Issue link: http://read.dmtmag.com/i/350705
F ruit mineral analysis during the growing season can guide produc- ers in their fertilizer programs and help them improve fruit quality. Dr. Bill Wolk, quality develop- ment manager with the B.C. Tree Fruits Cooperative in British Columbia, Can- ada, said research on fruit mineral analy- sis was done at the East Malling research center in the United Kingdom in the 1970s. Researchers and horticulturists in British Columbia began to take an interest during the 1980s and 1990s, with the idea of predicting storability of fruit delivered from different orchards at harvest. This was important in British Columbia, where packers were receiving fruit from many different small orchards. "This originated as a packing house storage thing," Wolk told members of the Interna- tional Fruit Tree Association during their annual meeting in Kelowna, British Columbia. "We weren't even thinking about this to help growers grow better fruit in the orchard." Now, it is used primarily as a guide for growers. Wolk said the cost of the analysis— at $40 to $60 per sample—is nothing compared to the value of the fruit the orchard will produce and the information and guidance it can give growers in their fertilizer programs. "It's really cheap," he said. "If you're not doing it, you should give it serious consideration." Working with Drs. Sam Lau and Gerry Neilsen with Agriculture and Agri-Food Can- ada in Summerland, Wolk conducted research initially with McIntosh, Spartan, and Golden Delicious apples. The fruit were tested for minerals, as well as for weight, den- sity, and dry matter. It was assumed that fruit analysis would give the best prediction of fruit quality when done at harvest. The scientists wondered how long before harvest fruit quality could be accurately predicted. Wolk and his colleagues tested fruitlets nine, six, and three weeks before harvest and at harvest. They then stored the fruit for different periods in com- mercial regular and controlled-atmosphere storage and looked for correlations between the results of the fruitlet analysis and postharvest fruit quality, such as firmness, sugar levels, and storage disorders. They were surprised to find that, for all three varieties, fruitlet analysis gave a bet- ter prediction of postharvest quality when done six weeks before harvest, rather than nearer harvest. The scientists developed nutrient recommendations for growers based on the actual storage data. Over the years, they added more varieties to the fruitlet anal- ysis database, and found that each one has different quality-mineral correlations. The program is currently testing Ambrosia, McIntosh, Gala, Honeycrisp, and Spartan. Calcium The recommended calcium level differs from variety to variety more than any other mineral, Wolk pointed out. For example, for Gala, the minimum recommended level when fruit is tested six weeks before harvest is 10 milligrams per 100 grams of fruit weight, compared with 7.0 mg for Fuji, 6.0 for Jonagold, and only 5.5 mg for Brae- burn (see "Minimum calcium levels"). Statistical analysis showed that in Jona- gold, for example, there was a level of cal- cium—4.9 mg of calcium per 100 g of fruit weight—below which there was a "tec- tonic shift," and the percentage of bitter pit increased dramatically, Wolk said. Often though, producers can "eyeball" the data and see how ranges in calcium levels relate to the percentage of bitter pit. Bitter pit is particularly high in Jonagold with less than 4.0 mg of calcium per 100 g. Although there's not a perfect relationship between the calcium level and amount of bitter pit, Wolk said fruitlet analysis can be used to improve the odds in favor of the producer. For example, a grower or packer who has Jonagold apples averaging less than 14 AUGUST 2014 Good Fruit Grower www.goodfruit.com Harvest Fruitlet analysis six weeks before harvest accurately predicts quality. by Geraldine Warner Minerals matter Minimum calcium levels Recommended minimum calcium levels vary from variety to variety. Variety Minimum Ca Gala 10.0 McIntosh 7.0 Golden Delicious 7.5 Spartan 7.5 Ambrosia 8.5 Jonagold 6.0 Braeburn 5.5 Fuji 7.0 SOURCE: Bill Wolk, B.C. Tree Fruits Cooperative