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  • Author or Editor: Riccardo Lo Bianco x
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Peach trees trained to modified spanish bush (MSB) and Y-trellis (Y) were evaluated and compared in the Mediterranean settings of southern Italy. The observations included two peach (Rich May and Summer Rich) and two nectarine (Big Bang and Nectaross) cultivars. In the MSB system, trees were spaced at 4.5 × 2.5 m (888 trees/ha), whereas in the Y system, trees were spaced at 5.5 × 2 m (909 trees/ha). Costs at planting, yield per tree, fruit size grade, unit price of sold peaches for each size grade, amount and cost of materials and labor for cultural management, and grower’s profit were quantified throughout all 6 years from planting and at full crop (year 4–6). Fixed costs of the MSB system were 45% lower at planting, 11% lower for fertilization, and 33% lower for pest control than in the Y system. Regardless of cultivar, the MSB system reported 19% lower yields, 29% less management labor, and 12% higher labor efficiency (kg fruit/h) than the Y system. The yield gap between the two systems tended to decrease after the 5th year. A greater percentage of fruit fell into large size categories in the MSB than in the Y system. Fruit unit value and yearly profit were similar in the two systems. Even for the most profitable cultivar under the Y system (i.e., Nectaross), the time needed to pay off the additional investment for establishing a Y by its additional profit was ≈11 years, indicating an advantage of the Y system over the MSB only by the 12th year from planting. Yield trends, along with the high initial investment and management labor and costs in the Y system, indicate better financial performance and more sustainable production in the MSB than in the Y system.

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The most important worldwide problem in citrus production is the bacterial disease Huanglongbing (HLB; citrus greening) caused by a phloem-limited bacterium Candidatus Liberibacter asiaticus. The earliest visible symptoms of HLB on leaves are vein yellowing and an asymmetrical chlorosis referred to as “blotchy mottle,” thought to be the result of starch accumulation. We tested the hypothesis that such visible symptoms are not unique to HLB by stem girdling 2-year-old seedlings of two citrus rootstocks with and without drought stress in the greenhouse. After 31 days, girdling had little effect on shoot growth but girdling increased the relative growth rate of shoots in drought-stressed trees. Starch content in woody roots of non-girdled trees was three to 19 times higher than in girdled trees. In non-girdled trees, drought stress induced some starch accumulation in roots, but there were no effects of drought stress on root starch or sucrose in girdled trees. Girdling induced a 4-fold greater starch content in leaves on well-watered trees but leaf sucrose content was unaffected. Girdling reduced leaf transpiration in well-watered trees but net assimilation of CO2 was unaffected by girdling or leaf starch accumulation. Leaves on girdled trees clearly had visible blotchy mottle symptoms but no symptoms developed on non-girdled trees. The increase in leaf starch, up to 50% dry weight (DW), resulted in an increase in leaf DW per leaf area (LA) and an artificial reduction of many leaf nutrients on a DW basis. Most of these differences disappeared when expressed on a LA basis. Leaf boron (B), however, was inversely related to leaf starch when both were expressed on a LA basis. In the absence of HLB, girdling increased leaf starch, decreased root starch, and duplicated the asymmetric blotchy mottled visual leaf symptoms that have been associated with HLB-infected trees. This supports our contention that such symptoms generally attributed to HLB are not uniquely related to HLB infection, but rather are directly related to starch accumulation and secondarily to nutrient deficiencies in leaves.

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