Incidence and geographical distribution of downy mildew on maize caused by Peronosclerospora sorghi in Nigeria

Abstract

Incidence and geographical distribution of downy mildew (Peronosclerospora sorghi) on maize (Zea mays) were determined in a systematic survey of 181 maize fields in the major maize‐growing regions and ecological zones of Nigeria. Downy mildew was observed in the forest and Guinea savanna ecologies, but no disease was detected in other ecologies. Highest levels of disease incidence (63%) were observed in the forest zone, and progressively less disease incidence was found at the southern and northern Guinea savanna zones. Spatial pattern analysis indicated an aggregation and randomness of infected plants in the northern Guinea savanna and the forest zone, respectively. Disease incidence was positively correlated with the presence of downy mildew infected sorghum plants and relative amount of sporulation on infected sorghum (Sorghum bicolor) but negatively correlated with plant age and cropping pattern. Relative sporulation on maize plants was negatively correlated with age of maize plants. Higher levels of disease incidence were observed when the previous crop was either maize or sorghum than when previous crops were cassava, okra, tomatoes, or rice.     

Molecular characterization of <Emphasis Type="Italic">Phoma tracheiphila</Emphasis>, causal agent of Mal secco disease of citrus,in Israel

Mal secco disease of citrus caused by Phoma tracheiphila is a devastating disease in the Mediterranean basin. Susceptible citrus species include lemon, citron, lime and others. Trees attacked by the fungus show characteristic symptoms; the smallest twigs die first, followed by the larger branches. Eventually, the whole tree is killed. The symptoms are clear in the orchards but by the time they are visible the disease is already well established. The need for a sensitive, reliable and rapid diagnostic method for the early identification of the fungus in trees and fruit exists. We have developed a PCR-based method for the identification of P. tracheiphila from plant tissues including fruit. Any such method must take into account the genetic variability in the pathogen population. Molecular methods were used to compare different isolates of P. tracheiphila. This study found no significant differences between different isolates from different citrus species from different parts of Israel.     

Spatial and climatic factors associated with the geographical distribution of citrus black spot disease in South Africa. A Bayesian latent Gaussian model approach

Foot rot is one of the most important phytosanitary problems in Jatropha (Jatropha curcas L), causing plant death. The objective of this paper was to determine the epidemiology of foot rot. Consequently, the spatiotemporal spread of the disease and its relationships with the environment was determined in two commercial Jatropha plantations (Fs1 and Nb) in 2015. Incidence of the disease in the period from March to November was 0.43% to 4.76% for plot Fs1 and for plot Nb it was 2.54 to 16.66%, with a gradual increase in the first months and a faster increase in the last months in both plantations. Monthly incidence was adjusted to a linear form of three non-flexible models and the results showed that the Gompertz model provided a better explanation (R² = 0.099) for the advance of foot rot in the two plots, with an apparent rate of increase for plots Fs1 and Nb of 0.0034 and 0.047 respectively. The disease progresses speed is associated with higher temperatures and greater relative humidity (p ≤ =0.05). Moreover, the dispersion of the disease, calculated by the Morisita index, showed a random spread in the first stages of the epidemic and formed aggregates in subsequent stages. The analysis of auto correlation and the geospatial graphs showed that plants with the diseases were grouped in numbers of 4 to 6 in a north to south direction. The implications of the epidemiological behavior in the management of the disease will be discussed.     

Mass spectrometric techniques as aids in the diagnosis of gangrene in potatoes caused by Phoma exigua var. foveata

Current diagnosis of gangrene in potato tubers, caused byPhoma exigua var.foveata, is based on isolation and identification of the causal organism or on thin-layer chromatographic (TLC) detection of the anthraquinone pigment pachybasin (1-hydroxy-3-methylanthraquinone). In this paper alternative diagnostic approaches are described based on detection of specific ions by pyrolysis mass spectrometry (Py-MS), direct probe mass spectrometry (DIP-MS) and gas chromatography-mass spectrometry (GC-MS). The advantages and disadvantages of these methods are discussed in comparison with the TLC approach. GC-MS is a promising technique because of its high specificity, sensitivity and suitability for automation. Moreover, the MS approaches may lead to a reduction of total expertise time.Samenvatting De huidige diagnostiek van gangreen in aardappelknollen, veroorzaakt doorPhoma exigua var.foveata, is gebasserd op de isolatie en identifikatie van de schimmel of op de dunnelaag-chromatografische (TLC) bepaling van het pigment pachybasine (1-hydroxy-3-methylanthrachinon).In dit artikel worden nieuwe diagnostische benaderingen beschreven die gebaseerd zijn op de detectie van specifieke ionen door middel van pyrolyse-massaspectrometrie (Py-MS), direct-probe-massaspectrometrie (DIP-MS) en gaschromatografie-massaspectrometrie (GC-MS). De voor- en nadelen van deze methoden worden behandeld en vergeleken met de dunnelaag-chromatografische methode.GC-MS is een veelbelovende methode vanwege de grote specificiteit, gevoeligheid en geschiktheid voor automatisering. Op den duur kunnen de MS-methoden leiden tot een verkorting van de totale expertisetijd.     

