Walnut Orchards Research Articles

Correction to: Predation rate linked to life table of Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae) fed on small walnut aphid (Chromaphis juglandicola) (Kalt.) (Hemiptera: Aphididae): with population and predation projections

Small walnut aphid (Chromaphis juglandicola (Kaltenbach) (Hemiptera: Aphididae) is important pest in walnut orchards in Lake Van Basin, Turkey. In this study, the life-table parameters reflecting population growth rate and predation rate of Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae), which is one of the important predators of the pest, were determined. Life table parameters were estimated according to age-stage, two-sex life table method. Variances and standart errors of population parameters were obtained according to Bootstrap method. The values obtained for the intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate (R0) and mean generation time (T) were 0.072 d−1, 1.070 d−1, 62.48 offspring and 57.16 d, respectively of C. carnea fed on Chromaphis juglandicola. The net predation rate (C0) was determined as 212.9 aphids. Pradation projection was performed by using timing program to prevent the predator’s decrease in predation capacity and to determine the most appropriate release quantities and the appropriate interval between releases (to fill predation gaps) for biological control. The possible effects of the findings on the bio-controls of Chromaphis juglandicola by C. carnea were discussed. Results obtained can be used in pest management program that will be prepared for this pest.

Association of a phytoplasma from ribosomal subgroup 16SrXII‐A with walnut witches’‐broom in Iran

Walnut trees displaying symptoms similar to those caused by phytoplasmas, including foliar chlorosis, yellowing and shortening of internodes, were found in a fruit orchard in the north of Fars province, Iran in 2020 (Fig. 1). Samples were collected and analysed by PCR to detect and identify possible phytoplasma(s) associated with diseased plants. Four diseased and four asymptomatic walnut trees were sampled and analysed for the presence of phytoplasma. Total DNA was extracted from 0.1 g of midribs using the CTAB method. Nested PCR was performed using universal phytoplasma primers P1/P7 (Deng & Hiruki, 1991) in the first round, and R16F2n/R16R2 (Smart et al., 1996) in the second. PCR products of the expected size, c. 1.2 kb, were obtained from all diseased plants but not from the symptomless ones. The nucleotide sequence was determined directly and submitted to GenBank (Accession No. MZ005313). A BLAST search showed that the phytoplasma associated with walnut witches’-broom had the highest sequence identity (99.9%) with Iranian alfalfa witches’-broom phytoplasma (KT763373), a member of the ribosomal subgroup 16SrXII-A (‘Candidatus Phytoplasma solani’). Virtual RFLP patterns obtained with iPhyclassifier (https://plantpathology.ba.ars.usda.gov/cgibin/resource/iphyclassifier.cgi) supported the sequence analysis results. Walnut witches’-broom phytoplasma was first reported in Iowa, USA and was associated with the group 16SrIII (‘Ca. P. pruni’) (Yun & Harrington 2011). In Iran, the 16SrXII phytoplasma group has been reported in alfalfa, almond, aubergine, grapevine, peach, plum and tomato (Siampour et al., 2019). It has also been identified from Cannabis sativa (Sichani et al., 2011) and Salix babylonica (Zamharir & Taheri, 2017). In Fars province, walnut orchards are adjacent to stone fruit orchards and vineyards, so it is likely that this phytoplasma has been transferred from such crops to walnut trees. Since large areas of walnut are grown in Iran, this phytoplasma may be a serious threat to walnut cultivation. To the best of our knowledge, this is the first report of the association of a 16SrXII-A related phytoplasma with walnut witches’-broom globally. The authors would like to thank Dr. Sadegh Sadeghi and Mr. Mohsen Amiri for great help in the field.

