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The study aim was to determine the optimal gamma irradiation dose for mutation breeding in Triticum turgidum ssp. durum L. Root, shoot and seedling growth, as well as the efficiency of energy conversion into growth were determined to examine the growth retardation effects of gamma irradiation that are the result of DNA damage (bridges, ring chromosomes, micronuclei, incomplete mitosis) in Triticum turgidum ssp. durum L. The kernels were irradiated with doses of 50, 150, 250 and 350 Gy using a 60Cobalt gamma-ray source. The kernels were placed in germination paper at 25 °C to grow for a 132 h period for the determination of shoot and root growth and the efficiency of energy conversion into growth. Root tips were collected and fixated over a 47.5 h growth period for the determination of the chromosomal abnormalities and incomplete mitosis. The control differed highly significantly (p p

Mutation breeding is used to modify a specific character of a plant, while all other characteristics remain the same. Adaptation obtained through mutation breeding to biotic (disease and insect pest resistance) and abiotic (aluminum toxicity, drought, high temperature, salt tolerance) stresses leads to better harvest growth, yield and quality. The main aim is to promote the efficiency of energy conversion into growth as a tool for the prediction of the optimal gamma irradiation dosage for mutation breeding in wheat. Cytogenetic analysis done on Triticum turgidum ssp. durum cv. Orania will be presented in the form of nucleolar activity to determine incomplete mitosis as well as in the form of bridges, fragments, micronuclei and ring chromosomes that will be compared with the efficiency of energy conversion into growth. Studies done on two Triticum aestivum cultivars, namely Ratel and Kwartel, included observation of double spikes, reduction in fertility and determination of the window for the optimal dosage for mutation breeding. Cultivars/breeding lines that are more resistant to gamma irradiation have a wider window for the optimal dosage range for mutation breeding. The ideal gamma irradiation dosage range for the three cultivars, namely, Orania, Ratel and Kwartel were determined.

Ionizing irradiation induces positive or negative changes in plant growth (M1) depending on the amount of irradiation applied to seeds or plant parts. The effect of 50–350 Gy gamma irradiation of kernels on nucleolar activity, as an indicator of metabolic activity, in root tip cells of tetraploid wheat Triticum turgidum ssp. durum L. cv. Orania (AABB) was investigated. The number of nucleoli present in nuclei and micronuclei as well as the mitotic index in the different irradiation dosages was used as an indicator of the cells entering mitosis, the chromosomes with nucleolar organizer regions that are active as well as chromosome doubling in the event of unsuccessful mitotic division. Nucleolar activity was investigated from 17.5 to 47.5 h after the onset of imbibition to study the first mitotic division and its consequences on the cells that were in G2 and G1 phases at the time of gamma irradiation. Untreated material produced a maximum of four nucleoli formed by the nucleolar organizing regions (NORs) on chromosomes 1B and 6B. In irradiated material, additional nucleoli were noted that are due to the activation of the NORs on chromosome 1A in micronuclei. The onset of mitosis was highly significantly retarded in comparison to the control due to checkpoints in the G2 phase for the repairing of damaged DNA. This study is the first to report on the appearance of nucleoli in micronuclei as well as activation of NORs in the micronuclei that are inactive in the nucleus and the effect of chromosome doubling on nucleolar activity in the event of unsuccessful mitotic division.

BackgroundA 50% growth reduction of seedling height (GR50) after acute gamma irradiation of dormant kernels is widely used as a measure of irradiation damage to obtain the ideal irradiation dosage for mutation breeding. It became clear in recent years that the GR50 is not sensitive enough to predict the ideal gamma irradiation dosage for mutation breeding and it predicts a value that is higher than ideal. The study aim was to determine whether root, shoot and seedling growth on the one side and the efficiency of energy conversion into growth on the other are measuring different growth retardation effects of gamma irradiation that are the result of DNA damage (bridges, ring chromosomes, micronuclei, incomplete mitosis) in Triticum turgidum ssp. durum. If the efficiency of energy conversion into growth is measuring different effects, the usefulness of efficiency of energy conversion into growth to predict the optimal dosage for mutation breeding will be investigated. ResultsThe kernels were gamma irradiated from 50 - 350 Gy using a 60Cobalt source. The kernels were left to germinate and grow for a period of 132 hours for the shoot and root growth and the efficiency of energy conversion into growth determination and for a period of 47.5 hours for the determination of the number of bridges, ring chromosomes, micronuclei and incomplete mitosis. The control differed highly significantly from 50 Gy and higher dosages and from 250 Gy and higher dosages for root and shoot growth respectively and from 250 Gy for the efficiency of energy conversion into growth. There was a highly significant increase in the number of bridges and micronuclei between 50 Gy and 150 Gy together with the higher irradiation dosages and only from 250 Gy for the ring chromosomes and interphase cells with incomplete mitosis. Root and seedling growth on the one hand and the efficiency of energy conversion into growth on the other were found to be measuring different effects of gamma irradiation on plant growth. ConclusionThe optimal dosage for mutation breeding was determined by making use of the efficiency of energy conversion into growth.

