Plant disease resistance

About: Plant disease resistance is a research topic. Over the lifetime, 12952 publications have been published within this topic receiving 381820 citations. The topic is also known as: plant innate immunity.

Induction and modulation of resistance in tomato plants against Fusarium wilt disease by bioagent fungi (arbuscular mycorrhiza) and/or hormonal elicitors (Jasmonic acid & Salicylic acid): 2-Changes in the antioxidant enzymes, phenolic compounds and pathogen related- proteins.

Abstract: Induction of plant defense against pathogen attack is regulated by a complex network of different signals. In the present study interaction between hormonal signals (jasmonic acid (JA) or salicylic acid (SA)) and bioagent (arbuscular mychorrhiza (AM) fungi) was used as new strategy to enhance tomato defense responses against wilt disease caused by Fusarium oxysporum (Fo). Thus changes in various physiological defenses including antioxidant enzymes, phenolic compounds and pathogenesis related (PR) proteins were investigated in leaves of tomato plants. Results appeared that 22 2 production of reactive oxygen species (ROS), mainly H O and O , and lipid peroxidation increased •- in tomato leaves by increasing the time of infection. Application with bioagent AM fungi and/or hormonal elicitors (JA & SA) markedly decreased these levels ,while LOX activity greatly increased as compared with infected control. SA- treated plants had the highest MDA level but JA + AM fungi treated plants recorded the highest LOX activity. Infection by Fusarium oxysporm significantly increased activity of antioxidant enzymes (SOD, APX and CAT) in tomato leaves at different stages of growth. T he highest activity was recorded in leaves of AM fungi + JA- treated plants, while 22 treatments with SA especially when applied alone markedly decreased H O scavenging enzymes 22 (APX and CAT) and greatly increased SOD activity. Thus, imbalance between H O -generation and scavenging enzymes in leaves may reflect a defense mechanism in tomato or a pathogenicity strategy of the fungus. Levels of certain phenolic acids greatly changed in tomato leaves in response to Fusarium oxysporum, AM fungi and hormonal elicitors. Benzoic and Galleic acids contents markedly decreased , however, contents of coumaric, cinnamic, chlorogenic and ferulic acids increased in leaves of all treatments. Also, activity of lignification enzymes POX, PPX and PAL significantly increased in leaves of infected tomato plants. JA-treated plants caused the highest POX and PPX activities, while SA-treated plants having the highest PAL activities. High accumulation of phenolic compounds and activity POX, PPX and PAL in these plants may reflect a component of many defense signals activated by bioagent and hormonal inducers which leading to the activation of power defense system in tomato against attack. Analysis of protein electrophoresis revealed that interaction between hormone signal (JA& SA) and bioagent AM fungi mediating the expression of the majority of different PR-proteins leading to increasing defense mechanism against Fusarium oxysporum infection. Thus, induction of protein bands of molecular weights 35, 33, 32, 31 (PR-2, â -1, 3 glucanase), 30.5 and 27 (PR-3,-4, chitinase) in infected leaves indicated the important role which played in disease resistance. Finally, the new mechanism of the combination strategy between bioagent and hormonal signals (either synergistically or antagonistically) played important roles for increasing various defense systems and altering expression of defense genes which leading to different PR-proteins working together to increased resistance in tomato plants against wilt disease caused by Fusarium oxysporum. In addition, results revealed that defense mechanism in plants treated with AM f ungi and JA are more effective than AM fungi plus SA- treated plants.

An experimental field study of anther-smut disease of Silene alba caused by Ustilago violacea: genotypic variation and disease incidence.

Abstract: Twenty cloned genotypes of Silene alba differed greatly (0-100%) in the percentage of flowering plants that became diseased by the anther-smut fungus Ustilago violacea following natural spore dispersal in a two-year field experiment. Male genotypes with the highest percentage of disease had high rates of flower production; this trait may increase the probability of spore deposition on flowers, a common site of infection. Because of this relationship, male genotypes with the highest percentage of disease also produced the most healthy flowers in the two-year period. Flowering early in the season was also a predictor of high disease levels for male genotypes in the first year. Variation among female genotypes in disease levels was not correlated with either flower production or phenology, suggesting that the sexes differ in their interaction with the pathogen. Plants of both sexes that remained nonreproductive the first year but flowered the second year could become diseased due to infection of vegetative tissue. Disease levels of the genotypes following natural spore dispersal were not correlated with disease levels of the genotypes following inoculation of vegetative tissue. This discrepancy points out that the methodology used to investigate genetic variation in disease resistance may affect the results obtained.

Occurrence and Impact of a New Leaf Rust Race on Durum Wheat in Northwestern Mexico from 2001 to 2003

Abstract: Durum wheat (Triticum turgidum var. durum) is the main irrigated winter crop in northwestern Mexico. Historically, leaf rust, caused by Puccinia triticina, had not induced significant losses to durum production in the area until 2001. That year, a new race, designated as BBG/BN, was detected that caused the most widely grown cultivar, Altar C84, which had remained resistant for 16 years, to become susceptible. Other recommended cultivars also became either moderately susceptible or susceptible. Detailed characterization of avirulence/virulence characteristics on Lr genes indicated that this race possibly did not evolve from the older races, but may have been introduced. Rust epidemics during the 2000-2001, 2001-2002, and 2002-2003 crop seasons have caused estimated losses of at least US$32 million. Although a majority of cultivars from 31 different countries, including the United States and Canada, and most of CIMMYT's durum wheat germ plasm were highly susceptible, diversity for both race-specific resistance and moderate levels of slow rusting resistance were identified. Jupare C2001, a resistant cultivar released in 2001, showed high levels of resistance and negligible losses in grain yield in a trial where Altar C84 suffered over 27% losses.

Pathogen-derived resistance provides papaya with effective protection against papaya ringspot virus.

Abstract: Transgenic Carica papaya plants (cv. Sunset, R0 clone 55-1) carrying the coat protein gene of papaya ringspot virus (strain HA 5-1) remained symptomless and ELISA-negative for 24 months after inoculation with Hawaiian strains of papaya ringspot virus under field conditions. Non-transgenic and transgenic control plants lacking the coat protein gene developed disease symptoms within one month after manual inoculation or within four months when natural aphid populations were the inoculum vectors. Mean trunk diameter was significantly greater in cloned 55-1 plants compared with virus-infected controls (14.7 cm versus 9.3 cm after 18 months). Fruit brix, plant morphology, and fertility of 55-1 plants were all normal, and no pleiotropic effects of the coat protein gene were observed. These results indicate that pathogen-derived resistance can provide effective protection against a viral disease over a significant portion of the crop cycle of a perennial species.