Ornamental bananas

Introduction

The plant family Musaceae is well known for economically important bananas and plantains. Bananas are the most popular fruit in the world, which are grown in more than 150 countries and plays a major role in terms of food security. However, there are many other types of bananas known for their ornamental flowers or foliage but not their fruit.  These ornamental types are easy to grow and flower and add lush tropical look to any garden.

South East Asia and Africa are considered as a primary and secondary centers of diversity (Simmonds, 1962, 1966) for banana. This monocotyledonous herbaceous perennial belongs to order Zingiberales and family Musaceae; Musa along with Musella and Ensete are the three genera of the family Musaceae. Each genera is further divided into sections based on basic chromosome number, inflorescence orientation and arrangement of the flowers.

Classification pattern of Family "Musaceae"

Botany

The banana plant (Musa, Musella, and Ensete) is a herbaceous perennial. The tree "trunk" is called a pseudostem because it does not lignify or undergo secondary growth. The pseudostem is a cylinder of tightly bound leaf petioles that arise directly from an underground stem, or rhizome. The pseudostem color may be green, red, or purple/black and can contribute to the ornamental quality of the plant. The pseudostem of Musella is swollen at the base whereas the pseudostems of Musa and Ensete tend to be the same width over their entire length. Each pseudostem will produce a single terminal inflorescence which hangs down beneath the leaf canopy on a long flower stalk in Musa and Ensete, but faces upward on a short flower stalk in Musella.

Bananas grow from underground storage organs called rhizomes. Musa and Musella, form offsets freely from the rhizome (suckers) but Ensete almost never forms any, the main pseudostem of bananas is monocarpic (it dies after flowering) after which the next oldest sucker grows to replace it. As a result, bananas tend to move around in the garden a few feet over the course of several years. With most bananas, many pseudostems will grow at the same time and form a colony covering a small area. Since Ensete plants do not sucker it dies after flowering.

The leaves are the main ornamental feature of the banana plant and impart a bold tropical look to the garden. The smooth, waxy leaves are generally quite large, reaching up to 6" wide by 2' long on dwarf plants, and up to 2' wide by 9' long on large ones. The leaves are normally dark green color, but variegation is quite common. Variegation appears as white, red or purple/maroon splotches or sectors on the leaf blade. The leaf midrib may have a contrasting color, which is usually red contrasting with the green leaf. Often, the color of the reverse side of the leaf contrasts with the front side and on windy days viewers are treated to flashes of color.

Banana flowers are very exotic looking. In temperate gardens some ornamental bananas may not flower because the season is too short. Each species has a set number of months that the pseudostem must grow in order to flower. Musa velutina, the pink velvet banana, is the only species that can die to the ground in winter and flower and fruit the following season, requiring only 20 weeks to complete its life cycle. Musella lasiocarpa takes several seasons to produce a pseudostem large enough to flower, but when it does, the inflorescence lasts several months. Other bananas must retain a pseudostem for more than one growing season in order to flower and produce fruit. Some species like Musa basjoo pseudostems will remain viable at 15⁰ F and subsequently flowers in the following season.

Technically, the "flowers" are inflorescences (clusters of flowers on a single structure), and a single inflorescence forms on a spike at the top of the plant. Musa and Ensete flower stalks are long and hang down beneath the leaf canopy, but Musella inflorescences are borne on short stalks and face upward. Bananas generally will not flower until there are 9-12 leaves on the pseudostem. The individual florets are slim and tubular and are subtended by very large, brightly-colored bracts that may be red, purple, orange, or yellow. The inflorescence starts off as a large purple tapered bud. The bud elongates as it opens up, revealing bracts which surround whorls of florets. Banana plants are monoecious meaning separate male and female flowers are produced on the same inflorescence. The female florets are grouped together in 5 to 15 rows at the basal end of the inflorescence, followed by a region of hermaphrodite or neuter flowers. Finally, there is a zone of male flowers near the tip of the inflorescence. The flowers open sequentially from the basal end to the apical end. The male flowers are shed a few days after they open, leaving the apical tip of the flower stalk bare, except for the growing point. The female flowers grow into bunches of bananas.

