The enigmatic monocotyledon family Triuridaceae is composed of inconspicuous mycoheterotrophs, that have been variously interpreted. We present here the first report of a thorough floral developmental series for any member of the Triuridaceae. The two known Mexican Triuridaceae species were studied with anatomical sections and scanning electron microscopy. While both species have ephemeral and reduced radially symmetric flowers arising in a counterclockwise spiral on racemose inflorescences, Lacandonia schismatica is hermaphroditic with a central androecium and Triuris brevistylis is dioecious. Tepals are connately fused at their bases, and during development the subapical caudal tips continue to elongate, while at maturity the tepals are reflexed. Carpel primordia develop centrifugally from compound primordia in both species, with contrasting androecium development. In Lacandonia schismatica stamen and carpel primordia arise from a common precursor. The two species differ in tepal and carpel number and timing of organ development. This paper provides a developmental framework to understand floral characters in the Triuridaceae. Notably, we addressed if L. schismatica and T. brevistylis bear true flowers or pseudanthia, and our data support the former. The role of particular genes in determining the floral developmental patterns studied and the evolutionary significance of these patterns are discussed.

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Spontaneous homeotic transformations have been described in natural populations of both plants and animals, but little is known about the molecular-genetic mechanisms underlying these processes in plants. In the ABC model of floral organ identity in Arabidopsis thaliana, the B-and C-functions are necessary for stamen morphogenesis, and C alone is required for carpel identity. We provide ABC model-based molecular-genetic evidence that explains the unique inside-out homeotic floral organ arrangement of the monocotyledonous mycoheterotroph species Lacandonia schismatica (Triuridaceae) from Mexico. Whereas a quarter million flowering plant species bear central carpels surrounded by stamens, L. schismatica stamens occur in the center of the flower and are surrounded by carpels. The simplest explanation for this is that the B-function is displaced toward the flower center. Our analyses of the spatio-temporal pattern of B-and C-function gene expression are consistent with this hypothesis. The hypothesis is further supported by conservation between the B-function genes of L. schismatica and Arabidopsis, as the former are able to rescue stamens in Arabidopsis transgenic complementation lines, and Ls-AP3 and Ls-PI are able to interact with each other and with the corresponding Arabidopsis B-function proteins in yeast. Thus, relatively simple molecular modifications may underlie important morphological shifts in natural populations of extant plant taxa. INTRODUCTION An ABC Model-Based Hypothesis of the Developmental Genetic Factors Underlying the Unusual Reproductive Morphology of Lacandonia schismaticaThe ABC model for the specification of floral organ identity Coen and Meyerowitz, 1991;Meyerowitz et al., 1991) has played a critical role in the modern explanation of the molecular-genetic determinants of the ontogenetic development of reproductive structures in angiosperms. This combinatorial genetic model has guided diverse plant evolutionary developmental biology studies, especially during the formative years of this young field (Cronk, 2001;Cronk et al., 2002;Pruitt et al., 2003). As part of the larger discipline of evo-devo, the articulation of explanatory tools like the ABC model is considered essential for understanding the developmental mechanisms that underlie morphological innovation throughout evolutionary time (Cronk et al., 2002;Carroll et al., 2004;Gilbert, 2006;Wolpert et al., 2006).The ABC model of flower development was based on the interpretation of floral homeotic phenotypes in Arabidopsis thaliana and Antirrhinum majus (Coen and Meyerowitz, 1991). However, the participation of homeotic transformations and other forms of heterotopy in the appearance of new organ arrangements during the evolution of angiosperms had already been considered in the botanical literature, long before the age of plant developmental genetics (e.g., Meyer, 1966;Sattler, 1984;Bowman et al., 1989;Weston, 2000). Outstanding instances of spontaneous floral homeotic phenotypes have continued to be recorded in well-characterized taxa (s...

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.

Epiphytic dinoflagellates were studied in 250 samples from 10 sites in Chelem (a semi-enclosed mangrove lagoon) and Dzilam de Bravo (an exposed coastal locality), on the northern coast of the Yucatan Peninsula, during five surveys in [2008][2009]. Temperature, salinity, turbidity, pH, dissolved oxygen, nitrates, nitrites, phosphates, silicates, urea, extractable water column chlorophyll-a, precipitation, and wind speed and direction were measured. The Chelem lagoon system showed minor variability in physical-chemical characteristics compared to the exposed site at Dzilam de Bravo. Dinoflagellates were associated with all the host macrophytes examined including four seagrass species and 33 macroalgal species representing 24 genera. A total of 20 dinoflagellate taxa from 12 genera were recovered from these substrates. The genus Prorocentrum contained the largest number of individual species. The variation in mean epiphytic dinoflagellate abundance over both localities ranged from ~200 to 3500 cells g -1 substrate wet weight. Cell abundances at individual sites, in contrast, ranged from ~100 to >25 000 cells g -1 substrate wet weight. This variation is typical of the patchy distribution of these species in time and space.

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.

The funicular cover of theOpuntia tomentosaseed limits imbibition; germination occurs only when the funicle is weakened or the funicular valve is removed. We investigated the role of fungi in funicular weakening and seed germination. Seeds that had been either buried in one of two sites or stored in the laboratory were germinated with and without a valve. Disinfected or nondisinfected seeds and their naked embryos were cultivated on agar or PDA. None of the 11 identified fungal genera grew on the disinfected control seeds or the embryos. The mycoflora present on disinfected and nondisinfected exhumed seeds suggest that the fungal colonization occurred in the soil and differed between the burial sites. Exhumed seeds with and without a valve germinated in high percentages, whereas only the control seeds without a valve germinated. Scanning electron micrographs showed that the hyphae penetrated, cracked, and eroded the funicular envelope of exhumed seeds.

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