The Dynamic Model Provides the Best Description of the Chill Process on ‘Sirora’ Pistachio Trees in Australia

Abstract

<jats:p>Determining the chilling requirement for ‘Sirora’ pistachio (<jats:italic>Pistacia vera</jats:italic> L.) production in Australia and monitoring winter chill accumulation is desirable to allow growers to take timely mitigating action in years of insufficient chill. Based on greenhouse work, historical data analysis, and field validation, the Chilling Hour, Utah, and Dynamic Models were compared. The Dynamic Model produced the best determination for fulfillment of chilling requirement with 59 chill portions. The required number of growing degree-hours above 4.4 °C from chill fulfillment to 50% bloom was 9633. Relations among the level of fulfillment of chilling requirement, bloom delay, and yield are discussed.</jats:p>

Identification of chilling and heat requirements of cherry trees—a statistical approach

“…While this variation may simply reflect variation in winter chill, we find it likely that the lower variation in the Dynamic Model is also an indication of the latter model’s higher accuracy. This finding supports earlier research showing the Dynamic Model to perform equally well or better than the other models (Luedeling et al 2009f; Ruiz et al 2007; Zhang and Taylor 2011), and it adds weight to several studies that have recommended using it more widely (Luedeling et al 2009f, 2011; Ruiz et al 2007; Zhang and Taylor 2011; Perez et al 2008; Erez 2000; Erez et al 1990; Luedeling and Brown 2011). Results from the analysis of walnuts in California (Table 3) also show the most clearly defined chilling requirements for the Dynamic Model, adding further evidence to the finding that Chill Portions are a more useful metric for winter chill than the traditional measures.…”

“…The equations that this model is based on are more complex than for the other models but have been described by several authors (Darbyshire et al 2011; Luedeling and Brown 2011; Luedeling et al 2009e). In model comparisons, the Dynamic Model typically performs equally well or better than the other models (Luedeling et al 2009f; Ruiz et al 2007; Zhang and Taylor 2011), leading several studies to recommend using it more widely (Luedeling et al 2009f, 2011; Ruiz et al 2007; Zhang and Taylor 2011; Perez et al 2008; Erez 2000; Erez et al 1990; Luedeling and Brown 2011). …”

“…Using an appropriate and at least somewhat accurate model is critical for reliably matching cultivars with site-specific agroclimatic conditions. For a number of sites, chilling models have been compared, with most comparisons favoring the Dynamic Model over the others (e.g., Luedeling et al 2009f; Ruiz et al 2007; Zhang and Taylor 2011; Luedeling 2012). Yet even if an ideal model were adopted globally, problems would remain in quantifying a cultivar’s chilling requirements.…”

Heat model for pistachio bloom and harvest

“…In Iran, heat requirements of pistachio trees are between 8852 and 15,420 GDH for bloom with T b of 4.5 • C. 'Kalle-Ghuchi' pistachio requires 8852-9637 GDH, 'Owhadi', 12,871-13,320 GDH and 'Akbari' 14,208-15,420 GDH (Rahemi and Pakkish, 2009). In Australia the cultivar 'Sirora' requires 9633 GDH from chill completion to full bloom with a base temperature of 4.4 • C (Zhang and Taylor, 2011).…”

“…Zhang and Taylor (2011) established the chill requirement model for 'Sirora' pistachio in Australia using the Dynamic model. This model offers reliable predictions.…”