Propagation

This plant can be propagated through suckers or corms and seeds. Sword-suckers with a well-developed rhizome, conical in shape with lanceolate leaves and actively growing central buds, weighing 500-750g, 2-4 months age plants  are generally used. Cut rhizomes called bits and peepers are also used successfully. Some genera like Ensete pare ropagated by seeds. Some of the seeds germinate readily after harvesting; shows no sign of dormancy and others become dormant after drying. Dormancy can be removed by giving pre-sowing treatments - scarification of seeds with sulphuric acid, chipping of testa, softening testa by soaking, use of alternating temperatures, etc.

Banana propagated through tissue culture is cost effective for the production of disease-free plants. Micro propagation has been preferred over conventional propagation owing to its faster multiplication, uniformity in planting material and disease-free material from transmissible pests and diseases.

Climate

Banana is well suited for cultivation from humid subtropical to semi-arid subtropics up to 2500 m above mean sea level (Hill banana, M.sikkimensis, Musell lasiocarpa) with a temperature of 15-35⁰C and rainfall of 500-2000 mm/year. Most of the species are susceptible to low temperature except genera like Musella and some of the Eumusa species like M.sikkimensis, Musa basjoo.

Soil and planting site

It can be grown in all kinds of soils having good drainage. In sandy soils, plants grow faster compared to vertisol or clay loam. Though soil pH of 6.5-7.5 is optimum, banana can be grown in soils having a pH up to 8.5 with suitable amendments.

The planting site should be chosen for protection from wind and cold weather, if possible. The warmest location in the home landscape is near the south or southeast side of the house.

Planting

Pot and Pit methods are generally followed in case of banana. Pits of 60 cm³ size are dug, and filled with a mixture of soil, sand and farmyard manure with a ratio of 1:1:1. Sucker or seedling is planted in the center of pit and the soil around the pit is compacted. Ornamental purpose bananas can be planted as close as 2-3’ apart. Dwarf statured plant species like Musella species and some dwarf types can be grown in containers.

Repotting can be done once in three years by replacing the old soil with the nutritive potting mix.  Bananas will grow, fairly slow in the indoor conditions. So care should be taken to provide plenty of light and humidity. Plants can be protected from the extreme temperatures and water logging. In temperate areas, gardeners may also elect to let their plants go dormant by slowly withholding water as the weather cools. Remove the main stem and place the container in a cool dark place till favourable weathers conditions prevails.

Use of growth regulators for dwarfing of the bananas

Most of the bananas are highly vigorous and not suitable for container gardening. Application of growth retardants significantly reduces the plant height; this effect improves the appearance of banana and increases the use of plant for ornamental gardening. Application of PP333 0.25 mg/plant (Gaspar et al, 1999) at end of hardening stage reduce the plant height two months after application. The incorporation of growth retardants (GR) such as Ancymidol (ANC) or Paclobutrazol (PBZ) in liquid culture media during multiplication stage of bananas decreases the excessive growth of stems and leaves. Soil application of Paclobutrazol also reduces the plant height by 25% without any adverse effect on the flowering.

Classification of ornamental bananas and its description

Sections Callimusa and Rhodochlamys belong to Musa genera contain most of the potential ornamental forms of banana. Some other ornamental species belongs to genera’s Musella and Ensete are also briefly described here.

Section Rhodochlamys

Most of the species in this section are best known for their brightly colour bracts on erect inflorescence, this feature makes them popular as ornamental plants. Section Rhodochlamys is the only section in Musa adapted to withstand the seasonal droughts. The natural habitat of Rhodochlamys species is Northeast India, Bangladesh, Myanmar and Northern Thailand, except for Musa rosea, which is native to Cambodia and southern Vietnam. Musa sanguinea is also known to occur in Yunnan, China. Among the nine identified species in this section seven species are well characterized. While remaining two, M. Siamensis and M. sanguinea are having less definite status. Various Rhodochlamys species found that they were suitable for indoor and greenhouse culture, and also can be grown outdoors during its growing season.

Important ornamental species of section “Rhodochlamys”

Section Callimusa (x = 10, 2n=20)

Plant bears upright flower stalk with variously coloured buds, flowers along with the seeded fruit. Some of the species are described here which are having ornamental value.

