Environmental and inoculum effects on epidemiology of bacterial spot disease of stone fruits and development of a disease forecasting system

Bacterial spot disease of stone fruits, caused by Xanthomonas arboricola pv. pruni, is of high economic importance in the major stone-fruit-producing areas worldwide. A better understanding of disease epidemiology can be valuable in developing disease management strategies. The effects of weather variables (temperature and wet/dry period) on epiphytic growth of X. arboricola pv. pruni on Prunus leaves were analyzed, and the relationship between inoculum density and temperature on disease development was determined and modeled. The information generated in this study, performed under controlled environmental conditions, will be useful to develop a forecasting system for X. arboricola pv. pruni. Optimal temperature for growth of epiphytic populations ranged from 20 to 30 °C under leaf wetness. In contrast, multiplication of epiphytic populations was not only interrupted under low relative humidity (RH) (< 40%) at 25 °C, but also resulted in cell inactivation, with only 0.001% initial cells recovered after 72 h incubation. A significant effect of inoculum density on disease severity was observed and 10⁶ CFU/ml was determined as the minimal infective dose for X. arboricola pv. pruni on Prunus. Infections occurred at temperatures from 15 to 35 °C, but incubation at 25 and 30 °C gave the shortest incubation periods (7.7 and 5.9 days respectively). A model for predicting disease symptom development was generated and successfully evaluated, based on the relationship between disease severity and the accumulated heat expressed in cumulative degree day (CDD). Incubation periods of 150, 175 and 280 CDD were required for 5, 10 and 50% of disease severity, respectively.     

Effect of controlled fluctuating low temperatures on survival of <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease of wheat worldwide. Understanding the survival of Pst during the winter is critical for predicting Pst epidemics in the spring. We used a real-time quantitative PCR (qPCR) method to quantify Pst CYR32 biomass in infected wheat seedlings under several fluctuating temperature regimes (three average temperatures 0, ?5 and ?10 °C, each with two daily fluctuating amplitudes 8 and 13 °C). The survival of Pst CYR32 increased with increasing average temperature but also varied greatly with the amplitude – larger amplitude led to lower survival, particularly at 0 and ?5 °C. Nevertheless the survival at both amplitudes was still significantly greater than under the corresponding constant temperatures. There were small, albeit statistically significant, differences between the two cultivars (Xiaoyan 22, low winter-hardiness; Lantian 15, high winter-hardiness) in Pst CYR32 survival. This study indicated potential errors that could result from using daily average temperatures to predict Pst survival during the winter.     

Thermal effects on the development of <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis> (Hendel) (Diptera: Tephritidae) and model validation in Taiwan

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a major polyphagous insect pest with a worldwide distribution. The effects of temperature on stage-specific development in B. dorsalis were investigated at eight constant temperatures (13.0 °C, 14.4 °C, 16.2 °C, 19.5 °C, 23.8 °C, 27.7 °C, 31.8 °C and 34.8 °C). B. dorsalis developed successfully from the egg stage to the adult stage at all the tested temperatures, except at the lowest temperatures (13.0 °C and 14.4 °C). Stage-specific lower developmental thresholds and thermal constants were determined using linear regression. The lower and higher temperature threshold (TL and TH, respectively) were estimated using the Sharpe-Schoolfield-Ikemoto model. The lower developmental threshold and thermal constant from egg to adult emergence were 9.8 °C and 325.5 degree-days, respectively. The intrinsic optimum temperatures of the egg, larval, pupal and egg to pupal stage were 20.7 °C, 21.8 °C, 21.1 °C, and 22.4 °C, respectively. The temperature range of the B. dorsalis total immature stage from TL to TH was 20.4 °C (13.8 °C - 34.2 °C). The stage-specific developmental completion of B. dorsalis was determined using a two-parameter Weibull function. The daily adult emergence frequency of B. dorsalis was estimated in relation to adult age and temperature using non-linear developmental rate functions and the Weibull function. The date of cumulative 50% adult emergence estimated using non-linear functions was approximately one day earlier than the experimentally observed date. Thermal performance was compared among B. dorsalis populations from different locations.     

