Periodicity and gradients in dispersal ofAlternaria linicola in linseed crops

Conidia ofAlternaria linicola produced on infected linseed crops were mainly dispersed by wind. The numbers of conidia in the air above linseed crops collected by a Burkard spore sampler were greatest between 1200 h and 1300 h, when the relative humidity was lowest. Although numbers of conidia collected decreased with increasing height within and above the crop canopy, air-borneA. linicola conidia were present up to 80 cm above the crop canopy. Conidia ofA. linicola were transported by wind up to at least 40 m downwind from an artificial line inoculum source, but their numbers decreased with increasing distance from the source. In 1991, 1992, and 1993, the dispersal ofA. linicola conidia above linseed crops followed a seasonal periodicity which was influenced by weather conditions and cultural practices. The greatest numbers of conidia were collected during July, August and early September and coincided with periods favourable for sporulation and with an increase in the incidence of the disease in the senescent crop. Air-borneA. linicola conidia produced on point or line inoculum sources (naturally infected linseed stem debris) were responsible for the spread of the disease in linseed crops. In 1992 and 1993, the disease was first detected downwind from the sources, but by the end of the growing seasons, it had spread in all directions and up to 20 m and 60 m from the sources, respectively. Disease gradients were initially steep near the inoculum sources but they became flatter with time due to the secondary spread of the disease.     

The effect of winter weather conditions on the ability of pseudothecia of Leptosphaeria maculans and L. biglobosa to release ascospores

Leptosphaeria maculans and L. biglobosa are damaging pathogens of oilseed rape. The infection of plants occurs predominantly in early autumn or spring by spores produced in pseudothecia. The aim of this study was to investigate whether pseudothecia formed in the autumn are still viable in the spring and to what extend they are destroyed by winter frosts. The studies presented here demonstrated that winter frosts can render pseudothecia unable to release spores. Nevertheless, ascospores present in pseudothecia unable to discharge ascospores, were fully capable of germination, regardless of the incubation temperature. No significant differences were found between the studied Leptosphaeria species in their response to frost. A multiple regression equation has been elaborated to forecast the ability of pseudothecia to release ascospores, based on winter temperatures. Considerable correlation was found between the ascospore release in the autumn and the ability of pseudothecia to release ascospores over the winter period and the subsequent symptoms of stem canker before harvest. We have demonstrated that the potential and the survival of inoculum can have a large impact on the success of the pathogen. This may be particularly important in the light of forecasted climate change. Higher winter temperatures may increase the ability of pseudothecia to release ascospores and the discharge of ascospores of L. maculans and L. biglobosa into the air, and cause early plant infections. This in turn will increase the number of infected plants, the disease incidence at harvest, and reduce the yield of oilseed rape.     

Effects of cultivar resistance and fungicide application on stem canker of oilseed rape (Brassica napus) and potential interseasonal transmission of Leptosphaeria spp. inoculum

Phoma stem canker is a damaging disease of oilseed rape (Brassica napus) that causes annual yield losses to UK oilseed rape growers worth approximately £100 million, despite the use of fungicides. In the UK, oilseed rape is sown in August/September and harvested in the following July. The disease epidemics are initiated by ascospores released from Leptosphaeria spp. pseudothecia (ascocarps) on stem stubble in the autumn/winter. Control of this disease is reliant on the use of cultivars with “field resistance” and azole fungicides. This study investigated the effects of cultivar resistance and application of the fungicide prothioconazole on the severity of stem canker before harvest and the subsequent production of pseudothecia on the infected stubble under natural conditions in the 2017/2018, 2018/2019, and 2019/2020 cropping seasons. The application of prothioconazole and cultivar resistance decreased the severity of phoma stem canker before harvest, and the subsequent production of Leptosphaeria spp. pseudothecia on stubble in terms of pseudothecial density. Results showed that stems with less severe stem cankers produced fewer mature pseudothecia of Leptosphaeria spp. on the infected stubble. This investigation suggests that the most sustainable and effective integrated control strategy for phoma stem canker in seasons with low quantities of inoculum is to use cultivars with medium or good field resistance and apply only one spray of prothioconazole when required.     

