May 3, 2005
Source: British Society for Plant Pathology, New Disease Reports, Vol. 11 [edited] <http://www.bspp.org.uk/ndr/july2005/2005-35.asp>

Leaf blight of wheat caused by aAlternaria triticina in Argentina
A.E. Perello, Consejo Nacional de Investigaciones Cientificas y Tecnologicas; and M.N. Sisterna, Comision de Investigaciones Cientificas (Provincia de Buenos Aires), Centro de Investigaciones de Fitopatologia-Facultad de Ciencias Agrarias y Forestales (Universidad Nacional de La Plata) - 60 y 119, (1900) La Plata, Buenos Aires, Argentina. Accepted for publication 19 Apr 2005.

Cultivars of wheat (_Triticum aestivum_) in the wheat-growing area of Buenos Aires Province expressed disease symptoms, including discolored, oval lesions on lower leaves. The disease progressed upwards; lesions enlarged and coalesced to form irregular, dark blotches, often with chlorotic margins. Severely infected seeds are discolored and shriveled.

Necrotic tissue fragments were surface-sterilized and plated on potato dextrose agar (PDA) from which _Alternaria_ specimens were isolated. Morphobiometrical and cultural features of the fungus were examined on PCA (potato carrot agar). Conidia were irregularly oval, ellipsoid conical, gradually tapering into a beak, 15-92 x 8-35 micrometers with 1-10 transverse septa and 0-5 longitudinal septa, light brown-to-dark olive buff in color, becoming darker with age.

All isolates obtained were identified as _A. triticina_ [At], following the morphological descriptions by Anahosur (1978), and were confirmed by comparison with reference strains of CABI Bioscience (IMI 289962 and IMI 178784) kindly sent by Dr. D. Mercado (Universite Catholique de Louvain, Unite de Phytopathologie, Belgique). One of the isolates has been lodged in the culture collection of La Plata Spegazzini (LPSC) (accession number 798).

Pathogenicity tests were conducted in the greenhouse. Susceptible wheat cultivars were inoculated at tillering and heading stages with a conidial suspension (200 000 conidia per ml). Control plants were treated with distilled water. After 10 days, typical leaf blight symptoms developed on inoculated plants, and At was recovered from
the lesions. No symptoms appeared on the control plants.

Infection of wheat by Alternaria leaf blight [ALB] caused by At results in significant yield losses in wheat on the Indian subcontinent, from where it originates and has spread throughout the world (Prasada & Prabhu, 1962). Although At has been detected previously in Argentina on wheat leaves and seeds (Perello et al., 1992), it has probably existed as a minor pathogen for many years without being noticed.

The recent increase in the severity of leaf blight may be due to new  cultural practices, such as conservation tillage, nitrogen fertilization, irrigation, use of new germplasm as well as favorable weather conditions. As At is a quarantine pathogen in many countries, it would be important to investigate the incidence and importance of
this disease in Argentinean wheat areas.

This is the 1st published record of At on wheat in Argentina and on any host in this country [but see Perello et al. below. - Mod.JW].

References:

Anahosur KH, 1978. Alternaria triticina. CMI Descriptions of Pathogenic Fungi and Bacteria. N [degrees] 583. Kew, Surrey, England: Commonwealth Mycological Institute.

Perello AE, Cordo C, Alippi HE, 1992. Tizon de la hoja del trigo ocasionado por Alternaria triticina Pras. & Prab. en Sud America. Proceedings of the VIII Jornadas Fitosanitarias Argentinas, Parana, Entre Rios, Argentina, 22.

Prasada R, Prabhu AS, 1962. Leaf blight of wheat caused by a new species of Alternaria. Indian Phytopathology 15, 292-293.

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[Alternaria leaf blight [ALB] is generally regarded as a weak, minor pathogen that mainly affects old local cultivars, particularly of durum wheat. The disease is common in the eastern and central areas of the Asian Subcontinent. ALB can be very severe if environmental conditions are favorable for disease development; major losses can result when susceptible cultivars are grown.

Link: <http://wheat.pw.usda.gov/ggpages/wheatpests.html#alternaria> - Mod.DH]