Plant disease resistance

About: Plant disease resistance is a(n) research topic. Over the lifetime, 12952 publication(s) have been published within this topic receiving 381820 citation(s). The topic is also known as: plant innate immunity.

Trichoderma species--opportunistic, avirulent plant symbionts.

Abstract: Trichoderma spp. are free-living fungi that are common in soil and root ecosystems. Recent discoveries show that they are opportunistic, avirulent plant symbionts, as well as being parasites of other fungi. At least some strains establish robust and long-lasting colonizations of root surfaces and penetrate into the epidermis and a few cells below this level. They produce or release a variety of compounds that induce localized or systemic resistance responses, and this explains their lack of pathogenicity to plants. These root-microorganism associations cause substantial changes to the plant proteome and metabolism. Plants are protected from numerous classes of plant pathogen by responses that are similar to systemic acquired resistance and rhizobacteria-induced systemic resistance. Root colonization by Trichoderma spp. also frequently enhances root growth and development, crop productivity, resistance to abiotic stresses and the uptake and use of nutrients.

Current Status of the Gene-For-Gene Concept

Abstract: One of the most successful means of controlling plant diseases has been the development of varieties with major or vertical resistance genes. This type of resistance is easily manipulated in a breeding program and is efIec­ tive until strains of the pathogen to which it does not confer resistance be­ come established. Then, if another gene that conditions resistance to the new strains of the pathogen is available, this resistance gene may be incorporated into the variety by the plant breeder. In doing this, the breeder either con­ sciously or unconsciously is applying the principle of the gene-far-gene hypothesis. Plants resistant to races that are virulent on old varieties possess the new resistance gene. With the diseases of some crops, this process has becn repeated at relatively frequent intervals (4D, 42, 82). However, in some instances a single gene has conferred adequate resistance for many years 80,82). In plant diseases caused by living organisms, the same phenomena: in­ fection type in rusts, percent of infected plants in smuts of cereals, fleck or lesion in apple scab, are criteria of both the reaction of the host and the pathogenicity of the parasite. They indicate the relative resistance or sus­ ceptibility of the host and the relative avirulence or virulence of the para­ site. The gene-for-gene hypothesis was proposed (20,25) as the simplest ex­ planation of the results of studies on the inheritance of pathogenicity in the .flax rust fungus, M elampsora lini. On varieties of flax, Linum usitatissimum that have one gene for resistance to the avirulent parent race, F 2 cultures of the fungus segregate into monofactorial ratios. On varieties having 2, 3, or 4 genes for resistance to the avirulent parent race, the F2 cultures segregate into bi-, trio, or tetra factorial ratios (20-22) respectively. This suggests that for each gene that conditions reaction in the host there is a correspond­ ing gene in the parasite that conditions pathogenicity. Each gene in either member of a host-parasite system may be identified only by its counterpart in the other member of the system.

Systemic resistance induced by rhizosphere bacteria

Abstract: Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species, and plants show variation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, siderophores, and salicylic acid (SA). Whereas some of the rhizobacteria induce resistance through the SA-dependent SAR pathway, others do not and require jasmonic acid and ethylene perception by the plant for ISR to develop. No consistent host plant alterations are associated with the induced state, but upon challenge inoculation, resistance responses are accelerated and enhanced. ISR is effective under field conditions and offers a natural mechanism for biological control of plant disease.

A receptor kinase-like protein encoded by the rice disease resistance gene, Xa21. - eScholarship

Abstract: The rice Xa21 gene, which confers resistance to Xanthomonas oryzae pv. oryzae race 6, was isolated by positional cloning. Fifty transgenic rice plants carrying the cloned Xa21 gene display high levels of resistance to the pathogen. The sequence of the predicted protein, which carries both a leucine-rich repeat motif and a serine-threonine kinase-like domain, suggests a role in cell surface recognition of a pathogen ligand and subsequent activation of an intracellular defense response. Characterization of Xa21 should facilitate understanding of plant disease resistance and lead to engineered resistance in rice.

A Receptor Kinase-Like Protein Encoded by the Rice Disease Resistance Gene, Xa21

Abstract: The rice Xa21 gene, which confers resistance to Xanthomonas oryzae pv. oryzae race 6, was isolated by positional cloning. Fifty transgenic rice plants carrying the cloned Xa21 gene display high levels of resistance to the pathogen. The sequence of the predicted protein, which carries both a leucine-rich repeat motif and a serine-threonine kinase-like domain, suggests a role in cell surface recognition of a pathogen ligand and subsequent activation of an intracellular defense response. Characterization of Xa21 should facilitate understanding of plant disease resistance and lead to engineered resistance in rice.