No abstract

SummaryThe seaweed concentrate 'Kelpak' is used commercially in the greenhouse and field to improve plant quality. 'Kelpak' was added to the in vitro culture medium of potato cv. 'BPI' and also applied as a leaf/soil drench immediately after transplanting. The addition of 0.25% seaweed concentrate to the medium improved plantlet quality and led to better establishment in the greenhouse. No beneficial effect of seaweed concentrate in the tissue culture medium was observed if a second cutting was part of the micropropagation process. Additional application of 0.5% seaweed concentrate in the greenhouse to plantlet cuttings derived from tissue culture was not beneficial.

The aim of this work was to investigate whether the application of soluble chitosan in potato micropropagation can improve microplant quality in vitro, help acclimatisation ex vitro, and increase yield and seed quality of minitubers. Potato cv. Désirée microplants were treated in vitro with soluble chitosan added to the semisolid tissue culture medium in different concentrations. Microplants were subsequently transferred to the greenhouse and sprayed with chitosan solutions or remained unsprayed. Untreated microplants were also established ex vitro and sprayed with chitosan, or left unsprayed as a control. Morphological and physiological parameters of plant growth were assessed in vitro and ex vitro. Plantlet quality was evaluated using a ranking system. Minitubers derived from greenhouse plantlets were planted in the field in subtropical conditions, and growth and yield parameters evaluated. The chitosan concentration most beneficial to the in vitro growth of microplants varied between years. In treatments with the best in vitro growth, minituber number and yield in the greenhouse was also increased. Foliar chitosan application at the acclimatisation phase stabilised the effect of in vitro treatment on yield parameters. The seed quality of minitubers derived from chitosan treatments in vitro alone and in combination with foliar treatment at acclimatisation was improved, giving rise to field plants with increased tuber numbers and yields. The combination of chitosan in vitro and foliar application during the acclimatisation phase ex vitro had a greater effect on minituber seed quality than the concentration applied in vitro.

Reaction to the culture filtrate of Alternaria solani (Sorauer) was used as an indicator in an in vitro screening test to select lines with decreased field susceptibility to early blight from a population of 1000 putative mutants. Plantlets of cv. ÔDesire´e derived from irradiated callus of potato were inoculated in vitro with a culture filtrate of A. solani (Sorauer). Of the 45 lines selected and subsequently evaluated under conditions of natural infection in the greenhouse six showed lesser degrees of early blight infection than the cv. Desire´e control. The six lines selected in the greenhouse retained lower degrees of infection during 2 years of field trials.

SummaryUsing visual selection for off-types and image analysis to select against maturation mutants, a line combining improved late blight resistance and yield was isolated in an in vitro mutagenesis programme from a population of 2101 putative mutants. The adventitious regener.ants from mutagenesis treatment, including spontaneous mutants (somaclonal variants), were subjected to serial subculture of the apical bud in vitro and two cycles of apical cuttings in vivo to breakdown chimeras. The selected line was stable in trials over five years; others were unstable or failed to combine improvement in late blight resistance with high yield. Leaf and tuber image analysis was used to characterize selected lines. Lines that differed most from cv. Golden Wonder in yield and late blight resistance were more easily distinguished from the control by image analysis. The role of image analysis in negative selection and in determination of the relatedness of mutants to the control is discussed.