Mating Relationships between Isolates of Phaeosphaeria nodorum, (anamorph Stagonospora nodorum) from Geographical Locations

Mating types of Phaeosphaeria nodorum isolates (from North Africa, North America, Australia, Europe and Near East) were determined in laboratory conditions. Although both mating types were found, MAT1-1 and MAT1-2 were not evenly distributed among the isolates. Sexual compatibility pairings with standard mating type testers revealed that 56 of 101 isolates could be assigned to MAT1-1 and 5 to MAT1-2. Although the teleomorph occurred in different countries, the two mating types were observed only among isolates collected from France, Great Britain, Germany and Morocco. For Morocco, where no P. nodorum pseudothecia have been reported, this is the first report of the existence of the two opposite mating types. The remaining 40 isolates could not be designated to a specific mating type. However, in 17 crosses, pseudothecial initials or sterile pseudothecia were observed on wheat straw after two months. The implications of the predominance of one mating type are discussed.     

The Occurrence of Mycosphaerella graminicola and its Anamorph Septoria tritici in Winter Wheat during the Growing Season

The disease septoria tritici blotch of wheat is initiated by ascospores of the teleomorph Mycosphaerella graminicola or pycnidiospores of the anamorph Septoria tritici. We report for the first time the presence of the teleomorph, M. graminicola, in Denmark. With the objective of elucidating the importance of the teleomorph for the development of septoria tritici blotch, data on the occurrence of fruit bodies of the anamorph (pycnidia) and the teleomorph (pseudothecia) stages were collected over three growing seasons. Pseudothecia were present in the springs, however, high numbers of pseudothecia compared to pycnidia were not observed until July, too late to influence the epidemic. On an individual leaf layer, pycnidia were observed well before pseudothecia. As the leaves aged, progressively higher proportions of fruit bodies were observed to be pseudothecia. The period from the appearance of pycnidia to detection of pseudothecia was estimated as 29–53 days. At harvest, high proportions of sporulating fruit bodies in the crop were pseudothecia, suggesting that the primary source of inoculum for new emerging wheat crops in autumn is likely to be ascospores.     

Microsatellite primers indicate the presence of asexual populations of<Emphasis Type="Italic">Venturia inaequalis</Emphasis> in coastal Israeli apple orchards

This study was initiated to determine whether differences in genotypic diversity among populations ofVenturia inaequalis (Cke.) Wint., as detected using neutral genetic markers, were related to the ecological conditions in which apples are grown in Israel. Since sexual reproduction in this fungal pathogen has an obligate requirement for sustained low winter temperatures, and since these requirements in Israel are met only on the Golan Heights, we were interested in whether lower elevation populations of this pathogen might be comprised of asexual clonal lineages. Unlike temperate apple growing regions, where the primary spring inoculum is ascosporic derived from overwintered pseudothecia, Israeli apple orchards at lower elevations in the Hula Valley and along the coastal plain rarely if ever experience low winter temperatures and pseudothecia have never been recovered. Two orchards were sampled from the Golan Heights (El Rom and Ortal, n=38) and three orchards from the Hula Valley and coastal plain (Sede Eliezer, Ginaton and Be’er Tuvia, n=40). Microsatellite primers were used to analyze population structure and the resulting binary data analyzed by both cluster and parsimony analysis. Populations from the coastal plain were genetically uniform within each of the orchards sampled, whereas populations from the Golan Heights showed levels of genotypic diversity ten times as high. The data support field observations that this pathogen does not reproduce sexually in regions characterized by the absence of low winter temperatures and is instead composed of clonal lineages. This may have bearing on control strategies for the disease in Israel. http://www.phytoparasitica.org posting April 21, 2003.     

