Abstract

The growth of two oil palm clones that were treated with six doses of paclobutrazol (0, 75, 150, 225, 300 and 375 mg per palm), applied just once to the soil, was measured under nursery conditions.  The 300- and 375-mg doses caused a significant reduction in growth beginning in the second month after application, an effect which was maintained even after six and a half months.  The intermediate doses slowed growth only up to four months.  The lowest dose showed a measurable effect only for the first three months after application.

Introduction

Paclobutrazol (PP333) is a growth regulator which inhibits biosynthesis of gibberellin, thereby slowing vegetative growth, inducing formation of flower buds, increasing flower tolerance to frost, and producing better fruit quality in different crops.  It can be absorbed through the stem, the leaves, or the roots, which means it can be applied by spraying, or as a soil treatment (Imperial Chemical 1984).

Due to the continual production of clone palms, in which plants are taken from the laboratory to the nursery on a weekly basis, it is important to make sure the plants are uniform in size when they are transplanted to the field.  One way to bring about uniform size in plants of different ages is the use of growth regulators.

Paclobutrazol is not normally used on oil palms, but its effects as a growth regulator have been evaluated on these plants (Sterling 1987; Hashim 1991).  The objective of this investigation was to evaluate various doses of paclobutrazol in order to determine its effects on the growth of two clones under nursery conditions.

Materials and Methods

The experiments were carried out from October, 1996 to April, 1997, in a nursery in the southern part of Costa Rica.  The six doses applied were 0, 75, 150, 225, 300 and 375 mg of active ingredient per plant, diluted in water and applied to the soil of plants between six and seven months of age.

The experiment was arranged in a split-plot design, where treatments were asigned in a randomized complete block with two replications. Large lots were two "ortet"-derived clones of compact material (Sterling et al . 1987) and the small lots, the six doses of paclobutrazol.

Seven growth evaluations were carried out (Breure and Verdooren 1995) on a monthly basis from October, 1996 (pre-application) to April, 1997.

Results and discussion

The comparison between the two clones revealed significant differences in the rachis length (nine months) and the leaf area ratio (12 months).  The growth-slowing effect of paclobutrazol could be seen beginning in the second month, and also affected leaf area and plant height.  No interaction between dose and clones was observed ( Fig.1 , Fig. 2 and Fig.3 ).

The 300- and 375-mg doses caused a significant reduction in growth beginning in the second month after application, an effect which was sustained through the last growth evaluation carried out (Figs. 1-3).  Between the third and fifth months, the plants treated with intermediate doses (150 and 225 mgs) showed a growth rate between that of the plants receiving the highest doses and the control plants.  Beginning in the fifth month, their growth was similar to that of the controls.  The plants given the lowest dose (75 mg) showed a significant reduction in height and rachis length during the second and third months after application.  Beyond that point, their growth was similar to that of the control, and was actually even greater during the last two evaluations carried out.

The 300- and 375-mg doses were linked to plants producing the lowest relative leaf area, which could be seen beginning in the second month.  The 150- and 225-mg doses were linked to an intermediate value for this variable, but only between three and four months after application.  The 75-mg treatment was no different from the control, and showed the highest relative leaf area at the end of the study.  Similar results were found by Hashim (1991), in which the effects of paclobutrazol treatment faded out between three and six months after application.

In very specific conditions, as in the case of clone management, the use of a product like paclobutrazol could be considered in order to produce uniform growth in a nursery with plants of various ages.  Moderate doses (150-225 mg per plant) could achieve this objective.  It is important, however, to take into account that the treated plants could experience undesirable side effects once they are transplanted to the field.  These effects must be evaluated before such products are used on a routine basis.

Bibliography

BREURE, C, J; VERDOOREN, L. R. 1995. Guidelines for testing and selecting parent palms in oil palm; practical aspects and statistical methods. ASD Oil Palm Papers. 9: 1-68

HASHIM, M. T. 1991. Paclobutrazol: a growth and flowering regulator of young oil palm. In 1991 Int. Palm Oil Conference, Agriculture. PORIM p. 85-94.

IMPERIAL CHEMICAL INDUSTRIES PLC. 1984. Boletín de datos técnicos. Paclobutrazol: regulador de crecimiento vegetal para frutas. 39 p.

STERLING, F. 1987. Utilización de paclobutrazol (PP333) para la extensión del período de permanencia de la palma aceitera en la etapa de vivero. Bol. Tec. Oil Palm Operations Chiquita Brands, Costa Rica 1(4): 89-93

STERLING, F.; RICHARDSON, D.L.; CHAVEZ, C. 1987. Some phenotypic characteristcs of the descendants of QB49:238, an exceptional hybrid of oil palm. Int. Oil Palm and Palm Oil Conferences. PORIM/ISP, Malaysia.