Identification and mapping of new genes for resistance to downy mildew in lettuce

Abstract Key message Eleven new major resistance genes for lettuce downy mildew were introgressed from wild Lactuca species and mapped to small regions in the lettuce genome. Abstract Downy mildew, caused by the oomycete pathogen Bremia lactucae Regel, is the most important disease of lettuce (Lactuca sativa L.). The most effective method to control this disease is by using resistant cultivars expressing dominant resistance genes (Dm genes). In order to counter changes in pathogen virulence, multiple resistance genes have been introgressed from wild species by repeated backcrosses to cultivated lettuce, resulting in numerous near-isogenic lines (NILs) only differing for small chromosome regions that are associated with resistance. Low-pass, whole genome sequencing of 11 NILs was used to identify the chromosome segments introgressed from the wild donor species. This located the candidate chromosomal positions for resistance genes as well as additional segments. F2 segregating populations derived from these NILs were used to genetically map the resistance genes to one or two loci in the lettuce reference genome. Precise knowledge of the location of new Dm genes provides the foundation for marker-assisted selection to breed cultivars with multiple genes for resistance to downy mildew.

Download Full-text

Distribution of Pathotypes of Rhynchosporium secalis and Cultivar Reaction on Barley in Alberta

Plant Disease ◽

10.1094/pdis.2003.87.4.391 ◽

2003 ◽

Vol 87 (4) ◽

pp. 391-396 ◽

Cited By ~ 11

Author(s):

K. Xi ◽

T. K. Turkington ◽

J. H. Helm ◽

K. G. Briggs ◽

J. P. Tewari ◽

...

Keyword(s):

Resistance Genes ◽

Environmental Conditions ◽

Rhynchosporium Secalis ◽

Pathogen Virulence ◽

Commercial Cultivars ◽

Major Resistance Genes ◽

Different Levels

Forty-four barley accessions and commercial cultivars with different levels of resistance to scald caused by Rhynchosporium secalis were evaluated for scald reaction from 1997 to 1999 at various sites in Alberta. The accessions Hudson, Atlas, Atlas 46, Atlas 68, Abyssinian, and Kitchin that have the major resistance genes were resistant to pathotypes of R. secalis at all sites. Although scald levels were low for these accessions, they were significantly different among years. Pathotypes of R. secalis and environmental conditions affected diseases levels on 32 commercial cultivars, resulting in significantly different scald reactions among sites and seasons. Resistance in commercial cultivars, AC Stacy, Kasota, and Seebe, held up at most sites with the majority of cultivars being intermediate to moderately susceptible. Cultivars that were previously considered resistant were intermediate in reaction and became increasingly susceptible at some sites from 1997 to 1999. Pathogen virulence was more diverse at the sites where the cultivars became increasingly susceptible compared with sites where the same cultivars were resistant. Scald reactions of the commercial cultivars depended on location, which reflected the presence of different pathotypes, as well as variation in environmental conditions. Consequently, scald management via cultivar choice will be dependent on location.

Download Full-text

Consensus mapping of major resistance genes and independent QTL for quantitative resistance to sunflower downy mildew

Theoretical and Applied Genetics ◽

10.1007/s00122-012-1882-y ◽

2012 ◽

Vol 125 (5) ◽

pp. 909-920 ◽

Cited By ~ 28

Author(s):

Patrick Vincourt ◽

Falah As-sadi ◽

Amandine Bordat ◽

Nicolas B. Langlade ◽

Jerome Gouzy ◽

...

Keyword(s):

Downy Mildew ◽

Resistance Genes ◽

Quantitative Resistance ◽

Consensus Mapping ◽

Major Resistance Genes

Download Full-text

Variation in seedling susceptibility to Bremia lactucae (lettuce downy mildew) in the absence of effective major resistance genes

Annals of Applied Biology ◽

10.1111/j.1744-7348.1984.tb02810.x ◽

1984 ◽

Vol 105 (1) ◽

pp. 147-157 ◽

Cited By ~ 10

Author(s):

JUDITH M. NORWOOD ◽

I. R. CRUTE ◽

KATHLEEN PHELPS

Keyword(s):

Downy Mildew ◽

Resistance Genes ◽

Bremia Lactucae ◽

Lettuce Downy Mildew ◽

Major Resistance Genes

Download Full-text

Transfer to wheat (Triticum aestivum) of small chromosome segments from rye (Secale cereale) carrying disease resistance genes

Journal of Applied Genetics ◽

10.1007/bf03195719 ◽

2010 ◽

Vol 51 (2) ◽

pp. 115-121 ◽

Cited By ~ 10

Author(s):

