P. Lopez

First report of Colletotrichum sansevieriae causing anthracnose of Sansevieria trifasciata in Florida.

Sansevieria Thunberg, a member of the Agavaceae, contains around 60 species indigenous to Africa, Arabia, and India. Several species and their cultivars are commercially produced for use as interior and landscape foliage plants. During August 2010, several local nurseries submitted Sansevieria trifasciata samples to the Florida Extension Plant Diagnostic Clinic in Homestead. Leaves had round, water-soaked lesions and as the disease progressed, lesions rapidly enlarged and coalesced, resulting in severe leaf blight. Both young and mature leaves were affected. Closer examination of mature lesions revealed numerous brownish black acervuli that were produced in concentric rings, which is characteristic of anthracnose. The fungus was identified as Colletotrichum sansevieriae Nakamura based on typical cultural characteristics, conidial and appressoria morphology (1). Conidia were straight, cylindrical, obtuse at the apex, slightly acute at the base with a truncate attachment point, and 12.5 to 33 (18.4) × 4 to 8.9 (6.5) μm (n = 50). Hyphopodia were ovate, dark brown, single celled, and 6.2 to 8.7 (7.7) × 6.3 to 7.5 (7.3) μm (n = 25). Colonies on potato dextrose agar (PDA) were grayish white, felted with aerial mycelium, reverse gray to dark olivaceous gray, and partly cream in color. Sequences of the rDNA internal transcribed spacer (ITS) regions of two isolates (GenBank Accession Nos. JF911349 and JF911350) exhibited 99% nucleotide identity to an isolate of C. sansevieriae (GenBank Accession No. HQ433226) collected from diseased sansevieria in Australia. In addition, a maximum parsimony analysis (MEGA v.5.0) indicates that the two C. sansevieriae isolates from Florida are monophyletic (86% bootstrap support) with the type species from Japan (SA-1-2 AB212991; SA-1-1 AB212990) and the Australian isolate. Pathogenicity of our sequenced isolates was evaluated in greenhouse experiments. Twelve- to fourteen-week-old sansevieria plants were inoculated with conidial suspensions (1 × 106 conidia/ml) of C. sansevieriae. Inoculum or autoclaved water was sprayed over the foliage until runoff. Four plants of each of two economically important cultivars, Laurentii and Moonshine, were sprayed per treatment and the experiment was repeated twice. Inoculated plants were placed in a greenhouse at 29°C with 70 to 85% relative humidity. Plants were observed for disease development, which occurred within 10 days of inoculation for both cultivars. No symptoms developed on the control plants. Foliar lesions closely resembled those observed in the affected nurseries. C. sansevieriae was consistently reisolated from symptomatic tissue collected from greenhouse experiments. On the basis of molecular phylogenetics and distinguishing morphological characters, Nakamura et al. erected C. sansevieriae as a novel species that appears to be restricted to the host sansevieria (1). To our knowledge, this is the first report of C. sansevieriae causing anthracnose of sansevieria in Florida. Reference: (1) M. Nakamura et al. J. Gen. Plant Pathol. 72:253, 2006.

Antifungal activity of five plant-extracted essential oils against anthracnose in papaya fruit

Abstract Inhibitory effects of five different plant essential oils were assessed against papaya fruit decay caused by anthracnose. Essential oils were extracted from savory, thyme, cinnamon, mint, and lavender plants and chemical components of each oil were identified by GC-mass spectroscopy. The polymerase chain reaction (PCR) method using the internal transcribed spacer (ITS) primer confirmed the identity of the Colletotrichum gloeosporioides isolate. Then different concentrations of each oil were tested in vitro and in vivo. The in vitro results revealed a 100% reduction of mycelium growth for savory and thyme essential oils. In the in vivo experiment, savory and thyme oils at 2000 μL L−1 caused a 59.26 and 58.40% reduction in lesion diameter and a 64.07 and 54.82% of fruit decay, respectively. Application of savory or thyme oil resulted greater maintenance of fruit firmness than the application of the other essential oils after fruit were inoculated with the anthracnose fungus. Savory oil with the main chemical compound carvacrol (71.2%), and thyme oil with the main chemical constituent thymol (73.3%) were the most effective of the oils tested at controlling anthracnose in vitro and in vivo. The half maximal effective concentration (EC50) of savory oil was the lowest among the extracted oils tested, resulting in EC50 = 58.42 μL L−1 for the in vitro test and EC50 = 1507.19 μL L−1 for the in vivo experiment. This study showed that savory oil is effective as a natural fungicide for controlling anthracnose decay and prolonging the storage life of papaya fruit.

