Ethylene

Smudging has been utilized to stimulate mango flowering in the Philippines. Only branches that attain sufficient age respond to smudging by forming reproductive shoots (Acala and San Pedro, 1935; Bueno and Valmayor, 1974). Rodriguez (1932), investigating smoke-induced flowering of pineapple, proposed that ethylene, generated by burning material, may stimulate flowering. Dutcher (1972) confirmed that smoke from smudge fires contained ethylene. Smudging and the use of ethephon in 1968 by F. Manuel (Barba, 1974) and others (Bondad, 1972, 1976) to promote mango flowering suggested that endogenous ethylene is integral for floral induction (Barba, 1974; Bondad, 1976; Chadha and Pal, 1986). Ethephon effectively promotes flowering of mangoes under specific conditions in the low-latitude tropics (Davenport and Nunez-Elisea, 1997).

The involvement of endogenous ethylene in flowering is supported by observations that indirectly link it to symptoms of ethylene production. Extrusion of latex from terminal buds occurs at the time of inflorescence initiation, and epinasty of mature leaves near the apex during expansion of the panicle has been observed (Davenport and Nunez-Elisea, 1990, 1991). Both are symptoms of plants exposed to high ethylene levels (Abeles, 1973). Indirect support also comes from reports that KNO3-stimulated flowering of mango is mediated by increased levels of endogenous ethylene (Thuck-Thye, 1978; Lopez et al., 1984). Mosqueda-Vazquez and Avila-Resendiz (1985) reported that the efficacy of KNO3 was negated by cobalt chloride (CoCl2) and silver nitrate (AgNO3), which inhibit the synthesis and action of ethyl-ene, respectively, when sprayed 1-4 h after KNO3. Saidha et al. (1983) reported a gradual increase in endogenous leaf ethylene production as the season of floral initiation approached. Ethylene production by stems producing reproductive shoots was up to fivefold that of resting stems.

Inconsistent (Pandey et al., 1973; Sen et al., 1973; Winston and Wright, 1986) or non-responsive results with ethephon (Pandey and Narwadkar, 1984; Ou and Yen, 1985; Pandey, 1989) or smudging (Sen and Roy, 1935), especially during warm, non-inductive conditions, have been reported. Davenport and Nunez-Elisea (1990, 1991) reported elevated ethylene production in mango stems in response to ethephon sprays without an accompanying floral response. Experiments were conducted during floral-inductive and non-inductive periods. Unlike Saidha et al. (1983), they observed no increase in ethylene production rates prior to or during panicle development.

The effect of ethylene on flowering is unresolved. It is likely that ethylene stimulates shoot initiation by inhibiting auxin transport from leaves to buds and stems (Morgan and Gausman, 1966; Beyer and Morgan, 1971; Riov and Goren, 1979, 1980; Ramina et al., 1986). This may increase the ratio of cytoki-nin to auxin in buds and stimulate shoot initiation (Davenport, 2000). Other factors (i.e. cool temperatures or aged leaves) may be responsible for floral induction (Ona and de Guzman, 1982; Davenport, 1993).

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