Fruit

The pepper fruit is botanically a drupe, but often referred as a berry. The fruit is single seeded, having a fleshy pericarp and hard endocarp. The seed has little endosperm but copious perisperm. The fruit differs in size and to some extent in shape also. Some cultivars have bold fruits (berries) (Panniyur 1, Balancotta, Vadakkan, Uddhaghere etc.), while in other cases the fruits are either medium or small. Jeerakamundi and Kuriyalmundi have the smallest fruits, and the largest are those of Vadakkan. The fruits are spherical in shape in most cases, obovate in a few and oblong in others. Fruit (berry) characters of pepper cultivars and Piper spp. are given in Table 2.7 and 2.9.

The fruits can be either free as in most species, or fused laterally as in P. longum and P. hapnium. Fruit shape is obovate-oblong in P. attenuatum, P. argyrophyllum, P. hymenophyllum, P. galeatum, P. wightii, P. sugandhi and P. schmidtii; elliptical in P. longum and P. mullesua; obovate in P. silentvalleyensis and spherical or rarely oblong in P. nigrum and P. trichostachyon. The fruits are minute in P. longum, P. mullesua and P. silentvalleyensis, bold in P. galeatum, P. trichostachyon, P. sugandhi and in certain P. nigrum collections; and medium in other species. The various species of Piper can also be subdivided on the basis of colour change of fruits on ripening. The two basic types are green turning to black on ripening; and green turning to yellow, orange or red on ripening. P. attenuatum, P. argyrophyllum, P. hymenophyllum, P. longum, P. mullesua, and P. silentvalleyensis belong to the first group. P. galeatum, P.

Table 2.9 Fruit (berry) characters of Piper species.

Species

Fruit nature

Fruit shape

Fruit taste

P. argyrophyllum

Free

Obovate-oblong

Bitter

P .attenuatum

Free

Obovate-oblong

Bitter

P. barberi

Free

Spherical

Bitter

P. hapnium

Fused

Elliptical

Bitter/spicy*

P. hymenophyllum

Free

Obovate-oblong

Spicy

P. galeatum

Free

Elliptical

Spicy

P. longum

Fused

Elliptical

Bitter

P. mullesua

Free

Obovate-oblong

Spicy

P. schmidtii

Free

Obovate

Bitter/spicy*

P. silentvalleyensis

Free

Spherical

Spicy

P. trichostachyon

Free

Obovate-oblong

Pungent

P. sugandhi

Free

Obovate-oblong

Pungent

P. sugandhi vai.brevipilis

Free

Obovate-oblong

Pungent

P. wightii

Free

Obovate-oblong

Bitter

* Bitter initially, gently spicy later.

* Bitter initially, gently spicy later.

trichostachyon, P. sugandhi, P. wightii, P. schmidtii and P. nigrum belong to the second group.

Fruits taste bitter in P. attenuatum, P. argyrophyllum, P. hymenophyllum, P. schmidtti and P. wightii. In P. galeatum and P. trichostachyon fruits taste bitter first and somewhat pungent later. The fruits of P. longum, P. mullesua and P. silentvalleyensis taste spicy and aromatic, while the fruits are pungent in P. nigrum and P. sugandhi.

DEVELOPMENTAL MORPHOLOGY

The origin and development of vascular system in Piper was studied by Pal (1961) on which the following discussion is mainly based. The tunica is two layered in P longum, P. nigrum and in P. betle; while it is three layered in P. ornatum. The tunica cells show high chromaticity and divide anticlinally. The foliar foundation initiates at the second tunica layer. The corpus cells are generally larger in size than the tunica cells and they divide at various planes.

The free apex in transverse section is almost round and it becomes oval as the foliar initials develop on one side. The primary meristem ring appears at the junction of the axis and the newly organized leaf primordium. The leaf traces are differentiated in this region. This primary meristem ring breaks up into 4-6 strands, each of which organizes into a separate bundle forming the central ring of vascular bundles. At this stage the leaf traces of the newly organized leaf primordium form an outer ring of vascular bundles in the stem (Fig. 2.15).