First Report of Rust Caused by Puccinia nakanishikii on Lemongrass, Cymbopogon citratus, in Florida

Lemongrass, Cymbopogon citratus (DC.) Stapf. (Poaceae), is grown widely in the tropics and subtropics as an ornamental, flavoring ingredient in Asian cooking, and for tea and fragrant oil (3). In February 2013, rust symptoms were observed on lemongrass in several gardens in Miami-Dade County, Florida. Symptoms began as small chlorotic flecks on both leaf surfaces that became crimson and enlarged to streaks ~1 cm in length. On the abaxial side of leaves, erumpent streaks ruptured to produce pustules in which urediniospores formed. Eventually, streaks coalesced to produce large patches of tan to purplish necrotic tissue that blighted most of the leaf surface and was often surrounded by chlorotic borders. These symptoms, fungal morphology, and nuclear ribosomal large subunit (28S) DNA analysis were used to identify the pathogen as Puccinia nakanishikii Dietel. Urediniospores were pyriform to globose, orange to crimson, slightly echinulate, and somewhat longer than a previous report (32.1 ± 3.4 (27 to 42) × 23.3 ± 2.4 (21 to 27) μm vs. 22 to 28 × 22 to 25 μm) (2). Uredinia contained clavate paraphyses, but teliospores were not observed. No aecial host is known for this pathogen. A 28S DNA sequence that was generated with the NL1 and LR3 primers (1,4) was deposited in GenBank under accession no. KC990123; it shared 99% identity with GenBank accession GU058002, which came from a specimen of P. nakanishikii in Hawaii. Voucher specimens of affected leaves of lemongrass have been deposited at the Arthur Herbarium, Purdue University. Although this disease has been reported in California, Hawaii, New Zealand, and Thailand, this is believed to be the first report from Florida (2). Based on rainfall and temperature conditions that are conducive to its development in South Florida, it has the potential to significantly reduce the health and production of this plant in area gardens. References: (1) C. P. Kurtzman and C. J. Robnett. Antonie Van Leeuwenhoek 73:331. 1998. (2) S. Nelson. Rust of Lemongrass. Univ. Hawaii PD-57, 2008. (3) USDA, ARS, GRIN Online Database. URL: http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?12797 , accessed 25 April 2013. (4) R. Vilgalys and M. Hester. J Bacteriol. 172:4238, 1990.

First report of Pythium myriotylum causing damping-off of Amaranthus tricolor in Florida.

Amaranthus tricolor ‘Garnet Red’ is an edible ornamental often sold for its striking color as well as its culinary uses. There are several cultivated species of amaranth that vary in shape, size, and color. This particular cultivar (Garnet Red) is praised for its high nutritional value. It can be harvested at any age, making it commonly used as either microgreens, sprouts, salad leaves, or for seed and grain. Amaranth is easy to grow and reasonable yields can be produced even in poor soils (Sealy et al. 1990), but damping-off of seedlings by Pythium sp. is a problem for producers and breeders (National Research Council 1984). In November 2011, amaranth seedlings cv. Garnet Red from a local nursery were submitted to the Florida Extension Plant Diagnostic Clinic in Homestead, FL. Symptoms began as a rot and that ultimately resulted in the loss of the entire planting of seedlings, causing post-emergent damping-off in both the greenhouse and shadehouse locations where the crop was grown. A Pythium sp. was confirmed via microscopic observations from cultures on PARP medium showing aplerotic oospores, about 20 to 27 μm in diameter and walls up to 2 μm thick (n = 15) (van der Plaats-Niterink 1981). The region of rDNA, the internal transcribed spacer (ITS), was amplified with primers ITS1 and ITS4 and the PCR product was sequenced. The resulting sequence was deposited in GenBank (accession no. KF008434). A 99% nucleotide identity was found with a BLAST search in GenBank with an isolate of P. myriotylum (HQ237488) associated with bud rot of oil palm. MEGA 6.06 software was used for the phylogenetic analysis by the maximum likelihood method (Tamura-Nei model). Our isolate grouped with other P. myriotylum isolates with high support (100% bootstrap values, 1,000 replicates). To confirm pathogenicity, amaranth ‘Garnet Red’ seeds were sown in 4-inch pots with Promix BX Mycorrhizae dry mix under greenhouse conditions where temperature ranged from 25 to 32°C. Seeds were inoculated 24 h after sowing by drenching with a 5 ml sporangial suspension (1 × 10⁶ sporangia/ml) of our P. myriotylum isolate. Control plants were drenched with an equal volume of sterile water. Five plants per treatment were used and the experiment was repeated. After 72 h, seedlings had collapsed. P. myriotylum was reisolated from symptomatic tissues and was confirmed through morphological and molecular analyses. No symptoms developed on the control plants. P. myriotylum is an aggressive pathogen causing important economic losses with a very large host distribution worldwide in warm regions. In south Florida, it had previously been reported causing aerial blight of tomato, and more recently, basal rot on Echeveria (Roberts et al. 1999; Suarez et al. 2016). To our knowledge, this is the first report of P. myriotylum causing damping-off of an Amaranthus species in Florida.

