Variations in the Phenolic Contents of Cocoyam Clones in Correlation to Resistance to Pythium Myriotylum
Phenolic compounds from leaves and roots of infected and healthy cocoyam clones resistant (RO1075), tolerant (RO1043), and susceptible (RO1157) to Pythium myriotylum were quantified and tested for their in vitro fungitoxicity on the causal agent of the cocoyam root rot disease. All clones, infected or not, have phenolic compounds showing fungitoxic activity. The phenolic content of the tolerant and susceptible clones is less than that observed in the resistant one meanwhile in the resistant clone RO1075, a large increase in phenolic content is observed particularly in the roots during attack by pathogen.
In vitro induction of multiple shoots, plant regeneration and tuberization from shoot tips of cocoyam
Des apex de macabo ont ete cultives sur milieu de Murashige et Skoog additionne de saccharose 3% et d'agar 0,3 %. Les bourgeons axillaires sont obtenus apres 15 jours de culture sur le milieu additionne de 6-benzylaminopurine jusqu'a 5 mM, avec un maximum a la derniere sous-culture. En revanche, la proliferation de bourgeons adventifs est obtenue apres culture dans les memes conditions, mais sur des milieux contenant differents rapports d'acide α-naphtalene acetique et de kinetine ou de 6-benzylaminopurine. Une microtuberisation peut etre observee apres 4 mois a partir de bourgeons axillaires, ou apres 2 mois a partir de bourgeons adventifs sur des milieux additionnes d'acide α-naphtalene acetique 1 mM. L'induction de cals peut etre obtenue par culture d'apex sur des milieux additionnes de 0,7 % d'agar et de concentrations elevees en acide 2,4-dichlorophenoxyacetique et faibles en 6-benzylaminopurine, alors que des rapports inverses de concentration permettent l'organogenese.
Temperature effects on lily development rate and morphology from the visible bud stage until anthesis.
Day (DT) and night temperatures (NT) influenced Lilium longiflorum Thunb. 'Nellie White' stem elongation and development rate from the visible bud stage (VB) until anthesis. Plant height increase after VB was a function of the difference (DIF) between DT and NT (DT-NT). Plant height increased 90% as DIF increased from - 16 to 16C. A cubic model described bud development rate as a function of temperature from 14 to 30C. A linear model adequately described bud development rate as a function of average daily temperature from 14 to 21C. Based on the linear model, bud development rate increased 0.05 per day for each 1C increase in average daily temperature. The base temperature for bud development, i.e., the temperature at which bud development rate was 0, was calculated as 3.5C. Greenhouse forcing of vernalized Easter lilies is commonly divided into three phases: I) placement of vernalized bulbs in the greenhouse to flower initiation, II) flower initiation to VB, and III) VB to anthesis (De Hertogh and Wilkins, 1971). Plant morphological development differs during each of the forcing phases (De Hertogh and Wilkins, 1971). Growth during phase I is vegetative and consists of stem elongation and leaf expan- sion. Flower initiation, leaf expansion, and stem elongation oc- cur during phase II. Inflorescence expansion and stem elongation occur during phase III. Lily responses to temperature during phase III differed from those during phases I and II (Wang and Roberts, 1983). Lily development rate, quantified as days to unfold a leaf, is a de- creasing linear function of average daily temperature between 14 and 30C during phases I and II (Karlsson et al., 1988). Lily development rate during phase III is a nonlinear function of temperature (Healy and Wilkins, 1984). The effect of temper- ature on the rate of lily development decreases as DT and/or NT increase during phase III (Rob and Wilkins, 1973; Healy and Wilkins, 1984). Easter lily morphological development is thermomorpho- genie. For instance, internode length increases as the DIF be- tween DT and NT increases (Erwin et al., 1989). In addition, leaf orientation, leaf length, and flower length are also influ- enced by diurnal changes in temperature.