Survival of pathogenic Colletotrichum isolates on dormant buds, twigs and fallen leaves of apple trees in commercial orchards
N.A. Hamada1,ª and L.L. May De Mio2
1 IFPR, Paraná Federal Institute of Education, Science and Technology, Palmas, Rodovia PRT, 280, Trevo da Codapar, 85555-000 Palmas, PR, Brazil
2.UFPR, Federal University of Parana, Department of Crop Protection, 80035-050, Curitiba, PR, Brazil
Introduction – Glomerella leaf spot on apple (Malus × domestica Borkh.), due to a complex of Colletotrichum species, causes severe leaf spot symptoms leading to early leaf fall, and eventual symptoms on fruit before and after harvest. Under the Brazilian conditions, it is the main apple disease responsible for severe damage in all production areas. This study aimed 1) to verify the survival of Colletotrichum spp. in dormant organs, fallen leaves and soil samples from fungicide-sprayed commercial orchards during winter; 2) to verify the survival of Colletotrichum spp. on asymptomatic leaves during the vegetative period; and 3) to identify the species complex and to confirm the pathogenicity of the isolates obtained from different parts of the plant (on fruit and leaves).
Materials and methods – The study was conducted in a commercial orchard during the winters of 2010 and 2011, assessing the pathogen survival on buds, twigs, asymptomatic leaves, fallen leaves and soil samples. Fungal isolates from different substrates were inoculated on fruit (with and without wound) and on leaves of apple cv. Gala to prove their pathogenicity.
Results and discussion – This is the first investigation on the survival of the Colletotrichum complex in apple under the conditions of Brazilian commercial orchards. All isolates (16) from dormant twigs and fallen leaves were identified as C. acutatum species complex. Five (5) isolates from dormant buds were identified as C. gloeosporioides species complex and three (3) as C. acutatum species complex. According to the data collected, Colletotrichum spp. are able to survive during winter in dormant buds, on dormant twigs and fallen leaves, but are most frequent on fallen leaves. The isolates obtained from buds, twigs and fallen leaves were pathogenic on leaves and fruit of apple. Copper sprays during the dormant stage did not completely eliminate the inoculum. The pathogen was not recovered from soil or from asymptomatic leaves with the methodology used.
Conclusion – Fallen leaves on the ground can be a source of inoculum from one season to the next, so they must be considered in disease management programs to avoid the spread of primary inoculum.
My Comments. This again points to the importance of sanitation in growing areas. Pick up fallen leaves, old fruit, remove remaining fruit from fruit trees, and do not leave old debris from the orchard or garden in the growing area unless it has been properly composted. Most other types of plant materials left as a surface mulch not related to the garden or fruit trees is fine.