Biostimulants to promote budbreak in kiwifruit (Actinidia chinensis var. deliciosa ‘Hayward’)

Abstract

In Portugal, kiwifruit is mostly grown in areas with mild winters, including the Bairrada region. Kiwifruit need at least 500-700 chilling hours to have satisfactory budbreak; however, in this region this does not always occur. Kiwifruit culture is expanding into new areas, and it is important to study new effective solutions that might help to break dormancy. One experiment was carried out in Bairrada with six commercial growth stimulants, including BluPrins® and BluAct (M1), Kiplant HB15 and Kiplant Inducer (M2), Siberio and Siberion (M3), Syncron® and NitroActive® (M4), W-Uniformity Superplus (M5), Organihum Plus and Organihum B-Plus (M6) and without any product application (M7). In the 2015-2016 season, only 198 chilling hours were accumulated, and none of the products helped to increase the rate of budbreak (p>0.05). The estimated production of the control (M7) had the best result (20 t ha-1) and was statistically higher compared with the M2 treatment (10 t ha-1) (p<0.05). These results were probably due to the abnormal progression of the temperature during winter and during the onset of budbreak. After the products’ application (M1, M2, M3 and M4 treatments), budbreak was stimulated, but it was interrupted due to the low temperatures in March and April, resulting in the abortion of flowers that were differentiating. Consequently, these treatments resulted in a heterogeneous budbreak, as observed by the phenological states, where there are two different phases in the progress of the budbreak.