1 www.envirochange.eu

CLIMATE CHANGE AND ONTOGENIC RESISTANCE

Thecapabilityofplantstodefendthemselvesindifferentphasesoftheirlifehasbeenstudiedforlongtime,withoutclearresults.Astudyonthismechanisminapplesshowspossiblenewperspectivesintheviewofclimatechange.

Initsgeneralsense,ontogenicresistanceisthecapabilityofplantstodefendthemselvesindifferentstagesoftheirdevelopment.I.e.olderleavesaremorerobustandgenerallyhaveanincreaseinchemicalandphysicaldefencestopathogeninvasion.

Ontogenicresistancehasbeenstudiedfornearlyacentury,butnoclearanswersemergedfromstudiesthatconsideredphysiologicalandbiochemicalchangesduringleafontogenesis.

Appleisoneofthemostimportantfruitcropinregionswithtemperateclimate.Applescabisconsideredoneofthemostharmfuldiseasesinappleorchards.

Key‐features

Climatechangemaynotonlyalterthephysiologicalresponseofapple,butalsoproductionofspores,germination,andsecondaryinfectionsofapplescab.

Climatechangeandontogenicresistancearetwoimportantfactorstobestudiedtoimplementfungicideapplicationinappleorchards.Consideringleafdevelopment,diseaseincidenceandfungalgrowthindiseaseforecastprogramsmaydecreasepesticideapplicationandsotheriskofbothhealthproblemstotheconsumerandthefarmeraswellastothedevelopmentoffungicideresistance.

1. Apples and pathogens

Apple (Malus x domestica) is one of the most cultivated fruit crop in temperate climate.

Black spots on apple have been first documented in the literature in the early nineteen century as reviewed by MacHardy (1996b), but some indices of the presence of the disease came from a painting from the seventeen century as documented in MacHardy et al. (2001).

Venturia inaequalis, a hemibiotrophic ascomycete, is considered as one of the most economically important fungal pathogen in apple orchards with temperate climate.

Relations between plant tissues-age and disease resistance have been widely investigated and age-related resistance (ontogenetic resistance) has been documented in numerous plant/pathogen systems.

bycourtesyofMicheleGusberti

bycourtesyofMicheleGusberti

2 www.envirochange.eu

2. Ontogenic resistance in apple

Ontogenic resistance has been studied for long time in apple. In the Malus-Venturia pathosystem, the first researcher who observed age-related resistance was probably Goethe (1887). A decade later Aderhold (1900) observed also that young apple leaves were more susceptible to apple scab disease than older ones. Keitt and Jones (1926) showed a difference in lesion formation between leaves of different age: lesions on the first two leaves, where ontogenic resistance is not yet functional, appeared between 12 and 19 days post inoculation (dpi). Lesions on the third leaf appeared between 17 and 24 dpi and on the fourth one between 19 and 41 dpi, while on the fifth leaf lesions took between 33 and 56 dpi. No lesions appeared on older leaves within the 56 days of the monitoring.

Thus, in apple plants the main effect of ontogenic resistance is an increase of the incubation and latent periods and a decrease of lesion intensity (Szkolnik, 1978) by increasing leaf age.

After these first studies numerous researches started to try to explain this type of resistance found in apple plants:

• Physical barriers, such as cuticula and papillae, are probably not connected to ontogenic resistance in apple (Gessler & Stumm, 1984; Stadler, 1988).

• Biochemical analysis of different pH between old (pH=5) and young (pH=6) leaves homogenates and the effect on enzymatic activity (e.g. phenilalanine ammonia lyase, polyphenoloxidase, β-glucosidase, chitinase, and fungal polygalacturonases) and on secondary metabolites (e.g. melanoproteins, phloridzin, flavan-3-ols, and polygalacturonases-inhibition proteins) in apple leaves were studied (reviewed by MacHardy, 1996a), without success.

