No abstract

To the extent of our knowledge, applications of DNA markers in marker-assisted breeding of cotton are handicapped due to low genetic diversity in cotton germplasm. Cotton leaf curl disease, a disease of viral origin, has substantially depressed cotton production in Pakistan, and this disease is also an emerging threat to the neighboring cotton-growing countries like China and India. The present study was designed to identify DNA markers, predominately simple sequence repeats (SSRs), associated with tolerance and/or resistance to the disease. Based upon 2 years of disease-screening field experiments, a total of 10 cotton genotypes (five highly tolerant, four highly susceptible, and one immune) of diverse origin were selected from the available cotton germplasm (~1200 accessions) of the National Institute for Biotechnology and Genetic Engineering, Faisalabad, Pakistan. In total, 322 SSRs derived from bacterial artificial chromosome end sequences of Gossypium raimondii (one of the progenitor species of cultivated tetraploid cotton) were screened. Out of these, 65 primer pairs were found polymorphic, and the extent of genetic similarity was in the range of 81.7% to 98.7%. A similarity matrix was used for studying their phylogenetic relationship using unweighted pair-group method with arithmetic means (UPGMA) analysis. The dendrogram showed the grouping of the genotypes into two distinct clusters comprising tolerant and susceptible genotypes, respectively. Out of the polymorphic markers, two SSR markers, PR-91 and CM-43, that were amplified only in tolerant genotypes showed significant association with resistance to the disease. These preliminary results set the stage for initiating indepth marker-trait association studies, which will be instrumental for initiating marker-assisted breeding in cotton.

Phytochrome (phy) photoreceptors are known to regulate plastic growth responses to vegetation shade. However, recent reports also suggest an important role for phys in carbon resource management, metabolism, and growth. Here, we use 13CO2 labelling patterns in multi-allele phy mutants to investigate the role of phy in the control of metabolic fluxes. We also combine quantitative data of 13C incorporation into protein and cell wall polymers, gas exchange measurements and system modelling to investigate why biomass is decreased in adult multi-allele phy mutants. Phy influences the synthesis of stress metabolites like raffinose and proline, and the accumulation of sugars, possibly through regulating vacuolar sugar transport. Remarkably, despite their modified metabolism and vastly altered architecture, growth rates in adult phy mutants resemble those of wild-type plants. Our results point to delayed seedling growth and smaller cotyledon size as the cause of the adult-stage phy mutant biomass defect. Our data signify a role for phy in metabolic stress physiology, carbon partitioning and illustrate that phy action at the seedling stage sets the trajectory for adult biomass production.

Sustainable production and improved genetic gains can be achieved by broadening the genetic window of elite wheat germplasm. Here, we induced mutations in two spring wheat varieties, viz., NN-Gandum-1 (NN-1) and Punjab-11 (Pb-11), by exposing their seeds to ethyl methane sulfonate (EMS) and γ-rays, respectively. We characterized >3500 lines of each NN-1 and Pb-11 derived population in three consecutive generations, viz., M5, M6, and M7, for important traits, e.g., plant height, heading date, spike morphology and rust resistance. We observed significant genetic variation and correlations in both populations for all investigated traits. We observed differences in terms of number of mutants between NN-1 (22.76%) and Pb-11 (26.18%) which could be ascribed to the genotype-by-mutagen interaction. High broad-sense heritability (H2) estimates, that are vital for higher genetic gains, were observed for all of the investigated traits in both populations (H2 = 0.69–0.91 in NN-1 and 0.84–0.98 in Pb-11). Particularly, to breed for rust resistance, we selected a subset (n = 239) of M7 lines that also showed phenotypic variation for other traits. Our studies (1) show the relevance to artificial mutagenesis to create genetic variation in elite germplasm for their immediate use in current breeding programs, and (2) provide material for downstream identification of genes associated with traits of high agronomic importance.