Important ornamental species of section “Callimusa”

Genera Ensete (2n=18, x=9) species belongs to this genus and are found throughout Africa and southern Asia. It contains as many as nine species. Among the species in these genera ar - Ensete glaucum, Ensete superbum (Rock banana), Ensete perrieri, Ensete ventricosum and its sub species like E. ventricosum Maurrelli (Abyssinian banana) and their dwarf types are suitable for home gardening.

Genera-Musella (2n=18, x=9) is the most fascinating unique member of the family. This genus comprising of two species (Musella lasiocarpa, M. splendida) is native to South East Asia including southwest china, Vietnam, Laos and Myanmar.

• Musella lasiocarpa (Chinese dwarf banana, Golden lotus banana) is native of Yunnan Province, China. It grows in high mountain regions up to an altitude of 2500m. Ornamental nurseries in western countries have extolled for its beauty, hardiness and resistance to cold temperatures.It is known for its yellow erect flower generally appearing during the second year of cultivation, which can last a few months. Just before opening, the flower resembles a lotus - from which the plant gets one of its names “Golden lotus bananas". The plant is small less than 60 cm tall with persistence leaf sheaths on pseudostem. Leaf blades are elliptical, up to 50cm long and 20cm wide with pointed tip. Inflorescence is erect, densely arranged, 20 to 25 cm long. Bracts are yellow, each subtending 4 to 5 flowers. A new and attractive variety ‘Musellalasiocarpa var. rubribracteata’ found by Ma Hang et al in the 2011 differs from the original species by its orange-red to red bracts and reddish to purple-red coloration of the leaf petiole and midrib.
• M.Splendida slightly differs from Musella lasiocarpa which is of nearly 1 to 1.2m height. The fruits of Musella splendida are seedless and parthenocarpic but those of Musella lasiocarpa bear viable seeds.

Improvement of ornamental banana

Somaclonal variations: Mass propagation of bananas through in vitro techniques can lead to a high percentage of non-true type plants. The percentage of Somaclonal variants in banana ranges from 5 to 50% or even higher in some cases. Variation has been found for plant height, leaf shape and colour, pseudostem morphology and colour, reproductive organs morphology and sucker emission rate. Some of these Somaclonal variants such as extra-dwarf or variegated types, might be interesting for their use in landscaping or for indoor pot cultivation.

Mutation Breeding: suitable variations for some of the characters can be created by using chemical as well as physical mutagens in case of banana. Suitable variants for disease resistance, dwarf stature were created in different edible varieties of banana. Same methods can be useful for creation of ornamental types too.

Development of ornamental hybrids: most of the edible and ornamental types of the bananas are evolved as a result of natural hybridization which occurred in their natural growing areas. Still enormous scope is there for the improvement of ornamental, edible or dual type cultivars by artificial hybridization techniques.

• Hybridization between Rhodochlamys and Eumusa: Sections Rhodochlamys and Eumusa are closely related having similar chromosome number (2n=22, x=11) and provide potential source of exploitable new genes.  Dual purpose varieties can be created through these hybridization techniques. The products of hybridization and introgression involving the Rhodochlamys are likely to be attractive, and will therefore have ornamental potential along with drought resistance nature.
• Hybridization between musa species with different basic chromosome number: very limited phenotypic information is available for inter-sectional hybridization between species with 2n=22 (Sec-Eumusa and Rhodochlamys) and 2n=20 (Sec-Callimusa and Australimusa). Sec-Australimusa (T-genome) has been reported to have very limited compatibility with A-genome species
• Hybridization with species from other genera: Limited number of studies were conducted to investigate the intergeneric hybridization Musaceae. Some of the studies were conducted between the Ensete superbum (2n=18) and Musa balbisiana (2n=22) with no successful results.

Major Pests and Diseases

In banana, major diseases are caused by fungi, bacteria as well as virus. Some major diseases are Fusarium wilt, sigatoka leaf spot, bacterial wilt, bunchy top and mosaic virus. Banana weevil, burrowing nematode (Radophilus similes) and root-knot nematode (Meloidogyne spp) are some of the major pests cause severe damage to these plantations.

Author: Aparna V, ICAR-CPCRI, Kasaragod, Kerala