Broccoli Heads Research Articles

Development of colour of broccoli heads as affected by controlled atmosphere storage and temperature

Colour is one of the most important quality attributes of broccoli. Yellowing due to senescence of broccoli florets is the main external quality problem. Controlled atmosphere (CA) storage is a very effective method to maintain broccoli quality. The aim of this paper is to characterise the colour behaviour (measured by RGB colour image analysis) of broccoli as affected by CA and temperature. Data on colour behaviour and gas exchange were gathered for broccoli heads stored in containers at three temperatures and subjected to four levels of O 2 and three levels of CO 2 concentrations. An integrated colour model is proposed that combines a colour model with a standard gas exchange model. The colour model is based on an existing colour model that describes the formation of (blue/green) chlorophyllide from the colourless precursor, the bidirectional conversion of chlorophyllide into (blue/green) chlorophyll and the decay of chlorophyllide. A multi-response approach was applied, accounting for 92% of the variance. Gas exchange parameters were estimated using the gas exchange model, the colour parameters were estimated using the colour model. Both models are linked via the reaction rate constant that describes the decay of chlorophyllide, as this reaction rate constant was found to be affected by the gas conditions. The integrated model might be applied to predict colour changes of MAP packaged broccoli as a low level of O 2 and a high level of CO 2 will only affect colour retention at higher temperatures.

Effects of Nitrogen Fertilizer on Yield Quality and Nutrient Content in Broccoli

ABSTRACT This study was conducted to determine the effects of nitrogen (N) doses on yield, quality, and nutrient content in broccoli heads. Treatments consisted of 0, 150, 300, 450, and 600 kg N ha− 1. Nitrogen rates significantly increased yield, average weight of main and secondary heads, and the diameter in broccoli compared to control. The highest total yield (34631 kg ha− 1) was obtained at 300 kg N ha− 1. At harvest, the highest amount of the total N in broccoli heads was measured at 450 kg N ha− 1 application. Potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), and zinc (Zn) content increased with increases in nitrogen treatments but, phosphorus (P), copper (Cu), manganese (Mn), boron (B), and sodium (Na) contents were not influenced. Also, removed nutrients by broccoli head were highest at 300 kg ha− 1N rate.

Electron-beam irradiation of fresh broccoli heads ( Brassica oleracea L. italica)

Broccoli is a popular item in the diet of the US population, commonly found in salads ready-to-eat. The recent recalls of fresh produce due to contamination with Escherichia coli and other pathogens emphasize the need to find effective means to treat minimally processed fresh foods. Our study assessed the effect of ionizing radiation using electron beams on the shelf-life, physicochemical properties, and consumer acceptability of broccoli florets. One-hundred broccoli heads were irradiated at 1, 2, and 3 kGy with a 10 MeV linear accelerator at 22 °C. We monitored pH, color, texture, respiration rate, weight loss, chlorophyll, total carotenoids, and vitamin C of irradiated and non-irradiated samples at 5-day intervals up to 14 days at 4 °C and 95% RH. Fifty consumer panelists scored the samples using a nine-point hedonic scale. Irradiation did not affect color, firmness, pH, and weight loss of the samples. Both irradiated samples and controls showed a slight change in color during storage, though the effect was not dose-dependent. Irradiation affected ( P < 0.05) the respiration rates on the first 5 days of storage (higher CO 2 levels) but all samples, including the controls, attained the same equilibrium value. Vitamin C content of all samples decreased ( P < 0.05) with storage time. Chlorophyll and total carotenoids content followed the same trend. In terms of overall acceptability, color, odor, and texture, all irradiated samples were highly accepted by the panelists with scores of 5 and above. By the end of shelf-life, only the controls showed significant quality decline (yellow color, off-odor) due to microbial spoilage. In summary, electron-beam treatment up to 3 kGy maintains the overall quality of fresh broccoli.

