal role of this gene in shaping fruit color variation in melon. This study demonstrates the power of combining bi- and multi-allelic designs with deep sequencing, to resolve lack of power due to high haplotypic diversity and low allele frequencies. Due to its central role and broad effect on pigment accumulation in fruits, the APRR2 gene is an attractive target for carotenoids bio-fortification of cucurbit crops.

A Novel Root-Knot Nematode Resistance QTL on Chromosome Vu01 in Cowpea

ABSTRACTThe root-knot nematode (RKN) species Meloidogyne incognita and M. javanica cause substantial root system damage and suppress yield of susceptible cowpea cultivars. The narrow-based genetic resistance conferred by the Rk gene, present in some commercial cultivars, is not effective against Rk-virulent populations found in several cowpea production areas. The dynamics of virulence within RKN populations require a broadening of the genetic base of resistance in elite cowpea cultivars. As part of this goal, F1 and F2 populations from the cross CB46-Null (susceptible) x FN-2-9-04 (resistant) were phenotyped for M. javanica induced root-galling (RG) and egg-mass production (EM) in controlled growth chamber and greenhouse infection assays. In addition, F2:3 families of the same cross were phenotyped for RG on field sites infested with Rk-avirulent M. incognita and M. javanica. The response of F1 to RG and EM indicated that resistance to RKN in FN-2-9-04 is partially dominant, as supported by the degree of dominance in the F2 and F2:3 populations. Two QTLs associated with both RG and EM resistance were detected on chromosomes Vu01 and Vu04. The QTL on Vu01 was most effective against aggressive M. javanica, whereas both QTLs were effective against avirulent M. incognita. Allelism tests with CB46 x FN-2-9-04 progeny indicated that these parents share the same RKN resistance locus on Vu04, but the strong, broad-based resistance in FN-2-9-04 is conferred by the additive effect of the novel resistance QTL on Vu01. This novel resistance in FN-2-9-04 is an important resource for broadening RKN resistance in elite cowpea cultivars.

Inheritance of Resistance to Papaya Ringspot Virus-Watermelon Strain in Watermelon

Sources of resistance to the watermelon strain of papaya ringspot virus-watermelon strain (PRSV-W) have been identified within the watermelon (Citrullus lanatus) germplasm collection. Inheritance of the resistance to PRSV-W was studied in three Citrullus amarus (formerly C. lanatus var. citroides) PI accessions: PI 244017, PI 244019, and PI 485583. Three susceptible parent lines, ‘Allsweet’, ‘Calhoun Gray’, and ‘New Hampshire Midget’, were crossed with resistant PI accessions to develop F1, F2, and BC1 progenies in six families. A single recessive gene was found to control the resistance to PRSV-W in all three resistant PI accessions. Allelism tests indicated that the three PI accessions carry the same resistance allele to PRSV-W. The gene symbol ‘prv’ is proposed for PRSV-W resistance in PI 244017, PI 244019, and PI 485583 in watermelon.

Characterization of genetic resistance in Andean common bean cultivar Amendoim Cavalo to Colletotrichum lindemuthianum

The Anthracnose, caused by Colletotrichum lindemuthianum (Sacc. and Magnus) Briosi and Cavara, is one of the most importante fungal disease of common bean. Several strategies have been used for its control, such as the use of pathogen-free seeds, chemical control and crop rotation. However, the most efficient method to control this disease is the use of resistant cultivars. Previous studies conducted by the Laboratory of Common Bean Breeding and Molecular Biology of the Nucleus of Research Applied to Agriculture (Laboratório de Melhoramento de Feijão Comum e de Biologia Molecular do Núcleo de Pesquisa Aplicada à Agricultura-NUPAGRI) revealed that the Andean cultivar Amendoim Cavalo is resistant to races 2, 7, 9, 19, 23, 39, 55, 65, 73, 89, 1545, 2047 and 3481 of C. lindemuthianum. The objective of this work was to characterize the genetic resistance to anthracnose in Amendoim Cavalo using inheritance and allelism tests. The results of inheritance tests in F2 generation of Amendoim Cavalo × PI 207262 cross, inoculated with 2047 race, fitted in a ratio of 3R:1S, proving the action of a single dominant gene in Amendoim Cavalo cultivar. Allelism tests demonstrated that the dominant gene present in Amendoim Cavalo is independent from the genes previously characterized. The authors propose the Co-AC symbol to designate the new resistant gene to C. lindemuthianum. The results show high contribution to breeding programs, once Amendoim Cavalo cultivar can be considered an important Andean source of resistance to C. lindemuthianum.

