The VII International Symposium on Mineral Nutrition of Fruit Crops

Mineral nutrition has long been linked to cracking, but given the complex nature of cracking, and the complex interactions between nutrition, irrigation and water flow transporting nutrients within trees it is difficult to tease out any nutritional impacts on cracking. The most common mineral employed in the management of fruit cracking has been calcium. Calcium is a xylem mobile mineral, and as fruit xylem connections and pathways are thought to be reduced during maturation, early accumulation is vital. Calcium has been implicated in building resilience to cracking into fruit, with many exploring the impact of late season calcium chloride spray applications on cracking. These trials have produced inconsistent results but early and repeated spray patterns for calcium uptake are supported by studies in apples. Enhanced calcium uptake rates have been recorded in the sweet cherry variety Van with the use of thickeners and surfactants. The stylar end of cherry fruit has been identified as the preferential site of calcium uptake in variety Bing. Calcium treatments, however, did not significantly affect the rate of water uptake through skin in detached Bing fruit immersed in solution. A major limitation of using direct calcium application to prevent cracking is the unsightly residue left on the fruit. Aluminium and boron sprays have been trialled in the USA, again with inconsistent results and residue deposits. In Poland, an extensive study of boron nutrition showed no effect of soil or foliar applied boron on the incidence of cracking. During the last growing season I analysed the fruit nutrient content of fruit with a high cracking index and a low cracking index, induced by different irrigation volumes. No significant differences in calcium, boron or silicon levels were found, but these will be investigated further in future seasons. In May 2012 I attended and presented some of my work on cherry fruit cracking at the International Society of Horticultural Sciences VII International Symposium on Mineral Nutrition of Fruit Crops. This served two important purposes; 1. Peer feedback and encouragement from other participants highlighted that the work was of scientific value, and 2. Knowledge gained from other presentations, discussions and field trips can be incorporated into future studies. The symposium started and ended with a focus on water. Thailand experiences high levels of rainfall and humidity, but work presented from all over the world also focussed strongly on nutrition interactions with climate. Water uptake, and the environmental influences on water movement in trees, was highlighted as of key importance. Transpiration is the driver of nutrient uptake such that more emphasis should be placed on considering climate in future nutrition trials. New theories on foliar uptake efficiency were also presented by keynote speaker Dr. Thomas Eichert from Germany. Studies have shown that stomata play a greater role in nutrient uptake than previously thought, but still only about 10% of leaf stomata are involved. This bodes well for more targeted and responsive foliar nutrition regimes. Boron was also a hot topic; Boron is a key component of cell walls. Keynote speaker Dr. Toru Matah from Japan explained new findings on how low boron levels induce membrane stretching and trigger the opening of cellular channels which increase cellular calcium. Boron and calcium balance must be maintained; Dr. Matah stressed the importance of ensuring Boron uptake to fruit before rapid fruit growth, as for calcium. Other work showed that boron application should be cultivar specific, as increased stem-end splitting in Gala apples was found with increasing boron levels, even though fruit boron levels were within the optimal range. Nutrient budgeting was also discussed widely. The general consensus being that any methods of nutrient analyses should be more user-friendly, and that simpler methods for budgeting could be developed. Dr. Massimo Tagliavini from Italy put forward a model where nutrient requirements can be estimated from parameters easily measured in the field such as branch circumference. The model is being developed from an extensive study in apples and citrus. Other work supported this approach, and many supported revisiting the timing and number of trees used when under undertaking nutrient sampling. The symposium ended with a presentation from keynote speaker Dr. Denise Neilsen from Canada which again highlighted the importance of water in nutrition. This presentation showed the potential changes in water availability at a regional level under a changing climate, and the flow-on effects on fruit production. This presentation encouraged growers, researchers and policy makers to work together to ensure water security into the future, and emphasised the importance of efficient and targeted resource use. Dr. Penny Measham Tree Physiology Research Fellow Perennial Horticulture Centre Tasmanian Institute of Agriculture (03) 6226 1870 0437 454 622 Penelope.Measham@utas.edu.au

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