Number Of Sporangia Research Articles

Undaria pinnatifida (Harvey) Suringar aqueous extract activates potato defense responses against Phytophthora infestans

Undaria pinnatifida is an invasive macroalga on the Argentinean coast and its use as a biostimulant was rarely investigated. The present work aimed to evaluate the effect of U. pinnatifida aqueous extract (AE) as an inducer of potato defense responses. Our results showed that AE protected potato plants against Phytophthora infestans infection. Application of AE by foliar spray (10% dilution), resulted in a significant reduction in disease severity. However, when antimicrobial activity was tested in vitro, a higher concentration of AE was needed to reduce P. infestans growth, showing hyphae morphological alterations and a reduction in the number of sporangia. These results indicate that AE at 10% induced defense responses in treated plants. The analysis of PR1 and IPII genes (Salicylic Acid and Jasmonic acid pathways markers, respectively), showed that the SA pathway would participate in the AE-induced resistance. Additionally, the accumulation of β-1,3-glucanase, guaiacol peroxidase activity, and changes in free polyamines were analyzed. An accumulation or enhanced activity was stimulated by AE. Moreover, the effect of AE treatment might be positive for the plant performance, since all the dilutions of AE tested showed an increment of chlorophyll content. These preliminary results strongly encourage further studies of the potential use of AE as an alternative tool for potato disease management using locally available seaweed in environmentally friendly conditions.

Red rust disease occurring in some fruits species in Cameroon

The knowledge of the red rust disease remains limited in Cameroon, with a view to developing a control method. This work consisted in studying red rust on some fruit species such as Annona muricata (soursop), Dacryodes edulis (safou), Psidium guajava (guava) and Theobroma cacao (cocoa).
 Diseased leaves were collected in the field in the Maham site, in west region of Cameroon.The symptomatology of disease (colour, number and diameter of lesions) was studied. Coefficient of variation ( %) was calculated. The incidence and severity of the disease was assessed in the different orchards surveyed. The measurement of the different structures of the thallus (length, width of sporangia and sporangiophores) was carried out using a microscope with a micrometer.
 The disease is characterized by circular orange to orange-brown spots on the upper surfaces and rarely on the lower surface. Number of lesions, varied from 245–510 respectively with D. edulis and T cacao. Lesion diameters varied from 0.1−1 cm, 0.1−7 cm, 0.1−1.5 cm in safou (African pear), guava and soursop respectively. The length and width of sporangiophores varied from 280.5−714×10.2−25.5 µm for A. muricata, 408−612×15.3−25.5 µm for Dacryodes edulis, 433.3−663×15.3−20.4 µm for P. guajava and 484.5−612×20.4−35.7 µm for T. cacao. The number of sporangiophores varied from 1 to 11 at the maximum threshold. But, number of sporangia was the same in the four species, 1−9. The pathogenicity test was negative.
 The data measurements show that the specie observed is Cephaleurus virescens which is a parasitic alga.
 The data obtained are a basis for the development of an integrated control strategy against this emerging disease

Pollen cones and in situ pollen of Aegianthus Krassilov from the Middle Jurassic of East Siberia, Russia

The paper documents in detail the morphological and epidermal characters of the pollen cones and in situ pollen of Aegianthus based on the study of specimens from the Prisayan Formation (Middle Jurassic) in the Irkutsk Basin (Siberia, Russia). An emended diagnosis is provided and a lectotype is selected for the type species, A. sibiricus, since a holotype/lectotype was not indicated in the previous publications of this species. Resin bodies are found in sporangiophores of A. sibiricus for the first time. The number of sporangia is specified as 10–12 per sporangiophore. This species differs from other Aegianthus species in smooth periclinal cell walls and lacking papillae on the subsidiary cells of the stomata in the abaxial epidermis of the peltate head. A new species, A. irkutensis, is described from the same Prisayan Formation of the Idan locality in the Irkutsk Basin. Unlike A. sibiricus, the cells of the outer epidermis of A. irkutensis are strongly papillate. A. irkutensis differs from other Aegianthus species by smaller resin bodies, numerous and longer sporangia. Pollen cones of both A. sibiricus and A. irkutensis were found in association with leaves of Sphenobaiera. The pollen of A. irkutensis are similar to those of A. sibiricus in morphology and ultrastructure. Pollen grains are boat-shaped, monosulcate. The exine surface is psilate or scabrate in the light microscope, and scabrate to granulate in SEM; the infratectum consists of large granules or columella-like elements. The exine ultrastructure of the Aegianthus pollen under study implies a ginkgoalean or gnetophytalean affinity.

