Distribution of Verticillium dahliae through watering systems in widely irrigated olive growing areas in Andalucia (southern Spain)

Abstract

Verticillium dahliae Kleb. causes Verticillium wilts in many herbaceous and woody species. Many hosts of the pathogen are commonly cultivated in Andalucía (southern Spain), particularly major crops such as cotton, vegetables, almond, peach and, particularly, olive, in which the fungus causes Verticillium wilt of olive. Infective structures of the pathogen (microsclerotia), produced in the late phases of the infection cycle in senescent tissues of the infected plants, can be spread over short or long distances by a number of dispersal methods. Irrigation water is one of the factors implicated in this spread of V. dahliae. Indeed, increasing irrigation dosages in crops or an inadequate irrigation schedule have been identified as cultural practices favouring Verticillium wilt onset and severity in olive and other hosts. Most of the cultivated areas in the Guadalquivir Valley of Andalucía are irrigated by pumping stations using modern infrastructures that supply water to thousands of hectares of farm land, which are usually associated with irrigation communities. This study demonstrates that the pathogen survives in the sediment and particles suspended in water used for irrigation in different facilities of an irrigation community, that were involved in distributing water (main canal and reception tank of a investigated pumping station, irrigation pools and sand from filters). Thus microsclerotia moves from the pumping station to individual plots (olive and cotton cultivated farm) as viable microsclerotia, free or embedded in soil particles and plant debris, suspended in the irrigation water, or deposited in the sludge in piping systems or water storage ponds. We have detected amounts of inoculum in the solid pellet samples in these facilities that ranged from 2.7 to 6.7 microsclerotia per gram. Besides this, water from drippers in cultivated plots released into the soil a variable amount of infective propagules of the pathogen over time that accounted for 3.75 microsclerotia/m 3 in some of the recording times. Therefore, irrigation water becomes an important source of inoculum that is very effectively involved in medium and long-distance spread of the pathogen.

Assessment of the effect of surface drip irrigation on Verticillium dahliae propagules differing in persistence in soil and on verticillium wilt of olive

“…Irrigation waters in Andalusian olive orchards can harbour and disperse V. dahliae propagules (Rodríguez‐Jurado & Bejarano‐Alcázar, ; García‐Cabello et al ., ), particularly those of the highly virulent, defoliating V. dahliae pathotype, which frequently causes death of the Picual cultivar (Jiménez‐Díaz et al ., ; Moraño‐Moreno et al ., ). This cultivar is one of the most economically (and historically) important in Spain (López‐Escudero & Mercado‐Blanco, ) and this could explain why it is still used in Andalusia instead of resistant cultivars, which are available (Rodríguez‐Jurado et al ., ; López‐Escudero et al ., ).…”

Scientific opinion on the pest categorisation of Verticillium dahliae Kleb

“…Contaminated water of irrigation systems, especially in wide cultivation areas, can disperse the pathogen's propagules (Rodriguez-Jurado and Bejarano-Alcazar, 2007;Garcia-Cabello et al, 2012). This dispersal of V. dahliae propagules by contaminated irrigation water has been demonstrated in several herbaceous crops (Easton et al, 1969).…”

Reduced introduction of Verticillium dahliae through irrigation systems and accumulation in soil by injection of peroxygen‐based disinfectants

“…The installation of filtration systems is a widespread practice aimed at preventing the clogging of drippers. It has been demonstrated that commercial sand filters fail to prevent V. dahliae spread through drip‐irrigation systems of Andalusian olive orchards (García‐Cabello et al ., ). On the other hand, treating V. dahliae ‐infested water with some disinfectants, namely OX‐VIRIN and OX‐AGUA AL25, reported potential efficacy in reducing the propagules of the fungus, which was enhanced by increasing both the exposure time and the concentration of the product.…”

“…García‐Cabello et al . () demonstrated that the pathogen was capable of surviving and dispersing as viable sclerotia when moved medium and long distances from a pumping station to research plots. Furthermore, Rodríguez‐Jurado et al .…”

“…Among the mechanisms contributing to the positive relationship between irrigation and VWO, the spread and introduction of inoculum to the root system through irrigation waters must be considered. Rivers, streams and natural ponds, as well as man-made reservoirs, canals or even wells, constitute a long-distance means for dispersal of V. dahliae propagules, enabling its introduction into pathogen-free soils (Rodr ıguez-Jurado & Bejarano-Alc azar, 2007;Garc ıa-Cabello et al, 2012;Baroudy et al, 2018). In Andalusia, Rodr ıguez-Jurado & Bejarano-Alc azar (2007) reported the presence of V. dahliae propagules in irrigation waters supplied from surface and subterranean sources in 85.7% of the surveyed olive orchards.…”