S. Fu ◽

Z. Tang ◽

Z. Ren ◽

H. Zhang

Keyword(s):

Triticum Aestivum ◽

Disease Resistance ◽

Resistance Genes ◽

Secale Cereale ◽

Small Chromosome ◽

Disease Resistance Genes ◽

Chromosome Segments

Download Full-text

Variation in Soybean Aphid (Hemiptera: Aphididae) Biotypes Within Fields

Journal of Economic Entomology ◽

10.1093/jee/toab058 ◽

2021 ◽

Author(s):

S J Bhusal ◽

R L Koch ◽

A J Lorenz

Keyword(s):

Resistance Genes ◽

Environmental Sustainability ◽

Soybean Aphid ◽

Aphis Glycines ◽

Aphid Resistance ◽

Soybean Cultivars ◽

Major Pest ◽

Single Field ◽

Aphis Glycines Matsumura ◽

Multiple Resistance Genes

Abstract Soybean aphid (Aphis glycines Matsumura (Hemiptera: Aphididae)) has been a major pest of soybean in North America since its detection in this continent in 2000 and subsequent spread. Although several aphid resistance genes have been identified, at least four soybean aphid biotypes have been discovered, with three of them being virulent on soybean cultivars with certain soybean aphid resistance genes. These biotypes are known to vary across years and locations, but information on their variation within single fields is limited. An investigation was conducted to study the variation of soybean aphid biotypes within single townships and fields in Minnesota. Screening of 28 soybean aphid isolates collected from seven soybean fields (six soybean fields in Cairo and Wellington Townships of Renville County, MN and one field in Wilmar Township of Kandiyohi County, MN) revealed the existence of multiple known biotypes of soybean aphid within single fields of soybean. We found up to three biotypes of soybean aphid in a single field. Two biotypes were found in five fields while only one field had only a single biotype. Three isolates presented reactions on a panel of resistant and susceptible indicator lines that were different from known biotypes. These results highlight the importance of characterizing soybean aphid biotypes in small geographical areas and utilizing generated knowledge to develop soybean cultivars pyramided with multiple resistance genes. The outcome will be decreased use of insecticides, thereby improving economic and environmental sustainability of soybean production.

Download Full-text

Development of Bacterial Spot on Near-Isogenic Lines of Bell Pepper Carrying Gene Pyramids Composed of Defeated Major Resistance Genes

Phytopathology ◽

10.1094/phyto.1999.89.11.1066 ◽

1999 ◽

Vol 89 (11) ◽

pp. 1066-1072 ◽

Cited By ~ 18

Author(s):

C. S. Kousik ◽

D. F. Ritchie

Keyword(s):

Disease Severity ◽

Resistance Genes ◽

Field Studies ◽

Residual Effects ◽

Specific Gene ◽

Near Isogenic Lines ◽

Bacterial Spot ◽

Isogenic Lines ◽

Major Resistance Genes ◽

Race 4

Disease severity caused by races 1 through 6 of Xanthomonas campestris pv. vesicatoria on eight near-isogenic lines (isolines) of Early Calwonder (ECW) with three major resistance genes (Bs1, Bs2, and Bs3) in different combinations was evaluated in the greenhouse and field. Strains representing races 1, 3, 4, and 6 caused similar high levels of disease severity, followed by races 2 and 5 on susceptible ECW. Race 3 caused severe disease on all isolines lacking resistance gene Bs2. Race 4, which defeats Bs1 and Bs2, caused less disease on isoline ECW-12R (carries Bs1 + Bs2), than on isolines ECW, ECW-10R (carries Bs1), and ECW-20R (carries Bs2). Similar results were obtained with race 4 strains in field studies conducted during 1997 and 1998. In greenhouse studies, race 6, which defeats all three major genes, caused less disease on isoline ECW-13R (carries Bs1 + Bs3) and ECW-123R (carries Bs1 + Bs2 + Bs3) than on isolines ECW, ECW-10R, ECW-20R, and ECW-30R (carries Bs3), but not on ECW-23R (carries Bs2 + Bs3). In greenhouse studies with commercial hybrids, strains of races 4 and 6 caused less disease on Boynton Bell (carries Bs1 + Bs2) than on Camelot (carries no known resistance genes), King Arthur (carries Bs1), and X3R Camelot (carries Bs2). Race 6 caused less disease on hybrid R6015 (carries Bs1 + Bs2 + Bs3) and Sentinel (carries Bs1 + Bs3) than on Camelot. Residual effects were not as evident in field studies with race 6 strains. Defeated major resistance genes deployed in specific gene combinations (i.e., gene pyramids) were associated with less area under the disease progress curve than when genes were deployed individually in isolines of ECW or commercial hybrids. Successful management of bacterial spot of pepper is achieved incrementally by integrating multiple tactics. Although there is evidence of residual effects from defeated genes, these effects alone likely will not provide acceptable bacterial spot control in commercial production fields. However, when combined with sanitation practices and a judicious spray program, pyramids of defeated resistance genes may aid in reducing the risk of major losses due to bacterial spot.

