The role of cover crops with biofumigation potential for the suppression of plant-parasitic nematodes in vineyards

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: Plant-parasitic nematodes, consisting of a wide range of species, can cause severe economic losses in most agricultural food crops. Meloidogyne spp. (root-knot nematodes), Criconemoides xenoplax (ring nematode), Xiphinema index (dagger nematode) and Pratylenchus spp. (lesion nematodes) are some of the economically important plant-parasitic nematodes that pose a threat to viticulture and other perennial crops in South Africa. Worldwide there is ever-increasing pressure on pre-plant synthetic soil fumigants and post-plant nematicides. For sustainable nematode management, it is important to have a holistic approach; taking into consideration cultural, biological and chemical options as part of an integrated management approach. Biofumigation has the potential to fit into such an integrated management system and previous research indicates the positive response on soil-borne diseases, nematodes and weeds. Biofumigation occurs where certain plant species, containing glucosinolates (GSL) in the vacuole of the plant cells, come into contact (after cell maceration), with the enzyme myrosinase (MYR) situated in the cytoplasm of the cell, to form active compounds such as isothiocyanate (ITC). When this green manure is applied to infested soil, the ITC has the potential to have a direct suppressive effect on the soil-borne pathogens and there is also an indirect effect that can be expected after green manure soil amendment, because microbial activity is enhanced in the soil. Brassicas are known to possess GSL and MYR in their cells and thus have the potential to be utilized as biofumigation crops. There are, however, differences in the potential within the Brassicaceae family, based on different types and concentrations of GSL present in the different species. To ensure effective biofumigation it is important to use the correct brassica species and have a good understanding of the factors that have a positive impact on the biofumigation action. Laboratory bioassays were done to determine the potential of different cover crops to suppress Meloidogyne javanica and C. xenoplax, when applied as a green manure. The cover crops used for the bioassays included Oats (Avena sativa cv. Pallinup), White mustard (Sinapis alba cv. Braco), Canola (Brassica napus cv. AV Jade), Caliente 199 (Brassica juncea cv. Caliente 199) and Nemat (Eruca sativa cv. Nemat). The plant material was cut into small pieces and mixed with sterilised soil inoculated with either M. javanica or C. xenoplax. Results from the bioassays showed a significant suppression of M. javanica by the three biofumigation species: White mustard, Caliente 199 and Nemat. These results supported previous research, indicating the nematode suppressing effect due to the biofumigation action of certain brassica crops. Canola did not have the same suppressing impact on the M. javanica and gave comparable results to the control, indicating that Canola is not a good biofumigation crop for M. javanica suppression. In terms of biofumigation effect oats did not differ significantly from the control or the three brassicas: White mustard, Caliente 199 and Nemat. In the bioassays done for C. xenoplax no significant differences were found between the green manure treatments and the control. These results indicate that the different crops tested, including the three well known biofumigation crops, did not suppress the C. xenoplax at the applied biomass concentrations used in the bioassay. Crops can also be classified according to their host status for certain plant parasitic nematodes. Crop host trials were conducted to determine the crop host status of the five different cover crops, to M. javanica and C. xenoplax. The crops were planted in sterilised soil, inoculated with the latter plant-parasitic nematodes and left for 60 days, after which, a root gall index analysis was done for M. javanica and for 85 or 92 days after which C. xenoplax was extracted from the