Internal Ethylene Concentration Research Articles

1-Methylcyclopropene plus high CO2 applied after storage reduces ethylene production and enhances shelf life of Gala apples

The effect of a combined treatment comprising a 35% CO2 atmosphere plus 250 nL L-1 1-methylcyclopropene (1-MCP) on shelf life of Gala apples app lied after removal from air or controlled atmosphere (CA) storage was evaluated. Fruit were removed from air storage at 10 and 18 wk and from CA storage at 18 and 22 wk, warmed to 20°C and then treated for 16 h with 1-MCP either in combination with or without 35% CO2. Treated fruit were held at 20°C in air for up to 15 d and assessed every 5 d. Onset of ethylene production was delayed and quality retention was only marginally improved with the 1-MCP treatment. In contrast, both were significantly affected when a 35% CO2 atmosphere was applied in combination with the 1-MCP treatment. Fruit that were treated with 1-MCP in a 35% CO2 atmosphere exhibited the lowest levels of internal ethylene concentration (IEC) and the smallest decline of flesh firmness and titratable acidity (TA) during holding at 20°C. No symptoms of CO2 injury were noted. In the high CO2 atmosphere, a 250 nL L-1 treatment with 1-MCP resulted in similar firmness and titratable acidity retention at room temperature as did a 1000 nL L-1 treatment with 1-MCP. Additionally, the application of the combined 1-MCP/high CO2 treatment after holding at 20°C for 24 h resulted in similar effects as seen if the treatment were applied only 2 h after removal from storage. Biochemical analysis showed that 1-MCP and high CO2 have two distinctly different effects on ACC-synthase activity, explaining the synergistic effect of the combined treatment. Key words: Post-storage ripening, 1-MCP, carbon dioxide, ethylene biosynthesis

MODULADORES DA BIOSSÍNTESE E DO MECANISMO DE AÇÃO DO ETILENO SOBRE O CRESCIMENTO IN VITRO DO PORTA-ENXERTO DE MACIEIRA MARUBAKAIDO

A utilização de frascos de cultura com tampas que dificultam trocas gasosas entre o ambiente interno e externo dos frascos resulta em aumento considerável na concentração interna de etileno nos frascos de cultura, o que freqüentemente ocasiona redução na taxa de multiplicação de material vegetal in vitro. A redução da concentração do etileno na atmosfera interna dos frascos de cultura, por meio de inibição da biossíntese, ou da inibição do seu mecanismo de ação, tem promovido o aumento na taxa de multiplicação, o que reduz o tempo e o custo de produção de mudas micropropagadas. Neste trabalho, objetivou-se aumentar a taxa de multiplicação in vitro para o porta-enxerto de macieira Marubakaido pelo uso de compostos conhecidos por inibir a biossíntese ou o mecanismo de ação do etileno. Segmentos nodais de Malus prunifolia cv Marubakaido cultivado in vitro foram inoculados em meio de cultura MS (MURASHIGE e SKOOG,1962) suplementado com 2,22 µM de Benzilaminopurina, e mantidos em sala de crescimento a 27 ± 2 ºC, fotoperíodo de 16 horas, Densidade de Fluxo de Radiação Fotossinteticamente Ativa (RFA) de 40 mmol.m -2 .s -1 e umidade relativa do ar de 75 ± 5%. AVG (L-a-(2-aminoetoxivinil-glicina), AIB (ácido a-aminoisobutírico), CoCl2 (dicloreto de cobalto), e os brassinoesteróides 28-HCTS (homoetilcastasterona) e 5F-HCTS (28-homoetil- 5-flúor-castasterona), compostos moduladores da biossíntese do etileno, além de STS (tiossulfato de prata) e 1-MCP (1-metilciclopropano), conhecidos inibidores do mecanismo de ação do etileno foram empregados neste estudo, pela adição à atmosfera interna do frasco de cultivo, no caso do 1-MCP, e de aplicação foliar, no caso dos brassinoesteróides, ou pela adição ao meio de cultura, no caso dos demais compostos químicos mencionados. As variáveis avaliadas foram: comprimento das partes aéreas e sua hierarquia; número de partes aéreas medindo 1,5 cm de comprimento ou mais e partes aéreas medindo menos de1,5 cm, com identificação de sua hierarquia; e taxa de multiplicação dos explantes (número de segmentos nodais e ápices caulinares, aptos a multiplicação in vitro). Os resultados obtidos mostraram que, dentre as variáveis avaliadas, o número de ramos principais < 1,5 cm apresentou aumento da ordem de 74% quando o AVG estava presente na concentração de 5 µM no meio de cultura . Para o CoCl 2 , houve redução significativa em todas as variáveis avaliadas. Nenhuma alteração significativa foi encontrada para comprimento de ramos, número de ramos laterais ou taxa de multiplicação quando o AIB estava presente no meio de cultura. Para os tratamentos com 1-MCP e STS, os resultados apontaram para redução na taxa de multiplicação do material vegetal. Dentre os brassinoesteróides testados, somente o 5F-HCTS apresentou respostas significativas. Aumento da ordem de 83% na taxa de multiplicação do ramo principal mostrou-se relacionado à dose de 1 µg.parte aérea -1 do 5F-HCTS, tendo também sido observada elevação da ordem de 52% no número de ramos laterais ³ 1,5 cm nesta dose de 5F-HCTS. Concluindo, o brassinoesteróide 5F-HCTS apresenta potencial para ser utilizado com o objetivo de aprimorar a técnica de propagação in vitro para o porta-enxerto de macieira Marubakaido.

