Predicting Wheat Leaf Rust Severity Using Planting Date, Genetic Resistance, and Weather Variables
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Leaf rust epidemics of wheat, caused by Puccinia recondita f. sp. tritici, were analyzed for the 1972 to 1990 growing seasons. The disease severity values recorded for leaf rust in early and late bread-wheat planting dates at Pergamino were used to identify the best genetic and environmental predictors of disease severity. Leaf rust severity (early planting date) could be predicted (R 2 = 0.88) as a function of heat accumulation (base daily mean temperature >12°C), days with relative humidity >70% without precipitation, and a cultivar resistance index. For late planting date, the predictive value of meteorological variables decreased, while the importance of the resistance index increased over that found for the early seeded trials. In general, predicted and observed leaf rust severity levels agreed during 1994 to 1996 at Pergamino, and for trials (1991) that were grown at some distance from the area where the original data for model development were recorded.Keywords:
Rust (programming language)
Wheat leaf rust
Soybean rust
In recent years soybean rust, caused by Phakopsora pachyrhizi has become one of the most serious threats to soybean production in Brazil. Breeding lines and varieties have been selected for resistance to soybean rust in Asia. However, differences in virulence between Asian and Brazilian rust populations should be considered in order to select and use resistant resources from Asia. Here, we suggest criteria for distinguishing resistant from susceptible types by the analysis of four resistance characters: frequency of lesions having uredinia, number of uredinia per lesion, frequency of open uredinia, and sporulation level, determined by the utilization of 63 genotypes. Under growth chamber conditions, a set of 13 soybean varieties were exposed to three rust populations-one from Japan and two from Brazil-and evaluated for the resistance characters mentioned above. The Japanese and Brazilian populations clearly differed in virulence, as did the two Brazilian populations. Only two resistance genes, Rpp4 from PI459025 and Rpp5 from Shiranui, commonly conferred resistance on all three rust populations. The number of resistant varieties or resistance genes useful in both countries appears limited. Therefore, a resistant cultivar that is universally effective against soybean rust should be developed by pyramiding some major resistance genes and by introducing horizontal resistance.
Phakopsora pachyrhizi
Rust (programming language)
Soybean rust
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Rust (programming language)
Puccinia recondita
Wheat leaf rust
Common wheat
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Wheat is the world's third big crop producing 600 million tonnes yearly. For example, wheat harvest in 2007 was 607 million tonnes compared to rice and maize production of rice was 652 million tonnes and production of maize was 785 million tonnes. Although, due to fungus diseases, we lose 10% of our crops yearly. Leaf rust (Lr), Stripe rust (Sr), and yellow rust (Yr) are the three types of rust that are present in wheat. In this article, we discussed leaf rust and its resistance genes. Leaf rust is also known as “Brown Rust”. This disease is caused by the fungus Puccinia recondita f. sp tritici, which is the most serious in common wheat (Triticum aestivum). These fungal pathogen-caused resistance genes degrade the amount and quality of wheat fields. Leaf rust is primarily found on leaves, but it can also infect glumes. Scientists studying the illness have discovered that there are many types of resistance genes present in Leaf rust, which is also known as Lr. Until today there are 80 resistance genes have been discovered in leaf rust (Lr). So, the resistance genes Lr1 to Lr3ka, Lr10 to Lr13, Lr14b to Lr17b, Lr20, Lr22b, Lr27, Lr30, Lr31, Lr33, Lr34, Lr46, Lr48, Lr49, Lr52, Lr60, Lr67 to Lr70, Lr73 to Lr75, Lr78 and Lr80 theses all resistance genes of leaf rust (Lr) present in wheat (Triticum aestivum). These genes, Lr9 and Lr76 were discovered in (Aegilops umbellulate). Lr14a is a subset of Lr14 (Triticum dicoccum). Lr18 and Lr50 (Triticum timopheevii). Lr19, Lr24, Lr29 (Thinopyrum ponticum). Lr21, Lr22a, Lr32, Lr39, Lr42 (Aegilops tauschii). Lr23, Lr61 and Lr72 are different LRs (Triticum turgidum ssp. Durum). Lr25, Lr26, and Lr45 (Secale cereale). Lr28, Lr35, Lr36, Lr47, Lr51, Lr66 (Aegilops speltoides). Lr37 is an abbreviated form of the word (Triticum ventricosum). Lr38 is a slang name for a (Thinopyrum intermedium). Lr44, Lr65 and Lr71 (Triticum aestivum spelta). Lr53 and Lr64 (Triticum dicoccides). Lr54 is the resistance gene assigned to (Aegilops kotschyi). Lr55 is slang (Elymus trachycaulis). Lr56(Aegilops sharonensis). Lr57(Aegilops geniculate). Lr58(Aegilops triuncialis). Lr59(Aegilops peregrina). Lr62 (Aegilops neglecta). Lr63 (Triticum monococcum). Lr77 (Santa Fe). Lr79 (Triticum durum). Different varieties of wheat include these resistance genes. These resistance genes were identified because farmers don’t use spares or toxic chemicals on wheat. After all, these chemicals affect human health, so these resistance genes were identified to save human health.
