Diaporthe ambigua Associated with Post-Harvest Fruit Rot of Kiwifruit in Chile
Authors: Auger J. , Pérez I. , Esterio M. 
Published: May 2013

Kiwifruit is an important, expanding commercial crop in Chile. Several fungi have been reported to be associated with post-harvest rots of kiwifruit worldwide (2). During 2011 and 2012, kiwifruit produced in the VI and VII regions of Chile, showing symptoms of inner rot, were investigated with the aim of identifying the disease agent. The affected fruits had brown pubescent skin at the stem end that became soft and lighter in color than the adjacent firm healthy tissues. A watery exudate and white to pale grayish mycelial mats frequently developed at the stem end of the fruit, causing a water-drop stain down the sides on the dry brown healthy skin. The underlying tissue accessed by peeling off the skin was usually water soaked, soft, and lighter green than the healthy tissue. A fermented sour odor occurred frequently on severely decayed fruits. After incubation at 25°C over 7 days on potato dextrose agar (PDA), white to grayish, pale aerial mycelial mats were recovered from fragments of symptomatic kiwifruit superficially disinfected with 95% ethanol. After 2 weeks, black, spherical pycnidia developed, bearing hyaline, ellipsoidal, biguttulate conidia (5.4 to 12.6 × 2.1 to 4.7 μm). After 3 weeks, abundant perithecia embedded in a distinct, black, elevated stroma developed. Perithecia were black, globose, 200 to 500 μm in diameter with necks sinuous, filiform, 550 to 840 × 50 to 95 μm. Clavate, sessile asci, 30.9 to 50.2 × 6.6 to 12.5 μm contained ascospores biseriate, hyaline, smooth, fusoid-ellipsoid, widest just above the septum, tapering towards both ends, medianly septate, constricted at the septum at maturity, with 1 to 2 guttules per cell ascospores, 5.9 to 9.7 × 2.5 to 4.3 μm. All colonies obtained from kiwifruit displayed the same morphological traits and were consistent with those of a Diaporthe sp. (1). The internal transcribed spacer (ITS) region was sequenced using ITS1/ITS4 primers (4). Analysis of ITS region of kiwifruit isolates Damb_12 and Damb_16 (GenBank Accession Nos. KC294545 and KC294544, respectively) revealed 100% nucleotide identity to Diaporthe ambigua (HM575420, HM575419, DQ286274, DQ286270, and DQ286271). Six millimeter plugs from fungal colonies growing on PDA at 25°C for 7 days were used to inoculate 15 healthy untreated, ripe ‘Hayward' kiwifruits. Control fruits were inoculated with agar plugs. Inoculated fruits were incubated at 25°C and 80% relative humidity. After 7 days, white to pale grayish mycelial mats developed only on the inoculated fruits, releasing a water drop stain. The underlying tissue was lighter green and water soaked. D. ambigua was reisolated only from the inoculated fruits. D. actinidiae has been previously reported on kiwifruit canes in Chile (3); however, to our knowledge, this is the first report on the occurrence of D. ambigua (Phomopsis ambigua) on kiwifruit in Chile. The fungal isolates (no. 1 to 21) have been deposited in the Laboratorio de Fitopatología Frutal y Molecular, Departamento de Sanidad Vegetal, Facultad de Ciencias Agronómicas de la Universidad de Chile.

References: (1) J. C. Jansen van Rensburg et al. Studies in Mycol. 55:65, 2006. (2) L. Luongo et al. J. Plant Pathol. 93:205, 2011. (3) A. Palma and E. Piontelli. E. Bol. Micol. 15:79, 2000. (4) White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.