2019 ASHS Annual Conference

WA38 is an apple variety developed by the Washington State University Apple Breeding Program as the result of a cross between ‘Enterprise’ and ‘Honeycrisp’. This apple variety will be sold commercially for the first time in 2019. One of WA 38 unique characteristics is the starch degradation and starch pattern development during maturation of the fruit. Starch is one of the maturity parameters utilized by the Washington apple Industry as a method to determine optimum harvest timing. When iodine is applied to the apple core it binds with starch particles and develop a dark coloration patter. Overtime starch converts to sugar and the dark pattern will start to clear. The objective of this experiment was to develop a variety specific starch scale to aid assessment of WA38 maturity. The scale values will range from 1 to 6, with 0.5 increments. To achieve a surface reflecting the middle of the core, WA 38 apples were cut, unlike other industry specific varieties, right through the equator and the surface was scraped to have a clean pattern. During the experiment, two predominant patterns were observed. The commonly known “flower” pattern, which is characterized by 5 “flower petals” growing with advancing maturity. The other pattern was named “radial”, and it can be compared with a “sunrise”. The patterns appeared in a 6:4 ratio in 2017 and in a 3:7 ratio in 2018. Another observation was the slow disappearance of dark color and consequently starch once fruit was harvested and placed into storage. The experiment also showed that the starch patterns took longer to develop, compared to other industry specific varieties. WA38 starch readings are possible in less than 5 minutes, but depending on fruit temperature and maturity, the development of a complete starch staining took up to one hour. In most cases the pattern developed fully after 28-30 minutes if the fruit is warm (72°F), 50-60 minutes if the fruit came from cold storage. In comparison, Granny Smith apples took up to 10 minutes, when the fruit came from cold storage and 2.5 minutes, when the fruit was warm (72°F). Sometimes the starch pattern was not even, showing more maturity on one side of the cut. It was hypothesized that it could be related to sun exposure, as in general, apples show advanced maturity on the sun exposed side. However, for WA38 this hypothesis could not be validated.