Download Full-text

CRISPR-Cas and Restriction-Modification Act Additively against Conjugative Antibiotic Resistance Plasmid Transfer in Enterococcus faecalis

mSphere ◽

10.1128/msphere.00064-16 ◽

2016 ◽

Vol 1 (3) ◽

Cited By ~ 43

Author(s):

Valerie J. Price ◽

Wenwen Huo ◽

Ardalan Sharifi ◽

Kelli L. Palmer

Keyword(s):

Antibiotic Resistance ◽

High Risk ◽

Enterococcus Faecalis ◽

Resistance Genes ◽

Treatment Options ◽

Antibiotic Resistance Genes ◽

Multidrug Resistant ◽

Content Type ◽

New Genes ◽

Restriction Modification

ABSTRACT Enterococcus faecalis is a bacterium that normally inhabits the gastrointestinal tracts of humans and other animals. Although these bacteria are members of our native gut flora, they can cause life-threatening infections in hospitalized patients. Antibiotic resistance genes appear to be readily shared among high-risk E. faecalis strains, and multidrug resistance in these bacteria limits treatment options for infections. Here, we find that CRISPR-Cas and restriction-modification systems, which function as adaptive and innate immune systems in bacteria, significantly impact the spread of antibiotic resistance genes in E. faecalis populations. The loss of these systems in high-risk E. faecalis suggests that they are immunocompromised, a tradeoff that allows them to readily acquire new genes and adapt to new antibiotics. Enterococcus faecalis is an opportunistic pathogen and a leading cause of nosocomial infections. Conjugative pheromone-responsive plasmids are narrow-host-range mobile genetic elements (MGEs) that are rapid disseminators of antibiotic resistance in the faecalis species. Clustered regularly interspaced short palindromic repeat (CRISPR)-Cas and restriction-modification confer acquired and innate immunity, respectively, against MGE acquisition in bacteria. Most multidrug-resistant E. faecalis isolates lack CRISPR-Cas and possess an orphan locus lacking cas genes, CRISPR2, that is of unknown function. Little is known about restriction-modification defense in E. faecalis. Here, we explore the hypothesis that multidrug-resistant E. faecalis strains are immunocompromised. We assessed MGE acquisition by E. faecalis T11, a strain closely related to the multidrug-resistant hospital isolate V583 but which lacks the ~620 kb of horizontally acquired genome content that characterizes V583. T11 possesses the E. faecalis CRISPR3-cas locus and a predicted restriction-modification system, neither of which occurs in V583. We demonstrate that CRISPR-Cas and restriction-modification together confer a 4-log reduction in acquisition of the pheromone-responsive plasmid pAM714 in biofilm matings. Additionally, we show that the orphan CRISPR2 locus is functional for genome defense against another pheromone-responsive plasmid, pCF10, only in the presence of cas9 derived from the E. faecalis CRISPR1-cas locus, which most multidrug-resistant E. faecalis isolates lack. Overall, our work demonstrated that the loss of only two loci led to a dramatic reduction in genome defense against a clinically relevant MGE, highlighting the critical importance of the E. faecalis accessory genome in modulating horizontal gene transfer. Our results rationalize the development of antimicrobial strategies that capitalize upon the immunocompromised status of multidrug-resistant E. faecalis. IMPORTANCE Enterococcus faecalis is a bacterium that normally inhabits the gastrointestinal tracts of humans and other animals. Although these bacteria are members of our native gut flora, they can cause life-threatening infections in hospitalized patients. Antibiotic resistance genes appear to be readily shared among high-risk E. faecalis strains, and multidrug resistance in these bacteria limits treatment options for infections. Here, we find that CRISPR-Cas and restriction-modification systems, which function as adaptive and innate immune systems in bacteria, significantly impact the spread of antibiotic resistance genes in E. faecalis populations. The loss of these systems in high-risk E. faecalis suggests that they are immunocompromised, a tradeoff that allows them to readily acquire new genes and adapt to new antibiotics.

Download Full-text