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*Corresponding author’s e-mail: kumar@rbccps.iisc.ernet.in.1Robert Bosch Centre for Cyber Physical Systems, Indian Institute of Science, Bengaluru 560 012, India.2National Institute of Advanced Studies, Indian Institute of Science, Bengaluru 560 012, India.

Agricultural Reviews, 37 (4) 2016 : 268-278Print ISSN:0253-1496 / Online ISSN:0976-0539

Critical abiotic factors affecting implementation of technologicalinnovations in rice and wheat production: A reviewS. Kumaraswamy*1 and P.K. Shetty2

Robert Bosch Centre for Cyber Physical Systems,Indian Institute of Science, Bengaluru-560 012, India.Received: 11-01-2016 Accepted: 17-09-2016 DOI: 10.18805/ag.v37i4.6457

ABSTRACTRice and wheat are two major staple food crops in India and worldwide. Over the years the yield potential of the crops hasbeen affected by abiotic factors, which is further projected to increase due to climate change induced environmentaladversities. Typically these two crops have different growing conditions, rice requiring high water for cultivation unlikewheat which is water demanding and sensitive to larger variability in temperature regimes. In the recent past drought anddisease stress, besides several other stresses, are considered to be critical factors affecting the growth and yield of crops,which is evident in the recent decades. Admittedly, drought stress coupled with biotic stress will further contribute fordeclining performance of crop varieties and difficult to alleviate even with innovative technological innovations. Few ofthe technological innovations like high yielding varieties, genetically modified cultivars, integrated nutrient management,integrated pest management, water conservation strategies and prophylactic measures to avoid the disease/pest outbreak,though with potential to augment the yield losses is affected by the stresses. Attempts have also been made to utilizetransgenic technologies to build intrinsic tolerance mechanisms by the plants through alteration to functional genes. However,sustainable technologies like classical breeding approaches and integrated farming principles are also being considered todevelop crops adaptation and/or enhance the adaptive mechanisms by aligning with technological interventions. Though,several technologies show promise but constrained by the limitations to achieve ‘one-fits-all’ model to overcome theinteractive effects of abiotic stressors. Visibly, the crop growth and yield enhancement through technological innovationsis call of the day as climate change induced aggravation of these stressors on crop production is imminent. Skilful integrationof technological innovations to suit the local and regional scale crop husbandry systems may have promise to address theabiotic stress to realize economic yield of crops like rice and wheat. The review will argumentatively analyse few criticalstressors that limit the successful implementation of technological innovations to sustain the rice/wheat crop productionand resilience building in the millennia.

Key words: Abiotic stressors, Bi-directional Model, Crop production, Climate change, Growth and yield, Rice-Wheatproductes, Technological innovations.

The challenge of sustaining the crop productivityin the changing growth conditions and environmental impactis increasingly felt in the recent decade. Several of the factors/stressors have been implicated to drastically affect the goalof achieving potential yield of crop. The explodingpopulation with eventual demand for food, dwindling naturalresources, climate change adversities have been consideredto be major constraints affecting the growth in agriculturesector­­ (Morton, 2007; Piao et al., 2010). In view ofalleviating these constraints there has been paradigm shiftin approaches to enhance the crop production throughfocused crop improvement programs and technologicalinnovations.

It is evident now that agriculture sector in India isconsidered to be most vulnerable to climate change.

Intergovernmental Panel on climate change (IPCC) projectedrise of temperature by 3-4 degrees by 2050 over current levels(IPCC, 2002; Meehl et al., 2007). The impending climatechange adversities are known to alter the abiotic stresseslike variable temperature regimes and their associatedimpacts on water availability leading to drought, increaseddiseases and pest’s incidence and extreme weather events atlocal to regional scale. Besides variable temperature regimesmay result in unpredictable disease epidemic across thegeographic regions (Gregory et al., 2009). Crop improvementprograms (Richards, 2006; Richards et al., 2007) areincreasingly directed on rice and wheat as the production ofthese food grains predicted to be affected leading toimbalance in attributes contributing to yield. Given thecomplexity of stress factors, most challenging is to crop

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adaptation without the loss of water and nutrient useefficiency under extreme climatic events.