Ionizing irradiation induces positive or negative changes in plant growth (M1) depending on the amount of irradiation applied to seeds or plant parts. The effect of 50-350 Gy gamma irradiation of kernels on nucleolar activity, as an indicator of metabolic activity, in root tip cells of tetraploid wheat Triticum turgidum ssp. durum L. cv. Orania (AABB) was investigated. The number of nucleoli present in nuclei and micronuclei as well as the mitotic index in the different irradiation dosages was used as an indicator of the cells entering mitosis, the chromosomes with nucleolar organizer regions that are active as well as chromosome doubling in the event of unsuccessful mitotic division. Nucleolar activity was investigated from 17.5 to 47.5 h after the onset of imbibition to study the first mitotic division and its consequences on the cells that were in G

The study was conducted to determine whether the efficiency of energy conversion into growth can be used as an indicator for the determination of the optimal gamma irradiation dosage for mutation breeding. To meet this objective, embryo growth, shoot growth, root growth, mobilization of food reserves, respiration and energy conversion were studied in gamma-irradiated wheat Triticum monococcum L. cultivar Einkorn kernels. Kernels were exposed to 50, 150, 250 and 350 Gy and germinated. Kernels were collected 12 h after onset of imbibition and then every 12 h until 168 h. Irradiated seed demonstrated retardation in all parameters, which increased as the gamma irradiation dosage increased. For the most, dosage and time, as well as dosage by time interaction were highly significant. Root growth appeared to be the most sensitive to gamma irradiation, followed by shoot growth, mobilization of food reserves and efficiency of energy conversion. Full recovery of the efficiency of energy conversion took place at 50 Gy, with an increase in inefficiency with an increase in dosage. The point where full recovery of efficiency of energy conversion into growth gives way to incomplete recovery (100 Gy) is in line with the suggested dosages for practical mutation breeding in Triticum monococcum L. by the FAO/IAEA and is therefore an ideal indicator for predicting the dosage that will be optimal for plant mutation breeding.

The original article was corrected. Author Muhammad Kundi should instead read: Muhammad Sohail.

To accelerate genetic gains in breeding, physiological trait (PT) characterization of candidate parents can help make more strategic crosses, increasing the probability of accumulating favorable alleles compared to crossing relatively uncharacterized lines. In this study, crosses were designed to complement “source” with “sink” traits, where at least one parent was selected for favorable expression of biomass and/or radiation use efficiency—source—and the other for sink-related traits like harvest-index, kernel weight and grains per spike. Female parents were selected from among genetic resources—including landraces and products of wide-crossing (i.e. synthetic wheat)—that had been evaluated in Mexico at high yield potential or under heat stress, while elite lines were used as males. Progeny of crosses were advanced to the F4 generation within Mexico, and F4-derived F5 and F6 generations were yield tested to populate four international nurseries, targeted to high yield environments (2nd and 3rd WYCYT) for yield potential, and heat stressed environments (2nd and 4th SATYN) for climate resilience, respectively. Each nursery was grown as multi-location yield trials. Genetic gains were achieved in both temperate and hot environments, with most new PT-derived lines expressing superior yield and biomass compared to local checks at almost all international sites. Furthermore, the tendency across all four nurseries indicated either the superiority of the best new PT lines compared with the CIMMYT elite checks, or the superiority of all new PT lines as a group compared with all checks, and in some cases, both. Results support—in a realistic breeding context—the hypothesis that yield and radiation use efficiency can be increased by improving source:sink balance, and validate the feasibility of incorporating exotic germplasm into mainstream breeding efforts to accelerate genetic gains for yield potential and climate resilience.

Seed germination, seedling growth, mitotic and nucleolar activity were investigated as indicators of metabolic activity in a diploid wheat, Triticum monococcum ssp. monococcum cv. Einkorn. Two developmental phases were identified, an initial lag phase during which reactivation of NOR's and the initiation of mitotic activity (10 h) took place prior to the appearance of the primary root (16 h). Dominance interactions were observed between the NOR's of chromosomes 1A and 5A with the NOR's of the one pair activated before the other and forming therefore larger nucleoli. The total number of nucleoli per 500 cells also varied according to the stages of the cell cycle over time. The mitotic activity had an initial exponential rise, but showed signs of flattening out after 10 h of mitosis with opposite levels of activity in the primary and first pair of lateral roots thereafter. Secondly, an exponential phase in root and shoot growth, mobilization of reserve food and respiration rate was observed during seedling growth. Comparisons were done on work from a previous investigation on two polyploid wheat accessions belonging toT. turgidum ssp. durum and T. aestivum species. T. monococcum displayed a higher embryo growth than the polyploids, that may be explained by having a lighter embryo and caryopsis weight that may influence the uptake of water and reactivation of metabolic activity. During the seedling growth period, the two polyploid species displayed a faster growth rate than the diploid probably due to the differences in the number of genomes, the hybrid nature of the polyploids and a more complex gene control in the polyploids.