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Floral biology and breeding behavior were studied in the bamboo Dendrocalamus strictus Nees. The inflorescence in this species is a large branching panicle. Fertile florets are intermixed with smaller sterile ones. There are six stamens. The ovary is stipitate and turbinate. The style is long and the stigma is bifid and plumose. Dendrocalamus strictus is typically dichogamous and protogynous. The gynoecium matures 3-4 days before the androecium, effectively preventing self pollination. Flower bloom, which took place over a period of 2 to 3 h, was dependent on air temperature and only occurred between 0600 and 1300 h. Dendrocalamus strictus is anemophilous. Flowers in the male phase were visited by insects. These insects completely neglected the flowers at the female phase. The insects fed on the pollen and were not pollen vectors. When wind was excluded by enclosing the inflorescences in bags there was no seed set, indicating that cross pollination by wind is necessary for fertilization and that parthenocarpy and apomixis are not occurring in this species. Pollen fertility was about 98% as indicated by staining fresh pollen at the time of anther dehiscence and pollen release with Alexander's stain (Alexander 1969). When placed on a modified Brewbaker-Kwak medium containing 1% glucose, the pollen grains germinated well, and the pollen tubes grew to 15-20 times the diameter of mature pollen grains. Although profound protogyny has its disadvantages in times of sporadic flowering, it can be useful in breeding programs because it eliminates the need for emasculation.

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The majority of bamboos (Graminae) are arborescent and perennial. The erect stems (culms) of woody bamboos are useful for a wide variety of purposes. Most bamboos flower only once at the end of very long vegetative growth phases and die afterwards. Flowering in bamboos is thought to be under genetic control, occurring somewhat like an alarm clock, going off at a preset time. The nature of this genetic clock and any interaction between the "internal clock' and the environment are not yet known. Because of this "peculiar' flowering behavim: bamboo seeds are available only at very long intervals. Obtaining concurrent flowering in two or more species (or varieties) in space and time is difficult, making perennial seed propagation and genetic improvement by breeding nearly impossible. Besides, this peculiar flowering behavior of bamboos is also believed to have brought the giant pandas to the verge of extinction. One of the spectacular developments in the area of bamboo genetic improvement has been the precocious in vitro induction of flowering. By this method it has been possible to rapidly accelerate the reproductive development (within 3-6 mo. versus 30~0 yr in nature). This has opened the possibility of perennial seed propagation and hybridization. In vitro induction of flowering can be obtained by diverse methods which show sonic similarities and differences. Induction of flowering is possible in cultures derived from both juvenile and mature explants. The proportion of seedlings induced to flower is possibly influenced by genotypic variation, though the role of methods used cannot be ruled out. A cytokinin or a shift in the auxin-cytokinin equilibrium is believed to bring about in vitro induction of flowering. The pH of the media also has an influence. Induction of flowering and rhizogenesis is considered to be an antagonistic phenomenon in vitro. A comparison between in vitro and in vivo flowering in Bambusa arundinacea has shown that though smaller, in vitro-induced florets are comparable to normal florets. There is reduced pollen fertility and some impairment in pollen wall development. Biochemical studies on the in vitro-induced flowering in bamboos have shown (1) selective expression of esterase and peroxidase isozymes during transition of nonembryogenic calluses to embryogenic calluses, somatic emb~o development, germination and subsequent flowering of somatic embryo derived shoots, and (2) minimal peroxidase activity before rhizogenesis and induction of flowering in vitro. There are reports of published and comparable methods having failed to induce flowering in vitro.

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