Chilling trends in a warm production area and their impact on flowering and fruiting of peach trees

• Chilling trends in warm production area revealed frequent lack of winter chill.
• A significant correlation between flowering and yield of peach and winter chill.
• The responses of peach to lack of chill seemed to be influenced by rootstocks.
• Dynamic model could be adopted as the suitable model for predicting winter chill.

Biological effects of contrasting chill accumulation on scion-rootstock combinations of peach were investigated using field observations during 2006–2010. Early and mid-season ripening peach cultivars (Early May Crest and Royal Glory, respectively) grafted on GF677 and Cadaman rootstocks were monitored over a five year period in the region of Mornag in northern Tunisia (36°41′N, 10°15′E). Flowering date, flowering duration and double fruits rate were observed over the entire experimental period. The phenological behavior, expressed as fruit set and flower buds abscission, was also surveyed. At harvest, yield, fruit size and number of commercial fruits were determined. Trends of chilling accumulation were characterized over twenty years using two chilling hours models (0–7.2 °C model, CH and Crossa-Raynaud model, CHCR), Utah and Dynamic models. Correlations among chilling models showed that the Dynamic model is more appropriate to estimate chilling accumulation in our warm production area. Climatic conditions during the five experimental years were variable, with chill accumulation in the range 127–421 CH, 82–294 CHCR, 298–860 chill units (CU) and 19–50 chilling portions (CP). Exceptionally warm conditions were observed in winter 2006–2007 and 2009–2010 with significant drop of chill accumulation to levels less than 50% of average chill accumulation. Flowering and fruiting of both early and mid-season maturing commercial cultivars were affected by chill accumulation variability. Warmer winter delayed flowering, extended flowering duration, increased bud abscission and affected fruit set. A chill accumulation less than threshold values of 25 CP, 200 CH, 100 CHCR, and 350 CU resulted in substantial decrease of yield and fruit quality. Cultivar responses to chilling conditions in term of flowering date and yield seemed to be rootstocks dependant. Adoption of appropriate scion-rootstock combination and cultural practices based on chill accumulation could be used in peach industry as means to adapt to increasing frequency of warm winters.