Antimicrobial enzymes such as chitinases, beta- glucanases, or peroxidases.

Antimicrobial proteins such as defensins, thionins, or PR-1.

Antimicrobial chemicals, including reactive oxygen species such as hydrogen peroxide or peroxynitrite, or more complex phytoalexins such as genistein or camalexin.

Cell wall reinforcement ( cellulose, lignin, suberin, callose, cell wall proteins).

Receptors that perceive pathogen presence and activate inducible plant defences.

Detoxifying enzymes that break down pathogen-derived toxins.

Antimicrobial chemicals (for example: polyphenols, sesquiterpene lactones, saponins).

Disease control is achieved by use of plants that have been bred for good resistance to many diseases, and by plant cultivation approaches such as crop rotation, pathogen-free seed, appropriate planting date and plant density, control of field moisture, and pesticide use.Ĭommon disease resistance mechanisms Pre-formed structures and compounds

However, disease control is reasonably successful for most crops. Across large regions and many crop species, it is estimated that diseases typically reduce plant yields by 10% every year in more developed nations or agricultural systems, but yield loss to diseases often exceeds 20% in less developed settings.

Plant pathogens can spread rapidly over great distances, vectored by water, wind, insects, and humans. Other epidemics include Chestnut blight, as well as recurrent severe plant diseases such as Rice blast, Soybean cyst nematode, Citrus canker. The current wheat stem rust, leaf rust and yellow stripe rust epidemics spreading from East Africa into the Indian subcontinent are caused by rust fungi Puccinia graminis and P. The world’s first mass-cultivated banana cultivar Gros Michel was lost in the 1920s to Panama disease caused by the fungus Fusarium oxysporum. The late blight Great Famine of Ireland of the 1840s was caused by the oomycete Phytophthora infestans. Plants in both natural and cultivated populations carry inherent disease resistance, but this has not always protected them. Plant disease resistance is crucial to the reliable production of food, and it provides significant reductions in agricultural use of land, water, fuel and other inputs. Plants consistently resist certain pathogens but succumb to others resistance is usually specific to certain pathogen species or pathogen strains. Although obvious qualitative differences in disease resistance can be observed when multiple specimens are compared (allowing classification as “resistant” or “susceptible” after infection by the same pathogen strain at similar inoculum levels in similar environments), a gradation of quantitative differences in disease resistance is more typically observed between plant strains or genotypes. However, plants do not have circulating immune cells, so most cell types exhibit a broad suite of antimicrobial defenses.

Disease outcome is determined by the three-way interaction of the pathogen, the plant and the environmental conditions (an interaction known as the disease triangle).ĭefense-activating compounds can move cell-to-cell and systematically through the plant's vascular system. Relative to a susceptible plant, disease resistance is the reduction of pathogen growth on or in the plant (and hence a reduction of disease), while the term disease tolerance describes plants that exhibit little disease damage despite substantial pathogen levels. Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Unlike the other two tomato blights, it doesn't affect the fruits or stems.Disease triangle with landscape-level disturbances Septoria blight, also known as septoria leaf spot, causes small dark spots less than an 1/8-inch in diameter all over the leaf. Late blight affects other species in the tomato family as well, such as potatoes and petunias. It can progress to engulf entire leaves, stems, and fruits, with the infected areas becoming covered in mold as they die. Late blight shows up later in the summer and is apparent by brown edges on the leaves of the plants, rather than spots in the center of the leaf. Early blight typically starts to affect tomatoes in early summer. The stems and fruits will develop dark, mushy spots as the disease progresses. Early Blight Advanced stage of late blightĮarly blight appears as pea- or dime-sized brown spots on the leaves that are lighter toward the center of the spot but exhibit a distinctive yellow border around the outer edge of the spot. There are several devastating fungal blights that attack tomatoes, some of which attack other species as well.

Crop blight definition