Other Apple Skin Disorders
Schrader's research has also revealed that several other apple disorders (e.g., 'Fuji'stain, lenticel marking, and "sunburn scald" of 'Granny Smith') appear after sunburn has occurred. These heat-induced disorders can be suppressed if sunburn is suppressed.
'Fuji' stain. This disorder appears during cold storage on sunburned 'Fuji' apples from certain orchards (See Fig. 3) and its incidence increases as the severity of sunburn increases and the time in cold storage is lengthened. The incidence of 'Fuji' stain after 2 to 4 months in cold storage is decreased by at least 50% in apples to which RAYNOX® was applied preharvest for sunburn protection. This suggests that UV-B radiation is a cause of 'Fuji' stain. The highest incidence of this disorder has been observed in fruit from orchards with excessive nitrogen applications. Major pigment changes occur during cold storage in the apples that show this stain disorder (Felicetti & Schrader, 2010).
|Fig. 3. 'Fuji' stain||Fig. 4. "Sunburn scald" of 'Granny Smith'||Fig. 5. Lenticel marking on 'Fuji'|
"Sunburn scald" of 'Granny Smith'. This skin disorder also appears after cold storage on certain lots of 'Granny Smith' apples that were sunburned earlier (Fig. 4). The dark brown or black spot develops on top of the area that was sunburned earlier, but it is not known why certain lots of fruit are more susceptible.
Lenticel marking. Lenticels within a sunburned area on fruit frequently become brown or black (Fig.5). This is referred to as "lenticel marking." The incidence and intensity of this disorder also increased as the severity of sunburn browning increases.
'Fuji' flecking. This disorder is thought to be a type of russet (Fig. 6). Its incidence varies from year to year, and some orchards have a higher incidence. Those orchards that have excessive irrigation or overhead cooling seem to have a higher incidence of this disorder.
Fig. 6. 'Fuji' Flecking
Larry Schrader, Horticulturist/Plant Physiologist
Tree Fruit Research & Extension Center, Wenatchee
Office Ph: 509-663-8181 x265
Office Hours: by appointment