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United States Department of Agriculture

Agricultural Research Service

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Research Project: IMPROVING FLOWERING OF LONGAN AND LYCHEE TREES IN HAWAII

Location: Tropical Plant Genetic Resources and Disease Research

2009 Annual Report


1a.Objectives (from AD-416)
1) Optimize chlorate-induced flowering & fruit production in longan;.
2)Determine the long-term effect of chlorate application on longan fruit quality;.
3)Determine floral induction for "Kaimana" Lychee;.
4)Evaluate new lychee cultivars for Hawaii; and.
5)Stimulate off-season flowering of lychee.


1b.Approach (from AD-416)
1) Foliar applications of alternative chemicals to chlorate will be evaluated & fruit thinning experiment will be conducted;.
2)Soil chlorate levels, plant nutrition, flowering & fruit quality will be evaluated on longan tree after repeated application of chlorate;.
3)Artificial cool temperatures will be used to determine floral induction for "Kaimana" lychee;.
4)Molecular markers will be used to identify lychee that flower & fruit in Hawaii; and.
5)Grafting experiments will be used to transmit floral stimuli from longan to lychee and between lychee cultivars with different floral initiation requirements. (Documents Trust agreement with UH Hilo. 425 log 31540). Formerly 5320-21000-009-07T (09/2008).


3.Progress Report

Comparison of the recommended thinning protocol of removing 2/3 of the flowering panicle and a foliar fertilizer schedule to increase fruit size is being evaluated. Preliminary results suggest that foliar fertilizer and hand thinning result in fruits of similar size and TSS (total soluble sugar). Fruits from this study were provided for the post-harvest quality study which showed that longan trees treated with excess foliar fertilizer results in diminished post-harvest quality and increased disease incidence.

Treatment of ‘Biew Kiew’ longan trees with low (50g) and high (300g) KClO3 levels were evaluated over a three year period. Lower chlorate treatments on trees not previously treated with chlorate resulted in flowering that ranged from 48% to 93% for year 1, 6% to 22% for year 2 and 34% to 71% for year 3. Higher chlorate treatments on trees not previously treated with chlorate resulted in flowering that ranged from 78% to 100% for year 1, 100% for year 2 and 52% to 91% for year 3. These results suggest that 50g KClO3 is too low a level to give consistent flowering and fruit production; un-thinned fruit size is not significantly different compared to thinned fruit from trees treated with 300g KClO3. The diminished flowering response was not observed until the 3rd application of chlorate at the higher rate of 300g KClO3 but a lower response was observed in year 2 with the lower chlorate treatment. A study has been initiated to synchronize the vegetative growth of the longan trees after fruit harvest to determine if the number of flushes prior to chlorate treatments will affect the flowering response.

Preliminary experiments to determine the cold requirements for ‘Kaimana’ flowering were conducted on ‘Kaimana’ potted plants moved to the Volcano experiment station (4000 ft elev) and exposed to cold temperatures for 4, 5 and 6 weeks. Exposure to average daily air temperatures of 56.69 °F and soil temperatures of 50.38°F for all exposure times resulted in 100% flowering of ‘Kaimana’ while untreated control plants kept in Hilo did not flower, suggesting that potted lychee plants are suitable to determine the temperature and duration required for floral induction of ‘Kaimana’. Preliminary experiments on exposure of ‘Kaimana’ to day temperatures of 72°F and night temperatures of 60°F or 65°F for 2 weeks did not result in lychee flowering. Other growth chamber experiments to determine the cold requirements of ‘Kaimana’ floral induction are currently being evaluated.

The ADODR monitored progress through site visitations, individual meetings with growers and presentations at the Hawaii Tropical Fruit Growers annual meeting.


Last Modified: 4/24/2014
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