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Abstract
Vegetatively-propagated female (cv. Hayward) and male (cv. Tomuri) kiwifruit plants (Actinidia chinensis Planch.) were grown from budbreak until at least the emergence of the 28th leaf in constant temperature conditions of 10, 15, 20, 25, and 30°C. At each temperature, Hayward was grown at 2 photosynthetic photon flux densities (PPFD; 280 and 650 μmol s-1 m-2), whereas Tomuri was grown only at the high photon flux density. Hayward showed a broad optimum for shoot elongation rate, leaf appearance rate, relative growth rate of the new shoot, and relative leaf area growth rate between 20 and 30°C at both high and low PPFD. All growth parameter values were considerably reduced at constant 10°C, and symptoms typical of chilling injury (including loss of chlorophyll and distorted leaf growth) were observed under the high PPFD conditions for this temperature. In contrast, for Tomuri the rates overall were generally higher and values for shoot elongation rate, leaf appearance rate, and estimated relative growth rate had optima probably above 30°C. Both the female and male cultivar studied were typical of other warm-temperate species. A comparison of long-term meteorological records with these responses suggests that the established production areas in New Zealand have normal summer temperatures close to the optimum for vegetative growth of kiwifruit. The decrease in PPFD from 650 to 280 μmol s-1 m-2 resulted in an increase in shoot elongation rate, particularly at 10°C, but resulted in only a small decrease in relative growth rate and a small increase in relative leaf area growth rate. The results indicate that excessive shading from artificial or natural wind-break structures will influence vine growth in orchards.