The Eurotiomycete <Emphasis Type="Italic">Apinisia graminicola</Emphasis> as the causal agent of a leaf spot disease on the energy crop <Emphasis Type="Italic">Miscanthus</Emphasis> x <Emphasis Type="Italic">giganteus</Emphasis> in Northern Germany

Miscanthus x giganteus is a fast growing, perennial energy crop for temperate climates. Because of its high annual biomass production rates and its characteristics as a low-input crop, an expansion of field cultivation can be anticipated to cover increasing demands for sustainable biomass production. However, knowledge about pathogens that could have an impact on biomass production is still limited for M. giganteus. Here, we report about the isolation of the filamentous fungus Apinisia graminicola from necrotic leaf lesions of M. giganteus grown on a field trial plot in Northern Germany. Inoculation assays with the isolated A. graminicola strain confirmed its capacity to cause a leaf spot disease on M. giganteus. Additional inoculation assays revealed that A. graminicola also caused necrotic lesions on leaves of the model grass Brachypodium distachyon. Generally, symptoms of A. graminicola-caused leaf spot disease were stronger on B. distachyon compared to M. giganteus. Incubation temperatures above 22 °C during A. graminicola infection resulted in stronger disease symptoms on both, M. giganteus and B. distachyon leaves. Microscopic analysis of cross sectioned, infected leaf tissue revealed an epiphytic mycelium formation on the surface and an endophytic colonization of the mesophyll leave tissue, especially in M. giganteus. Our results revealed that the isolated A. graminicola strain is a causal agent of a leaf spot disease on grass leaves. Its potential on endophytic growth in M. giganteus might open new possibilities in studying this type of plant-fungal interaction on a cellular and molecular level in an energy crop.     

Genetic structure of <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis> and <Emphasis Type="Italic">P. teres</Emphasis> f. <Emphasis Type="Italic">maculata</Emphasis> populations from western Canada

Infection by Pyrenophora teres f. teres (Ptt) or P. teres f. maculata (Ptm), the causal agents of the net and spot forms of net blotch of barley, respectively, can result in significant yield losses. The genetic structure of a collection of 128 Ptt and 92 Ptm isolates from the western Canadian provinces of Alberta (55 Ptt, 27 Ptm), Saskatchewan (58 Ptt, 46 Ptm) and Manitoba (15 Ptt, 19 Ptm) were analyzed by simple sequence repeat (SSR) marker analysis. Thirteen SSR loci were examined and found to be polymorphic within both Ptt and Ptm populations. In total, 110 distinct alleles were identified, with 19 of these shared between Ptt and Ptm, 75 specific to Ptt, and 16 specific to Ptm. Genotypic diversity was relatively high, with a clonal fraction of approximately 10 % within Ptt and Ptm populations. Significant genetic differentiation (PhiPT = 0.230, P = 0.001) was found among all populations; 77 % of genetic variation occurred within populations and 23 % between populations. Lower, but still significant genetic differentiation (PhiPT = 0.038, P = 0.001) was detected in Ptt, with 96 % of genetic variation occurring within populations. No significant genetic differentiation (PhiPT = 0.010, P = 0.177) was observed among Ptm populations. Isolates clustered in two distinct groups conforming to Ptt or Ptm, with no intermediate cluster. The high number of haplotypes observed, combined with an equal mating type ratio for both forms of the fungus, suggests that P. teres goes through regular cycles of sexual recombination in western Canada.     

Morphological and molecular identification of potato and cereal cyst nematode isolates from Algeria and their phylogenetic relationships with other populations from distant theirgeographical areas

A nematode survey conducted in 2013 in Algeria, revealed that potato cyst nematodes (PCN) and cereal cyst nematodes (CCN) are widely distributed in several potato and cereal growing regions of the country. Sixteen PCN populations from five localities and five CCN populations from four of these localities were collected and characterized at the morphological and molecular levels. The PCN populations were identified as Globodera rostochiensis and G. pallida occurring separately or in mixed populations. Two species of CCN were detected. Heterodera avenae was found in four localities, whereas H. hordecalis only in one locality in association with H. avenae. The morphological and morphometric identification of PCN and CCN was confirmed by diagnostic ITS-RFLP profiles and sequencing. Phylogenetic analysis of the ITS, D2-D3 expansion domains of the 28S rRNA gene and 18S rRNA gene was made for PCN and CCN populations. Globodera pallida and G. rostochiensis from Algeria show great similarity with European and South American populations. Because of the high divergence among Algerian populations of G. pallida and G. rostochiensis it can be assumed that they were multi-introduced in Algeria. The most divergent population of G. pallida, that formed a well-separated group with some populations from Chile and Peru, suggests a later or independent introduction of this population into Algeria. Heterodera avenae and H. hordecalis formed a well-supported cluster with the corresponding populations.     

