NITROGEN AVAILABILITY AND FRUIT YIELD GENERATION IN CACTUS PEAR (OPUNTIA FICUS-INDICA): IV. EFFECTS ON FRUIT QUALITY

The effect of N availability on fruit quality of cactus pear is not well known. The objectives of this work were to determine the effects of N shortage and/or excess on fruit quality during 4 weeks after harvest, under cold storage and room temperature (RT). The trial was carried out under irrigation at Santiago del Estero, Argentina, during 1998-1999 and 1999-2000 growing seasons, using ‘Amarilla sin Espinas’ cactus pear. Treatments were: N_low (16 t ha^-1 sucrose to immobilize N), N_medium (100 and 150 kg ha^-1 N), and N_high (200 and 300 kg ha^-1 N) the higher rates were used in 1999-2000. Fruits were analyzed at harvest and stored under cold conditions during 4 weeks. Fruit quality was analyzed at 7, 14, 21 and 28 d of storage. After each of these periods fruits were retrieved to RT conditions during 7 d. In 1999-2000 new treatments were added, maintaining fruits during 14, 21 and 28 d under RT without cold storage periods. Peel color, weight loss, firmness, total soluble solids (TSS), pH, pulp percent and fungus decay were evaluated in fruits. Fruit quality was more affected by year than storage conditions or N treatments. Cold storage maintained fruit firmness and reduced water loss and fungal decay; opposite to high N levels which reduced fruit firmness and increased fungal decay. Fruit quality during post-harvest showed the highest variation of fruit firmness and weight loss during the first week. No negative effects of N deficiency on fruit quality were detected. The results obtained may help optimize N fertilization and improve simulation models.