**8.2 Biological control**

International markets reject produce containing unauthorized pesticides, with pesticide residues exceeding permissible limits, and with inadequate labeling and packaging. Hence, biological control of postharvest diseases has great potential because postharvest environmental conditions like temperature and humidity can be strictly controlled to suit the needs of the biocontrol agent. Much information has been provided in relation to postharvest biocontrol and the problems faced by the development of commercial products [26, 27]. Biological control is used through microbes such as fungi, bacteria, actinomycetes, and viruses (bacteriophages) to control the postharvest disease of vegetables [1, 28–31]. The degree of disease control or disease suppression achieved with these bioagents can be comparable to that achieved with chemicals. As per estimates, the market of Indian bioagents is equivalent to 2.89% of the overall pesticide market in India with the worth of rupees 690 crores. It is expected to show an annual growth rate of about 2.3% in the coming years [32, 33]. In India, so far only 18 types of bio-pesticides have been registered under the Insecticide Act of 1968. Among agriculturally important microbes, *Trichoderma viride*, *T. harzianum*, *Pseudomonas fluorescens,* and *Bacillus subtilis* are the most potential bio-agents which as act as producers of biologically active metabolites like antibiotics and bacteriocin, elicitors and inducers of systemic resistance in plants. Biocontrol mediated pathogen inhibition is found to be more effective when the antagonist is applied prior to infection taking place. Antagonists which act against postharvest pathogens of vegetables by competitive inhibition at wound sites include the yeasts *Pichia* and *Debaryomces* species. Chitosan, for example, is not only an elicitor of host defense responses but also has direct fungicidal action against a range of postharvest pathogens. *Trichoderma* has potent antifungal activity against *Botrytis cinerea*, *S. sclerotiorum*, *Cortictum rolfsi,* and other important biotic stresses. Microbial pesticide active ingredients of *Streptomyces griseoviridis* K61 against bacterial soft rot, gray mold, *Phytophthora*; *Gliocladium catenulatum* against gray mold; *Candida oleophila* strain against postharvest diseases; *Coniothyrium minitans* against *Sclerotinia sclerotiorum*, *Sclerotinia minor*; *Trichoderma aspellerum* (formerly *T. harzianum*) against *Pythium*, *Phytophthera*, *Botrytis*, *Rhizoctonia*; *Trichoderma atroviridae* against *B. cinerea* and *B. subtilis* against *Botrytis* spp. is the most commonly used biocontrol agents for postharvest diseases.

Antagonistic yeast forms a biofilm to stick pathogen and parasitize on the hyphae of the pathogen. Bar-Shimon et al. [34] reported that biocontrol efficacy of yeast correlates with the production of lytic enzymes and their ability to tolerate high concentrations of salts. Further, molecular approaches were used to examine the role of glucanases in the biocontrol activity of the yeast *C. oleophila* and biocontrol activity was enhanced by overexpression of antimicrobial peptides. By early 2000, three postharvest biological products, Aspire™ (the USA and Israel), Bio-Save™ (the USA), and Yield Plus™ (South Africa) were available in the market. However, Aspire was initially involved to combine the product with a low concentration of postharvest fungicide [35] or salt solutions (1–2%) of calcium chloride or sodium bicarbonate and also with other additives which are commonly used in the food industry [36]. These products were also combined with physical treatments like hot air, curing, hot-water brushing, and combinations of the above with pressure infiltration of calcium for improvement of efficacy [37]. To increase bio-efficacy, the antagonists can also be combined with a sugar analogue (2-deoxy-D-glucose).

An effort has been made to develop two new products based on yeast antagonist *Candida saitoana* and a derivative of either chitosan (Biocoat) or lysozyme (Biocure). These products had been evaluated worldwide. They showed strong eradicative activity. The two commercial products based on the use of a heattolerant strain of *Metschnikowia fructicola* also contain other additives such as sodium bicarbonate. The additives are found highly effective to increase biocontrol efficacy to levels equivalent to those found with available postharvest fungicides. The product is marketed under the name ProYeast-ST and ProYeast-ORG in Israel by the company AgroGreen and found effective against rots incited by *Botrytis*, *Penicillium*, *Rhizopus,* and *Aspergillus*.

#### **8.3 Plant essential oils**

Botanical pesticides cause no adverse effects on non-target biota with biodegradability. It should be noted that most of the crops sprayed with botanical pesticides are quite safe for consumption after a short period after spraying. A large number of defensive of rich chemicals such as terpenoids, alkaloids, phenols, tannins, coumarins, flavonoids, etc. are present in plants which cause physiological effects on pathogens. These compounds have already been identified in the extracts/exudates of many plants. They have antimicrobial activities and are used for postharvest disease control.

The use of natural botanical products would be a supplement or an alternative to synthetic fungicide. Examples include 1,8-cineole, the major constituent of oils from rosemary (*Rosmarinus officinale*) and eucalyptus (*Eucalyptus globus*), eugenol from clove oil (*Syzygium aromaticum*), thymol from garden thyme (*Thymus vulgaris*), and menthol from various species of mint (*Mentha* species). The majority of research is progressing in this regard to develop plant oil-based pesticides. Therefore, essential oil-based formulations have great scope in the future to use as green pesticides as plant protectants in the integrated pest and disease management of value-added agriculture and horticulture crops.

Many exhaustive studies have been carried out on the utility of neem oil against various fungal pathogens. Its efficacy has been evaluated against fungal pathogens and found to be on par with the fungicide hymexazole in the control of the soil pathogens *Fusarium oxysporum*, *Fusarium ciceri*, *R. solani*, *S. rolfsii* and *S. sclerotiorum.* Researchers have reported *in-vitro* inhibition of 16 aromatic compounds against five major seed-borne fungal pathogens in the concentration range of 100–8000 ppm and the minimum inhibitory concentration (MIC) value for all the test fungi was 270–1704 ppm. Essential oils under commerce used as biopesticides have many problems, such as non-tariff barrier, scarcity of natural resources, need of quality control, and difficulties of registration. Some plant products have been commercialized. SPIC Science Foundation has developed a fungistatic product "Wanis" which has a single monoterpene as an ingredient and it is reportedly very effective in controlling more than 30 different types of phytopathogenic fungi. It is non-toxic to human beings and livestock. Recently, an antifungal agent by the name "TALENT", containing carvone as the active ingredient, derived from the essential oil of Carumcarvii, was commercialized. Mycotech Corporation product Cinnamite™, based on cinnamon oil, has been developed as a fungicide/miticide for

#### *Postharvest Diseases of Vegetable Crops and Their Management DOI: http://dx.doi.org/10.5772/intechopen.101852*

glasshouse and horticultural crops. World-leading essential oil-based pesticide producing EcoSMART technologies developed EcoPCORR under the name Bioganic™ as insecticide and miticide for nursery crops, horticultural crops, and value-added crops under glasshouse conditions. The EcoSMART formulation is based on rosemary oil, viz. EcoTrol™ (insecticide/miticide), Sporan™ (fungicide) and eugenol oil formulation Mataran™ (weedicides) were classify as generally recognized as safe (GRAS). The search for antifungal agents of plant origin is important, which can further broaden the arsenal for disease management and can be used as alternatives or complementary to synthetic fungicides. These chemicals of biological origin are safe to use, and in a few cases can even be produced by farmers and rural communities. Thus plant essential oils are safe to the user and the environment and have a good potential as crop protectants and integrated pest management under organic farming and value-added agricultural and horticultural crops [38].
