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Disease impact on the industry, consumers and country

The main potato variety used for processing (chipping) is Atlantic, which is very susceptible to late blight. There are some other varieties introduced by Frito Lay, however all of them are also very susceptible to LB. The main region, where potatoes are produced for the industry, is the Northwest (Sonora and Sinaloa States). In this region LB is not a constant problem, only in 1 of 5 years the climatic conditions are favorable for LB. Other important region for industrial potatoes is the Northeast (Coahuila and Nuevo Leon States). Climatic conditions in this region are favorable for LB 4 of 5 years. During the worst years, the availability of potatoes for the industry is very low and consequently the potato price is high. This is the same situation for the table potatoes. Yield variation is manly due to purple top (phytoplasms and Paratrioza cockerelli) and late blight. This year (2003), LB was a severe problem in the central part of Mexico, as always, because of the abundant rain. Purple top was a big problem in most of the potato regions of the country.

Disease occurrence and severity  

In Mexico, 60% of the potato acreage is grown in highlands during the rainy season. It is in these regions where each year late blight is a major problem. Some years are worse than others, but late blight is always present. The main states with LB problem are Mexico, Puebla, Tlaxcala, Hidalgo, Jalisco, Coahuila, Nuevo Leon, Chiapas, Veracruz.

Potato is the main crop affected by LB and rarely tomato.

The main inoculum sources are cull piles and volunteer plants. It has been demonstrated that sporangia and oospores may survive in the soil during the mild winter, however their relative importance as initial inoculum has not been assessed.

LB impact (foliar damage, yield losses, tuber rot occurrences)

In the highlands, yield losses may vary from 0 to 100%, depending on the varieties used and LB control. Foliar damage may be 100% if a susceptible variety and inefficient control are combined. If a susceptible variety and good control based on fungicide applications (2 per week) are used, then no foliar damage is present, However, if there is only one spray per week, then foliar damage may vary between 10–40% and yield losses 5–30%.

Tuber rot is rare in the central part of Mexico due to a suppressive effect of the soil. However in some States like Coahuila and Nuevo Leon tuber damage is important.

Disease managment successes and failures

Fungicide use

Most of the growers have to use a rotation of curative fungicides (Propamocarb, Metalaxyl, Cimoxanyl, Oxadixyl) and preventive fungicides (Maneb, clorotalonil, dimetomorf, copper fungicides). A total of 20 sprays are made when a susceptible variety is used, from which at least 10 are combinations of curative and preventive fungicides. In the worse regions (Jalisco State) growers have to spray 28 times.

Seed producers generally are able to control LB by using 2-3 sprays of fungicides per week. However, most of the growers producing table potatoes have some LB infection because they use less fungicide. The growers that use resistant varieties for the most part are poor and apply fungicides only 3–6 times during the growing season and generally have less than 10% of foliar infection.

Resistant cultivars

Ten years ago, 40% of the potato acreage was planted with resistant varieties. However, this acreage has been decreasing and in 2003 only 7% of the total potato acreage was planted with resistant varieties. Lack of certified seed of the resistant varieties and the preference for susceptible varieties in the market are among the factors that have influenced the decrease of acreage of the resistant varieties. Tollocan, Rosita, Norteña and Marciana are among the most important resistant varieties.

Forecasting

The application of fungicides is based mainly on the intensity of the rain and on the personal experience of the growers. Some forecast systems have been tested in Toluca Valley and results indicate that periodic sprays may work as well as the best forecasting system (Modified SIM-CAST) due to the constant conditions favorable for LB growth in this region.

Pathogen population characteristics

Virulence factors

In the Toluca Valley, 11 of the known virulence factors of Phytophthora infestans are present each year and it is assumed that there are more unknown virulence factors in this region of Mexico.

Mating type

Both mating types (A1 and A2) are usually present in Mexico in the same proportion. However in some years and regions the ratio A1/A2 is unbalanced.

Fungicide resistance

Resistant strains to metalaxyl have been found in all the potato growing regions in Mexico

Disease risks and/or major needs?

High risk is always present in 60% of the potato acreage in Mexico and LB control based on fungicides sprays is expensive and environmentally harmful. Thus, the major need is to have resistant varieties with high yield, good characteristics for the fresh and industry markets.

Any publications on late blight in the country?

Fernández-Pavia, S. P., Grunwald, N. J. and Fry W. E. 2004. Soilborne oospores of Phytophthora infestans in central Mexico survive winter fallow and infect potato plants in the field. Plant Disease 88:29-33.

Flier, W. G., Grunwald, N. J., Kroon, L. P. N. M., Sturbaum, A. K., Bosch, T. B. M. van den, Garay-Serrano, E., Lozoya-Saldana, H., Fry, W. E. and Turkensteen, L. J. 2003. The population structure of Phytophthora infestans from the Toluca Valley of Central Mexico suggests genetic differentiation between populations from cultivated potato and wild Solanum spp. Phytopathology 93 382-390.

