PA and DA meter – providers of the new ripeness index?

Abstract

New ripening instrumentation like the PA analyser and the DA meter offer non-invasive tools based on degradation of chlorophyll in the fruit peel; their values were compared with the Streif index measured by an ART system, as traditional ripeness viz., picking tool using 5-year-old 'Braeburn Hillwell' at Klein-Altendorf in autumn 2015, when environmental weather pattern delayed harvest by ca. 3 weeks. Treatments included two reflective mulches and two biostimulants with an untreated control. The study showed that: 1) DA meter values (IAD) gave consistent results for the four treatments at the six measuring dates before harvest; 2) DA meter values (IAD) highly correlated with r=0.84-0.94 with Streif indices (ART system); 3) when 'Braeburn' stopped ripening at Streif=0.18 (harvest window for Streif 0.25-0.14 and for starch 3-5), DA meter values still continued to decrease; 4) fruit with reflective mulch (Extenday) appeared earlier ripe with the DA meter but later ripe with the ART system; 5) if we start to manipulate ripening e.g., by chemicals (phosphates, biostimulants, reflective mulches, 1-MCP), Streif values may reflect those changes in ripening, whereas DA meter values (IAD) still continue to decline at the same rate, unless the treatment has a direct chlorophyll effect, where DA values may be tricky to use.