Associated bacterial diversity of insecticide-susceptible and -resistant brown planthopper, <Emphasis Type="Italic">Nilaparvata lugens</Emphasis> (Homoptera: Delphacidae) analyzed by culture-dependent and -independent methods

Nilaparvata lugens (Stål) is one of the major pests of rice throughout tropical and temperate Asia. Indiscriminate use of insecticides for suppressing N. lugens has resulted in the development of resistance to multiple insecticide classes, causing frequent control failures in the field. Analysis of gut bacterial diversity within an insect host is the initial step towards understanding the ecological roles of the symbionts. Present study aimed to survey the bacterial diversity associated with laboratory-reared (insecticide-susceptible) and field-collected (insecticide-resistant) populations of N. lugens by culture-dependent and PCR-Denaturing Gradient Gel Electrophoresis (DGGE) methods. Seventeen bacterial isolates were obtained by the culture-dependent method. Molecular characterization using the 16S rRNA gene and phylogenetic analysis revealed that the isolates belonged to Firmicutes and Proteobacteria. Taxonomic assignment placed these isolates into seven families representing 10 genera. Enterobacteriaceae was the most dominant family with its occurrence in four out of the five populations studied. The DGGE profiles indicated a low complex gut bacteria associated with N. lugens with limited number of bands. The Shannon-Wiener index ranged from 0.898 in insecticide-susceptible population to 0.946–1.035 in resistant populations. Sequencing and phylogenetic analysis revealed that the DGGE bands belonged to Firmicutes, Proteobacteria and Bacteriodetes. Results of this study illustrated that gut bacterial community associated with N. lugens is dominated by Proteobacteria and Firmicutes. Present findings could provide the basis for future work on the possible role of the bacterial symbionts in insecticide resistance and to formulate potential resistance management strategies.     

Host status of cultivated plants to <Emphasis Type="Italic">Meloidogyne hispanica</Emphasis>

The reproduction of a Meloidogyne hispanica isolate from Portugal was evaluated in 63 plant species/cultivars, in pot assays at 25?±?2.0°C, on the basis of root gall index (GI) and reproduction factor (Rf?=?final/initial egg density) at 60 days after inoculation. Cultivars of aubergine, bean, beetroot, broccoli, carnation, corn, cucumber, French garlic, lettuce, melon, onion, parsley, pea, potato, spinach, and tobacco and two of cabbage were susceptible (3?≤?GI?≤?5; 1.15?≤?Rf?≤?262.86). Cabbage cv. Bacalan, cauliflower cv. Temporão and pepper cv. Zafiro R2 were hypersusceptible or poor hosts (Rf??2) and pepper cvs. Aurelio and Solero were resistant (0.0?≤?GI?≤?0.4; 0.00?≤?Rf?≤?0.03). The response of the pepper cultivars and the Mi-1 resistant tomato cv. Rossol was also conducted in pots using two inoculum levels and four temperatures, three growth chamber (25?±?2.7°C, 29.3?±?1.8°C and 33.6?±?1.2°C) and one outdoors (24.4?±?8.2°C). At 24.4?±?8.2°C and 25?±?2.7°C, the reproduction on the resistant tomato was significantly lower compared to the susceptible cv. Easypeel. At all temperatures, resistance was evident for the pepper cultivars, despite the fact they were not found to contain any of the Me1, Me3, Me7 and N genes. The eggs obtained on cv. Aurelio at 33.6?±?1.2°C were used to get a selected resistance breaking isolate of M. hispanica that was able to reproduce on the three pepper cultivars. Our results suggest that the initial M. hispanica isolate is a mixture of virulent and avirulent individuals. The pepper cultivars tested, have potential to reduce M. hispanica populations in agro-ecosystems under certain conditions, but they should be used as a part of an integrated management strategy in order to prevent the development of virulent populations.     

