Viral Resistance

Natural Synergy

Traditional Chinese Medicine

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Finding useful markers for MAS of disease resistance requires several conditions. These include selection of a durable resistance source, use of characterized pathogen strains, a robust phenotyping method, sufficient polymorphism among parents, and simple genetic control of the resistance trait. Many of the resistance genes or QTLs are pathogen strain or race-specific. Therefore, it is essential to characterize the target pathogen population in order to select proper resistance sources and specific resistance markers for MAS.

Since the pioneering study of the Tm-2a resistance gene (Young etal. 1988), at least 11 virus resistance genes and one QTL locus, all originating from wild relatives oftomato, have been mapped and associated with DNA-based molecular markers which allow for MAS (Table 11). Three of these 12 genes/QTLs (Sw-5, Tm-2, Tm-22 )havebeenclonedasaresult ofthemolec-ular marker work (Folkertsma et al. 1999; Brommon-schenkel et al. 2000; Lanfermeijer et al. 2003,2005).

Table 11. Resistance genes and markers for the most common tomato viral diseases

Agent and disease

Resistance gene(s)

Molecular marker

Chromosome

Source

Reference

Alfamovirus

Alfalfa mosaic virus (AMV) Begomoviruses

Tomato chlorotic mottle virus (TCMV) Tomato mottle virus (ToMoV)

Tomato yellow leaf curl virus (TYLCV)

Cucumovirus

Cucumber mosaic virus (CMV)

Curtovirus

Curly top virus (CTV)

akac Beet curly top virus (BCTV)

Poleroviruses

Potato leaf roll virus (PLRV) Tomato yellow top virus (TYTV) Potexvirus

Pepino mosaic virus (PepMV) Potato virus X(PVX)

Am tcm-1

Ty-3 QTL

Ty-1

Ty-2

Ty-3

na na

Multigenic

AFLP

RAPD, SCAR, CAPS 6

RAPD 6

RFLP 6

RFLP 11

RAPD, SCAR, CAPS 6

RAPD 6

na 6

na 6

RFLP 12

S. habrochaites

S. peruvianum/ S. lycopersicumb S. chilense S. chilense

S. chilense S. habrochaites S. chilense S. pimpinellifolium S. cheesmaniae S. peruvianum

S. chilense

S. peruvianum

S. habrochaites S. pimpinellifolium

S. peruvianum

S. peruvianum

S. chilense S. habrochaites S. lycopersicum

Parrella et al. 2004

Giordano et al. 2005; Ji et al. 2007

Griffiths 1998; Griffiths and Scott 2001; Ji and Scott 2005; Ji and Scott 2006; Ji et al. 2007

Zamir et al. 1994; Chagüé et al. 1997; Ji and Scott 2005; Agrama and Scott 2006; Hanson et al. 2006; Ji and Scott 2006; Ji et al. 2007

Stamova and Chetelat 2000

Martin and Thomas 1986; Thomas and Mink 1998

Hassan and Thomas 1988; Thomas and Mink 1998 Hassan and Thomas 1988; Thomas and Mink 1998

Soler and Nuez 2000; Picó et al. 2002

Rashid et al. 1989

a Not available b The germplasm source of tcm-1 is not definitively known

Table 11. (continued)

Agent and disease

Resistance gene(s)

Molecular marker

Chromosome

Source

Reference

Potyvirus

Potato virus Y (PVY)

na

na

na

S.

pimpinellifolium

Legnani et al. 1997; Parrella et al. 2002

and Tobacco etch virus (TEV)

pot-1

AFLP

3

S.

habrochaites

Tobamovirus

Tomato mosaic virus (ToMV)

Tm-1

SCAR

2

S.

habrochaites

Ohmori et al. 1996;

aka Tobacco mosaic virus (TMV)

Tm-2

Cloned

9

S.

peruvianum

Lanfermeijer et al. 2003, 2005

Tm-21

Cloned

9

S.

peruvianum

(aka Tm-22)

Tospoviruses

Groundnut bud necrosis virus (GBNV)

Sw-5

PCR, Cloned

9

S.

peruvianum

Folkertsma et al. 1999

Groundnut ringspot virus (GRSV)

Sw-5

PCR, Cloned

9

S.

peruvianum

Boiteux and Giordano 1993

Tomato chlorotic spot virus (TCSV)

Sw-5

PCR, Cloned

9

S.

peruvianum

Boiteux and Giordano 1993

Tomato spotted wilt virus (TSWV)

Sw-la

na

na

S.

peruvianum

Finlay 1953; Stevens et al. 1992;

Sw-lb

na

na

S.

lycopersicum

Stevens et al. 1996b; Rosello et al. 1998;

sw-2

na

na

S.

lycopersicum

Folkertsma et al. 1999;

sw-3

na

na

S.

lycopersicum

Brommonschenkel et al. 2000;

sw-4

na

na

S.

lycopersicum

Rosello et al. 2001; Scott et al. 2005a;

Sw-5

PCR, Cloned

9

S.

peruvianum

Gordillo et al. 2007

Sw-6

na

9

S.

peruvianum

"Sw-7"d

na

na

S.

chilense

c Also known as d Sw-7 is not recognized in the literature as the gene responsible for this resistance at the time of this publication. Statistical evidence has been insufficient to report a single gene, nevertheless, all available evidence suggests resistance is conferred by a single dominant gene (Stevens unpublished data)

The 12 genes/QTLs represent resistance to six virus genera, Alfamovirus, Begomovirus, Cucu-movirus, Potyvirus, Tobamovirus, and Tospovirus (Table 11), which are pathogenic to tomato. Interestingly, resistance to all the major viral diseases of tomato has been identified from wild tomato species. Furthermore, several new viral resistance genes have been successfully introgressed from wild relatives into commercially released lines during the last decade and MAS has played a major role in this process. MAS is of major importance within a wide variety of commercial tomato breeding companies, especially when breeding for disease resistance (MR Stevens, pers. comm.).

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