soil. All the crops evaluated had a significantly lower root gall index for M. javanica than the control. Nemat and Oats was classified as poor hosts for M. javanica. A visual inspection of the root systems of all the crops was performed to determine whether M. javanica managed to complete its lifecycle in the different root systems. On all root systems, M. javanica managed to form root galls and produce egg masses, from which (J2) juveniles emerged. This indicates that M. javanica did complete its lifecycle in the different root systems of the crops evaluated and that all the cover crops acted as hosts. The expression of the gall symptoms were, however, less severe on Nemat and Oats, compared to the others. In the C. xenoplax crop host trials, all except the Nemat treatment showed a significant difference, compared to the Tomato treatment, with lower C. xenoplax numbers being present in the other crops. The nematode numbers in the different crops, compared well with the control (only inoculated soil), indicating that the crops did not stimulate the reproduction of C. xenoplax. Canola had the lowest numbers of C. xenoplax present after the growing cycle and Caliente 199 also showed a declining trend. In South Africa, the use of annual cover crops in vineyards is an established soil cultivation practice. In a field study, Oats, White mustard, Canola, Caliente 199 and Nemat were established in a vineyard as cover crops for three growing seasons (2009/10, 2010/11, 2011/12), and evaluated for their biofumigation impact, as well as their host impact on the suppression of certain economically important plant-parasitic nematodes. Two cover crop management practices, namely mechanical incorporation (MC) into the top soil and chemical removal of the cover crop (CC) were applied to the different cover crops. Nematode samples were taken in the work row and in the vine row at different times to determine the nematode status. These periods were April/May, before planting the cover crops, as well as 0, 15, 30 and 60 days after the management practices were performed. The crop biomass, measured as dry matter production (DMP) in tons/ha, differed significantly between the different crops, but also showed substantial increases during the three cover crop growing seasons for most crops. During the three consecutive seasons, Canola (CC) and Caliente 199 (CC) showed a constant reduction in the C. xenoplax population in the vine row based on the 60 day analysis. This trend was also observed for the total plant-parasitic nematode population in the vine row for the three seasons, based on 60 day analysis. The same trend took place during the three-year trial period for all the different sampling periods (0, 15, 30 and 60 days). The results can be attributed to the host status of these crops and not primarily because of the biofumigation effect. Both the Canola (CC) and the Caliente (CC) had a substantial increase in DMP during the three growing seasons that might have played a role in this trend. White mustard (CC and MC) showed a significant increase in the C. xenoplax population in the vine row, over the three year period, based on the 60 day analysis. The same trend was found Nemat (CC) and weeds and nematicide (CC) measured at the same period. A positive result from the Meloidogyne sp. analysis was that there was no significant increase in the Meloidogyne sp. in the vine row during the three growing seasons based on the 60 day analysis. This trend was seen in all the different treatments. The results from this study opens the possibility to apply these cover crops as part of a crop rotation programme without expecting an increase in the Meloidogyne sp. population to occur in the vine row through time.
