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Effects of metamitron under different relative humidity conditions on the fruit abscission of Malus domestica Borkh. cultivars
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Orientador(es)
Resumo(s)
Metamitron is an apple (Malus domestica Borkh.) fruit thinner that acts by reducing the
photosynthetic capacityof trees. Relativehumiditymayinfluence thinningefficacy; however, thebroadness
of this effect is not yet fully understood. Trials were set in Sint-Truiden (Belgium) in 2018 and Lleida and
Girona (Spain) in 2019, using 4-year-old cvs. Braeburn and Elstar trees in Belgium, and 16-year-old cv.
GoldenReinders trees in Spain. Four treatmentswere implemented at the stage of 12–14mmfruit diameter:
(a) CTR—control, trees under natural environmental conditions; (b) HH—high humidity, trees submitted
to artificially increased air relative humidity applied for 3 h prior to the beginning of the experiment;
(c)MET—trees sprayedwith 247.5mg/Lmetamitron; (d)MET + HH—trees submitted to the combination
of increased humidity (HH) and metamitron (MET) application. In Belgium, metamitron absorption by
leaves was greater than in Spain. This might be related to morphological characteristics of the leaves
which developed under greater natural relative humidity levels in Belgium than in Spain. Compared to
MET alone, ‘Braeburn’ and ‘Elstar’ demonstrated significantly greater metamitron absorption, 59% and
84%, respectively, underMET + HH, accompanied by declines in leaf net photosynthesis (10% and 32%,
respectively) and sucrose (31% and 26%, respectively). At harvest,MET + HH treatment reduced yield by
24% and 32% in ‘Braeburn’ and ‘Elstar’, respectively, when compared withMET alone. A large reduction
(considered over thinning) in the yield of ‘Elstar’ occurred. In contrast,metamitron absorption by ‘Golden
Reinders’ usingMET alone was similar toMET + HH; however, there was a slight foliar sugar reduction
in the latter treatment. In addition, both treatments enhanced shoot growth and increased fruit abscission
with similar improvements in fruit weight and size. In this study, high relative humidity enhanced fruit
thinning efficacy under certain circumstances, such as age or genetic predisposal, which left the tree
more susceptible to a negative carbohydrate balance. For instance, ‘Braeburn’ and ‘Elstar’ were easier to
thin when compared to ‘Golden Reinders’. In addition, this study raises a question that requires further
research regarding the impact of HH before and after spraying as well as its effect in combination with
higher temperatures
Descrição
Palavras-chave
absorption carbohydrate balance photosynthesis sucrose sorbitol thinning
Contexto Educativo
Citação
Horticulturae 2020, 6, 89
Editora
MDPI