Postharvest biocontrol of Colletotrichum gloeosporioides on mango using the marine bacterium Stenotrophomonas rhizophila and its possible mechanisms of action.

The marine bacterium Stenotrophomonas rhizophila was assessed in vitro and in vivo as biocontrol agent against anthracnose disease of mango fruit caused by Colletotrichum gloeosporioides. The results showed that in vitro inhibition of the colony diameter and spore germination of the phytopathogen was due to the production of VOCs, competition for nutrients, and lytic enzymes. When a concentration of 1 × 108 cells ml-1 of the antagonist bacterium was applied to the fruit, disease incidence was reduced by 95%, and the lesion diameter of anthracnose decreased by 85%, which offered greater protection than the synthetic fungicide. This is the first report of antagonistic mechanisms of the marine bacterium S. rhizophila against anthracnose disease in mango, which in this study was found to be more effective than the synthetic fungicide.

First Report of a Bionectria sp. Associated with a Stem Rot of Cardon Cactus (Pachycereus pringlei) in Baja California Sur, Mexico.

Giant cardon (Pachycereus pringlei ((S.Watson) Britton & Rose) is the most common cactus in northwestern Mexico and is endemic to the Baja California Peninsula and Sonora Desert. A large part of the peninsula (El Vizcaino Biosphere Reserve and Gulf of California) now consists of protected areas and is classified as a World Heritage site by UNESCO ( http://whc.unesco.org/en/list/1182 ). Cardon cactus is an important ecological resource for indigenous people and is used as feed for range cattle. Since 2000, in the central and southern part of the State of Baja California Sur, an apical stem rot has spread to ~17% of the natural cardon population around San Pedro (23°29'N, 110°12'W), La Paz (24°08'N, 110°18'W), and El Comitán (24°05'N, 110°21'W). Affected cacti display necrosis of apical branches, dry rot, cracks in the stem and branches, bronzing of mature spines surrounding the affected area, and reddish brown gummy exudate. Thirty samples from the edges of symptomatic lesions were surface disinfected for 2 min in 0.8% (wt/vol) NaOCl and ethanol (70%), rinsed in sterile, distilled water, and grown on potato dextrose agar at 27°C. A cottony, brownish fungus was consistently isolated from affected tissues. Koch's postulates were performed in pots of 10 cm in diameter with 5-year-old cacti inoculated (9-day-old mycelia) and incubated (15 days) at room temperature (26°C). The rough, dry, brownish, circular lesions that appeared were the same as those observed in the field. Healthy cacti inoculated with potato dextrose agar plugs were symptomless. The fungus was always reisolated from infected cacti and morphological examinations (2) were performed: one-septate, olive-green, smooth, ellipsoidal conidium and two-celled ascospores (15 to 20 × 5 to 7 µm) were present. Also present were conidial masses from monomorphic, penicillate conidiophores in sporodochia. Cottony and white-to-light yellow PDA colonies were observed. Genomic DNA was extracted from lyophilized hyphae using the method described by O'Donnell (1) or with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). The internal transcribed spacer (ITS) regions 1 and 2 of the 5.8, 18, and 28S ribosomal RNA genes were amplified with the primer pairs ITS1 and ITS4 (3). The expected amplicon of 571 bp was sequenced and compared with fungal sequences available from the GenBank-EMBL database using the BlastN and CLUSTAL programs (MegAlign, DNASTAR, Madison, WI). The closest nucleotide similarity had 99% identity with a Bionectria sp. (GenBank Accession No. HM849058.1). To our knowledge, on the basis of morphological characteristics, DNA comparisons, and pathogenicity tests, this is the first report of a Bionectria sp. causing an apical stem rot disease in cardon cacti in Mexico. Since there are no control measures in Mexico there is a permanent risk that the disease will spread to healthy areas. References: (1) K. O'Donell et al. Mycologia 92:919, 2000. (2) H. J. Schroers. Stud. Mycol. 46:1, 2001. (3) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

First Report of Sour Rot Caused by Geotrichum citri-aurantii on Key Lime (Citrus aurantifolia) in Colima State, Mexico.

