As everybody knows, the climate is changing and over the

next decade will be putting an increasing strain on agriculture

production. This paper aims at putting some focus on what

can really be addressed (the change in temperature) from what

really cannot be predicted and dealt with (rainfall). But even

the effect of one factor like temperature triggers a complex

myriad of effects and the paper structures what needs to be

done in relation to temperature, and focuses on recently discovered

mechanism to adapt to a change in temperature. The

paper then briefly reviews its biological basis, the mean to

phenotype for it at a high rate and precision, and how the use

of crop simulation can help us predict the effect of this trait on

yield..

Kholova, J

Vadez, V

ICRISAT Open Access Repository

4th International Agronomy Congress, 2016 55Lead Papers Vol. 4 : 4th International Agronomy Congress, Nov. 22–26, 2016, New Delhi, IndiaAs everybody knows, the climate is changing and over thenext decade will be putting an increasing strain on agricultureproduction. This paper aims at putting some focus on whatcan really be addressed (the change in temperature) from whatreally cannot be predicted and dealt with (rainfall). But eventhe effect of one factor like temperature triggers a complexmyriad of effects and the paper structures what needs to bedone in relation to temperature, and focuses on recently dis-covered mechanism to adapt to a change in temperature. Thepaper then briefly reviews its biological basis, the mean tophenotype for it at a high rate and precision, and how the useof crop simulation can help us predict the effect of this trait onyield.Future climate or how to deal with higher temperatureGeneral circulation models (GCM) for climate consensu-ally predict an increase in the temperature globally, only di-verging on the extent of that increase, i.e. 2 to 4 ºC. By con-trast, none of the 20 or so models agree with regards to rain-fall and whether these would increase or decrease, where andhow much. Therefore, an increase in temperature is the onlyexpected change. Before we get on analysing the kind of ef-fects temperature can have on crop productivity, two thingsneed to be kept in mind: (i) there will also be an increase inCO2 concentration, which is currently on-going. With a cur-rent yearly increase over 2 ppm, a concentration around 700ppm is expected toward the end of the century. High CO2leads to stomata closure and expectedly would increase wateruse efficiency and possibly yields under water limited situa-tion, which would in part alleviate some of the negative effectsof increased temperature; (ii) the changes in temperature areforeseen over a time scale of five to ten decades, whereas thetime frame in breeding is in the order of one decade. In otherwords, one thing at a time: we first need to develop the culti-vars of the next decade, because there is already enough tem-perature-related climate vagaries ‘today’ that need to be dealtwith, using the same entry points described in the next para-graph. Then as climate changes the environmental context ofthe breeding program will change and impose a new selectionenvironment in which breeding lines are tested that will likelyUnderstanding crop physiological processes for climate resilienceVINCENT VADEZ AND JANA KHOLOVACrop Physiology Laboratory, Theme Simulation Analysis for Climate Smart Agriculture, ICRISAT, Patancheru 502324,Greater Hyderabad, Telangana, Indiaalter the outcome of breeding selection. Breeders will thenneed to have their attention focused on what effects tempera-ture is expected to have and what traits are expected to be“promising responses” to these changing conditions.In relation to temperature stress, yield reductions arecaused by three different reasons: (i) higher temperature af-fects dramatically the reproductive biology and leads to a re-duced seed set. This area of research currently receives mostof the attention, for instance in rice, wheat, or chickpeas thatare known to be indeed sensitive to higher temperature at thetime of anthesis; (ii) higher temperature mechanically hastensthe phenological development and leads to a shortening of thecrop duration with expected negative effects on crop yield. Asimple solution to this is about breeding cultivars with an ex-tended crop cycle; (iii) higher temperature will also increasethe evaporative demand and have an effect on the plant waterbalance. In other words, while we often look at drought asbeing a scarcity of water in the soil profile, the effect of wa-ter scarcity in the atmosphere is often overlooked. An increasein the evaporative demand could be seen as a kind of “atmo-spheric drought”. In this paper, we will expand on that topic,which has so far received little attention and on which majorbreakthroughs have been recently achieved in relation to howcrop respond to this constraint, the range of genetic variations,how to phenotype for it and how to harness genomic regionsinvolved in this trait.Trait dissectionIn the last few years, strong evidences have been acquiredthat small amounts of water during the reproductive and grainfilling period are critical for enhancing grain yield under waterlimited conditions across dryland legume and cereal