Effect of Excess Fertilization with Potassium on the Occurrence of Black Spots on Broccoli Heads

Effect of Excess Fertilization with Potassium on the Occurrence of Black Spots on Broccoli Heads

Validation of irradiation of broccoli with a 10 MeV electron beam accelerator

Electron beam irradiation can inhibit pathogens in fresh produce while maintaining its quality. However, proper dose determination in complex-shaped produce is difficult, and needs further evaluation to ensure adequate irradiation treatment. The objective of this study was to establish the best treatment for irradiation of a broccoli head by comparing simulated dose distributions from Monte Carlo simulation and computed tomography (CT) scan data with those measured using standard dosimeters (alanine pellets and radiochromic films). Values of 3-D geometry and component densities of a broccoli head were entered into a radiation transport code (MCNP5) to simulate dose distribution. The broccoli head was irradiated with a 10 MeV double beam (top and bottom) linear accelerator. Dose levels ranged from 1 to 3 kGy. Several irradiation strategies were simulated (position of the product related to the beam entrance and, beam sources) and compared with the experimental data. The best results were obtained when the broccoli was irradiated at a 132.5° angle using the double beam configuration. The D max/ D min, a measure of the dose uniformity, was 1.72 around the floret and, 2.22 for the whole broccoli. These results provide valuable information for irradiation treatment planning of complex-shaped fresh produce, thus ensuring that the product is uniformly exposed to the target dose while preserving its quality attributes.

Some changes in postharvest physiology and activities of glutamine synthetase in broccoli head supplied with exogenous sucrose during storage

Sugars play indispensable roles in many metabolic processes in plants. In broccoli, the level of sugars, particularly sucrose, rapidly decline few days after harvest. This study investigated the in uence of exogenous application of 10% (w/v) sucrose to broccoli heads during storage at 20 o C. Hydration of the head was slowed down by sucrose treatment compared with the non-treated heads which gained weight by about 5% of the initial value at the end of the experimental period. Furthermore, sucrose application enhanced ethylene production as well as respiration rate. Glutamine synthetase (GS; EC 6.3.1.2) activity was higher in the  orets of sucrose-treated heads but, like the non-treated heads, the activity continuously declined until the end of the storage period. The relatively higher GS activity during the early period of storage caused the delay of the onset of ammonia accumulation by about a day. In the branchlet portion, GS activity was higher in the sucrose-treated heads until day 2 but declined thereafter. The decline in GS activity in this portion, however, did not result to ammonia accumulation. induced. However, in this study, sucrose was considered since sugars are transported to the sink tissues as sucrose; other forms of sugars could be hardly transported into the cells (Nishikawa et al., 2005). As mentioned earlier, sugar application improves the shelf life of perishable produce. However, the in uence of sucrose on glutamine synthetase activity and ammonia accumulation, which are believed to have important roles in the shelf life of broccoli, have not been investigated which formed the basis of this study. This report also presents the changes of some important physiological processes occurring in broccoli during storage.

Comparison of glucosinolate levels in commercial broccoli and red cabbage from conventional and ecological farming

Broccoli heads and red cabbage of both conventional and ecological origin were purchased from the market at monthly intervals over a 1-year period. After freeze-drying of the samples the glucosinolates were extracted, enzymatically desulphated and analyzed by HPLC-UV. Glucoraphanin, glucobrassicin and neo-glucobrassicin turned out to be the predominant glucosinolates in broccoli. Red cabbage contained similar amounts of glucoraphanin and glucobrassicin but, in addition, appreciable amounts of glucoiberin, progoitrin, sinigrin, gluconapin and glucoerucin, while neo-glucobrassicin occurred at trace levels only. No significance was found comparing the contents of glucoraphanin in the two cultivation groups for either broccoli or red cabbage. Organic broccoli and red cabbage both contained significantly higher amounts of glucobrassicin than their conventionally grown counterparts. Conventional crops of red cabbage yielded significantly higher quantities of gluconapin than ecological crops. Broccoli imported from Spain and Italy during the winter months yielded levels of glucosinolates similar to those of the home-grown products available in summer and autumn.

