Perennial cankers and consequent grapevine dieback are a major problem in vineyards of Sonora and Baja California, the most important grape-production areas of Mexico. In order to identify the canker-causing agents, symptomatic arms, cordons, and trunks were collected from 13 and 6 vineyards in Sonora and Baja California, respectively. Two Botryosphaeriaceae spp., Lasiodiplodia theobromae and Diplodia seriata, were isolated frequently from infected wood and identified based on morphological and cultural characters as well as analyses of nucleotide sequences of three genes, the internal transcribed spacer region (ITS1-5.8S-ITS2), a partial sequence of the β-tubulin gene, and part of the translation elongation factor 1-α gene (EF1-α). Although both L. theobromae and D. seriata were isolated from grapevine cankers in Baja California, only L. theobromae was found in vines in the Sonora region. Pathogenicity of both species was verified by inoculation of rooted cuttings and green shoots of Thompson Seedless and Chardonnay cultivars. Isolates of L. theobromae were more virulent, based on the extent of spread in the secondary wood and green tissue, than those of D. seriata. These findings confirm L. theobromae and D. seriata as the causal agents of dieback and canker formation of grapevines in northern Mexico.

Bright yellow, interveinal chlorosis was observed for the first time on leaves of the older and mid-growth of cucurbit plants in southern Arizona and Sonora (Mexico) during September and October of 2006. Some cultivars exhibited substantial yield losses of 30 to 80%. In Arizona, symptoms were in Cucumis melo (muskmelon and honeydew melon) fields in the Yuma Valley and Hyder. In Sonora, honeydew and muskmelon, Cucurbita pepo (acorn, spaghetti, and summer [yellow and zucchini] squash), and Citrullus lanatus (watermelon) were symptomatic in Hermosillo, whereas, in Caborca, honeydew and cantaloupe developed similar symptoms. Interveinal chlorosis was observed in 60 to 100% of the plants in each field. Crops planted mid-to-late season were 100% infected, whereas, the early-season fields experienced approximately 60 to 80% incidence. All symptomatic fields in the Sonoran Desert and vicinity were infested by the whitefly Bemisia tabaci (Genn.), which was identified as the ‘B biotype’ on the basis of mitochondria COI sequence analysis (data not shown). Whitefly population levels were variable and ranged from 5 to 200 per plant. Total RNA was isolated from leaf samples collected from symptomatic plants using Tri Reagent (Molecular Research Center, Cincinnati, OH). Purified RNA was used in reverse transcriptase-PCR with primers specific to the Cucurbit yellow stunting disorder virus (CYSDV) coat protein (CP) gene (RNA2-deoxyribonucleotide coordinates 4927-4950 and 5657-5679) for the suspected whitefly-transmitted bipartite CYSDV (4). PCR yielded the CYSDV CP fragment, at 753 bp (GenBank Accession Nos. EF21058 and EF21059), which was cloned into pGEM T-Easy and sequenced in both directions using universal primers. The CYSDV CP nucleotide sequences (n = 16) obtained from acorn squash, honeydew melon, muskmelon, yellow squash, and watermelon had 99 to 100% identity. The Arizona (AZ) and Sonora (SON) CYSDV CP sequences shared 99 to 100% identity with previously described CYSDV isolates from the Eastern Hemisphere (GenBank Accession Nos. DQ903105 and DQ903108) and also with two isolates of CYSDV collected during 2004 from Zacapa Valley, Guatemala (GenBank Accession Nos. EF21060 and EF21061) (J. K. Brown, unpublished data). CYSDV is a member of the genus Crinivirus, family Closteroviridae. CYSDV was first identified in cucumber and melon crops in the Middle East approximately 15 years ago and 10 years ago in Spain (1). Most recently, this virus was introduced into Texas (2), Guatemala (J. K. Brown, unpublished data), and Arizona and California (3). CYSDV has therefore emerged as an important and potentially worldwide threat to the production of cultivated cucurbits (3). The threat appears to be significant in light of the introduction or establishment of the exotic B. tabaci biotypes B and Q vectors, which also originated in the Middle Eastern-North African-Mediterranean region. To our knowledge, this is the first report of CYSDV infecting field-grown C. pepo (four types) and watermelon, reported previously only as experimental laboratory hosts, and of CYSDV in two types of melon (C. melo) in Mexico. References: (1) A. Celix et al. Phytopathology 86:1370, 1996. (2) J. Kao et al. Plant Dis. 84:101, 2000. (3) Y.-W. Kuo et al. Plant Dis. 91:330, 2007. (4) L. Rubio et al. J. Gen. Virol. 82:929, 2001.