cropsspecies. Water availability during grain filling is a conse-quence of a number of plant traits altering the plant waterbudget, and operating mostly in the absence of soil waterstress. Our current thrust is to crack the plant water budgetinto simpler “building blocks”, more amenable to geneticanalysis and breeding use. One such trait is the capacity of thecrop canopy of certain genotypes to restrict transpiration un-der high vapour pressure deficit (VPD). This trait is highly56 4th International Agronomy Congress, 2016relevant for drought and climate change adaptation. Geno-typic variation for this trait has been identified in soybean(Fletcher et al., 2007), pearl millet (Kholova et al., 2010)chickpea (Zaman-Allah et al., 2011a), sorghum (Gholipoor etal., 2010; Kholova et al., 2014), maize (Yang et al., 2012),groundnut (Devi et al., 2010). It has also been related to in-creases in grain yield under terminal stress conditions inchickpea (Zaman-Allah et al., 2011b) or pearl millet (Vadezet al., 2013a). A recent paper reviews the different traits thatcondition plant water use and in particular the transpirationresponse to increases in VPD (Vadez et al., 2013b). Figure 1below illustrates the different types of transpiration responsesto increases in VPD which were found in differentgermplasms of different species over the last several years.Another paper then explains how this trait leads to increasesin water use efficiency (Vadez et al., 2014), basically by low-ering the average daytime VPD at the leaf level, which me-chanically increases TE according to the theory.High throughput phenotypingFor many crops, the genomics revolution has given hopethat breeding would become easier and more efficient.Phenotyping is now a main bottleneck, especially for complexabiotic constraints, but phenotyping alone is not enough: Rel-evant phenotyping is needed and implies a thorough under-standing of the biological mechanisms, and their interactionwith the environment, conferring plant adaptation to abioticconstraints, and the “translation” of this knowledge into largescale and high throughput measurements. For assessing thetranspiration response to increases in VPD at a scale thatcould be applicable to a breeding program, two essential el-ements were needed: (i) the capacity to assess the leaf areafast, precisely, and dynamically; (ii) the capacity to assessplant transpiration seamlessly and independently of time-con-suming and labour intensive weighings. Toward that end, alarge phenotyping platform, LeasyScan (Vadez et al., 2015)has recently been developed. The imaging platform is basedon a novel 3D scanning technique, a scanner-to-plant conceptto increase imaging throughput, and analytical scales to com-bine gravimetric transpiration measurements. The scanningconsists in the projection of a laser line at a 940 nm wave-length on top of the crop canopy and in the picturing of its fullreflection by the canopy. The assembly of about 80 pictures s-1 allows to generate a 3D point cloud from which several plantparameters are computed, including the plant leaf area. Ana-lytical scales are also synchronised in the system and poll theweight of pots every few seconds and integrate the valuesover an hour, then providing a continuous assessment of thepot weights from which transpiration can be computed. Fig-ure 2 below represents the load cell setup at the LeasyScanplatform and gives an example of how transpiration is mea-sured over several days under different maximum VPD con-ditions in lines of pearl millet know to contrast in their re-sponse to increased VPD. As can be seen, the transpirationrate of VPD-insensitive H77/833-2 peaks at the highest VPDin each day, whereas the transpiration rate of VPD-sensitiveline PRLT-2/89-33 reaches a plateau is the circa 3 hours ofhighest VPD in each day. As such, this represents the firstexperimental evidence of the theory laid out earlier (Sinclairet al., 2005).Modelling of trait effectThe difficulty of breeding for crop adaptation to waterlimitation is that these limitations are never the same andlargely vary with time and geographical scales. Therefore,testing the effects of a given trait on crop yield across a rangeof environments that would represent the diversity of stresspatterns is virtually impossible experimentally. In that context,crop simulation modelling has become a critical tool to beable to predict the effect of such traits / trait-by-managementcombinations on yield across time and geographical scale, andthen to guide the choice of key breeding and agronomic man-agement targets. In the case of the transpiration to increasedVPD trait, it has shown that enormous yield benefits could beachieved in soybean across most environments in the US, andmore so in dry years (Sinclair et al., 2010). Similar resultshave been obtained for soybean in sub-Saharan Africa(Sinclair et al., 2014). In sorghum, evidence has been ac-quired that the introgression of staygreen QTL elicit a VPD-sensitive phenotype and a modelling analysis has shown alsomajor yield benefit across a large track of rabi sorghum inIndia (Kholova et al., 2010).CONCLUSIONIn this brief paper, we have shown that, besides an increasein CO2, most of the climate change effects that can be pre-dicted would be around an increase in temperature. While theeffects of temperature on reducing yield are several, here weFig. 