Leaf spot

About: Leaf spot is a research topic. Over the lifetime, 5865 publications have been published within this topic receiving 46238 citations.

Quantitative trait loci controlling resistance to gray leaf spot in maize.

Abstract: Gray leaf spot (GLS) (caused by Cercospora zeae-maydis Theon & Daniels) is a fungal disease of the maize (Zea mays L.) that can cause significant grain yield reductions. Quantitative resistance to GLS does exist; therefore, one method of controlling the disease is to develop hybrids with genetic resistance. The objective of this study was to identify quantitative trait loci (QTL) and type-of-gene action for GLS resistance in segregating families of three single-cross populations of maize using restriction fragment length polymorphisms (RFLPs) (.)

Mycosphaerella fijiensis, the black leaf streak pathogen of banana: progress towards understanding pathogen biology and detection, disease development, and the challenges of control

Abstract: SUMMARY Background: Banana (Musa spp.) is grown throughout the tropical and subtropical regions of the world.The fruits are a key staple food in many developing countries and a source of income for subsistence farmers. Bananas are also a major, multibilliondollar export commodity for consumption primarily in developed countries, where few banana cultivars are grown. The fungal pathogen Mycosphaerella fijiensis causes black leaf streak disease (BLSD; aka black Sigatoka leaf spot) on the majority of edible banana cultivars grown worldwide.The fact that most of these cultivars are sterile and unsuitable for the breeding of resistant lines necessitates the extensive use of fungicides as the primary means of disease control. BLSD is a significant threat to the food security of resource-poor populations who cannot afford fungicides, and increases the environmental and health hazards where large-acreage monocultures of banana (Cavendish subgroup, AAA genome) are grown for export. Taxonomy: Mycosphaerella fijiensis M. Morelet is a sexual, heterothallic fungus having Pseudocercospora fijiensis (M. Morelet) Deighton as the anamorph stage. It is a haploid, hemibiotrophic ascomycete within the class Dothideomycetes, order Capnodiales and family Mycosphaerellaceae. Its taxonomic placement is based on DNA phylogeny, morphological analyses and cultural characteristics. Disease symptoms and host range:Mycosphaerella fijiensis is a leaf pathogen that causes reddish-brown streaks running parallel to the leaf veins, which aggregate to form larger, darkbrown to black compound streaks.These streaks eventually form fusiform or elliptical lesions that coalesce, form a water-soaked border with a yellow halo and,eventually,merge to cause extensive leaf necrosis. The disease does not kill the plants immediately, but weakens them by decreasing the photosynthetic capacity of leaves, causing a reduction in the quantity and quality of fruit, and inducing the premature ripening of fruit harvested from infected plants. Although Musa spp. are the primary hosts of M. fijiensis, the ornamental plant Heliconia psittacorum has been reported as an alternative host. New opportunities: Several valuable tools and resources have been developed to overcome some of the challenges of studying this host‐pathogen system. These include a DNAmediated fungal transformation system and the ability to conduct targeted gene disruptions, reliable quantitative plant bioassays,diagnostic probes to detect and differentiate M. fijiensis from related pathogens and to distinguish strains of different mating types, and a genome sequence that has revealed a wealth of gene sequences and molecular markers to be utilized in functional and population biology studies.

Molecular systematics of citrus-associated Alternaria species.

Abstract: The causal agents of Alternaria brown spot of tangerines and tangerine hybrids, Alternaria leaf spot of rough lemon and Alternaria black rot of citrus historically have been referred to as Alternaria citri or A. alternata. Ten species of Alternaria recently were described among a set of isolates from leaf lesions on rough lemon (Citrus jambhiri) and tangelo (C. paradisi × C. reticulata), and none of these isolates was considered representative of A. alternata or A. citri. To test the hypothesis that these newly described morphological species are congruent with phylogenetic species, selected Alternaria brown spot and leaf spot isolates, citrus black rot isolates (post-harvest pathogens), isolates associated with healthy citrus tissue and reference species of Alternaria from noncitrus hosts were scored for sequence variation at five genomic regions and used to estimate phylogenies. These data included 432 bp from the 5' end of the mitochondrial ribosomal large subunit (mtLSU), 365 bp from the 5' end of the beta-tubulin gene, 464 bp of an endopolygalacturonase gene (endoPG) and 559 and 571 bp, respectively, of two anonymous genomic regions (OPA1-3 and OPA2-1). The mtLSU and beta-tubulin phylogenies clearly differentiated A. limicola, a large-spored species causing leaf spot of Mexican lime, from the small-spored isolates associated with citrus but were insufficiently variable to resolve evolutionary relationships among the small-spored isolates from citrus and other hosts. Sequence analysis of translation elongation factor alpha, calmodulin, actin, chitin synthase and 1, 3, 8-trihydroxynaphthalene reductase genes similarly failed to uncover significant variation among the small-spored isolates. Phylogenies estimated independently from endoPG, OPA1-3 and OPA2-1 data were congruent, and analysis of the combined data from these regions revealed nine clades, eight of which contained small-spored, citrus-associated isolates. Lineages inferred from analysis of the combined dataset were in general agreement with described morphospecies, however, three clades contained more than one morphological species and one morphospecies (A. citrimacularis) was polyphyletic. Citrus black rot isolates also were found to be members of more than a single lineage. The number of morphospecies associated with citrus exceeded that which could be supported under a phylogenetic species concept, and isolates in only five of nine phylogenetic lineages consistently were correlated with a specific host, disease or ecological niche on citrus. We advocate collapsing all small-spored, citrus-associated isolates of Alternaria into a single phylogenetic species, A. alternata.

Disease and insect resistance in rice.

Abstract: Publisher Summary This chapter reviews the progress made in developing rice that is resistant to diseases and insects. Among cereal crops, rice is the host of the largest number of diseases and insect pests. These cause serious yield loss annually. The magnitude of loss caused by diseases and insects, increases as the level of rice production per unit area increases. The chapter discusses the nature of the disease or insect, its distribution, genetic variability of the pathogen, host resistance, genetics of resistance, and breeding for resistance. Fungal diseases attack the plant foliage, stems, roots, leaf sheath, or inflorescence, and grains. Four fungal diseases: blast, sheath blight, brown spot, and narrow brown leaf spot; two bacterial diseases: bacterial blight and bacterial streak; and five virus diseases: tungro, grassy stunt, stripe, dwarf, and hoja blanca have been discussed in the chapter. To minimize yield loss from disease and insect attacks, varieties with multiple resistances to most major diseases and insects are required. Also, a systematic international survey of races or biotypes of major diseases and insects should be carried out with the use of differential varieties.