Puccinia pittieriana
(common rust of potato)

P. pittieriana is a microcyclic rust fungus occurring on potato [Solanum tuberosum], tomato [Solanum lycopersicum] and wild species of Solanum in South and Central America and is an EPPO A1 quarantine organism for Europe (EPPO, 1988). Probably capable of causing disease on potatoes in cool, moist regions of the temperate and tropical zones, this fungus can be transported in fresh or dried plant material or crop debris in soil. As the basidiospores are short-lived and not produced in large numbers, the fungus is not spread far by natural agents such as the wind.

P. pittieriana was first recorded in Costa Rica, where it was collected on cultivated potato [Solanum tuberosum], high on the slopes of Irazu volcano in 1903 and 1904 by Pittier (Arthur, 1920) and it was formally described by Hennings (1904). The rust was reported again in 1916 by Holway on wild potato (Hennings, 1904; Kern, 1933). Pachano reported it attacking both potato and tomato [Solanum lycopersicum] in Ecuador in 1919 (Kern, 1933). Chardon and Toro (1930) described its presence in Colombia on potato, causing severe losses in the central Cordillera region, primarily in Nariño and Tolima. In Peru, Abbott (1931) found this rust on potato only near Tarma. It was identified by Chardon in Venezuela in 1932 (Kern, 1933).

Reddick (1932) reported the presence of P. pittieriana on the wild potato, Solanum demissum, in central Mexico. Alvarez (1976) listed this species in Mexico, but no specimens exist in national collections.

In Brazil, Solanum rust was detected on cultivated potatoes and first reported by Goncalves da Silva (1939) for the state of Espirito Santo; it was later found in the state of São Paulo (Hennen et al., 1982). In Bolivia, Alandia-Borda (1966) reported P. pittieriana on leaves of the wild potato, Solanum platypterum, in Potosi, but this record is now doubtful (EPPO, 2000).

UK CAB International (1994) shows P. pittieriana in Bolivia, Brazil, Colombia, Costa Rica, Ecuador, Mexico, Peru, Paraguay and Venezuela. Paraguay has been listed because of an error in a citation of Hennings (1904); he only reports P. pittieriana as present in Costa Rica.

See also CABI\EPPO (1997).

As dissemination of the disease has not been recorded on tubers in trade, there is no apparent risk of spread of this disease on plant material, unless dried or infected living specimens are distributed for research to regions free of P. pittieriana (EPPO, 1988). Thurston (1973) considered this pathogen to have “limited threat potential”, but noted that it could be established in tropical countries where potatoes [Solanum tuberosum] are grown at high altitudes.

Field observations were made on cultivated tomato [Solanum lycopersicum], cultivated potatoes (Solanum tuberosum subsp. andigenum and subsp. tuberosum), and the wild potato, Solanum demissum. All other records of susceptibility listed are the results of greenhouse tests (Reddick, 1932; Buritica et al., 1968).

P. pittieriana affects the following cultivated and wild potato species in greenhouse tests:

- Cultivated potato: Solanum ajanhuiri, Solanum curtilobum, Solanum juzepczukii, Solanum phureja, S. tuberosum subsp. andigenum and S. tuberosum subsp. tuberosum.

- Wild potato species: Solanum antipoviczii [Solanum stoloniferum], Solanum cardiophyllum, Solanum commersonii, S. demissum, Solanum ehrenbergii, Solanum gibberulosum, Solanum famatinae [Solanum spegazzinii], Solanum malinchense [Solanum stoloniferum], Solanum oplocense, Solanum parodii [Solanum chacoense], Solanum schickii, Solanum simplicifolium [Solanum microdontum], Solanum stoloniferum and Solanum verrucosum (Buritica et al., 1968).

- Other species of Solanum affected are Solanum caripense and Solanum nigrum in Colombia (Buritica et al., 1968).

Arthur (1922b) considered the source of inoculum for commercial crops to be wild hosts in Costa Rica and Ecuador.