Rice and wheat are major food grain crops in Indiaoccupy large cultivated area amongst the agricultural crops.However, the productivity of rice and wheat has assumeddeclining trend and area of cultivation not shown anyexpansion (Hobbs and Morris, 1996). Moreover, Indianpopulation is predicted to reach 1.68 billion by 2030 fromthe present level of 1.21 billion (Anonymous, 2009). It callsfor intensive crop production practices, which is alreadyaffected by abiotic stressors of variable intensity. Thesestressors are known to cause 30-60% yield losses annually(Dhlamini et al., 2005). However, utilization of promisingtechnologies may pave way for overcoming the effects ofvarious stressors on crop production.

Highly heterogeneous and unpredictableenvironment pose paramount problems in addition to geneticvariability challenges to improve the crop adpatation bytechnological innovations. Nonetheless, new tools arebecoming more refined, accessible and extensively used forbuilding adaptive mechanisms to abiotic stresses in rice andwheat. Moreover, a synergistic approach to geneticimprovement in conjunction with innovative cropmanagement practices has been considered to be doublygreen revolution (Conway, 1997; Pingali, 2012) and suitablefor successful implementation of technological innovationsto address crop stress management.

Amongst the several of the crop productivitylimiting stressors drought, variable temperature regimes andsalinity are considered to be most critical abiotic stress(Zhang et al., 2000; Vincour and Altman, 2005). Since greenrevolution, in the quest for ensuring food security, the efforthas been to avert the effects of these human inducedenvironmental factors. In this direction, crop designingthrough conventional and modern biological approach hasassumed phenomenal importance to increase agriculturalproduction. On the contrary, organic farming is relativelyland intensive and regressive in technology usage. Unlikethe modern technologies, organic farming technology ischaracterized by low on chemical inputs (fertilizers/pesticides/herbicides), mixed farming dominated bytraditional varieties/cultivars, complex cropping systems,crop rotation to control pests/diseases and soil healthmaintenance through organic manures (OECD, 2003).Though these sustainable and environmentally friendlytechnologies have promise but the crop yield potential isless. Moreover, there is large gap between potential yieldand realizable yield of the crops, which is again affected bythe abiotic stresses.

Designing crop production technologies that arerobust and consistently produce desirable results for widespread adaptation is also a larger constraint. However, the

technological innovations must consider a bi-directionalrelationship (Figure 1) amongst basic science, translationalresearch with consequent technology development assituational event prediction to suite the future growthenvironments. A focused research and development modelwith public-private partnership are the source of novelagricultural technologies. Conceptually, it is realistic modelof the relationship between research and technologicalinnovations. However, magnitude of scientific output andusefulness of the agricultural technologies developed areunder continuous debate as many factors drive theiradaptability under climate change scenarios (Chhetri et al.,1996). Further, retrospective analysis of criterion used intargeted technological innovations to address the climaticconstraints at multiple scales in specific locations mayprovide better insights (Esterling, 1996; Parez-Aleman,,2011). A wide range of technological innovations inagriculture like genetic improvement (varieties), fertilizertechnology, adaptive microbial technology, pesticides, farmmachinery, agronomic and management practices (integratedmanagement of nutrients and pests) have been achievedthrough focused research programs to understand theirimplications in enhancing the crop productivity. Unlike inthe past, new discoveries and realization of potentials ofinnovation is difficult but possible to achieve throughadvances in basic and pre-inventions sciences (Evenson andGollin, 2003; Huffman and Evenson, 2006), which supportthe evolution of other crop technologies.

Significant advances made in the modern biologyinvolving molecular genetics technology have allowedunderstanding the stress resistance mechanisms of plants.For instance, improved tolerance to drought and temperatureregimes has been observed in transgenic plants that overexpress genes regulating molecular mechanisms of toleranceto stress conditions. Despite the evidence of advantages oftechnological interventions results seem to be not consistent,which is considered to be a limitation to explain theperformance of crops, engineered to survive the hostileenvironments.Critical abiotic factors: Mutually inclusive stressorsDrought: An imminent abiotic stress in the futureagriculture: Drought is the most important constraint torealize the potential yields of crops. Moisture stress accountsfor about 30 to70 per cent loss of productivity of field cropsduring the crop growth period. In India, as in many otherparts of semi-arid regions of the world, 78 per cent of thearea under agriculture is rainfed and is inescapably linkedto the short-fall and erratic rainfall patterns. Out of the totalgross cultivated area of the country, 56 m ha is subjected toinadequate and highly variable rainfall. The NationalCommission on agriculture identified 337 districts of thecountry as drought prone (http://www.nih.ernet.in/rbis/india_information/draught.htm).

