By P. I. Tzenov
Sericulture Experiment Station,
24
Mito Orozov Str., Vratza 3000,Bulgaria
E-mail:
<[email protected]>
Paper contributed to Expert Consultation on Promotion of Global Exchange of Sericulture Germplasm Satellite Session of XIX th ISC Congress, September 21st -25th Bangkok, Thailand
Food and Agriculture Organization of the United Nations,
Rome
2002
Collection of mulberry genetic resources and their conservation are important to meet the different breeding programs. The characterization of genetic resources is of utmost importance because it gives the idea whether the material collected is differing from existing ones.
Evaluation is essential to know the genetic potentiality of mulberry varieties. Without systematic evaluation of existing germplasm the available gene pool can not be utilized effectively.
As a prerequisite to efficient utilization of germplasm, it should be properly characterized, evaluated and catalogued on the basis of useful genetic characters. Systematic documentation and exchange of information thereafter plays a very important role in the ultimate use of resources. Documentation becomes the most critical activity to make the germplasm utilization feasible through providing the descriptive information to the breeders for decision making. In Bulgaria mulberry has grown naturally since the ancient times and now the following species are available in the country: Morus alba, M. bombycis, M.multicaulis, M.kagayamae, M.rubra and M. nigra.
One of the main activities of Sericulture Experiment Station (SES) in Vratza has been the collection, characterization and evaluation of the indigenous and exotic mulberry varieties. At the beginning of 20th century all the mulberry trees and plantations in Bulgaria were of the local wild variety, characterizing with excellent adaptation to the climatic and soil conditions, but having too low leaf yield.
12 mulberry varieties were introduced for the first time from Italy in 1930. After that mulberry varieties have been imported for many times from the Soviet Union (in 1956; 1958; 1965; 1967), Japan (in 1963; 1970; 1974), Rumania (1964), China (1967; 1982) and Egypt(1998). As a result now there are 79 exotic mulberry accessions at the germplasm, maintained at SES-Vratza, including 11 from Italy, 2 from Russia, 12 from Georgia, 17 from Japan, 10 from China, 8 from Azerbaidjan, 4 from Ukraine etc. The number of the indigenous mulberry accessions, maintained at the station is more than 50.
For enrichment of mulberry germplasm SES-Vratza has organized several field trips for collection of accessions. The imported from Italy exotic accessions and those collected in Bulgaria until 1932 were characterized and evaluated and the varieties N3, N21, N24, N26, N101, N106, N112 were recommended for use at the field level. From indigenous accessions, collected in 1950 and 1953 were selected the varieties N59, N51, N33 and N53 having higher leaf yield. In the period 1940-1950 were obtained several mulberry hybrids between the female varieties N24, N103, N106 and the male varieties N3, N21, N62, N112. As the best combinations were recommended N24 x N3, N103 x N3 and N106 x N3.
During the period 1957-1965 the varieties N3, N24, N59, N101, N106, Adreuli, Pobeda, Tbilisuri and Kokuso 70 have been tested in the main sericulture regions of Bulgaria. The varieties N106, Kokuso 70, Pobeda and Tbilisuri gave the best results and were approved by the government for commercial saplings production.
In the period 1967-1977 were investigated the hybrid offsprings of the varieties Georgia, Kinriu, Kokuso 20, Kokuso 27, N24 and N106 under natural pollination. It was detected that the offspring of Georgia, Kinriu and N24 had the biggest percentage unlobed leaves- 89%, 67% and 63% respectively.
During the period 1976-1978 the mulberry varieties Kokuso 21, Kokuso 27 and Kinriu, introduced from Japan and the selected at SES-Vratza new varieties Vratza 1 and Vratza 18 were tested and approved for commercial use.
New mulberry accessions were created by using the methods of experimental polyploidy and hybridization. Penkov (1980) made a hybridization between the varieties N3, N116, N118, and N120 belonging to the species M.alba, M.kagayamae and M. latifolia. High percentage of trees with unlobed leaves manifested the hybrids N24 x N116-90%, N117 x N3 - 85%, and N119 x N3 - 75%. These hybrids were approved by the government as hybrid varieties (Hybrid 50, Hybrid 78 and Hybrid 96) for commercial use in 1980.
The research work completed in 1981 proved that the F1 mulberry offspring had very high variation in leaf lobation type and the mother variety influenced in bigger extent the leaf lobation type in the progeny. The leaf size was inherited intermediately in F1. In 1995 a methodology for characterization and evaluation of mulberry accessions was developed by Petkov (1998).
Now the research work in mulberry selection is considered as very important activity in SES-Vratza. It is necessary to continue the collection of new mulberry varieties both exotic and indigenous. In the recent years more than 2500 hybrid seedlings were obtained, planted and now they are under evaluation.
The future direction of the breeding work should be so called “far” hybridization between varieties from different geographical regions, different species and especially between varieties having different chromosome number.
As a result of the hard breeding work at SES-Vratza were selected the highly productive mulberry varieties Vratza 1, Vezletz and Vratza 18 which could be of interest for introduction in other countries as well.