Correlations between antioxidative enzyme activities and resistance to Phytophthora leaf blight in taro

ABSTRACT The present study aimed to investigate the correlations between the activities of antioxidative enzymes (AOEs) and Phytophthora colocasiae Racib. (Pc) incidence in taro (Colocasia esculenta (L.) Schott) under induced epiphytotic conditions. The activities of AOEs in leaf tissues of taro were increased significantly (up to 7.6-fold) under Pc infestation compared with the control. Spot diameter had significant negative correlations with superoxide dismutase (SOD, r = –0.42), catalase (CAT, r =–0.36), ascorbate peroxidase (APX, r = –0.47), polyphenoloxidase (PPO, r = –0.41) and monodehydroascorbate reductase(MDAR, r = –0.44) activities. The number of sporangia was negatively correlated with guaiacol peroxidase (GPX, r = –0.375)and MDAR (r = –0.51) activities. The percentage of leaves infected and the infected leaf area were negatively correlated with GPX (r= –0.392 and –0.369, respectively), but they were positively correlated with the number of sporangia produced by Pc infection (r = 0.571 and 0.721, respectively). All the AOE activities were positively correlated with each other and negatively correlated with disease incidence. Spot diameter had a close association with disease severity, suggesting that this parameter could be reliable for the screening of taro genotypes for Pc. SOD,CAT, APX, PPO, and MDAR, exhibited strong roles in combating Pc infestation, as evidenced by the correlation matrix and principal component analysis (PCA). Taro genotype ‘RCMC–5ʹshowed resistance to Pc, with low disease incidence and higher AOE capacity than the other genotypes, suggesting the potential of this genotype for use in taro breeding programs.

Identification and characterization of defensin genes conferring Phytophthora infestans resistance in tomato

Defensins are widely distributed in all plants, and these proteins play important roles in the resistance to pathogens. In this study, two tomato defensin genes (SlyDF1 and SlyDF2) were cloned and characterized from tomato Solanum lycopersicum Zaofen No.2. Phylogenetic analysis classified SlyDF1 and SlyDF2 into Group II of the defensin family, and the two proteins were shown to have a closer genetic relationship with MtDef4 and PDF2.5. Both SlyDF1 and SlyDF2 transcripts were observed in the root, stem, leaf, flower and mature fruit of the tomato plant, and were strongly upregulated 1 and 2 days after inoculation of the whole plant with Phytophthora infestans. The tomato plants that overexpressed SlyDF1 displayed greater resistance to P. infestans infection, as evidenced by decreased P. infestans abundance, disease index, number of necrotic cells, lesion sizes, and number of sporangia per leaf compared to the control plants. SlyDF1 enhanced the activities of peroxidase (POD) and superoxide dismutase (SOD) to decrease the accumulation of H2O2, thereby preventing damage to the tomato cell membrane during resistance to P. infestans infection. The results suggest that tomato defensin might play a role of positive regulation in the response to P. infestans infection and could therefore be considered as a candidate gene for enhancing biotic stress-resistance in tomato.

Morphological and genetic diversity in citrus genotypes to substantiate rootstock breeding for root rot resistance

