Fruit quality trace-back casestudy

from Talking Avocados Autumn 2021

2020 export market analysis

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.

Figure 1. Symptoms observed at medium-soft ripe. 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 Zinc (Zn) (mg/kg) 5.4 9.2 Potassium (K) (mg/kg) 7200 7400 Silicon (Si - Acid Soluble) (mg/kg) 5.2 3

Boron (B) (mg/kg) 38 11 N/Ca ratio 26.3 35.6 Recommendation*

<33

(Ca + Mg)/K ratio * Perkins M et al (2021) pers. comm. 0.073 0.059 >0.065

While the cause of the fruit quality symptoms is rarely definitive, this case study illustrates the value of obtaining feedback on ripe fruit quality. This, combined with a little bit of investigation, provides an early warning and likely corrective action before a little problem becomes a big one. The AV18000 project team use commercial fruit quality assessors in Sydney and Melbourne. This service, through Rudge Produce Systems, is also available to avocado growers on a fee-for-service basis.

Further information on how to improve fertiliser / nutrition management can be found in: • Newett, S., Rigden, P., and Weinert, M. (2013) The Avocado

Problem Solver Field Guide (2013) p161, State of Queensland • BPR content under Growing / Nutrition / Calcium (avocado.org.au/bpr/) • Newett, S., Rigden, P., and Carr, B. (2018) Avocado plant nutrition review, Department of Agriculture and Fisheries. https://avocado.org.au/wp-content/uploads/2018/08/

AVOCADO-PLANT-NUTRITION-REVIEW-2018_cover.pdf • Newett, S., Perkins, M., Coates, L., Irvine-Brown, S., and

Joyce, D. (2021) ‘Review of pre-harvest mineral nutrition for post-harvest quality’, Talking Avocados, Summer V31#4, p54-57. • Smith, T.E., Hofman, P.J., Stephenson, R.A., Asher, C.J., and Hetherington, S.E. (1997) Improving boron nutrition improves ‘Hass’ avocado fruit size and quality. Proceedings from Conference ’97: Searching for Quality. Joint

Meeting of the Australian Avocado Grower’s Federation,

Inc. and NZ Avocado Growers Association, Inc., 23-26

September 1997. J. G. Cutting (Ed.). Pages 131 – 137, http:// www.avocadosource.com/Journals/AUSNZ/CONF97/

CONFERENCE_1997_PG_131-137.pdf

More information

Contact QDAF Principal Supply Chain Horticulturist Noel Ainsworth, on 0409 003 909 or email noel.ainsworth@daf.qld.gov.au.

Acknowledgement

The AV18000 project has been funded by Hort Innovation, using avocado research and development levy, co-investment from the Queensland Department of Agriculture and Fisheries, Western Australian Department of Primary Industries and Regional Development, and contributions from the Australian Government. Key project delivery partners also include Avocados Australia and Rudge Produce Systems.