Lenticel breakdown, left. Lenticel blotch, right.
Lenticel breakdown of apples is a skin disorder that usually becomes visible predominantly after the fruit has been packed. It appears as a sunken circles around lenticels and is often confused with lenticel blotch pit. Lenticel breakdown has caused severe economic injury to apple growers and packers in recent years.
There are many factors that affect the appearance of lenticel breakdown. Of all apple varieties, Gala is the most frequently affected, although lenticel breakdown can be seen on other varieties, usually after long-term storage. Fruit from many Gala orchards are not affected, and we are still not certain whether susceptibility is linked to cultivar, climate, or cultural (and spray) practices. This appears to be a key point, and it is unfortunate that more is not known about the influence of production practices on the incidence of this disorder.
Fruit harvested late in the harvest season are more often affected than fruit harvested early. Waiting for red color development by leaving apples on the tree often increases the risk of lenticel breakdown.
Postharvest practices influence the extent of lenticel breakdown in susceptible orchards. We are testing whether the interval between harvest and cooling has an effect. At this point, we don’t know. Our research has shown that apples that which are stored longer have more lenticel breakdown than those packed early in the season.
Using fruit from the 2004 harvest, we determined that fruit treated with SmartFresh (1-methylcyclopropene) were more susceptible to packing-line stress and developed more lenticel breakdown than untreated fruit. However, this was not found to be the case using fruit from the 2005 crop. In 2005-2006, there was no difference in the incidence of lenticel breakdown on treated or untreated fruit. We are repeating this work with fruit from this year’s harvest to sort this out.
During the very susceptible winter packing season, we found that fruit that which has been presized will develop more lenticel breakdown than fruit that has been packed without presizing.
A large difference in fruit temperature and packing-line water temperature (cold fruit in hot water) increases the incidence of lenticel breakdown in susceptible fruit. When fruit and water temperatures are closely approximated, less lenticel breakdown develops in susceptible fruit.
Chemicals on the packing line have a strong effect on the incidence of the disorder on susceptible fruit. Soaps or cleaners, acidic or alkaline, influence the development of lenticel breakdown. The concentration of cleaner applied to the fruit is very important. Cleaners applied to susceptible fruit at high concentrations promote the development of lenticel breakdown.
This year, we tested the effect of packingline brushes and brush speed on the appearance of lenticel breakdown. There was no difference in lenticel breakdown incidence when we cleaned the fruit with 0.022 PEX, 0.018 PEX, 0.015 PEX, alternating 0.022 and 0.018 PEX, foam, or no brushes (control) when speeds were reasonable and duration minimal.
When the brush belts were slow (below a 90:30 rpm ratio), there was less incidence of lenticel breakdown than when the brushes were run faster (180:30 or 180:60 rpm).
This season, we are further defining the role of maturity, and whether storage with SmartFresh influences lenticel breakdown susceptibility. We will also be working with Dr. Eric Curry, USDA plant physiologist, Wenatchee, Washington, and others on refining the dye test used to predict the susceptibility of fruit to lenticel breakdown. The key to effective reduction of lenticel breakdown is the determination of those orchard factors that lead certain orchards to grow fruit of high risk, and until this is solved, packers need to follow the guidelines described above.