Health & Environmental Research Online (HERO)


Print Feedback Export to File
6420805 
Journal Article 
First Report of Collophora hispanica and C. paarla Causing Branch Cankers of Almond in California 
Holland, LA; Nonni, MT; Crespo, MP; Holtz, BA; Yaghmour, MA; Doll, DA; Trouillas, FP 
2018 
1 
Plant Disease
ISSN: 0191-2917 
102 
8 
1663-1664 
WOS:000439743200048 
Almonds (Prunus dulcis) are produced in California’s Central Valley and have an annual economic impact of $21.5 billion (Sumner et al. 2014). Branches with reddish-brown discoloration of vascular tissues were observed in seven almond orchards between 2015 and 2016 in the Central Valley of California. Disease incidence ranged from 5 to 15% in the affected orchards. Necrotic wood pieces near the canker margin were surface disinfected in 70% ethanol followed by brief flaming before plating onto acidified potato dextrose agar medium (APDA; 2.6 ml of 25% [v/v] lactic acid per liter of medium). Plates were incubated at 25°C in a 12-h photoperiod for 7 to 10 days, and Collophora-like colonies were observed. To confirm identity, sequencing of the internal transcribed spacer region (ITS) using ITS1/ITS4 universal primers (White et al. 1990) and translation elongation factor 1a gene (TEF) using primers EF1-728F/EF1-986R (Carbone and Kohn 1999) was performed for four isolates (C. hispanica KARE919 and KARE138; C. paarla KARE209 and KARE278) from three of the seven orchards sampled. The two species were not isolated from the same lesion or orchard. Sequences were deposited into GenBank (ITS: MF942133, MF942134, MF942135, and MF942136; TEF: MG000587 and MG000588). A BLASTn search revealed high similarity (>98%) to C. hispanica CBS 128566 (ITS: JN808839; TEF: JN808850) and C. paarla CBS 120878 (ITS: GQ154575) and CBS 120877 (TEF: GQ154646). On PDA, C. hispanica colonies were red to vinaceous with a white margin and C. paarla colonies were pink to cream-colored, with a wrinkled center of the colony. Conidia of C. hispanica and C. paarla were single-celled, hyaline, and cylindrical. C. hispanica isolate KARE919 and C. paarla isolate KARE278 were selected for conidial measurements (n = 30 conidia) after 14 days on PDA; KARE919 4.7 to 6.6 × 2.5 to 3.7 µm; and KARE278 5.6 to 7.4 × 2.4 to 3.5 µm. Branches of healthy, 7-year-old almonds cv. Nonpareil were surface disinfected with 70% ethanol, wounded with a 5-mm-diameter cork borer, and inoculated with a 5-mm-diameter mycelial plug from the actively growing margin of 3-week-old colonies of C. hispanica isolate KARE919 and C. paarla isolate KARE278. Control branches were treated with 5-mm-diameter sterile PDA plugs. The inoculated area was covered with petroleum jelly and wrapped with Parafilm. Six branches per isolate were inoculated in a randomized complete block design. Vascular discoloration was measured after 6 months. There was a significant difference (P < 0.01) in vascular discoloration between C. hispanica (41 ± 3.3 mm) and C. paarla (67 ± 7.4 mm). Fungi were reisolated from the margin of lesions, completing Koch’s postulates. Control inoculations resulted in small lesions (18 ± 2.2 mm); C. hispanica and C. paarla were not isolated from controls. Recently, C. hispanica was reported causing wood cankers of almonds in Spain (Gramaje et al. 2012) and Iran (Arzanlou et al. 2016). To our knowledge, this work represents the first report of C. hispanica and C. paarla causing branch cankers of almond in California. The present findings suggest this may be an emerging disease of California almonds. 
; almonds; branches; color; conidia; culture media; discoloration; disease incidence; economic impact; emerging diseases; ethanol; fungi; genes; internal transcribed spacers; lactic acid; mycelium; orchards; peptide elongation factors; petrolatum; photoperiod; Prunus dulcis; translation (genetics); vascular tissues; wood; Central Valley of California; Iran; Spain/