Necrotic Patches Research Articles

A new host forPithomyces chartarum, the cause of a leaf spot disease onWithania somnifera

Withania somnifera, popularly known in India as ashwagandha, is an important medicinal plant. Root and leaves are used alone or in combination with other drugs for treatment of sexual and general weakness, rheumatism, scabies and sore eyes. Withaferin–A, an important withanolide has been reported to show anticancer properties (Janardhanan, 2002). During a survey for diseases of medicinal plants, a leaf spot disease was found on W. somnifera growing in field and nurseries near Jaipur, India. Symptoms of the disease were small circular to irregular necrotic spots of light brown colour which were scattered over the abaxial surface of the leaf, their size varied from 5–12 mm in diameter. In some cases, spots coalesced together, forming large necrotic patches. Individual spots had bright yellow halos. On the adaxial surface, spots were circular, grey to blackish in appearance and scattered over a major portion of the leaf lamina. Severely infected plants defoliated prematurely. A single spore culture was produced on potato dextrose agar. Colonies were fast growing, dark grey to black. Conidiophores formed laterally on hyphae, 2·4–10 × 1·5–3 µm in size. Conidia were multicellular, darkly pigmented, formed on small peg-like branches of the hyphae. They were broadly elliptical, pyriform, oblong and echinulate, 16–22 × 10–14 µm in size. The morphological characters including size of conidia (18–19 × 10–12 µm) fit the original description of Pithomyces chartarum (Ellis, 1971). A culture was deposited with the Agharkar Research Institute, Pune, India (Accession No. ARIFCC-1023). For pathogenicity testing, healthy leaves of potted plants of W. somnifera were spray inoculated with an aqueous suspension (105 conidia/mL) of a 10-day-old sporulating culture of P. chartarum. Inoculated plants and water sprayed controls were covered with polythene bags for 48 h and kept under natural light conditions and mean weekly temperature of 26°C. Typical symptoms started developing on the inoculated plants after 7–8 days. The fungus was re-isolated fulfilling Koch's postulates. Review of the pertinent literature revealed that P. chartarum is known to cause leaf spot diseases of various plants including medicinal plants (Ponappa, 1977). However, for W. somnifera, it is a new disease report for India and worldwide. The field symptoms showed that the disease was responsible for reducing W. somnifera bio-mass substantially and constitutes a potential threat to an important medicinal plant species.

Internal Heat Necrosis of Potato—A Review

Non-pathogenic necroses of potato tubers have been described in the literature since the early 20th century using different names including internal rust spot, internal browning, physiological internal necrosis, internal brown fleck, chocolate spot, internal brown spot and internal heat necrosis. These reports very likely describe either the same, or a collection of similar disorders, falling under the general umbrella of “internal necrosis”, with the expression of symptoms being significantly altered via genotype by environment interactions. A number of widely-grown cultivars (e.g. ‘Russet Burbank’, ‘Atlantic’ and ‘Yukon Gold’) are susceptible to internal necrosis, making it an economically significant problem. In Atlantic, this syndrome has been termed internal heat necrosis (IHN) in the eastern United States by several investigators because heat and drought are believed to be important triggers of this condition. Investigators in the midwestern and western United States term this same or similar disorder internal brown spot (IBS). IHN and IBS are an internal physiological disorder of potato characterized by brownish red necrotic patches of parenchymal tissue that typically, though not always, occur along and/or inside the vascular ring. Several reports indicate that IHN is most commonly associated with the vascular ring tissue near the apical end of the tuber, but IHN may form anywhere in the tuber. In many cases, it is very difficult to distinguish between IHN and IBS, and several overlapping environmental factors are associated with each of these disorders. High day and night temperatures early in the growing season, combined with low rainfall, have been shown to increase the frequency and severity of IHN and IBS in several cultivars. Considerable research has examined the role of calcium in ameliorating IHN and IBS expression. Much of this work suggests an important role for calcium in the development of IHN, but other biotic and abiotic factors undoubtedly affect IHN and IBS expression. The biochemistry and genetics behind internal necroses of potato have historically been the least-researched facets of this problem. Research has shown that enzymes involved in protecting cells from oxidative damage may be involved, and heritability studies have demonstrated that broad-sense heritability for IHN resistance is high. This review seeks to outline previous work on physiological internal necroses of potato due to high temperatures, summarize our current knowledge of IHN, and point to new areas of investigation to develop IHN resistant potato varieties.

