Screening for Resistance to Meloidogyne enterolobii in Capsicum annuum Landraces From Mexico.

Meloidogyne enterolobii has become an economically important plant parasitic nematode worldwide because of its high aggressiveness, increasing geographic distribution, wide host range, and pathogenicity in pepper (Capsicum annuum) cultivars carrying resistance genes to Meloidogyne incognita, Meloidogyne arenaria, and Meloidogyne javanica. The objectives of this study were to identify landraces of peppers resistant to M. enterolobii and analyze the relationship between resistance indicators and the phenotype parameters of plant height, stem width, leaf length, leaf width, relative chlorophyll, and number of flowers. Ninety landraces of C. annuum were collected from several states of Mexico and were inoculated with 2,000 eggs of M. enterolobii. Eleven resistant landraces were selected and confirmed with a second inoculation experiment. Seventy-five days after inoculation, in both experiments, the resistance of landraces UTC66, UTC90, UTC67, UTC88, and UTC81 to M. enterolobii was consistent. Although genotypes UTC24, UTC79, UTC65, UTC68, UTC69, and UTC25 were susceptible, these landraces had a significantly higher proportion of resistant plants, less root galling, and a lower reproductive index, in comparison with the rest of the 79 genotypes and the susceptible control, which were highly susceptible in both experiments. There was no correlation between resistant indicators and phenotypic parameters, although plant height, relative chlorophyll, and number of flowers were in general significantly affected compared with noninoculated controls, indicating that the nematodes reduce the growth and yield of peppers. Results indicate that all resistant plants from these landraces are promising sources of resistance for the development of pepper cultivars resistant to M. enterolobii.

First Report of Vinca Blight Caused by Phytophthora nicotianae in Northwestern Mexico.

Vinca (Catharantus roseus (L.) G. Don) is a common ornamental landscape plant. From July to September 2012, blighted and wilted vinca plants were found in retail stores, commercial nurseries, and urban landscape areas of Culiacan, Sinaloa, in northwestern Mexico. In several commercial nurseries and a retail store, incidence of the unknown disease on vinca plants ranged from 20 to 50%, resulting in significant economic losses. Symptoms of the disease started with a foliar blight, and if warm and wet conditions were present, the disease progressed, causing plant wilting and death. Surface-sterilized (0.5% NaOCl 1 min) diseased plant tissue was plated on V8 agar medium, and after 72 h of incubation at 25°C, white colonies of coenocytic mycelium were developed from the plated tissues. Isolates produced cottony colonies on V8 agar medium, grew well between 7 and 30°C (optimum of 25°C), and produced spherical, intercalary, and terminal chlamydospores (17 to 30 µm) and non caducous, papillate, spherical to ovoid sporangia of 30 to 39 × 21 to 31 µm. Based on these morphological characteristics, Phytophthora isolates were identified as Phytophthora nicotianae Breda de Haan (1,3). The identity of two representative isolates OV4 and OV11 was confirmed by sequence analysis of the rDNA internal transcribed spacers (ITS; GenBank Accession Nos. KC248202 and KC248201), and of the ß-tubulin (ß-tub; KC248404 and KC248403) and translation elongation factor 1-α (EF1-α; KC248206 and KC248205) genes. Comparative sequence analysis against the NCBI nucleotide database showed a high degree of identity with reference sequences of P. nicotianae (ITS, 99%; ß-tub, 99%; EF1-α, 100%) (2). A pathogenicity test with a representative isolate of P. nicotianae was performed on 10-week-old healthy vinca seedlings (n = 10). An aliquot of 10 ml of a zoosporic suspension (104 zoospores/ml) was sprayed onto the seedlings' leaves. An equal number of non-inoculated control seedlings were sprayed with sterile distilled water. Seedlings were maintained in a moist chamber at 25°C with 80 to 90% relative humidity and watered as needed with sterile water. Inoculated plants showed initial symptoms of foliar blight after 4 days, whereas control plants remained healthy. Ten days after inoculation, inoculated plants showed severe wilting. P. nicotianae was reisolated only from inoculated plants, thus fulfilling Koch's postulates. To our knowledge, this is the first report of P. nicotianae attacking annual vinca in northwestern Mexico. References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) L. P. Kroon et al. Fungal Genet Biol. 41:766, 2004. (3) F. N. Martin et al. Plant Dis. 96:1080, 2013.

First Report of Blue Mold Caused by Penicillium oxalicum in Tomato (Solanum lycopersicum) in Mexico.

Tomato is the primary vegetable exported from Mexico to the United States. In June 2007, stem rots were observed in tomato cv. Imperial plants growing in a greenhouse in the Culiacan Valley. Disease symptoms included stem rot with a mycelial growth with a grayish blue sporulation. The disease was observed to be affecting 1% of the tomato plants growing in the greenhouse, and has been observed sporadically in greenhouses during subsequent agricultural cycles in other tomato-growing areas in Mexico. Affected stems showed initial symptoms of a dark brown necrotic area surrounding only the cut regions of pruned leaves and stems. As the infection continued on the tissues, the spot grew and then became covered with a grayish blue sporulation. Severe stem rot led to death of the plants. Rotted stems of tomato plants were collected and samples of the infected tissues were plated onto potato dextrose agar (PDA) to isolate the fungus. The preliminary identification of the pathogen was Penicillium oxalicum Currie & Thom on the basis of morphological criteria with ellipsoidal conidia approximately 4 × 3 µm borne in columns, conidiophores mostly biverticillate, and ampulliform phialides (2). The identification was confirmed by sequencing internal transcribed spacer 1 (ITS1), 5.8S, and ITS2 regions of the ribosomal DNA (GenBank Accession No. HM452308). The isolate was deposited in the Coleccion Nacional Microbiana y de Cultivos Celulares CINVESTAV-IPN, Mexico. Koch's postulates were fulfilled by reproducing stem rots on healthy inoculated tomato stems. Pathogenicity testing involved fungal growth on PDA for 5 days, after which a 4-mm disk of actively growing mycelia was transferred to wounds (4 × 4 mm) made with a scalpel in stems of 6-week-old tomato cv. Imperial plants. Inoculated plants were covered with plastic bags to maintain a high relative humidity for 24 h and were maintained in a greenhouse at 25 ± 2°C. Seven days after inoculation, all of the inoculated stems showed rot symptoms similar to those observed in the greenhouse. Stems that were inoculated only with an agar disk did not show any symptoms of the disease. The pathogen was reisolated from inoculated plants but not from noninoculated plants. Artificial inoculation was performed twice. Although P. oxalicum has been previously reported as a causal agent of cucumber (1) and tomato stem rots in Japan (3), to our knowledge, this is the first report of P. oxalicum causing stem rot in tomato plants in Mexico. References: (1) T. M. O'Neill et al. Plant Pathol. 40:78, 1991. (2) J. I. Pitt. The Genus Penicillium and Its Teleomorphic States Eupenicillium and Talaromyces. Academic Press, London, UK, 1979. (3) S. Umemoto et al. J. Gen. Plant Pathol. 75:399, 2009.