Attempts to eradicate graft-transmissible infections through somatic embryogenesis in <Emphasis Type="Italic">Citrus</Emphasis> ssp. and analysis of genetic stability of regenerated plants

Ability to detect Pseudocercospora macadamiae infection in macadamia husk at least four months before symptoms become visible will aid the development of disease control measures. This study examined the distinctness of P. macadamiae within the phylogenetic lineages of the genus Pseudocercospora. In addition, we developed two quantitative PCR (qPCR) assays, as rapid diagnostic tools, for early detection and quantification of P. macadamiae in planta. Phylogenetic analysis of concatenated sequences of four gene loci (large subunits, internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF-1α) and actin of 47 P. macadamiae isolates showed that P. macadamiae is a distinct species in the genus Pseudocercospora. P. macadamiae isolates were partitioned into subunits in the cluster but the grouping of the isolates was regardless of location. Nucleotide diversity (0.02) and the coefficient of genetic differentiation (0.07) were low in the P. macadamiae population. Two qPCR primer sets, based on ITS (PMI) and TEF-1α (PME) were designed that consistently amplified P. macadamiae in fungal cultures (Ct = 16.93 ± 0.11 and Ct = 21.20 ± 0.11, respectively) and in planta (Ct = 32.36 ± 0.28 and Ct = 38.07 ± 1.20, respectively). The PMI primers also detected species in the genus Pseudocercospora, while PME was more specific and robust for quantification of P. macadamiae. Both primer sets detected P. macadamiae in asymptomatic tissue samples and strongly differentiated various stages of disease progression, which revealed approximately 10-fold increase in fungal biomass between each consecutive stage of symptom development.     

Mapping association of molecular markers and sheath blight (<Emphasis Type="Italic">Rhizoctonia solani</Emphasis>) disease resistance and identification of novel resistance sources and loci in rice

Sheath blight (ShB) disease caused by Rhizoctonia solani is one of the major threats to rice crop world-wide. Progress in breeding for resistant rice varieties is limited due to lack of highly resistant germplasm against sheath blight. In present study, diverse rice landrace were phenotyped against R. solani and resistant and moderately resistant sources were identified from the panel of 134 germplasm pool. Landrace Nizam shait showed resistance, where as Bidar local-2, Jigguvaratiga, NavaliSali, Jaddu and Tetep exhibited moderate resistance. Population structure was analysed by genotyping the accessions using 63 genome wide Rice Microsatellite markers which divided the mapping panel into two groups. Association mapping using GLM?+?Q model of TASSEL indicated significant association between twenty-one marker loci on nine chromosomes with ShB resistance with phenotypic variation (R²) ranging 3.02–22.71 per cent. We identified 13 new markers to be associated with ShB resistance. The present work validates previously identified eight markers flanking different shB QTLs. None of the allele from the tested markers was unique and common among resistant and moderately resistant landraces identified in this work except allele 420 bp of RM337 and allele 310 bp of RM5556 noticed only in Tetep. Our findings predict the possible presence of unreported QTL region in marker interval of RM337 and RM5556 on chromosome 8 for ShB resistance in Tetep which invites further investigation.