early-flowering crops such as blueberry and stone fruit. Freeze protection often requires large amounts of water for the duration of the freeze(s) ( Lyrene and Williamson, 2006 ). Tropical and subtropical fruit. Tropical and subtropical fruit production
Jeffrey G. Williamson and Jonathan H. Crane
Although postharvest handling schemes have improved during recent years, it is still possible to observe considerable variability in fruit quality between individual lots. Preharvest factors such as irrigation, nutrition and pest management practices, as well as rootstock and environmental variables, may greatly influence quality after harvest and may well account for some of the differences between individual lots. The influence of preharvest factors on postharvest quality of tropical and subtropical fruit will be discussed using pertinent examples from the literature. Emphasis will be given to those factors which can be manipulated to improve quality.
Bruce Schaffer, Frederick S. Davies and Jonathan H. Crane
The effects of flooding calcareous soil on physiology and growth have been studied for several subtropical and tropical fruit crops including avocado (Persea americana Mill.), mango (Mangifera indica L.), carambola (Averrhoa carambola L.), and several Annona species. In calcareous soils that have a high pH, short-term flooding can actually be beneficial to subtropical and tropical fruit crops by increasing the solubility of particle-bound nutrient elements such as Fe, Mn and Mg due to flooding-induced decreases in soil pH. Additionally, flooding reduces the redox potential in the soil, resulting in Fe being reduced from Fe3+ to Fe2+, which is the cation metabolized by plants. As with other woody perennial crops, one of the early physiological responses of subtropical and tropical fruit trees to flooding is a decrease in stomatal conductance and net CO2 assimilation. If the flooding period is prolonged, lack of O2 (anoxia) in the soil results in a reduction of root and shoot growth, wilting, decreased nutrient uptake and eventual death. The flooding duration required to cause tree mortality varies among species, among cultivars within species, and with environmental conditions, particularly temperature. Several tropical and subtropical fruit crops have anatomical or morphological adaptations to tolerate prolonged flooding, such as development of hypertrophied stem lenticels, adventitious rooting or formation of porous aerenchyma tissue. For grafted trees, flooding-tolerance is conferred by the rootstock and not the scion. Therefore there is a possibility to increase flood tolerance of subtropical and tropical fruit crops by identifying or developing flood-tolerant rootstocks.
Roberto Núñez-Elisea, Bruce Schaffer, Mongi Zekri, Stephen K. O'Hair and Jonathan H. Crane
Most tropical fruit trees in southern Florida are grown in calcareous gravelly soil that is mechanically trenched to a depth of about 50 cm (about 20 inches). Fruit trees are often planted at the intersections of perpendicular trenches to provide space for root development. Tree root systems are concentrated in the top 10 to 20 cm (about 4 to 8 inches) of soil. Extreme soil rockiness has made it difficult to obtain consistent and reliable measurements of soil water status and to collect soil samples for constructing soil-water characteristic curves in the laboratory. Multisensor capacitance probes andlow-tension [0 to 40 kPa (centibars) (0 to 5.8 lb/inch2)] tensiometers were installed adjacent to star fruit (Averrhoa carambola L.) and avocado (Persea americana Mill.) trees in trenches to simultaneously measure volumetric soil water content and soil matric potential in situ. Capacitance probes consisted of four sensors centered at depths of 10, 20, 30, and 50 cm (3.9, 7.9, 11.8, and 19.7 inches). Tensiometers were installed at 10- and 30-cm depths, adjacent to the 10- and 30-cm deep capacitance sensors. Measurements obtained with both instruments were used to generate in situ soil-water characteristic curves. Rock fragments were more abundant at 30 cm than at 10 cm (71% to 73% versus 26% to 38% of bulk soil volume, respectively) soil depth, which limited the precision of tensiometers at the greater depth. In situ soil water characteristic curves for the 10-cm soil depth can be used to determine parameters needed for irrigation scheduling by techniques such as the water budget method.