The effect of aluminium phosphide on the human brain: a histological study

The study was conducted on 317 cases of poisoning in the Varanasi region, India, between January 2002 and August 2003. Aluminium phosphide (Celphos) was used by 239 victims (75.40% of the total) and was used in 69.03% of male and 30.96% of female cases. It was commoner in males from both rural and urban areas and in the 21-30 year age group. Microscopic investigation of the cerebral and cerebellar cortex showed distinct changes due to the effect of celphos. Findings in the cerebral cortex revealed disorganisation of the different layers, round shaped neurons with a convex border, degenerated Nissl granules in the cytoplasm and a deeply stained degenerated eccentric nucleus. Findings in the cerebellar cortex included degenerated neurons, the infiltration of round cells into the molecular layer and the disappearance of the processes of Purkinje cells. Degenerate nuclei were surrounded by scavenger cells in the granular layer. The subcortical zone of the brain revealed a paucity of glial cells, degeneration of nerve fibres and the appearance of necrotic patches.

Effect of Zinc Humate on Growth of Soybean and Wheat in Zinc‐Deficient Calcareous Soil

Humic acids have many benefits for plant growth and development, and these effects may be maximized if these materials are combined with micronutrient applications. In the present study, pot experiments were conducted to evaluate the effects of zinc (Zn) humate and ZnSO4 on growth of wheat and soybean in a severely Zn‐deficient calcareous soil (DTPA‐Zn: 0.10 mg kg−1 soil). Plants were grown for 24 (wheat) and 28 days (soybean) with 0 or 5 mg kg−1 of Zn as either ZnSO4 or Zn humate. Zinc humate used in the experiments was obtained from Humintech GmbH, Germany, and contained 5% of Zn. When Zn was not supplied, plants rapidly developed visible symptoms of Zn deficiency (e.g., chlorosis and brown patches on young leaves in soybean and necrotic patches on middle‐aged leaves in wheat). Adding Zn humate eliminated Zn‐deficiency symptoms and enhanced dry matter production by 50% in soybean and 120% in wheat. Zinc‐humate and ZnSO4 were similarly effective in increasing dry matter production in wheat; but Zn humate increased soybean dry matter more than ZnSO4. When Zn was not supplied, Zn concentrations were 6 mg kg−1 for wheat and 8 mg kg−1 for soybean. Application of Zn humate and ZnSO4 increased shoot Zn concentration of plants to 36 and 34 mg kg−1 in wheat and to 13 and 18 mg kg−1 in soybean, respectively. The results indicate that soybean and wheat plants can efficiently utilize Zn chelated to humic acid in calcareous soils, and this utilization is comparable to the utilization of Zn from ZnSO4. Under Zn‐deficient soil conditions, plant growth and yield can be maximized by the combined positive effects of Zn and humic acids.

Evaluation of Caladium Cultivars for Sensitivity to Chilling

Caladium (Caladium ×hortulanum) leaves can be injured at air temperatures below 15.5 °C. This chilling sensitivity restricts the geographical use of caladiums in the landscape, and leads to higher fuel costs in greenhouse production of pot plants because warmer conditions have to be maintained. This study was conducted to develop procedures to evaluate differences among caladium cultivars for chilling sensitivity and to identify cultivars that might be resistant to chilling injury. The effects of two chilling temperatures (12.1 and 7.2 °C) and three durations (1, 3, and 5 days) on the severity of chilling injury were compared for three cultivars known to differ in their sensitivity to low temperatures. Exposure of detached mature leaves to 7.2 °C for 3 days allowed differentiation of cultivars' chilling sensitivity. Chilling injury appeared as dark necrotic patches at or near leaf tips and along margins, as early as 1 day after chilling. Chilling injury became more widespread over a 13-day period, and the best window for evaluating cultivar differences was 9 to 13 days after chilling. Significant differences in chilling sensitivity existed among 16 cultivars. Three cultivars, `Florida Red Ruffles', `Marie Moir', and `Miss Muffet', were resistant to chilling injury. These cultivars could serve as parents for caladium cold-tolerance breeding, and this breeding effort could result in reduced chilling injury in greenhouse production of potted plants, or in new cultivars for regions where chilling occurs during the growing season.