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Fig 1: Bi-directional research and development model and mutually inclusive approach to technological innovations (Bush, 1945).

The impending climate change eventualities arelikely to aggravate the drought intensity and occurrence,higher evapotranspiration as a consequence of risingtemperature regimes. Such a situation creates challengingenvironment for crop cultivation and ensure food securityin the 21st century and demand development of droughttolerant crops (Bush, 1945; Cassman, 1999; Borlaug, 2007;Pennisi, 2008). It is imminent to adapt two trajectories: i)development of integrated soil-crop system management toaddress constraints in existing crop varieties; ii) newervarieties with high yield potential under water and nutrientlimited environment and tolerant to disease and pests as well(Swaminathan, 2005; Baulcombe et al., 2009).

The emerging concept has been to tailor the cropswith suitable adaptive mechanism for drought situation andassociate environmental constraints (ex. high temperatureregimes) while optimizing the water use and nutrients withoutsacrificing the economical yield potential. Admittedly, withincreasing demand for water even the irrigated agro-ecosystem might experience moisture stress, which calls foradapting innovative water conserving technologies (Fan etal., 2011; Ward and Velazquez, 2008). Hence, the emphasismust be to increase the adaptation of crop plants to waterlimited conditions and to develop crop genotypes that wouldproduce more with less irrigation. From this context, one ofthe major global agenda has been to improve waterproductivity of crop plants with an emphasis of achieving‘more crop per drop’. In agriculture, the term drought refersto a situation in which the amount of available water through

rainfall and/or irrigation is insufficient to meet theevapotranspiration needs of the crop.

Plants have evolved diverse adaptive strategies tocope with water-limited environments. These mechanismsrange from cellular level tolerance leading to adaptation inresponse to stress and/or specific growth behaviours andmorphological characteristics (inherent traits) that avoidstress effects. These diverse plant physiological mechanismshave their relevance in enhancing stress adaptation. However,from the agronomic, perspective, mechanisms that cansustain growth under water limited environment need greateremphasis. Furthermore, the drought tolerance mechanismsand their relevance at specific target environment dependon intensity, magnitude, and frequency of occurrence.Therefore, the key to progress towards breeding for droughttolerant crops requires understanding the stress responsesof crop plants to identify the relevant drought adaptivemechanisms and/or traits (Kulkarni 2011; Blum, 1988;Federoff et al., 2010). Hence, the major focus has been todevice strategies for achieving the formidable challenge ofcrop designing to suite variable moisture limited situation.However, random and at times lasting drought spells maypose increasing threat to varieties, which are unlikely to haveadvantages. Variable intensity of drought occurring at plantgrowth stages like vegetation growth, flowering/pollinationand ear filling stages require different definition on toleranceto drought. It implies that achieving drought tolerance at allplant growth stages is impossible proposition (Evenson andGollin, 2003; Tester and Langridge, 2010). Designing crops

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to escape the drought stress at various growth stages needsdifferent modifications, which is difficult to achieve and thetolerant crop response would be unpredictable.Temperature regimesClimate change adversities: The impending climate changeis predicted to alter the cropping profiles of the agriculturallandscapes, which is attributed to poor adaptation of varietiesto high temperature regimes, increased drought due to unevenand/or insufficient rainfall, outbreak of newer diseases andpests. Crop improvement to develop adaptive varieties anddesign allied technologies to realize optimal yield isherculean task due to high levels of uncertainty in weatherevents and variability across the geographic locations. Itpredicted that the productivity of rice/wheat will increase infew locations but largely assume declining trends due totemperature effects on increased evapotranspiration ofmoisture with consequent susceptibility of crops to diseaseand pest incidence. Few lines of evidence suggest that hightemperature regimes due to climate change affect thephenology, reproductive biology, flowering times, pollenviability and pollinator populations (Antle and McGuckin,1993; Evenson and Gollin, 2003; Lake and Huges, 1999;Johnson and Lincoln, 2000) which, will adversely affect thecrop productivity. Wheat being self-pollinated may beaffected most under such situations. Hence, any technologicalinnovations have limitation to tailor the crops to withstandsuch morphological changes. However, natural evolutionaryprocess has yielded few wild relatives/land races that showadaptive mechanisms, which can be exploited for developingnewer varieties (Springer and Ward, 2007). This has beenscientific basis in approaching technological interventionseither transgenic technology and/or molecular breeding togenerate ecotypes of crops suitable for such environments.

