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R. Nunez-Elisea, M. L. Caldeira, and T. L. Davenport

Thidiazuron (TDZ; N-phenyl-N-1,2,3-thiadiazol-5-ylurea) stimulates axillary bud break in some horticultural crops. We are exploring its ability to initiate bud growth in mango trees in order to manipulate vegetative and reproductive shoot initiation. Axillary buds on defoliated, decapitated shoots were treated in late October, 1989 (about two months before normal floral initiation), with 0, 125, or 1000 ppm TDZ. Although timing or percent of bud-break was unaffected by TDZ, the compound influenced growth expression. TDZ (125 ppm) produced morphologically typical panicles (mixed or purely floral), while at 1000 ppm purely floral panicles were produced which were abnormally compact (similar to panicles affected by mango malformation). Non-treated buds produced only vegetative shoots. Sprays of TDZ (25 to 200 ppm) on developing panicles produced morphological anomalies in panicles such as thickening of the central axis and secondary branches, increase in flower size, and sprouting of the most basal buds on the central axis. Effect during the vegetative flushing period will be discussed.

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R. Núñez-Elisea, J.H. Crane, and M.L. Caldeira

Panicles of `Kohala' longan (Dimocarpus longan Lour.) trees often retain more than 250 fruit, which results in small fruit (<10 g) of reduced market value. During 1997 and 1998, we conducted experiments to increase fruit size in commercial groves. Trees flowered and fruited normally in 1997, but very scarcely and late in 1998. In 1997, treatments consisted of panicle pruning (clipping off half of the panicle) and/or removal of entire panicles (50% per tree) when young fruits were 5 or 10 mm in diameter. Control trees were left intact. The number of fruit per panicle varied greatly within trees. Panicles (pruned or intact) with <125 fruit generally developed fruit >15 g (32–33 mm equatorial diameter). Total soluble solid content of mature fruit generally decreased with increasing fruit size. Removing whole panicles did not increase average fruit size in remaining intact panicles, suggesting that panicles were fed primarily by leaves within the same branch. In 1998, treatments consisted of applications of GA3 and/or CPPU (a synthetic cytokinin) when fruits were 6 to 9 mm in diameter. Panicles were not pruned since they generally had <150 fruit. Control panicles were not sprayed. There was no consistent effect of treatments on average fruit weight, and no treatment significantly increased fruit size in relation to controls. These preliminary results indicate that other factors besides current fruit set, such as previous fruit load of a branch, branch position (exposure to sunlight and/or wind, and proximity to major limbs), and the amount/age of leaves, may influence the fruiting potential of individual branches.

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R. Nunez-Elisea, M. L. Caldeira, and T. L. Davenport

Thidiazuron (TDZ; N-phenyl-N-1,2,3-thiadiazol-5-ylurea) stimulates axillary bud break in some horticultural crops. We are exploring its ability to initiate bud growth in mango trees in order to manipulate vegetative and reproductive shoot initiation. Axillary buds on defoliated, decapitated shoots were treated in late October, 1989 (about two months before normal floral initiation), with 0, 125, or 1000 ppm TDZ. Although timing or percent of bud-break was unaffected by TDZ, the compound influenced growth expression. TDZ (125 ppm) produced morphologically typical panicles (mixed or purely floral), while at 1000 ppm purely floral panicles were produced which were abnormally compact (similar to panicles affected by mango malformation). Non-treated buds produced only vegetative shoots. Sprays of TDZ (25 to 200 ppm) on developing panicles produced morphological anomalies in panicles such as thickening of the central axis and secondary branches, increase in flower size, and sprouting of the most basal buds on the central axis. Effect during the vegetative flushing period will be discussed.

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R. Nunez-Elisea, M.L. Caldeira, W. Ferreira, and T.L. Davenport

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R. Nuñez-Elisea, B. Schaffer, M. Zekri, S.K. O'Hair, and J.H. Crane

Tropical fruit trees in southern Florida are grown in porous, oolitic limestone soil that has very low organic matter content and water-holding capacity. Thus, trees require frequent irrigation during dry periods. In these soils, a quantitative basis for monitoring soil water content to determine when and how much to irrigate has been lacking. Multi-sensor capacitance probes (EnviroSCAN™, Sentek, Australia) were installed in commercial carambola, lime, and avocado orchards to continuously monitor changes in soil water content at depths of 10, 20, 30, and 50 cm. Eight probes were installed per orchard. Volumetric soil water content was recorded at 15-min intervals with a solar-powered datalogger. Results were downloaded to a laptop computer twice a week. Monitoring the rate of soil water depletion (evapotranspiration) allowed irrigation before the onset of water stress. The time at which soil reached field capacity could be determined after each irrigation (or rain) event. Soil water tension was recorded periodically using low-tension (0–40 cbars) tensiometers placed adjacent to selected capacitance probes at 10- and 30-cm depths. Soil water tension was better correlated with volumetric soil water content at a 10-cm depth than at 30-cm depth. Using multi-sensor capacitance probes is a highly accurate, although relatively expensive, method of monitoring soil water content for scheduling irrigation in tropical fruit orchards. Whereas tensiometers require periodic maintenance, the multi-sensor capacitance probe system has been virtually maintenance free. The correlation between soil water content and soil water tension obtained in situ indicates that tensiometers are a less precise, but considerably cheaper, alternative for scheduling irrigation in tropical fruit orchards in southern Florida.