Distribution and development of necroticSphagnum patches in two Estonian raised bogs

Sphagnum mosses dominate the plant cover of boreal bogs and accumulate carbon as peat. However, discoloured necroticSphagnum patches are also common in bogs. NecroticSphagnum inhibits peat accumulation, and consequently these areas may sink with respect to their surroundings with healthy mosses and continuing peat accumulation. Therefore, necrotic patches in the moss carpet could have an important role in triggering the succession ofSphagnum communities and the differentiation of bog microtopography. Our main aim was to find out how necroticSphagnum patches are distributed on a microtopographic gradient and amongSphagnum species. Based on these results we discuss the development and likely role of necrotic patches. It was found that necrotic patches occur on all types of bog microforms and contain the most of commonSphagnum species. Necrotic patches were more common and larger in wet hollows. The development of necrotic patches depends on their location on the microtopographic gradient. Necrotic patches on higher microforms usually re-vegetate, whereas those in hollows can result in mud-bottom hollows.

The Diphenylether Herbicide Lactofen Induces Cell Death and Expression of Defense-Related Genes in Soybean

Lactofen belongs to the diphenylether class of herbicides, which targets protoporphyrinogen oxidase, which in turn causes singlet oxygen generation. In tolerant plants like soybean (Glycine max), the chemical nonetheless causes necrotic patches called "bronzing" in contact areas. Here it is shown that such bronzing is accompanied by cell death, which was quantified from digital microscopic images using Assess Software. Cellular autofluorescence accompanied cell death, and a homolog of the cell death marker gene, Hsr203j, was induced by lactofen in treated soybean tissues. Thus, this form of chemically induced cell death shares some hallmarks of certain types of programmed cell death. In addition to the cell death phenotype, lactofen caused enhanced expressions of chalcone synthase and chalcone reductase genes, mainly in the exposed and immediately adjacent (proximal) cells. Furthermore, isoflavone synthase genes, which are wound inducible in soybean, were up-regulated by lactofen in both proximal and distal cell zones in minimally wounded cotyledons and further enhanced in wounded tissues. Moreover, if the wall glucan elicitor from Phytophthora sojae was present during lactofen treatment, the induction of isoflavone synthase was even more rapid. These results are consistent with the fact that lactofen triggers massive isoflavone accumulations and activates the capacity for glyceollin elicitation competency. In addition, lactofen induces late expression of a selective set of pathogenesis-related (PR) protein genes, including PR-1a, PR-5, and PR-10, mainly in treated proximal tissues. These various results are discussed in the context of singlet oxygen-induced responses and lactofen's potential as a disease resistance-inducing agent.

First Report of Downy Mildew of Arugula Caused by Peronospora parasitica in Argentina

Acreage of arugula (Eruca sativa), a crucifer used as a component of green salad mixes, has increased recently in Argentina. During 2004, a foliar disease affected commercial crops in Pilar (northeast of Buenos Aires Province). Arugula plants were affected from the seedling stage to harvest. Severely diseased plants were unmarketable and not harvested. Sunken, round, necrotic lesions (1 to 4 mm in diameter) were observed on the cotyledons. Diseased leaves had irregular, necrotic lesions (2 to 3 mm in diameter) that sometimes became confluent, forming a linear pattern. Necrotic tan patches developed on older leaves. Lesions on the abaxial surface appeared depressed and a gray mold, a typical sign of a downy mildew, was visible. Sporangiophores had dichotomous branches ending in slender curved tips. Sporangia were ovoid with a mean length of 20 μm (17.8 to 22.1 μm) and a mean width of 16 μm (14 to 18.2 μm). Pathogenicity tests were conducted by placing excised diseased leaves onto healthy 30-day-old arugula plants (1). Inoculated plants were placed in plastic bags, previously sprayed with water, for 48 h and maintained in the greenhouse thereafter. Downy mildew symptoms and signs that were similar to those observed in the fields developed 10 days after inoculation. The pathogen was identified as Peronospora parasitica (2). To our knowledge, this is the first report of P. parasitica on arugula in Argentina.

Rubber Tree (Hevea brasiliensis) Bark Necrosis Syndrome I: Still No Evidence of a Biotic Causal Agent.

