Known and two new species of <Emphasis Type="Italic">Rhytisma</Emphasis> (Rhytismatales,Ascomycota) from China

Three species of Rhytisma are described based on recently collected specimens from the Anhui province, China. Rhytisma anhuiense is a new species causing a serious tar spot disease on Rhododendron simsii. Rhytisma yuexiense is a new species, which develops its stromata only on fallen leaves of Rhododendron ovatum. Rhytisma himalense on Ilex fargesii is a known species and probably widely distributed in China. Including the two new species, 11 species of Rhytisma are known from China which are presented in a key.     

Phyllachora species infecting maize and other grass species in the Americas represents a complex of closely related species

The genus Phyllachora contains numerous obligate fungal parasites that produce raised, melanized structures called stromata on their plant hosts referred to as tar spot. Members of this genus are known to infect many grass species but generally do not cause significant damage or defoliation, with the exception of P. maydis which has emerged as an important pathogen of maize throughout the Americas, but the origin of this pathogen remains unknown. To date, species designations for Phyllachora have been based on host associations and morphology, and most species are assumed to be host specific. We assessed the sequence diversity of 186 single stroma isolates collected from 16 hosts representing 15 countries. Samples included both herbarium and contemporary strains that covered a temporal range from 1905 to 2019. These 186 isolates were grouped into five distinct species with strong bootstrap support. We found three closely related, but genetically distinct groups of Phyllachora are capable of infecting maize in the United States, we refer to these as the P. maydis species complex. Based on herbarium specimens, we hypothesize that these three groups in the P. maydis species complex originated from Central America, Mexico, and the Caribbean. Although two of these groups were only found on maize, the third and largest group contained contemporary strains found on maize and other grass hosts, as well as herbarium specimens from maize and other grasses that include 10 species of Phyllachora. The herbarium specimens were previously identified based on morphology and host association. This work represents the first attempt at molecular characterization of Phyllachora species infecting grass hosts and indicates some Phyllachora species can infect a broad range of host species and there may be significant synonymy in the Phyllachora genus.     

短体属线虫一新种：（垫刃目：短体科）

作者对造成薯蓣Dioscorea opposita Thunb红斑病病原线虫进行了观察,鉴定该线虫为薯蓣短体线虫,新种Pratylenchus dioscoreae sp.nov.薯蓣短体线虫头部具有2个环纹,侧带处具6—8条侧线;雌虫口针长16.8—20.1(18.3) μm,V(％)=65.7—81.2(79.0)。雄虫和雌虫的比例近乎相等。     

First Report of Alternaria Leaf Spot on Gerbera (Gerbera jamesonii H. Bolux ex J. D. Hook) in Bulgaria

Alternaria leaf spots of gerbera (Gerbera jamesonii H. Bolus ex J. D. Hook) were observed on plants from different greenhouses on commercial plants in Bulgaria. The symptoms of the disease on the leaves were characterized by the development of brown, small, scattered dots, which gradually enlarged and coalesced to form large, oval, circular or irregular, brown to black lesions with concentric rings. Affected plants showed lower vitality, suppressed development and fewer, smaller, distorted in shape flowers. Alternaria isolates, obtained from infected leaf tissues were grown in pure culture and the morphological characteristics of the colony and sporulation apparatus were determined. DNA, extracted from the fungal isolates was subjected to polymerase chain reaction (PCR) with primers ITS1/ITS4, amplifying the internal transcribed spacer (ITS) regions. The resulting products were sequenced and compared for homology with other species in the GeneBank. The isolates showed 94% homology of the ITS region with either Alternaria alternata, A. arborescens, A. tenuissima, A. longipes, A. lini or A. smyrnii. None of the studied isolates was amplified with the A. alternata specific primers AAF2/AAR3, indicating that they are pathogenic varieties of it or belong to another species. Pathogenicity tests on 10 gerbera cultivars revealed that all of them were susceptible to Alternaria leaf spot. Additional tests on nine other crops (Solanum lycopersicum, Calendula officinalis, Capsicum annuum, Celosia argantea, Pelargonium spp., Petunia hybrida, Nicotiana tabacum, Cucurbita moscata and Raphanus sativus var. radicina) and on tomato or pepper fruits, potato tubers and carrot roots also indicated that all tested plant species were potential hosts of the disease. This is the first report of highly virulent isolates of Alternaria spp. in Bulgaria that cause leaf spots on gerbera in greenhouses.     

