Talking Avocados Autumn 2021

RESEARCH AND DEVELOPMENT Fruit quality trace-back casestudy Noel Ainsworth, Queensland Department of Agriculture and Fisheires

Investigating the root cause of poor fruit quality is a new component of the Avocado Supply Chain Feedback project (AV18000). During a 2020 assessment of fruit quality in a consignment, we came across the darkened flesh symptoms above and below the seed (Figure 1). The initial diagnosis was based on photos shown to Queensland Department of Agriculture and Fisheries (QDAF) and Queensland Alliance for Agriculture and Food Innovation (QAAFI) colleagues. It was suspected that the symptoms may be related to calcium deficiency, boron deficiency, frost damage or a combination of all three. These were compared with photos of vascular browning frost damage (p116), boron deficiency (p120) and calcium deficiency flesh discolouration (p121) images in The Avocado Problem Solver Field Guide (2013) and symptoms described by Smith (1997). To confirm the initial diagnosis, a traceback was initiated involving discussions with the packshed manager and the grower who supplied the fruit. This included details about frost incidence and leaf damage, tree age, tree vigour and rootstocks used plus the fertiliser program and results of leaf analysis. Naturally that information was vital to working out what might

have gone wrong and where improvements could be made. Information provided by the grower suggested that calcium nutrition may be a key factor. A sample of fruit from the source block plus a fruit sample from another block nearby (for comparison) were sent to Symbio Laboratories in Brisbane for nutrient analysis. Results are presented in Table 1, the most relevant result in these analyses is probably the N/Ca ratio. The fruit with symptoms had a ratio below the proposed threshold value of 33 whereas the symptomless fruit had a ratio above this threshold. In addition, both calcium and boron levels were lower in the affected fruit. The advice provided to the grower was to consider making suitable changes to their nutritional program, especially shifting the N:Ca balance and boron levels. It is important to remember that too much nitrogen promotes excessive vegetative growth which diverts calcium away from developing fruit. Timing is also important when it comes to calcium application, noting that there is a limited window of opportunity to apply calcium and this needs to be within the first six (6) to eight (8) weeks after fruit set, when calcium is deposited into the fruit.

Table 1. Fruit analysis results

Other sample

Poor quality

Total Kjeldahl Nitrogen (N) (%w/w)

0.42

0.31

Calcium (Ca) (mg/kg)

160

87

Magnesium (Mg) (mg/kg)

365

353