Overwintering and growth regulator treatment effects on celery (Apium graveolens L.) flowering and seed production

Celery (Apium graveolens L.) plants cv. Jason overwintered in a polythene tunnel flowered earlier and grew taller than similar plants given a 10-week cold-treatment at 5°C prior to transplanting in the same tunnel in mid-February. However, there was no significant difference in the yield of seeds obtained from both treatments, plants grown at a density of 4m^-2 yielded less seeds than those at 2m^-2, though the yield per unit area was slightly higher from the high density treatment. Treatment with 100 mgl^-1 GA₃ applied twice just prior to flowering and during anthesis increased flower stalk, flower pedicel and stamen length but delayed flower opening and seed ripening and decreased seed set and seed yield. Treatment with a mixture of 1000 mgl^-1 GA₄ and GA₇ plus 1000 mgl^-1 ethephon on three occasions during seed ripening decreased seed yield and reduced seed germination though those seeds capable of germinating were less dormant than seeds from untreated plants. The size distribution of seeds was unaffected by any treatment other than the preseeding spray with GA₃ which reduced the percentage of medium-size seeds.     

Effects of plant genotype and growth stage on the structure of bacterial communities associated with potato (Solanum tuberosum L.)

The effects of genotype, plant growth and experimental factors (soil and year) on potato-associated bacterial communities were studied. Cultivars Achirana Inta, Désirée, Merkur and transgenic Désirée line DL12 (containing T4 lysozyme gene) were assessed in two field experiments. Cross-comparisons between both experiments were made using Désirée plants. Culture-dependent and -independent approaches were used to demonstrate effects on total bacterial, actinobacterial and Pseudomonas communities in bulk and rhizosphere soils and endospheres. PCR-denaturing gradient gel electrophoresis fingerprints prepared with group-specific primers were analyzed using multivariate analyses and revealed that bacterial communities in Achirana Inta plants differed most from those of Désirée and Merkur. No significant effects were found between Désirée and DL12 lines. Plant growth stage strongly affected different plant-associated communities in both experiments. To investigate the effect of plant-associated communities on plant health, 800 isolates from rhizospheres and endospheres at the flowering stage were tested for suppression of Ralstonia solanacearum biovar 2 and/or Rhizoctonia solani AG3. A group of isolates closely resembling Lysobacter sp. dominated in young plants. Its prevalence was affected by plant growth stage and experiment rather than by plant genotype. It was concluded that plant growth stage overwhelmed any effect of plant genotype on the bacterial communities associated with potato.