Enhancement of sphaeropsis canker of aleppo pine by the Israeli pine bast scale

An interaction between the fungal pathogenSphaeropsis sapinea (Fr.) Dyko & Sutton, causal organism of Sphaeropsis canker, and the Israeli pine bast scaleMatsucoccus josephi (Homoptera: Margarodidae), causal agent of pine decline, was studied, since both were prevalent on Aleppo pine (Pinus halepensis) stands.Sphaeropsis sapinea was isolated from larvae (stage II) and molts of the Israeli pine bast scale collected in four Aleppo pine stands. When Aleppo pine saplings were infested with pine bast scale and subsequently inoculated withS. sapinea most plants died, whereas mortality of seedlings inoculated withS. sapinea alone without previous scale infestation was negligible. Scale infestation of saplings without subsequent fungal inoculation caused the death of one third of the plants. Wounding of pine shoot apices by removal of needle fascicles enhanced infection byS. sapinea. The results support the assumption thatM. josephi can play an important role in transmitting the fungal inoculum to the host tree as well as enabling its penetration to the shoots through wounds in the bark. http://www.phytoparasitica.org posting Dec. 20, 2004.     

Occurrence, isolation and biological activity of phytotoxic metabolites produced in vitro by Sphaeropsis sapinea, pathogenic fungus of Pinus radiata

Sphaeropsis sapinea was repeatedly isolated in Sardinia from symptomatic samples of the upper part of declining pine (Pinus radiata) plants. Observed symptoms mainly consisted of foliage chlorosis, drying of needles and cankers on branches. The S. sapinea strains were shown to produce phytotoxic metabolites in culture filtrates. Three metabolites were isolated for the first time from this fungus and identified by their spectroscopic and optical properties as R-(−)-mellein, (3R,4R)-4-hydroxymellein and (3R,4S)-4-hydroxymellein. When assayed for phytotoxic and antifungal activities on host and non-host plants and on some phytopathogenic fungi, the R-(−)-mellein showed significant activity, while the other two 3,4-dihydroisocoumarins showed only a synergic activity in both tests.     

Effect of different hosts onThaumetopoea pityocampa populations in northeast Portugal

A study was carried out at the Natural Park of Montesinho, NE Portugal, in order to evaluate the effect of different pine species (Pinus pinaster Ait.,P. nigra Arn. andP. sylvestris L.) onThaumetopoea pityocampa populations. The structure of the egg batches, the impact of the egg parasitoids on natural mortality of the pest and the species of parasitoids present, as well as their emergence dynamics, were analyzed. The length of the egg batches varied among pine species with the longest ones onP. nigra. The mean number of eggs per batch differed betweenP. sylvestris and the two other hosts studied, with fewer eggs per batch on the first. No differences were found in the size of eggs among pine species. The egg mortality varied between 25.8% and 33.0%, with no differences among hosts. Parasitism was the main cause of death.Baryscapus servadeii (Mercet.) was the most abundant parasitoid species, followed byOoencyrtus pityocampae (Dom.) andTrichogramma embryophagum Htg.B. servadeii dominated in the egg batches collected fromP. pinaster andP. nigra, whereasO. pityocampae was most frequent onP. sylvestris. The emergence ofB. servadeii started in the middle of March and continued until August, with the emergence peak at the end of May. The emergence ofO. pityocampae started at the end of April and continued throughout September, with maximum values in June. http://www.phytoparasitica.org posting Sept. 20, 2006.     

