Biotechnological Strategies for a Resilient Potato Crop

*Elena Rakosy-Tican and Imola Molnar*

#### **Abstract**

The aim of this chapter is to describe in a synthetic manner the most efficient biotechnological techniques which can be applied in potato breeding with emphasis on multiple resistance traits. To this end, most important results of all biotechnological techniques will be pointed out including new biotechnological tools of genome editing. The somatic hybridization will be the core of the presentation as the only non-GMO strategy with good results in transferring multiple resistances into potato gene pool. The chapter is presenting all data in a synthesized form and made comparisons between the existing techniques and their possible adoption in breeding in different parts of the world, depending on regulations and consumer choice. Moreover, the recently discovered value of potato as a healthy food and its possible applications in cancer treatment will be also discussed with new data on both potato and some of its wild relatives.

**Keywords:** advantages, genetic transformation, multiple resistance traits, new biotechnological techniques, potato breeding, somatic hybridization

#### **1. Introduction**

As a major food staple, the potato is contributing to the UN Millennium Development Goals of food security and poverty eradication. Today, potato is the most widly grown non-cereal crop [1] and important vegetable for human consumption [2]. The wide climatic adaptability and short growing time of potato facilitated its spread across diverse geographical regions. To date more than three thousand potato cultivars are cultivated in 165 countries with a production exceeding 350 million tonnes per year, particularly under temperate, subtropical and tropical regions, covering a major economic share in the global agricultural market [2]. For the last two decades, potato cultivation and utilization have also been notably increased in developing countries such as China, India and Bangladesh [3]. Although, classical breeding has developed thousands of new cultivars, potato is still sensitive to countless diseases and pests, which lead to 44.9% yield losses in every year [4]. Diseases such as late blight produced by the oomycete *Phytophthora infestans* (*Pi*)*,* viruses like potato virus Y (PVY) and pests as Colorado potato beetle (CPB) are able to completely destroy a potato field if left uncontrolled. Even today the main way to combat diseases and pests is massive application of pesticides. Pesticides increase pollution of the environment, are toxic for non-target organisms including humans and exert selection pressure on the diseases and pests, which develop resistance. New sustainable and effective ways to combat diseases and pests of potato are required and biotechnological approaches have been lately developed

**Figure 1.**

*Overview of classical breeding tools, as well as biotechnology and their applications for improving crops in general and potato resilience, in particular.*

also to address this challenging issue (**Figure 1**). Moreover, climate change has challenged potato production worldwide in the last decades and new strategies to develop resilient potato to drought, high temperature, salt and other abiotic stresses or multiple stresses are an urgent need for potato cultivation. To achieve these goals, both classical breeding and biotechnology are aware of the resources of resistance genes in the crop wild relatives, as for example the project of International Potato Centre (CIP). There are published several books and reviews dealing with potato biotechnology and breeding [1, 2, 5, 6], but in this chapter we are going to overview, synthetize and point out those techniques that are included in potato genetic improvement for a resilient potato crop in order to develop a sustainable agriculture and reduce poverty.

## **2. Genetic engineering sustainability for a resilient potato crop**

Modern biotechnology is defined as the technology which use living cells, microorganisms, or functional parts, such as enzymes, proteins, DNA or RNA molecules to develop basic research and deploy new useful products [7]. Genetic engineering, as part of plant biotechnology, covers techniques which change the genome of plants. In its larger sense, plant genetic engineering includes: (i) somaclonal variation, (ii) cell fusion and regeneration of somatic hybrid plants, (iii) gene transfer and (iv) genome editing. Since somaclonal variation has already been presented in detail and its results are currently not widely used in potato breeding [8], in this chapter we are presenting the other genetic engineering techniques and obtained results in developing resilient potato crop. Potato crop requires considerable inputs of: nutrients, pesticides, and water to maintain yield, tuber quality, and protection

#### *Biotechnological Strategies for a Resilient Potato Crop DOI: http://dx.doi.org/10.5772/intechopen.98717*

from its pathogens, pests and extreme climate conditions. Genetic variations for the most important traits is low in commercial cultivars, but related wild relatives contain many unique, valuable traits missing from cultivars, which represent a rich genetic source for potato improvement [9]. Potato breeding efforts have historically focused primarily on yield, fresh market and processing quality, storability as well as disease resistance. Only after developing genetic transformation and/or other biotechnological approaches, a faster transfer of valuable traits like quality of tuber composition and resistance to biotic and abiotic stresses became possible. Moreover, with using classical breeding one new cultivar can be produced in 10 to 15 years from the initial cross to cultivar release, while with biotechnology, particularly gene transfer, shorter time is required, from some months (6–12 months) to a few years, ignoring the long regulatory clearances [6]. There are many attempts and results on the transfer and integration of economically important genes in potato crop and some previous reviews have presented the state of art in plants or in this tuberous crop [6, 8, 10].