Investigations were conducted on six citrus rootstocks, viz., rough lemon (RL), trifoliate orange (TO), Swingle citrumelo (SC), X 639 (X), Rangpur lime (RA) and Gou Tou (GT), to assess the morphological and genetic variability; and reaction against Phytophthora. Smooth trunk surface was recorded in all the genotypes. Three genotypes had erect growth habit, while it was spreading in Gou Tou (GT), Rangpur lime (RA) and rough lemon (RL). The leaves of GT, RA and RL were of unifoliate, while trifoliate orange (TO) had trifoliate leaf and Swingle citrumelo (SC) and X 639 (X) had multifoliate leaf division. No variation was recorded with respect to flowering season in all citrus rootstocks, i.e. mid February to last week of March. Fifty-five SSR markers were used for evaluation of genetic diversity amongst the six rootstocks. Twenty markers exhibited high polymorphism and showed wide allelic diversity. Capacity of each SSR to show polymorphic loci, varied from 0.29 (F98) to 0.83 (CCSME46 and CCSMEc4) with an average PIC value of 0.61. The resolving power (Rp) was highest for the primer CCSME43 (8.33) and was lowest for F90 (1.33). Significant differences were observed in the value of MI and were found to be the highest for primer F40 (9.25), while minimum MI was recorded for F98 (0.38). The PIC values of a marker vary with the crop and the set of the genotypes used. The reduction in the number of sporangia and lesion size in trifoliate orange and Swingle citrumelo indicated their tolerance against Phytophthora nicotianae var. parasitica. The number of sporangia counted after 48 h of incubation showed that all leaf baits of each rootstock were attacked by large number of sporangia. The number of sporangia on each leaf disc of rootstocks decreased after 48 h as the sporangia germinated into mycelium on the edges of leaf discs.

Prevalence of chytrid parasitism among diatom populations in the lower Columbia River (2009–2013)

Summary We documented temporal (2009–2013) and spatial [river kilometre (rkm) 8–rkm 196] patterns of parasitic fungal infections on diatoms in the lower Columbia River, as evidenced by the presence of sporangia attached to diatom frustules. Multiple diatom species were infected by zoosporic fungi (‘chytrids’) throughout the year, with a maximum infection prevalence (Ip) among large diatoms of 36% in spring 2011. At a fixed site at rkm 85, up to 30–45% of the population of Asterionella formosa, the dominant spring diatom, was infected each year during the spring (2010–2013). During this time, high Ip was associated with high host density, low precipitation and low orthophosphate concentrations. Parasite load – the number of sporangia per infected diatom cell, also referred to as the mean intensity of infection, – increased with infection prevalence, but the population average never exceed two parasites per host. Net growth rates of chytrid populations exceeded those of A. formosa host diatoms in the spring under low‐flow conditions. In spring 2013, the prevalence of infection increased from 35 to 78% and the parasite load increased from 1.5 to 2.2 along a downstream transect, suggesting that zoospores were actively infecting hosts in situ and not simply transported allochthonously. The estimated loss of organic carbon associated with diatoms via the parasitic pathway was greatest in spring (averaging c. 10%), with a peak of c. 85 μg carbon L−1 (c. 45% of total large‐diatom carbon) lost from the diatom carbon pool to parasitism in May 2011. Parasites of microalgae may actively shape aquatic food webs within systems like the Columbia River by increasing the availability of large‐diatom carbon to higher trophic levels, thus decreasing downstream export losses to the estuary and coastal ocean.

The Life Cycle of Didymium laxifilum and Physarum album on Oat Agar Culture.

The plasmodial slime molds is the largest group in the phylum Amoebozoa. Its life cycle includes the plasmodial trophic stage and the spore-bearing fruiting bodies. However, only a few species have their complete life cycle known in details so far. This study is the first reporting the morphogenesis of Didymium laxifilum and Physarum album. Spores, from field-collected sporangia, were incubated into hanging drop cultures for viewing germination and axenic oat agar plates for viewing plasmodial development and sporulation. The spores of D.laxifilum and P.album germinated by method of V-shape split and minute pore, respectively. The amoeboflagellates, released from spores, were observed in water film. The phaneroplasmodia of two species developed into a number of sporangia by subhypothallic type on oat agar culture. The main interspecific difference of morphogenesis was also discussed.

MiR1918 enhances tomato sensitivity to Phytophthora infestans infection.