Global apples production in 2009 (http://faostat.fao.org):

• 71’286’632 t over 4’922’034 ha

Most important apple producers:

• China: 31.684.445 t 2.049.536 h • United States of America: 4.514.880 t

140’994 h • followed by Turkey, Poland, Iran, Italy,

France, India, and Russia

Most wholdwide important apple cultivars:

• Golden Delicious, Delicious, Gala, Fuji and Braeburn with some local variation of consumer acceptance (Kellerhals, 2009)

However, despite nearly half a century of research no clear pattern for ontogenic resistance was found. In both these approach some factors have been found to change during leaf ontogenesis, but none could be clearly linked to ontogenic resistance.

3 www.envirochange.eu

Fig. 1. Apple scab, symptoms on fruits.

3. Global warming: effects on Malus-Venturia pathosystem

Fig. 2. Apple scab, symptoms on leaves.

Global warming, at least +0.7°C in the last century (Mann & Bradley, 1999), is expected to become a serious problem in the next century with an increase of the temperature between 2 and 5.8°C depending on the different models used, different regions considered, and also on different human influences taken under consideration (Wigley & Raper, 2001; Meehl et al., 2005; CH2011, 2011).

In the 21st century trends for precipitations show a possible decrease in precipitation during summer and autumn (Kundzewicz et al., 2006; Dankers & Hiederer, 2008; CH2011, 2011), while an slight increase in precipitation during winter and spring is expected (Dankers & Hiederer, 2008).

Deciduous crop plants need two important factors to develop correctly in the following growing season. The first is a prolonged rest period during winter below a threshold temperature (i.e. chilling) and the second corresponds to a period of increased temperature (i.e. heat unit accumulation).

From the plant point of view, an increase of winter temperature may result in an insufficient chilling period, decreasing percentage of bud breaks (Gardea et al., 2000) and prolonging the flowering period (Landesberg, 1974).

Increasing of winter and spring temperatures, however, may lead to an anticipation of ascospores maturation and release (Gadoury & W.E., 1982; Stensvand et al., 1997), thus disease management strategies may be started earlier in the season. Moreover, this anticipation of bud break and growth could increase also the danger of injuries due to late frosts (Luedeling et al., 2009).

Higher summer temperature may decrease secondary (conidial) infections (Doran, 1922). Another important aspect of a general increase of temperature may be the extension of the vegetative season, thus an increase of the number of secondary infections may be expected.

For ascospores and conidia germination not only temperature but also moisture is an important factor for a successful tissue infection, thus an increase in spring precipitation may lead to an increase in number of severe primary leaf infections due to ascospores (Mills, 1944).

However, a decline of summer precipitations may decrease the number of severe secondary infections in apple orchards, since conidia are splash dispersed and germination is highly dependent on tissues wetness (MacHardy & Gadoury, 1989).

4 www.envirochange.eu

Ontogenic resistance has been shown to be fully expressed between 12 and 13 days after leaf unfolding, i.e. more or less when leaves finish their expansion (Schwabe, 1979). The leaf expansion and plant growth are generally correlated to the temperature, as shown in preceding works with other plant species (Milthorpe, 1959; Rawson & Hindmarsh, 1982). In apple plants, Calderón-Zavala et al. (2004) found out that temperatures up to 26/21°C (day/night temperatures) incited a positive response for shoot growth, but at temperatures 33/28°C shoot growth decreased.

4. Climate change and ontogenic resistance in apple

Gur et al. (1972) found out that the optimal soil temperature for growth was around 25°C and that at 35°C growth was drastically reduced. At this latter temperature the authors observed leaf discoloration, intervenous necrosis and shredding of leaves.

In the present work we analyzed the leaf expansion, disease incidence and relative fungal growth on young and old plants at different temperatures to assess the effect of climate change on ontogenic resistance in apple plants.