Accumulation of heavy metals in plants and potential phytoremediation of lead by potato, Solanum tuberosum L.

The use of sewage sludge as a source of nutrients in crop production is increasing in the United States and worldwide. A field study was conducted on a 10% slope at Kentucky State University Research Farm. Eighteen plots of 22 × 3.7 m each were separated using metal borders and the soil in six plots was mixed with sewage sludge, six plots were mixed with yard waste compost, and six unamended plots were used for comparison purposes. During a subsequent 3-year study, plots were planted with potato (year 1), pepper (year 2), and broccoli (year 3). The objectives of this investigation were to: (i) characterize chemical properties of soil-incorporated sewage sludge and yard waste compost; (ii) determine the concentration of seven heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) in sewage sludge and yard waste compost used for land farming; and (iii) monitor heavy metal concentrations in edible portions of plants at harvest. Concentrations of heavy metals in sewage sludge were below the U.S. EPA limits. Analysis of potato tubers, peppers, and broccoli grown in sludge-amended soil showed that Cd, Cr, Ni, and Pb were not significantly different from control plants. Concentrations of Zn, Cu, and Mo were significantly greater in tubers and peppers grown in sludge compared to their respective controls. Zn and Mo in broccoli heads were higher than their control plants. The ability of potato to accumulate lead needs additional investigation to optimize the phytoremediation of this pollutant element.

Genotypic and environmental effects on selenium concentration of broccoli heads grown without supplemental selenium fertilizer

AbstractSelenium (Se) is an important trace element in human nutrition that is essential to normal health. Broccoli is known to accumulate relatively high concentrations of Se, and there is strong evidence that consumption of Se‐enriched broccoli florets decreases cancer risk. In light of the above, this study was conducted to evaluate differences in Se concentration per head and total Se head content for a collection of broccoli hybrids (20) and inbreds (15) grown in field environments without supplemental Se fertilization. Our objectives were to assess the relative importance of genotype vs. environment in affecting Se levels and to determine if Se content is associated with other important horticultural traits. When analysed over three environments, there was a significant genotype effect for Se head concentration with hybrids, but not inbreds, but the environmental effect was about 10 times larger than that for genotype. Total Se content (ng/head) varied significantly among hybrids and inbreds, but as with concentration, environmental effects were also much larger for this trait. Head Se concentrations for hybrids ranged from 52.7 to 84.7 ng/g and total Se accumulation ranged from 563 to 885 ng/head. The same respective traits ranged from 49.3 to 80.0 ng/g and 678 to 876 ng/head for inbreds. There was no correlation between Se head concentration and head dry mass or days from transplant to maturity for either hybrids or inbreds. There was no evidence that Se might be diluted in broccoli heads as mass increases with cultivars that produce dense heads. Results indicate that it should be feasible to combine relatively high Se concentration or content with high head dry matter (DM), a phenotype that broccoli breeders might strive to achieve.

Nitrogen fertilization to broccoli cultivars at different planting times: Yield and nitrogen use

