Recessive Resistance Research Articles

The Optimization of Urban Ecological Network Planning Based on the Minimum Cumulative Resistance Model and Granularity Reverse Method: A Case Study of Haikou, China

In recent years, the high-speed urbanization process and human activities have led to the fragmentation and the connectivity reduction of natural landscape patches, resulting in the degradation of urban ecological services and biodiversity. The construction of ecological network and the optimization of landscape pattern are significantly important to improve the urban ecological environment and urban ecological security. In this paper, a case study of Haikou, an island city of China is performed, the selection of ecological source areas is optimized by granularity reverse method and principal component analysis. The minimum cumulative resistance model (MCRM) is used to construct the ecological resistance surface, and ecological corridors and ecological nodes are obtained, so as to optimize the urban ecological network and the connectivity of landscape patches. The results show that the 1400m granularity landscape component is the optimal landscape component structure for Haikou. There are 38 ecological source areas in Haikou, and 14 ecological landscape patches need to be added. The distribution of ecological source areas is mainly affected by topography and geomorphology. The northwest has huge and scattered ecological source areas, while the southeast has small and concentrated ecological source areas. In the areas around Meilan airport and Hongcheng lake, there is an ecological trap with significant difference between dominant and recessive ecological resistance separately. Haikou ecological network consists of 81 ecological corridors and 76 ecological nodes. Affected by the main urban area in the north, Haikou ecological network has the high density in the middle and southern areas. The construction of ecological network has significantly improved the overall connectivity of the ecosystem in the study region. This research provides a scientific basis for the future urban ecological environment planning of Haikou.

Design and thermal analysis of a novel permanent magnet-friction integrated brake for vehicle

This article focuses on a new type of permanent magnet-friction integrated brake. The design scheme of integrated brake is proposed. Taking the maximization of braking moment and the minimization of volume as the dual optimization objectives, the particle swarm optimization algorithm is used to optimize the integrated brake, and the main structure parameters of the integrated brake are obtained. Based on the obtained structure parameters, the 3-D model of integrated brake is established. The mathematical models of electromagnetic field and temperature field of integrated brake are given, respectively. Taking a typical braking process as an example, the magnetic field of integrated brake is analyzed based on COMSOL software, which verifies the correctness of the design model of permanent magnet brake. The eddy current loss in the magnetic field of permanent magnet brake and the thermal contact of friction brake are taken as heat sources of the integrated brake, then the temperature field of integrated brake is analyzed. The analysis results show that the integrated brake meets the requirements of braking performances, and improves the heat recession resistance compared with the traditional friction brake.

Marker-Assisted Introgression of Multiple Resistance Genes Confers Broad Spectrum Resistance against Bacterial Leaf Blight and Blast Diseases in PUTRA-1 Rice Variety

Bacterial leaf blight caused by Xanthomonas oryzae pv oryzae (Xoo) and blast caused by Magnaporthe oryzae are major diseases responsible for significant yield loss in rice production across all rice growing regions. Host plant resistance has been advocated as a sustainable means of guarding against the diseases. This experiment was conducted with the aim to introgress multiple resistance genes against bacterial leaf blight and blast diseases through marker-assisted backcross breeding. Two dominant (Xa4 and Xa21) and two recessive (xa5 and xa13) Xoo resistance genes were introgressed into a high yielding Malaysian rice variety Putra-1 with genetic background of three blast resistance (Piz, Pi2 and Pi9) genes. Eight polymorphic tightly linked functional and SSR markers were used for foreground selection of target genes. Seventy nine polymorphic SSR markers were used in background selection. The plants were challenged at initial stage of breeding and challenged again at BC2F2 with the most virulent Malaysian pathotypes of Xoo (P7.7) and Magnaporthe oryzae (P7.2) to test their resistance. Results obtained from foreground marker segregation analysis at BC1F1 and BC2F1 showed that the marker polymorphism both fitted into the Mendel’s single gene segregation ratio of 1:1 for both Xoo and blast resistance. At BC2F2, results indicated that foreground marker polymorphism fitted into the expected Mendelian ratio of 1:2:1 for blast resistance only. Marker-assisted background selection revealed high percentage of recurrent parent genome recovery (95.9%). It was concluded that the inheritance of blast resistance in the introgressed lines was mainly due to single gene action while the inheritance of Xoo resistance was substantially due to single nuclear gene action. The incorporation of four bacterial leaf blight and three blast resistance genes (Xa4 + xa5 + xa13 + Xa21; Pi9 + Pi2 + Piz) in the newly developed lines would provide for broad spectrum and durable resistance against the two major diseases studied.