A comparison of two pathosystems: Downy mildew on Spinacia oleracea and on Chenopodium album

The development of downy mildew (Peronospora farinosa) on a cultivated spinach crop (Spinacia oleracea) was compared to that on lambsquarters (Chenopodium album), a naturally occurring weed. Experiments were carried out on small spinach plots, in which epidemics could develop from point sources (PS) or area sources (AS).Two lambsquarter populations were studied, in which downy mildew epidemics arose from oospore infections. The downy mildew epidemics, on spinach and lambtquarters, were related to the environmental factors: temperature, vapour pressure deficit (VPD) and rainfall. It is concluded that the two different formae speciales ofP. farinosa, one on spinach and one on lambsquarters, react in the same way to weather changes. The epidemiological patterns were almost similar.Samenvatting De ontwikkeling van valse meeldauw (Peronospora farinosa) op het cultuurgewas spinazie (Spinacia oleracea) werd vergeleken met die op het zich natuurlijk ontwikkelende onkruid melganzevoet (Chenopodium album). Daarvoor werden experimenten uitgevoerd op spinazieperceeltjes, waarop in enkele gevallen puntbroninfecties (PS), en in andere gevallen oppervlaktebrondinfecties (AS) waren aangebracht. Er werd gevarieerd in inoculatietijdstip.Bij melganzevoet werden twee populaties bestudeerd, waarin de ziekte via oösporeinfectie op natuurlijke wijze was ontstaan.Het geheel werd in verband gebracht met de omgevingsfactoren: temperatuur, dampdruk-deficiet (VPD) en regenval. Geconcludeerd kan worden, dat deP. farinosa formae speciales zowel op spinazie als op melganzevoet op gelijke wijze reageerden op veranderingen in het weer. Het verloop van de epidemieeën was sterk vergelijkbaar.     

Evaluation of entomopathogenic nematodes for biocontrol of the european corn borer,Ostrinia nubilalis, on sweet corn in Israel

The potential of entomopathogenic nematodes for biological control of the European corn borer (ECB),Ostrinia nubilalis (Hübner), was evaluated under laboratory, screenhouse and field conditions. The ‘All’ and ‘Mexican’ strains ofSteinernema carpocapsae (Weiser) and the ‘HP88’ strain ofHeterorhabditis bacteriophora Poinar were compared in both dose response assays (5, 50 and 500 infective juveniles [IJ] per petri dish containing five 5th-instar ECB eggs; 72 h of incubation) and exposure time assays (3, 6 and 9 h of incubation). In the dose response assays the highest rates of ECB killing resulted from infestation with the Mexican strain ofS. carpocapsae. In the exposure time assays there were no significant differences between the killing rates of the three nematode strains. Sweet corn plants(Zea mays var.saccharata) grown in a screenhouse, were infested with ECB neonates and 4 days later sprayed with a suspension of the Mexican strain ofS. carpocapsae (50,000 IJ per plant). The number of ECB larvae found on treated corn plants after one week was significantly (P=0.05) lower (3- to 5-fold) than the number found on untreated plants. Similar treatment in the field significantly reduced the rate of economic ear damage from 20% to 5%. Contribution from the Agricultural Research Organization. No. 2260-E, 1997 series     

Detection of “Candidatus Phytoplasma asteris” associated with henon bamboo witches' broom in Korea

Witches' broom disease in bamboo (Phyllostachys nigra Munro var. henonis) was found in Yeoungyang, Korea. In transmission electron micrographs, phytoplasma-like bodies were detected in the phloem cells of diseased plants but not in those of healthy plants. The presence of phytoplasmas was confirmed by amplification of a 1.8-kb DNA fragment using a primer pair specific for the region containing a 16S rRNA gene and an intergenic spacer region between the 16S and 23S rRNA genes. Comparision of the 16S rRNA gene sequences showed that the causal phytoplasma belongs to “Candidatus Phytoplasma asteris,” and shared the highest degree of similarity with the sequence of the onion yellows (OY) isolate in Japan. This is the first phylogenetic identification of phytoplasma infection of bamboo in Korea.     

