Empirical threshold values for quantitative trait mapping.

The development of linkage maps with large numbers of molecular markers has stimulated the search for methods to map genes involved in quantitative traits (QTLs). A promising method, proposed by Lander and Botstein (1989), employs pairs of neighbouring markers to obtain maximum linkage information about the presence of a QTL within the enclosed chromosomal segment. In this paper the accuracy of this method was investigated by computer simulation. The results show that there is a reasonable probability of detecting QTLs that explain at least 5% of the total variance. For this purpose a minimum population of 200 backcross or F2 individuals is necessary. Both the number of individuals and the relative size of the genotypic effect of the QTL are important factors determining the mapping precision. On the average, a QTL with 5% or 10% explained variance is mapped on an interval of 40 or 20 centiMorgans, respectively. Of course, QTLs with a larger genotypic effect will be located more precisely. It must be noted, however, that the interval length is rather variable.

Accuracy of mapping quantitative trait loci in autogamous species.

Chapter 1 Citrus Rootstocks for Improving the Horticultural Performance and Physiological Responses under Constraining Environments Rafael V Ribeiro, Erick Espinoza-Nunez, Jorgino Pompeu Junior, Francisco A A Mourao Filho and Eduardo C Machado Chapter 2 Role of Silicon in Enrichment of Plant Nutrients and Protection from Biotic and Abiotic Stresses Durgesh Kumar Tripathi, Vijay Pratap Singh, Savita Gangwar, Sheo Mohan Prasad, Jagat Narayan Maurya and Devendra Kumar Chauhan Chapter 3 Transgenic Approaches for Phytoextraction of Heavy Metals Atul Bhargava and Shilpi Srivastava Chapter 4 Using an Allometric Model for the Accumulation of Mineral Nutrients in Crops Under Saline-Water Stress: A Field Experience in Fertigation Enrique Misle, Besma Kahlaoui, Estrella Garrido and Mohamed Hachicha Chapter 5 Control of Biotic and Abiotic Stresses in Cultivated Plants by the Use of Biostimulant Microorganisms Adriano Sofo, Maria Nuzzaci, Antonella Vitti, Giuseppe Tataranni and Antonio Scopa Chapter 6 Cyclic Nucleotides and Nucleotide Cyclases in Plants under Stress Malgorzata Pietrowska-Borek, Tamara Chadzinikolau and Slawomir Borek Chapter 7 Breeding and Transgenic Approaches for Development of Abiotic Stress Tolerance in Rice Satendra K Mangrauthia, P Revathi, Surekha Agarwal, Arun Kumar Singh and V P Bhadana Chapter 8 Mineral Bioavailability Through Mutation Breeding In Pulse Crops: A Review Mohammad Imran Kozgar, Mohd Rafiq Wani, Samiullah Khan and Parvaiz Ahmad Chapter 9 Abiotic Stress and Control of Yield in Cereals Bhinu V-S Pillai and Sreekala Chellamma Chapter 10 Improvement of Crop Production under Saline Stress by a Bio-Hydraulic Approach Besma Kahlaoui, Mohamed Hachicha, Enrique Misle, Belgacem Hanchi and Jorge Teixeira Chapter 11 Induced Mutagenesis for the Improvement of Pulse Crops with Special Reference to Mungbean-A Review Update Mohd Rafiq Wani, M Imran Kozgar, Samiullah Khan, M Abbas Ahangar and Parvaiz Ahmad Chapter 12 Crop Improvement through Tissue Culture L F De Filippis Chapter 13 Agricultural Pollution: An Emerging Issue Aqsa Abbasi, Ayesha Sajid, Namra Haq, Sammia Rahman, Zujaja-Tul-Misbah, Gul Sanober, Muhammad Ashraf and Alvina Gul Kazi

Improvement of Crops in the Era of Climatic Changes

Rapid identification of agronomically important genes is of pivotal interest for crop breeding. One source of such genes are crop wild relative (CWR) populations. Here we used a CWR population of <200 wild beets (B. vulgaris ssp. maritima), sampled in their natural habitat, to identify the sugar beet (Beta vulgaris ssp. vulgaris) resistance gene Rz2 with a modified version of mapping-by-sequencing (MBS). For that, we generated a draft genome sequence of the wild beet. Our results show the importance of preserving CWR in situ and demonstrate the great potential of CWR for rapid discovery of causal genes relevant for crop improvement. The candidate gene for Rz2 was identified by MBS and subsequently corroborated via RNA interference (RNAi). Rz2 encodes a CC-NB-LRR protein. Access to the DNA sequence of Rz2 opens the path to improvement of resistance towards rhizomania not only by marker-assisted breeding but also by genome editing.