Development of a PVY Resistant Flue-Cured Tobacco Line via EMS Mutagenesis of eIF4E

Recessive resistance against potyviruses, such as Potato virus Y (PVY), relies on mutations in the eukaryotic translation initiation factor 4E (eIF4E) or one of its isoforms. The eIF4E1-S mutants of burley tobacco (Nicotiana tabacum L.) exhibit recessive resistance against PVY strains. Here, we developed a TILLING population of flue-cured tobacco (N. tabacum cv. Yunyan87) using ethyl methanesulfonate (EMS) to identify eIF4E1-S mutants. M3 plants homozygous for a nonsense mutation in exon 1 of the eIF4E1-S gene demonstrated resistance against PVYMN. These M3 plants were backcrossed to ‘Yunyan87’, and BC4F3 plants were screened using derived cleaved amplified polymorphic sequence (dCAPS) markers. BC4F3 plants showing agronomic traits comparable to the recurrent parent ‘Yunyan87’ and resistance against PVYO, PVYN, and PVYNTN strains were identified. These genotypes would provide useful germplasm for future tobacco improvement and would aid in basic research on PVY resistance in flue-cured tobacco.

Plant susceptibility genes as a source for potyvirus resistance

AbstractVirus infection depends on the resources provided by the host plant. A number of host proteins that enable potyvirus infection have been identified. The genes encoding them are called susceptibility genes (S‐genes). Loss‐of‐susceptibility type of resistance is based on S‐gene modifications leading to incompatible host–virus interactions. An increasing number of examples show that this is a viable method for resistance breeding. While the recent advancements in genome editing and sequencing have remarkably reduced the technical limitations, we still need to tackle many biological challenges to be able to utilise S‐genes for durable and broad range potyvirus resistance to their full extent. Many lessons on functional redundancy between gene family members and durability of the resistance have been learned by studying the naturally occurring recessive resistance based on the interplay between eukaryotic initiation factors eIF4E and eIFiso4E and viral protein genome‐linked (VPg). Nevertheless, the outcomes of the S‐gene modifications on resistance or any other characteristic of the host plant cannot be predicted. In addition to the genetic background of the host, also the properties of the viral factors affect the efficiency of the resistance and the emergence of resistance‐breaking mutations. Many potyviral protein–protein interactions occur in multiprotein complexes. This suggests that the susceptibility factors may interact with viral proteins as a part of multifaceted protein–protein interaction networks. Rather than reviewing exhaustively the S‐genes involved in potyvirus infection, my intention here is to discuss in the light of selected examples, the prospects and challenges of the use of potyviral S‐genes in resistance breeding.

High-resolution genetic mapping of a novel bacterial blight resistance gene xa-45(t) identified from Oryza glaberrima and transferred to Oryza sativa.

A novel recessive bacterial blight resistance locus designated as a xa-45(t) was identified from Oryza glaberrima accession IRGC 102600B, transferred to O. sativa and mapped to the long arm of chromosome 8 using ddRAD sequencing approach. The identified QTL spans 80kb region on Nipponbare reference genome IRGSP-1.0 and contains 9 candidate genes. An STS marker developed from the locusLOC_Os08g42410was found co-segregating with the trait and will be useful for marker-assisted transfer of this recessive resistance gene in breeding programs. Bacterial blight, caused by Xanthomonas oryzae pv. oryzae, is one of the major constraints of rice productivity in Southeast Asia. In spite of having 44 bacterial blight resistance genes from cultivated rice and wild species, the durability of resistance is always at stake due to the continually evolving nature of the pathogen and lack of suitable chemical control. Here, we report high-resolution genetic mapping of a novel bacterial blight resistance gene tentatively designated as a xa-45(t) from an introgression line derived from Oryzaglaberrimaaccession IRGC 102600B. This introgression line was crossed with the susceptible riceindicacultivar cv. Pusa 44 to generate F2and F2:3populations for inheritance and mapping studies. The inheritance studies revealed the presence of single recessive locus controlling resistance to the Xanthomonas pathotype seven. A high-density linkage map was constructed using double-digest restriction-associated DNA sequencing of 96 F2 populations along with the parents. The QTL mapping identified a major locus on the long arm of rice chromosome 8 with a LOD score of 33.22 between the SNP markers C8.26737175 and C8.26818765. The peak marker, C8.26810477, explains 49.8% of the total phenotypic variance and was positioned at 202.90cM on the linkage map. This major locus spans 80kb region on Nipponbare reference genome IRGSP-1.0 and contains 9 candidate genes. A co-segregating STS marker was developed from the LOC_Os08g42410 for efficient transfer of this novel gene to elite cultivars.