Scald susceptibility and biochemical/physiological changes in respect to low preharvest temperature in ‘Starking Delicious’ apple fruit

‘Starking Delicious’ apples were harvested at weekly intervals from two orchards located at 500 and 800 m elevation. The number of hours below 10 °C accumulated in the orchard was measured. Flesh firmness, soluble solids content, starch index, internal ethylene concentration, colour, fatty acid composition of peel phospholipids and estimated “antioxidant” concentration (OD-200 nm values) of fruit also were measured at each harvest date, and related to flesh firmness, soluble solids and superficial scald incidence of fruit after storage. Our data confirm that the exposure of fruit to low temperatures (below 10 °C) before harvest could trigger adaptive changes that increase tolerance to cold storage.

Harvest date and fruit size affect postharvest softening of apple fruit

SummaryThe influence of harvest date and fruit size on the three phases of softening for Royal Gala and Cox’s Orange Pippin apple cultivars is currently not known. During storage at 0.5 or 3°C, late-harvested fruit had a shorter initial slow softening phase and required less time before the internal ethylene concentration exceeded 1.5 μl–1 than fruit harvested earlier. Rate of rapid phase softening was similar for fruit from each harvest date. Unlike harvest date, fruit size did not consistently affect the harvest indices of fruit from either cultivar. Once in storage at 0.5 or 3°C the softening profiles of different sized fruit from early harvests were similar. However, small fruit softened more slowly than medium and large fruit when harvested at a late stage of maturity. Results in this study indicate that softening of these apple cultivars is not linear in storage, and that both harvest date, and to a lesser extent fruit size, influenced the degree of non-linearity by influencing the duration of the initial slow softening phase. It is also suggested that the initial slow softening phase may be a continuation of the slow softening that occurs in fruit while still attached to the tree.

Production of aroma volatiles in response to deficit irrigation and to crop load in relation to fruit maturity for ‘Braeburn’ apple

Abstract Aroma volatiles are important quality attributes for apples and there is not enough information on how their production is affected by deficit irrigation (DI) or by crop load. We investigated effects of irrigation, crop load, and their interaction on maturity-related quality attributes (aroma volatiles, total soluble solids (TSS), titratable acidity (TA), and firmness) and maturity attributes (internal ethylene concentration, ‘percent ripening fruit’, and starch pattern index) for ‘Braeburn’ apple. Multivariate relationships between these two sets of attributes were also explored. Irrigation treatments were commercially irrigated control (CI) and DI applied throughout the season. Crop load treatments were commercial crop load (CCL) having six fruits per cm 2 of trunk cross-sectional area and light crop load (LCL) having four. There was no interaction between irrigation and crop load on any individual quality attributes. Control and DI fruit had similar maturity at harvest but DI fruit became more advanced in maturity during storage at 20 °C and after cold storage. DI enhanced volatile production during ripening and after cold storage. Firmness and TSS also increased in DI fruit but the increased firmness was lost during subsequent storage. Firmness and TSS increased in LCL in some occasions but crop load had no effect on maturity or aroma volatiles. Fruit TA was not affected by irrigation or crop load. Aroma volatiles poorly correlated with each individual maturity attribute. Canonical correlation analysis showed high multivariate correlation between maturity attributes and maturity-related quality attributes with two underlying dimensions that characterised their relationships. Quality enhancement in DI fruit was related, in part, to the advancement in ripening.