Severe yellow leaf curl and plant stunting symptoms were observed in tomato plants from two home gardens in central Arizona (Phoenix area) and a tomato field in Sonora, Mexico during the fall of 2006. Disease symptoms were reminiscent of those reported in Florida during 1994 (4) and more recently in tomato fields in the Pacific Coast state of Sinaloa, Mexico found to be infected with the exotic Tomato yellow leaf curl virus (TYLCV) (2). Total DNA was extracted from two symptomatic tomato plants from Arizona and Sonora and used as a template in PCR. PCR products of the core region of the begomovirus coat protein gene (Cp) were cloned (n = 3) and the DNA sequence was determined. BLAST analysis of the 579 bases with sequences available in the NCBI GenBank database indicated the closest match was to an isolate of the monopartite begomovirus TYLCV from Israel, which was known to have been introduced into the Caribbean region, including Puerto Rico, the southeastern United States, and Mexico from 1990 to 1996 (1,4). The full-length TYLCV genome (approximately 2,800 bases) was amplified for a field isolate from each location by rolling circle amplification (RCA) using TempliPhi (Amersham Biosciences, Piscataway, NJ). RCA products were cloned into the plasmid vector pGEM7 (Promega, Madison, WI) that had been previously digested with SacI endonuclease. The complete TYLCV genome sequence was determined for six clones from each RCA product. Nucleotide analysis indicated that the complete TYLCV genome sequences from Sonora and Arizona, respectively, shared 97.6 and 97.7% nt identity. The comparative sequence analysis indicated that TYLCV-Sonora (TYLCV-Son) (GenBank Accession No. EF210555) was 99.1% nt identical to TYLCV reported recently from Culiacan, Mexico (GenBank Accession No. DQ631892). In contrast, TYLCV-AZ (GenBank Accession No. EF210554) shared 99.3% identity with an isolate from Texas, TYLCV-TX (GenBank Accession No. EF110890) (3). Interestingly, the TX and AZ TYLCV isolates contained a unique 29-nt deletion in the intergenic region (IR) between the TATA-box and the nonanucleotide, initiating at nt coordinate 2696. Except for the deletion in the IR region of the AZ and TX isolates, these viruses shared 97.6 to 99.1% nt identity to other TYLCV isolates reported in the Western Hemisphere. The genome sequence for TYLCV-Son shares high nt identity with TYLCV isolates identified in the Yucatan Peninsula and Pacific Coast of Mexico (2), the Caribbean region, and the southeastern United States, suggesting that a single TYLCV species was introduced and has spread throughout North America and the Caribbean (4). The absence of other TYLCV isolates in the Western Hemisphere with the novel 29-nt deletion noted for the TX and AZ isolates suggests that the latter two isolates originated from the same U.S. source. In Mexico, TYLCV was first introduced in the east coast and Yucatan region approximately in 1996. From there, this isolate has spread to the western part of the country (Sinaloa and Sonora) from 2004 to 2006 (2). Similarly, in the United States, TYLCV was introduced and spread in the eastern U.S. states beginning in 1994 (4), where it had been confined until it was discovered in Texas (3) and now Arizona during 2006. References: (1) J. Bird et al. Plant Dis. 85:1028, 2001. (2) J. K. Brown and A. M. Idris. Plant Dis. 90:1360, 2006. (3) T. Isakeit et al. Plant Dis. 91:466, 2007. (4) J. E. Polston et al. Plant Dis. 78:831, 1994.

