Sustainable Agricultural Practices in Disease Defence of Traditional Crops in Southern Italy: The Case Study of Tomato Cherry Protected by Trichoderma harzianum T-22 Against Cucumber Mosaic Virus (CMV)

Antonella Vitti, Adriano Sofo, Antonio Scopa, and Maria Nuzzaci

Abstract Nowadays, crop production is at risk due to global warming, especially in Mediterranean areas where the increase of air temperature and/or reduction of precipitation is relevant. Climate changes that are occurring can severely prejudice plant defensive mechanisms during host-pathogen interactions by modifying growth and physiology of the host plant. In particular, viral diseases cause serious economic losses destroying crops and reducing agronomic productivity, and, in some cases such as tomato crops, they become the limiting factor production of both open field and under greenhouse cultivation systems. This is because plant viruses are obligate parasites and require living tissue for their multiplication and spread. Therefore, they are able to interfere with plant metabolism and compete for host plant resources, so determining a decrease of plant growth and productivity. Severe outbreaks of Cucumber mosaic virus (CMV) and other viruses caused disruption of tomato plants in the Mediterranean region and in Southern Italy since the 1970s. In such a scenario, it is necessary to introduce new strategies for controlling plant pathogens and parasites in order to help maintain ecosystems and to boost sustainable agriculture. The aim of this work is to give an up-to-date overview on the recent breakthroughs in the use of microorganisms on plants for improving crop yields, quality and plant tolerance against pathogens. In particular, here we report a case study regarding an innovative strategy to control a viral disease (CMV) in tomato, based on the use of rhizosphere microorganism (Trichoderma harzianum, strain T-22) as an antagonist biocontrol agent (BCA).

Introduction

In the Mediterranean basin, horticultural crops have a great economic relevance. If we think of the Mediterranean diet, which is considered as one of the healthiest amongst world cuisines, above all since November 2010, when it was inscribed on the representative list of the intangible cultural heritage of humanity of UNESCO, tomato (Solanum lycopersicum) is certainly the vegetable most widely consumed. In Italy, in particular in the South, tomato is not only the first vegetable employed for fresh consumption, but it also represents the principal ingredient of many dishes, and it is above all used cooked to prepare sauces. The importance of tomato consists in its nutraceutical properties, due to the presence of an antioxidant substances mixture, such as lycopene, ascorbic acid, phenolic compounds, flavonoids and vitamin E. For this reason, nowadays tomato is cultivated both in open field and under greenhouse conditions in order to be always available for both fresh consumption and industrial processing.

Unfortunately, crop production is at risk due to global warming, especially in areas where the increase of air temperature and/or reduction of precipitation is relevant. In addition, climate changes can prejudice plant defensive mechanisms and increase the risk of illness, through growth and physiology alteration of the host plant and also by modifying host-pathogen interactions. In particular, viral diseases cause serious economic losses destroying crops and reducing agronomic productivity. In many Mediterranean coastal areas, several viral infections have become the limiting factor in the tomato production of both open field and under greenhouse cultivation systems. For example, in Italy, Spain, Portugal and Greece, the cultivations are at risk due to Tomato spotted wilt virus (TSWV) infections (Pappu et al. 2009). Another important example is Tomato yellow leaf curl virus (TYLCV), which caused serious economic problems in the eastern Mediterranean basin in the 1970s, and it is still now a threat (Lapidot et al. 2014). In late summer 2000, more than 30 ha of Greek tomato greenhouses (Avgelis et al. 2001) were affected and the disease incidence by TYLCV, in 2001, in most cases, was 80–90 %, or even 100 % (Dovas et al. 2002). In the same the 1970s, Cucumber mosaic virus (CMV) severe outbreaks caused disruption and death of tomato plants in the Mediterranean region (Gallitelli et al. 1991). Tomato necrosis epidemic occurred in the eastern coastal area of Spain in the late 1980s and early 1990s (Garc´ıa-Arenal et al. 2000). During this period, in Southern Italy (Puglia, Basilicata and Campania regions), some high-quality varieties of tomato, i.e. San Marzano, were severely affected by the strong CMV epidemic (Valanzuolo et al. 1999).

Indeed, plant viruses are obligate parasites because they require living tissue for their multiplication and spread, interfering with plant metabolism and/or competing for host plant resources, and all this is translated as decreasing of plant growth and productivity. The ability of viruses to significantly interfere with physiological processes of plants is closely related to a range of symptoms caused by an abnormal growth, as stunting, galls, enations and tissue distortions. In particular, CMV is the plant virus with the largest host range of all RNA viruses; therefore, its spreading on crop plants may cause serious economic damages. It infects more than 1,200 plant

species in 100 families (Edwardson and Christie 1991) and has been widely studied because it represents an interesting model from a physico-chemical point of view, as it causes a wide range of symptoms, especially yellow mottling, distortion and plant stunting (Nuzzaci et al. 2009; Whitham et al. 2006).

In such a scenario, the present work contributed to elucidate the importance in the use of sustainable agricultural practices in disease defence. In addition, here we report a case study regarding an innovative strategy to control a viral disease (CMV) in tomato cherry, based on the use of rhizosphere microorganism (Trichoderma harzianum, strain T-22) as an antagonist biocontrol agent (BCA).

 
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