Mulberry genetic resources are the backbone of crop management. Collection, introduction and exchange can enrich existing gene pool and provide breeders a great scope for further improvement. There are more than 140 mulberry accessions in the germplasm, maintained at SES-Vratza, but only 113 out of them have been studied in details (Petkov et al., 1994).
The distribution of the mulberry accessions according to their species, type and geographical origin is presented in Tables 1, 2 and charts 1, 2 and 3. Most of mulberry accessions (59%) available are of Morus alba species, which is widely spread in Bulgaria.
Less number of accessions are from the species M. rubra, M. multicaulis, M. nigra, M. kagayamae, M. latifolia and M. bombycis. However there are 23 mulberry accessions with unknown species. The accessions - hybrids and branches are prevailing. The hybrid accessions are 35, that means the still important role of hybridization in the selection of mulberry.
The largest number are accessions - branches, what is connected with the vegetation type of propagation as well as the mass and individual cooling during the initial stages of mulberry selection. There are also 3 accessions, selected by the method of polyploidy, namely Kairiu improved, Tadgikian without seeds and Uzbekian. 25 accessions have unknown origin and type.
The data, shown in Table 3 and chart 3 manifest that there are accessions from nearly all countries practicing sericulture from the temperate and sub-tropical belt like Italy, Russia, Georgia, Japan, Armenia, China, Azerbaijan, Uzbekistan, Egypt and Ukraine.
The Bulgarian varieties are the biggest number -37.9 varieties have been recognized by the Bulgarian State Executive Agency for Variety Testing and allowed to be propagated for commercial use. These are Vratza 1, Vesletz, Vratza 18, N106, N24, Kinriu, Kokuso 20, Kokusu 27 and Tbilisuri. The last introduction of exotic mulberry varieties was in 1999 from Egypt.
Conservation is a process which starts after collection and multiplication and thereafter establishment of mulberry accessions in base collection.
All the accessions at SES-Vratza were planted in base collection. In Table 15 is shown the number of trees per each accession maintained. At present the plantation is maintained as tree form, bottom pruned once in a year, namely in the end of May/beginning of June, (when the trees are used for production of saplings the pruning is made in February) and used as active collection for recording data on morphology, anatomy, reproductive and growth parameters, as well as for production of saplings by hardwood cutting method. The recommended cultivation practice is maintained (Petkov and Penkov, 1981).
Mulberry Classification Methods - Phytogeographic Information
1. Botanic name - species; 2. Name of the variety; 3. Origin; 3.1. Indigenous; 3.2. Introduced; 4. Geographical origin; 5. Type of the variety; 5.1. line; 5.2. population; 5.3. hybrid; 5.4. branch; 5.5. polyployd.
Characterization of mulberry genetic resources
1. Crown; 1.1. Shape; 1.1.1. Pyramid type; 1.1.2. Egg type; 1.1.3. Pile type; 1.1.4. “Crying” type; 1.1.5 Brush type;
2. Position of the branches toward the stem (branching nature); 2.1. Erect-angle to 45o; 2.2. Semi-erect - angle from 45 to 90 o; 2.3. Spreading and dropping-angle more than 90o;
3. Shootlets; 3.1. Mature shoot color; 3.1.1. gray; 3.1.2. graybrown; 3.1.3. grayashy; 3.1.4. graygreen; 3.1.5. darkbrown; 3.1.6. greenbrown; 3.2. Shape of the shoot cut; 3.2.1. round; 3.2.2. oval; 3.2.3. folded; 3.3. Curve of the shoot; 3.3.1. stright; 3.3.2. curved; 3.3.3. slightly curved; 3.3.4. snake type;
