Evaluation of auxin, sucrose and nutrition effect on alternate bearing cycle in Satsuma mandarin (Citrus unshiu)

Alternate bearing is one important problem in some citrus varieties like Citrus unshiu. An alternate bear tree doesn’t produce a regular crop in consequence years. Reduced fruit quality in "on year" and decreased quantity in "off year" cause economic loss to producer. To evaluate possibility of reducing this disorder, an experiment was conducted in randomize complete block design with 5 treatments: 1. Control; 2. Optimum using of chemical fertilizers; 3. Optimum using of chemical fertilizers and NAA spraying; 4. Optimum using of chemical fertilizer and 2,4-D spraying and 5. Optimum using of chemical fertilizer and Sucrose spraying with 4 replications in 4 consecutive years on Citrus unshiu mature trees. Control trees had the most alternate bearing during 4 years, as showed one "on" year, two consecutive "off" years and one "on" year, respectively. On the other hand, other 4 treatments reduced number of "off" years to one, during 4 years. Treatment 2 had the highest yield in "off" year and the lowest yield in "on" year. The smallest and lightest fruit in first, second and fourth years was allocate to Control. During 4 years, the lowest total yield was recorded in Control plants. In conclusion treatment 2 by reducing yield in "on" year, increasing yield in "off" year and reduce number of "off" years compare to Control and treatments 3, 4 and 5 by reducing number of "off" years and increasing fruit size in on years caused adjusting alternate bearing cycle, increase total yield in consecutive years, decrease fruit losses and improve marketability in Citrus unshiu.