Fungicide sensitivity,growth rate,aggressiveness and frost hardiness of <Emphasis Type="Italic">Monilinia fructicola</Emphasis> and <Emphasis Type="Italic">Monilinia laxa</Emphasis> isolates

Monilinia fructicola, the most destructive pathogen of the genus Monilinia, has recently been introduced into Serbia and many other European countries. Since then, many studies have been conducted to evaluate the characteristics of Monilinia species that have a role in the establishment and survival of the pathogen in new areas. The present study assessed the capacity of M. fructicola to repress and replace Monilinia laxa in Serbia based on: fungicide sensitivity, growth rate and aggressiveness at different temperatures, as well as frost hardiness of the isolates of both species. The results showed that the isolates of M. fructicola, compared to M. laxa, were significantly less sensitive to the following fungicides: iprodione, tebucanozole, chlorothalonil, azoxystrobin, fluopyram, and boscalid. In addition, M. laxa isolates exhibited little variation in sensitivity to all of the tested fungicides, whereas M. fructicola isolates displayed a wide range of sensitivity. The temperature of 5°C favored M. laxa growth and aggressiveness, while at 30°C M. fructicola grew faster and had higher lesion expansion rate. These results support an assumption that M. fructicola will continue to spread in Serbian orchards in coming years, particularly on stone fruits harvested during hot summer weather.     

Comparative colonisation by virulent versus avirulent <Emphasis Type="Italic">Pyricularia oryzae</Emphasis> on wild <Emphasis Type="Italic">Oryza australiensis</Emphasis>

Pyricularia oryzae (rice blast) conidial development at pre-penetration stage determines success or otherwise of infection inside the rice host plants. Studies on conidial germination and growth on the leaf surface in commercial rice (Oryza sativa) report differently, dependent upon host type and level of blast resistance. Although wild rice (O. australiensis) is known to be an alternative host of blast, the interaction between P. oryzae conidia and wild O. australiensis on its leaf surface has not been previously studied. We found significant (P?<?0.001) differences in conidial development between two blast isolates with different virulence in terms of conidial germination, germ tube growth and appressoria formation on both wild and cultivated rice. Conidial germination at 6 h post-inoculation (hpi) for the virulent isolate was significantly (P?<?0.001) delayed. Germ tubes of the avirulent isolate conidia grew significantly (P?<?0.001) faster and with significantly (P?<?0.001) longer germ tubes than from virulent conidia. Appressoria development for the virulent isolate was significantly (P?<?0.001) faster at its later growth stages of 12 and 18 hpi when approximately 100% of germ tubes formed appressoria. In contrast, formation rate of appressoria for the avirulent isolate was significantly (P?<?0.001) slower and only reached 76% of germ tubes forming appressoria. Appressoria formation on O. australiensis was significantly (P?<?0.001) greater than the formation on O. sativa for both virulent and avirulent P. oryzae at 12 hpi, a clear indication that host type influences the extent of appressoria formation.     

A myosin passenger protein gene (<Emphasis Type="Italic">FaSmy1</Emphasis>) is an essential regulator of cell development,pathogenicity, DON biosynthesis,and resistance to the fungicide phenamacril in <Emphasis Type="Italic">Fusarium asiaticum</Emphasis>

Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are important viruses of wheat (Triticum aestivum L.) in the Great Plains of United States. In addition to agronomic practices to prevent damage from these viruses, temperature sensitive resistance genes Wsm1, Wsm2 and Wsm3, have been identified. However, threshold temperatures for Wsm1 and Wsm3 have not been clearly defined. To better understand these two resistance genes, wheat lines C.I.15092 (Wsm1), KS96HW10–3 (Wsm1), and KS12WGGRC59 (Wsm3) were evaluated for WSMV resistance at 27, 30, 33 and 35 °C and for TriMV resistance at 18, 21, 24, 27, 30, 33 and 35 °C. The results showed that only C.I.15092 remained resistant at 30 °C for both viruses. This line also tolerated TriMV at 33 and 35 °C with less sever symptom and lower infection rates. Wheat lines KS96HW10–3 and KS12WGGRC59 hold resistance to TriMV up to 21 °C. Molecular marker results suggested that the resistance in C.I.15092 is most probably conditioned by the resistance gene Wsm1 and additional gene(s) other than Wsm2 and Wsm3.     