The main constraint in rubber plantations worldwide is the cessation of latex production because of two syndromes: (i) tapping panel dryness (TPD), a reversible physiological response to overexploitation; and (ii) bark necrosis (BN), an irreversible syndrome spreading from the collar toward the tapping cut. Early BN symptoms develop in the inner phloem tissues but never affect the cambium. Necrotic patches appear in the outer phloem, inducing bark cracking and peeling, but these alterations never lead to tree death. BN spreads gradually to neighboring rubber trees, and evidence of linear disease centers suggest that a pathogen may be involved, possibly transmitted by the tapping knife. Several previous etiological investigations (fungi, phytoplasma, bacteria, and virus) were performed (3) on leaves, bark, and latex using different methods (e.g., isolation, transmission, chemical treatments, and optic and electron microscope studies). Recent works focused on mechanically transmissible pathogens, such as viroid (2) or virus/double strand RNA, using RNA extraction (nonionic cellulose and appropriate ethanol concentrations) and treatment with RNase A, followed with sequential polyacrylamide gel electrophoresis (s-PAGE), reverse transcription-polymerase chain reaction (RT-PCR), degenerate oligonucleotide primer-PCR (DOP-PCR), and cloning and sequence analysis. While numerous viroid-like (between 250 and 400 nucleotides) and double strand virus-like (1,800 bp) low-molecular-weight RNAs were observed, no definite correlation was found with the BN status of trees. Sequencing of the various isolated RNAs only identified plasmids, nonpathogenic bacteria and yeasts, but none of the suspected pathogens. In addition, previous and recent transmission trials (tapping knife disinfection, bud grafting, bark implantation, and etc.) failed to confirm the involvement of a biotic agent. In conclusion, since these etiological investigations were inconclusive, a physiological disease is now suspected that involves exogenous stresses, nonoptimal vascular relations at the rootstock/scion junction and impaired cyanide metabolism (1,4).

Effect of zinc fertilization on cadmium toxicity in durum and bread wheat grown in zinc-deficient soil

The effect of increasing application of zinc (Zn) and cadmium (Cd) on shoot dry weight and shoot concentrations of Zn and Cd was studied in bread and durum wheat cultivars. Plants were grown in severely Zn-deficient calcareous soil treated with increasing Zn (0 and 10 mg kg −1 soil) and Cd (0, 10 and 25 mg kg −1 soil) and harvested after 35 and 65 days of growth under greenhouse conditions. Growing plants without Zn fertilization caused severe depression in shoot growth, especially in durum wheat and at high Cd treatment. Cadmium treatments resulted in rapid development of necrotic patches on the base and sheath parts of the oldest leaves of both wheat cultivars, but symptoms were more severe in durum wheat and under Zn deficiency. Decreases in shoot dry weight from increasing Cd application were more severe in Zn-deficient plants. Severity of Cd toxicity symptoms in durum and bread wheat at different Zn treatments did not show any relation to the Cd concentrations in shoot. Increasing Cd application to Zn-deficient plants tended to decrease Zn concentrations in Zn-deficient plants, whereas in plants with adequate Zn, concentrations of Zn were either not affected or increased by Cd. The results show that durum wheat was more sensitive to both Zn deficiency and Cd toxicity as compared to bread wheat. Cadmium toxicity in the shoot was alleviated by Zn treatment, but this was not accompanied by a corresponding decrease in shoot concentrations of Cd. Our results are compatible with the hypothesis that Zn protects plants from Cd toxicity by improving plant defense against Cd-induced oxidative stress and by competing with Cd for binding to critical cell constituents such as enzymes and membrane protein and lipids.

Surveillance of potential pathogenic fungi associated with water hyacinth in Lake Kainji, Nigeria

The entire Kainji Lake and the riverine areas upstream of Yauri were surveyed monthly between February and May 2002 with a motorboat to make full inspection of fungi-infested water hyacinth plants. Various parts of water hyacinth plant showing symptoms of fungal infection were collected, dried between paper towels, labeled, treated and planted onto growth agar media in petri dishes sealed with parafilm. All isolates were characterised for identification. On some older plants with larger leaves were found sporulating Myrothecium roridum. On the smaller plants with purple flecking lesions were isolates of Alternaria eichhorniae of, which were necrotic patches surrounded by chlorotic halos. The presence of A. eichhorniae in Nigeria indicates a great promise as its choice in most African environment by the International Mycoherbicide Programme for Eichhornia crassipes Control in Africa (IMPECCA) for development into a mycoherbicide. Other fungal pathogens isolated included Rhizoctonia solani, Acremonium zonatum and Cercospora piaropi. Key words : Bio-control, pathogenic fungi, Kainji Lake, water hyacinth, identification Journal of Aquatic Sciences Vol.18(2) 2003: 125-130

