Plum Research and Growing in Latvia

Plums have been commercially grown in Latvia since the 19^th century. Plantations expanded especially in the 1920s–1930s. At that time, many cultivars were introduced, mostly from Western Europe. After the severe winters of 1939/40, 1941/42, 1955/56, and 1978/79, the plum orchard area significantly decreased because of a lack of winter-hardy cultivars. For this reason, cultivars from Russia, Belarus, and Estonia were introduced. Among the old landraces, highly winter-hardy ‘Latvijas Dzeltenā Olplūme’ is still important. Previously it used to be productive and had good fruit quality. Unfortunately, nurseries often propagated the hardiest clones, which lacked productivity. As Latvian consumers love yellow plums, at present breeding and propagation of productive clones from old orchards is ongoing. In the mid-20^th century, active plum breeding started in Latvia, crossing hardy genotypes with high quality donors. From this period ‘Lāse’ and ‘Minjona’ are still grown. Since the 1980s, plum breeding has been undedrtaken at the Institute of Horticulture. The crossing work in plums concentrated on the hexaploid group, aiming to combine large fruit size with good flavour, different time of ripening (in particular, early to medium late) and and good winter-hardiness. New cultivars include ‘Sonora’, ‘Ance’, and ‘Adelyn’, which have good quality, and productivity 20–30 kg per tree, and in some years up to 70 kg per tree.

The most widely used rootstocks are seedlings of Prunus cerasifera Ehrh. ssp. divaricata C.K. Schneid., which is more hardy that the common myrobalan plum. These rootstocks have good compatibility with most cultivars except gages, and are adapted to different soil types and are disease tolerant. Their drawback is a long growth season which reduces winter-hardiness of grafted cultivars. Also, they tend to form suckers around the stem. A hardy seedling PU-20651 (P. salicina ssp. ussuriensis × P. cerasifera) was bred at the Institute, which was shown to slightly reduce tree vigour. Testing of several Western European and Russian rootstocks did not result in their introduction into production. Trials are presently being carried out with size-reducing root-stocks originated from cultivar Wangenheim VVA-1, Weiwa, S766, and M633.

Commercial production of plums in Latvia is relatively small, as the area of orchards is the smallest among fruit trees. Plums are grown mostly for fresh consumption, with a small part for jams, yoghurt, and ice-cream additives. Fruits are sold mostly in small shops, markets and at farms. The main reason is the climate, which allows growing of a limited range of cultivars that tolerate the –30 °C winter temperatures in some years (about every five years). About 20 cultivars are grown commercially; the share of the six most popular plum cultivars is 69% of the total plum production. In recent years, plantations of new cultivars developed at our Institute have expanded, especially regarding the early ripening cultivar ‘Ance’.