Late blight of tomato is caused by the oomycete pathogen Phytophthora infestans. In our previous work, we identified and characterized a miR1918 in P. infestans (pi-miR1918), and showed that its sequence is similar to the sequence of tomato miR1918 (sly-miR1918). In this study, we used Arabidopsis thaliana pre-miR159a as a backbone to synthesize pi-miR1918 via PCR and mutagenesis. The artificial pi-miR1918 was used to investigate the role of miR1918 in tomato-P. infestans interaction. Trangenic tomato plants that overexpressed the artificial pi-miR1918 displayed more serious disease symptoms than wild-type tomato plants after infection with P. infestans, as shown by increased number of necrotic cells, lesion sizes and number of sporangia per leaf. The target genes of pi-miR1918 and sly-miR1918 were also predicted for tomato and P. infestans, respectively. qPCR analysis of these targets also performed during tomato-P. infestans interaction. The expression of target gene, RING finger were negatively correlated with miR1918 in the all Lines of transgenic tomato plants. In addition, we used the 5′ RACE to determine the cleavage site of miR1918 to RING finger. These results suggested that miR1918 might be involved in the silencing of target genes, thereby enhancing the susceptibility of tomato to P. infestans infection.

Modelling of Infection Mildew of Taro (<i>Phytophthora colocasiae</i>)

Mildew taro caused by Phytophthora colocasiae affection is the most devastating of taro cultivation in Cameroon since 2010. It has been studied in leading the influence that can have a parameter considered favourable in the kinetics of the disease, and secondly, the interaction between plots through zoospores that can move from one field to another while estimating their dispersal throughout the plant. These models have allowed us to demonstrate that the duration of pathogen latency period, the number of sporangia produced on the surface of a lesion as well as the severity of the infection taken individually, are parameters to be taken into account in the development of a variety resistant to late blight taro. The dynamics of the fungus over time is represented by a matrix. The latter was used to establish a detailed estimate of the number of new infections caused by a sporangium placed in a landscape of healthy leaves. This number is known as the net rate of breeding base name (R0). The incidence and severity of disease are significantly reduced when the rate is less than or equal to one. So our approach can be used to guide research programs or evaluate the effectiveness of control strategies to design throughout the plant.

Flutuação populacional de esporângios de Peronospora destructor no ar e sua relação com a severidade do míldio da cebola

Em experimento de campo nos anos de 2011, 2012 e 2013 quantificou-se a flutuação de esporângios de Peronospora destructore sua relação com a severidade de míldio em cebola. Mudas de cebola do cultivar Bola Precoce foram transplantadas em quatro repetições de 60 plantas. Os esporângios foram coletados através de um coletor de esporos tipo "cata-vento", contendo uma lâmina de microscópio untada com vaselina, a qual era quantificada semanalmente com auxílio de microscópio. A severidade da doença foi analisada através da porcentagem de área foliar afetada pela doença. O número de esporângios e a severidade do míldio da cebola foram submetidos ao cálculo do coeficiente de correlação linear de Pearson (r). Nos anos de 2011 e 2012 a coleta de esporângios ocorreu posteriormente à constatação da doença, provavelmente devido haver baixo inóculo no ar. Já no ano de 2013 a coleta de esporângios ocorreu anteriormente à ocorrência da doença, porém de forma esporádica e em pequena quantidade, presupondo que esses estavam no ar e foram capturados pelo coletor. A correlação entre as variáveis flutuações de esporângios e a severidade da doença foi significativa, r=0,90, r=0,94 e r=0,80; para os anos de 2011, 2012 e 2013 respectivamente. A severidade da doença em cebola é influenciada pela presença dos esporângios coletadas do ar.

Male Cone Evolution in Conifers: Not All That Simple

Despite the simple structure of male conifer cones, there is an enormous variability in cone properties observed upon more careful examination. The diversity ranges from simple cones to compound cones. Moreover, cones can be distinguished according to different spatial distributions on the tree. Simple cones are distributed either as solitary cones or as fascicular or clustered aggregations, while compound cones only exhibit fascicular or clustered aggregations. Here, we demonstrate that these different spatial distribution patterns correlate with distinct leaf types and variable branching frequencies. Furthermore, we provide new insights into the evolution of the sporangiophore, particularly in Taxaceae. Two notably important and fast-evolving characters of conifers are the number of sporangia per sporangiophore and the number of sporangiophores per cone. We demonstrate, across many species and types of cones, how these characters are able to adjust according to the optimal amount of pollen.

