Development in vitro of Nephrolepis exaltata cv. Bostoniensis Runner Tissues

Study of organogenesis in vitro in runner tissues of the fern Nephrolepis exaltata cv. Bostoniensis has shown that the process involves two stages: the first being primoirdium initiation and the second involving release of these primordia from an apparent quiescent state. In vitro shoot development from the primordia required light and an exogenous supply of carbohydrate. No exogenous growth regulators were necessary, but rate of shoot development was promoted by both NAA and kinetin. Root initiation occurred in both the light and dark and was promoted by 2,4-D and NAA, but neither was essential. Organogenesis was generally inhibited with standard levels of Murashige and Skoog inorganic salts, but inhibition could be avoided with the use of dilute levels.     

Phymatotrichum (cotton) root rot caused by Phymatotrichopsis omnivora: retrospects and prospects

Phymatotrichum (cotton or Texas) root rot is caused by the soil‐borne fungus Phymatotrichopsis omnivora (Duggar) Hennebert. The broad host range of the fungus includes numerous crop plants, such as alfalfa and cotton. Together with an overview of existing knowledge, this review is aimed at discussing the recent molecular and genomic approaches that have been undertaken to better understand the disease development at the molecular level with the ultimate goal of developing resistant germplasm. Taxonomy: Phymatotrichopsis omnivora (Duggar) Hennebert [synonym Phymatotrichum omnivorum (Shear) Duggar] is an asexual fungus with no known sexual stage. Mitosporic botryoblastospores occasionally form on epigeous spore mats in nature, but perform no known function and do not contribute to the disease cycle. The fungus has been affiliated erroneously with the polypore basidiomycete Sistotrema brinkmannii (Bres.) J. Erikss. Recent phylogenetic studies have placed this fungus in the ascomycete order Pezizales. Host range and disease symptoms: The fungus infects most dicotyledonous field crops, causing significant losses to cotton, alfalfa, grape, fruit and nut trees and ornamental shrubs in the south‐western USA, northern Mexico and possibly parts of central Asia. However, this fungus does not cause disease in monocotyledonous plants. Symptoms include an expanding tissue collapse (rot) of infected taproots. In above‐ground tissues, the root rot results in vascular discoloration of the stem and rapid wilting of the leaves without abscission, and eventually the death of the plant. Characteristic mycelial strands of the pathogen are typically present on the root's surface, aiding diagnosis. Pathogenicity: Confocal imaging of P. omnivora interactions with Medicago truncatula roots revealed that infecting hyphae do not form any specialized structures for penetration and mainly colonize cortical cells and eventually form a mycelial mantle covering the root's surfaces. Cell wall‐degrading enzymes have been implicated in penetration and symptom development. Global gene expression profiling of infected M. truncatula revealed roles for jasmonic acid, ethylene and the flavonoid pathway during disease development. Phymatotrichopsis omnivora apparently evades induced host defences and may suppress the host's phytochemical defences at later stages of infection to favour pathogenesis. Disease control: No consistently effective control measures are known. The long‐lived sclerotia and facultative saprotrophism of P. omnivora make crop rotation ineffective. Chemical fumigation methods are not cost‐effective for most crops. Interestingly, no genetic resistance has been reported in any of the susceptible crop species.     

Isolation and characterization of microsatellite loci from Eidothea hardeniana,an early Proteaceae

Eidothea hardeniana is a recently discovered rainforest species representing a basal Proteoid genus. It is known from a single location in New South Wales (Australia) with the only other member of the genus, Eidothea zoexylocarya, found in northern Queensland. We developed six microsatellite loci (five cross‐transferable) from an (AG) enriched library. The loci produced relatively high levels of diversity within 30 individuals of such a rare species. These microsatellites are now being used to provide new and useful information on the management of the species and on the processes shaping the evolution and persistence of ancient rainforest taxa.     

Characterization of microsatellite loci in the European green crab (Carcinus maenas)

Carcinus maenas (Decapoda: Portunidae) has proven a highly successful invasive marine species whose potential economic and ecological impacts are of great concern worldwide. Here, we characterize 14 polymorphic microsatellite loci in C. maenas and its sister species Carcinus aestuarii. These markers will prove useful for fine‐scale genetic analyses of native and introduced populations, for assessment of the sources and routes of invasion and for evaluation of post‐invasion population dynamics.     

