Series Of Near-isogenic Lines Research Articles

Virulence and DNA fingerprinting analysis of Xanthomonas oryzae pv. oryzae identify a new pathotype in Guangxi, South China.

Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive diseases affecting rice worldwide. However, little is known about the population structure of this organism in Guangxi Zhuang Autonomous Region, South China. Here, pathotypic and DNA fingerprint analyses were conducted to characterize the isolates of Xoo collected from rice leaves in five districts of the region from 2013 to 2016. Their pathogenicity was tested by leaf clipping, and the DNA fingerprints were analyzed by repetitive sequence-based polymerase chain reaction and endogenous insertion sequence element-based polymerase chain reaction assays using the repetitive extragenic palindromic sequence and enterobacterial repetitive intergenic consensus primers, respectively. Pathogenicity assays of 70 representative isolates were conducted using a series of near-isogenic lines and two new pathotypes were identified. All the pathotypes were found to be incompatible with xa5 and Xa7. One pathotype was virulent to Xa14, Xa21, and Xa23, whereas another virulent to Xa21 and Xa23, but incompatible with Xa14. A dendrogram generated for the data sets obtained from DNA fingerprinting suggested the prevalence of high genetic diversity of Xoo throughout Guangxi, and no association between the molecular haplotypes and pathotypes was identified.

Genetic analysis of Phn7.1, a major QTL conferring partial resistance to Phytophthora nicotianae in Nicotiana tabacum

The oomycete Phytophthora nicotianae is one of the most economically important pathogens affecting tobacco (Nicotiana tabacum L.). Genetic resistance is a preferred means of managing damage caused by Phytophthora, and genes conferring partial resistance are likely to be more durable over time than those controlling immunity. Characterization of specific genetic variability controlling partial disease resistance may aid the development of long-term strategies for minimizing crop plant disease loss. Previous mapping studies identified a quantitative trait locus (QTL) designated as Phn7.1 controlling partial P. nicotianae resistance. Favorable alleles at this QTL have been identified in cigar tobacco cultivars ‘Beinhart 1000’ and ‘Florida 301,’ and were thought to also be present in most modern elite US flue-cured tobacco germplasm. To gain increased insight of the location and effect of Phn7.1, this QTL was mapped using an increased number of molecular markers (SNPs) in the genomic region of interest. A series of near isogenic lines (NILs) and sub-NILs carrying the Phn7.1-associated genomic region introgressed from Beinhart 1000 in the genetic background of susceptible variety Hicks were developed and evaluated. The region was found to have an additive effect on resistance and the corresponding QTL was localized to within a genetic interval of approximately 3 cM. Genotyping of historical materials with Phn7.1-associated SNP markers strongly suggests that the favorable Phn7.1 allele(s) is present in most modern US flue-cured cultivars and absent in early predecessor germplasm. Information from this study may be useful in marker-assisted selection and for identification of Phn7.1 candidate genes in future investigations.

Variabilidade de Pyricularia oryzae Cav. em genótipos de arroz

A brusone, causada pelo fungo Pyricularia oryzae Cav., é uma das mais importantes doenças da cultura do arroz. O conhecimento das raças do fungo permite direcionar o melhoramento genético, visando ao desenvolvimento de cultivares resistentes. Este trabalho objetivou determinar a variabilidade do fungo e a prevalência de raças, em genótipos de arroz irrigado; avaliar as reações das linhagens quase isogênicas de CO 39 aos isolados de P. oryzae; e identificar os genótipos de arroz que possuem genes complementares de resistência a estes isolados. O estudo foi realizado com 36 isolados de P. oryzae, coletados em 18 cultivares de arroz irrigado, em quatro municípios do Rio Grande do Sul. Foram identificadas 21 raças, ocorrendo maior frequência das raças do grupo IA, em todos os locais de coleta, destacando-se, dentre elas, a IA-1. Reação de resistência foi observada nas cultivares BRS Firmeza, Bluebelle, Te-tep e BRS 7 (Taim) e de susceptibilidade em Fanny, Dawn, BRS Pelota e BRS Atalanta. A série de linhagens quase isogênicas obtidas da cultivar CO 39 foi resistente aos isolados na seguinte ordem: C101 A51 (resistente para todos os isolados); C101 PKT (12); C104PKT (11); C105HP4L23 (8); e C101-LAC (3). A partir do estudo destes isolados, concluiu-se que há variabilidade de P. oryzae, prevalência da raça IA, maior tolerância da cultivar BRS Firmeza e que o gene Pi-2 confere resistência à brusone, em todos os isolados analisados.

Analysis of a QTL for Spike Nodding Trait on Barley Chromosome 7(5H) Using Near Isogenic Lines

Nodding of barley spikes is a useful trait that decreases weathering damage. Peduncle curvature, along with the curvature of spike itself, determines the nodding of spikes. A major quantitative trait locus (QTL) for spike nodding as a result of peduncle curvature was previously mapped on barley chromosome 7(5H) using Steptoe × Morex doubled haploid mapping population. In the present study, spike nodding trait of Steptoe was successfully transferred into Morex background using RFLP markers, and a series of near isogenic lines were developed. Analysis of near isogenic lines located the QTL in a 43 cM interval flanked by ABG473-R3226 markers. A near isogenic line (H18) that contains up to 70 cM of Steptoe chromosome 7 was studied under field conditions. Kernel brightness and wort color and wort clarity properties were improved in HI8 compared to recipient cultivar Morex. However, yield of HI 8 was somewhat lower than that of Morex. A more detailed study of the QTL region, especially for grain yield, is required before the use of this locus in malting barley breeding programs.

A Genetic Approach to Studying the Morphology, Structure and Function of Starch Granules using Pea as a Model

A series of near-isogenic lines have been developed for mutations induced and identified at six independent loci controlling steps in starch biosynthesis of pea (Pisum sativum) seeds. The review describes the methodology associated with the development of these lines and with the characterisation of the starches produced, in particular the effects that the mutations have on the morphology, structure and properties of the starch granules. The shape of starch granules from lines containing mutations at either the r or rug5 loci, encoding a starch branching enzyme and a soluble starch synthase, differ significantly from granules found in the non-mutant parental line. Mutations at each of the six loci result in characteristic changes in granular structure, which has been studied using polarised light microscopy, wide angle X-ray diffraction, solid state NMR and differential scanning calorimetry. Relatively small but significant changes were found in the proportion of crystalline material within the granules and much greater differences in the spatial distribution of the crystals within the granules. In particular, granules from rand rugs mutants do not show the characteristic 'Maltese cross' pattern when viewed under polarised light. Large differences were found between the mutants in the proportion of A- and B-type crystallites within the granules, ranging from about 60% A-type in rug3 mutants to 100% B-type in rmutant lines. It is suggested that the pea lines are an invaluable resource for answering fundamental questions on the genetic control of starch granule structure and function.

Factors affecting systemic infection of Pisum sativum by Peronospora viciae

Glasshouse experiments with a series of near-isogenic lines showed that the st gene, which reduces stipule area, and the tl gene, which converts tendrils to leaflets, considerably increased susceptibility to systemic infection with Peronospora viciae . Similar effects were observed with these pea lines when naturally infected in the field, indicating that direct infection of the apex is an important route for systemic infection and that its incidence is influenced by morphology of the apical primordia. In a growth room experiment at 25 °C where leaf necrosis was associated with inhibited sporulation, symptomless invasion of the stem tissues resulted in systemic infection, indicating that some apical infection may originate from leaf lesions under high temperature conditions.