4. Buds; 4.1. Size; 4.1.1. Small - up to 2 mm; 4.1.2. Medium - from 2 to 5 mm; 4.1.3. Big- more than 5 mm; 4.2. Shape; 4.2.1. triangular; 4.2.2. oval; 4.2.3. tapering; 4.3. Color; 4.3.1. graybrown; 4.3.2. darkgray; 4.3.3. gray; 4.3.4. lightgray; 4.3.5. brown;
5. Leaf position; 5.1. Phytotaxis; 5.1.1. alternative position; 5.1.2. opposite; 5.2. Phyllotaxy grade; 5.2.1. ½; 5.2.2. 2/3; 5.2.3. 2/5; 5.2.4. 3/5; 5.2.5. 2/7; 5.3. Internodal distance; 5.3.1. Short - up to 2 cm; 5.3.2. Medium-from 2 to 5 cm; 5.3.3. long-more than 5 cm;
6. Stipules; 6.1. Type 6.1.1. simple(free lateral); 6.1.2. complicated (foliaceous); 6.2. Color; 6.2.1. graybrown; 6.2.2. gray 6.2.3. grayashy; 6.2.4. graygreen; 6.2.5. greengray; 6.2.6. brown;
7. Leaf petiole; 7.1. Shape; 7.1.1. tubular; 7.1.2. semitubular; 7.1.3. wing type; 7.1.4. flat; 7.1.5. flatten; 7.1.6. groove type; 7.2. Length; 7.2.1. short-up to 3 cm; 7.2.2. medium-from 3 to 5 cm; 7.2.3. long - longer than 5 cm; 7.3. Width; 7.4. Color; 7.4.1. lightyellow; 7.4.2. yellow; 7.4.3. yellowgreen; 7.5. Idioblast 7.5.1. With high length; 7.5.2. With low length;
8. Leaf; 8.1. Leaf lobation type; 8.1.1. unlobed; 8.1.2. lobed; 8.1.3. deep lobed; 8.1.4. pinnate; 8.1.5. finger type; 8.1.6. having different leaf lobation; 8.2. Leaf shape; 8.2.1. heart type; 8.2.2. triangular; 8.2.3. diamond; 8.3. Leaf size (length); 8.3.1. Very small-up to 5 cm length; 8.3.2. small- from 5 to 10 cm; 8.3.3. medium-from 10 to 15 cm; 8.3.4. semi-medium-from 15 to 20 cm; 8.3.5. big -from 20 to 25 cm; 8.3.6. very big - more than 25 cm length; 8.3. Leaf size(width); 8.4. Leaf thickness; 8.4.1. very thin-up to 70 mm; 8.4.2. thin-from 70 to 100 mm; 8.4.3. medium-from 100 to 150 mm; 8.4.4. thick-from 150 to 200 mm; 8.4.5. very thick-more than 200 mm; 8.5. Leaf apex; 8.5.1. accuminate; 8.5.2. acute; 8.5.3. caudate; 8.6. Leaf margin; 8.6.1. serrate; 8.6.2. crenate; 8.6.3. repand; 8.6.4. dentate; 8.7. Leaf surface; 8.7.1. smooth; 8.7.2. slightly rough; 8.7.3. rough; 8.8. Leaf surface brilliance; 8.8.1. dull; 8.8.2. low glazed; 8.8.3. glazed; 8.8.4. glossy; 8.9. Leaf color; 8.9.1. light green; 8.9.2. green; 8.9.3. deep green; 8.10. Leaf texture; 8.10.1. soft(membranous); 8.10.2. tender(chartaceous); 8.10.3. rough (coriaceous);
9. Reproductive structure; 9.1. Sex; 9.1.1. Male; 9.1.2. Female; 9.1.3. Bisexual; 9.2. Power of the flowering; 9.2.1. weak; 9.2.2. medium; 9.2.3. strong; 9.3. Racemes; 3.1. length; 3.2. width; 3.3. stem length; 3.4. number of racemes in one bud; 3.5. number of flowers in 1 raceme; 9.4. Fruits; 9.4.1. length; 9.4.2. width; 9.4.3. diameter; 9.4.4. petiole length; 9.4.5. fruit shape; 9.4.5.1. curved; 9.4.5.2. straight; 9.4.5.3. oval; 9.4.5.4. kidney type; 9.4.5.5. flattened; 9.4.6. fruit color; 9.4.6.1. black; 9.4.6.2. purple; 9.4.6.3. violet; 9.4.6.4. white; 9.4.7. fruit taste; 9.4.7.1. low sweet; 9.4.7.2. medium sweet; 9.4.7.3. very sweet; 9.4.7.4. sweet-sour; 9.4.7.5. sour; 9.5. Seeds; 9.5.1. color; 9.5.1.1. yellow; 9.5.1.2. light yellow; 9.5.1.3. yellowbrown; 9.5.1.4. brightbrown; 9.5.2. seed length; 9.5.3. seed width; 9.5.4. single seed weight in mg
EVALUATION OF MULBERRY GENETIC RESOURCES