Genetic patterns across multiple introductions of the globally invasive crab genus Carcinus

The European green crab Carcinus maenas is one of the world's most successful aquatic invaders, having established populations on every continent with temperate shores. Here we describe patterns of genetic diversity across both the native and introduced ranges of C. maenas and its sister species, C. aestuarii, including all known non‐native populations. The global data set includes sequences from the mitochondrial cytochrome c oxidase subunit I gene, as well as multilocus genotype data from nine polymorphic nuclear microsatellite loci. Combined phylogeographic and population genetic analyses clarify the global colonization history of C. maenas, providing evidence of multiple invasions to Atlantic North America and South Africa, secondary invasions to the northeastern Pacific, Tasmania, and Argentina, and a strong likelihood of C. maenas × C. aestuarii hybrids in South Africa and Japan. Successful C. maenas invasions vary broadly in the degree to which they retain genetic diversity, although populations with the least variation typically derive from secondary invasions or from introductions that occurred more than 100 years ago.     

Macroinvertebrate colonization and biofilm development on leaves and wood in a boreal river

• 1 Biofilms, the accumulation of micro-organisms, exoenzymes, and detritus particles on submerged surfaces, may change the quality of leaves and wood as sources of food and/or habitat for invertebrates. We examined the relationship between macroinvertebrate assemblages and biofilm development on leaves and wood in a boreal river.
• 2 Arrays of white birch ice-cream sticks and sugar maple leaves were placed at fast- and slow-current sites. Samples were collected periodically, and assayed for microbial biomass (ATP, ergosterol, chlorophyll a) and macroinvertebrate colonizers.
• 3 Microbial biomass and macroinvertebrate density were consistently greater on wood than leaves. Taxon richness was similar for all substratum/current combinations, but taxon density (number of taxa m^?2) was greater on wood. Macroinvertebrate density and taxon richness correlated with all microbial indicators when data from both substrata were pooled.
• 4 Leaves did not support as great a density of invertebrates as wood perhaps because of their faster breakdown rate and truncated biofilm development. Greater stability and the potential for surface complexity may make wood a site of higher macroinvertebrate diversity than leaves.

     

Spatial and temporal variation of microbial respiration rates in a blackwater stream

1. The extent of spatial and temporal variation of microbial respiration was determined in a first-order, sand-bottomed, blackwater stream on the coastal plain of south-eastern Virginia, U.S.A.
2. Annual mean respiration rates (as g O₂ m^–3 h^–1) differed significantly among substrata: leaf litter, 12.9; woody debris, 2.4; surface sediment, 0.8; hyporheic sediment, 0.4; water column, 0.003. Rates associated with wood were higher than those with leaves when expressed per unit surface area.
3. Highest respiration rates on leaves, wood and in the water column occurred during the summer, whereas rates in the sediments were greatest during the late autumn and winter. Water temperature, as well as particulate organic matter and nitrogen content of the substrata, was correlated positively with respiration rates.
4. A stepwise multiple regression showed that temperature and nitrogen content together explained 88% of the variation in respiration rates of leaves and wood. In contrast, particulate organic matter content and nitrogen content explained 89–90% of the variation in respiration in the sediments. Although water temperature was a significant factor in the sediment multiple regressions, its addition as an independent variable improved the regression models only slightly.
5. Annual mean respiration in the stream channel, based on the proportional amount of respiration occurring associated with each type of substratum during each month, was 1.1 kg O₂ m^–2 yr^–1. Seventy per cent of respiration in the stream occurred in the hyporheic zone, 8–13% occurred in the surface sediment, leaf litter or woody debris, and < 1% occurred in the water column. Approximately 16% of total detritus, or 40% of non-woody detritus, stored in the stream during the year was lost to microbial respiration.     

Patterns of Testa-imposed Seed Dormancy in Native Australian Legumes

The testa-imposed seed dormancy of 34 native Australian speciesof Faboideae and Mimosoideae was examined immediately afterthe seeds matured and again after 3.5 years of dry storage inthe laboratory. Three groups of dormancy patterns are recognized:17 species (of the Mirbelieae and Acacieae) that have a relativelysmall nondormant fraction (0–10%) of their ripe seedsand that maintain this fraction through time; ten species (ofthe Mirbelieae) that have a relatively large non-dormant fraction(10–40%) of their ripe seeds and that maintain this fractionthrough time; and seven species (of the Bossiaeeae and Phaseoleae)that have a relatively small non-dormant fraction when the seedsripen, and have this fraction increase significantly throughtime. The species in the second group have smaller seeds thando those of the first and third groups, while the species inthe third group have a different testa construction from thosein the first and second groups. For all of the non-dormant seedstested, the water permeability is not localized only at thelens. Leguminosae, Fabaceae, Mimosoideae, Papilionoideae, Faboideae, legume seeds, seed dormancy, hard-seededness, dormancy loss, germination