COMMON nitrogen and thus helps in sustainable agriculture.

GENERATIONCommon Bean: a crop that can secure
food for allThe common bean (Phaseolus vulgaris L.) is a legume
belonging to family-Leguminosae. It is the grain legume of greatest volume for
direct human consumption in the world and is an important staple crop for small,
poor, urban farmers with about 8.5 million metric tons produced annually in the
developing world (Broughton et al. 2003). Nutritionally, it is a good source of
quality protein, fibre, carbohydrate, mineral and vitamin contents. It has an
advantage of having antioxidants and very small amounts of fats (Zargar et al.
2017). Its nutritional composition acts as a boon to treat various fatal
diseases like, deficiency diseases (due to mineral), cardiovascular, blood
sugar, obesity, colon cancer and many more (I. Hayat et al., 2014). Besides
having the health and economic benefits, it has the agronomic benefit, as they
have the ability to fix atmospheric nitrogen and thus helps in sustainable
agriculture. Climate change and increasing population are the factors which
have affected almost every sphere of life and so the bean production. However,
such problems can be dealt by integrating the biotechnological and conventional
breeding approaches, so that we can prevent our crops from various
environmental insults and could improve agricultural production as well. Considering
the beneficial properties as well as the constraints the common bean is
possessing, we can work on improvement of beneficial properties and mitigation
of the constraints which can make common bean a crop, competent enough to
secure the food requirements for ever growing population.Possible consequences
of climate change on common bean:Climate change is predicted as a serious threat to food and
water securities of billions of people especially in developing countries. If
concerted global action will not be taken to adapt to the   predicted adverse effects related to climate
change, it can ultimately put human life at high risk. It is anticipated that by the of 21st century,
there will be a global temperature increase of 1.4-5.8?C and Sea Level Rise (SLR) of
1.8-5.9mm/yr. It can lead to considerable reduction in agricultural yield and
fresh water resources. Water scarcity, soil degradation, salinity intrusion, vegetation
competition and loss of cropland worldwide will have considerable influence on
food security. (Su Yean Teh and Hock Lye Koh, 2016).  According to the analysis done by Stephen
Beebe et al., 2011, there will be changes in rainfall and temperature and their
predicted effects on potential distribution of bean production. Water: drought and
waterloggingFor maximum production of a 60–120 day bean crop, water
requirements vary from 300 to 500 mm depending on its environment and nutrition
(White et al. 1995; Allen et al. 1998) Adaptation to drought stress includes, morphological,
physiological, and biochemical mechanisms, including a deeper root system,
stomatal control, and improved photosynthate remobilization under stress (Beebe
et al. 2008; Rao et al. 2007, 2009). Research on stomatal conductance and
canopy temperature depression  have confirm
that deep rooting genotypes can  access
more water, but partitioning to roots can be at the expense of grain production
(CIAT 2007, 2008; Beebe et al. 2010). So, the need of the hour is  to breed for roots that use the same biomass
more efficiently, for example, through longer root hairs, greater specific root
length, or greater organic acid exudation (Nord and Lynch 2009; Beebe et al.
2009; Rangel et al. 2009), while maintaining or
increasing partitioning to grain.  According to Nord and Lynch 2009, Genotypes
with more root whorls and basal roots can access more soil moisture in the
upper soil profile and can  be better
adapted to intermittent drought. Currently, a major research challenge is to develop
an  appropriate root system that can fit
to  each production system and can adapt
to changing climate.    Some other regions
could receive greater precipitation. Excess rainfall, waterlogging, and
associated root rots may lead to lack of oxygen to roots  that can inhibits both symbiotic N2
fixation and N uptake, reducing root growth and nodulation.  Different adaptive responses have been
reported in tolerant genotypes (Colmer and Voesenek 2009).  Tolerance may be associated with more
adventitious roots and/or aerenchyma in roots, nodules, and base of the stem.
And waterlogging requires rapid, reliable and robust screening methods.High temperature:High temperatures could limit productivity and could soon
become more worse, aggravating drought in several areas. Rising temperatures
will affect various factors like,  the
altitudinal range of genotypic adaptation, reduce root growth and accelerate
mineralization of soil organic matter, generating a more acute drought stress. Beans
are grown over a wide range of latitudes with mean air temperature of 14–35?C.
