Prunus necrotic ringspot virus isolates in stone fruit germplasm accessions and cultivars in Israel

Prunus necrotic ringspot virus (PNRSV) was detected in almonds, plum and apricot germplasm accessions and local almond cultivars in Israel. PNRSV was widespread both in wild and cultivated almond trees and uncommon in wild apricots and plums. The possible variation among the PNRSV isolates was initially evaluated by restriction analysis of PCR products representing the CP gene with the endonuclease RsaI and followed by nucleotide sequence analysis of selected isolates. It was concluded that all 13 isolates belong to group PV96, the largest cluster of PNRSV isolates, described previously. Two PNRSV isolates, one from a plum accession and one from an almond cultivar, were found to be distinct members of group PV96 with unique nucleotide modifications not found in other documented isolates of this virus. However, no PNRSV isolate typical to a specific host and/or to the Middle East region could be identified. This study expands the body of data on variability of PNRSV isolates and highlights the importance of assessing the virus status of germplasm collections by applying reliable diagnostic and differentiating methods.     

Biotic versus abiotic pollination in Oeceoclades maculata (Lindl.) Lindl. (Orchidaceae)

Geographical variation in the reproductive biology of widespread species often occurs at their distributional boundaries. We sought to determine whether such variation has occurred in an invasive orchid, Oeceoclades maculata, across its naturalized range. We compared its reproductive biology in a Brazilian population with that published for a population on the Caribbean island of Puerto Rico. In the state of São Paulo, O. maculata flowers between December and February, at the height of the rainy season. Similar fruit sets were observed in manual self (76%) and cross (70.4%) pollination treatments. The fruit set of plants protected from both pollinators and rainfall was 6.1%, whereas plants exposed only to rainfall had a fruit set of 41.4%, slightly less than the controls (48.3%). Like the Puerto Rico population, reproduction is primarily through rain‐assisted autogamy, but unlike observations made on the island, outcrossing can eventually occur. We observed two butterfly species (Heliconius ethilla narcaea and Heliconius erato phyllis) pollinating O. maculata. Secretory epidermal cells and trichomes of the spur lumen produced 0.7 µL of 25% (sucrose equivalents) nectar per flower each morning, which was stored in a dilated basal portion of the spur and reabsorbed by the afternoon. Thus, geographical variation in reproductive biology exists across the broad invasive range of O. maculata.     

Osmophore and elaiophores of Grobya amherstiae (Catasetinae,Orchidaceae) and their relation to pollination

Grobya amherstiae flowers release a honey‐like scent produced by an osmophore, comprising a papillate epidermis. The scent attracts bee pollinators (Paratetrapedia fervida), which collect floral oils produced by elaiophores on the lip apex and column base. The secretory tissue of the elaiophore on the lip apex consists of both palisade‐like epidermal cells and conspicuously elongated unicellular trichomes. From an anatomical point of view, this elaiophore differs in structure from those known in angiosperms to date. The elaiophore on the column base is exclusively composed of short unicellular trichomes. In addition, there is an elaiophore comprising a papillate epidermis on the internal surface of the lip. The elaiophores produce a heterogeneous secretion, composed of fatty acids and mucilage. The elaiophore on the internal surface of the lip produces oil in non‐collectible amounts, but it is enough to maintain the interest of the bees, guiding them to the elaiophore on the column base, a necessary step in pollination. The former elaiophore is here identified as an oil guide and it plays an essential role in ensuring pollination. The presence of three types of elaiophores on the flowers of this species of Orchidaceae is peculiar and noteworthy. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 408–415.     

