Glyphosate (Round-Up and generics) is a herbicide that kills weeds by blocking a critical enzyme pathway known as the shikimic acid patway. In other crops, it has been studied that the glyphosate exposure can reduce root growth and seed production and can affect seed quality and plant nutrient balances. In soil, the affinity of glyphosate for cations can reduce the availability of calcium, magnesium, manganese, copper, iron, nichel, and zinc either by direct chemical interaction or by negative effects on soil microbes involved in making these minerals available for plants. Glyphosate taken up by roots can interfere with movement and availability of minerals inside the fruit. It tends to accumulate in meristimatic tissue and storage organs.
Currently, no one knows how much of the glyphosate taken up by apple tree is moved to the apple fruit, but it seems possible that glyphosate may influence fruit physiology either by partially blocking the shikimic acid pathway or by affecting nutrient balance within the fruit.
The internal browning is a physiological disorder that can occur during controlled atmosphere (CA) storage and makes fruits unacceptable for fresh-cut processing. The incidence and the severity of internal browning vary from orchard to orchard, and the causes responsible of this problem must be yet determined.
In 2009, Rosenberg et al. started a study to determine if the exposure of ‘Empire’ apple trees to glyphosate might influence the incidence and severity of internal browning that develops in apples that are stored in CA for a long period. The study has been conducted in three farms on ‘Empire’ cultivar, which is known to produce fruits that developed internal browning during CA storage.
Three treatments have been compared:
- an untreated control,
- glyphosate applied to terminal shoots on lower fruiting limbs,
- glyphosate applied to fruit and leaves on lower fruiting limbs.
After harvesting, the apples were stored at 2.2°C with 2% oxygen and 2% carbon dioxide for 8 months, then the apples were moved to 20°C for 7 days before they were evaluated for internal browning. Internal browning was assessed by cutting trough the equatorial plane of the apple, three sections (distal, center, proximal) were crossed to evaluate the flesh browning severity according to a rating from 1 to 3 (1= slight, 2= moderate, 3= severe).
From the first results, glyphosate application to trees increased the incidence and severity of both flesh browning and core browning. However these are preliminary results, being collected data referring to only one trial year, testing one cultivar and one glyphosate application.
Thus, to confirm the negative effect of glyphosate on fruits, the researchers suggest the continuation of the study, testing timing of glyphosate exposure (spring versus summer), exposure route (via spray drift, through root suckers, or through bark), and glyphosate formulation, all these factors may affect the interaction between glyphosate and fruit internal browning.
Original study: Rosenberger D., Watkins C., Sazo M.M., Kahlke C., Nock J. "Glyphosate exposure contributes to internal browning of apples during long-term storage", 2010, New York fruit quarterly, Issue No. 18 (3), pagg. 15-18. For more details: www.nyshs.org/pdf/fq/10fall/glyphosate-exposure-contributes-to-internal-browning-of-apples-during-long-term-storage.pdf