Reproductive bud development in pears

Reynolds, Louis Percy (2004-03)

Thesis (MScAgric)--University of Stellenbosch, 2004.

Thesis

ENGLISH ABSTRACT: Reproductive bud development is the first step of sexual reproduction of plants and is a major factor determining yield. For consistent yields in pears, knowledge of the development of the reproductive bud is required. The development of the reproductive bud with emphasis on the primordial bourse shoot was studied. The bourse shoot is important because of the ability of a bourse shoot to become reproductive, which can lead to bourse-overbourse bearing. The progression of reproductive bud development in 'Forelle' and 'Rosemarie' was studied from primordial bourse shoot initiation until dormancy the following season. The primordial bourse shoot was initiated in January 2003. The primordial bourse shoot progressed during dormancy with a plastochron length of 60 days in June. The rate of preformed leaf formation increased rapidly until August when the plastochron was 5 days. 'Rosemarie's' primordial bourse shoot development was more advanced at full bloom, which is a possible reason for the higher bourse-aver-bourse bearing habit of the cultivar. The number of leaves of the bourse shoot was more than with the 'Forelle', which has a low tendency for bourseover- bourse bearing. Flower initiation of the terminal bourse shoot bud was 56 and 77 d.a.f.b. for the 'Forelle' and 'Rosemarie', respectively. Initiation was well correlated with bourse shoot growth cessation. An increase in mitotic activity occurred during flower differentiation of the terminal bourse bud with a peak of floral appendage formation during December and January. From February until dormancy enlargement of the floral parts took place. The influence of severe dormant pruning and the quality of 2- year-old wood, on reproductive bud sink strength of 'Packham's Triumph' trees were investigated. The sink strength of primary growth increased by 40 % for short bearing units (SBU's) and 140 % for thick bearing units (BU's) as compared to long bearing units (LBU's) and thin BU's respectively. The increase in primary growth was due to better fruit set and larger fruit in the SBU's and the thick BU's. Since the increase in primary growth is less for SBU's compared to thick BU's the conclusion, which can be made, is that branch diameter influenced sink strength more than branch length. With increase in branch diameter the size of the xylem transport system increases more than that of the phloem. The increase in xylem transported metabolites, in particular root derived cytokinin seems to predominantly influence the magnitude of the sink strength. The influence of scoring and 6-benzyladenine (BA) application, during the flower induction phase on 'Doyenne du Cornice' and 'Rosemarie', were studied. Scoring caused a 50 % increase in fruit number of 'Doyenne du Cornice', which resulted in a 38 % increase in yield compared to the control. The increase in fruit number was due to higher percentage reproductive buds and improved bud quality. For the 'Rosemarie' scoring at the correct time resulted in a 40 % increase in reproductive buds. Scoring disrupts basipetal transport in the phloem, which results in the removal of apical dominance and an increase in root derived cytokinin's. More meristems can respond to inductive conditions and high quality reproductive buds develop. The combination of BA and scoring, lead to more flowers per inflorescence in 'Doyenne du Cornice'.

AFRIKAANSE OPSOMMING: Reproduktiewe knopontwikkeling by die peer Reproduktiewe knopontwikkeling is die eerste fase van reproduktiewe voortplanting in plante en is belangrik, want dit bepaal die oesgrootte. Vir konstante oeste in peerproduksie moet reproduktiewe knopontwikkeling verstaan word. Die ontwikkeling van die reproduktiewe knop, meer spesifiek die primordiale beursloot is bestudeer. Die beursloot is belangrik a.g.v. die beurs-oorbeurs drawyse. Die ontwikkeling van die reproduktiewe knop van 'Forelle' en 'Rosemarie' is gevolg. Die primordiale beursloot is Januarie 2003 geinisieër en ontwikkel tydens die boom se dormante fase met 'n plastochron van 60 dae gedurende Junie. Preformeerde blaarvormingstempo neem toe tot Augustus waar die plastochron 5 dae is. 'Rosemarie' se primordiale beursloot ontwikkeling was meer gevorderd teen volblom, met meer beurslootblare reeds teenwoordig. Dit is dalk die rede vir die hoër tendens van beurs-oor-beurs drag van die kultivar in vergelyking met 'Forelle'. Die terminale beurslootknop is 56 en 77 dae na volblom geïniseer vir 'Forelle' en 'Rosemarie' respektiewelik. Inisiasie was goed gekorreleerd met beeïndiging van beurslootgroei. Blomdifferensiasie het inisiasie gevolg met 'n toename in mitotiese aktiwiteit, blomaanhangsel vorming het 'n piek bereik III Desember en Januarie. Vanaf Februarie tot dormansie het ontwikkeling hoofsaaklik in vergroting van blomorgane plaasgevind. Die invloed van strawwe dormante snoei en die kwaliteit van 2-jaar-oue dra-eenhede op sinksterkte van reproduktiewe knoppe van 'Packham's Triumph' pere is ondersoek tydens die 2002/03 seisoen. Die sinksterkte van primêre groei het 40 % toegeneem vir kort dra-eenhede en 140 % vir dik dra-eenhede in vergelyking met lang dra-eenhede en dun dra-eenhede respektiewelik. Die toename in primêre groei vir kort en dik dra-eenhede kon toegeskryf word aan beter vrugset en groter vrugte. Omdat die toename in sinksterkte minder is vir kort dra-eenhede in vergelyking met dik dra-eenhede kan die afleiding gemaak word dat dra-eenheiddikte sinksterkte meer beïnvloed as dra-eenheidlengte. Met 'n toename in dra-eenheiddikte, neem xileemvaatweefsel meer toe as floeëmvaatweefsel. 'n Toename in xileem getranslokeerde metaboliete, meer spesifiek wortel vervaardigde sitokiniene beïnvloed die sinksterkte van die reproduktiewe knoppe. Die invloed van ringelering (ringsnit deur floeëm sonder bas verwydering) en 6-bensielaldenien (BA) toediening tydens reproduktiewe knopinduksie van 'Doyenne du Cornice' en 'Rosemarie' is ondersoek. Ringelering het 'n 50 % toename in vrugaantal veroorsaak wat die oes met 38 % laat toeneem het in vergelyking met die kontrole, vir 'Doyenne du Cornice'. Die toename in vrugte was a.g.v. 'n hoër persentasie reproduktiewe knoppe en toename in blomkwaliteit. By 'Rosemarie' het ringelering 'n 40 % toename in reproduktiewe knoppe bewerkstellig. Ringelering onderbreek die basipetale vervoer in die floeëm, verwyder dus apikale dominansie, met die gevolg dat daar 'n toename in wortel geproduseerde sitokiniene is. Meer meristeme reageer op induktiewe toestande en reproduktiewe knoppe van hoë kwaliteit vorm. Die kombinasie van ringelering en BA -toediening het meer blomme per reproduktiewe knop veroorsaak.

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