Determination of Plant Parasitic Nematode Species of Tylenchida (Nematoda) in Apple (Pyrus malus L.) and Walnut (Juglans regia L.) Orchards in Bingöl Province of Turkey

Plant parasitic nematodes (PPNs) are the leading source of damage to crops in agricultural production and they can cause very serious yield reductions. The Tylenchida (Nematoda) constitutes the most important group of PPNs due to containing a large number of economically important plant parasitic species. This study was conducted in apple (Pyrus malus L.) and walnut (Juglans regia L.) orchards in Bingöl (Turkey) between 2016 and 2017. For this purpose, total of 52 soil/root samples were taken from 20-40 cm depth of related areas during summer months. In laboratory, active PPNs were extracted from soil and roots parts by modified Baermann Funnel method. Obtained nematodes were killed at 60°C, fixed in TAF in mounted slides. PPNs belonging to Tylenchida were identified morphometrically and morphologically under the light microscope. As result of the study; eighteen PPN species were determined and classified under the Tylenchida order as three suborders, three superfamilies, four families and seven genera in the apple and walnut growing areas. The most encountered PPN species in this study were Filenchus filiformis, Helicotylenchus canadiensis, H. digonicus, H. vulgaris, Pratylenchoides alkani and Psilenchus hilarulus. All species were determined for the first time in the nematoda fauna of Bingöl province in apple and walnut orchards.

Análisis de diversos aspectos económicos de la producción en huertas de nogales de alta y baja densidad. Estudio de caso

The cultivation of pecan nuts is one of the most important economic activities in Chihuahua, Mexico. In recent years, the price of the walnut has increased, causing a high profitability of the walnut, this has motivated several producers to establish new orchards, with high densities (204 trees per hectare). However, to date there is no reliable economic information to support that high densities are better than low ones. For this reason, the objective of this research was to economically analyze the production of high and low density walnut orchards. In this study, a quantitative research approach was used. The required information was collected through 66 surveys (three for each year of the 11 years analyzed of low and high density plantations) carried out to walnut producers with high and low density plantations (6 producers per year). From the information from the surveys, the production costs were determined by considering all the activities carried out in the high and low density plantations and the income from harvest sales. The results obtained indicate that production costs in the first four years were higher at low densities than at high densities. The yield per nut per walnut from the eighth year was higher at low densities than at high densities and the yield per hectare was higher at high densities due to the greater number of walnut trees per hectare that were planted at high densities. The cost benefit ratio was higher at low densities than at high densities. To date there is no information on the production of walnut in low and high density, so this study is important for farmers, especially in Mexico.

Exploring mycorrhizal fungi in walnut with a focus on physiological roles

Walnuts are an economically important forest tree used for timber and nut production, and the nut of fruits is rich in various nutrients, becoming one of the four important nuts in the world. Walnuts have deep roots, which can be colonized by either ectomycorrhizal fungi or arbuscular mycorrhizal fungi in the soil. These mycorrhizal fungi form beneficial symbioses in roots of walnut. A large number of ectomycorrhizal fungi have been identified, whilst Boletus edulis, Calvatia uiacina, and Cantharelles cibarius isolated from walnut orchards stimulated plant growth and gave the capacity of stress tolerance in walnut. Moreover, Carya illinoensis is a very good host plant for commercial production of truffles, especially Tuber indicum. In addition, ectomycorrhizal fungi accelerate plant growth and enhance potential stress tolerance of walnuts. Inoculation with arbuscular mycorrhizal fungi also showed the improvement of plant growth and nutrient acquisition of walnut, the enhancement of drought tolerance in walnut, nutrient redistribution under walnut interplanting patterns, and the delivery of juglone by mycorrhizal hyphae. A culturable in vitro arbuscular mycorrhizal like fungus Piriformospora indica also enhanced salt tolerance of walnut plants. In this mini-review, the physiological roles of mycorrhizal fungi, including arbuscular mycorrhizal fungi, ectomycorrhizal fungi and arbuscular mycorrhizal like fungus (P. indica) on walnut plants are summarized, and future outlooks in the field are proposed.

