Growth performance of juvenile pacu (Piaractus mesopotamicus) and dourado (Salminus brasiliensis) fed with lyophilized bovine colostrum

Growth performance was evaluated in juvenile pacu (Piaractus mesopotamicus) and dourado (Salminus brasiliensis) fed diets containing 0%, 10% and 20% of lyophilized bovine colostrum for 60 days. The performance variables of weight gain, relative weight gain, feed intake, feed conversion ratio, specific growth rate, total protein intake and protein efficiency ratio were evaluated as well as apparent digestibility coefficients of protein and energy in the diets. Inclusion of bovine colostrum did not induce differences in the performance of pacu and dourado (P > 0.05), indicating that the diets were adequate and met the nutritional needs of the juveniles. The protein digestibility in both species was improved with the inclusion of the bovine lacteal secretion. Based on the variables studied, the diets with lyophilized bovine colostrum inclusion were nutritionally suitable for both pacu and dourado indicating the possibility to use this lacteal secretion as a partial substitute of dietary protein.     

The use of sewage sludge as soil amendment. The need for an ecotoxicological evaluation

Background, aim, and scope  Sewage sludge use in agriculture should be limited by the presence of metals and other persistent environmental pollutants. The present study aims to contribute for the definition of a test battery of ecotoxicological assays that allows a proper ecotoxicological characterization of sludges, providing information on their potential hazard and identified “safe” application levels. Materials and methods  Three sludges from distinct sources (urban, olive-processing, and electroplating industries) were tested using avoidance and reproduction tests with earthworms (Eisenia andrei) and springtails (Folsomia candida) and plant growth tests with turnips (Brassica rapa) and oats (Avena sativa). Different soil–sludge mixture concentrations mimicking recommended/realistic field dosages were tested. Results  Only the sludge from the electroplating industry induced an avoidance response from the earthworms (EC₅₀ = 0.4 t/ha) and collembolans (no observed effect concentration (NOEC) = 15 t/ha). This sludge was the only sludge responsible for any effect on the reproductive output of the earthworms (EC₅₀ = 7.74 t/ha). Regarding collembolans, none of the sludges tested caused any significant decrease in reproduction. In higher plant tests, the two industrial sludges were toxic, causing a decrease growth in both species. The EC₂₀ values determined for B. rapa were 20.3 and 24.2 t/ha and for A. sativa 14.7 and 16.2 t/ha for sludges from olive-processing and electroplating industries, respectively. Discussion  The metal loadings of the different test sludges could partially explain the results obtained. The toxicity of the test sludge from electroplating industry observed on the tested invertebrates and plants could be explained by the high amount of total chromium from which 22.3% was in the most toxic oxidation state—Cr(VI). However, the toxicity caused by the sludge from the olive-processing industry in the test plants could be attributed to the presence of other compounds (not measured in this study) since the metal content was not high enough to induce such an effect. The absence of toxicity showed by the urban test sludge was in agreement with its low levels of metals. Conclusions  The response of the different test organisms and end points varied according to the sludge type. The urban sludge was non-toxic whereas the sludge from the electroplating industry caused a toxic effect on almost all parameters measured (avoidance behavior of both test organisms, reproduction of earthworms, and growth of both plant species). Sludge from the olive-processing industry only caused a toxic effect on growth of both plant species. By analyzing the sensitivity of the different parameters for the most toxic sludge, it was found that avoidance and reproduction were more sensitive than plant growth, whereas plant seed germination was not sensitive at all. Recommendations and perspectives  The ecotoxicological evaluation of wastes can be used as an environmental safety control of sludge use in agriculture. A tiered approach could be adopted for this purpose, incorporating avoidance tests in the first tier (screening level) and reproduction and plant growth tests in a second tier. But more evidence aiming to define the most suitable ecotoxicological test battery for specific sludges with a different contamination profile is still needed.     

Fitness costs associated with milbemectin resistance in the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite Tetranychus urticae Koch is one of the most important pests of a wide range of crops worldwide. Its control is still largely based on the use of acaricides. However, due to its short life-cycle, high fecundity and arrhenotokous reproduction, it is able to develop resistance to these compounds very rapidly. Preliminary studies for milbemectin resistance in T. urticae showed that, under laboratory conditions, such resistance was unstable in the absence of a selection pressure. The aim of this study was to evaluate the possible fitness costs associated with milbemectin resistance in T. urticae. Comparison of biological traits between resistant and susceptible strains indicated the occurrence of fitness costs associated with milbemectin resistance. The resistant strain showed a longer juvenile development period for females, lower fecundity and a higher proportion of males among the progeny. The figures for net reproductive rate (R ₀), intrinsic rate of natural increase (r _m) and finite rate of increase (λ) were higher in the susceptible strain. The instability of milbemectin resistance can be exploited in resistance management programmes.     