First Report of Downy Mildew on Gynura aurantiaca Caused by Plasmopara halstedii sensu lato in Florida

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First report of Phytophthora palmivora causing foliar blight of Pachira aquatica in Florida.

Pachira aquatica Aubl. is a member of the Bombaceae, indigenous to Central America and northern South America. Known as the money tree within the ornamental plant industry, this tropical species is well adapted to landscapes in south Florida, Hawaii, and milder areas in southern California. Recently, its become more popular as a potted plant for use in the interiorscape. During August 2011, several local nurseries submitted P. aquatica samples to the Florida Extension Plant Diagnostic Clinic in Homestead, FL. The foliage exhibited dark brown to black water soaked spots that became papery as the disease progressed, and rapidly enlarged and coalesced, resulting in severe leaf blight. Both young and mature leaves were affected. Phytophthora was initially confirmed by serological testing with a commercially available ImmunoStrip test (Agdia, Elkhart, IN). On closer examination, the pathogen was further identified as Phytophthora palmivora by the presence of numerous papillate, deciduous, ellipsoidal to ovoid sporangia with short pedicels. The sporangia averaged 53 × 32 μm with ranges of 48 to 59 × 29 to 35 μm (1). Phytophthora species-specific primers (pal1s and pal2a) targeting part of the 18S rRNA gene, the ITS 1, the 5.8S rRNA gene, and the ITS 2 resulted in a PCR product of 648 bp, testing positive for P. palmivora (2). The PCR product was cleaned (Qiagen Purification Kit) and sequenced (GenBank Accession No. JQ354937). The sequence from our isolate was nearly identical (exhibited 99% nucleotide identity) to an isolate of P. palmivora (GenBank Accession No. HE580280) collected from diseased cassava in China. To further support identification, phylogenetic analysis by the maximum likelihood method (Tamura-Nei model) was performed using the obtained sequence and several other Phytophthora and Pythium species from GenBank (MEGA 5.05). Our isolate grouped with other P. palmivora isolates with high support (100% bootstrap values, 1,000 replicates). Pathogenicity of the sequenced isolate was evaluated in shade house experiments. Six-month-old Pachira aquatica plants were inoculated with sporangial suspensions (1 × 106 conidia/ml) of P. palmivora. Inoculum or autoclaved water was sprayed over the foliage until runoff. Six plants were sprayed per treatment, and the experiment was repeated twice. Inoculated plants were placed in a shade house (70% shade) when temperatures ranged from 25 to 32°C with 78 to 98% relative humidity. Plants were observed for disease development, which occurred within 7 days of inoculation. No symptoms developed on the control plants. Foliar lesions closely resembled those observed in the affected nurseries and P. palmivora was reisolated from symptomatic leaf tissue. To our knowledge, on the basis of serological testing, molecular analysis, and distinguishing morphological characters, this is the first report of P. palmivora causing foliar blight of Pachira aquatica in Florida. The high incidence and severity of this disease may seriously influence local tropical foliage producers in the future. References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. American Phytopathological Society, St Paul, MN, 1996. (2) Tsai et al. Botanical Studies 47:379, 2006.