Rapid and multiregional adaptation to host partial resistance in a plant pathogenic oomycete: Evidence from European populations of Plasmopara viticola, the causal agent of grapevine downy mildew

Crop pathogens evolve rapidly to adapt to their hosts. The use of crops with quantitative disease resistance is expected to alter selection of pathogen life-history traits. This may result in differential adaptation of the pathogen to host cultivars and, sometimes, to the erosion of quantitative resistance. Here, we assessed the level of host adaptation in an oomycete plant pathogenic species. We analysed the phenotypic and genetic variability of 17 Plasmopara viticola isolates collected on Vitis vinifera and 35 isolates from partially resistant varieties (Regent and genotypes carrying the Rpv1 gene). Cross-inoculation experiments assessed two components of aggressiveness and a life-history trait of the pathogen: disease severity, sporangial production and sporangia size. The results contribute evidence to the emergence of P. viticola aggressive isolates presenting a high level of sporulation on the partially resistant Regent. By contrast, no adaptation to the Rpv1 gene was found in this study. The erosion of Regent resistance may have occurred in less than 5years and at least three times independently in three distant wine-producing areas. Populations from resistant varieties showed a significant increase in sporangia production capacity, indicating an absence of fitness costs for this adaptation. The increase in the number of sporangia was correlated with a reduction in sporangia size, a result which illustrates how partial plant disease resistance can impact selection of the pathogen’s life-history traits. This case study on grapevine downy mildew shows how new plant pathogen populations emerge in agro-ecosystems by adapting to partial host resistance. This adaptive pattern highlights the need for wise management of plant partial disease resistance to ensure its sustainability over time.

Phenotypic and histochemical traits of the interaction between Plasmopara viticola and resistant or susceptible grapevine varieties.

BackgroundGrapevine downy mildew, caused by Plasmopara viticola, is a very serious disease affecting mainly Vitis vinifera cultivated varieties around the world. Breeding for resistance through the crossing with less susceptible species is one of the possible means to reduce the disease incidence and the application of fungicides. The hybrid Bianca and some of its siblings are considered very promising but their resistance level can vary depending on the pathogen strain. Moreover, virulent strains characterized by high fitness can represent a potential threat to the hybrid cultivation.ResultsThe host response and the pathogen virulence were quantitatively assessed by artificially inoculating cv Chardonnay, cv Bianca and their siblings with P. viticola isolates derived from single germinating oospores collected in various Italian viticultural areas. The host phenotypes were classified as susceptible, intermediate and resistant, according to the Area Under the Disease Progress Curve caused by the inoculated strain. Host responses in cv Bianca and its siblings significantly varied depending on the P. viticola isolates, which in turn differed in their virulence levels. The fitness of the most virulent strain did not significantly vary on the different hybrids including Bianca in comparison with the susceptible cv Chardonnay, suggesting that no costs are associated with virulence. Among the individual fitness components, only sporangia production was significantly reduced in cv Bianca and in some hybrids. Comparative histological analysis revealed differences between susceptible and resistant plants in the pathogen diffusion and cytology from 48 h after inoculation onwards. Defence mechanisms included callose depositions in the infected stomata, increase in peroxidase activity, synthesis of phenolic compounds and flavonoids and the necrosis of stomata and cells immediately surrounding the point of invasion and determined alterations in the size of the infected areas and in the number of sporangia differentiated.ConclusionsSome hybrids were able to maintain an intermediate-resistant behaviour even when inoculated with the most virulent strain. Such hybrids should be considered for further field trials.

Infection by Pythium aphanidermatum increases production of phenolics in hydroponically grown peppers and predisposes healthy plants to root rot