The effects of three nitrogen (N) fertilizer rates (0, 120, and 240 kg N ha−1) and two planting times (May or late June/July) on yield and N use of the early cultivar ‘Milady’ and the late cultivar ‘Marathon’ of broccoli (Brassica oleracea var. italica) were investigated on three silty loam soils varying in soil mineral N (Nmin) in the southernmost part of Norway during 1999 and 2001. In all crops receiving fertilizer, rapid uptake of N started about three weeks after planting. The relative yield of broccoli heads increased with increasing soil available N (fertilizer N plus Nmin) at planting to 200–250 kg N ha−1 and then levelled off. The two lower fertilizer rates were more restrictive to yields in early-planted than in late-planted crops. A general increase in harvest index with increasing N rate reflected a stronger effect of N on the head yield than on the total above ground biomass production. The apparent recovery of fertilizer N decreased with increasing N rate and was on average 74% in total above ground biomass and 25% in broccoli heads. Despite a higher N uptake, the average soil mineral N level at harvest increased from 12 kg N ha−1 on unfertilized plots to 27 and 78 kg N ha−1 on plots receiving 120 and 240 kg N ha−1, respectively; this increase was stronger in early than in late plantings and stronger in ‘Milady’ than in ‘Marathon’. The yield of broccoli heads was similar in the two cultivars, but ‘Milady’ had a lower total biomass production and thus a higher harvest index, presumably due to earlier head initiation.

Mobility of dimethoate residues from spring broccoli field

Dimethoate [O, O-dimethyl-S-(N-methylcarbamoyl-methyl) phosphorodithioate] is a broad-spectrum systemic insecticide currently used worldwide and on many vegetables in Kentucky. Dimethoate is a hydrophilic compound (log KOW = 0.7) and has the potential of offsite movement from the application site into runoff and infiltration water. The dissipation patterns of dimethoate residues were studied on spring broccoli leaves and heads under field conditions. Following foliar application of Dimethoate 4E on broccoli foliage at the rate of 0.47 L acre−1, dimethoate residues were monitored in soil, runoff water collected down the land slope, and in infiltration water collected from the vadose zone. The study was conducted on a Lowell silty loam soil (pH 6.9) planted with broccoli under three soil management practices: (i) soil mixed with municipal sewage sludge, (ii) soil mixed with yard waste compost, and (iii) no-mulch rototilled bare soil. The main objective of this investigation was to study the effect of mixing native soil with municipal sewage sludge or yard waste compost, having considerable amounts of organic matter, on off-site movement of dimethoate residues into runoff and infiltration water following spring rainfall. The initial deposits of dimethoate were 6.2 and 21.4 μ g g−1 on broccoli heads and leaves, respectively. These residues dissipated rapidly and fell below the maximum residue limit of 2 μ g g−1 on the heads and leaves after 10 and 14 d, respectively, with half-lives of 5.7 d on broccoli heads and 3.9 d on the leaves. Dimethoate residues detected in top 15 cm of soil (due to droplet drift and wash off residues from broccoli foliage) one day (d) following spraying, were 30.5 ng g−1 dry soil in the sewage sludge treatment, and 46.1 and 134.5 ng g−1 dry soil in the yard waste and no mulch treatments, respectively. Water infiltration was greater from yard waste compost treatment than from no mulch treatment, however concentrations of dimethoate in the vadose zone of the three soil treatments did not differ.

High nitrogen during growth reduced glucoraphanin and flavonol content in broccoli (Brassica oleracea var. italica) heads

Broccoli (Brassica oleracea var. italica) heads are commonly consumed in the Western diet and frequent consumption is thought to help protect against certain cancers and cardiovascular disease. Broccoli heads contain relatively high levels of glucosinolates and flavonols, thought to be the key phytochemicals that contribute to the health benefits gained upon consumption. In this study, we investigated the effect of applied nitrogen (N) at either 0, 15, 30 or 60 kg/ha, or 30, 60, 90 or 150 kg/ha with applied sulfur (S) at 50 or 100 kg/ha on the glucosinolates glucoraphanin, glucobrassicin and progoitrin, and the flavonols quercetin and kaempferol in broccoli cv. Marathon florets. Trials were conducted in two sites in either heavy clay or sandy loam to also assess the effect of soil type on phytochemical content. Application rates were based around recommended N and S applications for this crop in south-east Australia. N applications over 30 kg/ha caused a decrease in the content of glucoraphanin (18–34%) and both flavonols (20–38%). Progoitrin content was not affected while glucobrassicin increased by up to 44% with N applications &gt;30 kg/ha. S applications of 50 or 100 kg/ha had no significant effect on either glucosinolates or flavonols. Crop yield (fresh weight), however, was significantly depressed (up to 40%) by N applications below 60 kg/ha. Fresh weight was also significantly depressed in plants grown in heavy clay compared with plants grown in a sandy loam, and phytochemical content increased, possibly due to a concentration effect. Therefore, low N applications to optimise phytochemicals may be only commercially useful if growers are producing mini-broccoli heads, as levels required to optimise phytochemical content (&lt;30 kg/ha) also caused a significant decline in yield.

