Identification of Alternaria spp. as causal agent of dead flower buds disease of pear (Pyrus communis) in the Netherlands and methods for disease control

Abstract

The occurrence of dead dormant flower buds is a common phenomenon of economic importance in the major pear production areas of Europe. Thus far, the cause of dead flower buds disease remained unknown. Several causes have been proposed, including insufficient tree chilling, unmet dormancy requirements, incompatibility between scion and cultivar, but also various biotic stress agents such as pathogens and pests. In this study, we tested the relationship between reduction of tree growth and dead flower bud incidences, but found no indication that growth regulation can prevent the occurrence of dead flower buds. It has been proposed that the bacterium Pseudomonas syringae pv. syringae may be the causal agent of dead flower buds of pear. However, although we found the bacterium as epiphyte and even as endophyte on and in flower buds, our findings argue that P. syringae pv. syringae is not the causal agent of dead flower buds disease in the Netherlands. In our research, Alternaria spp. were consistently found in diseased flower buds, and strong correlations between dead dormant flower buds and infection rates of flower buds with Alternaria spp. were recorded. The isolated Alternaria species were identified as A. arborescens SC and A. alternata SC. Field experiments for disease control showed that the disease may be controlled by specific fungicide applications. Thus, we propose that dead flower buds of pear in the Netherlands should be regarded as a fungal disease caused by A. alternata SC and potentially also A. arborescens SC.

Multigene Phylogeny and Pathogenicity Trials Revealed Alternaria alternata as the Causal Agent of Black Spot Disease and Seedling Wilt of Pecan (Carya illinoinensis) in South Africa

“…This is supported by previous studies on the wounding of plant tissues with Alternaria spp. [ 72 ]; wounding was shown in this study to be an important disease factor affecting the South African pecan industry. Nonetheless, a previous study [ 56 ] also showed that insects can cause wounding on pecans in South Africa, which contributed to the dissemination of fungal pathogens such as A. alternata .…”

“…This is also an indication that stress factors could play a role in the overall health of pecan trees [ 35 ]. This has been shown in other plants or crops, such cotton ( Gossypium hirsutum ) leaf senescence in China [ 74 ], cruciferous vegetables in Europe [ 68 ], and more recently on pear ( Pyrus communis ) in the Netherlands [ 72 ]. Control and management are challenging as A. alternata can only be eradicated systemically [ 75 ], and even harvested pecan nuts-in-shucks and kernels that appear healthy at this point can subsequently start showing symptoms due to endophytes such as A. alternata during storage and transport [ 76 ].…”

Efeito do plasma não térmico de descarga de arco deslizante no fungo "Alternaria alternata", nos seus metabólitos e no retardo da podridão marrom da maçã

“…Alternaria spp. pode colonizar partes de flores durante a floração e após a queda das pétalas, mas devido ao longo período de incubação, a doença não se desenvolve até que o fruto se torne suscetível durante um longo armazenamento (WENNEKER et al, 2019).…”