Proteomic analysis reveals suppression of bark chitinases and proteinase inhibitors in citrus plants affected by the citrus sudden death disease

Citrus sudden death (CSD) is a disease of unknown etiology that greatly affects sweet oranges grafted on Rangpur lime rootstock, the most important rootstock in Brazilian citriculture. We performed a proteomic analysis to generate information related to this plant pathogen interaction. Protein profiles from healthy, CSD-affected and CSD-tolerant stem barks, were generated using two-dimensional gel electrophoresis. The protein spots were well distributed over a pI range of 3.26 to 9.97 and a molecular weight (MW) range from 7.1 to 120 kDa. The patterns of expressed proteins on 2-DE gels made it possible to distinguish healthy barks from CSD-affected barks. Protein spots with MW around 30 kDa and pI values ranging from 4.5 to 5.2 were down-regulated in the CSD-affected root-stock bark. This set of protein spots was identified as chitinases. Another set of proteins, ranging in pI from 6.1 to 9.6 with an MW of about 20 kDa, were also suppressed in CSD-affected rootstock bark; these were identified as miraculin-like proteins, potential trypsin inhibitors. Down-regulation of chitinases and proteinase inhibitors in CSD-affected plants is relevant since chitinases are well-known pathogenesis-related protein, and their activity against plant pathogens is largely accepted.     

Effects of temperature and humidity on diseases caused by Phoma medicaginis and Leptosphaerulina trifolixs in lucerne (Medicago sativa)

The post-inoculation temperature and humidity conditions most favourable for development of Phoma black stem and leaf spot (Phoma medicaginis) and Leptosphaerulina leaf spot (Leptosphaerulina trifolii) diseases on lucerne (Medicago sativa) were determined using controlled-environment cabinets. P. medicaginis caused more severe leaf disease at day/night temperatures of 21/16 and 18/13°C compared with 15/10°C; petiole disease was most severe at 21/16°C compared with 18/13°C, and least severe at 15/ 10°C. L. trifolii generally caused more severe leaf disease at 18/13°C compared with 21/16°C or 15/10°C, but the most severe petiole disease occurred at 21/16°C with least at 15/10°C Leaf disease caused by either P. medicaginis or L. trifolii was always more severe with the longest period (168 h) of high-humidity incubation and, generally, increased with increasing periods of high humidity. The severity of petiole disease was much less affected than that of leaf disease by an increase in the period of high-humidity incubation.     

湖南省永州地区柑橘慢衰病与黄龙病病原鉴定及分布调查

为明确湖南省柑橘黄化症状与柑橘慢衰病和柑橘黄龙病的相关性,应用形态学和分子生物学方法对湖南省永州地区表现黄化症状的柑橘进行了两种病原的鉴定及分布调查。结果表明,造成该地区柑橘黄化现象的主要原因为柑橘半穿刺线虫和黄龙病菌对柑橘的侵染。所检样本中,柑橘慢衰病平均发生率为82.1%,土壤中的半穿刺线虫群体密度最高达到3 077条/100mL。永州地区柑橘黄龙病病菌属于韧皮部杆菌属类细菌亚洲种,平均检出率为64.3%。柑橘半穿刺线虫和黄龙病菌在柑橘园存在混合侵染现象,混合侵染率为53.6%。柑橘半穿刺线虫在永州地区柑橘产区分布广泛,是造成柑橘黄化症状的重要病因,重视并有效防控柑橘半穿刺线虫已迫在眉睫。     

Species spectra,distribution and host range of cucurbit powdery mildews in the Czech Republic,and in some other European and Middle Eastern countries

The occurrence and geographic distribution of powdery mildew on cucurbits was studied in the Czech Republic, Austria, France, Germany, Great Britain, Italy, Slovakia, Slovenia, Spain, Switzerland, the Netherlands, as well as in Turkey and Israel, during the period 1995–2000. In total, 599 leaf samples with powdery mildew symptoms were collected from cucurbits from 166 locations within the Czech Republic; an additional 69 samples were collected from 42 locations elsewhere. Two powdery mildews (Golovinomyces cichoracearum and Podosphaera xanthii) were identified. The host range included the cultivated cucurbits (Cucumis melo, C. sativus, Cucurbita pepo, C. maxima, and Citrullus lanatus) and several other species. P. xanthii was the only powdery mildew pathogen found in Spain, Israel, and Turkey. P. xanthii and G. cichoracearum were detected in the other surveyed countries, occurring in both mixed infections and separately. In the more northerly latitudes and higher elevations, G. cichoracearum is more often the single species. G. cichoracearum was the dominant powdery mildew species in the Czech Republic (detected in 98.8% of the locations there); P. xanthii was found as the lone species in 1.2% of locations. At 28.4% of locations, G. cichoracearum was found with P. xanthii as mixed infections. The hyperparasitic fungus Ampelomyces quisqualis was found in 30% of the samples from the Czech Republic and was also recorded in Austria, Italy, Slovenia, Switzerland, and Great Britain.     