EFFECT OF MATING DISRUPTION ON THE PHEROMONE TRAP CATCHES OF CODLING MOTH (CYDIA POMONELLA L.) AND FRUIT DAMAGE IN WALNUT (JUGLANS REGIA L.)ORCHARDS UNDER ORGANIC FARMING

ABSTRACT The codling moth (Cydia pomonella L.), a key pest in walnut orchards in Bulgaria, is managed mainly with broad spectrum insecticides. Insecticide application often resulted in destruction of beneficial species and environmental pollution. The present study was conducted during 2018 - 2019 in Pazardzhik region of Bulgaria in an isolated orchard. The pheromone trap catches of C. pomonella in the organically maintained walnut orchard in the presence of mating disruption (MD) dispensers was compared with the pheromone trap catches in the conventional control orchard. The Pherocon VI sticky traps, type Delta were baited with standard PHEROCON CM L2 – codlemone. CIDETRAK® CMDA COMBO™ MESO™ mating disruption dispensers containing a unique combination of codling moth pheromone and a patented male and female behavior modifying kairomone were used at the rate of 20 pieces per/ha in the organic orchard. There was reduction in fruit damage in the organic orchards, despite the lack of treatment with pesticides. In spite of 9 - 10 treatments with insecticides, fruit damage was higher in theconventional control orchard compared to the organic orchard. The present results brought out that the mating disruption using CIDETRAK® CMDA COMBO™ MESO™ dispensers against codling moth can provide more effective control against C. pomonella, than the pesticide treatments.

Orchard Mapping with Deep Learning Semantic Segmentation.

This study aimed to propose an approach for orchard trees segmentation using aerial images based on a deep learning convolutional neural network variant, namely the U-net network. The purpose was the automated detection and localization of the canopy of orchard trees under various conditions (i.e., different seasons, different tree ages, different levels of weed coverage). The implemented dataset was composed of images from three different walnut orchards. The achieved variability of the dataset resulted in obtaining images that fell under seven different use cases. The best-trained model achieved 91%, 90%, and 87% accuracy for training, validation, and testing, respectively. The trained model was also tested on never-before-seen orthomosaic images or orchards based on two methods (oversampling and undersampling) in order to tackle issues with out-of-the-field boundary transparent pixels from the image. Even though the training dataset did not contain orthomosaic images, it achieved performance levels that reached up to 99%, demonstrating the robustness of the proposed approach.

Dispersal and colonization risk of the Walnut Twig Beetle, Pityophthorus juglandis, in southern Europe

The Walnut Twig Beetle (WTB), Pityophthorus juglandis Blackman, is a small bark beetle native to Mexico and Southwestern USA recorded for the first time in Europe (NE Italy) in 2013. WTB attacks walnut (Juglans spp.) and wingnut trees (Pterocarya spp.) and is the vector of Geosmithia morbida Kolarík et al., a pathogen causing the thousand cankers disease (TCD). WTB and TCD represent a serious threat for walnut orchards in Europe. Spatiotemporal data of the WTB-TCD infestations recorded from an 8-year-long (2013–2020) monitoring conducted in 106 walnut orchards of NE Italy were used to develop a model in order to analyze: (i) the effective dispersal capacity of WTB, (ii) the factors affecting dispersal and (iii) the colonization risk of healthy walnut orchards. We registered a mean annual dispersal of 9.4 km, with peaks of about 40 km. Pest dispersal is affected by distance of suitable hosts from the nearest infested site, number of walnut orchards in the surroundings (both infested and healthy), orchard size and walnut species in the orchard. Using the model, it was also possible to calculate the colonization risk of a specific walnut orchard according to its characteristics showing, for instance, that a medium-size (5,000 trees) black walnut orchard located at 25 km from the nearest infested orchard has an infestation risk of about 50% of probability.

Modelling the yield and profitability of intercropped walnut systems in Croatia

In Croatia, farmers are showing increasing interest in establishing walnut orchards for nut production on arable land due to higher anticipated net margins. One way to address the lack of profitability in the initial years when nut yields are low may be to plant arable intercrops. The anticipated impacts of this practice were assessed using a biophysical simulation model (Yield-SAFE) to determine the growth and yield of crops and trees in arable, orchard, and silvoarable systems, and an economic farm model (Farm-SAFE) was used to assess their profitability. The walnut orchard and the intercropped orchard systems were simulated assuming tree densities of 170, 135, and 100 trees ha−1, to determine the profitability and break-even date of the systems. The biophysical simulation predicted a decline in arable intercrop yields over time in all tree density scenarios. However, analysis of productivity of intercropped systems showed that intercropping was more productive than separate arable and walnut production for all tree density scenarios. From financial aspect, the return from intercropping helped to offset some of the initial orchard establishment costs and the arable intercrop remained profitable until the sixth year after tree planting. The modelling predicted that a system with 170 trees ha−1 that included intercropping for the first 6 years provided the greatest cumulative net margin after 20 years. The financial benefit of intercropping over the first 6 years opposed to monoculture walnut fruit production appeared to be consistent across the three tree densities studied. These results suggest that silvoarable agroforestry is profitable approach to establishing walnut orchards.