Field crop responses to ultraviolet-B radiation: a review

This paper provides an overview of existing literature on the ultraviolet-B (UV-B) radiation effects on field crops. Earlier reviews on field crop responses to UV-B considered few physiological processes or crops. For this review, we easily located about 129 studies on 35 crop species published since 1975. Here, we report the effects of UV-B radiation on visual symptoms, leaf ultrastructure and anatomy, photosynthetic pigments, UV-B absorbing compounds, photosynthesis, growth and development, yield, genotypic differences, and finally, interactions of UV-B with abiotic and biotic factors of crop plants. Experiments conducted in glasshouses, in closed and open top chambers, and under field conditions, with varying source (solar or artificial) and intensity of photosynthetically active radiation (PAR, 50–1800 μmol m −2 s −1) and UV-B (0–50 kJ m −2 per day) are included. It is easy to conduct experiments that purport to evaluate the effects of projected UV-B intensities on crop species by providing supplemental irradiance with lamps or by reducing UV-B with filters; however, it is very difficult to simulate UV-B irradiance spectral changes that are likely to occur in nature. Collated results for each process are presented as percent change from control along with the experimental conditions in tabular format. Many of the studies showed dramatic effects of UV-B radiation, but under conditions with supplemental UV-B irradiance that was higher than would ever occur outside experimental conditions or in which the longer wavelengths in the PAR and UV-A, which moderate UV-B effects, were greatly reduced. Only 25 of the studies reviewed used experimental conditions and supplemental UV-B irradiance that approached realism. However, unrealistic the experimental conditions might be, an increase in understanding of basic plant physiology was gained from most of the studies. Visual symptoms consisting of chlorotic or necrotic patches on leaves exposed to UV-B were not unique. Both vegetative and reproductive morphology were altered by UV-B radiation. Leaf anatomy was altered due to changes in thickness of epidermal, palisade, and mesophyll layers. Enhanced UV-B generally decreased chlorophyll content (10–70%), whereas it increased UV-B absorbing compounds (10–300%) in many crops. Decrease in photosynthesis (3–90%), particularly at higher UV-B doses, was due to both direct (effect on photosystem) and indirect (decrease in pigments and leaf area) effects. The decreases in chlorophyll pigments and photosynthesis resulted in lower biomass and yield of most crop plants. Genotypes of crop species exhibited variability in leaf wax layer thickness, loss of chlorophyll, and increase in phenolics as mechanisms of tolerance to enhanced UV-B radiation resulting in changes in biomass/yield. Results from the few studies on interaction of UV-B with other abiotic and biotic factors did not lead to useful conclusions. Studies are needed to quantify the effects of UV-B radiation on crops in order to develop dose response functions that can facilitate development of dynamic simulation models for use in UV-B and other environmental impact assessments.

Cotton responses to ultraviolet-B radiation: experimentation and algorithm development

The potential impact of an increase in solar ultraviolet-B (UV-B) radiation due to human activity on higher plants has been the subject of many studies. Little work has been carried out so far on cotton responses to enhanced UV-B radiation. The objective of this study was to determine whether or not the current and projected increases in UV-B levels affect cotton growth and development, and to quantify and develop UV-B radiation functional algorithms that can be used in simulation models. Two experiments were conducted during the summer of 2001 using sunlit plant growth chambers in a wide range of UV-B radiations under optimal growing conditions. Leaves exposed to UV-B radiation developed chlorotic and necrotic patches depending on the intensity and length of exposure. Along with changes in visible morphology, cotton canopy photosynthesis declined with increased UV-B radiation. The decline in canopy photosynthesis was partly due to loss of photosynthetic pigments and UV-B-induced decay of leaf-level photosynthetic efficiency (maximum photosynthesis) and capacity (quantum yield) as the leaves aged. The total leaf area was less due to smaller leaves and fewer leaves per plant. Less plant height was closely related to a shorter average internode length rather than a fewer mainstem nodes. The UV-B did not affect cotton major developmental events such as time taken to square, time to flower, and leaf addition rates on the mainstem. Lower biomass was closely related to both smaller leaf area and lower photosynthesis. The critical limit, defined as 90% of optimum or the control, for stem elongation was lower (8.7 kJ m −2 per day UV-B) than the critical limit for leaf expansion (11.2 kJ m −2 per day UV-B), indicating that stem elongation was more sensitive to UV-B than leaf expansion. The critical limits for canopy photosynthesis and total dry weight were 7 and 7.3 kJ m −2 per day, respectively. The identified UV-B-specific indices for stem and leaf growth and photosynthesis parameters may be incorporated into cotton simulation models such as GOSSYM to predict yields under present and future climatic conditions.