The leaf primordium is initiated in the second tunica layer by periclinal division. By subsequent divisions of the tunica layers and the corpus cells, the foliar foundation is laid down at one side. The newly formed leaf primordium extends laterally to form the collar. The vascular supply of the leaf primordium differentiates in the primary meristem ring and it develops acropetally. The peripheral ring of vascular bundles comprise of the leaf traces and the additional vascular bundles (Pal 1961). The leaf traces are the branches of the medullary bundles and on approaching a node they become laterally extended and give out branches. The number of leaf traces is never constant, this also depends on the number of medullary bundles. The "additional vascular bundles" (peripheral or cortical vascular bundles) are organized from a separate meristem which appears de novo. This meristem at first appears at the second internode between the leaf trace bundles. The cells situated between leaf traces become highly meristematic and gradually get differentiated into vascular bundles. They ultimately form small bundles between the leaf traces. The number of peripheral bundles situated between the two lateral traces varies from 1-2. The two satellite leaf traces which run by the side of the medium bundle are organized in this peripheral meristem. Thus the peripheral ring of vascular bundles is made up of leaf traces and the cauline bundles. The leaf traces move out into the collar and they finally leave the axis when they enter into the adjacent leaf. In the node the peripheral bundles become laterally expanded and become meristematic in nature. They move inside and become continuous with the peripheral meristem of the upper internode.

Figure 2.15 Diagrammatic representation of origin and development of vascular system in black pepper. 1. T.S. of the shoot apex showing the primary meristematic ring with first leaf (lf1) primordium having the median leaf trace at one end. 2. T.S of shoot apex showing the primary meristematic ring and the peripheral leaf traces of second leaf (lf ); 3 and 4. T.S of

shoot apex showing the internode below lf2 and leaf sheath of lf3. Internode shows the differentiation of medullary bundles from the primary meristematic ring and the development of peripheral meristem in between the leaf traces. 5, 6, 7. T.S. through node showing the behavior of leaf traces of lf2 and the origin of bud traces. 8. T.S. of internode showing the leaf traces of lf2 and peripheral cauline bundles lying on the selerenchymatous band, four medullary bundles and central mucilage canal. (After Pal 1961).

Figure 2.15 Diagrammatic representation of origin and development of vascular system in black pepper. 1. T.S. of the shoot apex showing the primary meristematic ring with first leaf (lf1) primordium having the median leaf trace at one end. 2. T.S of shoot apex showing the primary meristematic ring and the peripheral leaf traces of second leaf (lf ); 3 and 4. T.S of

shoot apex showing the internode below lf2 and leaf sheath of lf3. Internode shows the differentiation of medullary bundles from the primary meristematic ring and the development of peripheral meristem in between the leaf traces. 5, 6, 7. T.S. through node showing the behavior of leaf traces of lf2 and the origin of bud traces. 8. T.S. of internode showing the leaf traces of lf2 and peripheral cauline bundles lying on the selerenchymatous band, four medullary bundles and central mucilage canal. (After Pal 1961).

The medullary bundles have been found to organize in the primary meristem ring. When they approach the nodes they become laterally expanded and then join each other and give out branches which diverge outward and form the leaf traces. After giving out the leaf traces they repair themselves into the medullary bundles. Thus the leaf traces are the branches of the medullary bundles. At certain stage of development in the nodal region three rings of bundles are noticed—the peripheral ring composed of leaf traces and the peripheral bundles, the intermediate ring composed of leaf traces just given out by the medullary bundles and the central ring of medullary bundles. As soon as the leaf traces leave the peripheral ring for the adjacent leaf, the peripheral bundles move inside and join the middle ring. At the fourth internode the cells below the peripheral meristem ring become highly chromatic and they divide into small cells. They form a complete ring of small cells, 4-7 cells deep, which later differentiate into a sclerenchymatous zone.

The axillary bud primordium appears first in the axil of third leaf. The process of development seems to be similar in all species of Piper. The medullary bundle after giving rise to the median leaf traces gives out the bud traces from its free ends. These two traces break down into smaller branches which form the vascular supplies to the axillary bud. The first leaf given out by the axillary bud always develops into a prophyll.

The development and distribution of the mucilage canals in Piper spp. was described by Van Teighem (1908). He grouped plants into three categories viz. species having one central canal accompanied by peripheral canals, those having only the central canal and in the third group they are absent. The central mucilage canal is present in P. nigrum, P. betle, P. hymenophyllum, P. attenuatum, P. sugandhi, P. longum, etc. The mucilage canal is absent in P. triochostachyon and P. galeatum (Ravindran 1991).

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