The type and concentration of phenolics found in the cytosol (free), cell wall (bound), and nutrient solution of hydroponic pepper (Capsicum annuum L.) inoculated with Pythium aphanidermatum (Edson) Fitzp. were compared with non-inoculated controls. The quantities and types of free phenolics found in the roots and nutrient solution were greater in inoculated than in control plants. With regard to bound phenolics, while there was no difference between the types of phenolics in inoculated and control roots, quantities were greater in inoculated roots. High Pressure Liquid Chromatography analyses revealed two compounds in root extracts, and one in nutrient solution extracts that were contributors to root discolouration caused by Pythium aphanidermatum colonization. The compounds were subsequently isolated and identified as 4-hydroxybenzoic acid and 3-methoxy-4-hydroxybenzoic acid (vanillic acid) by their High Pressure Liquid Chromatography retention times, UV signature and Nuclear Magnetic Resonance spectroscopic comparisons with pure standards. Addition of various concentrations of 4-hydroxybenzoic acid or vanillic acid to the nutrient solution predisposed healthy plants to infection by zoospores of Pythium aphanidermatum when compared to plants treated with only Pythium aphanidermatum. 4-hydroxybenzoic acid and vanillic acid had little or no effect on colony growth of Pythium aphanidermatum in vitro, but respectively increased and decreased numbers of sporangia produced. These results are the first demonstration of host predisposition to infection by Pythium aphanidermatum caused by phenolic compounds that accumulate in inoculated roots and leach into the nutrient system of hydroponic systems.

Phenotypic responses to water flow and wave exposure in aquatic plants

Plastic responses of 10 aquatic plant species from 5 rivers and 5 lakes in NW Poland were examined. <em>Chara fragilis</em>, <em>C. delicatula</em>, <em>Potamogeton pectinatus</em>, <em>P. perfoliatus</em>, <em>P. natans</em>, <em>Spirodela polyrhiza</em>, <em>Hydrocharis morsus-ranae</em>, <em>Salvinia natans</em>, <em>Nymphoides peltata</em> and <em>Juncus bulbosus</em> were the subject of research. In the running water of rivers, rhizophytes were generally bigger and they allocated from 0.6% to 58.6% more biomass for anchoring in the substrate than in stagnant water (ox bow lakes). In both flow variants rhizophytes allocated a similar biomass fraction for generative reproduction. On the other hand, under the influence of water flow pleustophytes reduced the mass of an individual (<em>Spirodela</em> by 25%, <em>Hydrocharis</em> 67%, <em>Salvinia</em> 77%) and emergent structures (p<0.001), and the number of sporangia (p<0.001). In both flow variants the input of biomass to generative reproduction was the same (<em>Salvinia</em>), or it was greater in running water (<em>Hydrocharis</em>; an increase from 4.9±1.3% to 15.1±3.6%). Under the conditions of strong wave action, in comparison with the lack of this environmental factor, <em>Chara delicatula</em> was several times shorter (p<0.001). However, it was also stouter, and as a result it had similar mass. In the areas of wave action the plant allocated 88.8% of its mass for anchoring in the substrate, whereas when there were no waves, only 22.7%.

Pathogenic Fitness of Oosporic Progeny Isolates of Phytophthora infestans on Late-Blight-Resistant Tomato Lines.

Four A1 field isolates and one A2 field isolate of Phytophthora infestans were crossed to produce oospores in tomato leaves. The oospores were extracted and mixed with perlite and water, and healthy tomato leaves were used as bait for oospore-progeny infection. Twenty-nine lesions were obtained from the four crosses and 283 single-sporangium isolates were recovered and tested on four tomato differential lines carrying different major genes (Ph-0, Ph-1, Ph-2, and 3707) for late blight resistance. The pathogenic fitness (number of sporangia per unit leaf area) of parental and progeny isolates was strongly dependent on the host genotype; it decreased in the order Ph-0 > Ph-1 > Ph-2 > 3707. The A2 parent had a higher pathogenic fitness than the A1 parents on Ph-0 and Ph-1 but similar, lower fitness on Ph-2. Different levels of pathogenic fitness were observed across all isolates on Ph-0, although Ph-0 lacks resistance genes. Pathogenic fitness on one tomato genotype was not related to the pathogenic fitness on the other tomato genotypes. Some isolates exhibited reduced pathogenic fitness relative to the respective A1 parent, whereas others demonstrated a higher pathogenic fitness compared with the A2 parent. The tomato genotype Solanum pimpinellifolium L3707/5 was resistant to all five parental isolates of P. infestans. However, 37 of the 283 progeny isolates from 11 different lesions had compatible reactions with this line, producing up to 31 × 103 sporangia/cm2. Overall, reduced fitness was more frequent among the progeny isolates than increased fitness.