Rainey and Griffiths 2003; Porch 2007, have investigated that day temperatures
>30?C or night temperatures >20?C could result in reduced yield. High
night temperatures at early flowering (and to a lesser degree, high day
temperatures) cause flower bud, flower and pod abortion, reduced pollen
viability, impaired pollen-tube formation in the styles, and reduced seed size
(Gross and Kigel 1994; Porch and Jahn 2001; Hall 2004). To  add on, beans also suffer from vegetative
stress and slower metabolism at high temperatures (Rainey and Griffiths 2003).
Beans  may  also loose 
biomass,  If respiration rate
surpasses that of photosynthesis(Maestri et al. 2002).Soil constraintsCoupled with drought and high temperature, low P supply
and/or aluminum (Al) toxicity could prove more severe. Low soil fertility is a major constraint to bean production
in tropics. An estimated 50% of bean production suffers from low-P
availability, while 40% may suffer from Al toxicity. Significant progress has
been made in improving adaptation of beans to low fertility soils (Beebe et al.
2008, 2009). In tropics, rooting zone has high air temperature plus high soil
temperature and thus leads to poor root formation. Temperatures of air, rooting zone, and subsoil may influence
days to flowering, seed germination, and tap or lateral root formation (White
and Montes-R. 1993). N2 fixation and root nodulation  is also inhibited  by high temperature(Graham and Ranalli 1997).
As beans are also susceptible  to soil
compaction,  it is required to develop
an  improved genotype with vigorous root
systems that can penetrate compacted soil layers to access moisture.  Viral diseases Climate change will likely alter distribution and local
severity of pathogens and diseases. Some diseases may decrease while others may
increase due to changes in precipitation and temperature (Garret et al. 2009). Even
some unknown pathogens may emerge,  especially
viruses if insect vector populations change significantly, as observed in the
appearance of new recombinant geminiviruses (Blair and Morales, 2008).Fungal diseases Most pathogenic fungi affecting beans require high humidity
for infection and establishment. Increases in precipitation are predicted for
the 2020s in many African countries that are important bean producers . Under
this scenario, common bean could be be more affected by angular leaf spot (caused
by Phaeoisariopsis griseola)and 
anthracnose (caused by Colletotrichum lindemuthianum). Root rot diseases
(Pythium and Fusarium spp.) are already severe in various areas where common
bean is grown and the conditions could become even more favorable to these
diseases. Regions affected by drought will be less prone to attack from fungal
pathogens, These pathogens can be destructive under conditions of high
temperature and drought (Abawi and Pastor-Corrales 1990). But for new
geographical zones that could become suitable for bean production, it is more
challenging to predict the pattern of diseases zones, as a result of climate
change.Insect pestsWhiteflies rank among the most serious insect pests of
beans. Bemisia tabaci (Gennadius) and Trialeurodes  vaporariorum (Westwood) are the pests  of roughly 250 plant species and acts as  vectors of some economically important
viruses (Anderson and Morales 2005; Morales et al. 2006). B. tabaci has been
limited in Latin America to areas below 1000 masl with mean temperatures of
25–28?C (Morales et al. 2006), while T. vaporariorum thrives at elevations
between 1000 and 3000 masl and with mean temperatures of 16–22?C. These
respective temperature ranges presumably bound the optimum temperature for each
whitefly species (Gerling 1990; Cardona 2005).Precipitation also influences heavily the abundance of
whiteflies, although it seems not to affect their distribution. Both B. tabaci
and T. vaporariorum occur in tropical areas with a mean annual precipitation of
600–1700 mm per year. An ongoing monitoring program at the CIAT campus for the
past 30 years revealed that white- fly densities during the dry season are
roughly three times those of the rainy season (CIAT, unpublished data). Novel
and more effective solutions to white- fly problems may be needed. No common
bean resistant to whiteflies is known to date. Efforts to identify germplasm
resistant to B. tabaci, T. vaporariorum, and the viruses they vector are
warranted and should broadly consider the Phaseolus genus and also the tools of
molecular biology (Blair and Morales 2008).Need for the
development of tolerance to abiotic stress in common bean Current climate-crop models predict that heat and drought
will cause widespread losses in yields of common beans which prioritise the
work towards increasing heat tolerance and drought resistance in common bean. It
is being predicted that drought resistance into bean could improve suitability
of some 3.9 million hectares of current bean area and would add another 6.7
million hectares currently not suitable. Heat tolerance could benefit 7.2
million hectares (some of which could also benefit by drought tolerance), and
could increase highly suitable areas by some 54% (Stephen Beebe et al., 2011).A therapy to climate
change The recent release of the Andean and Mesoamerican common
bean genomes is enabling a new wave to understand the evolution of the common
bean, synteny with other legumes and is a repository of genetic information for
molecular breeders. Not only this, it has the potential to throw light on
various gene functions and to enable the analysis of pathways and networks in
response to ?uctuating environmental conditions.

