Management practices to improve quality of apple nursery trees in containers

Truter, Werner Van Heerden (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The quality of nursery trees at planting has a significant effect on productivity during the early years of newly established orchards. Trees need to grow and fill their allocated space in the orchard as quickly as possible for optimal return on investment. One of the main concerns when establishing new orchards is the quality of nursery trees as well as the prolonged establishment period commonly referred to as transplant shock. Transplant shock occurs due to damage to the root system, which is aggravated by an imbalance in root to shoot volume. Different management practises and timing of these practises were evaluated on containerised apple nursery tree. The practises focussed on growth cessation and hardening-off, nitrogen reserve build-up, and defoliation. The effect of these management practises as well as different planting times and methods on spring bud break and new growth during the first growing season in a commercial orchard was investigated. Prohexadione calcium and abscisic acid showed no significant effect on growth cessation during the nursery phase, and no significant effect in spring bud break or new growth in the orchard. Trees planted in autumn showed earlier bud break whereas trees planted in spring had a higher bud break percentage. Foliar nitrogen (urea) during the nursery phase did not significantly affect spring bud break and new growth. At the rates applied, foliar copper, in comparison to 1-aminocyclopropane-1-carboxylic acid proved to be a more successful chemical defoliant in the nursery with no significant negative effect on the subsequent performance in the orchard. Dormancy management practises improved bud break in spring as well as the architecture of young trees planted in a commercial orchard. It is recommended that trees receive a six-week 6 °C cold storage period and a chemical rest breaking treatment to improve establishment. Different planting methods of containerised nursery trees did not significantly influence bud break in spring, but planting containerised trees with an undisturbed growing medium or only slightly loosening the growing medium before planting improved new lateral shoot growth and apical extension growth. Producing “feathered” single or double-leader apple nursery trees in containers proved to be difficult. Either the container was too small, thus restricting the root volume too much, or the rate and number of plant growth regulator (PGRs) applications were not enough. No clear conclusion could be made on the use of PGRs to harden-off trees or chemical defoliants in our trials. Trees planted during autumn, in a warm winter region, did not accumulate sufficient chilling, which resulted in reduced bud break during spring. This time of planting resulted in a basal dominant tree architecture. As trees were probably not managed ideally in the orchard, the treatment effects could have been masked by a lack of tree vigour during the first growing season in the orchard. A period of a six-week cold storage at 6 °C as well as a chemical rest breaking treatment are important dormancy management practises, regarding spring bud break and tree architecture, when trees are planted in warm regions. Because containerised nursery tree propagation is a new concept in South Africa, further research is needed on propagation and subsequent management of these trees.

AFRIKAANSE OPSOMMING: Die kwaliteit van kwekerybome speel ‘n belangrike rol in die produktiwiteit van nuut gevestigde boorde. Vir optimale opbrengs op ‘n belegging moet bome hul geallokeerde spasie in die boord so gou as moontlik vul. Een van die grootste bekommernisse tydens die vestiging van nuwe boorde is die kwaliteit van kwekerybome sowel as die uitgerekte vestigingsperiode wat as uitplantskok bekendstaan. Uitplantskok vind plaas as gevolg van ‘n wanbalans in die wortel tot loot volume, wat vererger word deur beskadiging van die wortelsisteem tydens hantering en vervoer van die bome. Die effek van verskillende bestuurspraktyke sowel as tydsberekeing van die praktyke was geëvalueer op appelkwekerybome wat in sakke geproduseer is. Die bestuurspraktyke het op groeistaking en afharding, opbou van stikstofreserwes en blaarval gefokus. Ondersoek was ingestel na die effek van hierdie bestuurspraktyke op knopbreek tydens die lente sowel as op nuwe groei in ‘n kommersieële boord. Proheksadioon-kalsium sowel as absissiensuur het geen betekenisvolle effek op groeistaking tydens die kwekeryproses getoon nie, asook geen betekenisvolle effek op knopbreek en nuwe groei nie. Bome wat in die herfs geplant is se knopbreek was vroeër, maar ‘n hoër knopbreekpersentasie was verkry as bome in die lente geplant is. Toediening van stikstofblaarvoeding (ureum) gedurende die kwekeryfase het geen betekenisvolle effek op knopbreek en nuwe groei gehad nie. Koperblaartoedienings was meer suksesvol in vergelyking met 1-aminosiklopropaan-1-karboksielsuur om blaarval te induseer met geen betekenisvolle negatiewe effek op die daaropvolgende produktiwitiet in die boord nie. Die persentasie knopbreek in die lente sowel as boomargitektuur was verbeter met die implimentering van dormansie bestuurspraktyke. Daar word aanbeveel dat bome ‘n ses-week periode van koelopberging (6° C), sowel as ‘n opvolg toediening van ‘n chemiese rusbreker behandeling ontvang om vestiging in die boord te verbeter. Verskillende plantmetodes het geen betekenisvolle effek op knopbreek in die lente gehad nie, maar om die bome met hul onversteurde groeimedium te plant, of om die groeimedium effens los te maak voor plant, was voordelig ten opsigte van nuwe laterale lootgroei asook apikale verlengingsgroei. Die produksie van geveërde enkel-leier bome sowel as dubbel-leier bome in sakkies was problematies. Die beperkte wortelvolume, as gevolg van die sakkie, of die lae dosis en aantal toedienings van plantgroei reguleerders (PGRs) was moontlik hiervoor verantwoordelik. Geen duidelike afleidings kon gemaak word rakende die gebruik van PGRs ten opsigte van afharding sowel as oor chemieseontblaringsmiddels nie. Verlaagde knopbreek was waargeneem gedurende die lente op bome wat in die herfs geplant is in ‘n warm winter klimaat waar onvoldoende koue geakkumuleer het. Boonop het die bome ‘n basaal dominante argitektuur getoon. Omdat bome nie optimaal in die boord bestuur was nie, kon ‘n tekort aan groeikrag gedurende die eerste groeiseisoen moontlik die effek van die verskillende behandelings maskeer het. Die opberg van bome in ‘n koelkamer vir ses weke by 6 °C, sowel as ‘n chemiese rusbreker behandeling was belangrike bestuurspraktyke met betrekking tot die dormansie periode. Hierdie praktyke was veral belangrik rakende knopbreek in die lente sowel as die boomargitektuur. Omdat kwekerybome wat in sakkies geproduseer word nog ‘n nuwe konsep in Suid-Afrika is, moet toekomstige navorsing fokus op die produksie sowel as die bestuurspraktyke van hierdie bome.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105870
This item appears in the following collections: