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'Gala' is an apple cultivar with a distinctive aroma and flavor. 'Gala' storage season is short in regular atmosphere (RA). Controlled atmosphere (CA) extends 'Gala' storage but volatile production is reduced. 'Gala' odor-active aroma compounds were identified using Osme, a gas chromatography and olfactometry technique. Changes in aroma after RA and CA storage were characterized by Osme and descriptive sensory analysis (DSA). Hexyl acetate, butyl acetate and 2-methylbutyl acetate were emitted in the largest amounts and were perceived with the strongest intensities, with "ripe apple", "solvent" and "fruity" descriptors. Production of hexyl acetate and butyl acetate after CA storage decreased significantly compared to apples stored in RA, along with perceived intensities. 2-Methylbutyl acetate only decreased in apples stored 20 weeks in CA. Other esters with an apple odor were butyl 2-methylbutyrate and hexyl 2-methylbutyrate. Methyl 2-methylbutyrate, ethyl 2-methylbutyrate and propyl 2-methylbutyrate had sweet, fruity, and berry-like odors. Ester production after CA storage decreased at different rates. The non-ester compounds 4-allylanisole (anise) and 0-damascenone (grape juice) as well as an unidentified compound (watermelon), were perceived mostly from RA stored fruit. Other unidentified peaks had cucumber, mushroom, adhesive tape or skunk odors. Comparison of mixtures of 'Gala' odor-active compounds in water with whole 'Gala' apples revealed that hexyl acetate, hexanal and butyl acetate were necessary to impart an apple odor. 2-Methylbutyl acetate and methyl 2-methylbutyrate also contributed to the least difference between mixture solutions and apples. DSA of 'Gala' apples stored in RA and CA confirmed the general decrease in fruity aroma following CA storage. A floral descriptor was also significantly affected by CA storage. A musty note appeared in CA stored fruit, which may have corresponded to a garlic odorant peak detected during Osme. 'Gala' apples stored 16 weeks in CA followed by 4 weeks in RA emitted more volatiles than fruit stored 20 weeks in CA. The difference in volatile production was perceived by Osme analysis, and differences in overall fruity aroma between 16 and 20 weeks CA stored fruit were perceived only for whole fruit. There was no difference between those two types of storage for fruit flavor. / Graduation date: 1998

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Dwarf apple tree growth and yield under several non-herbicidal ground management systems were compared. Six ground cover systems were established in two newly planted orchards. After two growing seasons, trees in the straw mulch and geotextile mulch treatments had larger trunk cross-sectional areas and more shoot growth than trees in the red fescue and insectary plant cover treatments. Growth of trees under the manure mulch and cultivation treatments was intermediate. When four of the systems were established along rows of five-year old trees in an existing orchard, the increase in trunk cross-sectional area over two growing seasons was greatest for trees in the manure mulch and straw mulch followed by tose in geotextile mulch, trees in the red fescue grew least. The use of a mulch, such as straw or geotextile, has a favourable effect on growth and has potential for use in organic orchards.

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Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Various experiments were undertaken over a period of five years to investigate the feasibility of initiating a large-scale programme of controlled apple breeding and selection for the improvement of climatic adaptation, using budbreak number (NB) as a practical criterion of selection. NB is preferred to time of budbreak as sole criterion on the grounds that early budbreak is associated with low NB under local conditions. Variation within and between adult and juvenile seedling families was investigated and the genetic control of the traits involved was assessed, as well as direct and correlated responses to selection. In initial experiments different rating criteria for NB as measure of chilling requirement were tested in association with vegetative and reproductive budbreak time and flowering duration, viz, a classification index based on number and distribution of budbreak (pDS grade), an index where shoot length with increased budbreak was included in the index calculation (pDS index) and bud break number expressed as number per 100 cm of shoot length (NB index). Variance analysis (ANOVA and Variance component analyses) detected significant variation within seedling families for budbreak time and NB, but estimates of genetic components of variance between families were generally low. High genetic variance among seedlings within families is most likely due to the high level of heterozygosity in the parental cultivars as is characteristic of vegetatively propagated crops. Intra-class correlation coefficients for clones within and between families indicate moderate genetic determination for NB with broad sense heritabilities around 30 percent. Realized heritabilities calculated from response to two-way truncation selection were between 40 and 60 percent. For budbreak time (reproductive and vegetative), the broad sense heritability averaged around 75 and 69 percent, respectively, indicating a high degree of genetic determination. Significant response to selection for NB of one-year-old shoots of young seedlings and from seedlings grown into adult trees showed that pre-selection for increased budbreak successfully identified seedlings genetically inclined to more and better distribution of budbreak within a set time of 21 days after initial budbreak. Correlated responses indicated additional advantages of practical and horticultural value, viz, uniformity and position of bud break, and the number and length of side shoots. In general, it is concluded from responses to two-way selection that utilizable genetic variance in NB is present within seedling families and thus that selection may successfully be applied as an early screening method for increased budbreak in adult trees. The NB index of intact one-year-old shoots under prevailing sub-optimal winter conditions is therefore proposed as criterion of selection for improvement of climatic adaptation, and combined selection utilizing genetic variation between and within crosses as the selection method. / AFRIKAANSE OPSOMMING: Verskeie proewe is oor 'n periode van vyf jaar uitgevoer om die toepaslikheid van 'n grootskaalse appelteel- en seleksieprogram vir die verbetering van klimaatsaanpasbaarheid te ondersoek met 'aantal knopbreke' (NB) as praktiese seleksiekriterium. NB word verkies bo tyd van knopbreek op grond daarvan dat vroeë knopbreek onder plaaslike toestande met lae NB gepaard gaan. Variasie binne en tussen volwasse en jong saailingfamilies en die genetiese beheer van die betrokke eienskappe is ondersoek, asook direkte en gekoreleerde seleksieresponsie. In die aanvangs-eksperimente is verskillende kriteria vir die kwantifisering van aantal knopbreke getoets as potensiële maatstawwe van die inherente kouebehoefte in appelsaailinge. Die tyd van vegetatiewe en reproduktiewe knopbreek en blomperiode is ook getoets. Die volgende indekse is gebruik: 'n klassifikasie-indeks om die aantal en verspreiding van knopbreke te beskryf (pDS graad), 'n indeks waar die lootlengte, met verhoogde aantal knopbreke, ingesluit is in die berekening van die indekswaarde (PDS indeks), en knopbreke uitgedruk as die aantal per 100 cm lootlengte (NB indeks). Variansie analise (ANOVA en variansie komponent analise) het betekenisvolle variasie binne saailingfamilies aangetoon vir tyd van, en aantal knopbreke. Ramings van genetiese komponente van variansie tussen families was relatief klein. Hoë genetiese variansie tussen saailinge binne families is waarskynlik te wyte aan die hoë vlak van heterosigositeit in die ouergenotipes, wat kenmerkend is van gewasse wat vegetatief voortgeplant word. Intraklas korrelasie koëffisiënte vir klone tussen en binne families het gedui op 'n middelmatige oorerflikheid in die breë sin (ongeveer 30 persent) vir aantal knopbreke. Verhaalde oorerflikhede wat bereken is vanaf responsie op twee-rigting atknottingsseleksie was tussen 40 en 60 persent. Vir tyd van knopbreek (vegetatief en reproduktief) was die breësin oorerflikhede ongeveer 75 en 69 persent, onderskeidelik, wat aanduidend is van 'n hoë graad van genetiese bepaling. Betekenisvolle responsie op seleksie vir NB van jong saailinge en saailingbome wat volwassenheid bereik het toon dat pre-seleksie vir knopbreke saailinge kan identifiseer wat geneties meer knopbreke en 'n beter verspreiding van knoppe binne 'n periode van 21 dae na die eerste knopbreek lewer. Gekorreleerde responsie op seleksie toon 'n addisionele voordeel van praktiese en tuinboukundige belang, naamlik, meer en langer sylote. In opsomming kan dit gestel word dat responsie op twee-rigting seleksie bruikbare genetiese variasie vir NB binne saailingfamilies ontgin het en dat seleksie vir verhoogde aantal knopbreke suksesvol toegepas kan word. Die NB indeks op een-jaar-oue hout word dus voorgestel as seleksiekriterium vir verbetering van klimaatsaanpasbaarheid onder plaaslike sub-optimale wintertoestande, en gekombineerde seleksie "combined selection" wat genetiese variasie binne en tussen kruisings benut as seleksiemetode.

Typescript (photocopy). / Digitized by Kansas Correctional Industries