The identity of the footrot fungus of flax

From comparative morphological studies and inoculation tests it is concluded that the footrot fungus of flax (current nameAscochyta linicola Naoum. & Vass.) can be distinguished from a ubiquitous soil-borne fungus (current namePhoma solanicola Prill. & Del.) only by its pathogenicity on flax and its general appearancein vitro. The correct name of the latter fungus proved to bePhoma exigua Desm. For the footrot fungus the new combinationPhoma exigua Desm. var.linicola (Naoum. & Vass.) Maas is proposed. A documentation of the synonymy and literature are given for both organisms, and misapplications are discussed.Samenvatting Om na te gaan in hoeverre de dode harrel-schimmel van vlas (in Nederland bekend alsAscochyta linicola Naoum. & Vass.) identiek is met een algemeen voorkomende zwak parasitaire grondschimmel (o.a. bekend alsPhoma solanicola Prill. & Del.) zijn een aantal stammen van deze twee schimmels aan een vergelijkend onderzoek onderworpen, waarbij behalve de morfologische kenmerken ook de totale habitus in vitro en de pathogeniteit ten opzichte van vlas zijn onderzocht. In verband met bepaalde literatuurgegevens is ook de koolparasietLeptosphaeria maculans (Desm.) Ces. & de N. (stat. con.Plenodomus lingam (Tode ex Fr.) Hoehn.) en de van vlaszaad beschreven maar algemeen voorkomende schimmelPeyronellaea nicotiae Leduc bij dit onderzoek betrokken.Het bleek, dat de dode harrel-schimmel alleen door zijn afwijkende uniforme groei in cultuur en door zijn veel grotere pathogeniteit ten opzichte van vlas is te onderscheiden van de algemeen voorkomende grondschimmel (fig. 1; tabel 1). Derhalve werd geconcludeerd, dat we hier het beste kunnen spreken van twee variëteiten van één schimmel, welke gezien de morfologische kenmerken thuishoort in het geslachtPhoma Sacc. De oudst bekende naam van de algemeen voorkomende grondschimmel bleekPhoma exigua Desm. te zijn. Voor de dode harrel-schimmel werd de nieuwe combinatiePhoma exigua var.linicola (Naoum. & Vass.) Maas geïntroduceerd. Van beide organismen is een documentatie gegeven van de synonymie, literatuurgegevens en onjuiste toepassingen.De twee andere onderzochte schimmels, welke morfologisch van een geheel ander type zijn danPhoma exigua, bleken niet pathogeen te zijn voor vlas (tabel 1). Voor de algemeen voorkomendePeyronellaea nicotiae bleek afgestorven vlas een bijzonder geschikt substraat te zijn. Het literatuurgegeven datPhoma lingam (=Plenodomus lingam) morfologisch veel overeenkomst vertoont met de dode harrel-schimmel bleek op een misidentificatie te berusten en heeft in feite betrekking op de algemeen voorkomende grondschimmel.     

The full life cycle of Leptosphaeria maculans completed on inoculated oilseed rape incubated under controlled conditions

Because epidemics of successive cropping seasons are not independent, epidemiological studies need to encompass the processes occurring during the transmission of epidemics from one season to the next. With Leptosphaeria maculans, infected stubble allows carry‐over of the fungus. Generation experiments using recurrent selection on field plots are a useful means of comparing the effects of selection pressures. However, the full life cycle of the fungus, from plant infection to the next generation of ascospores, has not yet been achieved under controlled conditions. Studies were undertaken to achieve an experimental set‐up with sexual reproduction under controlled conditions. Cankered oilseed rape stems were produced under controlled conditions, after inoculation with a mixture of 12 isolates across both mating types. Stems were cut longitudinally and attached to styropore plates. Stem halves were incubated outside or in climate chambers regularly soaked in tap water to ensure maturation. Incubation was stopped when mature pseudothecia were observed. In all three independent experiments, more stem halves had pseudothecia when incubated under controlled conditions (30–100%) than incubated outside (0–80%). To the authors’ knowledge, this is the first study achieving the full life cycle of the fungus under controlled conditions, from infection of the plant to mature pseudothecia. This opens up the prospect of running experiments year‐round to better understand inoculum production, to compare fungal fitness, or to run generation experiments with exotic pathogen populations.     

First report of oospore formation in Plasmopara viticola,the causal agent of grapevine downy mildew,in highland regions of southern Brazil

This work evaluates the formation of oospores of Plasmopara viticola, the causal agent of grape downy mildew (DM), in highland regions in southern Brazil. Leaves of susceptible and resistant grape genotypes naturally infected with the pathogen were collected in the autumn of 2017, 2018, and 2019 from vineyards located in the highlands of Santa Catarina state. Leaf tissues were evaluated by light microscopy and scanning electron microscopy. Oospores of P. viticola were identified in both susceptible and resistant host genotypes. They were concentrated in the central regions of the DM lesions, close to the leaf veins, and exhibited a rounded shape, yellowish colour, thick wall, and a diameter ranging from 16.28 to 49.15 µm. The formation of oospores is strong evidence that sexual reproduction is occurring in P. viticola in the climatic conditions of the highlands of southern Brazil. Sexual reproduction contributes to the maximization of genetic diversity via meiosis. Populations with high genetic variability are more likely to break resistance mechanisms conferred by resistance genes and to develop resistance to fungicides applied for disease control. To our knowledge, this is the first scientific study to prove the formation of P. viticola oospores in Brazil. The results presented provide a solid basis for further studies on sexual recombination in P. viticola. Genetic improvement programmes for grapevines, disease management methods, and disease prediction models need to consider the sexual reproduction of this pathogen, otherwise their effectiveness may be compromised.     