#### **2.1 Gene transfer to develop resilient potato to biotic and abiotic stresses**

Genetic transformation of potato was first achieved in 1988 [11, 12], potato being the third plant to be successfully transformed. This technology uses *Agrobacterium tumefaciens* - mediated gene transfer, which is reported as the most efficient for potato crop and some of potato wild relatives [13]. The first commercially grown potato was introduced by Monsanto as New Leaf™ in 1995, the first released genetically modified crop of the company. Besides gene transfer from bacteria, fungi, animal or other plant species commonly called transgenesis, more recently wild species are considered as a rich reservoir of resistance genes. The transfer of genes from the same genus, i.e. from related species that can be crossed, is called cisgenesis. Because the genes can be also integrated into the recipient plant genome by classical breeding, cisgenesis was thought to be exempted from GMO low in Europe. Plant own genes can be also transferred in order to increase their expression, and this technique is called intragenesis [14, 15]. *Solanum* wild species, that evolved to resist in diverse climates in South and North America, are indeed a rich reservoir of genes which can be introgressed in potato genome. It is estimated that around 190 wild tuber-bearing relatives of potato, in the section Petota of the genus *Solanum*, are available for resistance breeding [16, 17]. Moreover, besides their rich genetic resources, potato and its wild relatives benefit from a good amenability to *in vitro* tissue and protoplast culture, making it possible to exploit this diversity through genetic engineering [8].

#### *2.1.1 Single or multiple resistance gene transfer to improve pathogen and pest resistance*

Genetic engineering has the potential to transfer single genes to increase disease or pest resistance, if the selectable marker gene, which is necessary for transgenic plant selection is not considered. Such single genes can be introgressed in potato elite varieties to improve one resistance trait. The frequently used marker gene during potato gene transfer is *npt*II (bacterial neomycin phosphotransferase II gene), which renders transgenic cells resistant to aminoglycoside antibiotics, including kanamycin and G418 [18]. Selection based on kanamycin has been proven to generate escapes in potato crop [13]. In this study both genes: *npt*II and reporter *gfp* (green fluorescent protein), have been used to reveal the transgene transfer efficiency, which allowed to evaluate the escape events. In order to transfer single genes that increase host plant resistance to pathogens and pests, the researchers have

to identify and clone the genes of interest (GOI). At this stage, a good knowledge of mechanisms of host plant– pathogen interaction and gene characterization is necessary. In the last decades new insights into the complex molecular race between pathogens and/or pests and crop hosts were advanced and many genes are characterized and some cloned [19, 20]. With the advent of Potato Genome Sequencing Consortium [21] and completion of the first reference genome of potato [17], and later the release of genome data for some of its wild relatives i.e. *S. commersoni* [22], and *S. chacoense* [23], potato breeding and biotechnology entered into the genomicbased improvement era. Gene transfer is already taking advantage of genome sequencing data in first instance through the transfer of potato own resistance genes and secondly utilization of potato wild relative (PWR) genes. In **Table 1**, examples of the latest year's single and multiple gene transfer for improving potato resilience to biotic and abiotic stresses are given, as well as some results on insect resistance. Potato wild relatives have evolved defense mechanisms against pathogens and pests at multilayer level (**Figure 2**). The interaction between host potato species and its pathogens involves the following mechanisms: (1) physical and physiological barriers that prevent the pathogens to enter into the plant cells; (2) plasma membrane-bound and intracellular immune receptors that initiate defense responses upon the perception of pathogens; (3) interference RNA (RNAi) used by plants to detect invading viruses and fragment their RNA [20]. Pathogens as bacteria and fungi, respond to potato defense through: (1) production and release of cell-walldegrading enzymes; (2) production and delivery into host cytoplasm of effector proteins, some of which suppress host defense and promote susceptibility; (3) viruses produce suppressors of host plant RNAi and/or hijack host RNAi to silence host genes and promote viral pathogenicity [20]. On the other hand, the interaction between herbivorous insect pests and plants also involves various mechanisms: (1) non-glandular and especially glandular trichomes that act as physical and physiological barrier to insect feeding; (2) toxins such as glycoalkaloids, which are well characterised in the *Solanum* genera; (3) enzyme inhibitors such as protease inhibitors; (4) use of bacterial insecticidal genes [61] (references herein) (**Figure 2**). All genes involved in host plant resistance to pathogens and pests as well as pathogenesis susceptibility genes can be transferred to produce resistant potato crop.

For instance, genes for pattern recognition receptors (PRRs), from other species can recognize pathogen associated molecular patters (PAMPs) and activate defense responses, as was demonstrated in *Arabidopsis thaliana* lectin receptor kinase LecRK1.9 transferred into potato that increased resistance to *Phytophthora infestans* (*Pi*) (**Table 1**) [31]. This first level of defense is known as pathogen targeted immunity (PTI). It is likely that there are different type of PRRs in potato but one was identified as ELR protein, which was capable to recognize the INFI elicitin from *Pi* [62]. Others are known from tomato and other species [6]. The tomato PRR *Ve1*, which recognize the Ave1 protein from *Verticillium dahliae*, when was expressed in potato was conferring resistance to this disease [63]. Gene transfer gave good results when R genes could be isolated and cloned. R proteins represent the second level of defense recognizing specific effector proteins of the pathogen, called effector targeted immunity (ETI) (**Figure 2**) [6]. Compared to PRR system, effectors use a similar defense response in the host plant, but effectors coupled with R genes elicit a stronger response which activates hypersensitive reaction (HR) in resistant plants. HR imply cell death surrounding the pathogen attack and represent a barrier for further pathogen spread. Pathogen effectors have high diversity but R genes have two conserved domains: nucleotide binding (NB) and leucine reach repeat (LRR), which makes their identification easier [6]. In the last two decades many R genes were cloned from potato wild relatives that induce resistance to *Pi* and transferred into potato varieties, either as single or multiple genes (**Table 1**). Some examples


#### *Biotechnological Strategies for a Resilient Potato Crop DOI: http://dx.doi.org/10.5772/intechopen.98717*

