A. Ferenczy

Thermal inactivation kinetics of mixed microbial populations. A hypothesis paper

The authors have investigated inactivation kinetics of mixed microbial populations, which consist of component subpopulations following first-order inactivation kinetics. Populations which had undergone previous partial heat treatment were also included in the study. As the survivor ratio is the Laplace transform of the rate constant distribution, an analysis of survival functions following nth-order inactivation kinetics (n > 1) resulted in a gamma distribution of the first-order rate constants. The expected value of the gamma distribution is proportional to the resulting nth-order rate constant and inversely proportional to the nth-order time constant. According to the theory, the nth-order time constant and survivor ratio are independent of the initial microbial concentration. The temperature effect has been treated with the restriction that a monotonously increasing functional relationship exists between first-order rate constants at two different temperatures. This monotonous function relates first-order rate constants of the same subpopulation. The Laplace transformation method is applicable to create analytical functions for fitting them to measured semilogarithmic survivor curves, if these curves are of the concave type.

Some sprouting characteristics of microtubers

SummaryMicrotubers can be stored longer, transported and handled easier than plantlets, but they have some disadvantages related to long dormancy. Dormancy, number of sprouts per tuber and loss of microtubers under different storage temperatures were studied. Microtubers of four genotypes originated from different tuberization treatments (photoperiod combinations) were observed. We found that dormancy depended on cultivar and — in some cases — on the photoperiod treatment applied during tuberization. Generally, the dormacy was long and was greatly elongated by low storage temperature. One of the photoperiod treatments shortened while the other treatment prolonged the rest-period compared to the control, maybe due to a change in temperature accompanying the change in daily light (photoperiod combination). Besides, these treatments affected the number of sprouts per tuber. There was no significant difference in duration of dormancy between different tuber-size groups, but the loss increased significanctly with a decrease in tuber size. Based on this information we can use microtubers more effectively in the seed potato production programme.

Light and genotype effects on in vitro tuberization of potato plantlets

SummaryIn vitro tuberization responses of eleven clones of potato were evaluated under different photoperiods and light intensities. No growth regulators were added to the medium to avoid the potential modification of the response to the environmental stimuli.Plantlets were grown on MS medium containing 3% sucrose for four weeks under long days (16 h). Tuberization was induced by short days (8 h). Five photoperiodic combinations and three light intensity treatments were applied.Light applied after the tuber induction phase delayed or inhibited tuber initiation (at proper photoperiods both at 111 and 55 μmol m−2 s−1 light intensities at 24/15 °C day/night temperature). Darkness following the induction stage accelerated and synchronized tuber initiation after high light intensity. However, these effects of dark treatment depended on light intensity applied in short days before dark treatment. There was an interaction between the duration of darkness applied in photoperiodic treatments and the light intensity applied in short days on tuber initiation. No relationship was observed between the maturity groups of clones tested and their tuber initiation responses. Tight interaction (P≤0.01) of treatments and clones was proved by statistical analysis. Reliable tuberization and high rate of tuberization (1.20–1.52) can be reached using these hormon-free systems.