**3. Biotic factors affecting crop yields**

## **3.1 Diseases and pests**

Plant diseases are caused by different micro-organisms such as viruses, bacteria and fungi. In addition, various soil-borne and above ground insect pests also affect crop production. Variation in climatic conditions often favors the multiplication of pathogens while negatively affecting plant productivity and soil fertility. It causes the reduction of available resources for plants, which fail to produce enough biomass, seeds, and thus yield. Climate-driven migration allows the movement of pathogens and pests from one region to another. Thus, the locally adapted crop genotypes confront new biotic stress factors. The interaction of plants with microbes or microbe-associated molecular patterns can induce resistance to secondary infections by pathogens. This involves the production and systemic signal of a complex of low-molecular-weight plant metabolites, which are well described for dicotyledonous plants, but poorly understood for monocotyledonous plants such as cereal crops [43]. Because of climate variability and change, it is anticipated that new diseases and pests might appear, or that the virulence of the current types may increase.

The changing of the climate is bringing new types of diseases and pests that do not have any control methods yet. For example, maize lethal necrosis (MLN) is one of the most devastating diseases found in maize in Eastern and Central African countries. It is caused by the synergistic interaction between *Sugarcane Mosaic Virus* (SCMV) and *Maize Chlorotic Mottle Virus* (MCMV). It causes yield reduction ranging from 30 to 100% in farmers' fields depending on the time of infestation [44]. MLN is transmitted by beetles, rootworms, thrips, stem borers, several species of aphids in non-persistent manner, infected soil, infected seeds and any tools or materials used in the infected field [45]. Moreover, Russian Wheat Aphid (RWA)

**15**

changing climate.

cantly reduce crop yields.

**5. Strategies to overcome crop yield reduction**

*Factors Affecting Yield of Crops*

production.

*DOI: http://dx.doi.org/10.5772/intechopen.90672*

**4. Technological factors affecting crop yield**

is one of the world's invasive pests of wheat, barley and other cereal grains. It is widespread in cereal growing regions of Africa, Asia, Europe, Middle East, North and South America, recently in Australasia [46]. The visual symptoms of infestation in plants are chlorosis, necrosis, wilting, stunting, leaf streaking with whitish, yellow and purple longitudinal leaf markings, trapped awns, rolled leaves and heads that fail to flower [46]. These pests have high resistance to extreme weathers events. RWA caused yield losses up to 80% in wheat and 100% in barley. The main challenge associated with the RWA is that new biotopes that are tolerant to available insecticides continue to appear. Some of the biotopes also overcome resistance of some crop varieties. Elevated atmospheric carbon dioxide has also been found to alter the efficacy of some biotopes. They are therefore constant threat to crop

A wide range of technological innovations in agriculture like genetic improvement of varieties, fertilizer technology, adaptive microbial technology, pesticides, farm machinery, agronomic and management practices (integrated management of nutrients and pests) have been achieved through research programs to understand their implications in enhancing crop productivity [16]. It has been reported that 1 kg of nutrient fertilizer produces 8 kg of grain [47]. In addition, fertilizers are commonly believed to be very important in crop production since they contribute up to 50% of the crop harvest product [48]. The doubled increase of food production worldwide was partially attributed to a 6.9-fold increase in nitrogen fertiliza-

Different factors have negative influence in agricultural practices. In Bangladesh,

Climate smart agriculture (CSA) is now widely accepted as the best approach for addressing the effects of climate change in agriculture. It is defined as agriculture that sustainably increases productivity, resilience (adaptation), reduces/removes greenhouse gases (mitigation), and enhances the achievement of national food security and development goals. CSA promotes the transformation of agricultural systems and requires the transformation of agricultural policies to increase food production, to enhance food security, to ensure that food is affordable (low inputcost) while ensuring sustainable natural resource management and resilience to a

tion and a 3.5-fold increase in phosphorous fertilization in the 1990s [49].