Thieves,bats and fruit flies: local ecological knowledge on the weaver ant Oecophylla longinoda in relation to three ‘invisible’ intruders in orchards in Guinea

We held interviews with 100 mango and cashew growers in Guinea, West Africa. Fewer than 20 questions dealing with the tree-inhabiting weaver ant Oecophylla longinoda were developed, based on local context and related research conducted on farmers' knowledge in other countries. More than half of the growers reported that ants protect their orchard from thieves. Apart from deterring snakes, about 46% of the growers mentioned that weaver ants reduce damage by fruit-eating bats; some reported that bats do dislike the smell of weaver ants. Whereas the relationship between ants and humans or conspicuous fruit bats is well understood, a quantitative appreciation of the effect of Oecophylla on small insect pests, such as fruit flies, is more complex. Despite the fact that 57% of the growers reported that Oecophylla had a positive effect on mango fruit quality, many classified Oecophylla as a pest due to its nuisance during harvest, and they requested the plant protection staff to help them with pesticides. Strategies to strengthen local ecological knowledge are discussed.     

Guava decline: effect of root exudates from Meloidogyne enterolobii-parasitized plants on Fusarium solani in vitro and on growth and development of guava seedlings under controlled conditions

In guava decline, Fusarium solani-immune guava trees become susceptible to extensive root rot caused by this fungus after parasitism by Meloidogyne enterolobii. To understand the mechanisms involved in this disease, root exudates were collected from nematode-inoculated (NI) or uninoculated (UN) guava plants cultivated in sand. After filtration through a Millipore® membrane, NI and UN exudates were used: i) to prepare media to assess their effect on mycelial growth and production of propagules of F. solani isolate UENF/CF 163, and ii) to incubate macro- and microconidia to assess their effect on germination. NI exudates promoted (P?<?0.05) more mycelial growth and production of propagules than UN exudates or water. NI and UN exudates were used to water guava seedlings laid over seed germination paper inside plastic boxes. Half of the seedlings had an agar plug colonized by the fungus positioned in the collar region. Upon watering with NI exudates the fungus caused (P?<?0.05) extensive rotting of the seedlings’ rootlets. NI and UN exudates, either unlyophilized or lyophilized and re-suspended to the original concentration, were used to water guava seedlings grown in sterile sand before being inoculated (or left uninoculated) as described before. Solely upon watering with NI exudates, in its unlyophilized form or after lyophilization, the fungus caused a reduction (P?<?0.05) of shoot and root biomass associated with rotting of roots. These results suggest that M. enterolobii induces chemical changes in the root exudates of guava trees, which are necessary for root invasion causing root rotting by F. solani.     

A phytoplasma representative of a new subgroup, 16SrXIII-E, associated with Papaya apical curl necrosis

Papaya apical curl necrosis (PACN) has frequently been observed in several Brazilian states. Affected plants exhibit foliar chlorosis, curvature of the apex, shortening of the internodes leading to bunching of the crown leaves, necrosis of the young apical parts, leaf drop, and dieback. Naturally infected plants were sampled and subjected to PCR assays, which confirmed that a phytoplasma was associated with the disease. Sequencing of the 16S rRNA gene, conventional and computer-simulated RFLP analyses, and phylogenetic analysis allowed the determination of the PACN phytoplasma as a representative of a new subgroup, designated 16SrXIII-E. The phytoplasmas of various 16Sr groups, including 16SrI, 16SrII, 16SrX, 16SrXII, and 16SrXVII, are known to be involved in anomalies in papaya plants in several countries. However, the present study reports, for the first time, the occurrence of a 16SrXIII phytoplasma in association with a papaya disease.     