A deep learning approach for anthracnose infected trees classification in walnut orchards

This paper presents a novel approach for the detection of disease-infected leaves on trees with the use of deep learning. Focus of this study was to build an accurate and fast object detection system that can identify anthracnose-infected leaves on walnut trees, in order to be used in real agricultural environments. Similar studies in the literature address the disease identification issue; however, so far, the detection was performed on single leaves which had been removed from trees, using images taken in controlled environment with clear background. A gap has been identified in the detection of infected leaves on tree-level in real-field conditions, an issue which is tackled in our study. Deep learning is an area of machine learning that can be proved particularly useful in the development of such systems. The latest developments in deep learning and object detection, points us towards utilizing and adapting the state-of-the-art single shot detector (SSD) algorithm. An object detector was trained to recognize anthracnose-infected walnut leaves and the trained model was applied to detect diseased trees in a 4 ha commercial walnut orchard. The orchard was initially inspected by domain experts identifying the infected trees to be used as ground truth information. Out of the 379 trees of the orchard, 100 were randomly selected to train the object detector and the remaining 279 trees were used to examine the effectiveness and robustness of the detector comparing the experts’ classification with the predicted classes of the system. The best inputs and hyper-parameter configuration for the trained model provided an average precision of 63% for the object detector, which correctly classified 87% of the validation tree dataset. These encouraging results indicate that the detector shows great potential for direct application in commercial orchards, to detect infected leaves on tree level in real field conditions, and categorize the trees into infected or healthy in real time. Thus, this system can consist an applicable solution for real-time scouting, monitoring, and decision making.

Is Orius sauteri Poppius a Promising Biological Control Agent for Walnut Aphids? An Assessment from the Laboratory to Field.

Walnut aphids are major pests of walnut production with few commercially available natural enemies. We conducted laboratory and field experiments to evaluate the potential of Orius sauteri Poppius (Anthocoridae), a predatory bug, as a biological control agent against two walnut aphid species: the dusky-veined aphid (Panaphis juglandis Goeze) and the walnut aphid (Chromaphis juglandicola Kaltenbach). Both species co-occur on walnut trees; P. juglandis is distributed on the upper surface (adaxial) of leaves while C. juglandicola is found on the lower surface (abaxial) of leaves. Based on functional response experiments, O sauteri had a strong capacity for consuming both aphid species. Biocontrol efficacy of O. sauteri for each species in the laboratory and field experiments was high, 77% for P. juglandis and 80% for C. juglandicola, regardless if one or two predators being present. However, biocontrol efficacy declined 15-25% for C. juglandicola and 20-50% for P. juglandis when both aphid species were present on the same leaf. The efficacy of O. sauteri under (semi)-field conditions gave similar findings based on the percentage reduction of aphids and change in population growth rates of aphids. The reduced biocontrol efficacy of the predatory bug against mixed species populations of aphids can be explained by competition between the aphid species and differences in their preferred location on leaves. Our experiments showed that O. sauteri is a promising biocontrol agent, but biocontrol efficacy may decline when both aphid species are present on walnut trees. This should be considered in the commercial release of O. sauteri in walnut orchards to promote economic and environmental benefits of walnuts production.

Flooding by California Rivers Results in Walnut Scion Infections by Species of Phytophthora

Many walnut orchards were inundated by flooding from the Feather and Stanislaus Rivers in winter and spring 2017 and developed bleeding cankers in trunk, root, and crown tissues exposed to the water. Orchard surveys and diagnostic isolations associated Phytophthora pini, P. chlamydospora, and P. gonapodyides with the cankers in 2017. Pathogenicity of P. pini was confirmed in seedlings and excised shoots of Juglans regia, but the other species caused negligible amounts of disease. Feather River and associated flood waters were assayed using culture-independent sequencing of rRNA gene amplicons and pear baiting methods; 14 species of Phytophthora were detected, including P. chlamydospora and P. gonapodyides, but not P. pini. Severe and prolonged walnut orchard flooding from rivers, such as occurred in 2017, places diverse mixtures of Phytophthora species from multiple sources into close, infective proximity with susceptible walnut tree scions. Systemic chemical or genetic protection strategies may be valuable for orchards subject to such flooding.

