چكيده لاتين :
<strong >Introduction </strong >
Health and quality of potato (Solanum tuberosum L.) seeds are important in the potato seed production technology. Moreover, the basic seed materials must be free of pathogens. Therefore tissue culture techniques are used at this stage in the laboratory to produce disease free seeds. Mini-tubers can be produced after acclimatization from plantlets as tissue culture which are planted at high densities in the greenhouse in beds or containers using different substrate mixtures, or even in hydroponic culture. Foliar application of growth regulators is a way to increase potato mini-tuber production. Growth regulators influence on potato mini-tuber dormancy. Triazoles, a family which Paclobutrazol belongs to them, have both fungitoxic and plant growth regulatory effects. In addition, they can also protect plants against various stresses. Therefore, the triazoles have been characterized as plant multi-protestants. Paclobutrazol changes the relationship between source and sink and by this way, affects plant production. Also, it can inhibit giberellic acid biosynthesis. Some morphological changes observed in paclobutrazol-treated plants include the inhibition of plant growth, decreased inter-nodal elongation and increased root to shoot ratios. Time of paclobutrazol foliar application is an important factor which changes plant characters (Lim et al., 2004). This study implemented to evaluate foliar application of paclobutrazol concentrations at different time on production and mini-tuber dormancy.
<strong >Materials and Methods </strong >
The factorial experiment based on randomized complete block design with four replications was conducted at the faculty of agriculture’s research greenhouse, Ferdowsi University of Mashhad, Iran, in 2013. Plantlets of Agria cv. produced from nodal tissue culture in Murashinge and Skoog (MS) medium. After 25 days, plantlets of free disease and uniform exported to plastic pots with 12 cm diameter and 30 cm height. Perlite, cocopite and sand with 3:3:4 ratios, formed the substrate. Potato plantlets were fed with corrected Hoagland solution. Treatments were foliar application of paclobutrazol at two growth stages (stolen initiation and tuber initiation) and six concentrations (control, 20, 40, 60, 80 and 100 mg l-1). Foliar application of mentioned concentrations implemented in the final hours of day. After 95 days from transplanting, number of mini-tuber in plant, mini-tuber length, mini-tuber diameter and mean of mini-tuber weight were measured. Then, mini-tubers saved to fridge with 8±2ºC and 10% relative humidity. Two months later, mini-tuber’s germination was measured. Finally, time of achievement to 5, 10, 50, 90 and 95 germination percentage was measured with Germin program. Beside that, rate of germination was calculated with equation 1:
(1)
R50 and D50: rate of germination (1/h) and time of achievement to 50% germination, respectively.
Analysis of variance and correlation between trials was done with SAS 9.1 Software. Means comparison measured with least significant difference test (LSD) at 5% probability level.
<strong >Results and Discussion </strong >
The main effects and interactions of paclobutrazol foliar application and growth stages, on number of mini-tuber in plant, mini-tuber length, mini-tuber diameter, mean of mini-tuber weight and time of achievement to 5, 10, 50, 90 and 95 germination percentage trials were significant. But interaction between foliar application and growth stages was not significant at germination rate trial. The effect of foliar application on maintained trials in tuber initiation stage was lower than stolen initiation. Increase in paclobutrazol concentration increased mini-tuber dormancy and reduced germination rate. Paclobutrazol application in tuber initiation stage had more inhibition on mini-tuber germination. With increase in paclobotrazol concentration, time of achievement to 5, 10, 50, 90 and 95% germination were 11, 13, 17, 19 and 17% in comparison between foliar application growth stages (tuber initiation compared to stolen initiation).Significant negative correlation obtained between number of mini-tuber in plant, mini-tuber length, mini-tuber diameter, mean of mini-tuber weight trials with time of achievement to 5, 10, 50, 90 and 95 germination percentage..
<strong >Conclusions </strong >
Application of 20 mg l-1 paclobutrazol at stolen initiation, produced highest number of mini-tuber. But, maximum amount of mini-tuber length, mini-tuber diameter and mean of mini-tuber weight obtained in control treatment. Overall, in most cases paclobutrazol application had negative effect on production and germination of mini-tuber potatoes.