Effects of ultraviolet-B radiation on cotton (Gossypium hirsutum L.) morphology and anatomy.

Cotton (Gossypium hirsutum L.) crop, cultivated between 40 degrees N and 40 degrees S, is currently experiencing 2-11 kJ m-2 d-1 of UV-B radiation. This is predicted to increase in the near future. An experiment was conducted to study the effect of enhanced UV-B radiation on vegetative and reproductive morphology and leaf anatomy of cotton in sunlit, controlled environment chambers. From emergence to harvest, cotton plants were exposed to 0, 8 or 16 kJ m-2 d-1 of UV-B in a square wave approach for 8 h from 0800 to 1600 h. Changes in plant height, internode and branch length, mainstem node number, leaf area, length and area of petals and bracts, and anther number per flower were recorded. Epidermal cell and stomatal density, stomatal index, leaf thickness, and epidermal, palisade and mesophyll tissue thickness were also measured. Initial chlorotic symptoms on leaves turned into necrotic patches on continued exposure to enhanced UV-B. Exposure to high UV-B reduced both vegetative and reproductive parameters and resulted in a smaller canopy indicating sensitivity of cotton to UV-B radiation. Enhanced UV-B radiation increased epicuticular wax content on adaxial leaf surfaces, and stomatal index on both adaxial and abaxial leaf surfaces. Leaf thickness was reduced following exposure to UV-B owing to a decrease in thickness of both the palisade and mesophyll tissue, while the epidermal thickness remained unchanged. The vegetative parameters studied were affected only by high levels of UV-B (16 kJ m-2 d-1), whereas the reproductive parameters were reduced at both ambient (8 kJ m-2 d-1) and high UV-B levels. The study shows that cotton plants are sensitive to UV-B at both the whole plant and anatomical level.

Shoot biomass and zinc/cadmium uptake for hyperaccumulator and non-accumulator Thlaspi species in response to growth on a zinc-deficient calcareous soil

Thlaspi caerulescens is one of the best-known heavy metal hyperaccumulating plant species. It exhibits the ability to extract metals from soils and accumulates them in shoots at extremely high concentrations, particularly zinc (Zn) and cadmium (Cd). Using T. caerulescens (J. and C. Presl, ecotype Prayon) and a closely related non-accumulator species T. arvense, greenhouse experiments were carried out to study shoot growth (dry matter production) and Zn and Cd uptake from a severely Zn-deficient calcareous soil (DTPA-Zn: 0.09 mg kg −1 soil) supplemented with increasing amounts of Zn (0, 0.05, 0.5, 5, 25 and 75 mg kg −1 soil) and Cd (0 and 25 mg kg −1 soil). Shoot dry matter production of T. caerulescens was severely depressed by Zn deficiency, while in T. arvense, Zn deficiency slightly reduced growth. At the lowest Zn supplies (0 and 0.05 mg Zn kg −1 soil), T. caerulescens showed very severe Zn deficiency symptoms, including decreased leaf size and development of chlorosis and whitish-brown necrosis on the younger leaves. These symptoms were slight in T. arvense. At the highest Zn supply, leaves of T. caerulescens did not show any symptoms, but in T. arvense there were some necrotic patches on the margins of older leaves, probably due to Zn toxicity. With increasing Zn supply from 0 to 75 mg kg −1 soil, shoot dry matter production was increased by 4-fold in T. caerulescens and only 1.3-fold in T. arvense. Supply of Cd resulted in marked decrease in shoot growth of T. arvense, particularly under low Zn supply, but had no effect on the growth of T. caerulescens. At the low soil Zn levels (<0.5 mg Zn kg −1) shoot Zn concentrations were lower in T. caerulescens compared with T. arvense, and were below 10 mg Zn kg −1 dry weight. However, at the high supplies of Zn (>5 mg Zn kg −1), shoot Zn concentrations were considerably higher in T. caerulescens than T. arvense. Increase in Zn supply from 0 to 75 mg kg −1 enhanced shoot Zn concentrations by 84-fold in T. caerulescens and only 8-fold in T. arvense. Shoot Zn concentrations of both species were not affected by Cd supply, while increase in Zn supply did not affect Cd concentrations in shoot of T. caerulescens, but markedly reduced them in T. arvense. The results demonstrate that T. caerulescens is extremely sensitive to Zn deficiency in soils, but tolerant to excessive accumulation of Zn and also Cd in shoot, while T. arvense is tolerant to Zn deficiency but not to accumulation of Zn and Cd in shoot. Hyperaccumulation of Zn in T. caerulescens possibly depends on the existence of high concentrations of plant-available Zn in soils, which suggests that root-based mechanisms associated with increasing metal availability in the rhizosphere (e.g., rhizosphere acidification or release of Zn-mobilizing organic compounds from roots) only play a minor role in metal hyperaccumulation by T. caerulescens. The findings also suggest that the processes causing the metal hyperaccumulation trait in T. caerulescens also cause this plant species to be sensitive to Zn deficiency stress.

