Protection of olive planting stocks against parasitism of root-knot nematodes by arbuscular mycorrhizal fungi

The effects were investigated, under controlled conditions, of single and joint inoculation of olive planting stocks cvs Arbequina and Picual with the arbuscular mycorrhizal fungi (AMF) Glomus intraradices , Glomus mosseae or Glomus viscosum , and the root-knot nematodes Meloidogyne incognita and Meloidogyne javanica , on plant performance and nematode infection. Establishment of the fungal symbiosis significantly increased growth of olive plants by 88·9% within a range of 11·9–214·0%, irrespective of olive cultivar, plant age and infection by M. incognita or M. javanica . In plants free from AMF, infection by Meloidogyne spp. significantly reduced the plant main stem diameter by 22·8–38·6%, irrespective of cultivar and plant age. Establishment of AMF in olive plants significantly reduced severity of root galling by 6·3–36·8% as well as reproduction of both Meloidogyne spp. by 11·8–35·7%, indicating a protective effect against parasitism by root-knot nematodes. Infection by the nematodes influenced root colonization by AMF, but the net effect depended on the AMF isolate–olive cultivar combination. It is concluded that prior inoculation of olive plants with AMF may contribute to improving the health status and vigour of cvs Arbequina and Picual planting stocks during nursery propagation.     

Synthesis and phloem mobility of acidic derivatives of the fungicide fenpiclonil

A series of derivatives of the phenylpyrrole fungicide fenpiclonil was synthesized in which a carboxyl group was present at various sites of this non-phloem-mobile molecule. Using the Kleier model, all these acidic analogues were predicted to be moderately phloem-mobile, especially the N-substituted derivatives. One of these latter molecules, N-carboxymethyl-3-cyano-4-(2,3-dichlorophenyl)pyrrole, exhibited some fungicidal activity on the pathogenic fungus Eutypa lata, and was then tested as a phloem-mobile pesticide in the Ricinus system. The compound was indeed mobile in the sieve tubes and was not degraded to fenpiclonil in the phloem sap under our experimental conditions. Its concentration in the sap was closely correlated to the percentage of the undissociated form of the molecule in the external medium, and was similar under acidic conditions (external pH 4.6-5.0) to that of the herbicide glyphosate.     

Evaluation of sampling methods and assessment of the sample size to estimate the weed seedbank in soil, taking into account spatial variability

As field sampling is time consuming, it is necessary to develop efficient sampling techniques to obtain accurate estimates of the weed seedbank in soil. The relative efficiency between sampling schemes depends on the spatial variability in weed seed density across agricultural fields. Spatial variability of the weed seed density was characterized by theoretical correlograms. A systematic sampling (square grill) scheme was considered and it was found that, taking into account spatial variability, this sampling scheme was more efficient than simple random sampling. As a result, the sample size can be reduced in comparison with that given in previous studies, where spatial correlation was ignored. The reduction depends on the correlation structure defined as a function of the ratio, τ, between the nugget effect and the sill of the variogram. The maximum reduction of the sample size, without loss of either precision or confidence level corresponds to the case where there is no nugget effect, τ = 0. The opposite extreme case, where the reduction is nil, corresponds to the case of a pure nugget effect τ = 1. The abaci based on given expressions are provided to determine the sample size in species whose spatial pattern can be fitted either to a Poisson or to a negative binomial distribution.     

Acidic derivatives of the fungicide fenpiclonil: effect of adding a methyl group to the N-substituted chain on systemicity and fungicidal activity

A new acidic derivative of the fungicide fenpiclonil was synthesized containing a methyl group on the alpha-position of the carboxyl function of N-carboxymethyl-3-cyano-4-(2,3-dichlorophenyl)pyrrole. The phloem mobility of the resulting N-(1-carboxyethyl)-3-cyano-4-(2,3-dichlorophenyl)pyrrole was comparable with that of the former compound, but was higher at external pH 5.0. Unlike the derivatives previously synthesized, it was comparable with fenpiclonil in its fungicidal activity against the pathogenic fungus Eutypa lata.     

Activity of glutathione S-transferase toward some herbicides and its regulation by benoxacor in non-embryogenic callus and in vitro regenerated tissues of Zea mays

A procedure was developed to obtain non-embryogenic callus and regenerated lines from root segments of Zea mays grown in aseptic conditions. The activity of glutathione-S-transferases (GSTs), for non-embryogenic callus, was determined toward 1-chloro-2,4-dinitrobenzene (CDNB) and it was compared with that obtained for corn seedlings grown without hormones. For the callus masses, increases of specific activity toward CDNB and the kinetic parameter V_max were observed with respect to corn seedlings. The procedure permitted the regenerating of tissues from callus explants, therefore the GST(CDNB) activity and the effect of the safener benoxacor on its expression were investigated for the regenerated tissues grown in agarized substrate and in liquid medium. These explants showed a constitutive GST(CDNB) activity higher than corn seedlings and this activity was increased, for both tissues, in response to the presence of the safener benoxacor in the growing medium. The GST activity for the above tissues was also assayed toward benoxacor and terbuthylazine, metolachlor and fluorodifen herbicides. Measurable GST activity was found toward some of the above chemicals and it was found to be significantly enhanced in response to benoxacor treatment.     