The effect of nitrogen on the growth and development of giant witchweed,Striga hermonthica Benth.: effect on cultured germinated seedlings in host absence

For the first time in sterile nutrient media in the absence of the host plant, different forms and rates of nitrogen compounds were screened for their effect onS. hermonthica Benth. shoot development beyond seed germination. There was no shoot formation beyond the inoculation stages whenS. hermonthica germlings were grown in media devoid of nitrogen source. In culture media containing some nitrogen sources, healthy shoots were formed. Increasing concentrations of KNO₃, NaNO₃, Ca(NO₃)₂, Mg(NO₃)₂ and asparagine resulted in a significant increase inS. hermonthica shoot development. Inversely, increasing concentrations of (NH₄)₂SO₄, NH₄H₂PO₄, NH₄Cl and urea led to increasing significant reduction ofS. hermonthica shoot development. The amino acids, glycine and asparagine supported reduced shoot development ofS. hermonthica, indicating that organic nitrogen cannot replace inorganic nitrogen forStriga growth. The ammonium nitrogen compounds, (NH₄)₂SO₄ and NH₄H₂PO₄, suppressed further shoot elongation and total dry weight of 20 and 40 days oldStriga hermonthica plants, in sterile culture media. The organic compounds urea, allylthiourea and thiourea had an effect similar to ammonium compounds. Arginine and glycine on the other hand did not suppress the further development of the parasite. The suppressive effect of nitrogen however, was greater when the parasite was 20 days old than when it was 40 days old. This work provides data to show that some nitrogen compounds reduce the severity ofS. hermonthica attack by direct suppression ofStriga growth and development at the post-germination stage and after shoots have been formed.     

Insecticidal activity of crude seed extracts of<Emphasis Type="Italic">Annona</Emphasis> spp.,<Emphasis Type="Italic">Lansium domesticum</Emphasis> and<Emphasis Type="Italic">Sandoricum koetjape</Emphasis> against lepidopteran larvae

Crude ethanolic seed extracts ofAnnona muricata, A. squamosa (Annonaceae),Lansium domesticum andSandoricum koetjape (Meliaceae) collected from different locations and years in Maluku, Indonesia, were screened for inhibition of larval growth against the polyphagous lepidopteranSpodoptera litura (Noctuidae). Extracts ofA. squamosa were significantly more active (20-fold) than those ofA. muricata. A. squamosa collected from Namlea yielded the extracts with the greatest inhibitory activity. There were significant differences among locations for bothA. squamosa andA. muricata but not forL. domesticum andS. koetjape. Extracts ofA. squamosa, collected from Namlea, inhibited larval growth in a dose-dependent manner, with a dietary EC₅₀ (effective concentration to inhibit growth by 50% relative to controls) of 191.7 ppm fresh weight. Extracts ofA. squamosa collected from individual trees in Namlea also varied in growth inhibitory effect againstS. litura andTrichoplusia ni larvae. This species is a candidate for development of a botanical insecticide for local use in Indonesia. http://www.phytoparasitica.org posting Dec. 1, 2003.     

Reactive oxygen intermediates and oxalic acid in the pathogenesis of the necrotrophic fungus Sclerotinia sclerotiorum

An effective colonization of the host plant tissue by the necrotrophic fungus Sclerotinia sclerotiorum requires the secretion of the non-host specific toxin oxalic acid (OA), which is known to suppress the generation of reactive oxygen intermediates (ROI). A full-length cDNA coding for an oxalate decarboxylase (TOXDC), which converts OA into CO₂ and formate, was isolated from the basidiomycete Trametes versicolor. It was overexpressed in tobacco plants to study the role of ROI and OA in the interaction between tobacco and S. sclerotiorum. The transgenic plants contained less OA and showed a delayed colonization of S. sclerotiorum; furthermore a strong ROI accumulation and nearly no catalase activity compared to the wild type (WT) plants could be detected. In addition, inoculation experiments with transgenic catalase-deficient plants (CAT1AS) and in vitro studies showed that S. sclerotiorum copes with strong ROI stress. Our results indicate that OA supports the infection process caused by S. sclerotiorum and the fungus itself is able to tolerate high ROI concentrations. The nucleotide sequence data is available from the NCBI Genbank nucleotide-sequence database under the number AY370675     