The use of S1 nuclease treatment of hybrid PCR products for the differentiation between PVY isolates

A new strategy based on treating PCR hybrids with S1 nuclease was used to differentiate between two PVY isolates. Mixed denatured and annealed hybrid PCR products of two PVY isolates including a tested strain and a reference N strain were treated with S1 nuclease. Single-stranded mismatched regions were revealed by the S1 nuclease cleavage, yielding a characteristic pattern of bands in polyacrylamide gel by which virus isolates could be matched. Sequence analysis of the relevant PCR products revealed that only part of the mismatched regions were cleaved by the S1 nuclease. Still, the distinct pattern of degradation products enabled the differentiation between the PVY isolates. The general application of this procedure for strain differentiation is discussed.     

Typing Primus necrotic ringspot virus isolates by serology and restriction endonuclease analysis of PCR products

Primus necrotic ringspot virus (PNRSV) isolates were characterised by bioassays, serotyping and restriction fragment length polymorphism (RFLP) analysis of PCR products. Based on symptoms in host trees and bioassays it was concluded that only one of the 16 tested isolates is severe. The serotyping results demonstrated that by using four different MAbs in TAS-ELISA the tested isolates could be divided into four subgroups, however, the severe isolate could not be singled out. RFLP analysis of PCR products supported the serotyping data but did not differentiate between isolates of the two main serological subgroups. A restriction map, derived from sequence analysis of the PCR products obtained from selected isolates, allowed exact location of the restriction sites within the PCR products of each isolate. A mild isolate with a unique genome structure was identified by both serological and RFLP assays. As far as we are aware, this is the first report on sub-grouping of PNRSV isolates by bioassays, serotyping with MAbs and RFLP analysis.     

Physical and physiological costs of ectoparasitic mites on host flight endurance

1. Dispersal is essential for locating mates, new resources, and to escape unfavourable conditions. Parasitism can impact a host's ability to perform energetically demanding activities such as long‐distance flight, with important consequences for gene flow and meta‐population dynamics. 2. Ectoparasites, in particular, can adversely affect host flight performance by diminishing flight aerodynamics and/or by inflicting physiological damage while feeding on host tissue. 3. Experimental flight assays were conducted using two fruit fly‐mite systems: Drosophila nigrospiracula (Patterson and Wheeler) – Macrocheles subbadius (Berlese) and D. hydei (Sturtevan) – M. muscaedomesticae (Scopoli). Flies that are burdened by mites are expected to exhibit lower flight endurance compared to uninfected flies. 4. The results show that the presence of mites (attached) significantly decreased flight endurance by 57% and 78% compared to uninfected D. nigrospiracula and D. hydei, respectively. The physiological damage caused by M. subbadius was revealed through a 53% decline in flight time among previously infected flies (mites removed just prior to flight assay). Surprisingly, the presumably phoretic M. muscaedomesticae also caused a 62% reduction in flight endurance among previously infected D. hydei. 5. These results suggest a strong deleterious effect of ectoparasitic mites on host flight performance, mediated by a reduction in flight aerodynamics and damage to host physiology. Adverse effects on host flight and/or dispersal may have broad implications for gene flow, population genetic structure, and local adaptation in both host and parasite meta‐populations.     

Truncated Rep gene originated from Tomato yellow leaf curl virus-Israel [Mild] confers strain-specific resistance in transgenic tomato

Transgenic tomato plants carrying a truncated replication associated protein (T‐Rep) gene of the mild strain of Tomato yellow leaf curl virus‐Israel (TYLCV‐Is [Mild]) were prepared. The transgene encoding the first 129 amino acids of Rep conferred resistance only against the virus strain from which it was derived, while these plants were susceptible to the severe strain of TYLCV‐Is. This strain‐specific effect may be the result of high sequence divergence within the N‐terminal domains of the Rep genes of the two virus isolates which share a mere 78% sequence identity at the nucleotide level and 77% at the amino acid level. Although the transgenic tomato plants were totally resistant to whitefly inoculation with the mild strain of TYLCV‐Is, agroinoculation with the same virus strain resulted in variable resistance responses in the tested plants: while 21% of plants were totally immune to the virus, 33% were susceptible and 46% expressed a wide range of intermediate resistance characteristics. The applicability of TYLCV‐Is derived resistance in tomato is discussed.     

