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Metamitron and shade effects on leaf physiology and thinning efficacy of Malus X domestica Borkh
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Orientador(es)
Resumo(s)
Thinning strategies, namely shade or photosynthetic inhibitors, rely on the reduction of
carbon supply to the fruit below the demand, causing fruit abscission. In order to clarify the subject,
seven field trials were carried out in Lleida, Girona, and Sint-Truiden (2017 + 2018), using orchards
of ‘Golden’ and ‘Gala’ apple trees. At the stage of 9–14-mm fruit diameter, four treatments were
implemented: (A) CTR-control, trees under natural environmental conditions; (B) SN-shaded trees,
trees above which shading nets reducing 50% of irradiance were installed 24 h after metamitron
application date—without application of metamitron—and removed after five days; (C) MET-trees
sprayed with 247.5 ppm of metamitron; (D) MET + SN-trees submitted to the combined exposure
to metamitron application and shading nets. Low radiation significantly increased metamitron
absorption (36–53% in the three locations in 2018) and reduced its degradation. Net photosynthesis
and stomatal conductance were strongly reduced in all treatments, with minimum values 2 days after
spraying (DAS) and incomplete recovery 10 DAS in MET + SN. All treatments resulted in leaf sucrose
and sorbitol decreases, leading to a negative carbon balance. SN and MET + SN promoted the highest
thinning e cacy, increasing fruit weight and size, with MET + SN causing over-thinning in some trials.
Leaf antioxidant enzymes showed moderate changes in activity increases under MET or MET + SN,
accompanied by a rise of glutathione content and a reduction in ascorbate, however without lipid
peroxidation. This work shows that environmental conditions, such as cloudy days, must be carefully
considered upon metamitron application, since the low irradiance enhances metamitron e cacy and
may cause over-thinning
Descrição
Palavras-chave
carbohydrate balance fruit abscission photosynthesis reactive oxygen species RuBisCO shading
Contexto Educativo
Citação
Agronomy 2020, 10, 1924
Editora
MDPI