Comparison of the reproductive potential of <Emphasis Type="Italic">Monochamus galloprovincialis</Emphasis> on two pine species under laboratory conditions

Monochamus galloprovincialis Olivier (Coleoptera: Cerambycidae) is one of the vectors of the pinewood nematode Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle (Nematoda: Parasitaphelenchidae), the causal agent of pine wilt in susceptible pine trees. It is therefore important to study both the biological and ecological characteristics of the beetle. In this study reproductive potentials of female beetles reared on two pine species were investigated under laboratory conditions and compared using fertility tables constructed for beetles reared on each tree species. Beetle population parameters were compared between tree species. The intrinsic rate of increase and associated population parameters of beetles reared on Pinus sylvestris L. were consistently higher than those reared on P. nigra Arnold. This result suggests that P. sylvestris has a significantly greater positive effect on the reproductive potential of M. galloprovincialis populations than does P. nigra.     

First report of southern blight of common barley in Puerto Rico

In 1990–91, 96% of the test plants in a barley (Hordeum vulgare L.) winter nursery in Puerto Rico was lost toSclerotium rolfsii. Small necrotic lesions (1–3 mm long) developed at the base of the stem, followed by wilting and general chlorosis as the lesions progressed and eventually girdled the base of the stem. Sclerotia then developed on the plants at the stem base. Two morphologically different strains ofS. rolfsii that were mycelial incompatible were isolated. This is the first report of a destructive blight due toS. rolfsii on field barley in the Caribbean. The apparent rate of disease increase (r) was estimated to be 12.2% per day using the logistic model, with an initial disease incidence of 0.042% (R²=0.89, p<-0.001).     

Differential interactions ofPhytophthora capsici isolates with pepper genotypes at various plant growth stages

Pepper cultivars from diverse geographic origins were evaluated for resistance to different isolates ofPhytophthora capsici under controlled environmental conditions. All accessions tested were susceptible at the four-leaf stage to the six isolates ofP. capsici. Inoculation at the eight-leaf stage resulted in significantly different interactions among the accessions andP. capsici isolates. The Korean and U.S. cultivars tested were highly susceptible to the isolates ofP. capsici at this stage. In contrast, PI 201234 and PI 201238 had a differential interaction with someP. capsici isolates. At the twelve-leaf stage, Phytophthora blight developed slowly in the Korean and U.S. cultivars that were highly susceptible at the eight-leaf stage. Furthermore, the accessions from the Asian Vegetable Research and Development Center (AVRDC) became highly resistant toP. capsici at this stage.     

Phytophthora root and crown rot of raspberry in Bulgaria

Root and crown rot of raspberry (Rubus idaeus L.) was observed in a plantation at the experimental station of small fruits in Kostinbrod, Bulgaria. Isolates ofPhytophthora spp. were obtained from diseased plants. Colony morphology, growth rates, features of asexual and sexual structures were studied and as a result twoPhytophthora species were identified:Phytophthora citricola Saw. andPhytophora citrophthora (R.E. Sm. & E.H. Sm.) Leonian. Their pathogenicity was confirmed in artificial inoculation experiments. The isozyme (-esterase) patterns ofP. citrophthora andP. citricola isolates from raspberry and from the collection of the CBS, Baarn the Netherlands were compared, using micro-gel electrophoresis. Both species are reported for the first time as pathogens of raspberry in Bulgaria. This is only the second report in phytopathological literature ofP. citrophthora on raspberry, the first being from Chile [Latorre and Munoz, 1993].     

Host specificity of a brazilian isolate of<Emphasis Type="Italic">Alternaria cassiae</Emphasis> (Cenargen CG593) under greenhouse conditions

SeveralAlternaria cassiae isolates were recovered from diseased sicklepod plants (Senna obtusifolia) in the southern regions of Brazil. A representative isolate (Cenargen CG593) was tested for its host range under greenhouse conditions. The fungus promoted symptoms in sicklepod, cassava (Manihot dulce), tomato (Lycopersicon esculentum) and eggplant (Solanum melongena) when tested at a spore concentration of 10⁶ spores ml⁻¹. When the plants were inoculated with a suspension of 10⁵ spores ml⁻¹ and held at a dew period of 12 h (cassava) or 18 h (tomato and eggplant), the plants showed symptoms of the disease, but they recovered and continued their normal vegetative growth. These results show that the fungusA. cassiae is safe to use for the control ofS. obtusifolia under Brazilian conditions, because it did not cause excessive damage in the three plants tested. http://www.phytoparasitica.org posting Jan. 14, 2007.     