Efficacy of a formulated product containing <Emphasis Type="Italic">Quillaja saponaria</Emphasis> plant extracts for the control of root-knot nematodes

The nematicidal effect of a formulated product containing extract from Quillaja saponaria was evaluated against the root-knot nematodes. The product QL Agri® 35 (QL) was tested to record the effect on second stage juveniles motility, egg hatch and also against field populations in greenhouse experiments contacted in three different locations of Greece. Convulsive movement of second stage juveniles of Meloidogyne incognita was recorded after exposure for 8 days at a series of doses, while the most paralyzed juveniles were counted at the dose of 8 mg l^?1. There was also a gradual decrease in the number of juveniles emerging from egg masses of the same nematode species when the dose of Q. saponaria was increased from 0 to 8 mg l^?1. In greenhouse experiments, the use of Q. saponaria could control root-knot nematodes and prevent nematodes increase in soil. The present study demonstrates that the use of Q. saponaria extract has the ability to control root-knot nematodes. Control given by Q. saponaria in field populations infecting cucumber was similar to that of cadusafos (Rugby®) and oxamyl (Vydate®) under the tested dosages and the specific conditions of the experiments.     

Vertical distribution of resting spores of <Emphasis Type="Italic">Plasmodiophora brassicae</Emphasis> in soil

Pratylenchus zeae parasitizes various crops and damages the host roots, resulting in decreased yield and quality of the host plants. Alignments of mitochondrial DNA (mtDNA) Cytochrome Oxidase I (COΙ) sequences revealed the genetic variation among Pratylenchus species. The results indicated 0.2–2.4% intraspecific variations for mtDNA COI sequences among eight P. zeae populations, and 25.4–35.1% interspecific variations between P. zeae and other Pratylenchus species. Based on the mtDNA COΙ region, a loop-mediated isothermal amplification (LAMP) assay was developed for the rapid and specific detection of P. zeae. The optimal conditions for the LAMP assay were 64 °C for 40 min. The LAMP products were confirmed using conventional polymerase chain reaction (PCR), analysis with the restriction enzyme Bam HI and visual inspection by adding SYBR Green I to the products. The LAMP assay could detect P. zeae populations from different hosts and different geographical origins specifically. The LAMP assay was also sensitive, detecting 0.1 individual P. zeae, which was 10 times more sensitive than conventional PCR. This is the first report of the detection of Pratylenchus spp. using LAMP. In addition, the results also suggested that use of the COI gene might allow for good resolution at the Pratylenchus species level.     

Fungicidal activity of Thai medicinal plant extracts against <Emphasis Type="Italic">Alternaria brassicicola</Emphasis> causing black spot of Chinese kale

Crude ethanol extracts and six organic solvent fractions of 10 Thai medicinal plants were evaluated for their antifungal activity against Alternaria brassicicola in laboratory and under greenhouse conditions. The results showed that the ethanol extracts of Coscinium fenestratum, Piper betle, Syzygium aromaticus and Zingiber cassumunar displayed complete mycelial growth inhibition of A. brassicicola at a concentration of 0.1%. Meanwhile, the crude ethanol extract and methanol fraction obtained from the stems of C. fenestratum revealed the greatest inhibition against A. brassicicola at 10%, forming inhibition zones 2.55–2.58 cm in diameter. In the greenhouse experiments, crude ethanol extracts of C. fenestratum and P. betle at 1% significantly (P?<?0.05) reduced the disease incidence at up to 67%, indicating promising preventive and curative activities against A. brassicicola. This activity is similar to that of iprodione, a widely used commercial fungicide. Interestingly, Illicium verum extract showed a greater curative effect (58% disease reduction) than protective effect (47% disease reduction). Because the C. fenestratum extract showed the highest activity against the black spot pathogen both in vitro and under greenhouse conditions, its methanol fraction was further analyzed by spectroscopic techniques. We found that berberine is a key active substance inhibiting mycelial growth of A. brassicicola. The results of this study showed the potential of Thai medicinal plants as alternatives to the use of synthetic fungicides for controlling black spot in Chinese kale caused by A. brassicicola.     