Bionematicides as an alternative to methyl bromide fumigation.

Fumigant use in perennial crops can be reduced through prolonging the life of existing orchards. The longer an orchard remains healthy and productive, the less often it will be terminated, fumigated, and replanted. Two trials were conducted to determine the effectiveness of DiTera, a toxin produced by the fungus (Myrothecium verrucaria) and Nema-Q, an extract of the soap bark tree (Quillaja saponaria) for management of root-lesion (Pratylenchus vulnus) and ring (Mesocriconema xenopla) nematodes on walnuts. In the first trial, spring and fall treatments of DiTera were applied each year for four years to variety ‘Chandler’ scion on seedling ‘Paradox’ rootstock, and to own-rooted ‘Chandler’ trees. On ‘Paradox’ rootstock, both DiTera and Nema-Q increased walnut yields (P ≤ 0.05) and produced more vigorous trees (P ≤ 0.05) without significant reductions in nematode populations (P ≤ 0.05). A second trial was conducted with three rates of DiTera and four rates of Nema-Q, combinations of the two products, and an untreated control on ‘Chandler’ scion on ‘Paradox’ rootstock. The highest rate of Nema-Q (P ≤ 0.05), and a combination treatment of DiTera plus Nema-Q (P ≤ 0.05) increased trunk circumference. Several treatments showed reductions in root-lesion and ring nematodes (P ≤ 0.05). Bionematicides can improve yield, growth, and vigor in walnut orchards infested with plant-parasitic nematodes.

First Report of Alternaria alternata and Fusarium spp. Causing Brown Apical Necrosis in Walnut Fruit in Southern Chile

This is the first report of Alternaria alternata and Fusarium spp. causing brown apical necrosis (BAN) in walnut fruit in southern Chile. English walnut (Juglans regia L.) is the second most widely grown fruit in Chile. The bacterial pathogen Xanthomonas arboricola pv. juglandis affects walnut production in Chile and has been associated with apical necrosis symptom and premature fruit drop; this research focused on determining if fungal pathogens were associated with this damage. The presence of BAN in commercial walnut orchards in southern Chile reveals the need for improved phytosanitary programs to control this disease.

Etiology of bacterial diseases of young walnut trees in Serbia

In the summer and autumn of 2019-2020, young walnut orchards were monitored for the presence of bacterial diseases. Diseased walnut samples comprising trunks and branches with symptoms of vertical oozing canker (VOC), walnut bacterial blight (WBB) and superficial bark necrosis were collected from eight locations in Serbia. Based on phenotypic features, pathogenicity, and molecular assays using PCR with specific primers, 49 isolates obtained from samples showing VOC and WBB symptoms were identified as Xanthomonas arboricola pv. juglandis, while further two isolates obtained from bark necrosis were identified as Brenneria rubrifaciens. One tested X. a. pv. juglandis isolate obtained from a VOC sample produced deep cankers in the bark of inoculated trunks of young walnut trees (cultivars Chandler, Franquette and Sejnovo). Therefore, this is the first report of an association between X. a. pv. juglandis and VOC symptom in Serbia. Considering that X. a. pv. juglandis significantly endangers walnut production, the presence of this pathogen in walnut transplant imports needs to be assessed by an authorised laboratory. Furthermore, as this is also the first report of B. rubrifaciens on walnut trees in Serbia, it is noteworthy that this pathogen is not particularly harmful to young walnut trees.

