RESPONSE OF POTATO PLANTS TO DROUGHT STRE SS BY INCREASED PROLINE LEVEL IN TUBERS

Proline content in tubers was investigated in the field trial, and in five treatments of greenhouse trials with the possibility of climatiza tion. In the greenhouse trials (1986 to 1992) there were planted mostl y four varieties and in the field trial (1990) 11 varieties were plant ed. As for comparison and examination of plant water regime at planned different soil moisture, water saturation deficit determined accordin g to progress of Catsky (1960), was used. In the greenhouse trials, it was found out that proline content in tubers was affected by drought stress in all years, being effective both at tuber initiation and thei r initial growth, and during their intensive growth up to physiologica l maturity of the crop. Proline content was significantly increased wi th decreasing soil moisture or with increasing drought stress, resp. M uch greater differences in tuber proline content among treatments were shown at drought stress in period of bud formation to full flowering, rather than stress being effective in the end of vegetation. Highly c onclusive differences in proline content were also found among varieti es. In a greater part of measurements, variety Desiree, grown in the g reenhouse trials, showed its highest content. In the field trial, vari eties known for their resistance to drought (Ibis and Desiree), placed on the first places among varieties in proline content. At a high str ess (30% relative soil moisture), any high differences between varieti es were not shown, but at a moderate stress (50%) they were shown. In individual years and samplings during one vegetation period, more freq uently differences were in values of proline content in individual var ieties and variety sequence according to proline content level did not remain the same. Decision, whether proline accumulation has or has no t any practical significance for breeders, is not unambiguously set. S ome authors (for example, Stewart, Hanson, 1980; Levy, 1983) ascribe a great role to proline aminoacid, at origination of plant resistance t o drought, others (for example, Balasimha, 1983; Bansal, Nagarajan, 19 86) did not found positive correlation of proline content level to tol erance to drought, and they indicate, that proline accumulation cannot be used to test the variety resistance to drought. Our results suppor t the idea, that the changes in tuber proline content as response to d rought stress, could help in identification of potato variety resistan ce or sensitivity to drought. To deduce an explicit conclusion it woul d be necessary to verify the results in an extensive experiment under controlled conditions with a large number of varieties or in field exp eriments of several years.