Neoscytalidium dimidiatum Causing Canker, Shoot Blight and Fruit Rot of Almond in California

Abstract

Almond trees with trunk and branch cankers were observed in several orchards across almond-producing counties in California. Symptoms of cankers included bark lesions, discoloration of xylem tissues, longitudinal wood necrosis, and extensive gumming. Spur and shoot blight associated with rotted fruit were detected in two orchards in Kern County. The fungus Neoscytalidium dimidiatum was consistently recovered from the various cankers, infected fruit, and blighted shoots and its identity was confirmed based on phylogenetic and morphological studies. Phylogenetic analyses of the internal transcribed spacer, translation elongation factor 1-α, and β-tubulin genes comparing 47 strains from California with reference specimens within the family Botryosphaeriaceae and coupled with detailed morphological observations validated the identity of the pathogenic fungus. Pathogenicity tests conducted in the field using 1- to 2-year-old branches inoculated with mycelium plugs or conidial suspensions and attached fruit inoculated with conidial suspensions fulfilled Koch’s postulates. N. dimidiatum appeared highly virulent in almond-producing cankers of up to 22 cm in length within 4 weeks using mycelium plug inoculations as well as severe fruit rot combined with spur blight on the fruit-bearing spurs. This study reports, for the first time, the fungus N. dimidiatum as a pathogen of almond in California causing canker, shoot blight, and fruit rot. Disease symptoms are described and illustrated.

Molecular Characterization and Disease Control of Stem Canker on Royal Poinciana (Delonix regia) Caused by Neoscytalidium dimidiatum in the United Arab Emirates

“…The results obtained from the greenhouse experiment on young healthy plants after inoculation were similar to the disease symptoms on trees of royal poinciana located in the field, and that was confirmed by Koch's postulates when N. dimidiatum was frequently recovered from the inoculated seedlings. Our data match those in other trials using artificial inoculation of the same pathogen on royal poinciana [16] or other plant species [13][14][15]20,28]. Pathogenicity assays on seedlings of royal poinciana (Figure 4), F. benjamina and F. nitida [13] and eucalyptus, poplar and olive [30] clearly described that discoloration of vascular tissues, and drying and defoliation of leaves, were symptoms associated with stem canker caused by N. dimidiatum.…”

“…In general, we noticed dieback, canker and gummosis, which ultimately led to complete dryness and death of royal poinciana trees (Figure 1). Although some studies have reported several fungi to cause cankers on plant species [5][6][7][8], others have recorded N. dimidiatum on almond, dragon fruit, eucalyptus, fig and plum, displaying disease symptoms of canker and dieback in different places of the world [13][14][15]28]. In general, environmental stress has negative impact on the severity of disease, depending on the level and duration of the stress, and the sensitivity and developmental stage of the plant species.…”

“…Pathogenicity assays on seedlings of royal poinciana (Figure 4), F. benjamina and F. nitida [13] and eucalyptus, poplar and olive [30] clearly described that discoloration of vascular tissues, and drying and defoliation of leaves, were symptoms associated with stem canker caused by N. dimidiatum. There has been a rise in reports about N. dimidiatum causing diseases on fruits of pitahaya, plum and almond [12,14,15]. Apple fruit bioassays have been conducted to determine the effects of the fungal pathogen associated with canker diseases [5,36].…”

“…Neoscytalidium dimidiatum is another fungal pathogen that causes cankers and has a wide geographical and host range, including plum, almond (Prunus dulcis), mango (Mangifera indica), pitahaya (Hylocereus undatus), Citrus, Musa, Populus, and Ficus spp. in Australia, China, Egypt, Niger, Tunisia and the USA [9][10][11][12][13][14][15].…”

Bioprospecting for fungi with potential pathogenic activity on leaves of Agave tequilana Weber var. Azul

“…Neoscytalidium species have been related to stem canker, shoot blights and gummosis (Nouri, Lawrence, Yaghmour, Michailides, & Trouillas, ), and it has been described in plants such as Ficus carica , Hylocereus undatus , H. polyrhizus , Mangifera indica and root fruit (Nouri et al, ). The Eurotiales order, that includes Pencillium strains, was the second order with more isolates (13.3%) in this study.…”