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Citrus is grown in tropical, semitropical and subtropical climate conditions. In these regions high temperature lead to reductions of the plant growth and photosynthesis. In the citrus nursery, seedlings are frequently shaded to avoid heat damage. More recently, photo-selective shade materials designed specifically for manipulating plant development and growth has decreased solar radiation and temperature. In this work, we examined the effect of different colours and shade intensities (50% aluminet, 20% Red Leno, 13% Clear combined and 75% black shade net) on one-year-old 'Lane Late' seedling growth. Leaf number, plant scion diameter, plant rootstock diameter, SPAD and PSII parameters were investigated. At the end of the experiment, leaf number was found to be higher in 75 and 50% shade net treatments. In control plants leaf number was the least among the treatments. Scion and rootstock diameter were induced in 75 and 50% shade net treatments and the other treatments were found to be similar. PSII and chlorophyll content was found to be highest in 75% shade treatment. The lowest chlorophyll content was obtained from control plants.

An electronically-based model system was designed and constructed using a peltier (semiconductor technology) for inducing the expression of chilling injury in fruit and vegetables. The purpose of the model was to provide a method for inducing chilling injury on the surface of fruit or vegetable tissues while maintaining an accurate temperature treatment (+/- 0.2°C). This would allow for scientific and commercial comparisons to be made on the relative susceptibility of fruit and vegetables to expressing symptoms of chilling injury, and thus, provide information on appropriate cold storage handling protocols. Trials on citrus fruit successfully produced symptoms of chilling injury on treatment zones after a 21 day application of 1°C. Navel orange 'Lloyd A' was determined to be more sensitive to chilling injury than 'Leng' Navel, with 88% versus 81% of fruit, respectively, expressing symptoms on the treatment zone.

Young, fully expanded leaves of 'Hass' avocado on clonal 'Duke 7' rootstock, 2 years from budding, were used to assess changes in leaf NH3-NH4 content. Foliar application of 1.5 g low biuret urea per tree failed to increase the leaf NH3-NH4 content: compare 23.6 ± 5.8 versus 20.1 ± 5.7 μg NH3-NH4 per g fr. wt. leaf tissue (x ± STD. DEV., N = 3 trees per treatment) from trees treated with and without urea, respectively (Nevin and Lovatt, 1989). Foliar application of 1.5 g of low biuret urea per tree to 5-yearold rooted cuttings of the 'Washington' navel orange of comparable size increased the leaf NH3-NH4 content of the trees subjected to 4, 6, or 8 weeks of low temperature 1.7-, 2.2-, and 1.2-fold, respectively.