Damage thresholds and population dynamics of <Emphasis Type="Italic">Pratylenchus penetrans</Emphasis> on carrot (<Emphasis Type="Italic">Daucus carota</Emphasis> L. cv. Nerac) at three different seed densities

Yield and quality loss of carrot (Daucus carota L. cv. Nerac) caused by Pratylenchus penetrans and the population dynamics of this nematode were studied in a climate controlled glasshouse. A range of 12 nematode densities was used at three different seed densities of carrot; 2, 4 and 18 seeds pot^?1. Seinhorst’s yield loss model; y?=?m?+?(1 - m) 0.95 ^Pi/T-1 for Pi?>?T; y?=?1 for Pi?≤?T for Tylenchina was fitted to the yield and quality loss data. Seinhorst’s model for population dynamics of migratory nematodes with multiple generations; \( Pf=M* Pi/\left( Pi+M/a\right) \) was fitted to the data of the final population densities (Pf). P. penetrans had a significant impact on carrot taproot yield and its quality. The tolerance limits for the relative carrot taproot yield (T _y) were 1.51, 1.88, and 1.37 and those of quality yields (T _q) were 0.67, 0.18, and 0.40 P. penetrans (g dry soil)^?1 at 2, 4 and 18 seeds pot^?1, respectively. Both the minimum yield (0.20, 0.29, and 0.60) and the minimum quality yield (0.05, 0.07, and 0.20), expressed as a proportion, increased with seed density at 2, 4 and 18 seeds pot^?1, respectively. The model for population dynamics fitted well to the Pf data obtained. The maximum multiplication rates (a) were 19.58, 9.99, and 17.54, while the maximum population densities (M) were 49.86, 43.21, and 60.37 P. penetrans (g dry soil)^?1 at 2, 4, and 18 seeds pot^?1, respectively. Carrot cv. Nerac can be considered a good host for P. penetrans.     

Identification of <Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis> using real-time PCR and high resolution melting (HRM) analysis

To develop a molecular method to identify Pseudoperonospora cubensis in cucumber leaves with signs of downy mildew, we compared the nucleotide sequences of ribosomal DNA-internal transcribed spacer, cytochrome oxidase II, and β-tubulin genes of P. cubensis and P. humuli isolates. Seven single nucleotide polymorphisms (SNPs) distinguished P. cubensis and P. humuli based on variations in β-tubulin sequences, and one specific primer set was designed for further analysis. Real-time PCR and high resolution melting analysis showed that the primer set can be used to specifically identify P. cubensis in cucumber leaves with downy mildew.     

<Emphasis Type="Italic">Fusarium oxysporum</Emphasis> and <Emphasis Type="Italic">Fusarium avenaceum</Emphasis> associated with yield-decline of pyrethrum in Australia

Fusarium wilt, one of the destructive diseases of cucumber can be effectively controlled by using biocontrol agents such as Trichoderma harzianum. However, the mechanisms controlling T. harzianum-induced enhanced resistance remain largely unknown in cucumber plants. Here we screened the potent T. harzianum isolate TH58 that could effectively control F. oxysporum (FO). Glasshouse efficacy trials also showed that TH58 decreased disease incidence by 69.7 %. FO induced ROS over accumulation, while TH58 inoculation suppressed ROS over accumulation and improved root cell viability under F. oxysporum infection. TH58 inoculation could reverse the FO-induced cell division block and regulate the proportional distribution of nuclear DNA content through inducing 2C fraction. Moreover, the expression levels of cell cycle-related genes such as CDKA, CDKB, CycA, CycB, CycD3;1 and CycD3;2 in TH58 - pre-inoculated seedlings were up-regulated compared with those infected with FO alone. Taken together, these results suggest that T. harzianum improved plant resistance against Fusarium wilt disease via alterations in nuclear DNA content and cell cycle-related genes expression that might maintain a lower ROS accumulation and higher root cell viability in cucumber seedlings.     

Rutin promoted resistance of tomato against <Emphasis Type="Italic">Xanthomonas perforans</Emphasis>

Xanthomonas perforans is the causal agent of bacterial spot, one of the most devastating diseases of tomato that results in considerable yield losses worldwide. Rutin, as a polyphenolic substance, was used to induce resistance in tomato against X. perforans. Rutin at concentration of 2 mM had ability to reduce the disease severity of bacterial spot. On the other hand, 2 mM rutin had no antibacterial activity in vitro. Expression profiling of pathogenesis-related gene 5 (PR-5), Phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) was probed during the enhanced resistance by rutin. Pretreatment with rutin (rutin/ X. perforans) led to induction of PR-5, PAL and LOX compared to controls (water/ X. perforans). Our results suggest that rutin-induced resistance against X. perforans in tomato might be mediated through stimulation of some defense genes such as PR-5, PAL and LOX.     