R. Carrillo, J. Guerrero, M. Rodríguez, and C. Meriño-Gergichevich. 2015. Colonization of blueberry (Vaccinium corymbosum L.) plantlets by ericoid mycorrhizae under nursery conditions. Cien. Inv. Agr. 42(3): 365-374. The ericoid mycorrhiza is a symbiotic interaction that contributes to the improvement of the establishment and production of blueberries (Vaccinium corymbosum L.). The objectives of this paper were to assess the frequency (%) and intensity (%) of the colonization and growth of blueberry plantlets inoculated with ericoid mycorrhizae collected from three different edaphoclimatic conditions in the La Araucanía region of southern Chile under nursery conditions. Plantlets of three blueberry cultivars ("Brigitta", "Duke" and "Legacy") were grown under nursery conditions in sterile peat moss and a vermiculite substrate with fresh ericoid mycorrhizae propagules from Gaultheria pumila (collected in Villarrica National Park), Azalea sp., (from an urban garden in Temuco) or V. corymbosum cv. "Brigitta" (from an organic farm in Temuco). After six months, the development of hyphae characteristic of ericoid micorrhizal fungi was identified in root cells. The frequency and intensity of colonization was greater in the "Duke" cv. given the inoculum derived from V. corymbosum, followed by the "Brigitta" and "Legacy" cultivars treated with inoculum from the G. pumila inoculum. Colonization was lowest in those plants treated with the Azalea sp. inoculum. Contact between the inoculum sources and the fine roots of the micro-propagated blueberry plantlets under nursery conditions for six months was an effective method to promote mycorrhization. However, the development of mycorrhizae did not enhance the growth of the three blueberry cultivars during the evaluation period. The possibility of selecting ericoid inocula from site-specific conditions in southern Chile may eventually be used to support the micro-propagation of blueberry plantlets during acclimation and planting, assuming that mycorrhizal plants will improve conditions for establishment in the field.

Wheat (Triticum aestivum L.) is known for its ability to produce and release allelopathic compounds, which have potential for controlling weeds and diseases. Previous reports have shown the fungitoxic effects of allelochemicals present in wheat. Thus, these compounds can be exuded by roots to protect the tissues directly affected by Gaeumannomyces graminis var. tritici (Ggt) fungus that causes wheat take-all disease. The aim of this research was to evaluate in vitro the allelopathic effect of root exudate extracts from four Chilean wheat cultivars on Ggt growth. Root exudates were released from wheat seedlings to a sterile culture medium without nutrients. Afterward, the exudates in the culture medium were separated by liquidliquid extraction using ethyl acetate. Eight different concentrations were tested for each cultivar. The results showed that the degree to which the extracts strongly inhibit the phytopathogen growth is highly dependent on both the concentration and the cultivar. The root extract of the Domo cultivar was significantly active against Ggt (MIC=0.36 mg mL -1 ). IC 50 and MIC values obtained for Dollinco and Domo root exudate extracts showed toxicity to Ggt. These findings may be considered in future studies related to the use of allelopathic potential as a selection factor in order to reduce the yield losses caused by various take-all diseases, as an alternative to chemical controls.