Effects of Age and Cold Storage of Transplants on the Growth and Quality of Broccoli Heads

Effects of Age and Cold Storage of Transplants on the Growth and Quality of Broccoli Heads In the two-factor field experiment conducted in 2002-2004 the effect of transplant age and the time of storage on the yield of broccoli cv. ‘Lord F1’ was investigated. Transplants were stored in freon cold room without access to light at +2°C and a relative air humidity of 80-85%. Both investigated factors had no significant effect on crop acceleration. Plants obtained from 4-week old transplants gained marketable yield significantly higher than plants obtained from 10-week old transplants. Significantly higher yield was obtained from transplants stored in a cooling room as compared to non-stored transplants. No univocal effect of the transplant age on the percentage of hollow stems was demonstrated.

Glucoraphanin and flavonoid levels remain stable during simulated transport and marketing of broccoli ( Brassica oleracea var. italica) heads

Fresh broccoli heads contain relatively high levels of beneficial phytochemicals, particularly glucosinolates and flavonoids, but it is not clear whether or not the levels are affected by postharvest handling conditions. Accordingly, broccoli heads ( Brassica oleracea var. italica) were stored at temperatures of 1 or 4 °C, 99% relative humidity (RH), for 2, 7, 14 or 28 days to simulate domestic and export transport conditions. After removal from cool storage, heads were then placed at 8, 15 or 20 °C, with 99, 90 or 70% RH, respectively, for 3 days to simulate marketing conditions. At the end of both phases, heads were rated for visual quality, turgor, presence of rots and yellowing, and the contents of glucoraphanin, quercetin and kaempferol were measured. Visual quality declined significantly with increasing temperature and length of storage, caused primarily by increasing yellowing and loss of turgor. Glucoraphanin, quercetin and kaempferol contents were not significantly affected by storage and marketing temperature and time. These results suggest that current transport and marketing practices are not likely to have a deleterious effect on the levels of aliphatic glucosinolates and flavonols in broccoli.

Evaluation of Bacterial Antagonists for Biological Control of Broccoli Head Rot Caused by Pseudomonas fluorescens

ABSTRACT Pectolytic strains of Pseudomonas fluorescens are opportunistic pathogens of broccoli, causing head rot in temperate regions of the world. In this study, we investigated the potential of two bacterial isolates, P. fluorescens m6418 and Bacillus sp. A24, for biological control of broccoli head rot caused by P. fluorescens 5064, isolated from diseased broccoli in Scotland, UK. P. fluorescens m6418, a Tn5 mutant of wild-type 5064, is nonpathogenic and overproduces an extracellular metabolite with strong antimicrobial activity. In this study, we identified the anti-microbial metabolite produced by strain m6418 as pyrrolnitrin. P. fluorescens m6418 had significant inhibitory effects against strain 5064 both in culture and on broccoli leaves. In an excised broccoli head pathogenicity test, strain m6418, when coinoculated with P. fluorescens 5064, reduced disease by 41%. Bacillus sp. A24 produces an enzyme that can degrade N-acyl homoserine lactones, signaling molecules employed by bacteria for quorum sensing. Bacillus sp. A24 was capable of out-competing P. fluorescens 5064 when grown together in culture, and could degrade the quorum sensing signal of P. fluorescens 5064 (and thereby attenuate its virulence gene production). However, Bacillus sp. A24 had only a limited biocontrol effect on P. fluorescens 5064 in the excised broccoli head assay.

