UTILIZING A NON-DESTRUCTIVE APPROACH TO IMPROVE UNIFORMITY OF PHASE 2 FRUIT SAMPLES IN THE WASHINGTON STATE UNIVERSITY APPLE BREEDING PROGRAM – India Cain, MS Student in Horticulture, WSU

The Washington State University Apple Breeding Program is composed of three phases of selection. Phase 2 accessions consist of five replicate trees that are evaluated for several years at three geographically diverse sites in Washington. Each accession is harvested over three picks using subjective maturity assessments that include change in the background color and starch degradation. Lack of information regarding optimal harvest date, limited fruit and variable maturity throughout the canopy can lead to large within-sample variations of maturity in some accessions, as subjective methods do not ensure collection of uniform samples. The Delta Absorbance meter estimates maturity non-destructively by measuring the index of absorbance difference (I_AD) of fruit, where the absorbance at 720 nm (background of spectrum) is subtracted from the absorbance at 670 nm (near the chlorophyll-α absorption peak). Typically, I_AD is used to model variety-specific harvest windows for commercial apple cultivars, however, rapid turnover and limited fruit availability in Phase 2 accessions led us to explore if I_AD could be used to guide harvest without developing models. With an I_AD corresponding to a specific starch index rating, accessions were harvested using I_AD-guided sampling. Coefficient of variation (CoV) was used to calculate within-sample variability. In 15 out of 26 samples, within-sample variability of I_AD was reduced using I_AD-guided sampling. Sample variability was also determined using starch, soluble solids content, titratable acidity, and firmness. In at least three of these destructive trait measures, CoV of I_AD-guided samples was reduced compared to non-I_AD-guided samples in five, seven, and seven samples in picks 1, 2, and 3, respectively. Reductions of within-sample variability were accession, site, pick, and trait specific, with a strong effect of accession and site in all traits. I_AD-guided sampling is being used in combination with subjective maturity assessments to harvest all Phase 2 accessions in 2023.

This talk will be provided in the Horticulture Department’s weekly seminar series. Please contact the organizers if you would like a video conference link to attend remotely.