Tree yield and fruit minerals concentrations influence 'Hass' avocado fruit quality

To investigate the variation in quality of 'Hass' avocado fruit within an orchard, fruit were harvested at commercial maturity from 15 'Hass' trees of similar appearance, growing in three adjacent rows on the same soil type, and receiving similar management. Fruit were harvested at commercial maturity, and either ripened at 22 degreesC or stored at 2 or 7 degreesC for 3 or 5 weeks and then ripened. Significant positive correlations (based, on the mean for each datum tree) were noted between fruit flesh calcium (Ca) and magnesium (Mg) concentrations and the (Ca + Mg)/potassium ratio, and the number of days for the fruit to reach the eating ripe stage (DTR). Negative correlations were also observed between these minerals and anthracnose and mesocarp discolouration (MD) severity. Negative correlations were observed between fruit potassium (K) and phosphorus (P) concentrations and DTR. Fruit from trees with high fruit yield were generally smaller, with lower anthracnose and MD severity, ripened more slowly, and had higher flesh Ca concentrations. It is likely that cultural practices that maintain moderate to high fruit yield and reduce variation in yield will improve avocado fruit quality and reduce variability in quality. Since the main differences between adjacent trees in this trial were the seedling rootstocks of unknown origin, it is suggested that rootstocks can have a significant impact on avocado yield and fruit quality. (C) 2002 Elsevier Science B.V. All rights reserved.

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.