Characterisation of three ACC synthase gene family members during post-harvest-induced senescence in broccoli (Brassica oleracea L. var. italica)

We investigated the gene expression profiles of different members of the 1-aminocyclopropane-1-carboxilic acid (ACC) synthase (EC 4.4.1.14) gene family in broccoli (Brassica oleracea L. var. italica) during the post-harvest-induced senescence process. Using RT-PCR, three different cDNAs coding for ACC synthase (BROCACS1, BROCACS2 and BROCACS3) were amplified from floret tissue at the start of the senescence process. The three genes share relatively little homology, but have highly homologous sequences in Arabidopsis thaliana, and could be functionally related to these counterparts. Southern analyses suggest that BROCACS1 and BROCACS3 are present as single copy genes, while there are probably two copies of BROCACS2. All three genes showed different expression patterns: BROCACS1 is likely to be either wound - or mechanical stress-induced showing high transcript levels after harvesting, but no detectable expression afterwards. BROCACS2 shows steady expression throughout senescence, increasing at the latest stages, and BROCACS3 is almost undetectable until the final stages. Our results suggest that BROCACS1 could be required to initiate the senescence process, while BROCACS2 would be the main ACC synthase gene involved throughout the post-harvest-induced senescence. BROCACS3's expression pattern indicates that it is not directly involved in the initial stages of senescence, but in the final remobilization of cellular resources.

Acibenzolar-S-methyl and methyl jasmonate treatments of glasshouse-grown freesias suppress post-harvest petal specking caused by Botrytis cinerea

Compounds that activate host plant defence responses potentially offer socio-environmentally sound alternative methods for disease control. In a series of glasshouse trials over 2 years, pre-harvest sprays with acibenzolar-S-methyl (ASM) and methyl jasmonate (MeJA) were tested for suppression of post-harvest infection of cut Freesia hybrida L. flowers by Botrytis cinerea. For the ASM treatments, variability in reducing the incidence of B. cinerea disease was observed between years freesia varieties, incubation temperatures and ASM concentrations. In the first year, the greatest reductions in lesion numbers on ASM-treated var. 'Cote d'Azur' were recorded using 2.86 mM ASM. For three different post-harvest temperature regimes, the relative reductions in lesion numbers, compared to untreated controls, were 45% at 5 degrees C, 40% at 12 degrees C and 30% at 20 degrees C, respectively. In the second year, lesion numbers were most reduced using 1.43 mM ASM to treat freesia var. 'Dukaat' flowers. Here, the relative reductions were to 44% at 5 degrees C, 26% at 12 degrees C and 51% at 20 degrees C. MeJA treatments were, in general, more consistently effective than ASM treatments in reducing lesion numbers and lesion diameters on cut freesia flowers. MeJA-treated (0.2 mM) freesia flowers (var. 'Dukaat') incubated at 20 degrees C showed relative reductions of 62%, and 45% for lesion number and lesion diameter, respectively. The differing efficacy between ASM and MeJA treatments could be attributed to their differential abilities to induce the salicylic acid (SA)-mediated vs. the jasmonic acid (JA)-mediated host defence pathways, respectively.

Effect of modified atmosphere packaging on the quality of minimally processed pineapple cv.'Smooth Cayenne' fruit