The development and spread of the fungus requires average temperatures of approximately 10°C with 10-12 h of free moisture on the plant surface. Inoculum is wind-borne, spreading from earlier sown crops or wild hosts (Laundon and Rainbow, 1971). In vitro, teliospores germinate in 1 hour to produce a basidium (promycelium) which, at temperatures above 15°C, usually continues to grow vegetatively. Below 15°C, most basidia give rise to four basidiospores (sporidia) in 3-24 h. When detached, the basidiospores germinate immediately and the first symptoms appear in 14-16 days on potato at temperatures of 16°C or below. Lesions are fully grown in 20-25 days. Teliospores mature in 30-40 days after inoculation (French, 2001a). Lesion size may vary on different species of Solanum and possibly with different races (Castaño, 1952).

Common rust is the only rust that affects tomato [Solanum lycopersicum]; therefore, there can be no confusion on this crop. Potatoes [Solanum tuberosum] are affected by both common rust and deforming rust (Aecidium cantense), but these diseases produce different symptoms. Potato common rust produces typical telia in lesions on leaves and stems, whereas deforming rust produces saucer-shaped aecia and growth distortions of the leaves and stems (French, 2001a,b).

At least one sequence for the LSU region of rDNA is publicly available for comparison (NCBI, 2009).

There are no records of transported contaminated crop produce causing spread of P. pittieriana. The only risk of spread is by the transport of infected plants or plant material, which is usually prohibited. Field-grown potatoes [Solanum spp.] from highland areas in countries where this disease is known should not enter international trade. There is no need for detection and inspection procedures if appropriate transport restrictions are observed.

Potatoes [Solanum tuberosum] can be damaged by another disease, known as “deforming rust”, caused by Aecidiumcantense. Deforming rust also attacks ulluco (Ullucus tuberosus). These two rusts usually occur in distinct geographical areas in the Andes. Deforming rust occurs primarily in Peru, but has also been reported in Argentina. Symptoms are distinct; common rust produces typical Puccinia telia in lesions on leaves and stems, whereas deforming rust produces groups of saucer-shaped aecia on leaves, petioles and stems, causing distortion and swelling of the leaves and stems (French, 2001b).

Additional rust fungi reported on Solanum species, other than cultivated potato, are described and illustrated by Kern (1933) and Pardo-Cardona (2002). These are differentiated primarily by minor differences in teliospore morphology. Puccinia solani-tristis is reported on a number of wild Solanum species in Brazil (Mendes et al., 1998); that and eight other species are reported from Colombia (Pardo-Cardona, 2002).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control and Sanitary Measures

In areas of the steeply sloping Andes of Peru, where the disease is most severe, farmers often choose to plant potatoes [Solanum spp.] in fields in nearby microclimates that are less favourable to the disease (French et al., 1972).

Chemical Control

In northern Ecuador, where losses due to common rust can limit production, chemical control has been tested over a number of years. Diaz and Echevarria (1963) reported that the organic fungicides folpet, maneb, thiram and zineb, applied every 14 days, gave better preventative control than five other fungicides tested. Better results were obtained with the systemic fungicides oxycarboxin and propiconazole (Velastegui, 1991). Quijano and Molina Valero (1988) reported best control in field tests in Colombia with Tilt (propiconazole), Plantvax (oxycarboxin), and Sicarol 500 (pyracarbolid) reducing disease more than 80%; best yields were obtained with Plantvax, Tilt and Elosal 720 (azufre). Plantvax and Tilt inhibited teliospore germination in vitro.

Chemical control is not common in Peru, although applications of metiram every 7-10 days have been shown to reduce incidence (French et al., 1972).

Host Resistance

Resistance to common rust was found when 136 potato cultivars were screened by natural field infection at two locations in Tungurahua province, Ecuador. A total of 12 cultivars were reported as having adequate resistance. The three most resistant were Ecuadorian Potato Collection (Coleccion Ecuatoriana de Papa) numbers 305, 314 and 503 (Coronel-Orijalva, 1970).

The genetic relationship of P. pittieriana to other species of Puccinia on Solanum in South America should be studied to clarify the actual distribution of these pathogens and the threat of their introduction.

Peru: Centro Internacional de la Papa (CIP), Apartado 1558, Lima 12, http://www.cipotato.org

06/11/09 Updated by: