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Temperate trees require low temperatures during winter and subsequent warm conditions in early spring to flower and eventually bear fruit. Many parts of the Mediterranean region feature winters with low and sometimes marginal chill accumulation. To assess historic and future agroclimatic conditions for cultivating temperate trees (including almonds, pistachios, apricots, sweet cherries and apples), we mapped winter chill throughout this important growing region. We used on-site weather records (1974–2020) to calibrate a weather generator and produced data for historic and future scenarios. To broaden our analysis, we spatially interpolated chill for the whole Mediterranean basin. We supplemented our simulation outcomes by collecting expert knowledge (from farmers and researchers) regarding observed climate change impacts on temperate orchards as well as future risks and concerns generated by climate change. Results showed that northern African growing regions have experienced major chill losses, a likely cause of the irregular and delayed bloom highlighted by experts. The same regions, together with southern Europe, may lose up to 30 Chill Portions by 2050 under a moderate warming scenario. For the future, experts foresee increasing risk of spring frost in early-blooming cultivars, exacerbated bloom-related problems and increasing occurrence of heat waves. Our results provide evidence of likely climate change impacts on temperate orchards. Expert knowledge proved instrumental in interpreting the simulation results as well as in orienting climate change adaptation strategies. The results we present are useful for farmers and orchard managers planning new plantings, as well as for researchers and policy makers developing strategies to adapt fruit orchards to the impacts of climate change

In this document, we provide supplementary materials for the work ‘Climate change impacts on winter chill in Mediterranean temperate fruit orchards’ by Eduardo Fernandez and co-authors. The study is published in the journal Regional Environmental Change under the doi: 10.1007/s10113-022-02006-x. We conducted this work in collaboration with researchers from northern and southern Spain, Tunisia, Morocco and Germany under the umbrella of an international project (AdaMedOr) funded by the Partnership for Research and Innovation in the Mediterranean Area (PRIMA). Compared to previous similar studies, we provide now an analysis that combines the spatial interpolation of winter chill accumulation in the Mediterranean region under future scenarios with expert knowledge regarding the impacts of climate change on temperate orchards as well as future concerns of farmers cultivating temperate species. Our approach allowed us to frame and contextualize the results of our chill estimations, potentially contributing to the development of management strategies to adapt Mediterranean orchards to future climate conditions. We offer figures that were not included in the main manuscript, as well as additional information about the weather stations used for the analysis.

The agronomic performance and fruit quality traits were evaluated for ten Prunus rootstocks: Garnem, PADAC 150, PADAC 04-03, PADAC 04-01, Rootpac® 70, PM 105 AD, AGAF 0301-04, Krymsk® 1, Krymsk® 86 and PAC 847. These rootstocks were budded with ‘Subirana’ flat peach cultivar in September 2007 and planted in two adjacent plots in northern Tunisia (36°41′N, 10°15′E) on a heavy and calcareous soil typical of the Mediterranean area. Tree mortality, vegetative growth, rate of bud failure and fruit quality were assessed. Significant differences were found among rootstocks for the agronomic and fruit quality traits. Growing conditions generated varying levels of tree mortality, the highest with Krymsk® 1 rootstock. In contrast, all trees on PADAC 04-03 and PADAC 04-01 survived well. The lowest vigor was induced by Krymsk® 1 with a reduction of 90% in trunk cross-sectional area (TCSA) and canopy volume as compared to Garnem. PADAC 150 also expressed a low vigor. The highest canopy volume was found on Rootpac® 70 as similarly for Garnem. The remaining rootstocks induced a medium vigor level. Trees on vigorous rootstocks as Rootpac® 70 showed the lowest rate of bud failure, while dwarfing rootstocks induced the highest buds abscission. Yield was higher for AGAF 0301-04 in 2011 and 2012 as compared to the rest of rootstocks. The highest yield efficiency was recorded on PM 105 AD and AGAF 0301-04 rootstocks. Rootpac® 70 presented the highest fruit weight and fruit diameter. The highest level of soluble solids content (SSC) was recorded on Krymsk® 1, and the lowest on Garnem, although differences were not significant when compared to the other rootstocks. The less vigorous rootstocks seem to induce a better fruit quality of peach based on fruit sugar content. This study provides information that new Prunus rootstocks for peach can lead to a better agronomic performance than Garnem, mainly in vigor and in productive parameters. The peach-plum hybrid PADAC 04-03 induced good yield

Performance of fruit species from Prunus is highly dependent on rootstock. This study focused on evaluating the field performance of several Prunus rootstocks in the main fruit irrigated production area in Tunisia. Nine new rootstocks: PADAC 150 AD, PADAC 04-03, PADAC 04-01, ROOTPAC 70, PAC 941, AP1, Krymsk-1, PAC 0301-04 and PM 105 AD were tested of comparison to the most widely used rootstock (Garnem). The performance of a flat nectarine variety ‘Subirana’ budded onto these rootstocks was evaluated. Phenological stages, rate of bud failure, vegetative growth and chlorophyll index were monitored. The results of the evaluated Prunus rootstocks revealed contrasting effects on the nectarine variety depending on the vigor of the rootstocks. The PADAC 04-03 induced an important vigor identical to that of trees on Garnem, whereas Krymsk-1 produced the lowest tree vigor. Krymsk-1 and PAC 941 induced an early development of floral buds, while the other rootstocks delayed flowering by few days. The nectarine variety ‘Subirana’ showed SPAD chlorophyll index values above the threshold with all rootstocks, which seems to have good nitrogen nutrition. PAC 0301-04 and Garnem obtained the highest yields.