Ca-metalosate as an alternative Ca formulation for decreasing Ca related disorders in fruit trees

Le Roux, Eugene (2018-03)

Thesis (MScAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Generally, calcium (Ca) foliar applications are used to improve the Ca status of fruit and control the incidence of Ca-related disorders, viz. bitter pit (BP) in apples and albedo breakdown (AB) in citrus. The main aim of the study was to determine whether Ca-metalosate as an alternative Ca formulation is effective in decreasing Ca-related disorders in fruit trees. Firstly, the role of formulation of Ca and boron (B) foliar applications to improve fruit quality in ‘Golden Delicious’ apples was quantified. Secondly, evaluation of pre-harvest foliar applications of a chelated Ca and B combination to reduce AB in citrus was carried out. Thirdly, xylem functionality in developing fruitlets of different apple cultivars was determined, as it impacts on Ca transport into the fruit. Ca concentration of fruit 80 days after full bloom (dafb), was significantly increased by Ca nitrate [Ca(NO3)2] foliar applications compared to Ca-metalosate and the control. The incidence of BP was also significantly reduced by Ca(NO2)3 foliar applications compared to the control, but not compared to Ca-metalosate. Results indicated that Ca foliar applications with a nitrate carrier, higher Ca concentration (active), lower point of deliquescence and molecular weight/size are more effective at increasing Ca concentration of fruitlets and reduce BP incidence in ‘Golden Delicious’ apples. This confirms previous findings that formulation has an effect on the efficiency and penetration of Ca foliar applications. B-metalosate in combination with Ca-metalosate failed to significantly reduce the incidence of AB in both sweet orange cultivars (Turkey and Cara Cara). Further research under South-African conditions, with an amended protocol, including five or more Ca-metalosate foliar applications, starting from 81 dafb, is suggested to determine if metalosates can successfully reduce the incidence of AB. This protocol differs from the one used in this study, but was successful when applied as salt formulation foliar application. Ca-metalosate and control indicated lower Ca (%) in the albedo tissue of creased fruit compared to non-creased fruit, indicating that Ca plays a role in AB. At ±49 dafb, a steady decline in xylem functionality was observed in all six apple cultivars evaluated, supporting recommendations that additional Ca foliar applications should start before 40 dafb to decrease the incidence of Ca-related disorders in fruit trees. Less susceptible apple cultivars showed an earlier decline of xylem functionality (42 dafb) compared to susceptible apple cultivars (49 dafb). This is in contrast to previous findings. A relationship between Ca-related disorders and loss of xylem functionality early in the season could not be established in this trial. A slight recovery of xylem functionality in all six apple cultivars evaluated was observed later in the season, under both climatic areas and this has not been reported previously in apples. Further research on xylem functionality under South African conditions should continue. Studies should commence earlier, starting at 28 dafb, and continue until harvest, to determine whether apple cultivars experiencing an earlier loss of xylem functionality are more prone to Ca-related disorders and whether xylem functionality slightly increases later in the season. By including microscopy studies during this period, the physical disruption of xylem bundles should be confirmed.

AFRIKAANSE OPSOMMING: Oor die algemeen, word kalsium (Ca) blaartoedienings gebruik om die Ca status van vrugte te verhoog en die voorkoms van Ca verwante defekte te beheer, nl. bitterpit (BP) in appels en kraakskil in sitrus. Die hoofdoel van hierdie studie was om te bepaal of kalsiummetalosaat, as 'n alternatiewe Ca formulasie, effektief is om kalsium verwante defekte in vrugtebome te verminder. Eerstens is die rol van formulasie in Ca en boor (B) blaartoedienings gekwantifiseer om die vrugkwaliteit in 'Golden Delicious' appels te verbeter. Tweedens is gekombineerde Ca- en B-metalosaat geëvalueer as voor-oes blaartoedienings om kraakskil in sitrus te verminder. Derdens is xileemfunksionaliteit in ontwikkelende vrugte van verskillende appelkultivars bepaal. Die Ca konsentrasie van vrugte op 80 dae na vol blom (dnvb) is betekenisvol verhoog deur kalsiumnitraat blaartoedienings teenoor kalsiummetalosaat en kontrole. Die voorkoms van bitterpit is ook betekenisvol verminder deur kalsiumnitraat blaartoedienings in vergelyking met die kontrole, maar nie in vergelyking met Ca-metalosaat nie. Resultate dui aan dat Ca blaartoedienings met 'n nitraatdraer, hoër Ca konsentrasie (aktief), laer POD (punt van deliquescence) en molekulêre gewig/grootte meer effektief is om die Ca konsentrasie van vrugte te verhoog en BP voorkoms in 'Golden Delicious' appels te verminder as Ca-metalosaat. Dit bevestig vorige bevindings dat formulasie 'n uitwerking het op die doeltreffendheid en penetrasie van Ca blaartoedienings. Ca-metalosaat in kombinasie met B-metaalosaat het nie daarin geslaag om die voorkoms van kraakskil in beide kultivars (‘Turkey’ en ‘Cara Cara’) betekenisvol te verminder nie. Verdere navorsing onder Suid-Afrikaanse toestande met 'n alternatiewe protokol, vyf of meer Ca-metalosaat blaartoedienings vanaf 81 dnvb, kan oorweeg word om te bepaal of metalosate suksesvol sal wees in die vermindering van die voorkoms van kraakskil. Hierdie protokol was suksesvol met die gebruik van soutformulasie blaartoedienings (Treeby and Storey, 2002; Storey et al., 2002; Pham et al., 2012). Ca-metalosaat en kontrole het 'n laer Ca (%) in die albedo weefsel van vrugte met kraakskil aangedui, wat bevestig dat Ca 'n rol in die voorkoms van kraakskil speel (Treeby and Storey, 2002; Storey et al., 2002). Vanaf ±49 dnvb is 'n bestendige afname in xileemfunksionaliteit waargeneem in al ses appelkultivars wat geëvalueer is. Dit ondersteun vorige bevindings dat addisionele Ca blaartoedienings voor 40 dnvb moet begin om die voorkoms van Ca verwante defekte in vrugtebome te verminder (Lötze and Theron, 2006). Minder vatbare appelkultivars het vroeër 'n afname in xileemfunksionaliteit (42 dnvb) getoon in vergelyking met vatbare appelkultivars (49 dnvb). Dit is in teenstelling met vorige bevindings (Dražeta et al., 2004; Miqueloto et al., 2014). 'n Verhouding tussen Ca verwante defekte en verlies van xileemfunksionaliteit, vroeg in die seisoen, kon dus nie vasgestel word nie. Evaluasie het getoon dat xileemfunksionaliteit in al ses appelkultivars later in die seisoen herstel onder verskillende klimaatstoestande. Dit is nie voorheen in appels gerapporteer nie. Verdere navorsing onder Suid-Afrikaanse toestande rakende xileemfunksionaliteit word aanbeveel. Studies moet vroeër begin, vanaf 28 dnvb tot oes, om vas te stel of appelkultivars wat vroeër 'n verlies van xileemfunksionaliteit ervaar, meer vatbaar is vir Ca verwante defekte en of die funksionaliteit van die xileem effens later in die seisoen weer toeneem. Xileem vaatbondel disintegrasie moet bevestig word deur mikroskopie studies gedurende die seisoen.

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