In vitro competition between <Emphasis Type="Italic">Fusarium graminearum</Emphasis> and <Emphasis Type="Italic">Epicoccum nigrum</Emphasis> on media and wheat grains

Competitive effects between Fusarium graminearum, causing Fusarium head blight, and the endophyte Epicoccum nigrum, were performed in in vitro competition assays between the two species. Two E. nigrum isolates were isolated from wheat grains and tested as competitors against two F. graminearum isolates. A dual petri dish assay showed that E. nigrum reduced the mycelial growth of F. graminearum and vice versa. A glass slide assay revealed that E. nigrum crude cultural filtrate also had reducing effect on the growth of F. graminearum comparable to that of E. nigrum spore suspensions. Microscopy showed hyphae of F. graminearum and E. nigrum with many side branches when in close proximity, in contrast to pronounced apical hyphal growth when growing alone. Combinations of F. graminearum and E. nigrum on sterilised wheat grains were studied over time by qPCR. F. graminearum biomass was significantly reduced in inoculations applying E. nigrum three days prior to F. graminearum. In conclusion, these results showed competition and mycelial behaviour effects between F. graminearum and E. nigrum and support that E. nigrum may have potential to reduce F. graminearum infections in wheat. Competition experiments should be carried out in planta to study the interaction further.     

Control of infection of tomato fruits by <Emphasis Type="Italic">Alternaria</Emphasis> and mycotoxin production using plant extracts

Tomato fruits are susceptible to infection by Alternaria species. In addition, Alternaria species may contaminate the fruits with mycotoxins. There is thus interest in control systems to minimise pathogenicity and control toxin production. The objectives of this study were to examine the effect of plant extracts of Eucalyptus globulus and Calendula officinalis on the growth of strains of Alternaria alternata and A. arborescens, on pathogenicity of tomato fruits and mycotoxin production. The growth bioassays showed that the ethanolic and chloroformic fractions of E. globulus were the most effective in reducing growth of A. alternata (66–74 %) and A. arborescens (86–88 %), respectively at 2500 μg/g. The effects of plant extracts on mycotoxin biosynthesis were variable and strain dependent. The most effective fractions in decreasing mycotoxin accumulation were the ethanolic and chloroformic extracts of E. globulus, which reduced tenuazonic acid by 89 %, alternariol by 75–94 % and almost complete inhibition of alternariol monomethyl ether. All the tested fractions reduced percentage of infected tomato fruits when compared to the controls. The ethanolic and chloroformic fractions of E. globulus completely inhibited growth of A. alternata and A. arborescens on unwounded fruits and reduced the aggressiveness on wounded fruits of strains of both species significantly.     

Resistance assessment and biochemical responses of sugar beet lines against <Emphasis Type="Italic"> Pythium aphanidermatum,</Emphasis> causing root rot

Wood-staining fungi, moulds and decay fungi colonize freshly cut wood. Of these, only ophiostomatoid fungi are considered major agents of sapstain on logs and freshly sawn lumber because they can cause permanent staining and discoloration. Sapstain in pine pallets significantly reduces their market value and use in the food industry. The aim of this study was to identify the sapstaining fungi that colonize Scots pine wood used in pallet production. In addition, we evaluated the growth and stain intensity of six isolates of ophiostomatoid fungi on freshly cut Scots pine billets. Fungi were isolated from samples of Scots pine and identified based on morphology and DNA sequence comparisons for three gene regions (ITS, β-tubulin, TEF-1α). A total of 1259 isolates representing 31 fungal species were obtained from the pine samples in Poland during July and September. The isolates represented different ecological and taxonomical groups and belonged to the categories of staining fungi, decay fungi and surface moulds. The most frequently isolated fungi were ophiostomatoid fungi (14 species including an unknown Leptographium sp. and Ophiostoma sp.) and moulds (mainly Trichoderma and Mucor spp.). Of the ophiostomatoid species, Ophiostoma floccosum, O. piceae, O. piliferum and Endoconidiophora pinicola were the predominant species. The results of pine billet inoculation showed that among the six fungal species tested, E. pinicola exhibited the fastest growth in all three directions on the billets. Ophiostoma minus and O. piliferum displayed moderate growth rates in pine billets, while O. floccosum, O. piceae, and Leptographium lundbergii grew very slowly, especially in the tangential and radial directions. The information provided in this paper will help develop more effective control strategies for sapstain prevention in Scots pine.     