Effect of seed age and cultivation on seedling emergence and seed decline of Avena fatua L. in winter barley

Avena fatua was sown in a cultivation experiment in the autumn of 3 successive years. For each population seedling emergence and viable seeds in the soil were recorded for 4 years in crops of winter barley in which new seed production was prevented. About half of the seeds sown were recovered after 1 year. In subsequent years viable seeds in the soil declined more rapidly with tine cultivation than with ploughing. After 4 years up to 5% of the original seeds were still viable. One population exhibited greater seed dormancy than the other two populations, due it is thought to higher summer rainfall and the greater availability of moisture during seed maturation. Most seedlings emerged in the autumn and spring, between 12 and 18 months after sowing. A total of 950 seedlings emerged from 12 000 seeds sown; 21% of these seedlings came from new seeds (< 1 year old), 57% from seeds 1–2 years old, 14% from seeds 2–3 years old and 8% from seeds 3–4 years old. Autumn seedlings arose fairly evenly from all age groups while spring seedlings mostly came from the 1–2-year-old seeds. With tine cultivation total seedlings over 4 years represented 9–7% and with ploughing 6–2% of the original seeds sown. A. fatua was more persistent than in previous experiments in spring barley, which suggests that control measures would have to be applied for longer in a succession of winter cereals than spring-sown crops to reduce A. fatua to low populations.     

秋覆盖的保水效应及对春玉米生长的影响

设置高(9000 kg·hm^-2)、中(6000 kg·hm^-2)、低(3000 kg·hm^-2)3种不同量秸秆覆盖和平覆、垄覆2种不同方式的地膜覆盖,以全程不覆盖为对照,研究了秋季雨后覆盖(休闲期加生育期全程覆盖)对土壤水分及春玉米生长状况的影响。结果表明：在冬闲期,各覆盖处理(除秸秆覆盖3 000 kg·hm^-2处理)的土壤蓄水量分别较不覆盖处理(CK)增加了21.22 mm、20.49 mm、18.37mm和19.5mm,使玉米出苗较CK至少提前了3 d。在播种期~大喇叭口期(播后70 d),平覆地膜和垄覆地膜平均土壤蓄水量分别较对照增加15.57 mm和15.73 mm;秸秆覆盖6 000 kg·hm^-2和9 000 kg hm^-2处理平均土壤蓄水量分别较对照增加12.05 mm和12.03 mm。秸秆覆盖处理在玉米生长后期土壤蓄水量较对照增加不显著。秋覆盖处理均可促进春玉米个体的生长,地膜覆盖处理可以显著提高春玉米生长前期的单株干重、株高和叶面积,秸秆覆盖在生育后期较对照显著提高。平覆地膜、垄覆地膜两个处理的玉米籽粒产量和水分生产效率分别较对照增加14.6%、13.9%和11.0%、11.1%(P<0.05),秸秆覆盖处理增产均不显著。     

Nursery‐linked plantation outbreaks and evidence for multiple introductions of the pitch canker pathogen Fusarium circinatum into South Africa

In recent years, Pinus plantation forestry has been significantly hampered by outbreaks of pitch canker caused by the fungus Fusarium circinatum. This study investigated the role of Pinus host, geographic origin and reproductive mode in structuring the F. circinatum populations in plantations. For this purpose, 159 isolates originating from diseased plantation trees in the Western and Eastern Cape Provinces of South Africa were genotyped using 10 microsatellite markers. Analyses of these data revealed 30 multilocus haplotypes and that the populations were distinct based on geographic origin as well as host. However, shared haplotypes were observed between populations, showing that these populations are connected, possibly through the movement of haplotypes. A second aim was to determine whether the genetic variation found in these populations of the fungus could be attributed to outbreaks of the seedling disease caused by this pathogen in Pinus nurseries. To achieve this goal, an additional set of 43 isolates originating from pine seedling nurseries was genotyped and analysed. The results showed that the populations of F. circinatum in plantations most probably originated from the nursery outbreaks that occurred prior to the plantation outbreak. Inferences regarding reproductive mode further showed that sexual reproduction has little impact on the genetic makeup of the F. circinatum populations and that they primarily reproduce asexually. Overall, the results of this study showed that the F. circinatum diversity in South Africa has arisen due to multiple introductions of the pathogen and is not due to sexual reproduction.     

