Pollination and fruit set for 'Kordia' and 'Regina' sweet cherry trees in the south of Chile

'Kordia' and 'Regina'are partially self-compatible cultivars and usually their fruit set and crop load are low in the southern Chile. Insufficient pollen availability due to lack of flowering synchronisation with pollinisers are one of the problems in some seasons, also excessive fruitlets drops have been reported. Different trials were carried out over three seasons in order to understand the phenomenon and to improve fruit set. The main objective of this study was to determine appropriate polliniser cultivars and the effective pollination period (EPP) for 'Kordia' and 'Regina'. The research was carried out in commercial orchards in the Central South region. Eight experiments were performed to determine the intensity of fruit set, using pollen from the following compatible cultivars: 'Sam', 'Schneider', 'Staccato', 'Sunburst', 'Summit', 'Sandra Rose', 'Sylvia', 'Alex', 'Katalin' and 'Karina'. To assess the EPP six trials were conducted using pollen from different cultivars, 'Sam' and 'Sunburst' for 'Kordia' and 'Stacatto' and 'Schneider' for 'Regina'. In the third season, one orchard, planted with 'Regina' on rootstock 'Santa Lucia 64', was chosen to sample branches and study the EPP under controlled conditions of light and temperature; 'Kordia' and 'Katalin' were used to pollinate 'Regina'. The advance of pollen tube was observed under fluorescence microscope. In every season the flowering period was monitored. 'Regina' blossom coincided only with the second half of 'Kordia' flowering period. 'Sunburst', 'Summit' and 'Schneider' appear as better polliniser for 'Kordia' with fruit set of 12-30%. For 'Regina', 'Katalin' and 'Schneider' gave the best fruit set (30-40%). Considering the flowering period and 10% as minimum fruit set, 'Sunburst' is good polliniser for 'Kordia'; and 'Schneider', 'Summit' and 'Katalin' for 'Regina'. The EPP was about 5 to 6 days for 'Regina' and 'Kordia', highly influenced by temperature