Fig. 3. Colonization coefficient calculated at different time-points for leaf one (L1, youngest unfurled and expanding leaf), leaf 3 (L3) and leaf 5 (L5) of 'Gala' and 'Florina', respectively highly susceptible and highly resistant cultivars, inoculated with field inoculum of Venturia inaequalis. Data points represents means of three replicates and bars represent standard deviation from the means.

Firstly, we developed and validated (Gusberti et al., 2012) a real-time qPCR to enable relative fungal quantification in leaves of different age. The effect of ontogenic resistance

was visible with an 18-fold increase in pathogen biomass in leaf no. 1 by 21 dpi, while no fungal growth was observed in leaf 5 during the same period (Fig. 3).

5 www.envirochange.eu

Fig. 4. Preliminary results. Mean relative growth rate for each leaf position (enumeration starting from the top of the shoot) under different temperature regimes.

Fig. 5. Preliminary results. Disease incidence for each leaf position (enumeration starting from the top of the shoot), time point and temperature.

Secondly, we performed two independent experiments to follow leaf expansion, disease incidence and fungal growth at different temperatures (data under analysis). Preliminary results revealed a significant contribution of leaf position, time and temperature on the relative expansion rate of apple leaves. Leaf expansion decreased with increasing leaf age, increasing sampling points (dpi), and temperature. Leaf expansion increased in average between 15 and 24°C, but it decreased thereafter (Fig. 4). Disease incidence showed a statistical increase between 10 and 18 dpi, then between 18 and 21dpi and between 21 and 28 dpi no differences were found. The shortest incubation period was observed at 20° followed by 24 and 25°C, then by 15°C and the longest incubation period was found at 28°C. At this latter temperature we did not see any symptom on leaf 5 during the whole experiment (Figs. 5 and 6).

Fig. 6. Disease incidence for each leaf position (L1-L5) and temperature (15, 20, and 25°C).

6 www.envirochange.eu

5. Perspectives

Ontogenic resistance is an important aspect to be considered when planning either treatment against apple scab in the field or for replacing cultivars in apple orchards. Many factors could contribute to this type of resistance, two among the most important are leaf age and leaf expansion rate (Keitt & Jones, 1926; Szkolnik, 1978; Schwabe, 1979). In this work we analyzed leaf expansion rate, disease incidence and fungal growth in different climatic conditions to assess the impact of climate change on ontogenic resistance (data under analysis).

Preliminary results showed a decrease in leaf expansion rate between 25 and 28°C. These results were in accordance with previous scientific works. Disease incidence and fungal growth decreased also for temperatures above 25°C, but at above this threshold plants may suffer from the abiotic stress, showing leaf discoloration, intervenous necrosis and shredding of leaves (Gur et al., 1972).

However, ontogenic resistance is not the only factor to be taken into account in a world with increasing temperatures: specific chilling requirements of the used cultivars (short chilling vs. long chilling cultivars) as well as disease (production of ascospores, colonization of tissues, and secondary infections) may be studied more in details, in a scenario of increasing temperatures, to ensure a sustainable use of apple orchards in alpine regions.

7 www.envirochange.eu

To know more

Aderhold, R., 1900. Die Fusicladien unserer Obstbäume. Landwirtschaftliche Jahrbücher 29, 541-588.

Calderón-Zavala, G., Lakso, A.N., and Piccioni, R.M., 2004. Temperature effects on fruit and shoot growth in the apple (Malus domestica) early in the season. Acta Hort. 636, 447-453.

CH2011, 2011. Swiss Climate Change Scenarios CH2011, C2SM, MeteoSwiss, ETH, NCCR Climate, and OcCC, Zurich, Switzerland. 88 pp.

Dankers, R., and Hiederer, R., 2008. Extreme temperatures and precipitation in Europe: analysis of a high-resolution climate change scenario. JRC Scientific and Technical Reports EUR 23291 EN.

Develey-Rivière, M.-P. , and Galiana, E. , 2007. Resistance to pathogens and host development stage: a multifaceted relationship within the plant kingdom. New Phytol. 175, 405-416.