White spot syndrome virus (WSSV) transmission from rotifer inoculum to crayfish

To test the possibility that shrimp pond rotifer resting eggs and hatched rotifers could transmit white spot syndrome virus (WSSV) to crayfish (Procambarus clarkii), we injected crayfish with rotifer and resting egg inocula that were WSSV-positive only by dot-blot analysis of PCR products. No crayfish became WSSV-positive after challenge with the resting egg inoculum. However, 1/15 crayfish became WSSV-positive after challenge with the rotifer inoculum. The results demonstrated that rotifers constitute a potential risk for WSSV transmission to crayfish and other cultivated crustaceans. However, the actual quantitative risk of transmission in an aquaculture setting depends on many variables that remain untested.     

Taphrina maculans reduces the therapeutic value of turmeric (Curcuma longa)

Rhizomes of turmeric are used in several culinary preparations. They have been used as household remedies since time immemorial. Phenolics are found in plants only and they play a great role in human health. The high performance liquid chromatography of different parts of healthy and infected plants reveals that the phenolic acid content is reduced in diseased tissues including rhizomes which are commonly consumed by human beings in several countries of the world. Results also showed that the infected leaves had maximum phenolic acids as compared to healthy leaves which indicate that due to infection the amount of phenolic acids increased. We report for the first time that leaf spot (Taphrina maculans) of turmeric (Curcuma longa), which is an important disease, reduces the quantity and number of phenolics thereby damaging the therapeutic properties of turmeric.     

Evaluating “Hot Spots” of Soil Contamination (Redux)

Every day, thousands of soil samples are collected from properties suspected of being contaminated. The samples are sent to laboratories where the chemical constituents are quantified. Frequently, one or more samples are identified as constituting a “hot spot” of soil contamination. The consequences of such a determination—more sampling, more remediation, more reporting—are often quite expensive. Yet despite the often costly consequences of identifying a “hot spot,” there appears no supportable methodology for objectively deciding which spots are “hot” and which are “not.” This can lead to situations where sampling episodes are required to demonstrate that there is not a problem, even though just exactly what would comprise a “problem” is not particularly clear and sometimes is not stated. The authors provide a review and analysis of common and published information concerning “hot spots.” They then present a different point of view about “hot spots” from those in common practice, a point of view that will challenge many environmental professionals to reconsider how they evaluate sampling results.     

Red-Light-Induced Resistance in Broad Bean (Vicia faba L.) to Leaf Spot Disease Caused by Alternaria tenuissima

The effect of different light wavelengths on the development of lesions induced by Alternaria tenuissima in broad bean leaves was investigated. Lesion development was completely suppressed in red‐light‐irradiated broad bean leaflets, irrespective of isolate or spore concentration. Pre‐treatment of leaflets with red light for 24 h before inoculation also suppressed lesion development. Alternaria tenuissima failed to produce infection hyphae in red‐light‐irradiated broad bean leaflets. These results indicate that disease suppression in broad bean leaflets is due to light‐induced resistance. Spore germination fluid (SGF) of A. tenuissima allowed non‐pathogenic Alternaria alternata to infect wounded and unwounded broad bean leaflets kept in the dark, results suggesting that SGF induced susceptibility. Red light suppressed susceptibility induced by A. tenuissima SGF; thus, lesion formation and development were suppressed when leaflets inoculated with the spores of A. alternata suspended in A. tenuissima SGF were kept under red light. From these results, we conclude that red light induced resistance in broad bean to leaf spot disease caused by A. tenuissima, and that SGF induced susceptibility of broad bean leaflets to a non‐pathogenic isolate of A. alternata.     

Attempted DNA extraction from a Rancho La Brea Columbian mammoth (Mammuthus columbi): prospects for ancient DNA from asphalt deposits

Fossil‐bearing asphalt deposits are an understudied and potentially significant source of ancient DNA. Previous attempts to extract DNA from skeletons preserved at the Rancho La Brea tar pits in Los Angeles, California, have proven unsuccessful, but it is unclear whether this is due to a lack of endogenous DNA, or if the problem is caused by asphalt‐mediated inhibition. In an attempt to test these hypotheses, a recently recovered Columbian mammoth (Mammuthus columbi) skeleton with an unusual pattern of asphalt impregnation was studied. Ultimately, none of the bone samples tested successfully amplified M. columbi DNA. Our work suggests that reagents typically used to remove asphalt from ancient samples also inhibit DNA extraction. Ultimately, we conclude that the probability of recovering ancient DNA from fossils in asphalt deposits is strongly (perhaps fatally) hindered by the organic compounds that permeate the bones and that at the Rancho La Brea tar pits, environmental conditions might not have been ideal for the general preservation of genetic material.     

