- Author: Brooke Jacobs
A comprehensive search for pest related publications in 2012 and 2013 revealed a few
papers of broad interest to researchers working with English walnut (Juglans regia) in California.
Over the next few weeks I will post additional lists of 2012 - 2013 publications in fruit and nut tree crop biology.
University of California affiliated research on Armillaria resistance:
Citation - K. Baumgartner, P. Fujiyoshi, G. T. Browne, C. Leslie and D. A. Kluepfel. 2013. Evaluating Paradox Walnut Rootstocks for Resistance to Armillaria Root Disease. Hortscience. 48. 1. 68-72.
Abstract - The most common rootstock for Juglans regia (Persian or "English" walnut) in California is Paradox, typically a hybrid off hindsii (Northern California black walnut) x J. regia. Unfortunately, Paradox is very susceptible to Armillaria root disease. The relative resistance to Armillaria mellea of six clonally propagated Paradox rootstocks (AX1, Px1, RR4 11A, RX1, Vlach, VX211) was evaluated and compared with that of clonally propagated J. hindsii rootstock selection W17, J. regia scion cultivar Chandler, and Pterocarya stenoptera (Chinese wingnut). In a growth-chamber assay, plants were micropropagated and rooted in vitro before inoculating the culture medium with A. mellea. At two months post-inoculation, the most resistant and susceptible Paradox rootstocks were AX1 and VX211, respectively, with 9% vs. 70% mortality, and this finding was consistent across three isolates of A. mellea and three replicate experiments. This broad range of resistance within Paradox is consistent with past field trials that tested other genotypes. Our finding of similarly high susceptibility of 'Chandler' and W17 (61% vs. 69% mortality) is in contrast to two field trials, in which other J. regia genotypes were more susceptible than those off. hindsii. A third trial, however, identified some J. regia genotypes as more resistant than those off. hindsii. Therefore, it is possible that W17, which was not previously tested, is an Armillaria-susceptible genotype of J. hindsii. Based on our findings of repeatable mortality levels across three isolates of A. mellea and three replicate experiments, the growth-chamber assay has promise, albeit with confirmed resistant and susceptible controls, for identifying putative resistant rootstocks (e.g., AX1) in preparation for a field trial with controlled inoculations.
Use for walnut hull extracts in pest control:
Citation - G. Chrzanowski, B. Leszczynski, P. Czerniewicz, H. Sytykiewicz, H. Matok, R. Krzyzanowski and C. Sempruch. 2012. Effect of phenolic acids from black currant, sour cherry and walnut on grain aphid (Sitobion avenae F.) development. Crop Protection. 35. 71-77.
Abstract - The influence of naturally-occurring phenolic acid mixtures from selected plants was tested against the grain aphid (Sitobion avenae F.). Phenolic acids were extracted from the leaves of black currant (Ribes nigrum L), sour cherry (Prunus cerasus L) and walnut (Juglans regia L), as well as from the green husks of walnut. The highest content of total phenolic acids and individual compounds such as p-hydroxybenzoic, p-coumaric, chlorogenic and vanillic acids were determined in J. regia. Ferulic and tannic acids were found only in J. regia. In laboratory bioassays, the phenolic acids extracted from plants prolonged the aphid prereproductive period by 1.5-3.0 days and reduced daily fecundity by 1-1.5 offspring. The strongest effects were observed after application of phenolic acids from the leaves and green husks of J. regia. The grain aphid used glutathione S-transferase (GST), peroxidase (POD) and polyphenol oxidase (PPO) in response to the application of plant phenolic acids. An increase in aphid GST activity was found in response to treatment with all extracts. Induction of PPO and POD was shown 24 h after the application of phenolic acids mixture from leaves of walnut; inhibition was observed after 48 and 168 h in response to treatment with both extracts of walnut. An inverse relationship between the POD and PPO activity of the aphids was found 24 h after application of the black currant and sour cherry phenolic acids. After 168 h, the activities of these enzymes were higher in treated aphids compared to unsprayed insects. Mixtures of phenolic acids naturally occurring in phenol-rich plants might be used as biopesticides to control the grain aphid as a part of an integrated pest management programme. (C) 2012 Elsevier Ltd. All rights reserved.