Temperature and ethylene affect induction of rapid softening in ‘Granny Smith’ and ‘Pacific Rose™’ apple cultivars

The occurrence of rapid softening in apples (Malus domestica Borkh.) at ambient temperatures (10–20 °C) varies among cultivars, as some cultivars require exposure to low temperatures before autocatalytic ethylene biosynthesis occurs. The influence of time at 0.5 °C on subsequent softening at 20 °C was investigated for the slow softening ‘Granny Smith’ and ‘Pacific Rose™’ apple cultivars. Ethylene (100 μl l−1 for 24 h) was also applied to apples at 20 °C to determine if ethylene treatment could replace the requirement for cold treatment. ‘Granny Smith’ fruit without ethylene or cold treatment softened slowly at 20 °C, while both ethylene- and cold-treated fruit softened more rapidly than non-treated fruit. Non-treated ‘Pacific Rose™’ fruit also softened slowly or not at all at 20 °C, but in contrast to ‘Granny Smith’, did not soften rapidly after either ethylene or cold treatment. The mechanism by which both cold and ethylene treatments initiated rapid softening in ‘Granny Smith’ may be facilitated by ethylene, as these treatments induced maximum internal ethylene concentrations (IEC) that were two to threefold greater than in non-treated fruit at 20 °C. However, rapid softening at 20 °C was often delayed relative to the increase in IEC from basal concentrations for cold-treated ‘Granny Smith’ fruit. This delay for cold-treated ‘Granny Smith’ fruit, and absence of rapid softening in ‘Pacific Rose™’ fruit at 20 °C despite a maximum IEC of more than 100 μl l−1, suggests that fruit sensitivity to ethylene may be more important than IEC for regulating softening. ‘Pacific Rose™’ may be a genotype of apple with reduced capacity for ethylene biosynthesis and action, and hence softening. The role of ethylene in softening of both cultivars at shelf life temperatures may be clarified by research on changes in ethylene sensitivity that occur during maturation and ripening.

Stimulation of ‘Fuji’ apple skin color by ethephon and phosphorus–calcium mixed compounds in relation to flavonoid synthesis

The effect of ethephon (2-chloroethyl phosphonic acid) and a seniphos-like substance (SLS) (a mixture of 310 g/l P 2O 5, 56 g/l CaO and 30 g/l N: 1% NO 3 and 2% NH 3) on the coloring of skin of ‘Fuji’ apple were studied. Both treatments applied 4 weeks before commercial harvest, caused an enhancement of red peel color and an increase in concentration of flavonoid compounds. Anthocyanin, proanthocyanidins and flavonols showed different accumulation pattern with different treatments during fruit maturation, but eventually became similar concentrations at harvest. ACC (1-aminocyclopropane-1-carboxylic acid) oxidase activity and internal ethylene concentration were greatly increased by the ethephon treatment but slightly by SLS treatment. The ethephon treatment increased greatly the chalcone isomerase (CHI) activity, and moderately phenylalanine-ammonia lyase (PAL) activity, but showed no effect on UDP-3- O-galactosyltransferase (UFGalT), all of which are involved in flavonoid biosynthesis. On the other hand, the SLS increased PAL and UFGalT activities greatly and CHI activity moderately.

