Metatranscriptomics and small RNA analysis revealed that viral covert coinfection resulted in disease symptoms reminiscent of rice sterility

BackgroundViral pathogens are a major threat to stable crop production. The discovery of viral diseases traditionally concerns apparent infection that shows obvious symptoms in crop plants. However, little is known about the covert infection of crop plants by viruses. In this study, we used deep metatranscriptomic sequencing and small RNA analysis to identify covert infection of rice plants by viruses.ResultsOur results showed that introgression of the dominant brown planthopper (BPH) resistance gene Bph3 into the high-yielding but BPH-susceptible indica variety Ms55 via a backcross strategy significantly enhanced resistance to BPH. However, Bph3-carrying backcross lines infested by BPH exhibited panicle enclosure and failed to produce seed at the mature stage, which are typical characteristics of sterile rice plants. Using a metatranscriptomic analysis, we identified six RNA viruses in backcross line Rby1 and eleven RNA viruses in backcross line Rby2, including eight novel viruses that fell within existing families and orders. Furthermore, our small RNA analysis revealed the biogenesis of viral small interfering RNAs that represented active virus infection in rice plants.ConclusionBph3-carrying backcross rice lines are resistant to BPH but are susceptible to viral infection. We identified viral covert coinfection in sterile rice plants by deep metatranscriptomic sequencing and small RNA analysis. Our results suggested that covert coinfection of rice plants by RNA viruses resulted in disease symptoms reminiscent of rice sterility. To develop rice varieties resistant to BPH, it is necessary to introgress genes resistant to not only BPH but also viral infection.

Improved Tomato Fruit Color within an Inbred Backcross Line Derived from Lycopersicon esculentum and L. hirsutum Involves the Interaction of Loci

An inbred backcross (IBC) population derived from Lycopersicon hirsutum LA407 and L. esculentum was evaluated in replicated field trials to assess its potential for the improvement of red-fruited tomatoes. Significant phenotypic variation among genotypes was detected for the hue (tint), L (darkness), and chroma (saturation) of color. Significant effects due to environment and genotype × environment interactions also were observed. One superior inbred backcross line from this population, IBL 2349, was used to develop an F2 population and to explore the genetic basis of color. Two independent L. esculentum quantitative trait loci (QTL) associated with improved color were identified based on linkage to markers mapping to chromosome 4 and chromosome 11. Epistatic interactions were identified between the two L. esculentum loci. Unexpected epistatic interactions also were identified between L. esculentum loci and an LA407 introgression on chromosome 7 present within IBL 2349. The two L. esculentum QTL and the epistatic interactions were confirmed in replicated trials with F3 and F4 families. The loci identified in this study and their epistatic interactions may provide additional tools for the improvement of red-fruited tomatoes in breeding programs.

Acquired Resistance Functions in mlo Barley, Which Is Hypersusceptible to Magnaporthe grisea

Barley plants carrying a mutation in the Mlo (barley [Hordeum vulgare L.] cultivar Ingrid) locus conferring a durable resistance against powdery mildew are hypersusceptible to the rice blast fungus Magnaporthe grisea. It has been speculated that a functional Mlo gene is required for the expression of basic pathogen resistance and that the loss of Mlo function mediating powdery mildew resistance is an exception for this particular disease. Here, we report that the onset of acquired resistance (AR) after chemical as well as biological treatments is sufficient to overcome the hypersusceptible phenotype of backcross line BCIngridmlo5 (mlo) barley plants against M. grisea. Moreover, even barley plants bearing a functional Mlo gene and thus showing a moderate infection phenotype against rice blast exhibit a further enhanced resistance after induction of AR. Cytological investigations reveal that acquired resistance in mlo genotypes is manifested by the restoration of the ability to form an effective papilla at sites of attempted penetration, similarly to wild-type Mlo plants. In addition, the rate of effective papillae formation in Mlo plants was further enhanced after the onset of AR. These results demonstrate that treatments leading to the AR state in barley function independently of the Mlo/mlo phenotype and suggest that the Mlo protein is not a component of the AR signaling network. Moreover, it seems that only concomitant action of Mlo together with AR permits high level resistance in barley against blast. Higher steady state levels of PR1 and barley chemically induced mRNA correlate with higher disease severity rather than with the degree of resistance observed in this particular interaction.

AC Harper six-row feed barley

AC Harper is a six-row yellow aleurone, hulled, spring feed barley with smooth awns, suitable for the Canadian prairies. AC Harper was developed from a cross between a scald resistant backcross line of Galt and BT364, which has high grain yield and strong straw. It has a combination of high yield potential, good resistance to lodging, short straw, and resistance to scald. AC Harper has improved kernel plumpness, protein content, and kernel colour compared to the feed check, Brier.Key words: Hordeum vulgare L., barley (six-row spring feed)

Molecular markers linked to the leaf rust resistance gene Lr24 in different wheat cultivars

The aim of this study was to find molecular markers (RAPD and SCAR) for the wheat leaf rust resistance gene Lr24. A backcross line, RL 6064, possessing a single resistance gene to leaf rust (Lr24) and its recurrent parent 'Thatcher' were used to find RAPD markers linked to the Lr24 gene. Among 125 RAPD primers tested, only one (OP-H5) detected an additional band in the resistant line RL 6064. The genetic linkage of this molecular marker to Lr24 was tested on a segregating F2 population derived from a cross between the leaf rust resistant line RL 6064 and the susceptible line 'Chinese Spring'. This marker showed complete linkage to the Lr24 resistance gene. A more reliable and specific marker for this resistance gene was made by converting it into a sequence characterized amplified region (SCAR). The presence of a single amplification product allowed direct detection of the gene in the test tube by the addition of ethidium bromide. This SCAR marker linked to the leaf rust resistance gene Lr24 could be used easily in a practical breeding program. Key words : leaf rust, RAPD, SCAR, wheat, Agropyron elongatum.