1. Main types of transpiration (Tr) responses to increasing VPDconditions found in different germplasm of different speciesover the last few years. The differences in area between thedifferent curves potentially represent different water savings(reproduced from Vadez et al., 2013b)4th International Agronomy Congress, 2016 57have focused on the effect of temperature acting from theangle of plant water status via its effect on the vapour pressuredeficit. We have shown that plants vary for their capacity torestrict transpiration under high VPD and that this trait conferswater savings that are important under drought conditions.While this trait is typically a “climate change” trait, it hasimportance ‘today’ itself and is currently used toward breed-ing of cultivars adapted to high VPD conditions in the semi-arid tropics.REFERENCESDevi, J.M., Sinclair, T.R. and Vadez, V. 2010. Genotypic variationin peanut (Arachis hypogaea L.) for transpiration sensitivityto atmospheric vapor pressure deficit. Crop Science 50:191–196. doi:10.2135/cropsci2009. 04.0220.Fletcher, A.L., Sinclair, T.R. and Allen, L.H. Jr. 2007. Transpirationresponses to vapor pressure deficit in well-watered ‘slow-wilting’ and commercial soybean. Environmental and Ex-perimental Botany 61: 145–151. doi: 10.1016/j.envexpbot.2007.05.004.Gholipoor, M., Prasad, P.V.V., Mutava, R.N. and Sinclair, T.R. 2010.Genetic variability of transpiration response to vapor pres-sure deficit among sorghum genotypes. Field Crops Re-search 119: 85–90. doi:10.1016/j. fcr.2010.06.018.Kholová, J., Hash, C.T., Kumar, L.K., Yadav, R.S., Kocová, M. andVadez, V. 2010. Terminal drought tolerant pearl millet(Pennisetum glaucum (L.) R.Br.) have high leaf ABA andlimit transpiration at high vapor pressure deficit. Journal ofExperimental Botany 61: 1431–1440. doi:10.1093/jxb/erq013.Kholová, J., Tharanya, M., Kaliamoorthy, S., Malayee, S., Baddam,R., Hammer, G.L., McLean, G., Deshpande, S., Hash, C.T.,Craufurd, P.Q. and Vadez, V. 2014. Modelling the effect ofplant water use traits on yield and stay-green expression insorghum. Functional Plant Biology 41 (10-11): 1019–1034.Sinclair, T.R., Hammer, G.L.and van Oosterom, E.J. 2005. Potentialyield and water-use efficiency benefits in sorghum from lim-ited maximum transpiration rate. Functional Plant Biology32: 945–952.Sinclair, T.R., Marrou, H., Soltani, A., Vadez, V. and Chandolu, K.C.2014. Soybean production potential in Africa. Global FoodSecurity 3: 31-40.Sinclair, T.R., Messina, C.D., Beatty, A. and Samples, M. 2010.Assessment across the United States of the benefits of alteredsoybean drought traits. Agronomy Journal 102: 475–482.Vadez, V., Kholova, J., Hummel, G., Zhokhavets, U., Gupta, S.K.and Hash, C.T. 2015. LeasyScan: a novel concept combin-ing 3D imaging and lysimetry for high-throughputphenotyping of traits controlling plant water budget. Jour-nal of Experimental Botany 66(18):5581-5593. doi:10.1093/jxb/erv251.Vadez, V., Kholova, J., Medina, S., Aparna, K. and Anderberg, H.2014. Transpiration efficiency: New insights into an oldstory. Journal of Experimental Botany 65: 6141-6153.doi:10.1093/jxb/eru040.Fig. 2. Pictures of the load cell setup at the LeasyScan platform (left) and of the scanner supporting device (top right). The graph representsthe transpiration evolution over several days in two pearl millet lines that were identified earlier as VPD-insensitive or VPD-sensitive(from Kholova et al., 2010). The manifestation of this phenotype in the platform is in the plateauing of the transpiration rate in themiddle part of the day in the VPD-sensitive line (closed symbols). (Reproduced from Vadez et al., 2015)58 4th International Agronomy Congress, 2016Vadez, V., Kholova, J., Yadav, R.S. and Hash, C.T. 2013a. Smalltemporal differences in water uptake among varieties of pearlmillet (Pennisetum glaucum (L.) R. Br.) are critical for grainyield under terminal drought. Plant and Soil 371 (1): 447-462. doi 10.1007/s11104-013-1706-0.Vadez, V., Kholova, J., Zaman-Allah, M. and Belko, N. 2013b.Water: the most important ‘molecular’ component of waterstress tolerance research. Functional Plant Biology 40:1310-1322. http://dx.doi.org/10.1071/FP13149.Yang, Z.J., Sinclair, T.R., Zhu, M., Messina, C.D., Cooper, M. andHammer, G.L. 2012. Temperature effect on transpiration re-sponse of maize plants to vapour pressure deficit. Environ-mental and Experimental Botany 78: 157–162.Zaman-Allah, M., Jenkinson, D. and Vadez, V. 2011a. Chickpeagenotypes contrasting for seed yield under terminal droughtstress in the field differ for traits related to the control ofwater use. Functional Plant Biology 38, 270–281.doi:10.1071/FP10244Zaman-Allah, M., Jenkinson, D. and Vadez, V. 2011b. A conserva-tive pattern of water use, rather than deep or profuse rooting,is critical for the terminal drought tolerance of chickpea.Journal of Experimental Botany 62:  4239–4252.doi:10.1093/jxb/err139.

Understanding crop physiological processes for climate resilience

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Understanding crop physiological processes for climate resilience

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