Use of biostimulants as an alternate approach to achieve plant performance and fruit quality

Shereni, Clyde (2019-04)

Thesis (MSc)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Research in fruit crops using biostimulants as a strategy to improve tree performance by alleviating transplant shock and improving both yield and fruit quality under field conditions, is limited. The main aim of this study was thus to determine the efficacy of biostimulants to enhance plant performance and quality of fruit trees under South African conditions. The specific objectives were to determine: i) the effect of a combination of biostimulants on growth and fruit quality of bearing ‘Rubystar’ plum and ‘Forelle’ pear cultivars, ii) the efficacy of a combination of biostimulants to reduce transplant shock and promote establishment of non-bearing ‘Packham’s Triumph’ and ‘Celina’ pear trees and iii), the efficacy of the biostimulant application to improve transplanting and establishment success of ‘Nadorcott’ mandarin trees in the Western Cape, South Africa. The first experiment was conducted on the commercial farms of ‘Bourgogne’ in Franschhoek and ‘Avontuur’ in Villiersdorp, Western Cape, whereas the second and third experiments were conducted at the Stellenbosch University Welgevallen Experimental Farm, Stellenbosch. The first two studies consisted of two treatments: the control (no application) and a soil-based biostimulant combination (Rizofos Fruit®, Tri-Cure SP®, Premax® and Technical®). In the Franschhoek and Villiersdorp experiments, no significant differences were found between treatments, for either the plums or pears, with respect to vegetative growth and fruit quality parameters during the first season of application. However, a biological trend where the biostimulant treatment enhanced stem diameter, shoot length and yield efficiency, even though statistically non-significant compared to the control treatment in ‘Rubystar’ plums, warrants further investigation. Similarly, the second experiment also did not realise significant differences between treatments with respect to vegetative growth for either ‘Celina’ or ‘Packham’s Triumph’ trees during the first season. When considering physiology however, the biostimulant treatment recorded a significantly higher stomatal conductance for ‘Packham’s Triumph’ and ‘Celina’ compared to that of the control treatment. In the third experiment, five biostimulant treatments: compost (control), Terramax®, Kelpak®, RootAktiv® and Super Wortel® were evaluated. The RootAktiv® treatment had a significantly higher shoot growth than the Terramax® and Kelpak® treatments but was similar to the control. The Kelpak® treatment had a significantly higher root length and compared to the RootAktiv® and Super Wortel® treatments but was similar to the control. The Terramax® and Kelpak® treatments had a high SWP than Super Wortel® and RootAktiv® in March, whereas in May, Terramax®, Kelpak® and RootAktiv® treatments had a significantly higher SWP than the control and Super Wortel® treatments. The Kelpak® treatment showed significantly higher stomatal conductance than the control and Super Wortel® treatments, for the second evaluation date. Thus, contrary to expectations, significant differences and promising trends were already obtained after one season with young, non-bearing ‘Nadorcott’ mandarin trees. In addition, results suggest that the time of application and target organ (root or leaf) will be an important factor determining the efficacy of the applications. From the study, it was concluded that certain biostimulants, under specific conditions, showed promising trends in enhancing performance of perennial crops under field conditions. The importance of selecting the correct product for a specific goal, based on mode of action, was emphasised. Similarly, the lack of significant differences between treatments despite evident trends confirmed the importance of the conduction of field experiments over at least two or more consecutive seasons before final conclusions are drawn.