Genetic Structure of the Population of Pepino mosaic virus Infecting Tomato Crops in Spain

ABSTRACT The population structure of Pepino mosaic virus (PepMV), which has caused severe epidemics in tomato in Spain since 2000, was analyzed. Isolates were characterized by the nucleotide sequence of the triple gene block and coat protein gene and, for a subset of isolates, a part of the RNA-dependent RNA polymerase gene. The full-length sequence of the genomic RNA of a Solanum muricatum isolate from Peru also was determined. In spite of high symptom diversity, the Spanish population of PepMV mostly comprised highly similar isolates belonging to the strain reported in Europe (European tomato strain), which has been the most prevalent genotype in Spain. The Spanish PepMV population was not structured spatially or temporally. Also, isolates highly similar to those from nontomato hosts from Peru (Peruvian strain) or to isolate US2 from the United States (US2 strain) were detected at lower frequency relative to the European strain. These two strains were detected in peninsular Spain only in 2004, but the Peruvian strain has been detected in the Canary Islands since 2000. These results suggest that PepMV was introduced into Spain more than once. Isolates from the Peruvian and US2 strains always were found in mixed infections with the European tomato strain, and interstrain recombinants were detected. The presence of different strains of the virus, and of recombinant isolates, should be considered for the development of control strategies based on genetic resistance.     

A new standard area diagram set for assessment of severity of soybean rust improves accuracy of estimates and optimizes resource use

Soybean rust (SBR), caused by Phakopsora pachyrhizi, is the most important yield-damaging fungal disease of soybean due to severe reduction in healthy leaf area and acceleration of leaf fall. In experimental research, SBR severity is estimated visually aided/trained by a standard area diagram (SAD) developed and validated during the mid-2000s (Old SAD). In this study, we propose a new SAD set for SBR with six true-colour diagrams following linear increments (c. 15% increments) amended with four additional diagrams at low (<10%) severities, totalling 10 diagrams (0.2%, 1%, 3%, 5%, 10%, 25%, 40%, 55%, 70%, and 84%). For evaluation, 37 raters were split into two groups. Each assessed severity in a 50-image sample (0.25%–84%), first unaided and then using either the Old SAD or the New SAD. Accuracy, precision, and reliability of estimates improved significantly relative to unaided estimates only when aided by the New SAD (accuracy >0.95). Low precision (<0.78) and a trend of underestimation with an increase in severity were the main issues with the Old SAD, which did not differ from unaided estimates. Simulation to evaluate the impact of the errors by different methods on hypothesis tests, showed that the new SAD was more powerful for detecting the smallest difference in mean control (e.g., 70% vs. 65% disease reduction) than the Old SAD; the latter required a 2-fold increase in sample size to achieve the same power. There is a need to improve some SADs, taking advantage of new knowledge and technology to increase accuracy of the estimates, and to optimize both resource use efficiency and management decisions.     

Restoration and Rehabilitation of Mixed Espinales in Central Chile: 10-Year Report and Appraisal

A synthesis of progress achieved thus far is provided for a 10 - year research and development program aimed at the ecological and economic rehabilitation of agroecosystems in the unirrigated portions of the central valley of Chile's Mediterranean climate region. We review our data on (1) revised management techniques aimed at restoring the gross superstructure and former levels of diversity and productivity of a mixed espinales formation; (2) selection and utilization of ecotypes of the naturalized annual Medicago polymorpha L. and the N2-fixing microsymbiont Rhizobium meliloti, for gradual improvement of espinal soil fertility; and (3) studies of the outstandingly well adapted and fast growing Canary Island tree Chamaecytisus proliferus (L. fil.) Link ssp. palmensis (Christ) Kunkel (Tagasaste), which along with about three dozen other woody nitrogen - fixing legume and several nonlegume multipurpose trees, was considered to be of potential value for deep soil layer rehabilitation combined with economic improvements. In all these subprograms, efforts were made to identify techniques or organisms that could provide short-term benefits to landowners, especially in the form of wood, fuelwood, or forage for livestock. We also consider various approaches to be added to the program over the next decade, especially in view of the overarching goal of reintegrating fragmented landscapes and combining restoration with rehabilitation and reallocation at this spatial scale.     

Five-year survey uncovers extensive diversity and temporal fluctuations among fusarium head blight pathogens of wheat and barley in Brazil

We conducted a five-year survey (2011–2015) of barley and wheat fields in Paraná state, Brazil, obtaining 754 Fusarium isolates from spikes with fusarium head blight (FHB)-symptoms. Multilocus genotyping and TEF-1α gene sequence analyses confirmed the dominance of the F. graminearum species complex (FGSC, 75.7%), but F. poae (11.5%), as well as F. avenaceum and related members of the F. tricinctum species complex (FTSC, 8.1%) appeared as substantial contributors to FHB. Within the FGSC, F. graminearum of the 15-ADON genotype was dominant (63%), followed by F. meridionale of the NIV genotype (23.1%), F. cortaderiae of the NIV (7%) or 3-ADON (2.6%) genotypes, and F. austroamericanum (3.8%) of the 3-ADON genotype. Substantial variation in pathogen composition was observed across years, with F. poae and F. meridionale frequencies significantly elevated in some years. Most F. poae strains produced DAS, diANIV, and butenolide, but not neosolaniol, T-2, or HT-2. All FTSC species produced moniliformin. Enniatin production was widespread among FTSC species, with the single F. acuminatum strain found to be the strongest producer of enniatins. Our findings confirm FGSC as a major contributor to FHB and expand considerably our knowledge of the presence, frequency, and conditions under which other pathogens may emerge, altering the spectrum of toxins that may accumulate in grain.