Chlorophyll fluorescence for non-destructive measurement of flavonoids in broccoli

Chlorophyll fluorescence (ChlF) by excitation with two radiation beams of different wavelengths can be used for non-destructive quantitation of epidermal flavonoids in leaves. The method was tested on marketable broccoli heads, but including red light (685 nm) and green light (530 nm) in addition to ultraviolet (UV) radiation (382 nm) and blue light (450 nm) for excitation of ChlF. As a reference, the content of flavonoids was measured with high performance liquid chromatography. To induce flavonoids, postharvest treatment during 12 days with various combinations of visible and UV radiation was tried, but the achieved changes in the flavonoid levels were not statistically significant. Instead a large natural variation of flavonoid content among the broccoli heads was used to correlate it with the fluorescence data. It was possible to estimate the content of flavonoids in flower buds by means of ChlF: relative epidermal absorbance of blue light was well correlated with flavonoid content ( r = 0.69, p < 0.001). For quercetin alone the correlation was higher ( r = 0.77, p < 0.001). On the other hand, relative epidermal absorbance of UV radiation or green light had a much weaker correlation with flavonoid content ( r ≤ 0.40, p < 0.05). Within the broccoli heads, flower buds had 15 times higher levels of flavonoids than the floret stalks, which in turn had five times higher contents than the main stem. Repeated ChlF measurements on individual broccoli heads during cold storage could monitor small but significant changes in flower buds, possibly indicating a breakdown of constituents absorbing UV and green light.

How Natural Enemies and Cabbage Aphid (Brevicoryne brassicaeL.) Population Dynamics Affect Organic Broccoli Harvest

The cabbage aphid (Brevicoryne brassicae L.) is the primary broccoli (Brassica oleracea L.) pest in Monterey County. These aphids' ability to contaminate a broccoli head has sometimes led to zero-tolerance spray thresholds. To improve on these management practices, aphid arrival time, within-plant colony location, and abundance of natural enemies were tested against infestation of organic broccoli heads at harvest. Cabbage aphids predominately colonized the outer leaves of a broccoli plant. These colonies, however, did not significantly influence infestation at harvest. Center-located aphids were correlated with head infestation for both field seasons, as were aphids on leaf 2 in 2002. Aphid arrival time into a field was strongly correlated with infestation at harvest, with early arriving aphids being less likely to infest a head. This was in part caused by natural enemies, particularly syrphid larvae (Syrphidae), which were in greatest abundance in response to early aphid colonizers. Natural enemies showed a capability to positively affect infestation at harvest, although their success seemed dependent on sufficient early season cabbage aphid arrivals. Therefore, future research efforts should focus on management practices that encourage the early establishment of natural enemies.

