Resistance to bacterial spot race T4 and breeding for durable, broad-spectrum resistance to other races.
J.W. Scott1, S. F. Hutton1, J.B. Jones2, D.M. Francis3, and S.A. Miller4
1University of Florida, IFAS, Gulf Coast Research & Education Center, 14625 CR 672, Wimauma, FL 33598, USA email: jwsc@ufl.edu, sfhutton@ufl.edu
2University of Florida, IFAS, Plant Pathology Dept., 2515 Fifield Hall, P.O. Box 110680, Gainesville, FL 32611, USA email: JBJ@ufl.edu
3 Dept. of Horticulture and Crop Science, Ohio Agricultural Research and Development Center, The Ohio State University, 1680 Madison Avenue, Wooster OH 44691 francis.77@osu.edu
4Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, 1680 Madison Avenue, Wooster OH, 44691 miller.769@osu.edu
Four races of the bacterial spot pathogen in tomato have been isolated under field conditions (Jones et al., 2005) with some evidence that there might be a fifth race based on a lack of hypersensitivity to the avrXv4 gene in a strain that mutated from race T3 (Minsavage et al., 2003). In Florida race T3 largely replaced race T1 and the former was antagonistic to the latter (Jones et al., 1998). However, race T4 has been isolated in several locations in Florida since 1999 and it is evident that the best protection will be provided by varieties with resistance to races T3 and T4. In 2002, breeding line Fla. 8233 was the only line out of nearly 300 lines being bred for T3 resistance with homozygous resistance to a mixed infection of races T3 and T4. A breeding project was then started using this line as a source of resistance to both T3 and T4. Previously we have found sources of resistance to races T1, T2, and T3 (see Scott et al., 2003). Resistance to T4 has been identified in breeding lines Fla. 8233, as mentioned, and Fla. 8326 (Scott, 2004). The former likely derived the T4 resistance from PI 114490 while the latter appeared to have T4 resistance from S. piminellifolium accession PI 126932. Observations over several seasons have verified that these breeding lines have resistance, but also that their resistance is only partial under high disease pressure. Thus, we have been searching for other resistance sources and need to verify that the accessions mentioned above do in fact have T4 resistance. This is a main objective of this report. The broad goal of our resistance program is to identify bacterial spot resistance genes, determine their effects on all the tomato races, and to breed tomato varieties with broad-spectrum resistance that will not break down to races of the pathogen that may mutate in the future. So far, this pathogen has mutated at least 4 races in the absence of monocultures of resistant varieties. Herein, we present some data on some genotypes that appear to have some broad spectrum resistance.
In 2005 16 genotypes including a susceptible control were grown in a completely randomized design with three blocks and five plant plots at Citra, Florida (Table 1). The breeding lines were selected based on either previous performance under T4 infection and the accessions were included based on their presence in pedigrees of resistant breeding lines or on their resistance to other races of the pathogen. The plants were inoculated with race T4 and each plot was rated for disease severity using the Horsfall-Barratt (1945) scale. Data are also presented for eight breeding lines and five control genotypes that were inoculated for races T1 and T2 in Ohio and T4 in Florida at various locations and seasons (Table 2).
PI 114490 and PI 128216-T2 had less disease than did the susceptible control Horizon (Table 1). The other four PI’s did not have significantly less disease than did Horizon. This included PI 126932 which was expected to be resistant based on the resistance in Fla. 8326 which has this PI (and not Hawaii 7981) in it’s pedigree as a T3 resistance source. PI 126932 was also susceptible at Balm in 2005 (data not shown). Later in the season at Balm PI 126932 did not have bacterial spot lesions in the top of the plant and it is possible that this accession may have a mechanism that does not prevent an initial infection under conditions which favor the disease, but does prevent the secondary spread of the disease. Fla. 8326 and a related breeding line with this PI in their pedigrees did show resistance in the Citra trial (Table 1). This suggests resistance came from PI 126932 unless there is a mistake in the pollen originally used in these crosses. Two of the resistant breeding lines had PI 128216-T2 in their pedigree and thus it appears that resistance has been derived from this source. Furthermore, Fla. 8517 was highly resistant to T4 at Citra (another experiment) and Balm (Table 2). Fla. 8517 has PI 128216-T2 in it as well as PI 114490 and may have resistance gene(s) from both sources. However, Fla. 8517 did not look as resistant later in the season at Balm and more recently in Fletcher, NC. Further studies with this line are underway. The other breeding line with resistance has Richter’s Wild, a small cherry tomato, in its pedigree. This line was sent to us by Randy Gardner at North Carolina State University where he is working with it for it’s resistance to late blight. Unfortunately Richter’s Wild was not in this test but did show bacterial spot race T4 resistance at our old research center in 2003.
Forty breeding lines were tested for T1 and T2 resistance in Ohio and in several Florida locations for T4 resistance; those with the best broad spectrum resistance are in Table 2. This includes Fla. 8233 and Fla. 8326 that have already been mentioned above. Two of the lines derived from Fla. 8233 (Fla. 7776 and Fla. 8044 A lines) show a fair level of broad spectrum resistance (Table 2) and improved horticultural type. Many of the lines derived from Fla. 8233 have not had good resistance. This may relate to low disease pressure when the F2 selections were made in 2003. The most severe disease pressure was in the summer 2005 at Balm and higher disease ratings resulted in this germplasm (Table 2). The data indicate that there is potential to develop broad spectrum resistance. A gene from PI 114490 has shown resistance to races T2, T3, and T4 (Yang et al., 2005). Other genes with effects on multiple races may be identified in the future. However, it would be desirable to develop higher levels of resistance. This may require combining genes from different sources. Sam Hutton is studying the inheritance of T4 resistance from several of the sources mentioned and will be attempting to find molecular markers linked to the resistance genes. From this work it is hoped that breeding can be expedited with marker assisted selection and that testing can be done to verify which genes have broad-spectrum effects. Use of such genes may finally provide commercially acceptable varieties with durable bacterial spot resistance.