Intracellular proliferation of clover yellow vein virus is unaffected by the recessive resistance gene cyv1 of Pisum sativum.

The pea cyv1 gene is a yet-to-be-identified recessive resistance gene that inhibits the infection of clover yellow vein virus (ClYVV). Previous studies confirmed that the cell-to-cell movement of ClYVV is inhibited in cyv1-carrying pea plants; however, the effect of cyv1 on viral replication remains unknown. In this study, we developed a new pea protoplast transfection method to investigate ClYVV propagation at the single-cell level. Using this method, we revealed that ClYVV accumulates to similar levels in both ClYVV-susceptible and cyv1-carrying pea protoplasts. Thus, the cyv1-mediated resistance would not suppress intracellular ClYVV replication.

Engineering Broad-Spectrum Bacterial Blight Resistance by Simultaneously Disrupting Variable TALE-Binding Elements of Multiple Susceptibility Genes in Rice

Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial blight of rice, employs the transcription activator-like effectors (TALEs) to induce the expression of the OsSWEET family of putative sugar transporter genes, which function in conferring disease susceptibility (S) in rice plants. To engineer broad-spectrum bacterial blight resistance, we used CRISPR/Cas9-mediated gene editing to disrupt the TALE-binding elements (EBEs) of two S genes, OsSWEET11 and OsSWEET14, in rice cv. Kitaake, which harbors the recessive resistance allele of Xa25/OsSWEET13. The engineered rice line MS14K exhibited broad-spectrum resistance to most Xoo strains with a few exceptions, suggesting that the compatible strains may contain new TALEs. We identified two PthXo2-like TALEs, Tal5LN18 and Tal7PXO61, as major virulence factors in the compatible Xoo strains LN18 and PXO61, respectively, and found that Xoo encodes at least five types of PthXo2-like effectors. Given that PthXo2/PthXo2.1 target OsSWEET13 for transcriptional activation, the genomes of 3000 rice varieties were analyzed for EBE variationsin the OsSWEET13 promoter, and 10 Xa25-like haplotypes were identified. We found that Tal5LN18 and Tal7PXO61 bind slightly different EBE sequences in the OsSWEET13 promoter to activate its expression. CRISPR/Cas9 technology was then used to generate InDels in the EBE of the OsSWEET13 promoter in MS14K to creat a new germplasm with three edited OsSWEET EBEs and broad-spectrum resistance against all Xoo strains tested. Collectively, our findings illustrate how to disarm TALE-S co-evolved loci to generate broad-spectrum resistance through the loss of effector-triggered susceptibility in plants.

Bt resistance alleles in field populations of pink bollworm from China: Similarities with the United States and decreased frequency from 2012 to 2015.

Although most monitoring of pest resistance to widely cultivated transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) relies on bioassays, DNA screening for alleles associated with resistance has some advantages, particularly for rare, recessively inherited resistance. In China's Yangtze River Valley, where farmers first planted transgenic cotton producing Bt toxin Cry1Ac in 2000, bioassays have been used to monitor the recessive resistance of pink bollworm (Pectinophora gossypiella). Previous bioassay results show a small but significant increase in resistance to Cry1Ac during 2008-2010, followed by a significant decrease in resistance during 2011-2015 associated with extensive planting of second-generation hybrid cotton seeds that boosted the percentage of non-Bt cotton. Here we screened DNA from 19 748 pink bollworm collected during 2012-2015 from the Yangtze River Valley for seven alleles associated with resistance to Cry1Ac. These alleles were previously identified from lab-selected strains; three from the U.S. and four from China. The most common resistance allele was first identified from the U.S. and accounted for over 71% of all resistance alleles detected. Resistance was rare, with the total frequency of the seven resistance alleles showing a significant, 2.3-fold decrease from 0.0105 (95% CI: 0.0084-0.0132) in 2012 to 0.0046 (0.0031-0.0067) in 2015. The DNA screening data confirm results from bioassays showing pink bollworm resistance to Cry1Ac remained rare in the Yangtze River Valley from 2012-2015. The prevalence in China of the resistance allele identified from the U.S. implies a shared genetic basis of resistance that could facilitate molecular monitoring of resistance. © 2019 Society of Chemical Industry.

