Compost Uses and Markets
Compost Uses and Markets: Critical Info for Customers
Compost and other organic amendments are increasingly being used in agriculture to minimize losses from plant diseases. However, disease suppression with composts has been quite variable, limiting the widespread adoption of compost applications to control plant diseases in diverse cropping systems. Developing a better understanding of how composts suppress pathogens and diseases could increase the predictability of compost-induced disease suppression and, thereby, improve their effectiveness. Despite numerous investigations of compost-induced disease suppression, our understanding of the mechanisms that may lead to disease suppression remain insufficient to predict the pathosystems, soil conditions, and environmental conditions for which disease suppression may occur. Previous approaches to identify factors involved in disease suppression have focused largely on comparative analyses of the bulk properties of suppressive and nonsuppressive composts. A consistent pattern that has emerged from these studies is the central role of microbial activity in compost-induced disease suppression. These studies elucidate the mechanisms commonly associated with disease suppression that is observed when we apply compost and the working hypothesis is that compost suppresses pathogens via(1) nutrient competition, (2) parasitism, (3) antibiosis, and (4) induced systemic resistance (ISR). Nutrient competition occurs when a plant pathogen and the microorganisms found in compost compete for the same resource. For example, competition for plant exudates has been well documented. Several soil-borne plant pathogens are attracted to host plants through seed and root exudates. When compost microbes consume or alter exudates than the host is no longer detectable to the pathogen and suppression occurs. Parasitism is where one organism eats another. Trichoderma harzianum is a biocontrol fungus and a common example of where parasitism occurs in compost-mediated disease suppression. The hyphae of T. harzianum will wind around a pathogen, puncture its cell wall and consume the pathogen. Antibiosis refers to the ability of a biocontrol microorganism to produce antibiotics. Bacterial species such as Bacillus and Psuedomonas naturally produce antibiotics that are toxic to plant pathogens and eventually kill the pathogen. With ISR, a beneficial bacterium stimulates what can be loosely considered the plant’s ‘immune system’ so that it can protect itself from invading pathogens. These mechanisms, and a few others that have been recently identified, will be reviewed during the presentation in the context of cases studies and specific plant-pathogen interactions.