farmers were given chemical fertilizers and pesticides at a subsidized price and therefore increased fertilizer application to enhance crop yield. In the Philippines, because of the huge amount of lime and urea used by farmers over years, the sugarcane farms developed lime layer in the subsoil, which caused phosphorous deficiency while banana farms have excessive potash, which created an imbalanced ratio of potassium and magnesium. The average yield production of sesame in Jigawa State was reported to be 0.6 t/ha instead of 1.25 t/ha under well-managed farms [50]. In general, the application of inappropriate agronomic practices such as untimely planting, incorrect plant spacing, wrong method of planting, poor sowing depth, delayed weeding, ineffective pest and disease control, inappropriate use of fertilizers, untimely harvesting and use of low yielding varieties, will always signifi-

#### *Factors Affecting Yield of Crops DOI: http://dx.doi.org/10.5772/intechopen.90672*

*Agronomy - Climate Change and Food Security*

**3. Biotic factors affecting crop yields**

*Different levels of excess of water in crop environment [38].*

**3.1 Diseases and pests**

**Figure 2.**

As the duration of flooding increases, there is progressive decrease in soil reductionoxidation potential (redox potential) [38] (**Figure 2**). Flooding events can be classified by two categories: waterlogging where only the root system inside the soil is affected [39]; and submergence, where also parts or the whole shoot are under water [40]. In tree species with different flooding sensitivity, the importance of root-toshoot transport of metabolites to 'use rather than lose' is a relevant criterion used to identify the tolerant species [41]. Only non-wetland plants can survive flooding for a short period of time. The two survival strategies to flooding are plant avoidance of

Plant diseases are caused by different micro-organisms such as viruses, bacteria and fungi. In addition, various soil-borne and above ground insect pests also affect crop production. Variation in climatic conditions often favors the multiplication of pathogens while negatively affecting plant productivity and soil fertility. It causes the reduction of available resources for plants, which fail to produce enough biomass, seeds, and thus yield. Climate-driven migration allows the movement of pathogens and pests from one region to another. Thus, the locally adapted crop genotypes confront new biotic stress factors. The interaction of plants with microbes or microbe-associated molecular patterns can induce resistance to secondary infections by pathogens. This involves the production and systemic signal of a complex of low-molecular-weight plant metabolites, which are well described for dicotyledonous plants, but poorly understood for monocotyledonous plants such as cereal crops [43]. Because of climate variability and change, it is anticipated that new diseases and pests might appear, or that the virulence of the current types may

The changing of the climate is bringing new types of diseases and pests that do not have any control methods yet. For example, maize lethal necrosis (MLN) is one of the most devastating diseases found in maize in Eastern and Central African countries. It is caused by the synergistic interaction between *Sugarcane Mosaic Virus* (SCMV) and *Maize Chlorotic Mottle Virus* (MCMV). It causes yield reduction ranging from 30 to 100% in farmers' fields depending on the time of infestation [44]. MLN is transmitted by beetles, rootworms, thrips, stem borers, several species of aphids in non-persistent manner, infected soil, infected seeds and any tools or materials used in the infected field [45]. Moreover, Russian Wheat Aphid (RWA)

oxygen deficiency in tissues and the adaptation to oxygen deficiency [42].

**14**

increase.

is one of the world's invasive pests of wheat, barley and other cereal grains. It is widespread in cereal growing regions of Africa, Asia, Europe, Middle East, North and South America, recently in Australasia [46]. The visual symptoms of infestation in plants are chlorosis, necrosis, wilting, stunting, leaf streaking with whitish, yellow and purple longitudinal leaf markings, trapped awns, rolled leaves and heads that fail to flower [46]. These pests have high resistance to extreme weathers events. RWA caused yield losses up to 80% in wheat and 100% in barley. The main challenge associated with the RWA is that new biotopes that are tolerant to available insecticides continue to appear. Some of the biotopes also overcome resistance of some crop varieties. Elevated atmospheric carbon dioxide has also been found to alter the efficacy of some biotopes. They are therefore constant threat to crop production.