Resistance Against Melon Chlorotic Mosaic Virus and Tomato Leaf Curl New Delhi Virus in Melon.

Thirty-one melon accessions were screened for resistance to the begomoviruses Melon chlorotic mosaic virus (MeCMV) and Tomato leaf curl New Delhi virus (ToLCNDV). Five accessions presented nearly complete resistance to both viruses. Accession IC-274014, showing the highest level of resistance to both viruses, was crossed with the susceptible cultivar Védrantais. The F1, F2, F3/F4, and both backcross progenies were mechanically inoculated with MeCMV. Plants without symptoms or virus detection by enzyme-linked immunosorbent assay and/or PCR were considered as resistant. The segregations were compatible with two recessive and one dominant independent genes simultaneously required for resistance. Inheritance of resistance to ToLCNDV in the F2 was best explained by one recessive gene and two independent dominant genes simultaneously required. Some F3 and F4 families selected for resistance to MeCMV also were resistant to ToLCNDV, suggesting that common or tightly linked genes were involved in resistance to both viruses. We propose the names begomovirus resistance-1 and Begomovirus resistance-2 for these genes (symbols bgm-1 and Bgm-2). Resistance to MeCMV in IC-274014 was controlled by bgm-1, Bgm-2, and the recessive gene melon chlorotic mosaic virus resistance (mecmv); resistance to ToLCNDV was controlled by bgm-1, Bgm-2, and the dominant gene Tomato leaf curl New Delhi virus resistance (Tolcndv).

Recessive Resistance: Developing Targets for Genome Editing to Engineer Viral Disease Resistant Crops

Recessive Resistance: Developing Targets for Genome Editing to Engineer Viral Disease Resistant Crops

Recessive Resistance Governed by a Major Quantitative Trait Locus Restricts Clover Yellow Vein Virus in Mechanically but Not Graft-Inoculated Cultivated Soybeans.

Clover yellow vein virus (ClYVV) infects and causes disease in legume plants. However, here, we found that ClYVV isolate No. 30 (ClYVV-No.30) inefficiently multiplied or spread via cell-to-cell movement in mechanically inoculated leaves of a dozen soybean (Glycine max) cultivars and resulted in failure to spread systemically. Soybean plants also had a similar resistance phenotype against additional ClYVV isolates. In contrast, all but one of 24 tested accessions of wild soybeans (G. soja) were susceptible to ClYVV-No.30. Graft inoculation of cultivated soybean TK780 with ClYVV-No.30-infected wild soybean B01167 scion resulted in systemic infection of the cultivated soybean rootstock. This suggests that, upon mechanical inoculation, the cultivated soybean inhibits ClYVV-No.30, at infection steps prior to the systemic spread of the virus, via vascular systems. Systemic infection of all F1 plants from crossing between TK780 and B01167 and of 68 of 76 F2 plants with ClYVV-No.30 indicated recessive inheritance of the resistance. Further genetic analysis using 64 recombinant inbred lines between TK780 and B01167 detected one major quantitative trait locus, designated d-cv, for the resistance that was positioned in the linkage group D1b (chromosome 2). The mapped region on soybean genome suggests that d-cv is not an allele of the known resistance genes against soybean mosaic virus.

Fine mapping of wmv1551, a resistance gene to Watermelon mosaic virus in melon

Recessive resistance to Watermelon mosaic virus (WMV) in melon has previously been reported in the African accession TGR-1551. Using a population of recombinant inbred lines (RIL), derived from a cross between TGR-1551 and the susceptible Spanish cultivar ‘Bola de Oro’ (BO), a major quantitative trait locus (QTL) controlling the resistance was previously mapped to a region of approximately 760 kb in chromosome 11. Minor QTLs were also reported with lower effects, dependent on the environmental conditions. A genotyping by sequencing (GBS) analysis of the RIL population has provided new information that allowed the better location of the major QTL in chromosome 11. Moreover, three minor QTLs in chromosomes 4, 5, and 6 were identified. Generations derived from the RIL population were subsequently phenotyped for resistance and genotyped with SNP markers to fine map the resistance derived from TGR-1551. The results obtained have allowed to narrow the position of the resistance gene on chromosome 11, designated as wmv1551, to a 141-kb region, and the confirmation of a minor QTL in chromosome 5. The effect of the minor QTL in chromosome 5 was significant in heterozygote plants for the introgression in chromosome 11. The SNP markers linked to both QTLs will be useful in breeding programs aimed at the introgression of WMV resistance derived from TGR-1551. Future work will be directed to identifying the resistance gene, wmv1551, in the candidate region on chromosome 11.