The effects of modified atmosphere (MA) conditions on the quality of minimally processed pineapple slices were determined. Commercial pineapple slice packs sealed with 40 pm thick polyester film were kept at 4.5 degrees C for 14 d. The oxygen transmission rate of the film was 23 ml m(-2) day(-1) atm(-1) (at 25 degrees C, 75% RH). In-built atmospheres and the quality of the products were determined. O-2 concentrations within the packs stabilised at 2%, while CO2 concentrations increased to 70% by day 14. The high CO2 level suggested an inappropriate lidding film permeability for the product, and hence affected its quality. Three batches of pineapple slices were packed in the laboratory using lidding films with oxygen transmission rate of 75, 2790 or 5000 ml m(-2) day(-1) atm(-1) (at 23 degrees C, 0% RH). Headspace atmospheres from laboratory-packed pineapple slices suggested an optimum equilibrium modified atmosphere of ca. 2% O-2 and 15% CO2. Respiration data from the laboratory-prepared packs were pooled together and used to develop a correlation model relating respiration rates to O-2 and CO2 concentrations. The model showed a decrease in respiration rate with decreasing O-2 and increasing CO2 concentrations. Respiration rate stabilised at 2% 02 and 10% CO2. The high concentrations of CO2 observed in the commercial packs did not fit the range in the respiration model. The model could aid in selection of MA conditions for minimally processed pineapple fruit.

Characteristics of banana fruit from nearby organic versus conventional plantations: A case study

This case study reports the post-harvest qualities of conventionally versus organically grown banana fruit from nearby plantations in the Dominican Republic. The comparison involved six repeated harvests over the transition from cooler to hotter seasons. Green mature Cavendish 'Grande Naine' banana fruit were shipped to the UK. They were triggered to ripen with ethylene gas and kept under simulated retail conditions. Fruit mass, colour, firmness and flavour parameters were measured every second day over 12 d of shelf life. Sensory comparisons were conducted on four of the six harvest times. Significant differences (P<0.05) in measured quality attributes between conventionally and organically grown fruit were few and marginal. Moreover, any differences were inconsistent across harvest-times and during shelf life. Thus, organically and conventionally grown product had almost identical qualities. Sensory comparison confirmed that there was no flavour difference. This case study provides data that challenge a general perception that organic bananas have better flavour than conventional bananas.

Manipulating avocado fruit ripening with 1-methylcyclopropene

Previous investigations with 1-methylcyclopropene (1-MCP) on avocado (Persea americana Mill.) fruit have focussed mainly on improving storage life by reducing the severity of disorders causing discolouration of the flesh. Development of 1-MCP and ethylene treatments, which also help control the time to reach the eating ripe stage, may confer additional practical benefits. In this context, the current study investigated the potential of 1-MCP to accurately manipulate ripening of non-stored 'Hass' avocado fruit by treatment before or after ethylene and at different times during ripening. To investigate this, 500 nL L-1 1-MCP was applied within 1 day after harvest, followed by ethylene 0-14 days after 1-MCP. In addition, fruit were treated with ethylene, then 1-MCP 0-8 days after ethylene. Treatment of fruit with 500 nL L-1 1-MCP for 18 h at 20 degreesC provided the maximum effect by increasing the days from harvest to ripe (DTR) from 8 (with no 1-MCP) to 20. Fruit treated with 500 nL L-1 1-MCP for 18 h at 20 degreesC remained insensitive to 100 muL L-1 ethylene applied between 0 and 14 days after 1-MCP for 24 h at 20 degreesC. Ripening of fruit exposed to 100 muL L-1 ethylene for 24 h at 20 degreesC could be delayed by up to 3.3 days by applying 500 nL L-1 1-MCP for 18 h at 20 degreesC up to 2 days after ethylene treatment. However, once the fruit started to soften (sprung) there was little effect of 1-MCP on DTR, compared with no 1-MCP. 1-MCP treatment was associated with increased severity of body rots (caused mainly by Colletotrichum spp.) and stem-end rots (caused mainly by Dothiorella spp.), which was likely due to the increased DTR in these treatments. Significant differences in disease severity were found between orchards (replications), with replicates with low disease severity being less affected by 1-MCP treatment. These results indicate that 1-MCP can delay ripening, but careful sourcing of fruit is required to reduce the risk of diseases in ripe fruit. There is some capacity to delay ripening using 1-MCP after ethylene. There is little potential to control ripening using ethylene after treatment with 500 nL L-1 1-1-MCP, but lower concentrations may be more effective. (C) 2004 Elsevier B.V. All rights reserved.