KIWIFRUIT RESEARCH IN A SUBTROPICAL AREA

At Pietermaritzburg (altitude 750 m, latitude 29° 40’S), a cool subtropical area, high day temperatures (up to 30°C during winter) result in a negative Utah chill unit (UCU) total some years.
However about 23 "Dynamic Portions" (DP) accumulate by the end of August.
By counting only days with positive Utah chill unit (PCU) totals, a good indication of winter chilling is obtained with about 300 to 400 PCU accumulating. ‘Hayward’ kiwifruit vines fail to fruit, even with cyanamide sprays, but ‘Allison’ bears well after 4 to 6% Dormex® sprays in mid-August.
While flower primordia developed to the same stage before winter, lack of chilling prevented further differentiation of the high-chill ‘Hayward’ buds.
Copy plants of ‘Allison’ on local low-chill rootstocks are producing well. ‘Allison’ rooted cuttings appear to be the best low-chill rootstock.
The synergistic effect of evaporative cooling (by intermittent sprinkling from mid-June to mid-August) in reducing bud temperatures, and cyanamide sprays, enabled the production of large ‘Hayward’ fruits and excellent ‘Allison’ crops.
Evaporative cooling in autumn has delayed fruit maturity, which is normally about mid-May.
Shade netting (30%) had beneficial effects on yield and photosynthesis (P_net 7 to 10 vs 4 to 6 μmol CO₂ m^-2 s^-1 for control, with midday PPFD of 2000 μM m^-2 s^-1).

III International Symposium on Kiwifruit

P. Allan, G.C. Linsley-Noakes, D. M. Holcroft, S. A. Brunette, M.J. Burnett, A. Cathcart-Kay

Actinidia deliciosa var. deliciosa, chilling models, evaporative cooling, flower differentiation, hydrogen cyanamide, low-chill rootstocks, net photosynthesis, shading

https://doi.org/10.17660/ActaHortic.1997.444.2