Keeping in view the environmental insults the common bean may have to
face because of the climate shifts, we need to device such strategy/strategies which
can act as a therapy to such stressful environmental conditions. And in field
conditions our crop may not experience a single stress but has to face multiple
stresses. So, an action plan needs to be concocted through which our crop can
encounter maximum stressful conditions. We have proposed one such strategy, as
given in fig 1.          Fig 1: A therapy to
climate changeIn this strategy we have proposed that, by introducing some
resistant genes to abiotic and biotic stress which are most predicted to ensue
because of changing climate/ climate shifts in common bean and keep such genes under
the control of inducible promoters, so that when the climatic shifts may occur
only then our crop will shift to protective mode. But whenever we talk about
the transgenics, the things which immediately strike our mind are concerns
expressed by consumer and environmental groups on the use of antibiotic- and
herbicide-resistance genes from an ecological and food safety perspective. So, keeping
all those issues in view we have proposed a clean gene technology, for removing
or eliminating selection marker genes in transgenic plants. There are various
such technologies like,I. Excision of selectable marker
gene  a. Intra-genomic
relocation of transgenes via transposable elements,b. Site-
specific recombination systems (microbial recombinases)-(1) Cre/loxP
system from bacteriophage P1, where the Cre enzyme recognizes its specific
target lox P sites (2) FLP/ FRT
recombination system from Saccharomyces cerevisiae , where the FLP recombinase
acts on the FRT sites and (3) R/ RS
recombination system from Zygosaccharomyces rouxii , where R and RS are the
recombinase and recombination site. II. Intra-chromosomal
recombination system (ICR)III. Targeted gene replacementIV) Co-cultivation with multiple
T-DNAV. CRISPER-Cas technologyVI. Transformation without
selection marker geneAmong these CRISPR-Cas system is
the most efficient and reproducible technology at present. In this technology, sgRNA
(single guide RNA) can identify the target gene, and then the two domains of
Cas cleave the target sequence and then DSB (double-strand break) can be
repaired either through NHEJ or through HDR. NHEJ (non-homologous end-joining)
is imprecise and always results in a gene knockout mutation.  While in HDR (homology-directed repair) a
template is present, and it can results in gene replacement or knock-in. 


Fig 2: Sketch of CRISPR/Cas9 system showing the sgRNA (black
and red) that can identify the target gene, and then the two domains of Cas9
(pink) cleave the target sequence and then  DSB can be repaired through  NHEJ  which results in a gene knockout mutation.Tools for CRIPER-CAS9 system The design of sgRNA is one of the important steps in editing
of target gene using CRISPR/Cas. There are some online tools like, CRISPR
Design, E-CRISPR, CRISPR-P, Cas-OFFinder, Cas-Designer , Cas-OT, SSFinder which
make the design of sg-RNA easier. The construction of expression vector can be
done either by constructing binary vectors by combining  Cas9 
with sg-RNA that can result in marker 
gene elimination or construction of sg-RNA and Cas9 vectors,
respectively, that can eliminate the marker genes with sequential
transformation. Delivery of the vector can be done by various methods like
Agrobacterium, Particle bombardment, PEG-mediated transfection of protoplasts.
Finally we can identify the plants without marker genes through RT-PCR or other
such techniques.  (fig.3).


Fig 3: Editing of
target gene by CRISPRCas9 Conclusion:Keeping an eye on the trends of population and climate
shifts, we rather need to work on integrated strategies/approaches to give a
strong fight back to aforesaid burning issues. We also need to improve our understanding
regarding future target environments, so that we could prioritise our goals
regarding the genetic improvement of our crop. Moreover, we need to predict
that with change in temperature and rainfall patterns what could be the
possible response of pest and pathogens to such changes. Not only this, we need
to address the interaction between the changing climate and various
soil-related factors.  Infact, integrated
pest, soil, water, and nutrient management require a coordinated action.