Genetic resistance to Colletotrichum lindemuthianum in the Andean cultivar Jalo Pintado 2 of common bean

The anthracnose caused by fungus Colletotrichum lindemuthianum (Sacc. & Magnus) Briosi & Cavara is the most widespread disease and economically important fungal disease of common bean (Phaseolus vulgaris L.). The use of resistant cultivars is considered as one of the most effective methods in controlling this disease. The present study had as aim to characterize the genetic resistance of the Andean common bean cultivar Jalo Pintado 2 to the C. lindemuthianum through inheritance and allelism tests. The experiment was conducted under greenhouse conditions at Laboratório de Melhoramento do Feijão Comum e de Biologia Molecular do Núcleo de Pesquisa Aplicada a Agricultura (Nupagri) at Universidade Estadual de Maringá, Paraná, Brazil. The results of the F2 population from the crossing 'Jalo Pintado 2' (R) × Cornell 49-242 (S), inoculated with race 73 of C. lindemuthianum, adjusted to the ratio of 3R: 1S, demonstrating the action of a dominant gene in the cultivar Jalo Pintado 2. The allelism tests evidenced that the gene in the 'Jalo Pintado 2' is independent from those previously characterized: Co-1, Co-2,Co-3, Co-34, Co-4, Co-42, Co-43, Co-5, Co-6, Co-11, Co-12, Co-13, Co-14, Co-15 and Co-16. This gene is also independent from those genes not yet named present in Paloma, Perla and Amendoim Cavalo cultivars. The authors propose the Co-

PmLX66 and PmW14: New Alleles of Pm2 for Resistance to Powdery Mildew in the Chinese Winter Wheat Cultivars Liangxing 66 and Wennong 14

Wheat powdery mildew (caused by Blumeria graminis f. sp. tritici) can be effectively managed by growing resistant cultivars. ‘Liangxing 66’ and ‘Wennong 14’ are the current winter wheat cultivars grown in northern China where powdery mildew is epidemic. Both cultivars have been demonstrated to carry single dominant genes for resistance to powdery mildew, tentatively designated PmLX66 and PmW14, on chromosome 5DS and share common linked markers with Pm2. Allelism tests were performed using a total of 15,657 plants of F2 segregating populations to determine the relationship between PmLX66, PmW14, and Pm2. All progeny from the crosses Liangxing 66 × ‘Ulka/8*Chancellor’ (Ulka/8*Cc), Wennong 14 × Ulka/8*Cc, and Liangxing 66 × Wennong 14 were resistant when tested with B. graminis f. sp. tritici isolate E20, indicating that PmLX66 and PmW14 are allelic to Pm2 and to each other. Liangxing 66 was resistant to 76.7% of the 60 B. graminis f. sp. tritici isolates from northern China, a slightly smaller proportion than Ulka/8*Cc (78.3%). However, Wennong 14 (85.0%) was more resistant against this set of B. graminis f. sp. tritici isolates than Ulka/8*Cc and Liangxing 66. Liangxing 66 and Wennong 14 differed from Ulka/8*Cc in respect to a number of B. graminis f. sp. tritici isolates. Based on these findings, PmLX66 and PmW14 are new alleles at the Pm2 locus.