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Spectrum of in-vitro activity and efficacy of phosphonates for management of apple replant disease and Oomycete root rot pathogens in South Africa
Get PDFThesis (PhDAgric)--Stellenbosch University, 2018.ENGLISH ABSTRACT: In South Africa, apple replant disease (ARD) and Phytophthora root rot are two
soilborne diseases that are important in apple production. ARD occurs when old apple
orchards are replanted, causing a reduction in tree growth. Several biotic agents are
involved. In South Africa, a few Pythium spp. and Phytophthora cactorum were previously
shown to be prominent in the development of ARD, with Pratylenchus spp. occasionally
being involved. Phytophthora root rot, caused by P. cactorum, most often becomes
problematic in the 2nd or 3rd year post-plant causing tree death and reduced tree growth. The
pathogen is most likely introduced through nursery trees, irrigation water and residual soil
populations (unfumigated inter-row strips). Management of ARD mainly consists of preplant
fumigation of tree rows with chloropicrin/1,3-dichloropropene. Phytophthora root rot can be
controlled using phosphonate fungicides, but these are not registered for apples in South
Africa. Phosphonates, which breaks down to phosphite in plants, are highly mobile in plants
and can reduce disease through a direct toxic effect towards pathogens or the induction of
host plant defences.
Three orchard trials were conducted to determine whether ARD can be managed
using semi-selective chemicals and different chloropicrin formulations. In all three trials, tree
growth (trunk diameter and shoot growth) was improved significantly relative to the control
by preplant fumigation with either of two formulations of chloropicrin/1,3-dichloropropene
(formulations containing chloropicrin at 60.8% or 57.0%), or with a postplant semi-selective
treatment programme that included applications of fenamiphos, phosphite, imidacloprid and
metalaxyl. Yield increases did not always accompany the tree growth increases. In one
orchard, yield was only increased significantly by combining semi-selectives with a
fumigation treatment, whereas in the other two orchards all fumigation treatments
significantly increased yield. Phytophthora cactorum and Pratylenchus spp. likely interacted
synergistically and were important ARD pathogens.
In a second set of two orchard trials, the temporal nature of root phosphite
concentrations in asymptomatic apple trees [trees where oomycete pathogens were present
in roots, but no foliar symptoms were evident] was examined following different methods of
application of phosphonates (foliar sprays, stem sprays, soil drenching and trunk paints)
applied in summer and fall. A trunk paint application, was the best application method based
on root phosphite concentrations. Foliar sprays, which were only applied in summer, also
showed potential based on root phosphite concentrations. Phytophthora cactorum and
Pythium irregulare DNA quantities in the roots of trees receiving phosphonate treatments
were significantly lower than the quantities in the control treatment. In vitro studies showed that medium type (liquid or solid) and phosphate concentration significantly influenced the
percentage mycelial growth inhibition of P. cactorum and P. irregulare by phosphite. This
made it problematic to assess the relative effect of root phosphite concentrations as a
determinant of pathogen suppression in orchard tree roots.
A third set of trials were conducted, aimed at evaluating the curative efficacy of
phosphonates in three apple orchards with Phytophthora root symptoms. Different
phosphonate application methods (foliar sprays, trunk sprays and trunk paints), yielded
similar levels of shoot growth in trees, which was significantly better than the control in two
trials in the Grabouw region after 11-months, but not in the Koue Bokkeveld trial. Yield data
could only be obtained in the latter trial, which was also not significantly increased by
phosphonate applications. In the two Grabouw trials, all application methods yielded relative
high root phosphite concentrations for fall phosphonate applications 13-weeks postapplication, but not in the Koue Bokkeveld trial. In all three trials, P. cactorum root quantities
were not reduced by any of the phosphonate treatments.