Rice and wheat cultivation is spread across thegeographical locations with highly variable growthconditions. The high yielding varieties potential and alliedtechnologies used to boost the productivity of the crops maybecome counterproductive or ineffective under suchenvironments. Scientific programs have been directed toachieve the goal of developing genetically improved cropvarieties through introgression of genes/adaptive traits togenetically superior wild type/landrace in a geographiclocation (Ziska et al., 2012). Further technologicalinterventions to improve growth conditions have additiveinfluence on realizing the success of the innovations.Uncertainties related to response of improved crop varietiesand agronomic practices are still under various stages ofresearch to evolve region specific technological innovationsto counter the impact of high temperature regimes andassociated stresses.Salinity: Salinity effect on cultivable land area in Indiaaccounts for 6.73 million ha and under acid soils is 6.03million ha (Heisey et al., 2003). Salinity is considered to

increase in arid environments and highly irrigated basins ofrice growing regions. Besides, naturally salt affected soilsare not suitable for cultivation of currently available highyielding varieties. Moreover, salt tolerant traditional varietiesare low yielding with limited opportunity to exploit theadaptive traits attributable to narrow genetic variabilityamong the genotypes. Empirical evidences suggest thattechnological interventions have resulted in development offew varieties of rice/wheat, which show potential fortolerance mechanisms to salinity (Jones et al., 2008; Trivedi,2010).

Productivity of the salt affected soils is inherentlypoor and not amenable for soil fertility enhancing practiceslike introduction of biological nutrient fixers/mobilizers. Theexisting strains of N-fixers, P-solubilizers and mycorrihzamay not survive the salinity to perform their functions(Sairam and Tyagi, 2004; MacKill et al., 2010). It is pertinentto identify novel adapted strains of microorganisms for thesalt affected soils that may prove to be beneficial to advancethe technological innovations. Introduction of salt tolerantleguminous species is an option but is less feasible practicein rice-wheat system.

Crop improvement through altering the cellualrlevel tolerance mechanisms to exclude the salts and/orselectively uptake the nutrients is considered to be option todevelop salt tolerant rice/wheat varieties. Transgenictechnology has been effectively utilized to introgressfunctional genes that regulate the cellular level tolerance(Govindarajulu et al., 2005; Maillet et al., 2011). However,the criticism is that can these introduced genes be stableover generations to retain the adaptive characteristics ofvarieties. Evidently, salinity tolerance has been examined inmodel transgenic plants under variable growth conditions(Leung and An, 2004). Large number of reports clearly showsthat manipulation of metabolic pathways using geneticengineering is a strategy that improves the performance ofplants against abiotic stress. However, in most cases theimpact of transgene does not confer high levels of tolerance.There is a possibility to increase the tolerance throughsimultaneously expressing transgenes involved in severalmetabolic pathways. Alternatively, transcription factors thatregulate the expression of several defence genes at the sametime (Takeda and Matsuoka, 2008) is promising observation.Expression of several genes may confer higher tolerance notonly at low temperatures, but also to drought and salinity.Accordingly, genomic technologies have a central role inthe discovery of genes that regulate the intricate defencenetworks activated by plants in response to several types ofenvironmental challenges. Understanding complex responsefactor of introduced technological innovations in suchsituations makes it impossible to assess the utility, howevercircumstantial evidences show promise for implementingfocused crop improvement programs.

