BACKGROUNDER

            A Flowering in bamboo is a botanical enigma. The factors that switch a bamboo plant from vegetative to flowering state are not fully understood. Nearly all species of bamboo seem to have their own life histories. Some species outside of the Indian-Asian tropics, and a very few in these tropics, have populations composed of individuals that grow to maturity and then flower and seed annually for many years. The culms that flower often die after the fruit has developed but other culms and rhizomes survive and perpetuate the stand. Many of the more common Indian-Asian species have populations made up of individuals that seed synchronously at regular and long supra-annual intervals. After growing by rhizome and branch production for a species-specific period of 3-120 years, nearly all the members of one species in one area produce wind-pollinated flowers, set large quantities of seed and die. This seed germinates immediately or when the first rains come.

            According to their flowering habits, there are three types of bamboo: (i) those that flower annually or nearly so, e.g., Arundinaria spp. in India and Schizostachium brachycladum in Thailand; (ii) those that flower gregariously and periodically; (iii) those that flower irregularly. The flowering habit of Bambusa spp. and Dendrocalamus spp. in the tropical regions of Asia and of Phyllostachys and other genera in Japan belongs to types (ii) and (iii). P. edulis flowers sporadically, and the flowering occurs in small areas or in a few clumps. Periodical and gregarious flowering occurs in cycles; the cycles are more or less constant for a species in a given locality but differ between remote locations. Below are the flowering cycles of some Indian species:

 Although a wide range of research and discussion is going on, the flowering of bamboo is still unexplained and mysterious. There are several theories concerning the causes of flowering and death of bamboo:

1. Pathological theory, which postulates that flowering is brought on by the destruction of bamboo by organisms such as nematodes, fungi, insects and parasites;
2. Periodical theory, which proposes that the cycle starts with bamboo regeneration through asexual methods (rhizome and culm elongation), reaches maturity and results in flowering;
3. Mutation theory, which considers that bamboo regeneration through any methods of asexual propagation is mutation and brings about flowering of bamboos;
4. Nutrition theory, which proposes that flowering and fruiting are usually the result of a physiological disturbance arising chiefly from the poor growth of the vegetative cells, brought about by an imbalance in the carbon-nitrogen ratio;
5. Human theory, which states that human practices such as cutting and burning induce bamboo flowering.

It is generally believed that flowering in bamboo results in death of the bamboo. Subsequent to flowering, bamboos show different types  of mortality behaviour. In some bamboo, parts above the land perish or only underground parts die, complete plant die except rhizomes or the plant dies in totality where regeneration is possible only through seeds.

6. Flowering does not result in the death of either aerial or underground parts, e.g., some species of Arundinaria, Phyllostachys, Bambusa atra.
7. Flowering results in complete death of aerial parts only, the rhizomes remain alive and plants regenerate, e.g., Arundina amabilis, A. simonii, Phyllostachys nidularia.
8. Flowering results in complete death of aerial and underground parts and regeneration is only possible from seeds, e.g., Melocanna bambusoides, Thyrostachys oliveri, Bambusa arundinacea, B. tulda.

KP