A molecular phylogenetic and phylogeographic study of two forms of Calliptamus barbarus (Costa 1836) (Orthoptera: Acrididae,Calliptaminae) from two regions of Algeria

Calliptamus barbarus (Orthoptera: Acrididae) is the most polymorphic species within the genus Calliptamus. It shows a morphological polymorphism (three hind femoral spots, or only one hind femoral spot). Several studies have been made in order to distinguish the two forms: morphometry, number of ovarioles, sound production, protein and enzyme system. The aim of our work is to assess whether the two forms can be considered as different taxa and to perform a molecular phylogenetic study of two populations of C. barbarus collected from two different Algerian localities. No clear genetic differentiation was found between the samples with different morphologies. Additionally, the samples from Algeria do not form a monophyletic sister clade compared to the one formed by the sequences from GenBank from other geographical regions. Despite the morphological differences shown between the two populations, our molecular study indicates that there are no differences at a molecular level using the two mitochondrial genes COI and 16S.     

Factors affecting development of phoma canker (Leptosphaeria maculans) on stems of winter oilseed rape (Brassica napus) in southern England

In winter oilseed rape experiments at Rothamsted in 1997/98 (cvs Lipton and Capitol), 1998/99 (cv. Apex) and 1999/2000 (cvs Apex, Lipton and Capitol), development of crown canker and phoma stem lesions in spring was related to development of phoma leaf spot in the previous autumn/winter. There were differences in thermal time (degree‐days) from the first appearance of phoma leaf spot (autumn) to the first appearance of crown canker (spring) between cultivars (cvs Lipton and Capitol, 1220–1240; cv. Apex, 1120–1140 degree‐days) but not between growing seasons. In 1998/99 and 1999/2000, fungicide (November) treatment delayed the start of crown canker development in the spring but did not affect the rate of increase in severity. In 1997/98, fungicide treatments did not delay the appearance of crown canker but decreased the rate of increase in crown canker severity. In all three seasons, fungicide treatments generally decreased the proportions of plants at harvest with crown canker severity scores 3 or 4 and increased the proportions with scores 0 or 1. There were differences between seasons in the distributions of crown canker severity scores at harvest. The severity of both crown canker and phoma stem lesions increased linearly with accumulated degree‐days in plots with or without fungicide treatment in 1997/98 (cv. Lipton), 1998/99 (cv. Apex) and 1999/2000 (cv. Apex). Regressions showed that severity of crown canker at harvest in July was related to severity in the spring in 1997/98 (early June, cv. Lipton), 1998/99 and 1999/2000 (April, cv. Apex).     

不同苹果品种对褐斑病抗性的鉴定及抗性生理研究

对42个苹果栽培品种叶片褐斑病进行了田间发病状况调查与抗性鉴定,分析了叶片气孔密度和大小与抗病性之间的关系,同时研究了不同抗性品种离体叶片接种病原菌后超氧化物歧化酶（SOD）、多酚氧化酶（vPo）、过氧化物酶（POD）、苯丙氨酸解氨酶（PAL）活性和木质素含量的差异变化。依照抗性分级标准,供试材料中抗病品种有14个（其中高抗品种2个）,感病品种有28个（其中高感品种7个）;叶片气孔密度与病情指数之间存在显著正相关,相关系数r=0．683;叶片接种后,诱导了4种酶活性和木质素含量的升高,抗病和感病品种的SOD和PP0活性无显著差异,而抗病品种的POD和PAL活性以及木质素含量显著高于感病品种。苹果叶片的气孔密度、POD和PAL的活性以及木质素含量与褐斑病抗性有关。     

Isolate Virulence and Cultivar Response in the Winter Wheat: Pyrenophora tritici-repentis (Tan Spot) Pathosystem in Oklahoma

