Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
the soilborne pathogens Pythium and Rhizoctonia, which are major greenhouse pathogens. The
use of biocontrol is more prevalent in greenhouse and protected structures than in field crops,
even though greenhouses account for only 0.02% of the area used in agriculture. Some of the very
conditions that favor disease also favor the management of diseases with biological control
agents. Environmental conditions such as temperature and relative humidity can be tightly
controlled. Like the pathogen, biocontrol agents are also sensitive to environmental conditions,
and an unfavorable environment in the field has been cited as a reason for failure or inconsistent
performance. Conditions in the greenhouse can be optimized for the biocontrol agent. For
instance, biocontrol agents of powdery mildews are much more efficient when relative humidity
can be maintained above 80%, a condition that is easily monitored under glasshouse conditions.
The biological vacuum in soil substrates can also favor the establishment of biocontrol agents,
provided they are applied before pathogen introduction. Logistics and economics of applying
biocontrol agents in the greenhouse:
Products registered for biological control of soilborne pathogens: Several formulations of
either of the fungi Gliocladium-Trichoderma or the bacteria Pseudomonas and Bacillus have been
widely used for biocontrol of soilborne pathogens. These products are not only registered as
biofungicides but also used as plant strengtheners. In European countries, plant strengtheners
include inorganic compounds such as SiO 2 , NaHCO 3 , organic constituents such as compost,
homeopathic compounds, and some containing microorganisms such as Trichoderma harzianum,
Bacillus subtilis, Pseudomonas, and Pythium oligandrum. Details of available biocontrol agents for
green houses are as follows:
1. Coniothyrium minitans: Coniothyrium minitans is a mycoparasite which destroys sclerotia
of Sclerotinia sclerotiorum and S. minor. It is used for the control of Sclerotinia wilt of
lettuce in greenhouse and rape in the field. C. minitans reduced the sclerotial populations
at the soil surface, survived at least 39 weeks at a density of 10 4 –10 5 CFU/g, and spread to
infect sclerotia in control plots.
2. Gliocladium virens (Trichoderma virens): It is a soilborne fungi, developed for control of
Pythium ultimum and Rhizoctonia solani in soilless mixes. The fungus produces two
fungitoxic compounds, glioviren and gliotoxin compounds.
3. Trichoderma harzianum: T. harzianum reduces Fusarium crown and root rot of tomatoes
grown in potting mix containing T. harzianum and transplanted into the field. In greenhouse
trials, T. harzianum controlled R. solani in poinsettia, geraniums, and Catharanthus, and
Pythium on geraniums, impatiens, and petunias. It inhibits the pathogens by
mycoparasitism via production of chitinases, ¼ 1-3 glucanases and ¼ 1-4 glucanases,
antibiotics, competition, solubilization of inorganic plant nutrients, induced resistance, and
inactivation of the pathogen’s enzymes involved in the infection process.
4. Streptomyces griseoviridis: This culture is marketed in Europe and USA, under the
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