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.     

Identification mating-type locus structure and distribution of <Emphasis Type="Italic">Cochliobolus lunatus</Emphasis> in China

Cochliobolus lunatus (teleomorph: Curvularia lunata) is an important plant pathogenic fungus that causes the maize foliar spot, resulting in serious yield losses. In ascomycetes, a single mating-type (MAT) locus with two idiomorphs controls sexual development. The structure and arrangement of the MAT genes were examined to understand the MAT locus of C. lunatus. MAT loci were MAT1–1-1 or MAT1–2-1, flanked upstream and downstream by regions encoding GTPase activating protein, pyridoxamine phosphate oxidase domain, and β-glucosidase. A MAT1–1 or MAT1–2 idiomorph was identified in single isolate, and sexual reproduction in vitro indicated that the species was heterothallic. In vitro crossing between isolates with opposite MATs produced perithecia, asci, and ascospores. A multiplex MAT-specific PCR method was developed and used to test mating-type genes in 177 C.lunatus isolates collected from China. The ratio of isolates of each mating-type in China was consistent with a 1:1 ratio.     

Rice <Emphasis Type="Italic">terpene synthase 18</Emphasis> (<Emphasis Type="Italic">OsTPS18</Emphasis>) encodes a sesquiterpene synthase that produces an antibacterial (<Emphasis Type="Italic">E</Emphasis>)-nerolidol against a bacterial pathogen of rice

Plant volatile compounds, including terpenes, are known to be involved in the rice defense system. In the present analysis of a terpene synthase, OsTPS18, in rice, we found that OsTPS18 was localized in the cytoplasm and synthesized the sesquiterpenes (E)-nerolidol and (E)-β-farnesene. The amounts of (E)-nerolidol and (E)-β-farnesene increased after jasmonic acid (JA) treatment. (E)-Nerolidol had significant antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo). These results suggest that (E)-nerolidol plays an important role in JA-induced resistance against Xoo and that it functions as an antibacterial compound in rice.     

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.     

The effect of some cucumber cultivars on the biology of <Emphasis Type="Italic">Aphis gossypii</Emphasis> Glover (Hemiptera: Aphididae)

The development, reproduction, and population growth parameters of cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), were studied on three different Cucumis sativus cultivars (Beith Alpha Bal?kesir, B.T. Bursaalpha, Beith Alpha MR,) under controlled conditions (25?±?1 °C, 65?±?5% RH, and a photoperiod of 16:8 (L:D) h. Life table parameters were estimated according to age-stage, two-sex life table method. Results indicated that the Bt Bal?kesir are favorable hosts for A. gossypii because of the shorter preadult developmental time, lower preadult mortality rate, and higher total fecundity on this cultivar. The intrinsic rate of increase (r?=?0.4214 d^-1), the net reproduction rate (R₀?=?51.80 offspring), and the finite rate of increase (λ?=?1.5242 d^-1) values were higher on the Bt Bal?kesir. The effect of cucumber cultivars on the biology of A. gossypii was determined as significant and it was found that cv. Bt Bal?kesir was the most convenient cucumber cultivar in terms of the life cycle of A. gossypii. For an ecological and economic pest control, against aphids use of resistant or less favourable crop cultivars is considered one of the important components of integrated pest management. Therefore, results acquired might be used in pest management program that will be prepared for this aphid.     

Identification of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with soybean root rot in Sichuan Province,China

Soybean root rot is a worldwide soil-borne fungal disease threatening soybean production, causing large loss in yield and quality of soybean. Fusarium species are well recognized as the important causal agent of Fusarium root rot, which are often distinct with respect to various factors in different soybean-producing regions around the world. Recently, Fusarium root rot has been frequently reported in Sichuan Province of China, where is unique in its climate and diverse cropping patterns, but it is still unclear about the predominant Fusarium species and their pathogenicity on soybean. In this study, diseased soybean roots were collected from three regions of Sichuan Province during 2014–2015. Based on morphological characteristics and phylogenetic analysis of nucleotide sequences of the ribosomal internal transcribed spacer region and the translation elongation factor 1-α gene, 78 isolates of Fusarium were identified as nine distinct species. Pathogenicity tests showed that seven species of Fusarium were able to infect soybean, but differed in pathogenicity. F. oxysporum, F. equiseti and F. graminearum were the most aggressive species to soybean, whereas F. fujikuroi and F. verticillioides were not pathogenic to soybean. There was a strong positive correlation of the pathogenicity of Fusarium species with seedling emergence and fresh root weight. In addition, the diversity of Fusarium species varied among soybean-growing regions. To our knowledge, this report on population and pathogenicity of Fusarium species, in particular, F. graminearum, associated with soybean root rot in Sichuan Province of southwest China, will be helpful to provide effective control strategies for the disease.     

