Light & Temperature

Part 1

It is important to know which genetic and environmental factors regulate production of red pigments, or anthocyanins, in the skin of full red and blush cultivars of European pear. Insufficient red colour can reduce consumer appeal and profitability of production.

In apple the process of red colour development is relatively well understood but for pears, much less is known.

Development of red colour due to anthocyanin accumulation during fruit ripening is controlled by complex interactions between genetic and environmental factors. Light, temperature, carbohydrates, water stress and hormones all play a role but anthocyanin synthesis depends primarily on light.

Biosynthesis of anthocyanins in plant tissues either requires or is enhanced by solar radiation (i.e. sunlight) with intensity and wavelength key elements. In general, higher solar radiation tends to increase flavonoid content in most fruit types. It appears that shorter wavelengths, in the range of blue and ultraviolet (UV), show the most prominent effects in accumulation of anthocyanins.

However, specific information on responses to different light wavelengths is still scarce.

In conclusion, high levels of solar radiation stimulate anthocyanin synthesis in cool conditions but anthocyanin degradation may occur simultaneously when skin temperature increases, as may happen under Australian conditions.  Whether the result is a colour gain or colour loss depends on many factors which are not well understood in Australia. They include cultivar, level of temperature and exposure time. All these factors require further investigation under Australian conditions to more fully determine the dynamics of colour development in red and blush pear cultivars.

Figure 1

ANP-0131. 19th of January

Figure 2

ANP-0131. 23rd of February

Figures 1 and 2

A red blushed pear selection (ANP-0131) from the Australian National Pear Breeding Program (Tatura) that was photographed on 19 January (figure 1) and 23 February (figure 2). Fruit surface temperature was measured using a fine wire thermocouple inserted just below the skin. Note that blush has substantially faded most likely due to high fruit surface temperature from direct exposure to solar radiation (sunlight).

Resource from APAL website: Fruit surface temperature and sunburn damage of red blushed pears

Part 2 Orchard Practices

Acknowledgements

Graeme Thomson1 & Ian Goodwin2

Department of Economic Development, Jobs, Transport & Resources.

1AgriBio Centre, 5 Ring Road, La Trobe University Campus - Bundoora, Victoria 3083, Australia.

2Horticulture Centre of Excellence, Private Bag 1, Tatura, Victoria 3616, Australia.

References

Steyn WJ, Holcroft DM, Wand JE, Jacobs G (2004a) Regulation of pear color development in relation to activity of flavonoid enzymes.  J Amer Soc Hort Sci. 129(1): 6-12.

Steyn WJ, Holcroft DM, Wand JE, Jacobs G (2004b) Anthocyanin degradation in detached pome fruit with reference to preharvest red color loss and pigmentation patterns of blushed and fully red pears. J Amer Soc Hort Sci. 129(1):13-19.

Steyn WJ, Wand SJE, Holcroft DM, Jacobs G (2005) Red colour development and loss in pears. Proc. IXth IS on Pear Ed.: K.I. Theron, Acta Hort. 671, ISHS 2005, pages 70-85.

van den Ende B (2011) Grow perfect Forelle pears on Tatura. Good fruit Grower Sept 1, 2011. http://www.goodfruit.com/grow-perfect-forelle-pears-on-tatura/