Growth of Xanthomonas campestris pv. campestris populations at constant and variable temperatures

Quantitative data were collected to describe the relation between temperature and growth of the cabbage black rot pathogen,Xanthomonas campestris pv.campestris (Xcc). Relative growth rates derived from experiments at constant temperatures were used in dynamic simulation of bacterial population development. The relative growth rates were adequate to simulate growth ofXcc populations at constant temperatures but overestimated growth of populations at variable temperatures. This finding gives rise to the hypothesis, that under field conditions, disease development is slower than is expected on the basis of growth parameters obtained from studies with constant temperatures.     

Effect of simultaneous and sequential inoculations of <Emphasis Type="Italic">Meloidogyne incognita</Emphasis>, <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> and <Emphasis Type="Italic">Phomopsis vexans</Emphasis> on eggplant in sand mix and fly ash mix soil

Effects simultaneous and sequential inoculations of Meloidogyne incognita, Ralstonia solanacearum and Phomopsis vexans were studied on the growth, chlorophyll and carotenoid contents of eggplants grown in 25% fly ash and 25% sand mix soil. Plants grown in 25% fly ash mix soil had lesser plant growth than grown in 25% sand ash mix soil. Inoculation of M. incognita / R. solanacearum or P. vexans caused reduction in plant growth, chlorophyll and carotenoid contents in both types of soils but these pathogens in combination caused a greater reduction in than individual inoculation. Inoculation of M. incognita 20 days prior to R. solanacearum caused a greater reduction in plant growth than inoculation of M. incognita prior to P. vexans. Inoculation of P. vexans prior to R. solanacearum caused a lesser reduction in plant growth, chlorophyll and carotenoid contents than inoculation of P. vexans prior to M. incognita. Inoculation of R. solanacearum 20 days prior to M. incognita caused a greater reduction in plant growth, chlorophyll and carotenoid contents than inoculation of R. solanacearum prior to P. vexans. Galling and multiplication of M. incognita was higher in plants grown in 25% sand amended soil than with 25% fly ash soil. R. solanacearum and P. vexans had adverse effects on galling and nematode multiplication. Wilt and blight indices caused by R. solanacearum and P. vexans were 3 respectively. Wilt and blight indices were 4 when two pathogens were inoculated together.     

Effect of host resistance on genetic structure of core and accessory chromosomes in Irish <Emphasis Type="Italic">Zymoseptoria tritici</Emphasis> populations

In agricultural pathosystems resistant cultivars are typically only temporarily effective, as widespread growth of said cultivars drives selection for pathogen genotypes capable of infecting them. A gene-for-gene interaction between Z. tritici and wheat has been demonstrated for one cultivar; however results of studies into the relevance of these interactions in the field remain inconsistent. Because genetic drift does not appear to occur between Z. tritici populations that are not widely geographically separated, according to neutral genetic theory if adaptation to different host cultivars is occurring, reduced genetic variation, and some differentiation between populations sourced from different cultivars should be observed. Selectively neutral microsatellite markers were used to genotype 260 isolates of Z. tritici taken from two naturally infected randomized block trials of four different cultivars, representing a spectrum of resistance to Z. tritici from susceptible to resistant. By calculating genetic parameters such as overall heterozygosity and F _ST from this genotypic data, the presented study aimed to determine if genetic drift or host selection is impacting on the genetic structure of the Irish Z. tritici population. Results indicated that diversity was distributed almost entirely within, rather than among populations, with little or no differentiation, and almost no clone isolates were present in the dataset. However this result was not reflected in the accessory chromosomes, where evidence of minor but significant genetic structure was found. This lack of structure in the core chromosomes and weak structure in the accessory chromosomes confirms that forces of genetic drift and selection are minor compared to sexual reproduction, in concurrence with multiple previous studies on other populations worldwide.