First Report of Powdery Mildew (Podosphaera pannosa) of Roses in Sinaloa, Mexico.

Rose (Rosa spp.) is the most important ornamental plant cultivated in greenhouse and open fields in Mexico but its quality has been limited by powdery mildew (PM). High incidence and disease damage is common during winter in Sinaloa, Mexico (temperature range 18 to 25°C and prolonged episodes of relative humidity ≥90%). The fungus attacks leaves and flowers and grows abundantly on the pedicels, sepals, and receptacles, especially when the flower bud is unopened (2). Field advisors in Mexico have referred to Sphaerotheca pannosa (Wallr. ex Fr.) Lév. as a causal agent of the disease. However, there has not been solid scientific evidence to support this statement. Morphometric and molecular analysis were conducted to elucidate the identity of the fungal isolates collected from 2012 through 2013 in northern Sinaloa. PM specimens included eight different rose varieties. Conidiophores and conidia were observed under a compound microscope. The mycelium had a mean diameter of 4.7 to 6.0 µm; conidiophores (Euoidium type) 2 to 5 celled, occasionally 6 celled emerged from the superficial mycelium; conidiophores were unbranched with conidia produced in chains from the apex. The average length of the conidiophores was 54.9 to 98.0 µm; the foot cell of the conidiophores was straight and was 24.9 to 53.6 µm long with a diameter from 8.2 to 9.8 µm across its medium part. Conidia originated from unswollen conidiogenous cells, with fibrosin bodies, formed in long chains, and were cylindrical to ovoid, 25.8 to 30.4 µm long and 13.9 to 17.3 µm wide. The outline of the conidial chains was crenate. Conidia exhibited a slight constriction at one end. The germ tubes emerged from a shoulder of the conidia. The outer wall of partially collapsed conidia showed longitudinal and transversal wrinkling and slight constrictions at the ends; the terminal end of the conidia was concentrically ridged. For molecular characterization, the ITS region of the specimens was amplified with primers ITS1F and ITS4. Phylogenetic analysis was performed with MEGA 6.0 (bootstrap = 1,000) using Kimura 2 parameter (K2P) substitution model. The resulting phylogeny grouped our specimens (GenBank KM001665 to 69) within a clade of Podosphaera pannosa (Wall.: Fr.) de Bary (formerly known as Sphaerotheca pannosa) sequences (e.g., AB525938; bootstrap (1,000) = 98). Phylogenetic and morphometric data are in agreement with descriptions of the anamorphic P. pannosa (1,3). Morphological studies indicate that P. macularis (previously known as S. humuli) and P. pannosa are not indistinctly different (2). Phylogenetic analysis showed relationship to P. pannosa, but not to P. macularis. Typical symptoms caused by P. pannosa were observed. Morphological studies (4) reported the anamorph of P. pannosa on Rosa spp. in central Mexico. To date, no report exists on the molecular identification of P. pannosa associated to roses in northern Sinaloa, Mexico. Future research directions should focus on finding the teleomorph of the fungus to support its identity, and to explore disease management tools such as effective fungicides and developing resistant rose cultivars. References: (1) U. Braun et al. Page 13 in: The Powdery Mildews: A Comprehensive Treatise. APS Press, St. Paul, MN, 2002. (2) R. K. Horst. Compendium of Rose Diseases. APS Press, St. Paul, MN, 1983. (3) L. Leus et al. J. Phytopathol. 154:23, 2006. (4) Yañez-Morales et al. Some new reports and new species of powdery mildew from Mexico. Schlechtendalia 19:46, 2009.

First Report of Powdery Mildew (Pseudoidium anacardii) of Mango Trees in Sinaloa, Mexico.

Powdery mildew of mango is an important disease in Mexico's northern Sinaloa state. Identification of the causal fungal agent has been hindered by the absence of information regarding its teleomorph, as well as a detailed morphometric analysis of the anamorph and molecular characterization. The first symptoms of the disease appear in mango inflorescences of early February, and it subsequently affects young fruits. The disease progresses during March and early April, causing significant fruit abortion and a scabby appearance in a high percentage of fruits that remain attached to the trees. We observed the disease on inflorescences but not in leaves during our sampling period. Powdery mildew specimens were collected during 2011 and 2012 and included Kent and Keith varieties from commercial orchards, and creole materials from backyards of private residences in the Ahome and Fuerte Counties of northern Sinaloa, Mexico. Symptomatic inflorescences were analyzed morphologically. Conidiophores and conidia were prepared by touching the whitish lesions with clear adhesive tape, which was then placed over microscope slides with a drop of distilled water and observed under a compound microscope. The anamorph structures of the pathogen were measured. The mycelium was septate and ramified on the surface of the host, forming a dense coat of branching hyphae. The mycelium had a diameter of 2.5 to 8.7 µm; conidiophores (Pseudoidium type) emerged from the superficial mycelium, were unbranched, and consisted of 1 to 3 cells with conidia forming singly from the apex. The length of the conidiophores varied from 30.0 to 77.5 µm; the foot cell of the conidiophores was straight, 10.0 to 47.5 µm long and with a diameter of 5.0 to 15.5 µm across its midpoint. Conidia without fibrosin bodies were borne singly, and were ellipsoid/ovoid, 22.5 to 46.2 µm long and 15.0 to 27.5 µm wide. Eighty percent of the germ tubes were forked (lobed); the rest were simple, emerged from the end, and were occasionally on the side of the conidia. Germ tubes ranged from 2.0 to 7.2 µm at the midpoint. The surface of the conidia appeared smooth under the scanning electron microscope, and elliptical conidia appeared constricted at their ends; this, however, was not observed in the ovoid conidia. In both cases, the terminal end of the conidia was smooth. The teleomorph was not found. Molecular and phylogenetic analysis of the ITS rDNA (2) region showed that samples are closely related to specimens of Pseudoidium anacardii (1) (teleomorph: Erysiphe quercicola [4]) collected from mango trees in diverse countries. Measurements of somatic and asexual structures are in agreement with descriptions of P. anachardii (formerly known as Oidium mangiferae) from India (3). The nucleotide sequences derived from this research were deposited in GenBank (Accession Nos. JX893951 to JX893957). To our knowledge, this is the first report of P. anacardii associated to mango inflorescences in Sinaloa, Mexico. Due to the economic importance of powdery mildew of mango trees in Sinaloa, future research directions should focus on finding the teleomorph of the fungus to support its identity. References: (1) U. Braun and R. T. A. Cook CBS Biodiversity Series No. 11, 2012. (2) S. Limkaisang et al. Mycoscience 47:327, 2006. (3) O. Prakash and K. C. Srivastava. Mango diseases and their management. A World Review Today and Tomorrow Publishers. New Delhi, India, 1987. (4) S. Takamatsu et al. Mycol. Res. 111:809, 2007.