RESUMO
In recent years, an increase of collapsed and dead strawberry plants has been observed in several fields in central Chile, specifically in San Pedro, Melipilla, an important area for strawberry cultivation in the country. To determine the causal agent of the disease and the extent of the problem, 25 sample sites of 1 ha each, distributed in different San Pedro zones, were surveyed at the end of the 2011 season (from December 2010 to February 2011). Cross sections of the crowns of symptomatic strawberry plants showed necrotic tissue and brown-red to dark brown areas on the vascular ring. Samples of the affected crowns were superficially disinfested and plated on potato dextrose agar with 200 µg/ml of streptomycin sulfate. Dark gray colonies were observed after 7 days of incubation at 24°C. Pure cultures of the pathogen showed aerial mycelium and abundant dark oblong sclerotia. Fifty sclerotia were measured, averaging 120 × 74 µm. Twenty-one isolates were identified molecularly utilizing the species specific primers MpKFI and MpKRI (2) that yielded a 350-bp fragment. The amplified DNA fragments were sequenced and BLAST analysis showed a 99% nucleotide sequence identity with Macrophomina phaseolina (GeneBank Accession No JX535007.1). Both morphological and molecular analyses confirmed that the isolated species corresponded to M. phaseolina, causal agent of crown and root rot in strawberry. Four representative isolates were selected to conduct pathogenicity tests. Inoculum was prepared by incubating the pathogen for 28 days at 20°C in sterilized oat seeds. Pots of 1.5 liters were filled with a mixed substrate of peat and perlite (2:1), amended with inoculated oats at 9 g per liter of substrate. 'Camarosa' strawberry plants were planted and grown in a glasshouse for 1 month. Six replicated plants per isolate and six plants growing on non-inoculated substrate were left as controls. Ninety-five percent of the inoculated plants showed wilt and collapse symptoms 22 days after transplant, whereas no symptoms were observed in the control plants. M. phaseolina was reisolated from the crowns of symptomatic plants, fulfilling Koch's postulates. The pathogen was isolated from symptomatic strawberry plants in 14 of the 25 sampled sites. Although M. phaseolina was described previously on other crops in Chile, to our knowledge, this is the first report of M. phaseolina causing crown rot of strawberry. The disease has been recently reported in Spain, the United States, and Argentina (1,3,4). References: (1) M. Avilés et al. Plant Pathol. 57:382, 2008. (2) B. Babu et al. Mycologia 99:797, 2007. (3) O. Baino et al. Plant Dis. 95:1477, 2011. (4) S. Koike. Plant Dis. 92:1253, 2008.
RESUMO
A new rot of stored apples was observed in local and export markets on apples that were grown in the south-central region of Chile during 2004. Circular, pale brown spots with a darker outer ring were observed at least 3 months after harvest in cvs. Braeburn, Fuji, Granny Smith, Pink Lady, and Royal Gala. Lesions developed from lenticel cavities or wounds and reached 2 to 3 cm in diameter after 1 week at room temperature. Symptoms resembled those produced by the bull's eye rot pathogens on apple that occur in other parts of the world. Acervuli developed in the rotted areas, and microscopic examination revealed the presence of the fungus Neofabraea alba (Guthrie) (anamorph Phlyctema vagabunda Desm.) characterized by production of curved macroconidia and absence of microconidia (1). Pure culture on potato dextrose agar (PDA) yielded a characteristic white sterile mycelium. Four cv. Pink Lady apples were wound inoculated with mycelium of the pathogen and four apples were wound inoculated with a 5 × 104 CFU/ml conidial suspension. Four apples were wounded and inoculated with sterile water as a negative control. The fruit was held at 20°C. Symptoms appeared after 4 and 5 days in the mycelium and conidial inoculated apples, respectively. Resulting symptoms were similar to those originally observed. Abundant macroconidia were produced at the inoculation sites, and a sterile, white mycelium was recovered after isolation on PDA. To our knowledge, this is the first report of apple fruit rot caused by N. alba in Chile. Reference: (1) J. L. Henriquez et al. Plant Dis. 88:1134, 2004.