A complex eIF4E locus impacts the durability of va resistance to Potato virus Y in tobacco.

SummaryMany recessive resistances against potyviruses are mediated by eukaryotic translation initiation factor 4E (eIF4E). In tobacco, the va resistance gene commonly used to control Potato virus Y (PVY) corresponds to a large deletion affecting the eIF4E‐1 gene on chromosome 21. Here, we compared the resistance durability conferred by various types of mutations affecting eIF4E‐1 (deletions of various sizes, frameshift or nonsense mutations). The ‘large deletion’ genotypes displayed the broadest and most durable resistance, whereas frameshift and nonsense mutants displayed a less durable resistance, with rapid and frequent apparition of resistance‐breaking variants. In addition, genetic and transcriptomic analyses revealed that resistance durability is strongly impacted by a complex genetic locus on chromosome 14, which contains three other eIF4E genes. One of these, eIF4E‐3, is rearranged as a hybrid gene between eIF4E‐2 and eIF4E‐3 (eIF4E‐2‐3) in the genotypes showing the most durable resistance, while eIF4E‐2 is differentially expressed between the tested varieties. RNA‐seq and quantitative reverse transcriptase‐polymerase chain reaction experiments demonstrated that eIF4E‐2 expression level is positively correlated with resistance durability. These results suggest that besides the nature of the mutation affecting eIF4E‐1, three factors linked with a complex locus may potentially impact va durability: loss of an integral eIF4E‐3, presence of eIF4E‐2‐3 and overexpression of eIF4E‐2. This latter gene might act as a decoy in a non‐productive virus–plant interaction, limiting the ability of PVY to evolve towards resistance breaking. Taken together, these results show that va resistance durability can in large part be explained by complex redundancy effects in the eIF4E gene family.

Oxidation and recession of plain weave carbon fiber reinforced ZrB2-SiC-ZrC in oxygen–hydrogen torch environment

The oxidation and recession of four plain weave carbon fiber reinforced ZrB2-SiC-ZrC composites with different matrix compositions were compared with those of a plain weave carbon fiber reinforced ZrB2-SiC matrix composite. These composites were fabricated using a silicon melt infiltration method. The composite with the higher ZrC content also formed ZrSi2 in the matrix instead of residual silicon. The composites were oxidized at 1700 and 1800 °C in an oxygen–hydrogen torch environment. The oxides consisted of ZrO2 and SiO2, which formed on the surface of all samples. Carbon fiber at the surface was lost due to oxidation. The recession resistance of ZrB2-SiC-ZrC matrix composites remained constant at 1700 °C, even if the matrix composition varied, while the resistance at 1800 °C increased with the matrix of ZrC and ZrSi2. The ZrB2-SiC-ZrC matrix composite with the higher ZrC and ZrSi2 compositions formed a sintered ZrO2-rich layer, which was denser than the ZrO2-SiO2 and improved the recession resistance.

Bulked segregant RNA-sequencing (BSR-seq) identified a novel rare allele of eIF4E effective against multiple isolates of BaYMV/BaMMV.

A novel rare allele of the barley host factor gene eIF4E for BaMMV/BaYMV infection was identified in an Iranian landrace that showed broad resistance to barley yellow mosaic virus disease, and molecular markers facilitating efficient selection were developed. The soil-borne yellow mosaic virus disease caused by different strains of barley yellow mosaic virus (BaYMV) and barley mild mosaic virus (BaMMV) is a major threat to winter barley (Hordeum vulgare) production in Europe and East Asia. However, the exploration of resistant germplasm or casual genes for barley breeding is rather limited in relation to the rapid diversification of viral strains. Here, we identified an Iranian barley landrace 'HOR3298,' which represented complete resistance to BaYMV and BaMMV. In contrastto rym4 and rym5, which act as the predominant source in Europe and East Asia for breeding resistant cultivars over decades and which have been overcome by several virulent isolates, this landrace showed broad-spectrum resistance to multiple isolates of BaYMV/BaMMV in the fields of Germany and China. By employment of bulked segregant RNA sequencing, test for allelism, and haplotype analysis, a recessive resistance gene in 'HOR3298' was genetically mapped coincident with the host factor eukaryotic translation initiation factor 4E (eIF4E, causal gene of rym4 and rym5). The eIF4EHOR3298 allele encoded for a novel haplotype that contained an exclusive nucleotide mutation (G565A) in the coding sequence. The easily handled markers were developed based on the exclusively rare variation, providing precise selection of this allele. Thus, this work provided a novel reliable resistance source and the feasible marker-assisted selection assays that can be used in breeding for barley yellow mosaic virus disease resistance in cultivated barley.