The study showed that phosphonates have potential for managing Phytophthora root
rot in apple orchards. Phosphonates combined with other semi-selective chemicals
(fenamiphos, imidacloprid and metalaxyl), can also be used to manage ARD. The
relationship between phosphite concentrations required in tree roots for suppression of P.
cactorum and P. irregulare, and phosphite concentrations required for pathogen suppression
in vitro is unclear due to (i) various factors influencing the in vitro sensitivity of isolates and
(ii) the seasonal fluctuation of root phosphite concentration in apple trees. Future work
should focus on determining whether root phosphite concentrations are important for direct
pathogen suppression by co-quantification of root phosphite and pathogens in time course
studies in orchard trials. Furthermore, the effect of root phosphite concentrations on host
plant defence induction must be investigated.AFRIKAANSE OPSOMMING: In Suid-Afrika is appel herplantsiekte (AHS) en Phytophthora wortelvrot twee
grondgedraagde siektes wat belangrik is in appelverbouing. AHS kom voor wanneer ou
appelboorde herplant word, en veroorsaak ‘n vermindering in boomgroei. Verskeie biotiese
agente is betrokke. In Suid-Afrika was ‘n paar Pythium spp. en Phytophthora cactorum
voorheen aangewys as prominent in die ontwikkeling van AHS, met Pratylenchus spp. soms
betrokke. Phytophthora wortelvrot, veroorsaak deur P. cactorum, word meestal problematies
in die tweede en derde jaar ná plant, en veroorsaak boom-afsterwing en verminderde
boomgroei. Die patogeen word heel waarskynlik deur kwekerybome, besproeiingswater en
oorblywende grondpopulasies (nie-berookte tussen-ry stroke) ingebring. Bestuur van AHS
bestaan hoofsaaklik uit vóór-plant beroking van boomrye met chloropikrien/1,3-
dichloropropeen. Phytophthora wortelvrot kan beheer word deur die gebruik van fosfonaat
fungisiedes, maar dit is nie vir appels in Suid-Afrika geregistreer nie. Fosfonate, wat in plante
na fosfiet afbreek, is hoogs beweeglik in plante en kan siekte verminder deur ‘n direk
toksiese effek teenoor die patogene, óf deur die induksie van gasheer plantverdedigings.
Drie boordproewe is uitgevoer om te bepaal of AHS bestuur kan word deur die
gebruik van semi-selektiewe chemikalieë en verskillende chloropikrien formulasies. In al drie
proewe is boomgroei (stamdeursnit en lootgroei) betekenisvol verbeter relatief tot die beheer
deur vóór-plant beroking met enige van twee formulasies van chloropikrien/1,3-
dichloropropeen (formulasies bevattende chloropikrien teen 60.8% of 57.0%), of met ‘n náplant semi-selektiewe behandelingsprogram wat toedienings van fenamifos, fosfiet,
imidacloprid en metalaksil insluit. Opbrengs toenames het nie altyd met die boomgroei
toenames saamgegaan nie. In een boord is opbrengs slegs betekenisvol verhoog wanneer
semi-selektiewe chemikalieë met ‘n berokingsbehandeling gekombineer is, terwyl in die
ander twee boorde alle berokingsbehandelings opbrengs betekenisvol verhoog het.
Phytophthora cactorum en Pratylenchus spp. het moontlik sinergisties op mekaar gereageer
en was belangrike AHS patogene.
In ‘n tweede stel van twee boordproewe, is die temporele aard van
wortelfosfietkonsentrasies in asimptomatiese appelbome [bome waar oömiseet patogene in
wortels teenwoordig was, maar geen blaarsimptome sigbaar was nie] ondersoek, volgende
op verskillende metodes van toediening van fosfonate (blaarspuite, stamspuite,
gronddrenkings en stamverwe) toegedien in die somer en herfs. ‘n Stamverf toediening was
die beste toedieningsmetode gebaseer op wortelfosfietkonsentrasies. Blaarspuite, wat slegs
in die somer toegedien is, het ook potensiaal getoon gebaseer op wortelfosfietkonsentrasies.