AFRIKAANSE OPSOMMING: Navorsing rakende die gebruik van biostimulante as strategie vir boom prestasie via bemiddeling van oorplantskok en verhoging van opbrengs en vrugkwaliteit onder veldtoestande, is beperk. Die hoof doel van die studie was om die efektiwiteit van biostimulante op verhoging van plant prestasie en vrugkwaliteit van vrugtebome onder Suid-Afrikaanse omstandighede te ondersoek. Die spesifieke doelwitte was die bepaling van i) die effek van ‘n kombinasie van biostimulante op groei en vrugkwaliteit van draende ‘Ruby Star’ pruim- en ‘Forelle’ peer kultivars, ii) die effektiwiteit van ‘n kombinasie van biostimulante op die verminderin van oorplantskok en bevordering vanvestiging van nie-draende ‘Packham’s Triumph’ en ‘Celina’ peerbome en iii), die effektiwiteit van biostimulant toedienings ter bevordering van oorplant en vestiging van ‘Nadorcott’ mandaryn bome in die Weskaap, Suid-Afrika. Die eerste studie is uitgevoer op die kommersiële plase Bourgogne, in Franschhoek, en Avontuur, in Villiersdorp. Die tweede en derde eksperimente is uitgevoer op die Welgevallen Navorsingsplaas in Stellenbosch. Die eerste twee eksperimente het bestaan uit twee behandelings: die kontrole (geen toedienings) en ‘n grondgebaseerde biostimulant kombinasie (Rizofos Fruit®, Tri-Cure SP®, Premax® and Technical®). In die Franschhoek en Villiersdorp eksperimente, is geen betekenisvolle verskille in die pruime of pere tussen behandelings gevind ten opsigte van vegetatiewe groei en vrugkwaliteitsparameters gedurende die eerste seisoen van toediening nie. Desnieteenstaande was daar ‘n tendens wat getoon het dat die biostimulant behandelings gelei het tot ‘n toename in stamdeursnit, loot lengte en opbrengseffektiwiteit (nb) in vergelyking met die kontrole by die ‘Ruby Star’ pruime, wat ‘n opvolg studie regverdig. Soortgelyk, het die tweede studie ook nie betekenisvolle verskille tussen behandelings getoon vir die vegetatiewe groei vir ‘Celina’ of ‘Packham’s Triump’ pere gedurende die eerste seisoen nie. In soverre dit blaar fisiologie aangaan, het die biostimulant behandeling ‘n betekenisvolle hoër huidmondjie geleiding getoon vir beide ‘Celina’ en Packham’s Triumph’, in vergelyking met die kontrole. In die derde studie, is vyf biostimulant behandelings geëvalueer: kompos (kontrole), Terramax®, Kelpak®, RootAktiv® en Super Wortel®. Die RootAktiv® behandeling het ‘n betekenisvolle hoër lootgroei getoon as die Terramax® en Kelpak® behandelings, maar was soortgelyk aan die res van die behandelings. Die Kelpak® behandeling het ‘n betekenisvolle hoër wortelvolume getoon as die RootAktiv® en Super Wortel® behandelings, maar was soortgelyk aan die res van die behandelings. Die Terramax® en Kelpak® behandelings het ‘n laer stamwaterpotensiaal (SWP) getoon as die RootAktiv® en Super Wortel® in Maart, teenoor die Terramax®, Kelpak® en RootAktiv® behandelings se betekenisvolle laer SWP as die kontrole en Super Wortel® behandelings in Mei. Die Kelpak® behandeling het ‘n betekenisvolle hoër huidmondjie geleiding getoon as die kompos en Super Wortel® behandelings tydens die tweede evaluasie datum. Dus, in teenstelling met verwagtings, is betekenisvolle verskille tussen behandelings reeds na een seisoen gekry in die jong, nie-draende ‘Nadorcott’ mandaryn bome. Bykomend, het resultate gedui daarop dat die tyd van toediening en teiken orgaan (lote of blare) belangrike faktore is wat die effektiwiteit van die goedienings sal beïnvloed. Uit die studie kon afgelei word dat sekere biostimulante, onder spesifieke omstandighede, belowende tendense getoon het in die verhoging van prestasie van meerjarige gewasse onder veld toestande. Die belang van die keuse van die korrekte produk vir ‘n spesifieke doelwit, gebaseer op die aksie van die produk, is beklemtoon. Soortgelyk, het die belowende tendense van die effekte van die biostimulante op boom prestasie parameters, maar gebrek aan betekenisvolle verskille tussen behandelings, die belang van die uitvoer van proewe in die veld oor ‘n langer tydperk, bevestig voordat die finale gevolgtrekkings gemaak kan word.

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