Factores edáficos que predisponen a la infestación por nemátodo agallador (Meloydogine spp) en nogal pecanero

Carya illinoinensis (Wangenh.) K. Koch) es el frutal de mayor importancia en la región agrícola de delicias. Chihuahua, ocupando el sitio número uno en la producción de este producto a nivel nacional (SAGARPA, 2018). El nogal es atacado por diferentes microrganismos que causan serios problemas que reducen el rendimiento de los mismos. Es importante conocer algunas características edáficas que favorezcan o condicionen la presencia del nematodo en huertas de nogal, para en base a esta información los productores de nuez puedan prestar más atención al control del nematodo. El objetivo del presente estudio de caso fue determinar cuáles son los factores edáficos que influyen en la presencia del nemátodo Meloidogyne sp en el nogal pecanero. El estudio se llevó a cabo en los municipios de Delicias, Meoqui, Saucillo y Rosales del estado de Chihuahua Figura 1. Se tomaron 243 muestras de suelo de 60 nogaleras de septiembre del 2016 a enero del 2018. Los resultados indican que el nemátodo Meloidogyne sp., no es exclusivo de algún tipo de textura y puede estar presente en diferentes clases texturales de suelo. Se encontró una relación significativa entre la alta concentración de Fósforo-Olsen y un mayor número de árboles con presencia de hembras de Meloidogyne sp. parasitando la raíz del nogal. Se encontró una relación significativa entre la concentración del valor muy bajo de Zinc y la presencia de hembras de Meloidogyne sp. parasitando la raíz del nogal.

Multi-objective optimization of energy use and environmental emissions for walnut production using imperialist competitive algorithm

Although the agricultural sector is an important source of bioenergy production, this production can be considered sustainable when energy consumed and environmental emissions are optimal. As such, the assessment of energy flow, environmental emissions of walnut orchards in Alborz province of Iran and their simultaneous optimization by multi-objective imperialist competitive algorithm are the main goals of this investigation. Input-output energy analysis, IMPACT 2002+ method of life cycle assessment, and multi-objective imperialist competitive algorithm are used in the energy-environmental evaluation for optimization in this study. Results ascertain that energy uses of the entire output and input are computed to be 31,015 and 27200 MJ ha−1, respectively and that gasoline with 40% is the dominated consumer of energy. Moreover, energy use efficiency is 0.88, which indicates energy inefficiency in walnut production. Environmental results shows that On-Orchard emissions with a share more than 50% in ecosystem quality, human health, and climate changes and gasoline in resources category are the main hotspots. Multi-objective optimization illustrates that the reduction in total energy is 19316 MJ ha−1 (about 62%) and gasoline with 58% is the most energy saving input among all. On the other hand, the total weighted emission decreases by about 1.47Pt (about 40%). Generally, results reveal that timely maintenance can help orchardist attain close to optimal condition. Furthermore, the application of imperialist competitive algorithm not only can offer optimum pattern of walnut production, but also be extended to the world for different crops.

Nutrient imbalance diagnosis in walnut orchards by using DRIS and PCA Approaches in the northern part of Erbil governorate-Iraq.

The use of Integrated Diagnosis and Recommendation System (DRIS) on the concept of a plant's nutritional balance has become an efficient method for assessing plant nutritional status; this method places nutrient limitations in order of plant demand, enabling the nutritional balance between the nutrients in the leaf sample. Aim of this study is to establish walnut DRIS norms and diagnosis nutrient imbalance by using DRIS and PCA methods. One hundred four leaf samples were collected during two consecutive years (2016 and 2017) from three walnut orchards in Erbil governorate/ Iraq. The results show that the smallest average NBI values are 125.6 and 27.2 respectively for both studied years which was coincided by high walnut productivity. The most limiting nutrient descending order as Fe>Na>Ca>K>P>N>Mg respectively for first-year samples, and N>Na>P>Fe>Mg>Ca>K respectively for the second year. From the result of principal component analysis (PCA) reveal that the nutrient concentration was explained in the low and high yield subgroups and the DRIS index by 61.95%, 87.75% and 58.67% respectively for first-year and 79.22%, 60% and 65.95% respectively for second-year sampling. Several nutrient interventions in a single PC indicate that no nutrient imbalance in isolation could be diagnosed.