Development of the teleomorph of Ascochyta rabiei on culture media

Ascochyta blight caused by Didymella rabiei (anamorph: Ascochyta rabiei) is an important foliar disease of chickpea in many countries. The fungus is heterothallic and requires the pairing of two compatible mating types for the teleomorph to develop. In nature, the teleomorph only develops on chickpea debris that overwinters on the soil surface in the presence of both mating types. When natural and synthetic agar media were seeded with conidial suspensions of compatible isolates of D. rabiei from Spain and the United States and incubated under favourable conditions for teleomorph development, the teleomorph only developed on 2?% water agar amended with powdered chickpea stems or hot water extracts of chickpea stems, but not on 14 other natural or synthetic media. Ascospore isolates of D. rabiei from pseudothecia that developed on agar media were indistinguishable in cultural and morphological characteristics from isolates of the fungus from chickpea. Production of pseudothecia and ascospores on the best culture medium was always lower than on stem pieces of chickpea straw used as a control treatment. Ascospores discharged from pseudothecia that developed on powdered chickpea stem media onto chickpea seedlings were pathogenic, inducing symptoms identical to those caused by ascospores from chickpea stem pieces or conidia from a chickpea isolate of the fungus. This is the first report of the teleomorph of D. rabiei developing on culture media.     

Epidemiology of Blackleg (Leptosphaeria maculans) of Canola (Brassica napus) in Relation to Maturation of Pseudothecia and Discharge of Ascospores in Western Australia

ABSTRACT The timing of maturation of pseudothecia and discharge of ascospores of the blackleg fungus (Leptosphaeria maculans) is critical in relation to infection early in the cropping season of canola. During 1998 to 2000, development of pseudothecia was investigated on residues of the previous year's canola crop collected from four agroclimatically different locations: Mount Barker (southern high rainfall), Wongan Hills (central medium rainfall), Merredin (central low rainfall), and East Chapman (northern low rainfall) in Western Australia. The pseudothecia matured on residues at different times after harvest in various regions. In general, pseudothecia maturity occurred earlier in the high-rainfall areas than in medium- and low-rainfall areas. An ascospore discharge pattern was investigated from residues of crop from the previous year (6-month-old residues) at three locations-Mount Barker, Wongan Hills, and East Chapman in Western Australia-and from 18-month-old residues that were burnt and raked in the previous year at Mount Barker and East Chapman. Ascospore discharge commenced earlier in high-rainfall (>450 mm) areas (Mount Barker) and late in northern low-rainfall (<325 mm) areas (East Chapman). The major ascospore showers took place during May (late autumn) and June (early winter) at Mount Barker and during July and August (mid- to late winter) at East Chapman. The number of ascospores discharged was extremely low at East Chapman compared with Mount Barker. At both locations, the number of ascospores discharged from 18-month-old residues that were raked and burnt in the previous year were only approximately 10% of those discharged from previous year's residues left undisturbed. The discharge of ascospores on any given day was negatively correlated with accumulated temperatures, maximum temperature, evaporation, minimum and maximum soil temperatures, and solar radiation and was positively correlated with the minimum temperature, rain, and minimum relative humidity. This is the first report describing how pseudothecia mature on residues in different rainfall areas in Western Australia, and it potentially can be used in developing a forecasting system to avoid the synchronization of major ascospore showers with the maximum susceptibility period of canola seedlings.     

Microconidia act the role as spermatia in the sexual reproduction of <Emphasis Type="Italic">Botrytis cinerea</Emphasis>

In the sexual reproductive cycle of Botrytis cinerea, large numbers of microconidia were observed in all the crosses that formed sexual bodies. To clarify the role of the microconidia in sexual reproduction, they were separated using a sucrose density gradient and then used in crossing tests with fungal sclerotia. Sexual bodies were formed in all the crosses in the five mating combinations, demonstrating that microconidia are able to function as spermatia during sexual reproduction of B. cinerea.     

Regulatory Mechanisms and Dynamics of an Island Population of Clethrionomys glareolus (Schreber, 1780)1

A scheme of density regulation in an island population of Clethrionomys glareolus (Schreber) is presented. The key factor for the changes in numbers was mortality of untrappable voles. A peak in population numbers followed low mortality of the spring generation, and, in peak years, mortality of the autumn generation was always high. An experimentally enriched food supply resulted in low mortality of both the spring and autumn generations. Natality, which is usually stable, increased slightly as a consequence of the additional food supply. This was due to an earlier start of the breeding season (6 weeks earlier) and to an increase in numbers of mature (i.e. capable of reproduction) females.     

