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Insect repellent and chemical agronomic treatments to reduce seed number in ‘Afourer’ mandarin. Effect on yield and fruit diameter

Garmendia, Alfonso, Beltrán, Roberto, Zornoza, Carlos, Breijo, Francisco, Reig, José, Bayona, Irene, Merle, Hugo
Scientia horticulturae 2019 v.246 pp. 437-447
Capsicum annuum, adverse effects, bees, copper sulfate, cross pollination, farmers, fruits, gibberellic acid, insect repellents, mandarins, seeds, tangors, zinc
Obtaining citrus fruits without seeds is a recurrent objective for farmers as it is one of the most valued characteristics, especially in mandarins. ‘Afourer’ tangor is a highly valuable well-established mandarin, and a high percentage of seeded fruits are produced under cross-pollination conditions. Several agronomic techniques have been suggested to control presence of seeds, such as covering with nets and copper sulfate (CuSO4) and gibberellic acid (GA3) treatments. Natural bee repellents are also proposed to reduce the number of seeds per fruit. In this study, we aimed to compare the effect of several agronomic treatments to reduce the seed number in 'Afourer' mandarin. To this end, we assessed the effect of chemical and bee repellent treatments on the seed number per fruit and the side effect on yield and fruit diameter. Under these experimental conditions the two bee repellents, one based on zinc and one based on Capsicum annuum, were not useful for reducing the seed number per fruit in ‘Afourer’ mandarin. The copper sulfate + GA3 treatment reduced the seed number per fruit by only 35%, and this efficiency was clearly not enough to reduce the seed number for commercial purposes. The most effective method to reduce the seed number per fruit was covering with nets, but this technique led to markedly reduced yields. Yield data was highly variable. Fruit diameter correlated positively with the seed number, but it was a weak relationship as the seed number explained only 15% of fruit size variability (R2 = 0.15).