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Ambiphotoperiodic flowering response of Kenaf (cv. Guatemala 4)

R.L. Williams

NSW Agriculture, Trunk Road 80, Private Mail Bag, Yanco NSW 2703

Kenaf, Hibiscus cannabinus, is a fast growing erect annual plant whose stem could be used as the raw material of paper pulp. Stem yields of crops with adequate nutrition and irrigation are limited by the duration from planting to flowering. The understanding of the control of flowering is therefore critical in producing maximum stem yields in irrigation areas in northern Australia. The literature reports that Guatemala (G4) is a quantitative short day plant in Australia (1) and is photoperiod insensitive in the south-east of the United States (2). This aims to attempt to reconcile these two observations.

Methods

A multilocational trial at a range of latitudes from 17°15'S to 34°33'S was established to determine the control of flowering of G4 in a range of environments. There were 10 approximately monthly sowings of G4 at Ayr (-19°32')with a two sowings in early summer at Kairi (-17°15'S), three at Biloela (-24°21'), Hermitage (-27° 12') and Narrabri (-30°20'), and six sowings at Yanco (-34°33'). Date of 50% flowering, defined as when 50% of the plants had flowered, was recorded for all plantings.

Results and discussion

Days to flower from the 10 sowings at Ayr ranged from 90 to 221 days. No sowing flowered during the long days of summer, with four sowings 2 September, 30 September, 4 November, and 2 December all flowering between 11 and 25 April. Analysis of the data suggested that at latitudes of 19°32'S (i.e., Ayr) and lower, G4 behaves as a quantitative short day plant with a critical photoperiod of 13.6 hr, above which it was not induced to flower. However at latitudes greater than this for all 14 summer plantings, G4 flowered at 70 to 100 days after sowing even though they were in photoperiods greater than 13.6 hr that prevented flowering at more northern latitudes.

It is hypothesised that G4 demonstrates an ambiphotoperiodic response whereby flowering is induced at photoperiods less than 13.6 hr and greater than 14.2 hr, but not at intermediate photoperiods. Ambiphotoperiodic flowering response has been determined for 13 other species in controlled environments using artificial daylengths. G4 is unique in the literature in displaying an ambiphotoperiodic response in natural environments. The ambiphotoperiodic response of kenaf could be utilised to separate the seed and fibre production regions so that maximum stem yields in irrigated environments in northern Australia could be obtained.

It is suggested that the ambiphototperiodic flowering response of G4 is the prime reason for the different conclusions between Australian and American workers on the control of flowering in G4. In Australia, published flowering data of G4 was observed in northern Australia, where the plant does not flower above a critical photoperiod. However, American workers in the southeastern States are at a much greater latitude, where longer daylengths are experienced. At this location, G4 flowers at a similar time after planting, regardless of planting date. The ambiphotoperiodic response of G4 identified in this paper is able therefore to explain a major discrepancy in the current literature.

References

Muchow,R.C. 1981. Proc. Kenaf Conf., Brisbane, May.

White, G.A. 1970. Production Research No. 13, Agricultural Research Service, USDA

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