Sour rot caused by Geotrichum citri-aurantii (Ferraris) R. Cif. & F. Cif. (synonym G. candidum Link) is a disease that causes postharvest losses of lemon (Citrus limon Burm, f.), mandarin (C. reticulata Blanco), and orange (C. sinensis (L.) Osbeck) (2-4) worldwide, but it has not been described on key lime (C. aurantifolia (Chistm.) Swingle) from the State of Colima, Mexico. During the agricultural cycle from 2005 to 2007, 300 fruits of key lime were analyzed. Symptoms observed on approximately 40% of the fruits were wounds with a sour, fermented smell with 30% of the softened area covered with white mycelium. A Geotrichum sp. was isolated on potato dextrose agar (PDA). On the basis of morphological criteria (1) and sequencing the internal transcribed spacer (ITS1-5.8s-ITS2) region of rDNA (GenBank Accession No. EU131181), the fungus was identified as G. citri-aurantii. A sample of the fungus was deposited in the Biology Collection of Yeast and Fungi (Reg. No. CLT20) of Centro de Investigaciones Biológicas del Noroeste, Mexico. Key limes were inoculated with G. citri-aurantii by placing three drops (20 µl each) of a sterile water suspension of 106 arthroconidia/ml in three punctured wounds of 3-mm diameter produced with a sterile scalpel on the fruit surface. Ten plastic boxes with five fruit each were stored for 2 weeks at 20°C and 85% relative humidity. Sour rot symptoms on key lime inoculated with G. citri-aurantii were identical to fruit in the field. The control fruit inoculated with sterile water did not develop symptoms. The fungus was reisolated, confirming Koch's postulates. The test was repeated three times to confirm our diagnosis. To our knowledge, this is the first report of G. citri-aurantii causing sour rot on key lime in Colima, Mexico. References: (1) S. Gente et al. J. Ind. Microbiol. Biotechnol. 33:1019, 2006. (2) P. Plaza et al. J. Hortic. Sci. Biotechnol. 79:935, 2004. (3) J. L. Smilanick et al. Post. Biol. Tech. 47:226, 2008. (4) V. H. Tournas and E. Katsoudas, J. Food. Microbiol. 105:11, 2005.

Fruit Rot Caused by Penicillium italicum on Lemon (Citrus aurantifolia) in Colima, Mexico.

Postharvest rotting caused by Penicillium italicum Wermer is responsible for significant economic losses of orange (Citrus sinensis (L.) Osbeck) and lemon (C. limon Burm. f.) worldwide, but until now was not described on lemons (C. aurantifolia (Chistm.) Swingle) in Mexico. During May 2002, we analyzed 400 fruits of lemon collected in the state of Colima, which is the most important lemon producer in Mexico. Rotting and softened areas covered with a white mycelium and blue conidia were observed on approximately 30% of the fruits. Affected tissue was plated onto potato dextrose agar (PDA) for fungal isolation and identification. Following the morphological criteria (1) and the internal transcribed spacer 1 (ITS1), 5.8S, and ITS2 region of the ribosomal DNA (2) (GenBank Accession No. DQ991463), the fungus was identified as P. italicum and deposited in the Colección Microbiana y de Cultivos Celulares CINVESTAV-IPN, México. For the pathogenicity test, the fungus was grown on PDA for 1 week. Four drops (15 µl each) of a sterile water suspension of 106 conidia per ml were placed in four wounds of 3 × 3 × 3 mm produced with a scalpel on the fruit surface. Five plastic boxes with six fruits each were placed in an environmental chamber at 12°C and 90% relative humidity. After 10 days, all fruit rotted in a similar way as naturally infected fruit on trees. Control fruits inoculated with sterile distilled water were symptomless. The test was repeated and the results were similar, confirming Koch's postulates. To our knowledge, this is the first report describing the isolation and pathogenicity of P. italicum on lemon (C. aurantifolia) in Colima, Mexico, which may have important implications in fruit quality and storage. References: (1) Z. Kozakieweicz. IMI Descriptions of Fungi and Bacteria. 155, Sheet 1548, 2002. (2) M. J. Pianzzola et al. Plant. Dis. 88:23, 2004.