Temperature induces differential softening responses in apple cultivars

Loss of firmness in ‘Royal Gala’ (RG), ‘Cox's Orange Pippin’ (COP), ‘Granny Smith’ (GS) and ‘Pacific Rose™’ (PR) apples (Malus domestica Borkh.) was quantified in fruit held continuously at temperatures from 0 to 35 °C. Softening was triphasic, consisting of an initial slow softening phase, followed by a rapid phase, and a final slow softening phase. Loss of firmness at each temperature was described by an asymmetric, sigmoidal equation. Rate of firmness change (k) at different temperatures was described by a modified Arrhenius equation for RG and COP, where k increased with temperature from 0 through ∼22 °C, and decreased through 35 °C. This equation did not describe k at different temperatures for GS and PR, as k was similar from 0 to 12 °C, and could not be calculated for fruit at 20–35 °C as rapid phase softening was not initiated. Transition between the initial slow softening phase and the rapid softening phase was related to a rapid increase in internal ethylene concentration (IEC) for all cultivars. GS and PR had slow softening at 20–35 °C, and had delayed and slow increases in IEC. Equations used in this study could be used to estimate firmness loss at different parts of the commercial post-harvest handling chain, especially where fruit are at non-optimal storage temperatures.

An ethanol spray at veraison enhances colour in red wines

Aqueous ethanol (5% v/v) was sprayed onto bunches of Vitis vinifera L. cv. Cabernet Sauvignon 8–9 weeks following full flowering (controls were sprayed with water). Internal ethylene concentration in treated berries increased to a maximum within 6 hours, and berry colour subsequently increased substantially (maximum attained 2–3 weeks after spraying). Berry fresh weight at harvest was unaffected by ethanol treatment, but wine made from treated grapes showed greater colour intensity compared with control grapes.

The Progression of Ethylene Production and Respiration in the Tissues of Ripening `Fuji' Apple Fruit

`Fuji' apple (Malus ×domestica Borkh.) fruits were harvested periodically prior to and during fruit ripening. Ethylene evolution and respiration rates of skin, hypanthial, and carpellary tissue was determined in each fruit. Additionally, whole fruits were used for analyses of internal ethylene concentration, volatile evolution, starch content, flesh firmness, and soluble solids content. Ethylene production was greatest in the carpellary tissue at all sampling dates except the one occurring just before the rise in whole fruit internal ethylene concentration, when production in the skin and carpellary tissue was similar. Respiration was always highest in the skin, in which the climacteric rise was most drastic. Higher ethylene production in the carpellary tissue of pre- and postclimacteric fruit and higher respiration in the skin tissue, including a noticeable climacteric rise, is indicative of a ripening initiation signal originating and/or transduced through the carpels to the rest of the fruit.

An allele of the 1-aminocyclopropane-1-carboxylate synthase gene (Md-ACS1) accounts for the low level of ethylene production in climacteric fruits of some apple cultivars

An allele of the apple ripening-specific 1- aminocyclopropane-1-carboxylate (ACC) synthase gene (Md-ACS1–1) has a 5′-flanking region possessing an inserted retroposon-like sequence. Apple species can be classified into three groups that are heterozygous or homozygous for the ACS1–1 and ACS1–2 alleles. We measured the internal ethylene concentration (IEC) in climacteric fruit of 35 apple cultivars with respect to genotype. Eleven ACS1–2 homozygous cultivars exhibited much lower IECs than cultivars homozygous or heterozygous for ACS1–1. Furthermore, F1ACS1–2 homozygous progeny derived from crosses between heterozygous cultivars had fruit with a very low IEC. These results are in accord with previous data indicating the absence of transcription from ACS1–2 in a heterozygous cultivar. Since the low level of ACS1 mRNA in climacteric fruit was observed in several ACS1–2 homozygous cultivars, we conclude that the low level of ethylene production in some cultivars is caused by the mutated allele of ACS1, which is the main gene responsible for ethylene production during ripening.

