# Lactic Acid Bacteria as Biocontrol Agents against Potato (_Solanum tuberosum_ L.) Pathogens
## 1 Introduction  
The potato (_Solanum tuberosum_ L.) is cultivated in 160 countries. These tubers are so prominent among consumers and farmers due to their remarkable yield per unit area, versatility and high nutritional value [1]. In European Union (EU), potato cultivation acreage in 2020 was 1.66 million ha. In Poland, the area of potato cultivation, according to the estimates of Statistics Poland, amounted to approx. 0.2 million ha in 2021. Around 55.3 Mt of tubers are harvested in the EU, with Belgium, France, the Netherlands and Germany being the largest producers. The potato harvest in 2021 in Poland amounted to approx. 7.10 Mt [2, 3]. However, the annual production of potatoes in many countries is slightly decreasing; in the leading ones (China and India), a steady increase is observed [4]. Since healthy and robust plants produce good crops, proper attention is required in the context of preventing infections. Diseases caused by phytopathogens are the source ofsevere losses for farmers due to lower yield and disposal of crops [5]. In order to prevent it, there are facilities designed to maintain temperature and humidity during potatoes storage on large farms specialised in cultivation. Annual losses during potato storage average about 7.5% in the United States, the fifth largest producer in the world [4; 6] and importantly, some of the tuber defects emerge only after the farmer has invested an entire season of inputs in cultivating the crops [7]. The source of infection is often seed potatoes or contaminated crop residues in the field after previous cultivation. Diseases caused by bacterial phytopathogens are particularly hindering potato production agents, and they can lead to severe damage to crops and tubers--the most important parts from an economic point of view. The bacterial genera _Pectobacterium_ have been used as a model pathogen for phytobacteriology research and currently include 12 species with a wide range of host plants, including potatoes. In Europe, it is associated with soft rot in storage or blackleg disease [7; 8]. Another economically important bacterial disease is common scab caused by _Streptomyces_ species. It causes necrosis in all underground potato parts and can reduce roots' growth from seed tubers [9]. In turn, fungi belonging to the genera: _Fusarium_, _Alternaria_, _Rhizoctoni_ and _Phoma_ are fungal pathogens of potato, causing gangrene, dry rot of stored tubers or other rot symptoms, and they are responsible for significant crop losses [10; 11]. The phytopathogens may act as primary or secondary invaders [10]. Considering the multitude and the threat of phytopathogens, farmers use a variety of pesticides such as metalaxyl, fluopicolide or mancozekb. Such chemically synthesised substances exhibit a strong antimicrobial effect but pose a potential environmental threat. While in use, they tend to migrate deep into the soil, destabilise the populations of microorganisms, and contaminate groundwater [12; 13; 14]. Currently, in the EU, there is a trend to limit the use of this type of chemical plant protection products, especially in organic farms, which constitute more than 13% of all potato holdings [2]. This agricultural production places the highest emphasis on environmental and wildlife protection and avoids synthetic chemicals such as fertilisers and pesticides, replacing them with biological and mechanical methods, along with cultural techniques, for instance, hand weeding, pruning or mulding [15]. In order to achieve it, biological control is often applied, which refers to the use of microbial antagonists to suppress phytopathogens causing plant diseases. A high antimicrobial effect characterises multiple biological control agents against specific pathogens, and currently, different types of interactions are sought, such as the production of antimicrobials, lytic enzymes, unregulated waste products, physical or chemical interference or competition for space [16].