Influence of different rootstocks on the growth and yield of plum cultivars

The seedlings of myrobalan (Prunus cerasifera) are the most popular rootstocks for plums in Latvia. Vigorous trees, incompatibility between rootstock and some cultivars as well as intensive suckering are the reasons why we are looking for new rootstocks more suitable for intensive orchards. In two experiments at the Dobele Horticultural Plant Breeding Experimental Station, several vegetatively propagated forms of plum rootstocks of different origin and vigor were compared for their influence on the yield and growth of five plum cultivars (2 diploid 'Kometa' and 'Skoroplodnaya' and 3 hexaploid - 'Victoria', 'Lase' and 'Minjona'). In 1995, a preliminary experiment was established to evaluate three forms of rootstocks, which are inter-species hybrids bred in Russia. The significantly highest yield of all cultivars was obtained on the more vigorous rootstock 1AP-11. Particularly impressive was the increase of yield of the cultivars 'Skoroplodnaya' and 'Lase' obtained on this rootstock. Less beneficial results were obtained with the cultivars 'Kometa' and 'Victoria'. The yields on rootstocks 'SVG 11-19' and 'Druzhba' were lower. In 1998, we established an experiment with cultivars 'Kometa' and 'Minjona'. The significantly largest total yield over three years was on the most vigorous rootstock 'Myruni', but at the same time the yield efficiency (yield in relation to trunk cross-sectional area) was not significantly different between rootstocks. On the rootstock 'Saint Julien A' the obtained yield was somewhat larger than on the rootstock 'Saint Julien GF 655/2' for both cultivars. The cultivar 'Kometa' was significantly more productive than 'Minjona'. The interaction between rootstocks and cultivars was not significant. The increase of trunk cross-sectional area was significantly different between rootstocks. The largest increase of trunk cross-sectional for both cultivars was on the rootstock 'Myruni'. In both experiments, the influence of rootstock on average fruit weight was not significant. Fruit size depends more on cultivar traits and on the amount of yield.