Comparison between benzyladenine and metamitron as chemical thinning agents in Gala, Kanzi, Pink Lady and Red Delicious apple cultivars

• Autor(es): Rosa, Nídia Diana Heleno
• Data: 2016
• Identificador Persistente: http://hdl.handle.net/10400.5/12172
• Origem: Repositório da UTL
• Assunto(s): abscission; benzyladenine; chemical thinning; fruit growth rate; metamitron
• Tipo de Documento: Dissertação de mestrado
• Idioma: Inglês
• Orientador(es): Oliveira, Cristina Maria Moniz Simões; Verjans, Wim
• Contribuidor(es): Repositório da Universidade de Lisboa

Descrição

Mestrado em Engenharia Agronómica - Instituto Superior de Agronomia - UL

This experiment was conducted in PCFruit Research Station orchards in Sint-Truiden, Belgium in 2015, in ‘Gala’, ‘Kanzi®’, ‘Pink Lady®’ and ‘Red Delicious’. Four treatments were tested: untreated, manual thinning, two applications of 165 ppm of metamitron at 8 and 12 mm and one application of 150 ppm of benzyladenine between 8 and 12 mm fruit diameter. All cultivars were sprayed on the same days. Fruit drop was counted, phytotoxicity evaluated after June drop, fruit growth rate was assessed and photosynthetic efficiency was measured. Fruit drop was higher in all cultivars with metamitron application than with benzyladenine (P<0.05). A greater growth rate in fruits treated with metamitron was registered, as well as, a positive correlation between the sum of the PSII efficiency and the thinning percentage (R2=0.98). A relation between the duration of the blocking effect of metamitron and phytotoxicity level in the trees was observed. At harvest, metamitron and manual thinning showed the best results in average fruit weight, in all cultivars. Despite the size improvements, the only influence in quality was observed in ‘Pink Lady®’ Brix° values. All cultivars thinned with 150 ppm benzyladenine were far from the ideal crop load for fruit size, probably due to the poor weather conditions after application, while with two times 165 ppm metamitron sprays had the same results as manual thinning. ‘Pink Lady®’ was the easiest cultivar to thin, with a slight over thinning effect, followed by ‘Gala’, that achieved the ideal crop load and ‘Red Delicious’ was the most difficult to thin. It was not possible to compare ‘Kanzi®’ with the other cultivars due to the poor fruitset observed before the product’s application. Metamitron doses can be adjusted to achieve optimum results; in ‘Pink Lady®’ the dose should be lower while in ‘Red Delicious’ higher. A simpler version of the Greene model was tested the percentage of error was 7.5% for fruits treated with metamitron while in benzyladenine treated fruits was 18%.