Inheritance of resistance to <Emphasis Type="Italic">Meloidogyne enterolobii</Emphasis> and individual selection in segregating populations of <Emphasis Type="Italic">Psidium</Emphasis> spp

Interaction between the phytonematode Meloidogyne enterolobii and the fungus Fusarium solani has caused direct and indirect losses in the entire guava production chain and consequent extermination of guava plantations throughout Brazil. The combined action of these two pathogens is known as “guava decline”. In order to obtain and assess Psidium spp. interspecific hybrids for resistance to the nematode M. enterolobii, interspecific crosses of P. guineense (susceptible araçá) x P. cattleyanum (resistant araçá); P.guineense (susceptible araçá) x P. guajava (susceptible guava) and P. cattleyanum (resistant araçá) x P. guajava (susceptible guava) were conducted. These crosses resulted in hybrid immune, susceptible and resistant to Meloidogyne enterolobii. The chi-square test rejected the hypothesis of monogenic inheritance with incomplete dominance, which corroborates that this trait has polygenic action. Predictions of genetic values ??and parameters were obtained by the REML / BLUP procedure, at individual level. Finally, the 30 selected individuals (immune and resistant) were obtained, which will be backcrossed with guava for the recovery of the agronomic traits desired and subsequent release of a new cultivar.     

Identification of blast resistance genes in 358 rice germplasms (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) using functional molecular markers

Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most devastating diseases of rice (Oryza sativa L.), and neck blast is the most destructive phase of this disease. Although neck blast causes tremendous yield loss, little is known about the molecular mechanisms underlying the neck blast resistance. To address this issue, we collected 358 rice varieties from different ecotypes in China and assessed them for the neck blast resistance under natural conditions favoring disease development in Jining, Shandong Province. Our results showed that 124 (34.6%) and 234 (65.4%) varieties were resistant and susceptible to M. oryzae under natural field conditions, respectively. Among the 358 rice varieties that were screened for the presence of 13 major blast resistance (R) genes against M. oryzae by using functional markers, 259 varieties contained one to seven R genes. In addition, the relationship between the presence of R genes and the disease reactions was also investigated by integrative analysis of phenotyping and genotyping based on functional markers. Our results showed that the rice blast resistance gene Pi2 was significantly correlated with neck blast resistance. Furthermore, any of the 13 major blast R genes was absent from 32 rice varieties exhibited obvious neck blast resistance, which would be the potential materials for identifying novel neck blast R genes. Taken together, our findings provide insight into the distribution of the 13 major blast R genes in the tested Chinese rice germplasm resources, which will serve as a basis for developing rice blast resistant. Furthermore, 32 rice varieties exhibited neck blast resistance, but they did not harbor any of the 13 major blast R genes. In the future, these varieties may be used to identify novel neck blast R genes.     

A new species and observations on the genus <Emphasis Type="Italic">Ramularia</Emphasis> from Iran

Ramularia ranunculicola sp. nov. (Mycosphaerellaceae) is described from Iran on Ranunculus muricatus and compared with other species reported on Ranunculus spp. Ramularia carletonii on Lactuca tuberosa and R. nagornyi on Centaurea solstitialis are newly reported from Iran, and Picris strigosa is a new host for R. picridis (= R. inaequalis s. lat.).     

Diversity and potential impact of Botryosphaeriaceae species associated with <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> plantations in Portugal

Eucalyptus globulus, a non-native species, is currently the most abundant forest species in Portugal. This economically important forest tree is exploited mainly for the production of pulp for the paper industry. The community of Botryosphaeriaceae species occurring on diseased and healthy E. globulus trees was studied on plantations throughout the country. Nine species from three different genera were identified, namely Botryosphaeria (B. dothidea), Diplodia (D. corticola and D. seriata) and Neofusicoccum (N. australe, N. algeriense, N. eucalyptorum, N. kwambonambiense, N. parvum and Neofusicoccum sp.). Of these, N. algeriense, D. corticola and D. seriata are reported for the first time on E. globulus, while N. algeriense, N. eucalyptorum and N. kwambonambiense correspond to first reports in Portugal. The genus Neofusicoccum was clearly dominant with N. australe and N. eucalyptorum being the most abundant species on both diseased and healthy trees. In artificial inoculation trials representative isolates from all nine species were shown to be pathogenic to E. globulus but there were marked differences in aggressiveness between them. Thus, D. corticola and N. kwambonambiense were the most aggressive while B. dothidea and D. seriata were the least aggressive of the species studied.     