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Technological innovationsPotentials and limitations: Rice and wheat crops are grownacross the world on various agro-climatic and soil fertilityconditions. The crop improvement program since theselection to conventional breeding until the green revolutionhas contributed immensely for developing crop genotypeswith desired traits. Post green revolution, introduction ofhigh yielding varieties of rice and wheat, which demand highinput management has contributed phenomenally to meetthe food grain demands in last 50 years (Ou, 1985). Thecrop improvement programs to increase productivity alonehave contributed for 1% per annum for wheat and 0.8% forrice as consequence of adopting high yielding varieties(Evenson and Gollin, 2003). Few of the technologicalinnovations that have shown potentials and options toimprove the crop production of rice and wheat in the futureare listed in the Table 1. Nonetheless, these technologieshave contributed greatly for achieving the food security inthe last decades (Sadras, 2002; Pingali, 2001). Consequently,industrial agricultural activities with the high inputmanagement have also adversely affected the naturalresources of agricultural landscapes (Haymi and Herdt,1977). For instance, genetic resources of tolerant traditionalvarieties/cultivars have been phased out due to introductionof high yielding varieties. It has also resulted in degradationof water resources and introduction of high water demandingvarieties has resulted in difficulty to build resilience toincreasingly felt abiotic stress affecting the crop production.The effort to counter the impact through advancedtechnological innovations by genetic manipulation has notbeen able to alleviate the challenges.

Crop adaptation and resilience building byharnessing the technological innovations has multitude ofimplications in sustaining the productivity of rice and wheatwith variable input management. The germplasms resourcesof these crops have provided substantial leads to identifytolerant genotypes for abiotic stresses. However, thebreakthrough in identifying the adaptive traits andintrogression of these traits to genetically superiorbackground has met with mixed outcome. Consequently,scientific understanding of abiotic factors that promote geneflow is of considerable interest and also met with criticism(Johnson and Loncoln, 2000). The scepticism and concernarises from the introduction of genes in domesticated cropsthat gene flow between genetically transformed touncultivated relatives may alter the original genetic makeupwith subsequent impact on the evolutionary fitness (Fugile,2010; Hobbs et al., 2000). Furthermore, abiotic factors maydifferentially affect out crossing and gene flow betweenspecies, which influence the population size, geneticdiversity, meta-population dynamics and trajectory ofevolution (Hobbs et al., 2000). Early inconclusive evidencesuggests gene flow in rice systems from genetically modified

phenotype, which may result in undesirable biotype of thepreferred crop (Ellstrand et al., 1999). The empiricalevidences for out crossing rates and gene transfer is limitedand how demographic variations in stress factors affect suchprocess is not clear yet (Lu and Snow, 2005; Takebayashiand Morrel, 2001). However, adaptive transgenic technologyand molecular breeding strategies are currently consideredas panacea technological innovations for crop improvementprogram. Considerable research progress has been made ongolden rice in International Rice Research, Philippines,which have promise for sustaining the yield (Gealy et al.,2003). Preliminary evidence of transgenic rice varietiestolerant to drought and pest stress is also one such exampleconfirming the utility of technological advancement.However, the field scale performance of these transgenicsintrogressed with adaptive traits and their stability underclimate change eventualities and aggravated impact of abioticstresses is still an unresolved concern. Some of the innovativetechnologies that show promise especially in rice includeaerobic rice technology, which is preferentially suitable forwater limited situations with comparable yield potential(Cleland et al., 2007). It is argued that transgenic technologycould play a significant role in increasing the productivityto offset the impact of growing demand for cereals. It canalso provide option to focus research on developing varietiessuitable for semi-arid environments, dominant with droughtand temperature stress and also salinity to increase theproductivity. The contention is that in the future cropimprovement program without transgenic technology it isdifficult to develop crops with better nutrient acquisition,improved photosynthetic abilities, increased conversion drymatter to grain, improved water mining and tolerance todisease and pests (Eckert et al., 2009; Hossain et al., 2003).Some of the relevant technologies have been identified withtheir scientific relevance and limitations (Table 1).The way forward: Do new discoveries and innovationshold the promise?