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Puccinia recondita
Wheat leaf rust
Puccinia
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Phakopsora pachyrhizi
Soybean rust
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Phakopsora pachyrhizi is adapted to a wide range of temperatures (15 to >30 degrees C) and can cause yield losses in all regions in which leaf wetness occurs for more than 6 hours. The first lesions often are visible within 4–5 days after infection under favorable conditions and the first fruiting bodies (uredinia) and urediniospores within 6–7 days. Under severe inoculum pressure, it is almost impossible to prevent some yield loss. Severe soybean rust causes early defoliation, reduced pod set, and reduced number and size of seeds. Thus, rust affects all yield components. The extent of loss depends on the growth stage during which the plants are infected, the inoculum pressure, and the ensuing environmental conditions. Yield losses may be as high as 100%. The earlier the infection occurs, the greater and faster the defoliation and consequently the higher the yield loss and the lower the grain quality. In severe cases, when defoliation occurs during vegetative, flowering, early pod set, or the beginning of pod fill, rust can cause enough yield loss that harvesting may not be economically justified.
Soybean rust
Phakopsora pachyrhizi
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Urediniospore
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During a three‐year project from 2003 to 2006, two models have been developed to predict leaf rust ( Puccinia recondita and P. triticina ) occurrence and to simulate disease incidence progress curves on the upper leaf layers of winter rye (PUCREC) and winter wheat (PUCTRI). As input parameters the models use air temperature, relative humidity and precipitation. PUCREC and PUCTRI firstly calculate daily infection favourability and a cumulative infection pressure index and, in a second step, disease incidence is estimated. An ontogenetic model (SIMONTO) is used to link disease predictions to crop development. PUCREC and PUCTRI have been validated with data from 2001 to 2005. Both models give satisfactory results in simulating leaf rust epidemics and forecasting dates when action thresholds for leaf rust control are exceeded.
Rust (programming language)
Wheat leaf rust
Winter wheat
Puccinia recondita
Puccinia
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Puccinia recondita
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Wheat leaf rust
Puccinia
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Genes for resistance to leaf rust(Lr) in twenty-four important wheat cultivars from six wheat breeding institutes or companies were analyzed using fourteen isolates of Puccinia triticina. Six Lr genes:Lr1,Lr3,Lr13,Lr23,Lr26,Lr30 of the fourty-four tested genes were postulated as present in nineteen wheat cultivars, either alone or in combinations. Of them, Lr1,Lr3,Lr26 were the main genes for resistance to leaf rust of the tested materials. Adult plant resistance of twenty-four wheat cultivars was identified with five Puccinia triticina pathotypes in the field. Two cultivars displayed good resistance at adult stage and three cultivars with the heterogeneous response and twelve cultivars with slow-rusting resistance.
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Leaf rust (caused by Puccinia recondita f. sp. tritici) is the most widespread and regularly occurring rust on wheat. Genetic resistance is the most economical method of reducing yield losses due to leaf rust. To date, 46 leaf rust resistance genes have been designated and mapped in wheat. Resistance gene expression is dependent on the genetics of host-parasite interaction, temperature conditions, plant developmental stage, and interaction between resistance genes with suppressors or other resistance genes in the wheat genomes. Genes expressed in seedling plants have not provided long-lasting effective leaf rust resistance. Adult-plant resistance genes Lr13 and Lr34 singly and together have provided the most durable resistance to leaf rust in wheat throughout the world. Continued efforts to isolate, characterize, and map leaf rust resistance genes is essential given the ability of the leaf rust fungus to overcome deployed resistance genes.
Rust (programming language)
Puccinia recondita
Wheat leaf rust
Puccinia
Stripe rust
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