European hazelnut (Corylus avellana L.) is an emerging crop for export, mainly in southern Chile. Stem cankers and dieback of twigs on six-year-old European hazelnut cultivar Barcelona were observed during the 2012 growing season on plantations in Panguipulli (39° 38′ 37.12″ S and 72° 20′ 10.87″ W), Region de Los Rios, Chile. The incidence has been variable according to the place of plantation; it was estimated at approximately 15%. Cankers were characterized by brownish-gray and brown to reddish discoloration of the vascular stem system. Hazelnut plants between 1 and 3 years old developed stem basal canker, especially at conditions of high humidity and overpopulation of weeds; at critical conditions, the affected plants generally die. Small pieces of cankered stems, selected from 10 European hazelnuts, were surface sterilized in 0.5% sodium hypochlorite for 2 min and rinsed twice in sterile distilled water prior to incubation in a humid chamber for 7 days (25 ± 2°C) to stimulate production of reproductive bodies. Black sub-epidermal perithecia with unitunicate, cylindrical-clavate, 8-spored asci (n = 20) were obtained. Ascospores were septated, hyaline, multigutulate, and slightly constricted at the septum, the average measurements were (n = 20) 13.4 ± 0.6 μm × 3.9 ± 0.2 μm. The ascospores were transferred to potato dextrose agar (PDA) and incubated for 6 days at 25°C in the dark, then hyphal tips were transferred to fresh PDA and obtained a mycelia with white, cottony, and sparse colonies. Pycnidia and smooth, unicellular, hyaline, and biguttulate alpha conidia of 6.1 to 7.2 μm × 2.8 to 3.1 μm (n = 40) were observed. Beta conidia were not observed in culture media. Mature pycnidia were also detected on hazelnut shells remaining on the soil from the previous season. The identification of the species (isolate IMI-501237) was confirmed at CABI, United Kingdom, using an internal transcribed spacer (ITS), rDNA, BLASTn analysis of the 524-bp fragment, and showed 100% identity with Diaporthe australafricana Crous & J.M. van Niekerk (accessions KC343039, KC343038). These molecular and morphological characteristics were similar that reported from Vitis vinifera (2) and Chilean blueberry (3). The sequence obtained was deposited in GenBank (Accession No. JX316218.1). A pathogenicity test was conducted with isolate IMI-501237 on four 1-year-old plants from the hazelnut cultivar Barcelona. Plants were maintained in individual bags in greenhouse conditions (14/10 h dark/light, 20°C; 70% relative humidity). Prior to inoculation, plant tissues were surface disinfected with 2% sodium hypochlorite and rinsed with sterile distilled water. Each plant was inoculated at fresh wound sites on three stems and three vegetative buds on twigs. The inoculum consisted of an agar plug with mycelia (5 mm) from the edge of an actively growing colony cultured on PDA for 6 days. Each inoculation was covered with moistened cotton and sealed with Parafilm; a control plant was inoculated in the same way with agar only. After 30 days, necrotic lesions and discolored vascular tissue were only observed on inoculated stems and twigs. Symptomatic tissues were removed and incubated on PDA. D. australafricana was consistently recovered from these tissues, satisfying Koch's postulates. The control plant showed no symptoms of the disease. D. australafricana were previously reported on Vitis vinifera in Australia and South Africa (2,4), and Vaccinium corymbosum in Chile (1,3). To our knowledge, this is the first report of Diaporthe australafricana on Corylus avellana cultivar Barcelona in worldwide. References: (1) K. Elfar et al. Plant Dis. 97:1042, 2013. (2) R. Gomes et al. Persoonia 31:1, 2013. (3) B. Latorre et al. Plant Dis. 96:5, 2012. (4) J. M. van Niekerk et al. Australas. Plant Pathol. 34:27, 2005.

Boron (B) is an essential micronutrient required for physiological and biochemical processes in fruit crops such as highbush blueberry (Vaccinium corymbosum L.), well adapted species to acidic soils (pH water ≤ 5.5) with relatively low B availability. However, an optimal range of B supplies is quite narrow, particularly among cultivars, making it easy to under-or over-fertilize which could lead to boron toxicity. Under controlled conditions, cultivars Brigitta and Legacy were grown in a peat moss substrate (pH 4.5) with five B concentrations (0, 50, 200, 400 and 800 µM). Plant biomass, nutrient concentration, water potential (Ψ leaf ), oxidative stress and antioxidant activity were determined at 30 d. Concentrations of 400 and 800 µM B reduced shoot and root growth in both cultivars, and 800 µM B decreased Ψ leaf in Legacy and significantly increased it in Brigitta. Boron applied at 400 µM resulted in the highest B accumulation in leaves of Brigitta (5-fold) and Legacy (2-fold), whereas Brigitta roots showed up to 60% increased B accumulation in comparison with 50 µM B, respectively. High B caused more severe oxidative stress in leaves of Legacy than B deficiency. The antioxidant activity was increased from 50 to 400 µM B in both cultivars. Boron added at 400 and 800 µM impaired physiological and biochemical performance probably due to toxicity, demonstrating that highbush blueberry in a genotype-dependent manner has relatively low B requirement.

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