The effect of biostimulants on the performance of newly planted apple trees in fumigated soil

Thesis (MScAgric)--Stellenbosch University, 2021.

ENGLISH ABSTRACT: Apple replant disease (ARD) is a consequence of replanting apple orchards in suitable climatic areas with limited availability of virgin soils. Fumigation of ARD infected soils provides alleviation of the disease pressure. However, the influence thereof on the dynamics of natural occurring beneficial soil microbe communities has become an environmental concern. Documentation of the addition of biostimulants for sustainable rehabilitation of the soil microbial community after fumigation and enhancement of tree performance is limited under South African conditions. The aim of this study was to evaluate the effect of biostimulants on the performance of young, non-bearing apple trees, planted in fumigated soil, under local conditions. The objectives were to determine: i) the effect of biostimulants on root growth dynamics quantified with destructive and non- destructive measurements, ii) investigate the effect of biostimulants on the microbial colonization of tree roots and iii), the effect of biostimulants on aerial vegetative parameters and physiology. Treatments included Mycorrhiza, three different formulations of Trichoderma based products (Trich 1 & Trich 2), L-AA, Plant Extract, Compost and an untreated Control. The experiment was conducted on Lovenstein farm, Vyeboom, in the Western Cape on ‘Granny Smith/MM109’ trees in a randomised complete block design. Paper 1 showed significant differences between treatments for root dynamics, occurring primarily in the top layers of the soil, for both destructive and non-destructive parameters. During the first season, the lowest total root number and total root length were observed in the Mycorrhiza treatment, while Trich 1 and Trich 2 treatments showed the highest values. Seasonal trends showed that the Mycorrhiza treatment had the most prominent effect on total root area and total root volume. Significant differences between treatments regarding the total root number were reported in Paper 2, with treatments Trich 1 and 2 differing significantly from all other treatments. Additionally, possible antagonism between Trichoderma spp. and sclerotic bodies in the Compost and Trich 2 treatments was also observed. No significant differences were observed between treatments in Paper 3, neither for stress remediation nor vegetative, aerial growth. The effect of biostimulants on plant performance varied according to parameters used for quantification and product. This supported current literature reporting a lack of consistency and inconclusive results when biostimulants are applied in the field. It also indicated the importance of knowledge about the mode of action of biostimulants and the best time of intervention, in addition to selecting the correct equipment for the just phenological stage to capture plant responses after application. Nevertheless, significant differences between selective treatments in Paper 1 suggest that an adaption of the protocol may lead to more conclusive differences when repeating the study.

AFRIKAANSE OPSOMMING: Appelhervestigingsiekte (AHS) is die gevolg van die hervestiging van appelboorde in geskikte klimaatsareas met beperkte beskibaarheid van maagdelike grond. Beroking van AHS geïnfekteerde grond verskaf ‘n opsie om siektedruk te bestuur. Daarteenoor staan die groeiende bekommernis rakende die effek daarvan op die dinamika van natuurlike voordelige mikrobe-gemeenskappe in die omgewing. Dokumentasie oor die toediening van biostimulante vir die volhoubare rehabilitasie van grondmikrobe-gemeenskappe en die verhoging van boomprestasie is beperk onder Suid-Afrikaanse omstandighede. Die doel van hierdie studie was om die effek van biostimulante op die prestasie van jong, nie- draende appelbome, geplant in ‘n berookte grond, onder plaaslike toestande, te evalueer. Die oogmerke was om te bepaal: i) wat die effek van biostimulante is op wortegroeidinamika, gekwantifiseer deur destruktiewe en nie-destruktiewe metings, ii) ‘n ondersoek na die effek van biostimulante op mikrobe kolonisasie van boomwortels en iii), die effek van biostimulante op bogrondse vegetatiewe parameters en fisiologie. Behandelings het die volgende behels: Mikorrhizae, drie formulasies van Trichoderma gebaseerde produkte (Trich 1 & Trich 2), L-AA, Plantekstrak, Kompos en ‘n onbehandelde Kontrole. Die eksperiment is uitgevoer op Lovenstein, Vyeboom, in die Weskaap op ‘Granny Smith/MM109’ bome in ‘n volledig, gerandomiseerde blok ontwerp. Artikel 1 het betekenisvolle verskille tussen behandelings aangedui vir worteldinamika wat primêr in die boonste grondlae voorgekom het, in beide die destruktiewe en nie-destruktiewe parameters. Gedurende die eerste seisoen, is die laagste aantal wortels en totale wortellengte opgemerk in die Mikorrhiza behandeling, terwyl behandelings Trich 1 en Trich 2 die hoogste waardes getoon het. Seisoenale tendense het getoon dat die Mikorrhiza behandelings die prominentste effek op die totale wortelarea en totale wortelvolume gehad het. Betekenisvolle verskille tussen behandelings ten opsigte van die totale aantal wortels is gerapporteer in Artikel 2, met behandelings Trich 1 en 2 wat betekenisvol verskil het van die res van die behandelings. Bykomend, is ‘n moontlike antagonisme tussen Trichoderma spp. en sklerosia liggame in die Kompos en Trich 2 behandelings waargeneem. Geen betekenisvolle verskille is waargeneem tussen behandelings in Artikel 3 vir stres verligting of vegetatiewe, bogrondse groei nie. Die effek van biostimulante op plantprestasie het verskil afhangende van die parameter wat gebruik is vir kwantifisering en die produk. Dit het bestaande literatuur bevestig wat berig het oor die wisselvalligheid en onvolledige resultate wanneer biostimulante in die veld toegedien word. Dit dui ook op die belangrikheid van kennis rakende die metode-van-aksie van biostimulante en die beste tydstip van ingryping, ter aanvulling van die keuse van die korrekte toerusting en bepaling van die juiste fenonologiese fase om die plantreaksie na toediening, vas te lê. Desondanks het die betekenisvolle verskille tussen spesifieke behandelings in Artikel 1 aangedui dat ‘n aanpassing in die protokols mag lei tot meer konkrete verskille indien die studie herhaal sou word.

Masters