Projected changes in the organic carbon stocks of cropland mineral soils of European Russia and the Ukraine, 1990–2070

In this paper, we use the Rothamsted Carbon Model to estimate how cropland mineral soil carbon stocks are likely to change under future climate, and how agricultural management might influence these stocks in the future. The model was run for croplands occurring on mineral soils in European Russia and the Ukraine, representing 74 Mha of cropland in Russia and 31 Mha in the Ukraine. The model used climate data (1990–2070) from the HadCM3 climate model, forced by four Intergovernmental Panel on Climate Change (IPCC) emission scenarios representing various degrees of globalization and emphasis on economic vs. environmental considerations. Three land use scenarios were examined, business as usual (BAU) management, optimal management (OPT) to maximize profit, and soil sustainability (SUS) in which profit was maximized within the constraint that soil carbon must either remain stable or increase. Our findings suggest that soil organic carbon (SOC) will be lost under all climate scenarios, but less is lost under the climate scenarios where environmental considerations are placed higher than purely economic considerations (IPCC B1 and B2 scenarios) compared with the climate associated with emissions resulting from the global free market scenario (IPCC A1FI scenario). More SOC is lost towards the end of the study period. Optimal management is able to reduce this loss of SOC, by up to 44% compared with business as usual management. The soil sustainability scenario could be run only for a limited area, but in that area was shown to increase SOC stocks under three climate scenarios, compared with a loss of SOC under business as usual management in the same area. Improved agricultural soil management will have a significant role to play in the adaptation to, and mitigation of, climate change in this region. Further, our results suggest that this adaptation could be realized without damaging profitability for the farmers, a key criteria affecting whether optimal management can be achieved in reality.     

Molecular characterisation and differential diagnosis of a necrotic PVY isolate in tomato

A PVY isolate which causes strong necrotic lesions in tomato was isolated and characterised. It did not infect potato and did not react with antiserum specific to the N-strain of PVY. Restriction endonuclease cleavage patterns of PCR products derived from the 5′-end of the virus genome (Hinc II and Rsa I) clearly distinguished the tomato, pepper and potato strains. Additional sequence analysis indicated that the tomato and pepper isolates were closely related, while both markedly differed from the necrotic strains of potato. Hence, it was concluded that the necrotic tomato isolate is uniquely specific for tomato.     

Effect of some disaccharides, hexoses and pentoses on nitrate reductase, glutamine synthetase and glutamate dehydrogenase in excised pea roots

The effects of exogenous sucrose, lactose, d -glucose, d (-)fructose, d -galactose, d -mannose, l -sorbose, l -arabinose and d -xylose on nitrate reductase (NR), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) levels, on anaerobic nitrite production and on respiratory O₂ consumption were studied in excised roots of pea (Pisum sativum L. cv. Raman). Sucrose, glucose and fructose increase NR and GS levels and decrease GDH level (when compared with roots cultures without any sugar) at all concentrations used, but the extent of this effect varies. NR induction is enhanced by all sugars within the concentration range studied. Precultivation of roots with mannose and galactose results in an increase in anaerobic nitrite production in a medium consisting of phosphate buffer and KNO₃. GS reaches its maximum at lower sugar concentrations, this fact being especially clear-cut with galactose. The decrease in GS level observed in roots cultured without sucrose is enhanced by higher sorbose concentrations. The increase in GDH level occurring in roots cultured without sucrose is depressed by low galactose and mannose concentrations but enhanced by high galactose, mannose, xylose and a wide range of sorbose concentrations. Lactose exerts only slight influence on the enzymes. The effects of sugars are in no case consistent with their effect on respiratory O₂ consumption which is most pronounced with NR. The above results show that the effects of sugars on NR, GS and GDH are not mediated by one universal mechanism.