Lovastatin Inhibits α-Farnesene Biosynthesis and Scald Development in `Delicious' and `Granny Smith' Apples and `d'Anjou' Pears

Effects of Lovastatin treatment on ethylene production, α-farnesene biosynthesis, and scald development were studied using `Delicious' and `Granny Smith' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] and `d'Anjou' pears (Pyrus communis L.) stored in air at 0 °C. During 6 months storage, Lovastatin did not affect internal ethylene concentration but reduced α-farnesene production in a concentration dependent manner in both apples and pears. Lovastatin reduced scald at 0.63 mmol·L-1 and inhibited scald completely at 1.25 or 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. In `d'Anjou' pears, Lovastatin at concentrations from 0.25 to 1.25 mmol·L-1 inhibited scald completely. After 8 months storage, inhibition of scald in both apples and pears by Lovastatin was concentration-dependent but none of the concentrations totally eliminated scald. Compared with 11.8 mmol·L-1 diphenylamine, Lovastatin treatment reduced scald to the same level at 1.25 mmol·L-1 in `d'Anjou' pear and 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. Lovastatin did not affect apple or pear fruit color, firmness, soluble solids content, or titratable acidity during storage in either apple or pear compared with the controls. Chemical name used: [1S-[1a (R °), 3α, 7β, 8β (2S °, 4S °), 8αβ]]-1,2,3,7,8,8α-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1-naphthaienyl 2-methylbutanoate (Lovastatin).

Citrus Fruit Abscission Induced by Methyl-jasmonate

Methyl jasmonate (MJ) was tested as a potential abscission chemical to enhance mechanical harvest of `Hamlin' and `Valenica' orange [Citrus sinensis (L.) Osb.]. In field experiments, a solution of 1, 5, 10, 20, or 100 mm MJ was applied either as a stem wrap to individual fruit or as a spray to entire trees or canopy sectors. Solutions of 10, 20, and 100 mm MJ resulted in significant and consistent reduction of fruit detachment force and caused fruit drop within 7 to 10 days. Fruit loosening was preceded by an increase in the internal ethylene concentration of fruit similar to that of other experimental abscission compounds. While concentrations of 10 mm and less caused no or negligible phytotoxicity, solutions exceeding 10 mm MJ induced unacceptable levels of leaf abscission.

439 Cultivar Variation in Response to 1-Methylcyclopropene Application to Apple Fruit in Air and Controlled-atmosphere Storage

The inhibitor of ethylene binding, 1-methylcyclopropene (1-MCP) has been applied to `Gala', `Cortland', `McIntosh', `Empire', `Delicious', `Jonagold', and `Law Rome' apples under air and/or controlled atmosphere (CA) storage conditions. 1-MCP gas concentrations ranged from 0 to 2 mL·L–1. Effects of 1-MCP were greater in CA than air storage. A dose response of internal ethylene concentrations and flesh firmness to 1-MCP was found in cultivars such as `McIntosh' and `Law Rome', whereas in others, such as `Delicious' and `Empire', ripening was generally prevented by all 1-MCP concentrations. We have further investigated the effects of 1-MCP on `McIntosh' by increasing rates of the chemical to 50 mL·L–1, and confirming that fruit of this cultivar respond poorly if fruit have entered the climacteric prior to 1-MCP application. Efficacy of 1-MCP is affected by cultivar and storage conditions, and that successful commercial utilization of the chemical will require understanding of these relationships.

184 Lovastatin Inhibits α-Farnesene Biosynthesis and Scald Development in `Delicious' and `Granny Smith' Apples and `d'Anjou' Pears

Effects of Lovastatin treatment on ethylene production, α-farnesene biosynthesis, and scald development were studied using `Delicious' and `Granny Smith' apples and `d'Anjou' pears stored in air at 0 °C. During 6 months of storage, Lovastatin did not affect internal ethylene concentration, but reduced α-farnesene production in a concentration-dependent manner in both apples and pears. Lovastatin reduced scald at 0.63 mmol·L-1 and inhibited scald completely at 1.25 or 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. In `d'Anjou' pears, Lovastatin at concentrations from 0.25 to 1.25 mmol·L-1 inhibited scald completely. After 8 months of storage, the inhibition of scald in both apples and pears by Lovastatin was concentration-dependent, but none of the concentrations eliminated scald. Compared with 11.8 mmol·L-1 diphenylamine (DPA), Lovastatin treatment reduced scald to the same level at 1.25 mmol·L-1 in `d'Anjou' pear and 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. Compared to the controls, Lovastatin did not affect fruit color, firmness, soluble solid contents, or titratable acidity during storage in either apple or pear.

