How nutrient management can affect pome fruits

Fruit number in pome fruit trees results from a variety of factors, including planting density, orchard system, pruning and thinning practices and also crop nutrition. The desired fruit size should be considered when managing crop load since allowing too many fruits to remain on the tree will result in smaller fruits and reduce tree vigour.

Size is a critical characteristic for grading pome fruits. A minimal size, determined by the diameter of the equatorial section, is required on all grades. An evenly shaped and sized fruit is desired for the fresh market and also for canning. Pome fruit size is greatly influenced by pruning and thinning practices and also by crop nutrition.

Pome fruit weight is an important element for increasing yields. Provided that a desired quality is maintained, the aim of growers is to produce heavier fruits. Crop nutrition plays an important role on increasing apple weight.

Colour of the skin is a very appealing pome fruit quality to consumers. Therefore, growers generally seek to improve fruit colouration. Crop nutrition can help to achieve the desired appearance.

Over-use or late applications of nitrogen reduces apple firmness, potentially resulting in more damage in transit and storage, and a reduced shelf life.

Pome fruit flavor and taste are related to the level of soluble solids in the fruit, which are mainly sugars. Total Soluble Solids (TSS) is therefore of extreme importance to measure the quality of pome fruit. Referred to as oBrix, TSS is assessed by refractometry or near-infrared spectroscopy and can be used to check fruit maturity and ripeness, important to determine harvest timing. A balanced crop nutrition can influence TSS content of fruit.

Bitter pit is a physiological disorder associated with low levels of calcium in the pome fruit tissue, which reduces pome fruit quality and marketability.

Lenticel are slightly sunken blotches that result in underlying tissue drying out and becoming brown and spongy. Its occurrence is more prominent than that of bitter pit. Lenticel blotch is associated with hot summers, late harvests and excessive use of nitrogen. Pitting is always associated with a lenticel.

Water core develops in mature pome fruit when the sugar sorbitol is translocated into the fruit faster than it can be assimilated. The area surrounding the core becomes water-soaked or translucent and may appear glassy and hard. Only in severe instances are symptoms found on the outside of the fruit. Water core is more likely to occur in pome fruit exposed to heat and sunlight. Inadequate supply of calcium is a major contributing factor.

Internal breakdown in pome fruit is the breakdown of internal tissues resulting from fluid oxidation. In severe cases, tissues become spongy. It can be associated with intense water core disorder, cold storage, and boron and phosphorus deficiencies. A good crop nutrition can help to minimize internal breakdown incidence in pome fruit.

Sunscald or sunburn in pome fruit accounts for yellow or flushed areas on the fruit skin due to direct sun damage often following a period of cooler, cloudy weather. In severe instances, the scald damage turns dark while the fruit is still on the tree, with the underlying tissue becoming spongy. It is also associated with poor calcium content in the fruit. A balanced crop nutrition can help avoid sunburns.

Many disease-causing pathogens (fungi, bacteria, viruses and nematodes) attack pome fruit trees.

Plant nutrients are essential building blocks of crops. In order to obtain high pome fruit yields it is important to achieve the right balance of fruit number on the tree.