Author(s): Luedeling, Eike; Girvetz, Evan H; Semenov, Mikhail A; Brown, Patrick H | Abstract: BackgroundTemperate fruit and nut trees require adequate winter chill to produce economically viable yields. Global warming has the potential to reduce available winter chill and greatly impact crop yields.Methodology/principal findingsWe estimated winter chill for two past (1975 and 2000) and 18 future scenarios (mid and end 21st century; 3 Global Climate Models [GCMs]; 3 greenhouse gas emissions [GHG] scenarios). For 4,293 weather stations around the world and GCM projections, Safe Winter Chill (SWC), the amount of winter chill that is exceeded in 90% of all years, was estimated for all scenarios using the "Dynamic Model" and interpolated globally. We found that SWC ranged between 0 and about 170 Chill Portions (CP) for all climate scenarios, but that the global distribution varied across scenarios. Warm regions are likely to experience severe reductions in available winter chill, potentially threatening production there. In contrast, SWC in most temperate growing regions is likely to remain relatively unchanged, and cold regions may even see an increase in SWC. Climate change impacts on SWC differed quantitatively among GCMs and GHG scenarios, with the highest GHG leading to losses up to 40 CP in warm regions, compared to 20 CP for the lowest GHG.Conclusions/significanceThe extent of projected changes in winter chill in many major growing regions of fruits and nuts indicates that growers of these commodities will likely experience problems in the future. Mitigation of climate change through reductions in greenhouse gas emissions can help reduce the impacts, however, adaption to changes will have to occur. To better prepare for likely impacts of climate change, efforts should be undertaken to breed tree cultivars for lower chilling requirements, to develop tools to cope with insufficient winter chill, and to better understand the temperature responses of tree crops.

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Climate change affects winter chill for temperate fruit and nut trees

A progressive global increase in the burden of allergic diseases has affected the industrialized world over the last half century and has been reported in the literature. The clinical evidence reveals a general increase in both incidence and prevalence of respiratory diseases, such as allergic rhinitis (common hay fever) and asthma. Such phenomena may be related not only to air pollution and changes in lifestyle, but also to an actual increase in airborne quantities of allergenic pollen. Experimental enhancements of carbon dioxide (CO2) have demonstrated changes in pollen amount and allergenicity, but this has rarely been shown in the wider environment. The present analysis of a continental-scale pollen data set reveals an increasing trend in the yearly amount of airborne pollen for many taxa in Europe, which is more pronounced in urban than semi-rural/rural areas. Climate change may contribute to these changes, however increased temperatures do not appear to be a major influencing factor. Instead, we suggest the anthropogenic rise of atmospheric CO2 levels may be influential.

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Changes to Airborne Pollen Counts across Europe

Recent temperature increases have elicited strong phenological shifts in temperate tree species, with subsequent effects on photosynthesis. Here, we assess the impact of advanced leaf flushing in a winter warming experiment on the current year’s senescence and next year’s leaf flushing dates in two common tree species: Quercus robur L. and Fagus sylvatica L. Results suggest that earlier leaf flushing translated into earlier senescence, thereby partially offsetting the lengthening of the growing season. Moreover, saplings that were warmed in winter–spring 2009–2010 still exhibited earlier leaf flushing in 2011, even though the saplings had been exposed to similar ambient conditions for almost 1 y. Interestingly, for both species similar trends were found in mature trees using a long-term series of phenological records gathered from various locations in Europe. We hypothesize that this long-term legacy effect is related to an advancement of the endormancy phase (chilling phase) in response to the earlier autumnal senescence. Given the importance of phenology in plant and ecosystem functioning, and the prediction of more frequent extremely warm winters, our observations and postulated underlying mechanisms should be tested in other species.

https://www.pnas.org/content/pnas/111/20/7355.full.pdf

Variation in leaf flushing date influences autumnal senescence and next year’s flushing date in two temperate tree species

The onset of the growing season of trees has been earlier by 2.3 days per decade during the last 40 years in temperate Europe because of global warming. The effect of temperature on plant phenology is, however, not linear because temperature has a dual effect on bud development. On one hand, low temperatures are necessary to break bud endodormancy, and, on the other hand, higher temperatures are necessary to promote bud cell growth afterward. Different process-based models have been developed in the last decades to predict the date of budbreak of woody species. They predict that global warming should delay or compromise endodormancy break at the species equatorward range limits leading to a delay or even impossibility to flower or set new leaves. These models are classically parameterized with flowering or budbreak dates only, with no information on the endodormancy break date because this information is very scarce. Here, we evaluated the efficiency of a set of phenological models to accurately predict the endodormancy break dates of three fruit trees. Our results show that models calibrated solely with budbreak dates usually do not accurately predict the endodormancy break date. Providing endodormancy break date for the model parameterization results in much more accurate prediction of this latter, with, however, a higher error than that on budbreak dates. Most importantly, we show that models not calibrated with endodormancy break dates can generate large discrepancies in forecasted budbreak dates when using climate scenarios as compared to models calibrated with endodormancy break dates. This discrepancy increases with mean annual temperature and is therefore the strongest after 2050 in the southernmost regions. Our results claim for the urgent need of massive measurements of endodormancy break dates in forest and fruit trees to yield more robust projections of phenological changes in a near future.

