Plant diseases caused by viruses, specialized bacteria, viroids and mycoplasmas are often considered by many to be incurable and terminal. That is, if your plants are afflicted with any of these virulent pathogens, remission and curing of the disease is impossible and death is imminent.
It is true that diseases caused by obligate parasites are both systemic and chronic. Being systemic, they tend to be beyond the reach of conventional, prophylactic sprays. Being chronic, they tend to persist throughout the life of the host plant. However, for the past several decades I have had the opportunity to develop and examine technologies that minimize infection and place the disease and parasite into remission. The following is a brief synopsis of the rationale and results of these trials.
Basic Classification of Organisms
Organisms can be grouped according to the nature of their host-parasite relationship.
Those that live on dead tissues and debris are referred to as ‘saprophytic’ (‘sapros-’ being Greek for ‘decay’ or ‘decomposition’). Saprophytes are also referred to as “free-living”. They can adapt to many types of nonliving substrates and thus host numerous genes that allow adaptation to a multitude of conditions. It is their adaptability to various situations that has allowed this group to survive over millions of years.
Organisms that can live on both dead and living tissues are referred to as ‘facultative parasites’ (‘facultas’ being Latin for ‘ability’). The facultative parasite represents a transitional group that, like its cousin, the saprophyte, retains an ability to colonize dead or dying tissues. However, there arose an advantageous set of characteristics that allowed the facultative parasite to colonize living tissues. The ability to colonize living tissues, then, allowed these parasites to gain a survival advantage over their cousins, the saprophytes. An ability to colonize a living host reduced the facultative parasites’ competition with the saprophytes.
Organisms that are dependent upon securing sustenance entirely from a living host are referred to as ‘obligate parasites’ (from the Middle English ‘obligare,’ ‘to bind’). The most sophisticated organism group is the obligate parasites. Such an organism has grown to be entirely dependent upon a living host. The association is highly sophisticated and developed, so that the parasite can tap into the host’s nervous system and react accordingly. When the host’s health is compromised, the chemical communication from the host to the parasite is: “It is safe to replicate and multiply.” However, when the host physiology is superior and efficient, the message communicated to the parasite is: “Lay low. It is unsafe to multiply.” Were it not for this chemically based communication, the success and survival of the parasite would have been gravely impacted and stifled.
The Role of Precise, Balanced Nutrition for Resistance Expression
Many will argue that good plant health merely supports a greater reproductive capacity for the parasite. If based upon their definition of good health (rapid, succulent growth borne of high nitrogen treatments), then yes, this will be true.
However, my definition of good plant health is one borne of “high performance, balanced nutrition.” It is a physical state of high tissue integrity. It is also a physiological state that hosts the highest level of photosynthetic efficiency, maximizing the carbon and energy harvest.
Resistance to infection or stress is a rate-related phenomenon. That is, upon being challenged with environmental stress or a pathogen, a susceptible plant generally requires 96+ hours before it attempts to engage a resistance response. However, healthy plants that express effective resistance mount a resistance response within 24 hours. Correspondingly, to conserve energy, these plants then suppress the defensive response once the stress and/or intruder is effectively contained.
Role of Efficient Carbon & Energy Harvest
This rate-related defense response is directly correlated to the magnitude of efficient photosynthetic harvest of carbon and energy by the plant. The more carbon and energy the plant harvests, and the more efficiently it does it, the more fuel is available to drive the plant’s machinery.
With respect to obligate parasites, such as viruses, the quick and timely initiation of a defense response by the host entails the rapid production of resistance compounds. Many of these resistance compounds are derivatives of phenolic compounds produced by the pentose phosphate pathway.
An important principle to remember is that almost all plant species and cultivars have the ability to mount a defense response. What determines whether or not that defense response becomes effective, however, is generally governed by the promptness and thoroughness of its activity. This is why I previously stated that “resistance is a rate-related phenomenon.” A physiologically efficient plant responds quickly to stress and/or pathogen challenge. Promptness of metabolic reactions is always superior in plants that have received precise balanced nutrition. Furthermore, a strong and sustained defense response can only occur in plants that have harvested sufficient carbon and energy in amounts well beyond those needed solely for growth and maturation.
Plant Prioritization of Carbon & Energy Utilization
Remember that the highest priority of plant growth and development is to reproduce. Thus, plants with meager carbon and energy harvest will channel this to the crop. Second in line for carbon and energy reserves are the support tissues, such as roots, leaves, shoots, and bark, as well as next season’s buds. Last in line are the resistance response reactions.
Thus, efficient physiological functions, particular carbon and energy harvest capacity, is a prerequisite for expressing resistance. Precise manipulation of the plant’s nutritional requirements will optimize the timely expression of resistance.
Key Model Examples of Inciting Expression of Resistance
For example, I have taken VFN tomato cultivars resistant to verticillium wilt, fusarium wilt and root-knot nematode, and compromised their physiology with imbalanced fertility. This caused them to become susceptible to all three agents to which they were previously resistant.
Conversely, I have taken Rutgers tomatoes, which are rated susceptible to verticillium wilt, fusarium wilt and root-knot nematode, and treated them with precisely balanced programs nutritional programs. They were subsequently resistant to all 3 of these pathogens. Thus, the primary criterion for the expression of resistance to stress and/or pathogen challenges is not in a unique set of genes, but rather providing nutrition, allowing the expression of inherent, latent resistance behaviors.
Examples of Virus Disease Remission
Our laboratory has incited effective resistance responses and disease remission responses in various plant species to a number of viral pathogens, including:
- Spotted wilt virus in tomatoes and peppers
- Prunus necrotic ringspot virus in almonds and cherries
- Cucumber mosaic virus in peppers and cucumbers
- Watermelon mosaic virus in papayas and watermelons
- Tobacco mosaic virus in tomatoes
This is best achieved by testing (1) tissue mineral analysis, (2) soil chemistry, (3) water chemistry and (4) soil biology at SunBurst PDC. All examined parameters are integrated and scrutinized towards the eventual development of a field-specific remedial program.
Should you encounter an outbreak of disease or unexplained malady (including herbicide drift and/or accidental toxicity sprays), we would welcome the opportunity to assist you in developing an effective, field-specific, problem-specific remedial program.