Calamansi (× Citrofortunella microcarpa) for potential citrus fruit production for the island of Guam

Calamansi (× Citrofortunella microcarpa) is a very popular citrus for local cuisine in the tropical island of Guam. A study was conducted to determine the fruit yield of field-grown calamansi from 2004 to 2016 in a calcareous soil. Rooted stem cuttings of local calamansi were planted in 2002 with an intrarow spacing of 2.4 m and an interrow spacing of 6 m. There were four 60 m rows, each with 28 plants, totaling 112 trees. The yield increased steadily from 2004 (0.7 t ha^-1) to 2009 (12.2 t ha^-1), and then plateaued with the average yield of 11.8 t ha^-1 from 2009 to 2016. The highest fruit yield of 14.6 t ha^-1 was observed in 2014. When the monthly fruit yield was compared with the rainfall pattern from 2008 to 2016, floral initiation appeared respond to decreased rainfall during September to November. Fruit production peaked during the dry months of February to April. A preliminary biochemical analysis of calamansi juice was performed at three different fruit maturity stages: green, yellow, and orange fruits. The sugar content (°Brix), pH, vitamin C content, and Trolox equivalent antioxidant capacity (TEAC) were examined. Fruits of all stages had a pH of 2.4 and TEAC did not differ among the three stages of fruit maturity. However, sugar and vitamin C content increased from green to yellow to orange ripe fruits.