Doran, W. L., 1922. Effect of external and internal factors on the germination of fungous spores. Bulletin of the Torrey Botanical Club 49, 313-340.

Gadoury, D.M., and W.E., MacHardy, 1982. Effects of temperature on the development of pseudothecia of Venturia inaequalis. Plant Dis. 66, 464-468.

Gardea, A.A., Carvajal-Millàn, E., Orozco, J.A., Guerrero, V.M., and Llamas, J., 2000. Effect of chilling on calorimetric responses of dormant vegetative apple buds. Thermochimica Acta 349, 89-94.

Gessler, C., and Stumm, D., 1984. Infection and stroma formation by Venturia inaequalis on apple leaves with different degrees of susceptibility to scab. J. Phytopathol. (Berl.) 110, 119-126.

Goethe, R., 1887. Weitere Beobachtungen ueber den Apfel und Birnenrost, Fusicladium dentriticum (Wallr.) Fuckel und Fusicladium pyrinum (Lib.) Fuckel. Gartenflora 36, 293-199.

Gur, A., Bravdo, B., and Mizrahi, Y., 1972. Physiological responses of apple trees to supraoptimal root temperature. Physiol. Plant. 27, 130-138.

Gusberti, M., Patocchi, A., Gessler, C., and Broggini, G.A.L., in press. Quantification of Venturia inaequalis growth in Malus x domestica with quantitative Real-Time Polymerase Chain Reaction. Plant Dis., accepted for publication the 5th July 2012.

Keitt, G.W., and Jones, L.K., 1926. Studies of the epidemiology and control of apple scab. Agricultural Experiment Station, University of Wisconsin, Research Bulletin 73, 104 pp.

Kellerhals, M., 2009. Introduction to Apple (Malus x domestica). In: Folta K.M., Gardiner S.E. (Eds.), Genetics and Genomics of Rosaceae, Vol. Plant Genetics and Genomics: crops and Models 6, Springer, 73-84.

Kundzewicz, Z.W., Radziejewski, M., and Pinskwar, I., 2006. Precipitation extremes in the changing climate of Europe. Clim. Res. 31, 51-58.

Landesberg, J.J., 1974. Apple fruit bud development and growth; analysis and and empirical model. Ann. Bot. (Lond.) 38, 1013-1023.

8 www.envirochange.eu

Luedeling, E., Blanke, M., and Gebauer, J., 2009. Auswirkungen des Klimawandels auf die Verfügbarkeit von Kältewirkung (Chilling) für Obstgehölze in Deutschland. Erwerbs-Obstbau, 81-94.

MacHardy, W.E., 1996a. Ontogenic resistance to scab in Malus, Apple Scab Biology, Epidemiology, and Management. APS Press, St. Paul, Minnesota, pp. 104-116.

MacHardy, W.E., 1996b. The pathogen, Apple Scab Biology, Epidemiology, and Management. APS press, St. Paul, Minnesota, pp. 398-411.

MacHardy, W.E., and Gadoury, D.M., 1989. A revision of Mills's criteria for predicting apple scab infection periods. Phytopathology 79, 304-310.

MacHardy, W.E., Gadoury, D.M., and Gessler, C., 2001. Parasitic and biological fitness of Ventuia inaequalis: relationship to disease management strategies. Plant Dis. 85, 1036-1051.

Mann, M.E., and Bradley, R.S., 1999. Northern hemisphere temperature during the past millenium: inferences, uncertainities, and limitations. Geophysical Research Letters 26, 759-762.

Meehl, G.A., Washington, W.M., Collins, W.D., Arblaster, J.M., Hu, A., Buja, L.E., Strand, W.G., and Teng, H., 2005. How much more global warming and sea level rise? Science 307, 1769-1772.

