USE OF INDIVIDUAL DARK CHAMBERS AS A METHOD FOR OBTAINING ETIOLATED SHOOTS IN NURSE PLANTS OF 'DUKE' AVOCADO (PERSEA AMERICANA)

Two trials were conducted under not controlled nursery conditions to study the efficiency of opaque pvc plastic tubes and black polyethylene bags, arranged in various ways as individual dark chambers (IDC), in order to produce etiolated shoots of ‘Duke’ avocado rootstock. In the first trial conducted in the fall, the nurse plants were covered when the growth of buds had already started using tubes of 35 cm in length and 7.5 cm in diameter and 5-L plastic bags. After 20 days, etiolated shoots percentages on nurse plants varied from 56.7 to 90.0%. The best results were associated with better ventilation and control of the excess of humidity inside the IDC. In the second trial, between late spring and early summer, only plastic tubes of two sizes were used: large (the same dimensions as in the previous trial) and small (25 cm in length and 5 cm in diameter). Both were placed in two different moments. The best results were achieved in nurse plants that were covered when the growth of buds had already begun. Under these conditions, the percentages of nurse plants with healthy etiolated shoots were 86.7 and 78.3% for small and large tubes, respectively. When the IDC were placed on nurse plants whose grafted buds have not started to show new growing shoots yet, the percentages were lower: 45.0% for small tubes and 31.7% for the large ones. In the nurse plants that formed etiolated shoots, the average number of them was 1.5 to 1.9 shoots per plant.