Can phenological models predict tree phenology accurately in the future? The unrevealed hurdle of endodormancy break.

Partial Least Squares Regression for analyzing walnut phenology in California

Temperate fruit trees cultivated in regions of mild winter conditions, show several anomalies. Such anomalies are described, in a general way, as the budbreak absence and/or flowering delay. But after budbreak, fruit trees go on displaying anomalies like: paralysis of the shoot growth, development of small leaves, development of small flat shape fruits, low rate of effective fructification and reduction of the flowering-maturation cycle. Budbreak inductors do not influence the development of new leaves, and several times they stop the growth after budbreak. Among the problems of lack of chilling, the size and shape of the fruits, the low effective fructification and formation of small leaves in the shape of rosette are those that manifest more after artificial budbreak induction. INTRODUCTION A series of anomalies occurs when apple trees are cultivated in regions of mild winter, where the chilling requirements are not satisfying. Such anomalies, regarding to budbreak and flowering, have been described by several authors (Iuchi, 2002; Black, 1953; Bulon and Faust, 1995; Skinner, 1964; Saure, 1985; Chariani and Stebbins, 1994; Petri et al., 1996). But after budbreak and flowering, others anomalies go on persisting or manifesting during the cycle of the culture, and few studies describe and suggest measures that can minimize these problems. Nee and Fuchigami (1992) suggested two different approaches for overcoming rest: exit of the dormancy and elongation of the buds. The budbreak inductors can affect only the process of exit of the dormancy. However, the budbreak inductors do not influence the second approach, which involves the growth of the axillary buds and the development of the new leaves and fruits. The aim of this work is discuss and show the principle anomalies relating to the lack of chilling observed in the south of Brazil. MATERIAL AND METHODS The experiments were carried out in Cacador and Sao Joaquim, SC, Brazil. Cacador is located at 26°46 S latitude, at 960 meters altitude, with 1067 chilling units (North Caroline modified model, Shaltout and Unrath, 1983). Sao Joaquim is located at 28°7  S latitude, at 1353 meters altitude, with 2025 chilling units. The parameters analyzed were budbreak percentage, leaf area, average number of leaves by fructification organs and fruit size. They were sampled in five-years-old trees. The samples were collected in 10 randomized trees and for each tree 10 buds per type of bud (small spur, medium spur, big spur and brindle) were sampled. For statistical analysis Duncan test was used. RESULTS AND DISCUSSION Considering the great variability of the cold intensity in the different growing regions in the south of Brazil (Fig. 1), a series of anomalies, relating to the lack of chilling, are observed and present different intensities according to the region and year. Proc VII on TZFTS Eds. K.K. Jindal et al Acta Hort 662, ISHS 2004

Consequences of insufficient winter chilling on apple tree bud-break

A cultura da macieira no Brasil iniciou seu desenvolvimento comercial na decada de 70, sendo que ate esta data foram poucos os plantios comerciais, representando menos de 100 ha. Com a iniciativa de alguns produtores pioneiros, incentivos fiscais que permitiam aplicar parte do Imposto de Renda na implantacao de pomares e pelo apoio dos governos estaduais com projetos de desenvolvimento, a cultura da macieira teve grande impulso a partir da decada de 80. Destaca-se que, na decada de 70, o Brasil dependia de importacoes, representando na epoca mais de 100 milhoes de dolares. Nessa decada, produziamos 13.263 t, passando para 183.299 t e 857.615 t na decada de 80 e 90, respectivamente. Atualmente, o Brasil conta com uma area em torno de 37.000 ha, com 3.450 produtores, sendo que, na safra de 2009/2010, foram colhidas 1.253 mil toneladas. Desde 1994, o Brasil passou a exportador de macas, sendo que, a partir do ano de 2000,as exportacoes vem superando as importacoes. A cultura da macieira e uma importante fonte de geracao de emprego, com tres empregos diretos e indiretos por ha, o que representa mais de 100 mil empregos na cadeia produtiva da maca. Estes avancos devem-se a importantes tecnologias que foram introduzidas ao longo dos anos, que tambem permitiram um aumento de qualidade e produtividade por unidade de area, onde, na decada de 70 e 80, era inferior a 15t e atualmente esta proxima de 40 t/ha, com alguns pomares produzindo acima de 50 t/ha. A evolucao ocorreu com as cultivares, com os primeiros plantios realizados com as cultivares Golden Delicious, Starkrimson, Blackjon, entre outras, as quais logo foram substituidas por 'Gala" e 'Fuji, e, na decada de 90, plantando-se os clones destas cultivares com melhor coloracao vermelha dos frutos. Grande evolucao ocorreu com a qualidade do material vegetativo em que porta-enxerto e copas estavam infectados com viroses. A introducao de material livre de virus propiciou aumento na produtividade, permitindo tambem a utilizacao de porta-enxertos ananizantes, com plantios em alta densidade. No inicio dos plantios de macieira, eram plantadas de 500 a 800 plantas por ha, sendo que atualmente sao utilizadas 2.500 a 3.000 plantas em media por ha. Como a regiao produtora de maca no Sul do Brasil nao tem o frio suficiente para atender as necessidades para a saida da dormencia, tecnologias foram desenvolvidas para a inducao de brotacao e floracao, permitindo estabilidade na producao. Afora estas tecnologias, devem ser ressaltados os avancos nos sistemas de conducao e poda, manejo de colheita, raleio quimico, polinizacao, controle fitossanitario e conservacao e armazenagem da fruta, sendo que esta ultima permitiu o abastecimento do mercado nos 12 meses do ano com fruta de otima qualidade. A maca foi pioneira na implantacao do sistema de producao integrada, sendo a primeira fruta brasileira a ser certificada neste sistema.

