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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

6.5.3.1.2 Transgenic Approaches for Disease Resistance

The next yield-limiting factor is a disease that causes the major loss of

production of crops. The stress causes the destruction of crop plant from

germination to maturity and plant is always in the state of dilemma to combat

the disease-causing organisms. The best way to introduce disease resistance

in the plant is through Transgenic approaches. The gene-like pathogenesis-

related (PR) genes, glucanase, and chitinase can effectively disintegrate the

cell wall of disease-causing organisms against fungal and bacterial and viral

diseases (Bill et al., 2016).

Similarly, the disease resistance can be introduced with the help of

systemic acquired resistance (SAR)-related genes responsible for expressing

many downstream genes like pathogenesis-related genes (Chen et al.,

2017). Transgenic orange has been developed, which showed tolerance to

Phytophthora citrophthora by introducing the tomato PR-5 gene (Takemoto

& Mizuno, 2016). Transgenic tomato shows tolerance to Tomato mosaic

virus (TMV), which has been developed by introduction of non-expression

of pathogenesis-related (NPR-1) gene taken from Arabidopsis thaliana

(Bubici et al., 2017).

Transgenic tomato showed tolerance against bacterial wilt and fusarium

wilt owing to the NPR1 gene expression. Transgenic apple overexpressing

NPR1 gene is resistant to apple cedar rust due to the attack of Gymnospo­

rangium juniper-Virginiana and V. inaequalis, but blight disease of apple is

owing to Erwinia amylovora (Thakur et al., 2018). Transgenic plant having

Chitinase gene is tolerant against many fungal diseases such as tobacco ChiC

gene in carrot (Su et al., 2015). Similarly, transgenic lines of potato have

been developed by introducing the chitinase gene from P. vulgaris to tackle

early blight in potatoes (Chen et al., 2018).

Transgenic guava has been developed by introducing the endochitinase

gene from Trichoderma, which is responsible for the resistance against

Fusarium oxysporum (Kumar et al., 2016). Recently, CRISPR Cas9 and

RNAi have been widely used to overcome the issues regarding biotic and

abiotic stress (Rani et al., 2016).

6.5.3.1.3 Transgenic Approaches for Virus Resistance

Viruses are the biotic agent that badly affects crop yield and physiology, and

traditional breeding methods cannot tackle viral diseases (Trebicki et al.,