Relation between plant nutrition, hormones, insecticide applications, bacterial endophytes, and Candidatus Liberibacter Ct values in citrus trees infected with Huanglongbing

Intensive insecticide and nutrient management have been attempted worldwide to reduce citrus huanglongbing (HLB) symptom development and yield loss. However, effects of insecticide and nutrient applications on HLB have been poorly understood. Leaf nutrients, jasmonic and salicylic acid contents, cycle threshold (Ct) values of Ca. Liberibacter asiaticus (Las), and community structure of endophytic α-proteobacteria were evaluated after insecticide treatment, ‘nutrition’ treatment (including systemic resistance inducing agents), or both in comparison with a control in a two-factor field experiment in 2008–2012. Leaf N, Mn, Zn and B significantly increased whilst Cu decreased after nutrient applications. Salicylic acid significantly increased in old leaves treated with insecticides, nutrients or both, and in young leaves treated with nutrients only. The jasmonic acid concentration was highest after the nutrition treatment in both old and young leaves. Ct values of Las and leaf area and weight significantly increased after long-term nutrient applications in 2011 and/or 2012. Redundancy analysis of the endophytic α-proteobacteria community structure indicated that the communities were mainly separated according to nutrient applications, which were positively associated with Ct values of Las and Ca, Mn, Zn, B, Mg, and Fe contents in leaf samples collected in 2012. Thus, effects of insecticides on HLB were significant in the early 2-year period whilst nutrients had significant effects on Las content and leaf size and weight after at least 3 years of application.     

Genetic diversity of 16SrIII group phytoplasmas in Argentina. Predominance of subgroups 16SrIII-J and B and two new subgroups 16SrIII-W and X

Twelve Argentinean 16SrIII (X-disease)-group phytoplasma strains were analyzed. Ten of them, detected in daisy (Bellis perennis), garlic (Allium sativum), ‘lagaña de perro’ (Caesalpinia gilliesii), periwinkle (Catharanthus roseus), ‘rama negra’ (Conyza bonariensis), ‘romerillo’ (Heterothalamus alienus), summer squash (Cucurbita maxima var. zapallito) and tomato (Solanum lycopersicum), are new phytoplasma strains while two strains, detected in garlic and China tree (Melia azedarach), have been previously described. The plants showed typical symptoms of phytoplasma diseases, such as leaf size reduction, proliferation, stunting and virescence. The identification and genetic diversity analysis of the phytoplasmas were performed based on 16S rDNA and ribosomal protein gene sequences. The classification into 16Sr groups and subgroups was established by actual and virtual RFLP analysis of the PCR products (R16F2/R16R2) compared with reference strains. According to the classification scheme, strains HetLL and ConWB-A and B represent two new subgroups 16SrIII-W and X, respectively. On the other hand, strains CatLL, TomLL and CaesLL are related to subgroup 16SrIII-B, and strains BellVir, TomRed, CucVir and GDIII-207 are related to subgroup 16SrIII-J. Ribosomal protein genes were amplified using primers rpF1/rpR1 and rpIIIF1/rpIIIR1. RFLP analysis performed with AluI, DraI and Tru1I (MseI isoschizomer) distinguished three new rp profiles within subgroup 16SrIII-B, one for subgroup 16SrIII-J, and one shared with strains of the new subgroups 16SrIII-W and X. The phylogenetic analysis based on 16S rDNA and ribosomal protein gene sequences confirmed the separation of HetLL and ConWB strains in two new subgroups and the close relatedness among subgroup J phytoplasmas, which have been detected only in South America.     

Susceptibility evaluation of Picea abies and Cupressus lusitanica to the pine wood nematode (Bursaphelenchus xylophilus)

Pine wilt disease (PWD), recently introduced into Europe, is caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus and is a devastating illness that affects mainly pine trees. It is known that the PWN is capable of infecting other conifers; however, there is currently no information on which other plant species may be susceptible to PWD. In this study, the potential susceptibility of two common species of European forests, Picea abies and Cupressus lusitanica, to PWN was assessed through the monitoring of visual external symptoms, dimension and localization of the nematode population in stems, quantification of total chlorophyll, total soluble phenolics and lignin, at 7, 14, 21 and 28 days after inoculation. The degree of susceptibility was established through the comparison of symptoms with Pinus pinaster, a well‐known PWN host. Furthermore, the stem ultrastructure of P. abies, C. lusitanica and Pn. pinaster was analysed by scanning electron microscopy. The results suggest that P. abies and C. lusitanica are resistant to PWN, and that lignin biosynthesis in these species is affected at an early stage of the infestation. Nevertheless, P. abies seems to be a compatible host that could act as a repository for PWN.