Flores-Gutiérrez, F. X. 1997. Resistencia de campo al tizón tardío Phytophthora infestans (Mont.) de Bary en variedades y clones de papa Méxicanos. Agric.Téc. Méx. 23: 15-25.

Flores-Gutiérrez, F. X., and Cadena-Hinojosa, M. A. 1996. Evaluation of horizontal resistance and effects of R-genes in ten Mexican cultivars against potato late blight (Phytophthora infestans) under natural conditions in the central plateau of Mexico. Rev. Mex. Fitopatol. 102: 97-102.

Fry, W. E., Goodwin, S. B., Dyer, A. T., Matuszak, J. M., Drenth, A., Tooley, P. W., Sujkowski, L. S., Koh, Y. J., Cohen, B. A., Spielman, L. J., Deahl, K. L., Inglis, D. A., and Sandlan, K. P. 1993. Historical and recent migrations of Phytophthora infestans: chronology, pathways, and implications. Plant Dis. 77: 653-661.

 Goodwin, S. B., Spielman, L. J., Matuszak, J. M., Bergeron, S. N., and Fry, W. E. 1992. Clonal diversity and genetic differentiation of Phytophthora infestans populations in northern and central Mexico. Phytopathology 82: 955-961.

Grünwald, N. J., Cadena, M., Rubio, O., Rivera, A., and Fry, W. E. 1999. Contribution of host-resistance to integrated control of late blight in the Toluca valley. Phytopathology 89: S30.

Grunwald Niklaus J.,  Mateo A.  Cadena Hinojosa, Oswaldo Rubio Covarrubias, Antonio Rivera Peña, John S.  Niederhauser and William E.  Fry. 2002. Potato cultivars from the Mexican national program: Sources and durability of resistance against late blight (Phitophthora infestans). Phytopathology. Phytopathology 92: 688-693.

Grünwald, N. J., Flier, W. G., Sturbaum, A. K., Garay-Serrano, E., van den Bosch, T. B. M., Smart, C. D., Matuszak, J. M., Lozoya-Saldaña, H., Turkensteen, L. J., and Fry, W. E. 2001. Population Structure of Phytophthora infestans in the Toluca Valley Region of Central Mexico. Phytopathology 91: 882-890.

Grünwald, N. J., Rubio-Covarrubias, O. A., and Fry, W. E. 2000. Potato Late-Blight Management in the Toluca Valley: Forecasts and Resistant Cultivars. Plant Dis. 84: 410-416.

Lozoya-Saldaña, H., Grünwald, N. J. , Brown, C., Garay-Serrano, E., Sturbaum-Abud, A. and Belmar, C. 2003. Population substructuring of Phytophthora infestans on American potato clones in the Toluca Valley, México. Acta Horticulturae: 619: 183-188.

Mills, W. R., and Niederhauser, J. S. 1953. Observations of races of Phytophthora infestans in Mexico. Phytopathology 43: 454-455.

Niederhauser, J. S. 1954. Report on 1953 Toluca (Mexico) Field Test for Late Blight Resistance of Seeldings sent by Dr. F. J. Stevenson. 241-245.

Niederhauser, J. S. 1961. Genetic studies of Phytophthora infestans and Solanum species in relation to late-blight resistance in potato. 491-497 1:

Niederhauser, J. S. 1962. Evaluation of multigenic "field resistance" of the potato to Phytophthora infestans in 10 years of trials at Toluca, Mexico. Phytopathology 52: 746.

Niederhauser, J. S. 1991. Phytophthora infestans: The Mexican connection. 25-45 in: Phytophthora. J. A. Lucas, R. C. Shattock, D. S. Shaw and L. R. Cooke. J. A. Lucas, R. C. Shattock, D. S. Shaw and L. R. Cooke, eds. Cambridge, Cambridge University Press.

Niederhauser, J. S., Cervantes, J., and Servin, L. 1954. Late Blight in Mexico. Am. Potato J. 31: 233-237.

Niederhauser, J. S., Fernandez, J., Cervantes, J., Perez, G., and Delgado, S. 1959-1960. Tres variedades de papa resistentes al tizón tardío. Agricultura técnica en México 9: 28-30.

Parga Torres V. M., Jesús Fernández Elguezabal, Isaac Sánchez Valdez, Oswaldo A.  Rubio C. , J. Víctor Magallanes G. , Antonio Rivera P. , Carlos Díaz H., José T. Borbón S. , José L. Mendoza R. , Luis M. Macias V., Javier Ireta M.  , Arturo Paredes T. , Francisco X. Flores G., Humberto López D. , Román Flores L. , Telésforo Zavala Q.,  Mateo Cadena H. y Margarita Díaz V.  Norteña: Variedad de papa resistente al tizón tardío ( Phytophthora infestans Mont De Bary. 2001. Agricultura Técnica de México Vol. 27 (2): 175-176.