Evidence that α-farnesene biosynthesis during fruit ripening is mediated by ethylene regulated gene expression in apples

The effect of ethylene regulation on α-farnesene biosynthesis in preclimateric ‘Delicious’ and ‘Granny Smith’ apples was studied using an ethylene inducer and inhibitor, α-farnesene biosynthesis precursors, and protein transcription and translation inhibitors. α-Farnesene was not detectable when internal ethylene concentrations were less than 1 μl l −1 . Correlations between internal ethylene and α-farnesene production fit the exponential growth equation and were significant in ‘Delicious’ ( y = e 0.17 ; r 2 =0.68) and ‘Granny Smith’ ( y = e 0.18 ; r 2 =0.83). When applied at harvest, aminoethoxyvinylglycine (AVG) at 200 mg l −1 inhibited both internal ethylene accumulation and α-farnesene production, whereas ethephon at 200 mg l −1 accelerated both. Adding ethephon to AVG-treated fruit after 18 days at 20°C induced internal ethylene accumulation and α-farnesene production. Ethephon induced α-farnesene production in discs from preclimacteric fruit peel as well as AVG-treated fruit peel, but α-farnesene was undetectable when cycloheximide (CHI, 50 mM), actinomycin D (Act D, 50 mM), or silver nitrate (150 mg l −1 ) were added to the ethephon-treated discs. In preclimacteric fruit discs at harvest, with or without AVG treatment, α-farnesene biosynthesis was induced by 50 μM mevalonic acid lactone (MAL) or farnesyl pyrophosphate (FPP), but not by hydroxymethylglutaric acid (HMG). Adding CHI or Act D to these discs did not affect the induction of α-farnesene by MAL or FPP.

Responses of early, mid and late season apple cultivars to postharvest application of 1-methylcyclopropene (1-MCP) under air and controlled atmosphere storage conditions

The potential for commercial application of 1-methylcyclopropene (1-MCP) to maintain quality of ‘McIntosh’, ‘Empire’, ‘Delicious’ and ‘Law Rome’ apples under air and controlled atmosphere (CA) storage conditions was investigated. These cultivars represent early, mid and late season apples with ripening rates ranging from fast to slow. 1-MCP gas concentrations used were 0.5, 1 and 2 m ll 1 , generated from measured amounts of Ethylbloc™ powder. Fruit of each cultivar were removed from storage at 6 week intervals during 30 weeks in air, or at 8 week intervals during 32 weeks in CA, and evaluated after 1 and 7 days at 20°C. Effects of 1-MCP were greater in CA than air storage. A dose response of internal ethylene concentrations and flesh firmness to 1-MCP was found in ‘McIntosh’ and ‘Law Rome’, but ‘Delicious’ and ‘Empire’ ripening was generally prevented by all 1-MCP concentrations. 1-MCP reduced superficial scald incidence, and accumulations of a-farnesene and conjugated trienols during air storage. The results indicate that the efficacy of 1-MCP is affected by cultivar and storage conditions, and that successful commercial utilization of the chemical will require understanding of these relationships. © 2000 Elsevier Science B.V. All rights reserved.

Effects of herbivory on internal ethylene production and sex expression in Cucurbita texana

Abstract1. Field‐grown Cucurbita texana was used in a study to determine if stress ethylene from damaged leaves promotes changes in sex expression.2. Internal ethylene concentrations were experimentally enhanced by inserting an ethylene‐filled syringe into the hollow chamber of an internode seven nodes from the growing tip of a branch. Branches enhanced with ethylene produced significantly more pistillate buds than control branches and experienced greater bud abortion later in floral development.3. The timing and magnitude of Diabrotica beetle leaf damage was simulated using a paper‐hole puncher (15% removed from all leaves). Simulated herbivory was applied to new growth every 3 days throughout the growing season.4. Endogenous ethylene concentrations recovered from the internode adjacent to the growing tip were significantly greater in damaged plants than undamaged plants 1 day after damage to new growth during the second and third week of the experiment, and 2 days after damage during the fourth and fifth week. By the sixth week, no significant differences were evident.5. Damaged plants produced fewer pistillate buds than undamaged plants, indicating that stress ethylene from simulated herbivory does not induce femaleness. A second messenger that suppresses pistillate bud production may be produced during damage.