Breeding Wheat for Zinc Efficiency Improvement in Semi-arid Climate-A Review

Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world. Zinc deficiency is one of the most common deficiencies in soils worldwide. Several plant metabolic processes and biological functions are impaired under Zn deficient conditions. The most visible symptoms of zinc deficiency are a reduction in shoot growth, decrease in leaf size, chlorophyll degeneration and the emergence of whitish-brown necrotic patches on leaves. The genotypes that show the highest percent response to added Zn and are unable to grow well without Zn are defined as being susceptible to Zn deficiency and vice versa. Zinc efficiency is the ability of a plant to grow and produce grain when Zinc availability is low. Breeding cereals with enhanced zinc efficiency can decrease fertilizer dependency, improve seed-ling vigor, increase resistance to abiotic and biotic stress and enhance yield and nutritional value of wheat. A survey of the literature, as well as own experiences, show that there is enough genetic variation in wheat and alien species, particularly rye, for suitable zinc-efficient alleles. Genetic control is fairly simple, making breeding for this trait feasible. Since selection for Zinc efficiency in a breeding program is limited by the high spatial variability of zinc in field sites, better field screening techniques and selection criteria are needed to allow screening of early-generation segregating materials. Zn specific diagnostic methods like reflectance analysis and molecular markers (proteins /DNA markers) could complement the screening of wheat genotypes for zinc efficiency. Breeding wheat for enhanced zinc efficiency and higher grain yield would require concentrating the quantitative trait loci governing these traits in a few agronomic backgrounds through recombination breeding. This literature review paper delves into genetic variability, screening methods, plant breeding options and methodologies and other related issues for improving zinc efficiency in wheat.

First Report of Powdery Mildew of Kenaf Caused by Leveillula taurica in South Africa.

Kenaf (Hibiscus cannabinus L.) is a fast-growing, bamboo-like annual plant belonging to the Malvaceae. The stem, which ranges from 1.5 to 4 m, presents a source of high-quality cellulose fibers. The plant is being investigated in South Africa with a view to commercial production. In April 2001, at least 50% of 4- to 5-month-old kenaf plants grown from seed in trials near Rustenburg, Northwest Province, South Africa, were observed as having powdery mildew. Signs included extensive growth of white, superficial mycelium and emergent conidiophores on the abaxial leaf surface, followed by partial defoliation. On older leaves, the abaxial leaf surface was completely covered by powdery mildew, and chlorotic and necrotic patches were clearly visible on the adaxial surface. Symptoms were observed on all five planted cultivars (Everglades 41, Cuba 108, El Salvador, SF459, and Tainung 2), and no difference in disease severity was noted among cultivars. Leveillula taurica (Lév.) Arnaud (anamorph Oidiopsis taurica [Lév.] Salmon) was subsequently identified by the presence of endophytic mycelia, often branched conidiophores, and dimorphic conidia borne singly or in short chains (1). In 100 measurements of each type, pyriform conidia averaged 69 ± 5 × 18 ± 2 μm and cylindrical conidia averaged 62 ± 6 × 16 ± 2 μm. The teleomorph was not observed. The source of L. taurica for this reported outbreak is unknown, and powdery mildew was not observed in a field of mature cotton (Gossypium hirsutum L.) growing within 10 m of the kenaf plot. L. taurica was reported on kenaf in Texas in 1992 (2) and in Italy in 1995 (3). The pathogen can cause significant losses in seed yield and reduce seed quality in susceptible kenaf cultivars. Although L. taurica has been reported from Hibiscus sabdariffa in Egypt (4), to our knowledge this is the first report of the pathogen occurring on kenaf in Africa.

