Mitotic analysis of sticky chromosomes in aluminum tolerant and susceptible wheat lines grown in soils of differing aluminum saturation

Aluminum toxicity of acid soils is an important growth limiting factor which can reduce crop yields. Breeders have used various screening techniques for the rapid selection of Al tolerance lines. Al toxicity is complex having multiple effects on plant growth. The question becomes can plant selection for tolerance at one specific Al saturation result in tolerance at multiple aluminum saturation levels. Six near-isolines and three wheat (Triticum aestivum L.) cultivars differing in aluminum response on the basis of Al exclusion in the root cell wall were used in this study. Seeds of each line were planted in three soil treatments, 0.5%, 27% and 65% aluminum saturation respectively. Mitotic analysis was carried out on root tip cells. Soils with aluminum saturation were seen to induce sticky chromosome damage in both tolerant and susceptible lines. Lagging chromosomes, chromosome fragments and anaphase bridges were seen in cells of root tips grown in soils with increased aluminum saturation. The number of cells in susceptible lines exhibited an increase in stickiness as the aluminum saturation of the soil increased. In tolerant lines, the number of cells with stickiness increased at 27% saturation, but then decreased at 65% aluminum saturation. The amount of chromosome stickiness appears to be not only dependent upon the plant response to phytotoxic Al but also the aluminum saturation level at which the plant is grown. Tolerance as measured by reduced chromosomal stickiness did not occur until the plants were grown in very high soil Al saturation, indicating a single selection scheme for Al tolerance may not be adequate to develop the highest degree of tolerance.