Harvest maturity, storage temperature, and 1-MCP application frequency alter firmness retention and chlorophyll fluorescence of 'Redchief Delicious' apples

Fruit of 'Redchief Delicious' apple [Malus sylvestris (L) Mill. var. domest ica (Borkh.) Mansf.] were harvested 1 week before the climacteric (harvest 1), at the onset of the climacteric (harvest 2), and 1 week after the onset of the climacteric (harvest 3). Fruit were stored at 0, 5, 10, 15, or 20 d egreesC and were treated with 0.7 muL.L-1 1-MCP on a once-per-week, once-pe r-2-week, once-per-month, and once-per-year basis or were left nontreated. The initial 1-MCP treatment was at 20 degreesC and subsequent applications were at storage temperatures. The compound slowed softening at all temperat ures relative to nontreated fruit, however as temperature decreased, the be nefits of 1-MCP application became less pronounced. Effectiveness of 1-MCP declined slightly as harvest maturity increased. Efficacy of 1-MCP treatmen t increased with greater frequency of application at 5, 10,15, and 20 degre esC, but not at 0 degreesC. Fruit stored without refrigeration (20 degreesC ) for more than 100 days did not soften significantly when treated once per week with 1-MCP. However, decay was a significant problem for treated and nontreated fruit stored at temperatures >5 degreesC; 1-MCP application redu ced, but did not prevent decay. Rate of decline in titratable acidity incre ased with storage temperature and 1-MCP had no significant effect on retard ing the decline in acid content. Minimal (Fo) and maximal (Fm) chlorophyll fluorescence was altered markedly by 1-MCP application, but the ratio of (F m-Fo)/Fm was only slightly affected. The most effective 1-MCP treatment fre quency was once per week and, at all elevated temperatures (5, 10, 15, and 20 degreesC), slowed loss of firmness to a greater extent than refrigeratio n (0 degreesC) alone. Application of 1-MCP resulted in greater retention of firmness than controlled atmosphere (CA) with O-2 and CO2 at 1.5 kPa and 3 kPa, respectively. Data suggest that 1-MCP application, has the potential to reduce reliance on refrigeration and CA storage for maintaining firmness of 'Redchief Delicious' apple, especially for relatively short storage dur ations (<50 days) when fruit are harvested within a week of the ethylene cl imacteric. Chemical name used: 1-methylcyclopropene (1-MCP).