ADDITION OF SORBITOL WITH KMnO4 IMPROVES BROCCOLI QUALITY RETENTION IN MODIFIED ATMOSPHERE PACKAGES

ABSTRACT The objective of this study was to determine if the addition of sorbitol (a water absorbent) to packages containing potassium permanganate (KMnO 4 ) on an inert carrier (a volatile adsorber) could be used to enhance the removal of volatiles associated with off‐odors in broccoli (Brassica oleracea L., Italica group) during storage in modified atmosphere packaging (MAP). Broccoli heads were held in PD‐961EZ bags (five per bag), to allow CO2 to accumulate above the recommended 5–10%. Six treatments within MAP were investigated: (1) control − 0‐g sorbitol + 0 g‐KMnO4; (2) 0‐g sorbitol + 20.0‐g KMnO4; (3) 2.5‐g sorbitol + 20.0‐g KMnO4; (4) 5.0‐g sorbitol + 20.0‐g KMnO4; (5) 10.0‐g sorbitol + 20.0‐g KMnO4; and (6) 20.0‐g sorbitol + 20.0‐g KMnO4. Broccoli heads in MAP with sorbitol had better appearance, firmness and odor ratings after 29 days of storage at 0–1C, compared to the controls. Furthermore, the odor rating was higher (less off‐odor) as the amount of sorbitol was increased (1.9 control versus 3.9 for 20‐g sorbitol). Slight increases in weight loss (≤1.3%) of the broccoli were also noted with the addition of sorbitol, although not near an amount that would affect marketability. Acetaldehyde concentrations were higher in the control bags with no sorbitol or KMnO4 after 29 days of storage at 0–1C (0.21 versus 0.00–0.02 μL/L with KMnO4 and/or sorbitol), while ethanol content was greater in both control bags and those with only KMnO4 (0.12–0.13 versus 0.00–0.06 μL/L with sorbitol). Chlorophyll fluorescence (ΦPSII) began to decrease more rapidly in the control broccoli, as the ethanol and acetaldehyde began to accumulate. Overall, the use of sorbitol (≥2.5 g) with KMnO4 in MAP could enhance the removal of volatiles that are responsible for off‐odors and off‐flavors in broccoli, and thus maintain the quality and marketability longer.

UV-C treatment delays postharvest senescence in broccoli florets

Central broccoli heads (cv. de Cicco) were harvested and treated with UV-C light (4, 7, 10, or 14 kJ m −2). All treatments delayed yellowing and chlorophyll degradation at 20 °C but the irradiation dose of 10 kJ m −2 allowed retaining the highest chlorophyll content yet had lower amounts of pheophytins than every treatment other than 7 kJ m −2. This dose was selected to analyze the effect of UV-C on postharvest broccoli senescence at 20 °C. The UV-C treatment delayed yellowing, chlorophyll a and b degradation , and also the increase in pheophytins during storage. The activity of chlorophyll peroxidase and chlorophyllase was lower in UV-C treated broccoli. Instead, Mg-dechelatase activity increased immediately after the treatment, but after 4 and 6 d this activity was lower in UV-C treated florets than in controls. Treated broccoli also displayed lower respiration rate, total phenols and flavonoids, along with higher antioxidant capacity. The results suggest that UV-C treatments could be a useful non-chemical method to delay chlorophyll degradation, reduce tissue damage and disruption, and maintain antioxidant capacity in broccoli.

The Production of Marker-Free Genetically Engineered Broccoli with Sense and Antisense ACC synthase 1 and ACC oxidases 1 and 2 to Extend Shelf-Life

The production of transgenic broccoli (Brassica oleracea) with increased shelf-life using an Agrobacterium rhizogenes-mediated co-transformation protocol is reported. An Agrobacterium rhizogenes Ri vector, pRi1855:GFP was constructed to allow expression of the green fluorescent protein to identify insertion of Ri TL-DNA into plant cells. The Brassica oleracea ACC synthase 1 and ACC oxidase 1 and 2 cDNAs in sense and antisense orientations were co-transformed into GDDH33, a doubled haploid calabrese-broccoli cultivar. Transformation efficiency was 3.26%, producing 150 transgenic root lines, of which 18 were regenerated into mature plants. The floral buds from T0 broccoli heads were assayed for post-harvest production of ethylene and chlorophyll levels. Buds from T0 lines transformed with ACC oxidase 1 and 2 constructs produced significantly less post-harvest ethylene at 20 °C than the untransformed plants and chlorophyll loss was significantly reduced over a 96 h post-harvest period. The T0 plants transformed with sense and antisense ACC synthase 1 had a significantly reduced 24 h post-harvest ethylene peak and delayed chlorophyll loss. A positive correlation between post-harvest bud ethylene production and chlorophyll loss was described by a regression. This demonstrates that the shelf-life of a very perishable vegetable may be increased up to 2 days at 20 °C by reducing post-harvest ethylene production.