On the agronomy and botany of salak (Salacca zalacca)

Keywords: Salak, Salacca zalacca, Palmae, dioecious, haustorium, simple leaf, compound leaf, sucker, phyllotaxis, seedling, inflorescence, fruit, hand pollination, farm yard manure, fertilizer, shading, walking palm.

Salak is a dioecious, suckering palm, grown for its fruit, mainly in Indonesia. Traditionally, plants are raised from seed and planted in market gardens under the shade of existing trees. Crop care is largely limited to roguing of most male plants, cutting excess suckers and ageing leaves, and hand pollination. Each production centre mainly grows its own favoured variety, but in the 1990s 'Pondoh', originally from Yogyakarta, became popular also elsewhere. Yield varies widely (say 5 - 13 kg per plant per year). A better understanding of the crop can presumably greatly increase yield levels. This fits in with Indonesia's strategy to develop fruit growing with a view to improving nutrition and increasing exports. Salak is one of the fruit crops selected under this strategy. This thesis reports explorative research on the agronomy and botany of the crop.

Agronomy

Intensive pollination of this dioecious species leads to heavy fruit and seed set. Seed shape is determined by the number of seeds per fruit. A correlation between seed shape and sex of the seed as assumed by salak growers in Indonesia is unlikely.

Pollination and pollen quality influence both quality and quantity of the fruits. Choice of pollen depends on the cultivar to be pollinated.

Salak seed is recalcitrant and endosperm plays an important role in germination. Without endosperm the embryo is unable to grow and develop. Storage of salak seed in charcoal can sustain its viability and enhance seedling growth compared to storage in ambient air or even in sawdust.

Germination of salak seeds was retarded when planted in heavy soils. Organic matter is needed to improve the physical properties of the soil, particularly of heavy soils. A higher organic matter content also increased N and P levels in the soil and nutrient levels in the leaves. In the nursery, salak seedlings need 50 - 75% shade and an adequate supply of nitrogen.

During later stages of growth inorganic fertilizer reduced the numbers of split and decaying fruits, thus increasing the numbers of good fruits per bunch.

Botany

In young seedlings, the leaf shape is simple but leaves emerging later are pinnate. The duration of leaf formation from emergence and spear growth until expansion and maturation varies considerably from one leaf to the next.

Leaf area assessment is cumbersome; simple leaf characteristics may be measured to estimate leaf area, but the relationships with leaf area vary, depending on growing conditions.

Suckers are produced from short horizontal stems radiating from the mother stem. Their number needs to be reduced in commercial growing.

In a variety trial, the first inflorescence emerged 23 - 34 months from sowing; after 42 months the percentage of flowering plants ranged from 50 - 84%. The inflorescence bud develops into a spear and splits the base of the subtending leaf to break into the open.

Female and male plants are similar in morphology. The sex should be known at planting, to allow optimal spacing of fruit-bearing plants in an orchard and to include enough pollinator plants from the start. This can be achieved through vegetative propagation, if necessary through tissue culture, or possibly by the genetic markers indicating the sex of seedlings.