First Report of Diaporthe cynaroidis and D. australafricana Associated with Walnut Branch Canker in Chile

In 2017, with more than 40,000 planted hectares, Chile became the second exporter of English walnut (Juglans regia) worldwide with a production of about 100,000 tons1. In 2017, low incidence of branch canker from old pruning wounds was observed in young walnut orchards cv. ‘Chandler’ in the Maule region of Chile. Fifty symptomatic wood samples were collected from ten trees in two orchards. Isolates were recovered from the wood necrotic lesions displaying a light to dark brown discoloration in the cortical and vascular tissue as previously described2. The isolates were identified as Diaporthe cynaroidis and Diaporthe australafricana based on morphological characteristics and DNA sequencing. Both species were grown on Potato Dextrose Agar medium and sterile grape leaves to induce sporulation but only D. cynaroidis produced alpha conidiospores. Alpha conidia were fusiform to ellipsoid, with a truncate base and an acutely rounded apex, initially aseptate, becoming brown at maturity, with size of 6.1 µm ± 0.5 × 2.5 µm ± 0.1. Beta conidia were extremely rare. Fungal DNA was extracted from fungal colonies with the DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). The internal transcribed spacer (ITS), elongation factor (EF) and s-tubulin (sT) loci were amplified using primer pairs (ITS1/ITS4, EF728F/EF987R, and Bt2a/Bt2b) and methods previously described3. One isolate from each species was sequenced and D. cynaroidis (isolate #2248) and D. australafricana (isolate #2249) showed 99.13% and 99.65% sequence homology with NCBI voucher specimens MB#506209 and MB#344439, respectively. Sequences were deposited in the GenBank database; D. australafricana accession numbers ITS, KC343038; EF, KC343764; BT, KC344006; and D. cynaroidis accession numbers: ITS, KC343058; EF, KC343784; BT, KC344026. Pathogenicity tests were performed by drilling a hole in stems of two-year old walnut trees cv. ‘Chandler’ (n=20) and inoculating with D. cynaroidis and D. australafricana isolates using 25 µl of inoculum at 1×104 spores/µl. Ten control plants were treated with 25 µl sterile water. The experiment was repeated two times on separate sets of trees. After 16 weeks of incubation in a shaded open house, the lesions were light to dark brown in both the cortical and vascular tissues. The lesion length produced by D. australafricana averaged 31.9 mm ± 8.8 mm, D. cynaroides averaged 26.5 mm ± 7.1 mm and both were significantly longer (P <0.0082 and P <0.0061, respectively) than the control, which averaged 1.3 mm ± 0.6 mm. Both Diaporthe species were re-isolated from all the inoculated plants and identified by colony morphology in order to fulfill Koch’s postulate. Previously, only D. neotheicola and D. rushicola were reported to be pathogenic to walnut in California2 and Spain4. D. australafricana was only reported as the causal agent of stem canker of grapevine (Vitis vinifera L.) in Australia and South Africa5 and of blueberry (Vaccinium corymbosum L.) in Chile6. Additionally, D. cynaroidis has been identified as a pathogen of king protea (Protea cynaroides L.) in South Africa6. Blueberry, grape, and king protea are all grown in Chile and these findings warrant further investigation in order to determine the host range, distribution and incidence of these pathogens in the area.

Effects of straw mulching practices on soil nematode communities under walnut plantation

Agricultural management techniques such as mulching with crop straw can impact soil properties and may in turn change the structure and function of the soil food web. We investigated different straw mulching types and straw mulching coverage levels on soil nematodes community structure in walnut orchards. We set up a randomized experimental design with three straw mulch types, and three straw mulch distance treatments in a walnut plantation. The results indicated that the number of soil nematodes after straw mulching was lower than that found in the control (CK). However, the metabolic and structure footprints of the omnivore-predator nematodes showed higher values as compared to CK. The abundances of plant parasite and omnivore-predator nematodes were negatively correlated with ammonium nitrogen (NH4+–N) and dissolved organic nitrogen (DON), whereas soil moisture content (SM) had a negative correlation with the abundance of total nematodes. High structure index (SI), maturity index (MI) and low enrichment index (EI) values revealed a structured soil food web, medium soil enrichment, and fungal decomposition channel under the mix straw mulching treatments. Soil nematodes should be used as an indicator of soil functional changes resulting from straw mulching.