1. Leaves percentage from the whole vegetation yield; 2. Leaf yield by 1 tree; 3. Leaf annual yield per 1 ha; 4. Leaf biochemical composition; 4.1. dry matter; 4.2. crude protein; 4.3. crude fiber; 4.4. crude fats; 4.5. crude ash; 4.6. protein extract matter; 5. Propagation; 5.1. Phenological phases; 5.1.1. Flowering; 5.1.1.1. beginning; 5.1.1.2. mass flowering; 5.2. Ripe fruits; 5.2.1. beginning; 5.2.2. mass; 5.3. Yellowing leaves; 5.3.1. beginning; 5.3.2. mass; 5.4. Leaf fall; 5.4.1. beginning; 5.4.2. mass; 5.5. Bud swelling; 5.5.1. beginning; 5.5.2. mass; 5.6. bud sprouting; 5.6.1. beginning; 5.6.2. mass; 5.7.1st -2nd leaf sprouting; 5.7.1. beginning; 5.7.2. mass; 5.8.4th -5th leaf sprouting; 5.8.1 beginning; 5.8.2. mass; 5.9. Rooting ability; 5.9.1. cuttings having bark cracking in %; 5.9.2. cuttings having beginning of roots growing in %;5.9.3. cuttings having roots in %; 5.9.4. Dry matter content in the cutting in %.
The purpose of mulberry breeding is to develop or evolve varieties that are efficient in nutrients so that they give high yield of quality leaves per unit area, varieties that can withstand extreme conditions and resist to diseases. The main characters for mulberry selection are as follows:
* The selected plant to have good rooting ability, allowing easy propagation by hardwood cutting method.
* Height of the plant * Branching habit. * Shorter internodal
distance
* High percentage of leaves from the whole vegetation yield.
*
Leaf size and lobation type. * To have more branches per tree.
*High
nutritive value for the silkworms. *High leaf yield per one tree and unit
area.
*Resistance to the local mulberry diseases *Response to indigenous
cultural practices
The following main methods are implemented in mulberry breeding in Bulgaria:
1. Collection of different mulberry forms obtained by natural open pollination
Mulberry is a highly heterozygous plant that is open for cross fertilization. Therefore the seeds that are formed through open pollination are natural hybrids. Seedling population from such seeds provide wider chances for selection of superior types whose characters are perpetuated through vegetative propagation. At SES-Vratza many mulberry varieties were selected by this method, namely N3, N24, N26 etc.
2. Artificial hybridization
Female and male parents are selected for hybridization. The technique of hybridization mainly consists of processes to ensure the pollen and stigma of known plants being brought together. After selection of desired seedlings they are further propagated by the vegetation method. By this method at SES-Vratza was evolved the highly productive variety Vratza1, which is an inter-species hybrid between the Japanese variety Kinriu (Morus kagayamae Koidz) and the wild Bulgarian mulberry (Morus alba L.).
3. Polyploidy breeding
Polyploidy in mulberry, either natural or artificial has a great economic value in evolution of superior varieties so that are possibly used in breeding. At SES-Vratza by treatment of selected saplings and seedlings of the varieties N117, N24, N155, N106 and the hybrids N117 x N118, N117 x N120 etc. with colchicine were obtained experimental polyploidy forms and after further evaluation were selected the new varieties P 26, P 28, P 29 and P 30.
4. Mutation breeding
Inducing mutations artificially might also be beneficial to eliminate certain undesirable characters. Such beneficial mutant characters can successfully be perpetuated through clonal propagation, without disturbing the genetic balance of the original variety. Mutations in mulberry are spontaneous or induced. Many mulberry varieties in practical use are believed to have arisen through spontaneous mutation. At SES-Vratza by spontaneous mutation appeared in 1969 on an Italian N 119 variety was evolved the new highly productive Bulgarian variety Vesletz.