AFRIKAANSE OPSOMMING: Plantparasitiese nematodes, wat bestaan uit 'n wye verskeidenheid van spesies, kan lei tot ernstige ekonomiese verliese in die meeste landbou gewasse. Meloidogyne spp. (knopwortel nematode), Criconemoides xenoplax (ring nematode), Xiphinema index (dolk nematode) en Pratylenchus spp. (letsel nematode) is van dié belangrikste plantparasitiese nematodes wat 'n bedreiging inhou vir wingerd en ander meerjarige gewasse in Suid-Afrika. Wêreldwyd is daar tans toenemende druk op die uitfasering van voor-plant chemiese grondberoking middels en so ook op nauitplant nematisiede. Vir volhoubare nematode bestuur, is dit belangrik om 'n holistiese benadering te volg, in ag genome kulturele, biologiese en chemiese maatreëls as deel van 'n geïntegreerde benadering. Bioberoking het die potensiaal om deel uit te maak van so 'n geïntegreerde benadering en baie vorige navorsing bevestig hierdie positiewe reaksie, in terme van onderdrukking, wat bioberoking op grond-gedraagde siektes, nematodes en onkruid kan hê. Bioberoking kan beskryf word as die reaksie, wat plaasvind wanneer glukosinolaat (GSL), wat teenwoordig is in die vakuool van die plantselle, in kontak kom met die ensiem mirosinase (MYR), nadat selbreking plaasgevind het en die aktiewe verbinding isothiosianaat (ITC) en ander sekondêre metaboliete gevorm word. Wanneer hierdie groen plantmateriaal in die grond ingewerk word, kan ʼn direkte onderdrukkings effek, as gevolg van die ITC, asook ʼn indirekte onderdrukkings effek as gevolg van die stimulasie van mikrobe aktiwiteit, verwag word. Brassica gewasse is bekend daarvoor dat daar GSL en MYR in die plantselle teenwoordig is en hulle besit dus die potensiaal om ITC te vorm. Daar is egter verskille in hierdie potensiaal binne die Brassicaceae familie, wat gebaseer is op verskillende tipes en konsentrasies GSL. Die keuse van ʼn brassica spesie is dus belangrik, tesame met ʼn verskeidenheid van ander faktore, om optimale bioberoking te verseker. Laboratorium biotoetse is gedoen om die bioberokings effek van verskillende dekgewasse op Meloidogyne javanica en C. xenoplax, wanneer dit aangewend word as groenbemesting, te bevestig. Die dekgewasse wat gebruik is sluit in: Hawer (Avena sativa cv. Pallinup), Wit mosterd (Sinapis alba cv. Braco), Canola (Brassica napus cv. AV Jade), Caliente 199 (Brassica juncea cv. Caliente 199) en Nemat (Eruca sativa cv. Nemat). Die plantmateriaal is fyn opgesny en ingewerk in gesteriliseerde grond wat met onderskeidelik M. javanica en C. xenoplax geïnokuleer is. Resultate van die biotoetse vir M. javanica toon dat die drie gewasse; Wit mosterd, Caliente 199 en Nemat, wat alombekend is vir hul bioberoking potensiaal, ʼn betekenisvolle onderdrukkings op M. javanica tot gevolg gehad het. Hierdie biotoetse ondersteun vorige navorsing, waar effektiewe onderdrukking van sekere Meloidogyne spesies as gevolg van bioberoking verkry is. Die resultate dui ook aan dat Canola nie ʼn goeie opsie is vir effektiewe bioberoking om M. javanica onderdrukking te verkry nie. Die Hawer behandeling het nie betekenisvol van die kontrole of van die ander bioberokings gewasse verskil nie. Daar is geen betekenisvolle verskille verkry tussen die kontrole en die ander gewasse tydens die C. xenoplax biotoetse nie. Die resultate dui aan dat die dekgewasse, insluitende die drie bekende bioberokings gewasse, nie C. xenoplax onderdruk teen die toegediende biomassa konsentrasies nie. Gewasse kan ook geklassifiseer word op grond van hul gasheer status vir sekere nematode. Gasheer toetse is gedoen om die gasheer status van die verskillende dekgewasse vir M. javanica en C. xenoplax te bepaal. Dieselfde vyf verskillende dekgewasse is geplant in grond, wat vooraf onderskeidelik met M. javanica en C. xenoplax geïnokuleer is. Plante is gelos om vir `n spesifieke periode te groei waarna ʼn galindeks evaluasie is gedoen om die gasheer status vir M. javanica te bepaal en ʼn nematode ontleding gedoen is om die gasheer status vir C. xenoplax te bepaal. In die M. javanica gasheer toetse was die galindeks van al die gewasse betekenisvol laer as die kontrole. Nemat kan geklassifiseer word as ʼn swak gasheer vir M. javanica en het betekenisvol minder galle as al die ander gewasse, behalwe die Hawer, waarvan dit nie betekenisvol verskil het nie. Nemat pas dus goed in ʼn dekgewas program waar die doel is om die M. javanica populasie te onderdruk tydens die groei van die gewas. ʼn Visuele inspeksie van die wortelstelsels is ook gedoen ten einde