Prevalence of tan spot of wheat caused by the fungus Pyrenophora tritici-repentis has become more prevalent in Oklahoma as no-till cultivation in wheat has increased. Hence, developing wheat varieties resistant to tan spot has been emphasized, and selecting pathogen isolates to screen for resistance to this disease is critical. Twelve isolates of P. tritici-repentis were used to inoculate 11 wheat cultivars in a greenhouse study in split-plot experiments. Virulence of isolates and cultivar resistance were measured in percent leaf area infection for all possible isolate x cultivar interactions. Isolates differed significantly (P < 0.01) in virulence on wheat cultivars, and cultivars differed significantly in disease reaction to isolates. Increased virulence of isolates detected increased variability in cultivar response (percent leaf area infection) (r = 0.56, P < 0.05) while increased susceptibility in cultivars detected increased variance in virulence of the isolates (r = 0.76, P < 0.01). A significant isolate × cultivar interaction indicated specificity between isolates and cultivars, however, cluster analysis indicated low to moderate physiological specialization. Similarity in wheat cultivars in response to pathogen isolates also was determined by cluster analysis. The use of diverse isolates of the fungus would facilitate evaluation of resistance in wheat cultivars to tan spot.     

Does bird predation influence the spot-number variation in Maniola jurtina (Lepidoptera)?

For six years samples of the satyrine butterfly Maniolajurtina L. were collected on small islands in southern Sweden and scored for beak marks, i.e. damage on wings presumably resulting from attacks by birds; in the present study area mainly Red-backed Shrike Lanius collurio L. An overall mean of 8% (5–1496 in different years) of the females and 1396 (10–2296) of the males had beak marks. Both sexes of M. jurtina show variation in spot-number on the hindwings and there is some evidence that in some years the frequencies of different spot-number phenotypes with beak marks differ significantly from randomness. Although it is not known how beak mark frequencies are related to predation pressure (reflecting rates of predation or escapes?) it is suggested that, due to behavioural differences of spot-number phenotypes, birds act as a selective factor influencing the spot-number variation. The results are discussed in relation to a recent model proposed by Brakefield attempting to account for variation in spot-number in M. jurtina.     

对虾白斑综合征病毒中国地方株变异区基因的比较

对虾白斑综合征病毒(White spot syndromevirus,WSSV)是对虾养殖的主要病原之一,它是目前发现的基因组最大的动物病毒,为环状双链DNA病毒[1,2],全基因组序列分析结果显示,对虾白斑综合征病毒和其他杆状病毒相差甚远,最新病毒分类报告已将该病毒划归新建立的线头病毒科(Nima-viridae)白斑病毒属(Whispovirus)[3,4]。目前Gen-Bank公布有3个版本的WSSV全序列[1,2],其基因组大小的测定结果相差较大。不同的WSSV毒株可能在形态结构、理化性质上无法区分,但病毒基因组限制酶切片段长度多态性(RFLP)可以将之区分开来,Marks等[6,7]通过计…     

Rhizobium radiobacter conjugation and callus-independent shoot regeneration used to introduce the cercosporin export gene cfp from Cercospora into sugar beet (Beta vulgaris L.)

Leaf spot disease caused by Cercospora is responsible for crop and profitability losses in sugar beet crops in the US and worldwide. The cfp gene that encodes a protein that exports phytotoxic cercosporins from Cercospora was conjugally transferred to sugar beet using Rhizobium radiobacter (Agrobacterium tumefaciens), to improve Cercospora-induced leafspot resistance. Conditions for shoot regeneration were optimized to increase regeneration/transformation efficiencies. Low-light and room-temperature conditions were favorable to sugar beet regeneration without callus when cytokinin had been added to the tissue culture medium. Using this procedure adventitious shoots from leaf pieces were obtained in a simple, one-step regeneration procedure. T7, a cfp-transgenic clone verified by PCR with gene-specific primers, is being propagated for leaf spot disease resistance evaluation.     

Incidence and severity of foliar diseases of sesame (Sesamum indicum L.) intercropped with maize (Zea mays L.)