Spring Dead Spot Resistance and Quality of Seeded Bermudagrasses under Different Mowing Heights

Bermudagrass (Cynodon spp. L.C. Rich.) cultivars resistant to spring dead (SDS) caused by Ophiosphaerella herpotricha (Fr.) Walker and winter‐kill are important for residential and commercial use in transition zone climates. Field research was conducted on ‘Mirage’, ‘OKS 91‐11’, and ‘Jackpot’ seeded bermudagrasses [Cynodon dactylon (L.) Pers. var. dactylon] at Stillwater, OK, between 1996 and 1999 to determine their resistance to SDS. Plots were inoculated in 1996 with O. herpotricha isolate KS 188 and mowed to a height of either 1.3 cm or 3.8 cm. The SDS necrotic patch area of all cultivars increased each year and patch area was greater in turf at the higher mowing height. OKS 91‐11 had a smaller SDS necrotic patch area than the other cultivars. Mirage had necrotic patch area equal to Jackpot at 1.3 cm and less necrotic area than Jackpot at 3.8 cm. OKS 91‐11 had greater shoot survival density in necrotic patches than Jackpot or Mirage in 2 of 3 yr at 1.3 cm. Cultivars did not differ in shoot survival density at 3.8 cm. Higher overall quality was provided by OKS 91‐11, when compared with Mirage and Jackpot in 3 of 4 and 2 of 4 yr, respectively. Jackpot had better quality than Mirage in 2 of 4 yr. Early spring green‐up was negatively correlated with SDS patch size and positively correlated with shoot survival in SDS patches. Winter‐kill was positively correlated with SDS patch size and negatively correlated with shoot survival in SDS patches.

Necrotic patches affect Acropora palmata (Scleractinia: Acroporidae) in the Mexican Caribbean.

An outbreak of necrotic patches was observed affecting Acropora palmata in the Mexican Caribbean in the summer of 1999. This study documents the tissue loss produced by these patches. Following a marked initial increase in the number of patches, there was a decrease in the appearance of new patches but the size of the patches increased throughout the study. In some cases patches expanded but in most cases they enlarged due to fusion of 2 or more patches. Patches recovered but not sufficiently to overcome damage in most colonies surveyed. Percentage tissue loss does not appear to be directly related to temperature but may be related to a combination of factors associated with prolonged summer doldrum-like conditions. The necrotic patch syndrome can have a substantial impact in tissue loss in affected A. palmata colonies.

Accumulating monocytes in the vasculature of rat renal allografts: phenotype, cytokine, inducible no synthase, and tissue factor mRNA expression.

Necrotic patches and hemorrhagic lesions develop in the renal tissue between day 4 and day 5 after transplantation of fully allogeneic DA rat kidneys to LEW recipients. These lesions are at least in part due to destruction and obstruction of blood vessels. Damage of graft endothelial cells and blood coagulation are likely to be mediated by intravascular graft leukocytes. However, this cell population has not been thoroughly characterized before. We perfused untreated control kidneys, renal isografts, and allografts on day 4 after transplantation with phosphate-buffered saline/ethylenediaminetetraacetic acid to harvest leukocytes from both the blood stream as well as from the marginal intravascular pool. The mRNA expression of typical products of activated monocytes was analyzed in reverse-transcriptase polymerase chain reaction experiments. Graft monocytes were purified and their immunophenotype was investigated by flow cytometry. Allograft rejection led to a 10-fold increase in the number of intravascular graft leukocytes compared to isografts. A mean number of about 100x10(6) leukocytes was harvested from a single allogeneic kidney, about 73% of these cells were monocytes and most of them displayed an activated phenotype. Compared to isografts, intravascular allograft leukocytes displayed an increased expression of tumor necrosis factor-alpha, inducible NO synthase and tissue factor. Our study shows that large numbers of activated monocytes accumulate inside allograft vessels. As they express genes the products of which might damage the allograft by inducing cell death or thrombosis, we speculate that they directly participate in allograft destruction.