Integration of Post-Harvest Disease Management Strategies

In this article we will discuss about the integration of post-harvest diseases management strategies.

Integration of disease management strategies in fruits and vegetables emerged an answer to shortcomings of reliance on chemical control. It deals with integration of all available disease control methods to manage the diseases effectively and economically to satisfy human needs at the same time guarding the quality of harvested produce and environment.

Several studies have highlighted the advantages of Post-harvest application of biological control agents over field or soil application.

The major advantages are the convenience of bringing the antagonist in contact with the commodity as compared to its addition to the soil and the possibility of acting under controlled conditions, created and maintained during storage. Likewise, it is possible to introduce Bacillus subtilis into the wax applied to peaches in the packinghouse to protect them from the brown rot caused by Monilinia fructicola.

The antagonistic yeast Pichia guilliermondii can be introduced into the wax mixture applied to citrus fruit in packinghouse. Compatibility between a microbial antagonist and a synthetic fungicide offers the option of using the antagonist in combination with reduced levels of the fungicide.

Applying the yeast antagonist, Pichia guilliermondii to citrus fruit in combination with substantially reduced concentrations of thiabendazole reduced Penicillium digitatum decay to a level similar to that achieved by the currently recommended concentration of thiabendazole applied alone.

Thus, an integrated pest management system adaptation provides effective pest control and maintains very low levels of chemical residues.

The intensive studies on biocontrol of Post-harvest diseases have led to the registration of two biological products for commercial Post-harvest applications on citrus fruits i.e. Aspire, which is Candida oleophila, and Bio-Save 1000 from Pseudomonas syringae.

The biological agent must have low sensitivity to any of the supplemented chemical fungicides. Combining Aspire with each of the chemicals used improved the results; sometimes combinations with a low rate of fungicide were sufficient to achieve effects similar to those obtained by the chemicals at standard rates.

Safe compounds or natural products of plant origin have been suggested as alternatives to synthetic and conventional fungicides could also be used in combination with biocontrol agents, complementing their activity. Pathogens treated with such antifungal substances might be weakened and become more vulnerable to the antagonist activity.

The integration of Post-harvest biocontrol into modern production, storage and handling systems must begin before harvest. Several preharvest factors that affect fruit quality may have profound effects on the efficacy of Post-harvest biological control agents.

Preharvest calcium sprays during the growing season of apples and pears can increase fruit firmness, decrease the incidence of certain disorders and enhance resistance to Post-harvest infection. Calcium amendments and Post-harvest application of some antagonistic yeasts can be additive in reducing fruit decay and significantly increase disease control compared with either treatment alone.

The advantages in increased firmness, enhanced resistance to Post-harvest decay and enhanced biocontrol efficacy under some circumstances reflect the multiple benefits of integrating Post-harvest biological control with cultural and production practices.

Post-harvest factors may have a major impact on the effectiveness of biological control. Fruit maturity at harvest and the application of antagonists is affecting Post-harvest biological control. Delayed picked and over matured fruits are more susceptible to decay than are fruits picked at optimal storage maturity.

Roberts (1990, 1994) found that fruit maturity in apples and pears markedly affected biocontrol efficacy of antagonistic yeast Cryptococcus, while excellent control was achieved on freshly harvested fruit and treatments of ripened fruit gave much lower levels of control.

Temperature management is a critical factor in the maintenance of fruit quality and pathogen development, may enhance biological control of storage decay.

Janisiewicz (1991) demonstrated that as the storage temperature of apples and pears decreased, there was a reduction in the concentration of pyrrolnitrin (a metabolite of Pseudomonas cepacia and other Pseudomonas spp.) needed to protect the fruit from gray mould (Botrytis cinerea) and blue mould caused by Penicillium expansum.

An integrated strategy to control Post-harvest decay in pome and stone fruits has been advanced in recent years comprises several pre and Post-harvest components viz., alteration of fruit nutrient status, calcium applications as sprays during the growing season, lower fruit nitrogen content have been associated with reduced disease severity and influence the susceptibility of pome fruits to decay.

Controlled atmosphere storage with reduced O₂ and elevated CO₂ can reduce the severity of Post-harvest fungal decay in apples by inhibiting fruit senescence and maintaining host resistance to infection.

Integration of early harvest, low fruit nitrogen, high fruit calcium, yeast or yeast + one-tenth of the dose of thiabendazole along with a controlled atmosphere (2% O₂, 0.6% CO₂) were found to reduce blue mould severity in picked pears.

All the components of the integrated approach were found to be compatible with thiabendazole fungicides used for the management of Post- harvest decay and blue mould (P. expansum) in harvested pears.

Several yeast species such as Cryptococcus laurentii, are capable of colonizing wounds of pear fruit under conditions of low temperature, ambient or reduced O₂ and CO₂ therefore, can be integrate into Post-harvest strategies.

The two Post-harvest treatments, biological control and modified atmosphere packaging were combined with preharvest iprodione spray; the incidence of the brown rot was reduced from 41.5 per cent in the control to only 0.4 per cent.

A combined strategic approach was elaborated by various worker to control wound infecting pathogens by a series of treatments including disinfection of the fruit surface and environment, eradication or suppression of fungal spore germination at wound sites by a combination of fungicides and reduction of wound susceptibility to infection by the addition of biocontrol antagonists which act as protecting agents.

It is being apparent that a multifaceted integrated approach has been advantageous over the use of solitary measures. Thus, the application of antagonists, induced resistance, physical treatments, chemicals, natural and safe fungicides etc. can be utilized in a unified way to provide greater consistency and efficacy to management of Post-harvest diseases.