Mapping aluminum tolerance loci in cereals: a tool available for crop breeding

Aluminum (Al) toxicity is the main factor limiting crop productivity in acidic soils around the world. In cereals, this problem reduces crop yields by 30-40 percent. The use of DNA-based markers linked to phenotypic traits is an interesting alternative approach. Strategies such as molecular marker-assisted selection (MAS) in conjunction with bioinformatics-based tools such as graphical genotypes (GGT) have been important for confirming introgression of genes or genomic regions in cereals but also to reduce the time and cost of identifying them through genetic selection. These biotechnologies also make it possible to identify target genes or quantitative trait loci (QTL) that can be potentially used in similar crops to increase their productivity. This review presents the main advances in the genetic improvement of cereals for Al-tolerance.

Phytoplasma and virus detection in commercial plantings of Vitis vinifera cv. Merlot exhibiting premature berry dehydration

A new and devastating physiological disorder of Vitis vinifera cv. Merlot was recently reported, known as premature berry dehydration (PBD), which is characterized by plant growth reduction, induction of general senescence and pedicel necrosis in the fruit, causing significant reductions in vineyard production. The causes of this disease remain unclear and previous reports suggest that it may be associated with phloem disruption and water provision. For this reason, any factor causing phloem disturbances could cause an important change in the berry water status. As some micro-organisms have been reported to disrupt phloem flow, we analyzed the occurrence of phytoplasma and viruses in commercial vineyards presenting PBD. In this study, a phytoplasma was detected by electron microscopy and nested PCR while virus infections were diagnosed by RT-PCR in samples collected during two growing seasons. The presence of phytoplasma only in samples from grape plants with PBD suggests that this pathogen may be one of the causal agents of this disorder. We suggest that the influence of other factors, such as virus infections, agronomic handling and environmental conditions also modulate berry dehydration. This is the first study at the microscopic and molecular levels that correlates phytoplasma presence with PBD.

Expression of the crucifer-infecting TMV-Cg movement protein in tobacco plants complements in trans a TMV-U1 trafficking-deficient mutant

Tobamovirus movement proteins play a determinant role in the establishment of infections in plants, allowing the local movement of viral RNA genome through plasmodesmatas. We expressed the movement protein (MP) of the crucifer- and garlic-infecting Tobacco Mosaic Virus strain Cg (TMV-Cg) in both resistant Xanthi NN and sensitive Xanthi nn Nicotiana tabacum plants. MP-Cg function was assayed by inoculating transgenic plants with a trafficking-deficient mutant of TMV strain U1. Following infection, local necrotic lesions were developed in resistant transgenic plants, and a systemic infection was produced in sensitive tobaccos. Thus, movement function of the mutant virus was complemented in trans by MP-Cg expressed in transgenic plants, causing the same symptoms as wild-type strain. We demonstrated that the function of MP-U1 could be replaced efficiently by MP-Cg, even though these proteins share only 36% of identity. Similar hydrophobic patterns of MP-Cg and MP-U1 suggests structure and function conservations of both proteins. This work is an example of how two tobamoviruses differing in their host range help to understand viral movement mechanism during the infection.

Replicase mediated resistance against Potato Leafroll Virus in potato Desiree plants

Potato leafroll virus (PLRV) is a major menace for the potato production all over the world. PLRV is transmitted by aphids, and until now, the only strategy available to control this pest has been to use large amounts of insecticides. Transgenic approaches involving the expression of viral replicases are being developed to provide protection for plants against viral diseases. The purpose of this study was to compare the protection afforded by the differential expression of PLRV replicate transgene in potato plants cv. Desirée, Plants were genetically modified to express the complete sense PLRV replicase gene. Two constructions were used, one containing the constitutive 35SCaMV promoter and the other the phloem-specific RolA promoter from Agrobacterium rhizogenes. Transgenic plants were infected with PLRV in vitro, using infested aphids. In plants in which 35SCaMV controlled the expression of the PLRV replicase gene, signs of infection were initially detected, although most plants later developed a recovery phenotype showing undetectable virus levels 40 days after infection.