This study evaluates the effects of different row arrangements on incidence and severity of Cercospora leaf spot (CLS) and Alternaria leaf blight (ALB) diseases and seed health of sesame intercropped with maize. Row arrangements were: sesame intercropped with maize in alternate pair of rows (2:2), two rows of sesame intercropped with one row of maize (2:1), sesame intercropped with maize in single alternate rows (1:1) with sole sesame as control. Intercropping maize with sesame reduced the incidence and severity of diseases. Sesame intercropped with maize in a (1:1) ration recorded a significantly lower number of infected leaves by CLS and ALB incidence than other row arrangements. ALB lesion number was between 17 and 20 in the (1:1) arrangement relative to 65–104 and 28–43 in the sole crop and other row arrangements, respectively. ALB lesion size was also reduced in the (1:1) than other row arrangements. Fungal infection of harvested sesame seeds was significantly reduced in the intercrop relative to the sole crop. CLS incidence was significant and negatively correlated with seed weight while defoliation was significant and positively correlated with ALB or CLS incidence. Rainfall was significant and positively correlated with CLS or ALB incidence while intercropping induced microclimatic effects that influenced disease incidence. Grain yield, weight of 1000-seed, number of capsules/plant and weight of seed/plant were significantly higher in the (1:1) row arrangement than the sole crop or other row arrangements. The study demonstrates that intercropping sesame with maize in a single alternate row (1:1) arrangement can be used to reduce foliar diseases of sesame.     

Relationships between phoma leaf spot and development of stem canker (Leptosphaeria maculans) on winter oilseed rape (Brassica napus) in southern England

Models were constructed to describe the relationships between incidence of phoma leaf spot at different growth stages in autumn/winter or early spring and incidence of stem canker (basal canker or stem lesions) in summer on winter oilseed rape in southern England. Model 1, describing the phoma leaf spot/basal canker relationship, was y₁=β₀+β₁x₁+β₂(x₂ ‐ x₁) if x₂ > x₁, and y₁=β₀+β₁x₁ if x₂≤x₁, in which y₁ was the incidence (% plants affected) of basal canker at harvest, x₁ was the maximum incidence of phoma leaf spot during the period from sowing to growth stage (G.S.) 1,6‐1,7 (about 100 days after sowing) and x₂ was the maximum incidence of phoma leaf spot between G.S. 1,7 and G.S. 2,0 (start of stem extension). Model 2, describing the phoma leaf spot/stem lesion relationship, was y₂=α₀+α₁x₃+α₂x₄, in which y₂ was the incidence of stem lesions at harvest, x₃ was the incidence of phoma leaf spot at G.S. 3,3–3,5 (flower buds visible) and x₄ was the incidence of phoma leaf spot at G.S. 4,5–5,5 (flower buds opening). Data from field experiments with four winter oilseed rape cultivars at Boxworth or Rothamsted in the 1992/93, 1993/94, 1996/97, 1997/98 or 1998/99 seasons were used to test the models. The values of R² for the regression equations testing model 1 for the phoma leaf spot/basal canker relationship were 0.75, 0.93, 0.91 and 0.89 for cvs Apex, Bristol, Capitol and Envol, respectively. The values of R² for the regression equations testing model 2 for the phoma leaf spot/stem lesion relationship were 0.58, 0.57, 0.54 and 0.71 for cvs Apex, Bristol, Capitol and Envol, respectively. The phoma leaf spot/basal canker relationship (model 1) could also be fitted to the combined data set for all four cultivars (R²= 0.65), whereas the phoma leaf spot/stem lesion relationship (model 2) could not to be fitted to the combined data set for the four cultivars. The relationships between incidence and severity of stem canker were examined and the values of R² for the regressions of severity on incidence were 0.91 for basal canker and 0.89 for stem lesions.     

红螯光壳螯虾白斑综合症血液病理学研究

采用Wright-Geimsa染色法和电镜技术对人工感染的红螯光壳螯虾(Cherax quadricarinatus)白斑综合症(White spot syndrome,WSS)血液病理学进行了研究。结果显示:患病螯虾血细胞总数、透明细胞(AH)数量极显著减少(P<0.01),大颗粒细胞(LGH)极显著增加(P<0.01);病毒感染后3种血细胞大小均有增加趋势,透明细胞和大颗粒细胞的核质比(NP)较感染病毒前极显著下降(P<0.01)。显微病理学变化主要表现为血涂片中血细胞明显减少,病变、破损或解体的细胞增多,至濒死期螯虾血液呈典型的溶血状态。超微病理学变化表现为血细胞受到了损伤。高尔基体变形、线粒体结构模糊破损;核膜变形核固缩、细胞核高度异染色质化;濒临死亡的螯虾血细胞细胞器和染色质溶解,胞浆水肿,细胞溶解坏死。在患病螯虾的血细胞核中清晰可见WSSV粒子。