The effective pollination period in ‘Clemenules’ mandarin, ‘Owari’ Satsuma mandarin and ‘Valencia’ sweet orange

The effective pollination period (EPP) determines the success of seed set in Citrus. In this research, the EPP was studied in three citrus species with different seed set abilities, C. clementina Hort. ex Tanaka, C. unshiu Marcovich and C. sinensis (L.) Osbeck, so as to identify the factors affecting seed set and flower receptivity. The objective of this research was to enhance agronomical efforts [C. Mesejo, A. Martínez-Fuentes, C. Reig, F. Rivas, M. Agustí, The inhibitory effect of CuSO4 on Citrus pollen germination and pollen tube growth and its application for the production of seedless fruit, Plant Sci. 170 (2006) 37–43] to prevent seed presence in fruits given that seedlessness is the main factor of quality for fresh citrus fruit consumption.The EPP was determined and the factors affecting the EPP were evaluated through fluorescence microscopy [R.R. Williams, Techniques used in fruit set experiments, in: R.R. Williams, D. Wilson (Eds.), Towards Regulated Cropping, London Grower Books, 1970, pp. 57–61; J. Sanzol, P. Rallo, M. Herrero, Stigmatic receptivity limits the effective pollination period in ‘Agua de Aranjuez’ pear, J. Am. Soc. Hort. Sci. 128 (2003) 458–462]. The EPP, measured as the capacity to set seeds after pollination with ‘Fortune’ mandarin pollen, was 8–9 days for C. clementina and C. sinensis, and 2–3 days for C. unshiu. Pollen tube development did not appear to be a limiting factor, whereas C. clementina and C. sinensis stigmatic receptivity closely fit the effective pollination period and thus appeared to be the main factor determining seed set in these two species. In C. unshiu, shorter ovule longevity appeared to be the factor determining seed set.We conclude that Citrus flower receptivity is genotype-dependent either on ovule longevity, as in C. unshiu, or stigmatic receptivity, as in C. clementina and C. sinensis.