Physiological responses of pears to exogenous ethylene and pre-harvest factors influencing post-harvest quality with reference to 'Forelle' and 'Packham's Triumph' pears

Thesis (MScAgric)--University of Stellenbosch, 2000.

ENGLISH ABSTRACT: The major sites for fruit ripening and softening are found in the middle lamella where enzymatic and non-enzymatic mechanisms seem to degrade pectin polymers to a more soluble state and in the primary cell wall bring about the release of neutral sugars. Calcium plays a very important role in sustaining cell wall structure and cell membrane integrity. Calcium regulates various cellular functions through calmodulin, a calcium binding protein. Cell wall hydrolytic activity is a consequence of, rather than a prelude to ethylene synthesis. Fruit firmness decreased linearly in reaction to exogenously applied ethylene and a threshold level exists to which immature fruit will react on ethylene treatment. The onset of autocatalytic ethylene production rather than the respiratory climacteric seems to be critical in the ripening sequence. 'Forelle' pears are held in cold storage for 12 weeks, otherwise they will not reach a proper climacteric and will ripen unevenly. The result is that this cultivar, which already has a very late harvesting date, reaches the marketplace even later. In 1998, 'Forelle' pears harvested at commercial maturity were treated with ethylene at 0, 10 or 100 ~L·L-l. Both 10 and 100 ~L-L-l ethylene treatments significantly hastened ripening, but differences between these concentrations were negligible and it was concluded that the storage period for 'Forelle' can be shortened to 4 weeks by exogenous ethylene. In 1999, 'Forelle' pears were harvested at three maturity levels and treated with ethylene at a concentration of 50 ~L-L-l for periods of 12, 24 or 36 hours to evaluate the effect of harvest maturity and treatment length on ethylene treatment. All harvesting times required a minimum of 24 hours of ethylene to attain a physiological response. It was concluded that the storage period for 'Forelle' could be shortened to four weeks with exogenous ethylene gassing irrespective of harvest maturity. The time of attainment of a yellow ground colour and a loss of firmness differed significantly between harvesting maturities. Ethylene treated fruit in 1998 and 1999 held their firmness in cold storage very well for the whole 12 week period and fruit held at 20°C for seven days ripened normally. It seems that there is no risk of deterioration in quality for fruit held in cold storage after treatment with ethylene. 'Packham's Triumph' pears are characteristically yellow, juicy and soft when ripe, but highly susceptible to bruising. Firmer fruit are less prone to bruising injury during picking, grading, packing and transport. In 1998, physiologically young and physiologically old 'Packham's Triumph' and 'Forelle' orchards were treated with foliar applied calcium nitrate (0.7%), calcium chloride (0.7%) and urea (750 g.100L-l water) one week before harvest and harvested according to bearing position. Fruit was stored under controlled atmosphere (CA) for a period of 9 months. The four treatments had no significant effect on the storage potential of 'Packham's Triumph' and 'Forelle' pears.

AFRIKAANSE OPSOMMING: FISIOLOGIESE REAKSIE VAN PERE OP EKSOGENE ETILEEN EN VOOR-OES FAKTORE WAT NA-OES KWALITEIT BEÏNVLOED MET VERWYSING NA 'FORELLE' EN 'PACKHAM'S TRIUMPH' PERE OPSOMMING Die belangrikste fokuspunte vir vrugsagwording en rypwording is in die middel lamella en in die primêre selwand waar ensiematiese en nie-ensiematiese maganismes onderskeidelik pektien polimere afbreek na 'n meer oplosbare vorm en waar neutrale suikers vrygestel word. Kalsium speel 'n belangrike rol in die onderhoud van selwand struktuur en integriteit. Kalsium dien as 'n reguleerder van 'n verskeidenheid sellulêre funksies deur calmodulin, 'n kalsium bindende protein. Selwand hidrolitiese aktiwiteit is meer as gevolg van, as 'n voorvereiste tot, etileen sintese. Vrugstewigheid daalliniêr in reaksie op eksogene etileen en daar bestaan 'n drempelwaarde waarbyonvolwasse vrugte sal reageer op etileen. Die begin van autokatalitiese etileen produksie, nie die respiratoriese klimakterium, blyk krities te wees in die rywordings proses. 'Forelle' pere word vir 12 weke in koelopberging gehou anders sal hulle nie 'n voldoende klimakterium bereik nie en saloneweredig ryp word. Die implikasie is dat die kultivar, wat reeds 'n laat oesdatum het, die markomgewing nog later sal bereik. In 1998 is 'Forelle' pere, wat om komrnersieële volwassenheid geoes is, met onderskeidelik 0, lOof 100 f-lL·L-1 etileen behandel. Beide die 10 en 100 f-lL·L-1 etileen behandelings het rypwording betekenisvol vervroeg, maar die verskil tussen die konsentrasies was weglaatbaar klein. Die gevolgtrekking is dat die koelopberging van 'Forelle' pere verkort kan word tot 4 weke met die behandeling met etileen. Om die effek van vrug volwassenheid en behandeling lengte op etileen behandeling te evalueer is 'Forelle' pere tydens drie stadiums gedurende volwassewording geoes en behandel vir onderskeidelik 12, 24 en 36 ure met 50 f-lL·L-1 etileen. Alle stadiums van oesvolwassenheid het 'n minimum etileen behandeling van 24 uur benodig om 'n fisiologiese responsie te bewerkstellig. Die gevolgtrekking is dat die koelopberging van 'Forelle' pere verkort kan word tot vier weke met die behandeling met etileen ongeag oesvolwassenheid. Oesvolwassenheid het wel betekenisvol verskil in die tyd benodig tot die verkryging van 'n geel agtergrond kleur en 'n daling in vrugstewigheid. Etileen behandelde vrugte in 1998 en 1999 het hul vrugstewigheid uitstekend gehou gedurende die 12 weke koelopberging en het normaal sag en ryp geword wanneer pere gehou is teen 200e vir sewe dae. Daar blyk geen gevaar te wees van 'n daling in kwaliteit in koelopberging wanneer vrugte behandel is met etileen nie. 'Packham's Triumph' pere is kenmerklik geel, sappig en sag wanneer ryp, maar baie kwesbaar vir beserings. Stewiger vrugte is minder kwesbaar vir besering gedurende oes, gradering, pak en vervoer. In 1998 is fisiologiese jong en fisiologiese ou 'Packham's Triumph' en 'Forelle' boorde een week voor oes met onderskeidelik kalsium nitraat (0.7%), kalsium chloried (0.7%) en ureum (750 g.100L-l water) as 'n blaarvoeding behandel en geoes volgens draposisie. Vrugte was daarna vir 9 maande onder beheerde atmosferiese toestande (BA) opgeberg. Die vier behandelings het geen betekenisvolle effek op die opbergingspotensiaal van 'Packham's Triumph' en 'Forelle' pere gehad nie.

Masters