Rivera-Peña, A. 1990. Wild tuber-bearing species of Solanum and incidence of Phytophthora infestans (Mont.) de Bary on the Western slopes of the volcano Nevado de Toluca. 2. Distribution of Phytophthora infestans. Potato Res. 33: 341-347.

Rivera-Peña, A. 1990. Wild tuber-bearing species of Solanum and incidence of Phytophthora infestans (Mont.) de Bary on the Western slopes of the volcano Nevado de Toluca. 3. Physiological races of Phytophthora infestans. Potato Res. 33: 349-355.

Rivera-Peña, A., and Molina-Galan, J. 1989. Wild tuber-bearing species of Solanum and incidence of Phytophthora infestans (Mont.) de Bary on the Western slopes of the volcano Nevado de Toluca. 1. Solanum species. Potato Res. 32: 181-195.

Rivera Peña A. and Rubio C.O.A. 1999. The mexican potato gen bank and late blight  (Phitophthora infestans) resistant varieties released. Proceedings of the Global Initiative on Late Blight Conference. Quito, Ecuador.

Rubio Covarrubias, O. A., Rivera Peña, A., Rangel González, J. A., Cadena Hinojosa, M., Flores López, R., Rocha Rodríguez, R., Magallanes González, J. V., Ortíz Trejo, C., Díaz Hernandez, C., López Delgado, H., Zavala Quintana, T. E., Díaz Valasis, M., and Paredes Tenorio, A. 2000. Manual para la Producción de Papa en las Sierras y Valles Altos del Centro de México. Instituto Nacional de Investigaciónes Forestales, Agrícolas y Pecuarias, Zinacantepec, Estado de México, México.

Rubio Covarrubias O.A. and Grunwald N.J. 2000. Relationship between nitrogen fertilization of potato plants and late blight severity. 84 th Annual Meeting of the Potato Association of America. Colorado Springs, Colorado, USA.

Rubio Covarrubias O.A., Díaz H. Carlos y Díaz V. Margarita. 2002. Field evaluation of horizontal and vertical resistance to late blight (Phitophthora infestans)  in potato in the Toluca Valley, Mexico. Abstracts GILB Conference: Late Blight, Managing the Global Threat. Hamburg, Germany.

Rubio Covarrubias, Oswaldo A.; Cadena Hinojosa, M. y López Delgado H.  2002. soil application of lime decreases foliar and tuber late blight (Phytophthora infestans)  infection in potatoes grown in Toluca, Mexico.Abstracts XXVI^th  International Horticultural Congress. Toronto Canadá. (Aceptado para su presentación).

Rubio Covarrubias O.A. and Grunwald N.J. 2000. Relationship between nitrogen fertilization of potato plants and late blight (Phitophthora infestans)  severity. Abstracts 84^th Annual Meeting of the Potato Association of America. Colorado Springs, Colorado, USA.

Rubio Covarrubias O.A., Magallanez G.V., Díaz H.C., Rivera P.A., López D.H. y Zavala Q.T.E. 2000. Zafiro y Malinche: Nuevas variedades de Papa Mexicanas. Memorias del XIX Congreso de la Asociación Latinoamericana de la Papa. La Habana, Cuba. p. 94.

Rivera Peña A., Sánchez I. Garza G., Yépes L., López H., Rubio O., Díaz C. Y Zavala T. 2000. Modesta Blanca: Nueva variedad de papa resistente al tizón tardío (Phitophthora infestans). Memorias del XIX Congreso de la Asociación Latinoamericana de la Papa. La Habana, Cuba.

Ugent, D. 1968. The potato in Mexico: Geography and primitive culture. Economic Botany 22: 108-123.

Is tuber blight an increasing problem?

In Mexico, tuber LB is not a problem. It seems to be a contradiction that while foliar infection is a big problem, tuber LB is not. The explanation is that in most of the potato growing areas in the highlands, where LB is a major problem, soils have a suppressive effect. This suppressive effect is likely associated with microorganisms living in the soil, but these microorganisms have not been identified yet. Other factor, which also could contribute to lessen the tuber LB problem, is the fact that table tubers generally are not stored — they are sold in few days after harvest. This is because in Mexico, potatoes can be harvested all year around.

Other comments

Lb is a major concern in potato production in Mexico, however there also others important problems like the potato psillid (Paratrioza cockerelli) and phytoplasms (Purple top).

The LB problem may be solved by a combination of the use of resistant varieties, production of seed of these varieties and a campaign among consumers and marketers for acceptance of these varieties.

Report prepared by Oswaldo Rubio, INIFAP, Programa Nacional de Papa, Metepec, Mexico. Email: oswaldorubio(at)terra.com.mx