Literature cited:
Horsfall, J.G. and R.W. Barratt. 1945. An improved grading system for measuring plant diseases. Phytopathology 35:655.
Jones, J.B., H. Bouzar, G.C. Somodi, R.E. Stall, K. Pernezny, G. El-Morsy, and J.W. Scott. 1998. Evidence for the preemptive nature of tomato race 3 of Xanthomonas campestris pv. vesicatoria in Florida. Phytopathology 88:33-38.
Jones, J.B., G.H. Lacy, H. Bouzar, G.V. Minsavage, R.E. Stall and N.W. Schaad. 2005. Bacterial spot-Worldwide distribution, importance and review. Acta Horticulurae 695:27-33.
Minsavage, G.V., B. Balogh, R.E. Stall and J.B. Jones. 2003. New tomato race of Xanthomonas campestris pv. vesicatoria associated with mutagenesis of tomato race 3 strains. Phytopathology 93:S62.
Scott, J.W., D.M. Francis, S.A. Miller, G.C. Somodi, an J.B. Jones. 2003. Tomato bacterial spot resistance derived from PI 114490: Inheritance of resistance to race T2 and relationship across three pathogen races. J Amer. Soc. Hort. Sci. 128:698-703.
Scott, J.W., J.B. Jones, and D.M. Francis. 2004. Resistance to bacterial spot race T4 in tomato. Proc. Tomato Breeders Roundtable, Beltsville, MD
Yang, W., S.A. Miller, J.W. Scott, J.B. Jones, and D.M. Francis. 2005. Mining tomato genome sequence databases for molecular markers: Application to bacterial resistance and marker assisted selection. Acta Horticulturae 695:241-249.
Table 1.
Bacterial spot race T4 disease severity for tomato (S.
lycopersicum) and
S.
pimpinellifolium
genotypes at Citra, Florida Fall 2005.
|
|
Disease severityz |
|
|
|
|
|
|
(Fla. 7655 ×RW) F5 |
6.7 ay |
Hawaii 7998 and Richter’s Wild |
|
PI 126932-1-2x |
6.0 ab |
|
|
PT 195002 |
5.7 a-c |
|
|
Fla. 7335 |
5.3 bc |
Hawaii 7998 |
|
Horizon |
5.3 bc |
Susceptible control |
|
PI 155372-S1 |
5.0 b-d |
|
|
(Fla. 8022 ×RW) F5 |
5.0 b-d |
Richter’s Wild |
|
PI 126428 |
4.7 c-e |
|
|
Fla. 8326 |
4.0 de |
PI 126932 and Hawaii 7998 |
|
PI 128216-T2x |
4.0 de |
|
|
PI 114490 |
3.7 ef |
|
|
(050624-SBK) F7 |
3.7 ef |
PI 128216, Hawaii 7981 and Hawaii 7998 |
|
(Fla. 7987 × Fla. 7981) F6 |
3.7 ef |
PI 126932, Hawaii 7998 |
|
(050542-SBK) F7 |
3.7 ef |
PI 128216 and Hawaii 7998 |
|
Fla. 8233 |
3.7 ef |
PI 114490, Hawaii 7981 and Hawaii 7998 |
|
(Fla. 7776 × RW) F4 |
2.7 f |
Richter’s Wild |
|
z Horsfall-Barrett (1945) scale, lower numbers indicate less disease. y Mean separation in column by Duncan’s multiple range test at P<0.50. x S. pimpinellifolium accession. |
||
|
|
Location and race |
|||||
|
|
Fremont Ohio |
Wooster Ohio |
Homested |
Balm |
Citra |
Balm |
|
Genotypey |
T1 |
T2 |
T4 |
T4 |
T4 |
T4 |
|
|
|
|
|
|
|
|
|
Fla. 8233 |
2.5 |
4.0 |
3 |
4.5 |
4 |
4 |
|
Fla. 8286 |
3.5 |
3 |
2 |
6 |
5 |
(5.5)x |
|
Fla. 8326 |
4.5 |
4.5 |
3 |
5 |
4 |
4.5 |
|
(Fla. 7776 × Fla. 8233) F4A |
3 |
2.5 |
3 |
5 |
4 |
5 |
|
(Fla. 7776 × Fla. 8233) F4B |
5 |
4.5 |
3 |
7 |
4.5 |
--- |
|
(Fla. 8044 × Fla. 8233) F4A |
4.5 |
5 |
2 |
6.5 |
6 |
4.5 |
|
(Fla. 8044 × Fla. 8233) F4B |
3.5 |
4.5 |
2 |
7 |
5.5 |
6 |
|
Fla. 8517 |
--- |
--- |
--- |
--- |
3 |
3 |
|
PI 114490 |
2 |
2 |
1 |
3.5 |
4.5 |
2.5 |
|
Hawaii 7998 |
5 |
7 |
4 |
7 |
6 |
6 |
|
Hawaii 7981 |
7 |
6 |
5 |
7 |
6 |
6.5 |
|
C-28 |
4.5 |
5.5 |
4 |
7 |
5.2 |
5 |
|
Susceptible controlsw |
6.5 |
6.0 |
5 |
7 |
5.2 |
7 |
|
z
Horsfall-Barratt (1945) Scale. Lower
numbers indicate less disease. |
||||||