/pdf/crop-wild-relative-populations-of-beta-vulgaris-allow-direct-244h8h7uwi.pdf

Crop wild relative populations of Beta vulgaris allow direct mapping of agronomically important genes

Amplified fragment length polymorphism (AFLP™) is one of the most widely applied molecular marker detection systems used today. Among the reasons for its popularity are its reproducibility, capacity to generate large numbers of data points in a single assay, and “off-the-shelf” universal applicability. The original AFLP protocol was developed using radioactive detection. The transfer of this technique to fluorescent detection on automated DNA fragment analysers not only removed the undesirable requirement for radioactivity but also provided the possibility for increased effectiveness and detection throughput. Unfortunately, a number of problems are frequently encountered with fluorescent AFLPs, particularly failure to amplify high molecular-weight fragments and generation of nonuniform peak distributions. Here, we describe an improved generic protocol for fluorescent AFLPs achieved mainly thorough optimization of the multiplexed selective amplification reaction. This improved protocol gives increased prod...

Getting the most out of fluorescent amplified fragment length polymorphism

Sugar-beet powdery mildew, caused by the fungus Erysiphe betae, now occurs in all sugar-beet growing areas and can reduce sugar yield by up to 30%. Powdery mildew resistant plants from three novel sources were crossed with sugar beet to generate segregating populations. Evaluation of resistance was carried out in artificially inoculated field and controlled environment tests. The resistance level in two of the sources was found to be significantly higher than that in currently available sugar-beet cultivars. AFLP analysis was used in combination with bulked segregant analysis to develop markers linked to the resistant phenotype in each population. Five dominant major resistance genes were identified and assigned the proposed symbols Pm2 to Pm6. Pm3 conferred complete resistance to powdery mildew; the other genes conferred high levels of partial resistance. From the use of anchoring SNP markers, two genes were located to chromosome II and three to chromosome IV. Two of the genes on chromosome IV mapped to the same location and one of the genes on chromosome II mapped to the same region as the previously identified Pm1 gene. With the availability of these genes there is now excellent potential for achieving durable resistance to sugar-beet powdery mildew, thus reducing or obviating the need for chemical control.

Mapping of five resistance genes to sugar-beet powdery mildew using AFLP and anchored SNP markers

Beet yellows virus (BYV) can dramatically reduce yield from sugar beet crops. A BYV resistant plant from a Beta germplasm accession was crossed with a sugar beet plant to generate the segregating population BYV1. This population was evaluated for BYV resistance and analysed with amplified fragment length polymorphism and single-nucleotide polymorphism markers to identify resistance loci. At 2 weeks after inoculation a number of plants displayed either mosaic or vein-clearing disease symptoms on infected leaves. The locus that largely controlled this disease reaction was mapped to chromosome IV. We refer to this novel genetic locus as Vc1. Three BYV resistance quantitative trait loci (QTLs) were identified and mapped to chromosomes III, V and VI. QTL mapping results suggested that the chromosome III and V QTLs acted only in plants with mosaic symptoms and that the chromosome VI QTL acted only in plants with the mosaic symptom allele of Vc1. These findings agreed with further statistical tests using general linear model analysis. There is now the potential to breed for BYV resistance using molecular marker technology.

The action of three Beet yellows virus resistance QTLs depends on alleles at a novel genetic locus that controls symptom development

Sugar beet (Beta vulgaris ssp. vulgaris L.) has a relatively narrow genetic base and several programmes have sought to evaluate the potential for introducing novel traits from wild and cultivated Beta germplasm into the crop. In particular, resistance to important sugar beet diseases has been identified within individual Beta accessions. We report here the successful transfer of resistance to Beet mild yellowing virus (BMYV) from garden beet, fodder beet and leaf beet accessions to progeny populations in initial crosses with sugar beet. Twelve plant populations derived from different Beta accessions were inoculated with viruliferous aphids carrying BMYV and the virus content of individual plants subsequently quantified by an ELISA test. Seven populations were significantly more resistant than a control sugar beet cultivar (P ≤ 0.05). BMYV resistance was successfully inherited in BC 1 and BC 2 generations, suggesting that resistance could potentially be introgressed from these sources into elite sugar beet lines.

Beet mild yellowing virus resistance derived from wild and cultivated Beta germplasm

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Mapping of five resistance genes to sugar-beet powdery mildew using AFLP and anchored SNP markers

The action of three Beet yellows virus resistance QTLs depends on alleles at a novel genetic locus that controls symptom development

Beet mild yellowing virus resistance derived from wild and cultivated Beta germplasm