Bananas– The war on wilt, Morphology

Bananas– The war on wilt, Morphology ;Rody Blom, Saskia Bollerman, Janna Horjus, Koen Rurenga
Bananas are the very variable fruits derived from crossed species within the genus Musa, therefore a general morphological description of the genus Musa is included.
The banana plant is a large, perennial, monocarpic (fruiting once, then dying), monocotyledonous herb 2-9 m in height that arises from large, subterranean rhizomes (Nelson et al., 2006). The roots are adventitious,
spreading 4-5 m laterally, descending to 75 cm, but mainly in the top 15 cm,
forming a dense mat (Moore, 1992). Suckers spring up around the main plant forming a clump or "stool'', the eldest sucker replacing the main plant when it fruits and dies, and this process of succession continues indefinitely (Morton, 1987).
Leaves are produced by a single apical meristem, which typically forms only a low short stem or pseudobulb (McClatchey, 2000).
Smooth, oblong or elliptic, fleshy-stalked leaves, numbering 4 or 5 to 15, are arranged spirally. They may be entirely green, green with maroon splotches, or green on the upper side and red purple beneath (Morton 1987).
The petioles of the leaves are long and expanded below into long, sheathing and stem-encircling leaf-bases forming a pseudostem (Cheesman, 1947).
New leaves originating from the corm grow up continuously through the centre of the pseudostem with their laminas tightly rolled.
The emerging leaf unfolds a large oblong blade, 150-400 cm x 70-100 cm, with a pronounced supporting midrib and well-marked, pinnately arranged, parallel veins (Moore, 1992).
One terminal inflorescence rises from each corm, its axis (peduncle) extending through the centre of the pseudostem and bending down when exserted (Moore, 1992).
The spike, at first, is a large, long-oval, tapering, purple-clad bud.
As it opens, it is seen that the slim, nectar-rich, tubular, toothed, white flowers are clustered in whorled double rows along the floral stalk, each cluster covered by a thick, waxy bract, purple outside, deep-red within.
Normally, the bract will lift from the first hand in 3 to 10 days. If the plant is weak, opening may not occur until 10 or 15 days (Morton, 1987).
The bracts open in sequence (about 1 per day) from base to top while the peduncle elongates.
They often become reflexed when the flowers develop and they are shed when the fruits start to develop, but this differs between species.
Female flowers develop in the proximal 5-15 rows, male flowers at the distal end of the inflorescence, in the middle sometimes neuter flowers are present (Moore, Figure 1. Basic morphology of the banana plant 1992).
The flowers contain 5 stamens and an inferior, trilocular ovary.
The perianth (according to the usual interpretation) usually consists of two parts: a compound tepal (calyx) essentially tubular, but split to the base on the adaxial side, 5-toothed at the apex (Cheesman, 1947).
In about one day after the opening of the flower clusters, the male flowers and their bracts are usually shed,
leaving most of the upper stalk naked except at the very tip where there usually remains an unopened bud containing the last-formed of the male flowers.
However, there are some mutants such as 'Dwarf Cavendish' with persistent male flowers and bracts which wither and remain, filling the space between the fruits and the terminal bud (Morton, 1987).
The fruits are variable in size, shape and colour. They are generally elongate-cylindrical, straight to strongly curved, 3-40 cm long and 2-8 cm in diameter.
The fruit apex is important in variety identification; it may be tapered, rounded or blunt (Nelson, 2002).
The endocarp, ivory-white to yellow or pink, may be firm, even gummy with latex when unripe, turning tender and slippery, or soft and mellow or rather dry and mealy or starchy when ripe.
The flavour may be mild and sweet or subacid with a distinct apple tone.
The common cultivated types are generally seedless with only vestiges of ovules visible as brown specks (Morton, 1987).
Seeds are often present in wild Musa species.
When seeds are present, they vary among species in shape and morphology.
Seeds of Musa balbisiana are dark brown, ovoid, about 4 mm long with a conspicuous white, powdery endosperm (Nelson, 2002).