Therefore, optimal management of biotic and abiotic constraints is a
multidimensional problem that requires genetic approaches as well as farming
approaches. Otherwise, the interactions that are implicit in these factors may
overshadow the genetic gains of our crop.                           References :Broughton WJ, Hernandez G, Blair M, Beebe S, Gepts P,
Vanderleyden J (2003) Beans (Phaseolus spp.)—model food legumes. Plant Soil
252:55–128Zargar, S.M. et al., Common bean proteomics: Present status
and future strategies, J Prot (2017I.Hayat, A. Ahmad, T. Masud, A. Ahmed, S. Bashir,
Nutritional and health perspectivesofbeans(Phaseolus vulgarisL.):anoverview,
CRC Crit. Rev.FoodSci.Nutr.54 (2014) 580–592.Su Yean The and Hock Lye Koh.(2016). CLIMATE CHANGE AND SOIL
Journal of Agriculture, Forestry and Plantation, Vol. 2Allen RG, Pereira LS, Raes D et al. (1998). Crop
evapotranspiration—guidelines for computing crop water requirements. FAO
Irrigation and drainage paper 56. FAO, Rome, Italy. White JW, Hoogenboom G, Jones JW et al. (1995) Evaluation of
the dry bean model Beangro V1.01 for crop production research in a tropical
environment. Experimental Agriculture 31: 241–254Beebe  S, Ramirez J, Jarvis A, Rao IM , Mosquera G ,  Bueno JM, and Blair MW.(2011). Genetic
Improvement of Common Beans and the Challenges of Climate Change. Crop Adaptation to Climate Change.
19:35. 362-369.Beebe SE,
Rao IM, Cajiao C et al. (2008) Selection for drought resistance in common bean
also improves yield in phosphorus limited and favorable environments. Crop
Science 48: 582–592.Rao IM,
Beebe S, Ricaurte J et al. (2007) Phenotypic evaluation of drought resistance
in advanced lines of common bean (Phaseolus vulgaris L.). Paper presented at
ASA-CSSA-SSSA International Annual Meeting, New Orleans, LA, November 4–8,
2007.Rao IM,
Beebe SE, Polan´?a J et al. (2009) Physiological basis of improved drought
resistance in common bean: the contribution of photosynthate mobilization to
grain. Paper presented at Interdrought III: The Third International Conference
on Integrated Approaches to Improve Crop Production Under DroughtProne
Environments, Shanghai, China, October 11–16, 2009.CIAT
(2007) Annual report 2007. Outcome line SBA-1. Improved beans for the
developing world, pp. 5–30.CIAT
(2008) Annual report 2008. Outcome line SBA-1. Improved beans for the
developing world. p. 46; p. 63. RepBeebe
SE, Rao IM, Blair MW et al. (2010) Phenotyping common beans for adaptation to
drought. In: JM, Ribaut and P Monneveux (eds) Drought Phenotyping in Crops:
From theory to Practice. Generation Challenge Program Special Issue on
Phenotyping, pp. 311–334.Nord EA,
Lynch JP (2009) Plant phenology: A critical controller of soil resource acquisition.
Journal of Experimental Botany 60(7): 1927–1937.Beebe S,
Rao I, Blair M et al. (2009) Breeding for abiotic stress tolerance in common bean:
Present and future challenges. Proceedings of the 14th Australian Plant
Breeding & 11th SABRAO Conference,  August
10–14, 2009, Brisbane, Australia.Colmer
TD, Voesenek LACJ (2009) Flooding tolerance: Suites of plant traits invariable environments.
Functional Plant Biology 36: 665–681.Rainey
K, Grif?ths P (2003). Evaluation of common bean yield components under heat stress.
Hort Science 38:682.

Porch T G,
Bernsten R, Rosas J C etal. (2007). Climate change and the potential economic
bene?ts of heat tolerant bean varieties for farmers in Atl´antida, Honduras.
Journal of Agriculture of the University of Puerto Rico 91:133–148.