Leaf blight of wheat caused by Alternaria triticina in Argentina

A.E. Perelló*¹ and M.N. Sisterna²

¹ Consejo Nacional de Investigaciones Científicas y Tecnológicas, Centro de Investigaciones de Fitopatología-Facultad de Ciencias Agrarias y Forestales (Universidad Nacional de La Plata) - 60 y 119, (1900) La Plata, Buenos Aires, Argentina
² Comisión de Investigaciones Científicas (Provincia de Buenos Aires), Centro de Investigaciones de Fitopatología-Facultad de Ciencias Agrarias y Forestales (Universidad Nacional de La Plata) - 60 y 119, (1900) La Plata, Buenos Aires, Argentina

Accepted for publication 19/04/05

During routine investigations across the wheat (Triticum aestivum) growing area of the Buenos Aires Province, diseased leaf samples were collected from different wheat cultivars. Discoloured, oval lesions appeared on lower leaves. The disease progresses upwards, lesions enlarge and coalesce to irregular, dark blotches, often with chlorotic margins. Severely infected seeds are discoloured and shrivelled.

Necrotic tissue fragments were surface sterilized and plated on potato dextrose agar (PDA) from where 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 µm, with 1-10 transverse septa and 0-5 longitudinal septa, light brown-to-dark olive buff becoming darker with age. All isolates obtained were identified as A. triticina following the morphological descriptions by Anahosur (1978) and confirmed by comparison with reference strains of CABI Bioscience (IMI 289962 and IMI 178784) kindly sent by Dr D. Mercado (Université Catholique de Louvain, Unité de Phytopathologie, Belgique). One of the isolates has been lodged in the culture collection of La Plata Spegazzini (LPSC) (accession number 798).

Figure 1 (above): Leaf blight of wheat caused by Alternaria triticina Figure 2 (right): Conidia of Alternaria triticina LPSC 798 isolated from wheat Magnification x 400

Pathogenicity tests were conducted in the greenhouse. Susceptible wheat cultivars were inoculated at tillering and heading stages with a conidial suspension (2×10⁵ conidia per ml). Control plants were treated with distilled water. After 10 days, typical leaf blight symptoms developed on inoculated plants and A. triticina was recovered from the lesions. No symptoms appeared on the control plants.

A. triticina causes significant yield losses in wheat on the Indian subcontinent, from where it originates and has spread throughout the world (Prasada & Prabhu, 1962). Although A. triticina has been detected previously in Argentina on wheat leaves and seeds (Perelló 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 favourable weather conditions. As A. triticina 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 first published record of A. triticina on wheat in Argentina and on any host in this country.

References

Anahosur KH, 1978. Alternaria triticina. CMI Descriptions of Pathogenic Fungi and Bacteria. Nº 583. Kew, Surrey, England: Commonwealth Mycological Institute.

Perelló AE, Cordo C, Alippi HE, 1992. Tizón de la hoja del trigo ocasionado por Alternaria triticina Pras. & Prab. en Sud América. Proceedings of the VIII Jornadas Fitosanitarias Argentinas, Paraná, Entre Ríos, Argentina, 22.

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

The British Society for Plant Pathology