THE ROLE OF MINERAL NUTRITION ON YIELDS AND FRUIT QUALITY IN GRAPEVINE, PEAR AND APPLE

ABSTRACT Fertilization of temperate fruit trees, such as grapevine ( Vitis spp.), apple ( Malus domestica), and pear ( Pyrus communis) is an important tool to achive maximum yield and fruit quality. Fertilizers are provided when soil fertility does not allow trees to express their genetic potential, and time and rate of application should be scheduled to promote fruit quality. Grapevine berries, must and wine quality are affected principally by N, that regulate the synthesis of some important compounds, such as anthocyanins, which are responsible for coloring of the must and the wine. Fermenation of the must may stop in grapes with low concentration of N because N is requested in high amount by yeasts. An N excess may increase the pulp to peel ratio, diluting the concentration of anthocyanins and promoting the migration of anthocyanins from berries to the growing plant organs; a decrease of grape juice soluble solid concentration is also expected because of an increase in vegetative growth. Potassium is also important for wine quality contributing to adequate berry maturation, concentration of sugars, synthesis of phenols and the regulation of pH and acidity. In apple and pear, Ca and K are important for fruit quality and storage. Potassium is the most important component of fruit, however, any excess should be avoided and an adequate K:Ca balance should be achieved. Adequate concentration of Ca in the fruit prevents pre- and post-harvest fruit disorders and, at the same time, increases tolerance to pathogens. Although N promotes adequate growth soil N availability should be monitored to avoid excessive N uptake that may decrease fruit skin color and storability

IDENTIFYING THE MYSTERIOUS EGRET SOURCES: SIGNATURES OF POLAR CAP PULSAR MODELS

The advent of the next generation of gamma-ray experiments, led by GLAST, AGILE, INTEGRAL and a host of atmospheric Čerenkov telescopes coming on line in the next few years, will enable ground-breaking discoveries relating to the presently enigmatic set of EGRET/CGRO UID galactic sources that have yet to find definitive identifications. Pulsars are principal candidates for such sources, and many are expected to be detected by GLAST, some that are radio-selected, like most of the present EGRET/Comptel pulsars, and perhaps even more that are detected via independent pulsation searches. At this juncture, it is salient to outline the principal predictions of pulsar models that might aid identification of gamma-ray sources, and moreover propel subsequent interpretation of their properties. This review summarizes relevant characteristics of the polar cap model, emphasizing where possible distinctions from the competing outer gap model. Foremost among these considerations are the hard X-ray to gamma-ray spectral shape, high energy cutoffs and pulse profiles, and how these characteristics generally depend on pulsar period and period derivative, as well as observational viewing angle. The polar cap model exhibits definitive signatures that will be readily tested by the detections of GLAST and other experiments, thereby establishing cogent observational diagnostics. The paper focuses on different classes of pulsars that might define agendas and parameter regimes for blind gamma-ray pulsation searches; examples include the highly-magnetized ones that are currently quite topical in astrophysics. 1 2 1