Articles
Etiology of walnut fruit rot, spur and twig dieback in southwestern France
Article number
1420_44
Pages
345 – 352
Language
English
Abstract
With an average of 40,000 t produced annually on more than 20,000 ha, walnut is France’s second most cultivated orchard crop after apples.
The southwestern region of Périgord is one the largest and most historical walnut producing region of France.
During the summer of 2018, numerous brown to black necrotic walnut fruits were observed in orchards and harvest bins, with estimated yield losses ranging between 40 to 70%. During the following spring of 2019, field observations from these orchards also revealed abundant twig and shoot dieback in trees.
Many fruit spurs and twigs had died following previous year fruit infections, thus leading to further reduction of the orchard production capacity.
The objective of this study was to identify and characterize the main fungal pathogens associated with fruit rot and twig dieback of walnut trees in southwestern France.
In May 2019, 21 walnut orchards were surveyed.
Declining shoots and twigs were sampled and symptomatic tissues were placed on potato dextrose agar (PDA) for the isolation and morphological identification of fungal pathogens.
In August 2019, walnut fruit expressing the black walnut syndrome were sampled and necrotic tissues were isolated in PDA. Fungal identifications were confirmed by morphology as well as by sequencing and phylogenetic analyses of the internal transcribed spacer rDNA. Isolation results from declining spurs and twigs showed a high proportion of Diaporthe (syn. Phomopsis) spp. associated with dieback, ranging from 45 to 100% of shoots and twigs across the sampled orchards.
Additional fungal species isolated from shoots and twigs included Botryosphaeriaceae, Colletotrichum, Fusarium, Boeremia and Melanconium spp.
From the fruit sampling, Diaporthe/Phomospis species also prevailed in orchards, followed by Colletotrichum and Botryosphaeriaceae spp. Fusarium species also were found occasionally from diseased fruits.
Main species identified from this study included Diaporthe eres, Neofusicoccum parvum, Botryosphaeria dothidea, Colletotrichum godetiae and Fusarium juglandicola or lateritium.
The southwestern region of Périgord is one the largest and most historical walnut producing region of France.
During the summer of 2018, numerous brown to black necrotic walnut fruits were observed in orchards and harvest bins, with estimated yield losses ranging between 40 to 70%. During the following spring of 2019, field observations from these orchards also revealed abundant twig and shoot dieback in trees.
Many fruit spurs and twigs had died following previous year fruit infections, thus leading to further reduction of the orchard production capacity.
The objective of this study was to identify and characterize the main fungal pathogens associated with fruit rot and twig dieback of walnut trees in southwestern France.
In May 2019, 21 walnut orchards were surveyed.
Declining shoots and twigs were sampled and symptomatic tissues were placed on potato dextrose agar (PDA) for the isolation and morphological identification of fungal pathogens.
In August 2019, walnut fruit expressing the black walnut syndrome were sampled and necrotic tissues were isolated in PDA. Fungal identifications were confirmed by morphology as well as by sequencing and phylogenetic analyses of the internal transcribed spacer rDNA. Isolation results from declining spurs and twigs showed a high proportion of Diaporthe (syn. Phomopsis) spp. associated with dieback, ranging from 45 to 100% of shoots and twigs across the sampled orchards.
Additional fungal species isolated from shoots and twigs included Botryosphaeriaceae, Colletotrichum, Fusarium, Boeremia and Melanconium spp.
From the fruit sampling, Diaporthe/Phomospis species also prevailed in orchards, followed by Colletotrichum and Botryosphaeriaceae spp. Fusarium species also were found occasionally from diseased fruits.
Main species identified from this study included Diaporthe eres, Neofusicoccum parvum, Botryosphaeria dothidea, Colletotrichum godetiae and Fusarium juglandicola or lateritium.
Publication
Authors
F.P. Trouillas, M.-N. Hébrard, V. Aurelle, P. Jargeat, E. Tranchand
Keywords
walnut, fungi, fruit rot, twig dieback
Groups involved
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