New thermal protection system using high-temperature carbon fibre-reinforced plastic sandwich panel

Herein, a new lightweight thermal protection system was proposed to reduce the weight of a re-entry capsule. The proposed system employs an ablator as a thermal protection material, and a high-temperature polyimide carbon fibre-reinforced plastic (CFRP) sandwich panel as a structure member. The sandwich panel was designed to exhibit high thermal insulation and good mechanical properties at high temperature, and simultaneously ensure that the ablator has low thickness. Three-point bending was carried out at a high temperature up to 300 °C to evaluate shear strength and flexural rigidity of the sandwich panel. Further, the proposed thermal protection system was examined using an arc-heated plasma wind tunnel to evaluate its thermal protection performance and thermal response. The shear strength and the flexural rigidity of this high-temperature structure were 76.8 and 86.9% of that at room temperature, respectively, when evaluated at 300 °C. The proposed system achieved more than 40% weight reduction while maintaining high thermal insulation and recession resistance.

Manipulating Cellular Factors to Combat Viruses: A Case Study From the Plant Eukaryotic Translation Initiation Factors eIF4.

Genes conferring resistance to plant viruses fall in two categories; the dominant genes that mostly code for proteins with a nucleotide binding site and leucine rich repeats (NBS-LRR), and that directly or indirectly, recognize viral avirulence factors (Avr), and the recessive genes. The latter provide a so-called recessive resistance. They represent roughly half of the known resistance genes and are alleles of genes that play an important role in the virus life cycle. Conversely, all cellular genes critical for the viral infection virtually represent recessive resistance genes. Based on the well-documented case of recessive resistance mediated by eukaryotic translation initiation factors of the 4E/4G family, this review is intended to summarize the possible approaches to control viruses via their host interactors. Classically, resistant crops have been developed through introgression of natural variants of the susceptibility factor from compatible relatives or by random mutagenesis and screening. Transgenic methods have also been applied to engineer improved crops by overexpressing the translation factor either in its natural form or after directed mutagenesis. More recently, innovative approaches like silencing or genome editing have proven their great potential in model and crop plants. The advantages and limits of these different strategies are discussed. This example illustrates the need to identify and characterize more host factors involved in virus multiplication and to assess their application potential in the control of viral diseases.

Strategies for Breeding Durable Resistance to Rice Blast Using pi21

Rice blast caused by Pyricularia oryzae (syn. Magnaporthe oryzae) is a destructive disease of rice worldwide that poses a serious threat to rice production. Strengthening blast resistance is an important objective in rice breeding programs. Race-specific resistance genes (R-genes) confer complete resistance to blast, but new races of blast pathogen can overcome it. After the first report of breakdown of resistance conferred by the R-gene Pik in 1963, this type of resistance has frequently been broken 1–7 years after the release of resistant varieties to farmers in Japan and other countries. To overcome this genetic vulnerability, Japanese rice breeders have focused on the use of race-nonspecific resistance in Japanese upland rice varieties whose resistance has been maintained for a long time. However, linkage drag between genes controlling this type of blast resistance and undesired traits has hindered its use. Therefore, researchers genetically dissected race-nonspecific resistance to rice blast. Among detected QTLs, a single recessive resistance gene, pi21, was identified by map-based cloning. The use of pi21 has improved durable resistance in rice breeding programs.

Development of Potato virus Y (PVY) resistant pepper (Capsicum annuum L.) lines using marker-assisted selection (MAS)

Several alleles at the pvr2 locus are known to control recessive resistance to Potato virus Y (PVY) in pepper. In this study, PVY resistant F2 pepper lines were developed from local germplasm carrying recessive genes (pvr21 and pvr22) using marker-assisted selection (MAS). The F1 and F2 generations were assessed for the presence of resistant/susceptible alleles (pvr2+/pvr21/pvr22) at the pvr2-elF4E locus using the tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) procedure. Our results show that ARMS-PCR can be used to successfully screen pepper genotypes for alleles that confer PVY resistance thereby contributing to the improvement of pepper production.