New walnut pest in Europe:
Citation - U. Bernardo, R. Sasso, M. Gebiola and G. Viggiani. 2012. First record of a walnut shield bearer Coptodisca (Lepidoptera: Heliozelidae) in Europe. Journal of Applied Entomology. 136. 8. 638-640.
Abstract - A leafminer of the Nearctic genus Coptodisca Walsingham (Lepidoptera: Heliozelidae), a species of potential economic interest, is reported for the first time from Europe, infesting the black (Juglans nigra L.) and the common walnut (Juglans regia L.). Mines were collected since September of 2010 in several sites of two Italian regions (Campania and Lazio). The species is rather similar to Coptodisca juglandella (Chambers), the only Coptodisca known to attack walnuts, but at present, an unambiguous identification cannot be provided because of the unsatisfactory characterization of this leafminer and congeneric species. Three generations were recorded per year and leafminers overwinter as mature larvae. The first adults emerged in MayJune while mature larvae of the last generation started the overwintering in September. During the last generation of the year, infestation levels of leaves were 100% in all sampled localities. Several species of parasitoids were reared from infested mines, with specimens belonging to the genus Chrysocharis (Hymenoptera: Eulophidae) being the most frequent parasitoids.
Walnut blight resistance:
Citation - A. Solar, J. Jakopic, R. Veberic and E. Stampar. 2012. Correlation between xanthomonas arboricola pv. juglandis severity and endogenous juglone and phenolic acid in walnut. Journal of Plant Pathology. 94. 1. 229-235.
Abstract - Endogenous phenolic compounds in walnut fruits were correlated with the severity of walnut blight caused by Xantbomonas arboricola pv. juglandis (Xaj) assessed in the field, to determine the possible role of phenolics in resistance to the disease. Healthy fruits of the cvs Franquette, Cisco, and Sampion with different susceptibilities to infection by Xaj were sampled from diseased trees three times during growth and analysed using HPLC with a PDA detector. An identical phenolic profile, consisting of juglone and six phenolic acids (ellagic, gallic, syringic, p-coumaric, caffeic, and chlorogenic), was detected in the studied cultivars. Juglone was the most abundant,, ranging between 373 mg 100 g(-1) and 5,074 mg 100 g(-1) DW, compared to the least abundant caffeic and p-coumaric acids, which did not exceed 10 mg 100 g(-1) DW. A negative correlation between the total amount of phenolics present in the fruit tissues and blight severity was found in all cultivars, indicating the role of these compounds in the fruit-bacteria interactions. As the major phenolic characterized by the strongest seasonal fluctuations, juglone seemed to have the main and negative relation with disease development during the year. Thus, its involvement into the defence mechanism of walnut against bacterial blight is strongly suspected. The same may apply to gallic acid, considering its seasonal variations with respect to disease incidence. Additional studies including in vitro determination of the anti-bacterial activity of some phenolics, and their response to artificial inoculation with Xaj seem desirable to clarify the role of phenolic compounds in walnut resistance against this bacterium.
Fungal flora associated with walnut in Saudi Arabia:
Citation - A. Bahkali, A. M. A. El-Samawaty, M. A. Yassin, M. A. El-Naggar and M. H. Mahmoud. 2013. Toxigenic Fungal Biota Associated with Walnut in Saudi Arabia. Journal of Pure and Applied Microbiology. 7. 2. 1079-1086.
Abstract - Mycoflora associated with 120 walnut samples was examined using agar plate method. Data of isolation frequency were statistically analyzed. Mycotoxin productivity of obtained fungi was assayed using HPLC. Twelve species belonging to six fungal genera were isolated in this work. Aspergillus flavus, Aspergillus niger and Rhizopus stolonifer were the most predominant, with highest distribution over samples. Significant to highly significant positive correlation was found among some isolated fungi. Most of Aspergillus flavus isolates were capable of producing sterigmatocystin, maltoryzine and aflatrem. Meanwhile, all tested isolates of Aspergillus niger were capable of producing oxalic acids ranged from 300-850 mg/ml in the culture media. Both of Fusarium proliferatum and Fusarium sub glutinans were toxigenic and varied in their productivities of ipomeanine, neosolaniol, nivalenol and NT-2 toxin. In respect to citrinin and citreovirdin, Penicillium aurantiogriseum was more productive than Penicillium brevicompactum.