安徽省小麦孢囊线虫田间分布及危害调查

在田间用涕灭威作播前土壤处理抑制土壤中线虫虫口,测定分析田间小麦孢囊线虫对3个小麦品种分蘖期和孕穗期的生长影响。结果表明：小麦孢囊线虫田间分布模型为聚集分布,土壤中其卵密度范围为0～42．8粒／g土,平均密度为6．5粒／g土,已达到危害水平以上。小麦中前期生长调查表明,小麦孢囊线虫没有对分蘖期小麦生长造成显著影响;孕穗期小麦孢囊线虫的危害能造成小麦每株穗数减少13．8％、鲜重降低14．5％,但对株高没有影响;孕穗期小麦品种对孢囊线虫的反应差异显著,受小麦孢囊线虫危害后,新麦12和皖麦50的单株鲜重量分别降低23．3％和22．5％,孕穗数分别减少了25．9％和11．1％,但徐州8562孕穗数减少不显著。     

Phenotypic and genetic characterization of Pseudomonas syringae strains associated with the recent citrus bacterial blast and bacterial black pit epidemics in Tunisia

In the spring of 2012, symptoms of a disease resembling citrus blast and citrus black pit were observed in some orchards in Tunisia. The epidemic spread rapidly in the following years. Twenty‐four commercial citrus orchards from four Tunisian regions showing characteristic symptoms of bacterial diseases were surveyed during a 3‐year study. Eighty‐eight Pseudomonas‐like bacterial isolates were successfully obtained from the northeast and west of Tunisia. No isolates were recovered from the central region. Overall, 46 isolates were identified as Pseudomonas syringae pv. syringae and most of them showed similar phenotypic and genetic profiles. The virulence of three selected isolates differed from one plant cultivar to another as well as from the type of plant organ used for the inoculation. In a bioassay test, all isolates produced syringomycin, which was confirmed by molecular detection based on the syrB and syrD genes. Only EC122 possessed syrD but not syrB. DNA fingerprints, based on repetitive sequence‐based polymerase chain reaction (rep‐PCR) and PCR melting profile (PCR MP), were used to determine the potential genetic diversity among strains. Clustering of PCR MP fingerprinting data matched with rep‐PCR fingerprinting data. The generated distribution tree showed that Tunisian isolates were closely related to the citrus reference strain LMG5496. In contrast, EC112, isolated from citrus, and the almond isolate EC122 were distantly related to the type strain LMG1247^T isolated from lilac. Such studies have not been reported until now for P. syringae from citrus.     

Alien scale insects (Hemiptera Coccoidea) in European and Mediterranean countries: the fate of new and old introductions

This contribution focuses on recent interceptions and introductions of alien scale insects and their current distribution in European and Mediterranean countries. Data and collections were gathered in markets, nurseries, and botanical gardens, mostly in Italy, either indoors or outdoors. New or recent records of the following alien species are presented: Exallomochlus hispidus (Morrison); Ferrisia virgata (Cockerell) (Pseudococcidae); Coccus viridis (Green); Milviscutulus mangiferae (Green) (Coccidae); Aonidiella orientalis (Newstead); Aspidiotus destructor Signoret; Aulacaspis tubercularis Newstead; Fiorinia fioriniae Targioni Tozzetti; Lepidosaphes pinnaeformis (Bouché); Pseudaulacaspis brimblecombei Williams (Diaspididae). New data and pest status of Phoenicococcus marlatti Cockerell (Phoenicococcidae) and Trabutina mannipara (Hemprich & Ehrenberg) (Pseudococcidae) are also reported. The possible repeated introductions of the latter from North Africa to south Italy by trans-Mediterranean winds, is hypothesized.     

Virulence spectrum in populations of the barley powdery mildew pathogen, Erysiphe graminis f. sp. hordei in Tunisia and Morocco in 1992

The virulence of 57 single colonies of Erysiphe graminis f. sp. hordei from Tunisia and Morocco was investigated using the Pallas near-isogenic differential set. Virulence patterns in general were similar in both countries. Va8, Va10+Du2, V41/145, VLa and VRu2 appear to be common in the region. The resistance alleles Mla7 and Mla9, in combination with other resistances, were highly effective against the isolates tested. No virulence against mlo and Mla9 + k was detected in Tunisia. No virulence on Mla7 and Mla9 was detected in Morocco. The frequency of virulence against several resistances was significantly higher in Morocco than in Tunisia. On the other hand, virulence against other resistances was higher in Tunisia than in Morocco. Three isolates from Morocco infected mlo to an extent greater than previously described. All pathotypes were unique. An attempt is made to interpret the results by comparison with pathotype evolution in Europe.