Jonathan H. Crane, Bruce Schaffer and Richard J. Campbell
101 WORKSHOP 13 (Abstr. 669–674) Long-term Recovery Dynamics of Perennial Species Following Tropical Cyclone Damage
Jonathan Lynch and Alonso González
We thank Johannes van Beem, Ivan Ochoa C., Nubia Rodriguez H., and Clara Inés Quintero G. for technical assistance in the field, the venerable Marcos Longa for skillful canoe navigation on the Calima River, the staff of the Tropical Forestry Center
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.
Michael B. Thomas, Jonathan H. Crane, James J. Ferguson, Howard W. Beck and Joseph W. Noling
The TFRUIT·Xpert and CIT·Xpert computerbased diagnostic programs can quickly assist commercial producers, extension agents, and homeowners in the diagnosis of diseases, insect pest problems and physiological disorders. The CIT·Xpert system focuses on citrus (Citrus spp.), whereas the TFRUIT·Xpert system focuses on avocado (Persea americana Mill.), carambola (Averrhoa carambola L.), lychee (Litchi chinensis Sonn.), mango (Mangifera indica L.), papaya (Carica papaya L.), and `Tahiti' lime (Citrus latifolia Tan.). The systems were developed in cooperation with research and extension specialists with expertise in the area of diagnosing diseases, disorders, and pest problems of citrus and tropical fruit. The systems' methodology reproduces the diagnostic reasoning process of these experts. Reviews of extension and research literature and 35-mm color slide images were completed to obtain representative information and slide images illustrative of diseases, disorders, and pest problems specific to Florida. The diagnostic programs operate under Microsoft-Windows. Full-screen color images are linked to symptoms (87 for CIT·Xpert and 167 for TFRUIT·Xpert) of diseases, disorders, and insect pest problems of citrus and tropical fruit, respectively. Users can also refer to summary documents and retrieve management information from the Univ. of Florida's Institute of Food and Agricultural Sciences extension publications through hypertext links. The programs are available separately on CD-ROM and each contains over 150 digital color images of symptoms.
B. Schaffer, A.W. Whiley and C. Searle
Banana (Musa sp.), mango (Mangifera indica), and avocado (Persea americana) plants were grown in controlled-environment glasshouses in ambient (350 μmol CO2/mol) and enriched (700–1000 (mol CO2/mol) atmospheric CO2 concentrations. At each CO2 concentration, plants were either exposed to sink-limiting (root restriction) or non-sink-limiting conditions (no root restriction). Total carbon assimilation and dry matter accumulation were generally greater for plants in the enriched CO2 environment than for plants grown in ambient CO2. However, plants grown in the enriched CO2 environment were less efficient at assimilating carbon than plants grown in ambient CO2. There was a downward regulation of net CO2 assimilation due to root restriction that resulted in less dry matter accumulation than in non-root-restricted plants. This may explain the lower net CO2 assimilation rates often observed for tropical fruit trees grown in containers compared to those of field-grown trees. Atmospheric CO2 enrichment generally did not compensate for reductions in net CO2 assimilation and dry matter accumulation that resulted from root restriction.
H.H. Hirae and M.A. Nagao
Monitoring the nutrient status of a crop by soil and tissue analysis is an important tool in maximizing yields and avoiding nutrient deficiencies or toxicities. A nutritional management system is presented that uses a computer database to compile periodic soil and leaf tissue analyses to assist in the development of rational fertilizer recommendations for banana and macadamia nut orchards. Database management allows the Extension Agent to organize parameters (soil type, rainfall, elevation, tree age, tree spacing, and previous fertilizer practices) used in nutritional recommendations for individual farms. Graphs depicting nutrient trends over time and comparison of nutrient levels to nutritional standards, present visual illustrations of problems and encourage grower acceptance of fertilizer recommendations. Growers are also able to see graphic responses to application of corrective fertilizers and soil amendments.