Interaction between polygalacturonase-inhibiting protein and jasmonic acid during defense activation in tomato against <Emphasis Type="Italic">Botrytis cinerea</Emphasis>

Oligogalacturonic acids (OGAs) generated from in vitro interaction between fungal polygalacturonase (PG) and bean PG-inhibiting protein (PGIP) were shown to activate phytoalexin biosynthesis in soybean. Based on this observation, it was hypothesized that PGIP-dependent generation of OGAs activates plant defence responses in vivo. We tested the hypothesis that PGIP activates jasmonic acid-dependent responses to pathogens. For this purpose, a population of tomato plants segregating for a mutation in the jasmonate receptor CORONATINE INSENSITIVE1 (coi1) and for overexpression of pear PGIP (pPGIP) was challenged with Botrytis cinerea. The coi1 mutant was hypersensitive to B. cinerea, but overexpression of pPGIP in the coi1 mutant background reduced pathogen susceptibility, suggesting that these two genes independently alter defence responses. In addition, pPGIP overexpression suppressed pathogen induction of salicylic acid in the coi1 mutant and activated expression of acidic ß-1,3-glucanase independently of the coi1 mutation. However, expression of proteinase inhibitor II (PIN II) in pPGIP overexpressing tomato plants was dependent on COI1. Effects of pPGIP overexpression on defence are therefore complex and only in the case of PIN II pPGIP acts through COI1.     

Suppression subtractive hybridization and microarray analysis reveal differentially expressed genes in the <Emphasis Type="Italic">Lr39/41</Emphasis>-mediated wheat resistance to <Emphasis Type="Italic">Puccinia triticina</Emphasis>

Wheat leaf rust caused by Puccinia triticina (Pt) is one of the most severe fungal diseases threatening the global wheat production. The use of leaf rust resistance (Lr) genes in wheat breeding programs is the major solution to solve this issue. Wheat isogenic line carrying the Lr39/41 gene has shown a moderate to high resistance to most of the Pt pathotypes detected in China. In the present study, a typical hypersensitive response (HR) was observed using microscopy in leaves of the Lr39/41 isogenic line inoculated with the avirulent Pt pathotype THTT from 48 h-post inoculation. Two Lr39/41 resistance-associated suppression subtractive hybridization (SSH) libraries with a total of 6000 clones were established. Microarray hybridizations were performed on all obtained SSH clones using RNAs extracted from leaves of the Pt-inoculated and non-inoculated Lr39/41 isogenic lines, and leaves of the Pt-inoculated and non-inoculated Thatcher susceptible lines. Differentially expressed clones were analyzed by significance analysis of microarrays (SAM), followed by further sequencing. A total of 36 Lr39/41-resistance-related differentially expressed genes (DEGs) were identified, many of which had been previously reported to be involved in the plant defense response. The expression levels of eight selected DEGs during different stages of the Lr39/41-mediated resistance were further quantified by a qRT-PCR assay. Several pathogenesis-related (PR) and HR-related genes seem to be crucial for the Lr39/41-mediated resistance. In general, a brief profile of DEGs associated with the Lr39/41-mediated wheat resistance to Pt was drafted.     

Natural enemies of <Emphasis Type="Italic">Diaspis echinocacti</Emphasis> in Greece and first records of <Emphasis Type="Italic">Aphytis debachi</Emphasis> and <Emphasis Type="Italic">Plagiomerus diaspidis</Emphasis>

Two hymenopteran parasitoids of the cactus scale Diaspis echinocacti (Bouché) (Hemiptera: Diaspididae) on Opuntia ficus-indica (L.) Mill. (Cactaceae) are recorded in Greece. Aphytis debachi Azim, 1963 (Aphelinidae) is first recorded for Europe and Plagiomerus diaspidis Crawford, 1910 (Encyrtidae) is first recorded for Greece. Preliminary data on phenology and natural enemies of the scale D. echinocacti on O. ficus-indica are presented. Parasitism of D. echinocacti by P. diaspidis reached 86% in southern Greece (Kalamata) and parasitism by A. debachi reached 9.3% and 12% in Kalamata and Athens, respectively. Two predators, Cybocephalus fodori Endrödy-Youga (Coleoptera: Nitidulidae) and a mite species (Prostigmata: Bdellidae), were found to be associated with D. echinocacti.