Fruit Physiological Disorders

Crisosto, C. H. and E. J. Mitcham 2020. UC Davis Postharvest Specialists.

Asian pears are also called Oriental pears, Chinese pears, Japanese pears, Salad pears and Apple pears. The cultivated varieties of Chinese and Japanese pears were developed from Pyrus ussuriensis Maximowicz, P. Serotina Rehder (P. pyrifolia [Burman] Nakai) and possibly other native species.

Flesh Spot Decay and Internal Browning

Occurrence
Most Japanese (Pyrus pyrifolia) pear varieties are roundish, while Chinese pears are pyriform. Both have a crispy texture like apples but in contrast to European pears, and a flavor entirely different from apples. Flesh spot decay is more frequent on large size (300 g) fruit and over mature Japanese pear cultivars such as ‘Shinseiki’, ‘Nijisseiki’, ‘Kikusui’, and ‘Hosui’.

Importance
Flesh Spot Decay limits opportunities to grow and market Japanese pears.

Symptoms
Partial browning of spots and/or development of cavities in Asian pear flesh. It appears along and around the vascular bundles when the symptoms are severe, but there is no external indication of the disorder. Generally, Flesh Spot Decay is more pronounced above the equator of the fruit (towards the stem end), but it can also be observed all the way down to the calyx. Cavities are usually dry and surrounded by apparently healthy tissue. This disorder can occur in fruit while still on the tree. It is more obvious, during cold storage.

Causes
The cause of flesh spot decay is still unknown. However, climatic factors, such as a fluctuating hot and cool summer, or high rainfall right before harvest increased incidence of this disorder.

Control

Since definite causes have not been identified; there is no effective way to control Flesh Spot Decay. The inability to predict or diagnose Flesh Spot Decay without cutting the fruit makes it difficult to study the problem. Further research needs to be carried out to determine the causes and variety susceptibility, and to understand preharvest and/or postharvest practices that will reduce Flesh Spot Decay losses. Meanwhile, AVOID whenever possible the following conditions that might induce Flesh Spot Decay: low crop load and therefore large fruit; advanced maturity; sunburn; erratic irrigation (amount and timing) near harvest; harvesting fruit during warm temperatures and cooling the fruit within 24 hours.

References

Arzani, K. 2019. Asian pear. In: S. Tonetto de Freitas and S. Pareek (eds.) Postharvest Physiological Disorders in Fruits and Vegetables. CRC Press, Boca Raton, FL, pp. 329-349.

Bai J., R. Prange, and P.M. Toivonen. 2009. Pome fruit. In: E.M. Yahia (ed.) Modified and Controlled Atmospheres for the Storage, Transportation, and Packaging of Horticultural Commodities. CRC Press, Boca Raton, FL, pp. 267-285.

Behboudian, M.H. and G.S. Lawes. 1994. Fruit quality in ‘Nijisseiki’ Asian pear under deficit irrigation: Physical attributes, sugar and mineral content, and development of flesh spot decay. N.Z. J. Crop Hort. Sci. 22:393-400.

Caspari, H., M.H. Behboudian, D.J. Chalmers and B.E. Clothier. 1996. Fruit characteristics of ‘Hosui’ Asian pears after deficit irrigation. HortScience 31(1):162.

Crisosto, C.H. 2016. Asian pear. In: K.C. Gross, C.Y. Wang, and M. Saltveit (eds.) The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. USDA Agriculture Handbook 66, pp. 205-209.

Griggs, W., and B. Iwakiri. 1977. Asian Pear Varieties in California. DANR Pub. No. 4068, University of California, Oakland, CA.

Lallu, N. 1990. Fruit growth, handling and storage. In: A.G. White (ed.) Nashi, Asian Pear in New Zealand, DSIR Publishing, Wellington, New Zealand, pp. 53-74.

2020