Mills, W.D., 1944. Efficient use of sulfur dusts and sprays during rain to control apple scab. Cornell Extension Bulletin 630.

Milthorpe, F.L., 1959. Studies on the expansion of the leaf surface. I. The influence of temperature. J. Exp. Bot. 10, 233-249.

Panter, S.N., and Jones, D.A., 2002. Age-related resistance to plant pathogens. Adv. in Biol. Res. 38, 251-280.

Rawson, H.M., and Hindmarsh, J.H., 1982. Effect of temperature on leaf expansion in sunflower. Aust. J. Plant Physiol. 9, 209-219.

Schwabe, W.F.S., 1979. Change in scab susceptibility of apple leaves as influenced by age. Phytophylactica 11, 53-56.

Stadler, B., 1988. Quantitative Untersuchungen der varietalen und ontogenetischen Resistenz der Apfelblätter von Golden Delicious, Liberty und Malus floribunda gegenüber Venturia inaequalis, Swiss Federal Institute of Technology ETHZ, Ph.D Thesis no. 8685, Zurich, Switzerland, pp. 72 pp.

Stensvand, A., Gadoury, D.M., Amundsen, T., Semb, L., and Seem, R.C., 1997. Ascospore release and infection of apple leaves by conidia and ascospores of Venturia inaequalis at low temperatures. Phytopathology 87, 1046-1053.

Szkolnik, M., 1978. Relative susceptibility to scab and production of conidia among 30 apple varieties. N.Y. Agric. Exp. Stn. Spec. Rep. 28, 11-14.

Wigley, T.M.L., and Raper, S.C.B., 2001. Interpretation of high projections for global-mean warming. Science 293, 451-454.

EnviroChangeiscoordinatedby:• FondazioneEdmundMach‐IstitutoagrariodiS.Micheleall'Adige

(FEM,http://www.ismaa.it),ResearchandInnovationCentre,Italia

Scientificcoordinator:IlariaPertot,ilaria.pertot@fmach.it

Partners:• FondazioneBrunoKessler(FBK,http://cit.fbk.eu/en/home),Italia

Scientificpartner:CesareFurlanello,furlan@fbk.eu

• AgriculturalResearchOrganization(ARO,http://www.agri.gov.il/en/departments/12.aspx),TheVolcaniCenter,IsraelScientificpartner:YigalElad,elady@volcani.agri.gov.il

• SwissFederalInstituteofTechnologyZurich(ETH,http://www.path.ethz.ch),

Instituteofplantsciences,SwitzerlandScientificpartner:GesslerCesare,cesare.gessler@usys.ethz.ch

• UniversitàdeglistudidiTrento,(UNITN,http://portale.unitn.it/deco),

Dipartimentodieconomia,ItalyScientificpartner:RobertaRaffaelli,roberta.raffaelli@unitn.it

TheprojectisfundedbyProvinciaAutonomadiTrento,Italy

THE ENVIROCHANGE PROJECT

Authorofthisessayis:MicheleGusberti(michele.gusberti@usys.ethz.ch)

SwissFederalInstituteofTechnologyZurich,Instituteofplantsciences,Switzerland

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA. All the images are property of Fondazione Edmund Mach, or from open sources. In any other case, pictures are courtesy of the authors and they are quoted in the caption. Editing by Federica Manzoli: federica.manzoli@gmail.com.

The EnviroChange project focuses on global changeand sustainablemanagement of agriculture in highlydevelopedmountainenvironment.Itaimsatassessingtheshort‐termbiological,environmentalandeconomicimpactofclimaticchangeonagricultureattheleveloftheTrentinoregionparticularlyonquality

and pest management that are more likely to beinfluencedby climate change in the short term. Thefinalaimistopreserveandimprovethequalityoflifeofhabitants,protectingenvironmentandbiodiversityfor the future generations, as well as to represent amodelforsustainabledevelopmentofmountainareas.

PublishedbyFondazioneEdmundMachSeptember2012