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Avanços na cultura da macieira no Brasil

Despite the high efficiency of some chemicals on budbreak induction of temperate fruit trees, the high toxicity showed by these compounds is one of the main problems related to its use. Preliminary results indicated that Erger®, an organic nitrogen compound, combined with calcium nitrate, has similar effect to hydrogen cyanamide, with the advantage of being less dangerous to the environment. Thus, the present study aimed to evaluate the efficiency of Erger® and calcium nitrate as budbreak promoter in apple trees. The experiment was carried out in Cacador/SC, in 2007, where was done the application of different budbreak promoters in 'Imperial Gala' and 'Fuji Suprema' apples. The budbreak promoters tested were Erger® 3% + calcium nitrate 3%, Erger® 5% + calcium nitrate 5%, Erger® 7% + calcium nitrate 7%, mineral oil 3.2% + 0.34% hydrogen cyanamide and control (without application). It was evaluated occurrence dates of early, full and end blooming stages, budbreak of axillary and terminal buds, axillary budbreak uniformity and fruit set. The budbreak promoters increased significantly axillary and terminal budbreak, and it increased the budbreak uniformity and the blooming overlap of 'Imperial Gala' and 'Fuji Suprema' apples. Because of negative effects on fruit set of 'Imperial Gala' apples, it is indicated Erger® and calcium nitrate application at concentrations below 7%.

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Budbreak in 'Imperial Gala' and 'Fuji Suprema' apples by use of Erger and calcium nitrate

The basic conditions of fruit set (synchronic bloom, transfer of pollen, etc.) still do decide definitely the fate of the flower (Cano-Medrano & Darnell, 1998) in spite of the best weather conditions (Stosser, 2002). Beyond a set quantity of fruits, the tree is unable to bring up larger load. A system of autoregulation works in the background and causes the drop of a fraction of fruits in spite of the accomplished fertilisation and the equality of physiological precedents (Soltesz, 1997). There are also basically genetic agents in action. The further development of fruits maintained on the tree depends mainly on the growing conditions (e.g. water, supply of nutrients, weather adversities, pruning, fruit thinning, biotic damages, etc.), which may cause on their own turn fruit drop especially at the time of approaching maturity.

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Fruit drop: the role of inner agents and environmental factors in the drop of flowers and fruits

Apple tree cultivars demand several requirements in cold but there's a little of information about what temperatures are the most efficient. Apple tree cultivars Condesa, Baronesa, Daiane, Imperatriz, Fuji and Gala were studied on quantity of cold and different temperatures for shooting inducement. Experimental delineation was full casualized on the factorial system, with six cultivars, five levels of cold unities and three temperatures. Average time for shooting was minor when the cultivars were exposed to 1,500 cold unities independently of the temperature. Effective temperature in order to accumulate cold ranges according to the cultivar, and it is able reaching until 15oC in case of cultivar of lower demand in cold.

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José Luiz Petri

Papers

Consequences of insufficient winter chilling on apple tree bud-break

Avanços na cultura da macieira no Brasil

Budbreak in 'Imperial Gala' and 'Fuji Suprema' apples by use of Erger and calcium nitrate

Fruit drop: the role of inner agents and environmental factors in the drop of flowers and fruits

Temperaturas efetivas para a dormência da macieira(Malus domestica Borkh)