Development of Integrated Disease Control Measures for the Valorisation of Traditional Crops in Southern Italy: The Case Study of Fagioli di Sarconi
Pietro Lo Cantore, Annalisa Giorgio, Bruno Campion, and Nicola Sante Iacobellis
Abstract The cultivation of Fagioli di Sarconi (FS), a pool of traditional varieties protected with the mark PGI (Protected Geographical Indication) cultivated in the National Park of Agri Valley in Basilicata (southern Italy), is limited by common bacterial blight (CBB), caused by the seed-borne bacterium Xanthomonas axonopodis pv. phaseoli (Xap) and X. a. pv. phaseoli var. fuscans (Xapf), whose control is difficult because of the lack of safe bactericides. Hence, studies were undertaken to assess the susceptibility/tolerance of selected varieties toward the pathogens and to develop eco-compatible measures for the disease management. Five FS varieties showed a differential response to inoculations with virulent strains of the pathogens, and hence, two tolerant cultivars were selected for the introgression of CBB resistance characters. Among the main active components of some essential oils, eugenol determined a highly significant reduction of Xap density on bean seeds, though at the higher dosage, the seed germination reduction was observed. These data indicate eugenol as potentially useful for bean seed disinfection from Xapf, though further studies appear necessary. Among 162 bacterial isolates from bean rhizosphere, six caused a clear reduction of lesions size ranging from 30 to 66 % suggesting that induced systemic resistance may be involved in that feature.
Common bean (Phaseolus vulgaris L.) is one of the most important legumes due to its commercial value and its high content of quality carbohydrates, proteins, minerals and vitamins. FAO data (FAO Statistics Division 2014) on bean production in Europe indicate that in 2012, Belarus, Spain and Italy were the main bean producers. In fact, bean production was 227.259 t in Belarus (only for dry beans), 175.300 t in Spain (165.400 for string and 9.900 for dry beans) and 145.933 t in Italy (134.124 for string and 11.809 for dry beans). In Italy, besides the commercial cultivars, there is an abundance of traditional varieties with unique nutritional features and for which there is a traditional market (Dinelli et al. 2006). This is the case of the Fagioli di Sarconi (FS), a pool of traditional high-value traditional varieties, selected from various landraces (Masi et al. 1999; Piergiovanni et al. 2000) and protected by the European Union (Reg. CEE No. 1263/96) with the mark PGI (Protected Geographical Indication).
FS are cultivated in the National Park of the Agri Valley in Basilicata (southern Italy) for dry seed production (Brandi et al. 1998). The germplasm, preserved on farm by the Consorzio di Tutela dei Fagioli di Sarconi, has been extensively characterised for its biochemical and nutriceutical traits (Piergiovanni et al. 2000; Lioi et al. 2005; Dinelli et al. 2006) but nothing is known about its response to diseases. As a matter of fact, the above varieties are plagued by the common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Smith) Dye (Xap) and X. a. pv. phaseoli var. fuscans (Xapf) (Vauterin et al. 1995), and since 2002, there have been several severe outbreaks of this disease. Bean field surveys in 2001–2002 showed that at the end of the production cycle, nearly 100 % of the plants were infected, with the consequent heavy crop loss. The disease is endemic and some evidences indicate its introduction by long time. The use of bean seed grown on farm, possibly infected and/or contaminated by the pathogens, the limited copper sprays and the use of overhead irrigation have facilitated the dissemination of the pathogen and the maintenance of a high level of the inoculum potential. Year by year, bacterial disease outbreaks have been greatly facilitated by the particular climatic conditions which, as observed in the above years, were characterised by heavy rains during the periods from July to September (Lo Cantore et al. 2004a). CBB pathogens infect all the plant organs and the disease development is favoured by warm temperature (25–35 oC) and humid conditions (Gilbertson and Maxwell 1992; Saettler 1989). CBB symptoms on foliage are water-soaked spots that enlarge forming dark brown necrotic lesions often surrounded by chlorotic zones. Infected pods exhibit circular water-soaked areas that turn to reddish-brown lesions. Pod infection often causes discoloration, shrivelling and bacterial contamination/infection of seeds though in some cases, they may appear healthy (Saettler 1989).
The causal agents of CBB, Xap and Xapf, are distinguished from each other only because Xapf produces a brown pigment when grown on some specific agar media (Schaad et al. 2001). Nevertheless, there is considerable genetic diversity between Xap and Xapf (Chan and Goodwin 1999; Mkandawire et al. 2004; L'opez et al. 2006; Mahuku et al. 2006), as recent AFLP analyses have confirmed (Lo Cantore and Iacobellis 2007; Alavi et al. 2008; Lo Cantore et al. 2010b). For that, a revision of the two pathogens classification has been proposed (Schaad et al. 2005, 2006).
Dissemination in the field is mainly determined by wind-driven rain and overhead irrigation, but also by insects, field workers and contaminated equipment (Gilbertson and Maxwell 1992; Saettler 1989), which may play an important role. Common bacterial blight is the major seed-borne disease of common bean worldwide (Tarlan et al. 2001; Miklas et al. 2003), and the best way to manage CBB includes the use of pathogen-free seed (Zanatta et al. 2007). In order to control CBB, the use of bean cultivars with genetic tolerance/resistance to the disease is the most practical method (Coyne and Schuster 1974; Yoshii et al. 1978) though the availability of CBB-resistant cultivars is limited. In most of the cases, the resistance/tolerance of traditional varieties to CBB is unknown. This is the case of FS varieties. Furthermore, pathogen-free seed is a prerequisite for a healthy crop, but to date no efficient disinfection method is available (Lo Cantore et al. 2009). Antibiotics, in fact, are actually restricted or forbidden in the agricultural practices in many countries (McManus et al. 2002) and the use of copper compounds, because of their general toxicity and impact on the environment, is constrained in Europe (EU rule no. 473/2002). Furthermore, chemical disinfectants such as chlorine, inorganic acids, organic acids and heat treatments have been used for disinfection of potentially contaminated seeds surface or to cure infected seeds, but seed devitalisation has been reported (Claflin 2003).
The above consideration prompts the need to assess, first, the response of the selected FS bean varieties to CBB with the final aims to select resistant/tolerant traditional varieties and to introgress tolerance/resistance characters into the FS varieties of interest. Moreover, of interest was the development of alternative methods for the control of CBB to be used in integrated crop management as well as in bio-organic agriculture. Several studies have pointed out the possibility to use essential oils and/or their components in medical and plant pathology as well as in the food industry for the control of microorganisms pathogenic to consumers and/or responsible for food spoilage (Seow et al. 2014). Nevertheless, most of the studies are mainly focused on the in vitro assessment of the antimicrobial activity (Si et al. 2006; Terzi et al. 2007), and the exploitation of essential oils for the control of plant diseases is still in its infancy (Tinivella et al. 2009; Kotan et al. 2010). Another opportunity for plant defence towards diseases is the use of beneficial bacteria inhabiting plant rhizosphere. In several works, it was demonstrated that some bacteria belonging to Pseudomonas and Bacillus genera are able to provide different mechanisms (direct or plant mediated) for suppressing plant diseases (Saharan and Nehra 2011).
In this chapter, we report some of the results obtained in studies aimed to develop methods for integrated control of CBB.