Phytophthora cactorum en Pythium irregulare DNS hoeveelhede in die wortels van bome wat fosfonaat behandelings ontvang het, was betekenisvol laer as die hoeveelhede in die
kontrole behandeling. In vitro studies het getoon dat mediumtipe (vloeistof of vastestof) en
fosfaatkonsentrasie betekenisvol die persentasie miseliumgroei inhibisie van P. cactorum en
P. irregulare deur fosfiet beïnvloed. Dit maak dit moeilik om die relatiewe effek van
wortelfosfietkonsentrasies as ‘n determinant van patogeen onderdrukking in boord
boomwortels vas te stel.
‘n Derde stel proewe is uitgevoer met die doel om die kuratiewe effektiwiteit van
fosfonate in drie appelboord met Phytophthora wortelsimptome te evalueer. Verskillende
fosfonaat toedieningsmetodes (blaarspuite, stamspuite en stamverwe) het soortgelyke
vlakke van lootgroei in bome opgelewer, wat betekenisvol beter was as die kontrole in twee
proewe in die Grabouw area ná 11 maande, maar nie in die Koue Bokkeveld proef nie.
Opbrengs data kon slegs in die laaste proef verkry word, wat ook nie betekenisvol deur
fosfonaat toedienings verhoog is nie. In die twee Grabouw proewe, het alle
toedieningsmetodes relatiewe hoë wortelfosfietkonsentrasies vir herfs fosfonaat toedienings
13 weke ná toediening opgelewer, maar nie in die Koue Bokkeveld proef nie. In al drie
proewe is P. cactorum wortel hoeveelhede nie deur enige van die fosfonaat behandelings
verminder nie.
Die studie het getoon dat fosfonate potensiaal het om Phytophthora wortelvrot in
appelboorde te bestuur. Fosfonate, gekombineer met ander semi-selektiewe chemikalieë
(fenamifos, imidacloprid en metalaksil), kan ook gebruik word om AHS te bestuur. Die
verhouding tussen fosfietkonsentrasies nodig in boomwortels vir die onderdrukking van P.
cactorum en P. irregulare, en fosfietkonsentrasies nodig vir patogeen onderdrukking in vitro
is onduidelik weens (i) verskeie faktore wat die in vitro sensitiwiteit van isolate beïnvloed en
(ii) die seisoenale fluktuasie van wortelfosfietkonsentrasie in appelbome. Toekomstige werk
moet daarop fokus om vas te stel of wortelfosfietkonsentrasies belangrik is vir direkte
patogeen onderdrukking deur ko-kwantifisering van wortelfosfiet en patogene in
tydsverloopstudies in boordproewe. Verder moet die effek van wortelfosfietkonsentrasies op
gasheerplant verdediging induksie ondersoek word.Doctora
Screening indigenous nematicidal plants in Zimbabwe against Meloidogyne javanica: paper presented at a conference held on the 14th-16th July 2015, Elephant Hills Resort, Victoria Fallls, Zimbabwe
No full textTheme: 1st International Research Conference On Driving Socio-Economic Development Through Value Addition And Sustainable Use Of Resources,Plant parasitic nematodes are one of the major economically important pests of Solanaceous plants in many regions of the world including Zimbabwe, with Meloidogyne javanica, (rootknot nematode) being considered the most destructive. Recent prohibition of main soil chemical fumigants for the control of Meloidogyne javanica has prompted for the search of other alternatives to manage root knot nematodes in the horticultural industry. The present research explored plants with nematicidal properties against root knot nematode, M. javanica. Depending on plant medicinal value, leaves or bark or roots of 19 indigenous medicinal plants were screened invivo on highly susceptible tomato variety (Red khaki). Ten plant
extracts caused more than 50% gall reduction during screening under acetone extraction method. Application of botanicals was found to significantly (p≤ 0.05) reduce the formation of root galls on tomato plants. It was concluded from this study that plant extracts are potential botanical nematicides as they have ability to suppress the attack of tomato plants by phyto- nematodes and they can be used as a safe and resourceful control strategy, which can complement other control tools
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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