Asexual Reproduction of Phytophthora capsici as Affected by Extracts from Agricultural and Nonagricultural Soils

ABSTRACT Formation of sporangia and zoospores in species of Phytophthora is known to be influenced by soil microbial and chemical composition. In Phytophthora capsici, the study of the relationship of soil chemical composition to production of sporangia and zoospores has been limited. P. capsici is a soilborne pathogen of a wide array of vegetable crops, including chile pepper (Capsicum annuum) in New Mexico. Production of sporangia and zoospores by P. capsici was evaluated in extracts of soils from three different environments in New Mexico: (i) agricultural environments with a long history of chile pepper cropping and occurrence of P. capsici (CP), (ii) agricultural environments with no history of chile pepper cropping and no occurrence of P. capsici (Non-CP), and (iii) nonagricultural environments consisting of forests and rangelands (Non-Ag). There was a significant difference in production of P. capsici asexual propagules, expressed as natural log (number of sporangia x number of zoospores), among the three environments (P = 0.0298). Production of propagules was 9 to 13% greater in Non-Ag than in CP or Non-CP environments. Stepwise multiple discriminant analysis and canonical discriminant analysis identified the edaphic variables Na, pH, P, organic matter content, and asexual propagule production as contributing the most to the separation of the three environments. Two significant (P < 0.0001) canonical discriminant functions were derived with the first function, accounting for approximately 75% of the explained variance. Based on the two discriminant functions, approximately 93, 86, and 89% of observations in CP, Non-CP, and Non-Ag environments, respectively, were classified correctly. Soils from agricultural and nonagricultural environments differentially influence production of sporangia and zoospores in P. capsici, and soil samples could be effectively classified into agricultural and nonagricultural environments based on soil chemical properties and the production of asexual propagules by P. capsici in soil extracts.

Comparative Host Susceptibility and Sporulation Potential of Phytophthora ramorum

Phytophthora ramorum, causal agent of ramorum blight of woody shrub species, has caused serious damage to cultivars and species of camellia in commercial nurseries. Reports of relative susceptibility of camellia to P. ramorum have indicated a range from high to low susceptibility, both in nurseries and under experimental conditions. We inoculated a series of cultivars of camellia to determine their relative susceptibility to infection, and then compared lesion size to the capacity of the pathogen to produce sporangia on the lesions. We found, as did others, a wide range of susceptibility among cultivars, but lack of correlation between susceptibility (lesion size) and potential to produce sporangia that might spread the pathogen within the nursery. These results indicate that on some cultivars the pathogen might produce small or inconspicuous lesions, yet still produce copious numbers of sporangia that could spread the disease, both within the nursery and from nursery to nursery. Accepted for publication 10 April 2007. Published 22 August 2007.

The pollen cones of Ginkgo from the Early Cretaceous of China, and their bearing on the evolutionary significance

A well-preserved pollen cone of the genus Ginkgo was found in the Yixian Formation (Early Cretaceous) of Liaoning Province, China, and is described as the new species Ginkgo liaoningensis. The pollen cone, catkin-like, consists of a main axis bearing scales at its base and spirally arranged sporophylls bearing 3–4 (−2) oval or elliptical sporangia. The sporangia are pendulous and dehiscent by a longitudinal slit. The mature pollen grains are monocolpate and elongate-elliptical, and the juvenile pollen grains are found in the tetrad stage. The characteristics of G. liaoningensis are very similar to those of the living Ginkgo biloba, but the sporophylls of G. liaoningensis bear 3–4 (−2) sporangia, whereas those of G. biloba bear mostly two sporangia. G. liaoningensis differs from fossil cones of Ginkgo huttoni from the Jurassic of Yorkshire, UK, and an unnamed specimen of Ginkgo from the Upper Cretaceous of Alberta, Canada, in the size and number of sporangia. The comparison between G. liaoningensis (fossil) and G. biloba (living) supports the reduction hypothesis of ovule organs in Ginkgo, with the number of sporangia having experienced the process of reduction from three or four to two since the Early Cretaceous.