Crop plants are unable to dislocate in its ownenvironment therefore they have evolved to solve abioticstress with internal mechanisms of tolerance. Consequently,the gene must evolve to perform and adapt quickly toenvironmental changes. Over the years, crop growth supporttechnologies like fertilizer, adaptive microbial technologiesand several circumstantial cultural practices have beendeveloped and refined to counter the plant stresses at variouslevels. Evidently, several new technologies are in the horizonand evolving each year. So far, major focus in cropimprovement program has been to enhance the yield andalso to bridge the gap of achieving the potential yield incrops. In view of the increasing problems posed by abioticstresses, the technologies development should focus onmitigating the impact of abiotic stress to sustain theproductivity.

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Second generation molecular technologies likerapid DNA sequencing followed by selection on genomictraits, marker assisted breeding including functional markers,doubled haploids, random DNA markers for associated withdesired traits, biostatics analytics coupled with the experienceand methods of classical geneticists will contribute forrealizing the increased crop production under abiotic stresswith special reference to rice-wheat (Ju et al., 2009; Sutton,2009; Raul et al., 2005). These technologies can be appliedfor most of the abiotic stress to elucidate the geneticmechanisms of tolerance and their variability under similarstress conditions to identify superior genotypes to evolve asvarieties. Predictably, better impacts can be visualized asthose observed during the green revolution (Pingali, 2012)paving way for second green revolution through skilfultechnological innovations.

Several lines of evidence support cross-talk betweenabiotic stress responses. It is one the major constraints insuccessful implementation of technological innovations inrice and wheat crop production. However, the modernbiological techniques provide wider options to developgenetically improved crop varieties and allied growth supporttechnologies to counter the abiotic stresses to sustain thegrowth and productivity of crops.Summary and perspectives

The predicted population growth by 2050 requiresincrease of 70% in food production to meet the demand(Leung, 2008). The demand for staple food grains (rice-wheat) will phenomenally increase calling for continuedfocus on shifting the yield frontiers. Meeting such a paradigmrequires focus on improving tolerance to abiotic stresses.However, implementation of technological innovations inthe future crop production systems must critically considerproductivity enhancement in marginal environments throughthe mitigation of abiotic stresses and also to provide toolsfor adaptation to climate change.

Despite several promising technologies for cropimprovement with consequent realizable yield improvement,success in comprehensively address the stresses like droughtand diseases affecting the crop growth and performance hasnot been achieved to the satisfaction. Transgenic adaptationstrategy has paved way for genetic capability enhancementand/or adaptive plant trait pyramiding to address the stressors(Yano and Tuberosa, 2009; Cancado, 2009). However, the

challenge has been to convincingly prove any advertenteffects of transgenics on original genetic resources of otherspecies and any health hazards. Admittedly, policy changesrelevant to crop improvement using modern biological tools/techniques also have been a constraint. The policies changesmust not become structural impediments rather promote andcontribute for sustaining agricultural resources for staple crop(rice-wheat) production. These technological innovationshave provided leap frog progress in understanding plantphysiological response to abiotic stressors in rice and wheat.

Sustainable technologies have also been tested inan innovative approach with un-economical yield of cropsunder intensive abiotic stress. The crop improvementprogram must consider a holistic approach to skilfulutilization of modern biological tools/techniques to developcrops while integrating the sustainable technologies toovercome the limitation offered by abiotic stressor in cropproduction. It paves way for development of resilient cropgenotypes for these stressors with improved adaptivemechanism to climate change adversities. The abioticstressors like drought and diseases limiting the technologicalinterventions to achieve improved crop yields in rice andwheat is need not be a constraint but has not been possibleto achieve high level of tolerance. However, the geneticimprovement of crops for abiotic, through technologicalinterventions, has the promise for sustenance of cropproduction, if not higher productivity, in resource poor andgrowth limiting environments. Admittedly, the challengeposed is how to integrate these productivity enhancingtechnologies in small-holder and marginal environments withprofitability. The impending climate change adversities willexert compounding effect on agricultural systems especiallyrice-wheat in resource poor countries. Thus implementingdoubly green revolution will require sequencing thetechnological innovations with time to overcome thechallenges posed by abiotic factors in crop improvement toachieve sustainable change. The competitive technologiesthat mitigate the impact of abiotic factors are needed torealize the sustainable and economic productivity of crops.ACKNOWLEDGEMENTS

The article is an outcome of several informaldiscussions had with colleagues from various disciplines. Ithank them all for inquisitive debate on various topicsrelevant to agriculture.

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