The importance of seeds and sexual reproduction in the population biology of Cirsium arvense - a literature review

In this review the available information on the sexual reproduction of Cirsium arvense L. (Scop.) is summarized and discussed in an ecological context. Certain aspects of its sexual reproduction system have given C. arvense a reputation for low efficiency: the dioecious mating system and dependence on insects for pollination and non-adaptive features for wind dispersal. The seeds are moderately persistent in soil and, for a temperate weed, have a high temperature requirement for germination. It is concluded that the contribution that sexual reproduction makes to the survival and spread of this species has been underestimated, partly owing to an inadequate number of studies. Seedling recruitment via sexual reproduction may be an important mechanism for initiating continued genetic diversity at intra- and inter-population levels.     

Genetic structure and phylogeny of Italian and Czech populations of the cucurbit powdery mildew fungus Golovinomyces orontii inferred by multilocus sequence typing

Cucurbit powdery mildew caused by Golovinomyces orontii is a serious disease that affects cucurbit crops in temperate areas. In northern Italy, the species is responsible for the early infections at the beginning of the growing season. However, chasmothecia have never been recorded in Italy and the impact of either asexual or sexual reproduction of G. orontii remains to be determined. To investigate and compare the genetic structure of Italian populations with those from the Czech Republic, where chasmothecia are sporadically recorded, seven housekeeping gene fragments (tef‐1α, csI, ITS, H3, tub2, IGS and mtLSU) were amplified and used in a multilocus sequence typing (MLST) approach. The four‐gamete test was performed to detect recombination between and within populations. Phylogeny was inferred using both Bayesian and minimum evolution analyses. Results from MLST revealed the presence of 141 single nucleotide polymorphisms and the existence of 13 different haplotypes. Phylogenetic analysis revealed the existence of two main distinct phylogenetic groups that were also highly genetically different, confirming that G. orontii is a species complex. Recombination was detected within both the phylogenetic groups and the geographical populations, indicating that sexual reproduction could have occurred. However, considering the lower haplotype diversity and the high frequency of ST3 (17 isolates) and ST7 (eight isolates) haplotypes, the Italian population could be predominantly clonal, while sexual reproduction may occasionally occur due to the introduction of genotypes similar to those from the Czech Republic.     

Genetic structure of the grapevine fungal pathogen Phaeomoniella chlamydospora in southeastern Australia and southern France

In this study, 18 microsatellite loci were used to examine the genetic structure and mode of reproduction of Phaeomoniella chlamydospora, the fungus that causes Petri disease of grapevine and is involved in another grapevine disease, esca. A total of 60 southeastern Australian isolates were tested and compared with 64 isolates from southern France. The French population possessed relatively high genotypic diversity (G = 29·2) whilst the Australian population showed low genotypic diversity (G = 11·1), consistent with a limited founder population. Haplotypes from four different grapevine cultivars were not significantly differentiated (Φpt values effectively zero). Likewise, genetic differentiation of haplotypes from different regions within each country was not significant, although small but significant genetic differentiation (9%) was identified between Australia and France. Based on bootstrapped cluster analysis, there did not appear to be any genetic groups within the overall sample of isolates. Significant linkage disequilibrium identified in both countries, together with overrepresented, widespread identical haplotypes, indicated limited genetic recombination and a largely clonal structure consistent with the absence of an observed sexual cycle in this species.     

三种不同干旱动态监测指数在陕西省的适用性研究

运用陕西省96个站1981—2012年近32年的逐日气温、降水、风速、相对湿度等资料,分别计算出各站逐日(向前滚动30天)的三种干旱动态监测指数：降水距平百分率(P_a)、相对湿润干旱指数(MI)、标准化降水指数(SPI),并将陕西省按地域由北至南分为陕北、关中、陕南,按季节分为春(3—5月)、夏(6—8月)、秋(9—11月)、冬(12—2月),分别统计出不同干旱动态监测指数对应的干旱发生的频率并与历史记载中实际干旱情况进行比对,对三种干旱动态监测指数在陕西省的适用性进行分析。结果表明：夏季MI指数得到的干旱频率最高,P_a指数最低,冬季MI指数得到的干旱频率最低,P_a指数最高; 在春、冬季节P_a指数的适用性较好,在夏、秋季节MI指数的适用性较好; 陕西省夏季容易发生局地强降水,而在秋、冬季容易出现长时间的无降水,导致SPI指数在夏、秋、冬季节的适用性不太好。