The role of the monoterpene composition inPinus spp. needles, in host selection by the pine processionary caterpillar,Thaumetopoea pityocampa

This paper presents preliminary results on attempts to extract and characterize the volatile secondary metabolites contained in needles of differentPinus species and to ascertain the role played by these substances on the behavior ofThaumetopoea pityocampa (Denis et Schiffermüller) females, which show a marked preference, during the oviposition period, for some indigenous and exotic species of host plants existing in mixed formation. Limonene is the most abundant monoterpene extracted fromP. pinea needles, the least favored species of pine processionary caterpillar (PPC) females, although it is present in only very low amounts in otherPinus species. An increase was observed in limonene production byP. pinea at the start of the flight period of the PPC adult, and subsequently at the beginning of the females’ oviposition period. Assays carried out in two pine stands in central Italy showed that limonene, emulsified with water and sprayed on foliage of four different pine species plants,P. sylvestris, P. nigra, P. pinaster andP. radiata, during the PPC oviposition period, provided a satisfactory degree of protection. In fact, the number of egg clusters collected from treated plants was often lower than the number of egg clusters collected from control plants and was comparable to the number of egg clusters laid onP. pinea plants. In particular (R)-(+)-limonene, although not produced in nature by pines, was the most effective deterrent. However, the effect of (S)-(-)-limonene, the enantiomer biosynthesized by pines, was also adequate.     

Calcium reducesBotrytis c1nerea damages to plants ofRuscus hypoglossum

Plants ofRuscus hypoglossum L. were grown in containers with perlite, an inert medium, or with soil, under similar-to-commercial conditions, for three winter seasons. Constant fertilization with soluble calcium [Ca(NO₃)₂] through the root zone resulted in a reduction of up to 78% in postharvest rot caused by artificial inoculation withBotrytis cinerea Pers. ex Fr. Control plants were treated by fertilization with N,P,K and all other elements, identical to the fertilizer containing calcium. Foliar application of Ca(NO₃)₂ to ruscus bushes or application of this compound or of CaCl₂ or CaSO₄ to mature cut branches standing in water, resulted also in a significant reduction in postharvest phylloclade rot. Application of CaSO₄ and Ca(H2PO₄)₂ + CaSO₄ to ruscus plants, from fertilizers containing 22% Ca and releasing the cation gradually, effectively reduced the susceptibility of cut branches to infection by_{B. cinerea.}     

Screening for highly effective isolates ofBacillus thuringiensis againstSpodoptera exempta andSpodoptera littoralis

Several new isolates ofBacillus thuringiensis Berliner have shown significantly higher levels of insecticidal activity than the previous best isolates (Bt₂₄-entomocidus and IH-A-aizawai) against bothSpodoptera littoralis Boisd. andSpodoptera exempta Walker. The best ones, in the following descending order of potency, were: againstS. littoralis — K26–21, MF4B–2, MR1–37, K28–30, K26–8; againstS. exempta — Bt-3, K30–3, HD-133, MR1–37, Bt-17, K26–8, K26–21, MF4B-2, HD-593. Larvae ofS. exempta were considerably more susceptible (4.12–1.25 fold) to some of the isolates (Bt-3, K30–3, HD-133, MR1–37, Bt-17, K26–8, HD-593) thanS. littoralis.     