Cell Wall Metabolism and Induction of Ripening Capacity in `La France' Pear as Influenced by 2,4-DP

Effects of the synthetic auxin 2,4-DP on fruit ripening of `La France' pear (Pyrus communis L.) on `Quince C' (Cydonia oblonga Mill. rootstock) were investigated. A solution of 2,4-DP at 90 μL·L-1 was applied 143, 151, and 159 days after full bloom (DAFB) to whole trees and compared with nonstored nontreated fruit and stored nontreated fruit (harvested 165 DAFB). Internal ethylene concentration in 2,4-DP-treated fruit increased more than in nonstored nontreated fruit and the level was higher the earlier the application time. Fruit firmness decreased earliest for fruit treated with 2,4-DP at 143 DAFB, followed by 151 DAFB-treated fruit and then 159 DAFB-treated fruit. In the nonstored nontreated fruit, firmness also showed a slight decrease with time. In all 2,4-DP treatments, water-soluble polyuronide (WSP) increased with ripening and hexametaphosphate-soluble polyuronide (HMP) and HCl-soluble polyuronide (HP) concentrations decreased. Most notably, WSP concentration increased earliest in fruit treated with 2,4-DP at 143 DAFB. Total concentration of neutral sugars from cell walls in each treatment decreased with time, and the levels in fruit treated with 2,4-DP at 143 DAFB were lowest at each sampling time. Arabinose concentrations were high compared with other neutral sugars throughout fruit ripening for each treatment, while glucose concentrations were high in nonripened fruit. At 193 DAFB, ≈85% of the fruit treated with 2,4-DP at 143 DAFB reached edible condition (firmness not more than 0.4 N·mm-2) on the tree. Furthermore, ≈85% of the fruit treated with 2,4-DP at 151 DAFB reached edible condition on 200 DAFB and close to 100% of the fruit treated with 2,4-DP at 159 DAFB on 207 DAFB. When ripened in a controlled room at 20 °C and 90% relative humidity after 2,4-DP treatment, the fruit treated earliest reached edible condition the soonest. Results demonstrate that 2,4-DP treatment can be used as an effective method of producing good quality fruit ripened on the tree, and that 2,4-DP may be an adequate replacement for cold storage conditioning to induce ripening capacity. Chemical name used: 2,4-dichlorophenoxy-propionic acid (2,4-DP).

Fruit Characteristics of `York' Apples during Development and after Storage

Firmness, soluble solids concentration (SSC), starch index (SI), internal ethylene concentration (IE), and titratable acid concentration (TA) of `York Imperial' apple (Malus ×domestica Borkh.) fruit changed linearly with harvest date between 152 and 173 days after full bloom (DAFB). Firmness was positively correlated with TA, SSC was correlated with SI, and SI was negatively correlated with TA. After 150 days of refrigerated-air (RA) storage, there was no relationship between DAFB at harvest and firmness or superficial scald, but the malic acid concentration declined linearly and storage decay increased linearly with DAFB. Firmness had declined to a plateau and was not correlated with any variable at harvest. Malic acid concentration after CA storage was correlated with DAFB, firmness, SSC, and SI; scald was correlated with firmness and SI; and decay was correlated with DAFB, firmness, SSC, and SI. During 150 days of controlled-atmosphere (CA) storage (2.5% O2, 1.0% CO2), firmness and TA decreased as a linear function of DAFB. Percentage of fruit with scald and scald rating changed quadratically with DAFB, and decay increased linearly with DAFB. After 150 days of CA, firmness was correlated with DAFB, SI, and IE at harvest; TA was correlated with DAFB, firmness, SSC, TA, and SI; scald was correlated with firmness and SI; and decay was correlated with DAFB, SSC, and scald index at harvest. During 250 days of CA storage, firmness, TA, scald, and decay changed linearly with DAFB in only 1 or 2 years out of 3. Formulas were created to predict firmness after CA within 10 to 12 N (2.0–2.5 lb-f) and TA to within 25%.