te bepaal of die lewensiklus van M. javanica voltooi is. Wortelgalle en eiersakkies was teenwoordig in die wortels van al die verskillende gewasse en larwes het uit die eiers uitgebroei. Dit dui aan dat M. javanica daarin geslaag het om sy lewenssiklus op al die dekgewasse suksesvol te voltooi. Daar was aansienlik minder eiersakke by Nemat en Hawer; wat hul swak gasheer status bevestig. In die biotoetse vir die gasheerstatus van C. xenoplax het al die gewasse, behalwe Nemat, betekenisvol laer C. xenoplax getalle, in vergelyking met die Tamatie behandeling, tot gevolg gehad. Die nematode getalle was soortgelyk aan die kontrole (slegs geïnokuleerde grond), waar geen gewas in medium geplant is nie, en dui dus aan dat die getalle op die verskillende gewasse nie vermeerder het nie. Die Canola behandeling het die laagste C. xenoplax getalle gehad, gevolg deur Caliente 199. Hierdie gewasse toon dus die meeste potensiaal om aangewend te word in 'n rotasie stelsel of dekgewas program, waar die doel is om die C. xenoplax populasie te onderdruk. In Suid-Afrika is die aanwending van spesifieke eenjarige gewasse, as dekgewasse in wingerde, reeds ʼn standaard praktyk met verskeie voordele. In veldproewe oor ʼn tydperk van drie jaar (2009/10, 2010/11, 2011/12) is Hawer, Wit mosterd, Canola, Caliente 199 en Nemat aangeplant as dekgewasse in ʼn wingerd proefperseel. Die doel van die veldproewe was om die effek van dekgewasse op die plantparasitiese nematodes, wanneer dit aangewend word as bioberokings gewasse, te bepaal. Die gasheer status van die gewasse is ook ondersoek om te bepaal wat die effek sal wees op die nematode getalle. Twee dekgewas bestuurspraktyke is toegepas; meganiese inwerk van die dekgewasse in die bogrond (MC) en chemiese beheer van die dekgewasse (CC) en nematode monsters is op verskillende tye in die werksry en in die wingerdry geneem. Hierdie periodes sluit in April/Mei, voor die vestiging van die dekgewasse en 0, 15, 30 en 60 dae nadat die bestuurspraktyk toegepas is. Die dekgewas se biomassa produksie is, op grond van die droë massa produksie (DMP), in ton/ha gemeet, wat betekenisvol verskil het vir die verskillende dekgewas. Daar het ook `n duidelike toename in DMP plaasgevind oor die drie seisoene vir meeste gewasse. Gedurende die drie jaar periode het die Canola (CC) en Caliente 199 behandelings, gemeet 60 dae na die bestuurspraktyk, ʼn konstante afname getoon in die C. xenoplax in die wingerd ry. Dieselfde tendens het ook voorgekom gedurende hierdie periode in die totale plantparasitiese nematodes teenwoordig in die wingerd ry. Daar is ook ʼn geleidelike afnemende tendens in die C. xenoplax in die wingerd ry, oor die verskillende periodes 0, 15, 30 en 60 dae vir die drie opeenvolgende seisoene, waargeneem. Hierdie resultate kan primêr toegeskryf word aan die gasheer status van die dekgewasse, wat in die gasheer proewe as swak gashere vir C. xenoplax aangetoon is. Nog ʼn faktor wat hier ʼn rol speel is die feit dat beide die Canola (CC) en die Caliente 199 (CC) ʼn toename in DMP van meer as 2 ton, gedurende die drie jaar periode, gehad het; wat op sigself ook ʼn bydraende rol kon speel. Wit mosterd (CC en MC) het oor die drie seisoene ʼn betekenisvolle verhoging in die C. xenoplax populasie tot gevolg gehad, gebaseer op die 60 dae ontleding. Dieselfde tendens is ook opgemerk vir die ander behandelings, onder andere Nemat (CC) en die onkruid en aalwurmdoder (CC) behandeling. ʼn Baie positiewe resultaat na afloop van die drie seisoene is die feit dat daar nie ʼn betekenisvolle verhoging in die Meloidogyne sp. populasie in die wingerdry, op grond van die 60 dae onledings, plaasgevind het nie. Dit was ook die geval vir al die ander behandelings. Hierdie resultate ondersteun die moontlikheid om hierdie bioberokings gewasse deel te maak van ʼn geïntegreerde dekgewas benadering, sonder om in die proses die Meloidogyne sp. in die wingerd ry te verhoog.
Thesis (MSc)--Stellenbosch University, 2013.
Grapes -- Diseases and pests, Plant-parasitic nematodes, Theses -- Conservation ecology and entomology, Dissertations -- Conservation ecology and entomology