Induction of systemic resistance byPseudomonas fluorescens Pf1 againstXanthomonas oryzae pv.Oryzae in rice leaves

When lower leaves of rice plants were inoculated with powder formulation of a saprophytic strain ofPseudomonas fluorescens, Pfl, upper leaves, in addition to the inoculated lower leaves, showed resistance to the rice bacterial blight pathogenXanthomonas oryzae pv.oryzae. When the leaves were challenge-inoculated withX. oryzae pv.oryzae 4 days afterP. fluorescens application on lower leaves, the disease intensity in upper leaves decreased from 6.7 to 1.1. When rice seeds were treated with the formulation ofP. fluorescens Pfl and sown, 30-day-old seedlings showed resistance toX. oryzae pv.oryzae and the disease intensity decreased from 6.8 to 1.2. The induced resistance was transient; leaves sprayed withP. fluorescens Pfl at 30 days after treatment and leaves of 60-day-old seedlings fromP. fluorescens-treated seeds did not show resistance to the pathogen. In field trials, seed treatment followed by foliar application of the powder formulation ofP. fluorescens Pfl effectively controlled rice bacterial blight and increased the yield. In the induced resistant leaves a sharp increase in lignification and activities of peroxidase, phenylalanine ammonia-lyase and 4-coumarate: CoA ligase was observed when the leaves were challenge-inoculated withX. oryzae pv.oryzae. An approximately threefold increase in lignin content, peroxidase activity and phenylalanine ammonia-lyase activity and a fivefold increase in 4-coumarate: CoA ligase activity were observed 5 days after challenge inoculation withX. oryzae pv.oryzae in rice leaves pretreated withP. fluorescens for 5 days. A similar increase in defense-related activities was not observed in susceptible interactions or inP. fluorescens-treated plants at later stages of interactions when no resistance to the pathogen was observed.     

Susceptibility of pure and hybrid willows to isolates ofMelampsora epitea rust

Pure species and F₁ hybrid families ofSalix viminalis andS. dasyclados were tested for resistance to four single uredinium isolates ofMelampsora rust in laboratory experiments using excised leaves. Rust isolates were derived from:S. viminalis, S. dasyclados, aS. viminalis x triandra hybrid, andS. daphnoides. Incidence of infection, number of uredinia per leaf, and numbers of spores per uredinium were measured. As expected, the isolate fromS. daphnoides did not infect any of the willow species or hybrids tested. For the other three rust isolates that were tested, the parent from which the isolate was derived was susceptible, the other parent was resistant, and hybrids were intermediate in resistance for incidence and uredinia per leaf. These patterns indicate additive inheritance of these resistance traits in hybrids. Numbers of spores per uredinium were similar on the hybrids and the susceptible parent for one rust isolate, suggesting dominant inheritance of this trait in the hybrids.     

Further studies on the role of monoterpenes in pine host selection and oviposition ofThaumetopoea pityocampa

In a young mixed pine plantation (Pinus nigra andP. pinea) in central Italy, the influence of the pine needle monoterpenes (R)-(+)-limonene, (S)-(−)-limonene and (1S)-(−)-β-pinene on the oviposition activity of the pine processionary moth,Thaumetopoea pityocampa (Denis et Schiffermüller), was assessed. Two application methods were compared: spraying the trees with the substances emulsified with water, and setting up polyethylene dispensers from which the monoterpenes evaporated. During the moth’s flight period weekly treatments (at 500 mg of monoterpene /l water) were carried out and the evaporation from the polyethylene dispensers (each with 5 g of a single monoterpene) was checked on each occasion by weighing the dispensers. The GLM analysis did not uncover any difference between the methods of application or between the pine species.T. pityocampa laid a significantly (P=0.01) lower number of egg masses on the trees treated with (1S)-(−)-β-pinene than on those treated with the other substances and on the control trees. A ∼45% reduction in egg mass number was obtained on the pines treated with (1S)-(−)-β-pinene, independent of the level of infestation, method of application or pine species. (R)-(+)-limonene and (S)-(−)-limonene were not effective. http://www.phytoparasitica.org posting July 29, 2008.