CHARACTERIZATION OF NEW GEORGIAN MULBERRY SILKWORM BREEDS RELATIVELY RESISTANT TO THE DISEASE «NUCLEAR POLYHEDROSIS»

The paper considers biotechnological characteristics of new breeds of mulberry silkworm „V-1“ and „V-2“, which are relatively resistant to the worm disease „nuclear polyhedrosis“. The hybreeds were obtained from mulberry silkworm breeds „Dighmuri“ and „Iveria“. Breed “Iveria” is characterized by short period of feeding; it was created for the west Georgia zone, while the cocoon thread length of the breed “Dighmuri” is 1800-2000 meter, silk capacity of live cocoon is 25-26%, but these breeds are characterized by relatively low viability [1,2,3]. Our research aimed to improve namely this flaw. As a result of complex selection works carried out for the improvement of the above stated viability and other major indices we received new highly productive breeds, which by their indices equal or exceed initial breeds. KEYWORDS

Introduction. From the beginning of selction works (1930 y.) more than 50 local selection breeds of mulberry silkworm were obtained. Selected breeds obtained in the first period of works were characterized by short thread length and thinness (800-900 meter, metric number 2000-2200). Because of it, to receive complex silk thread (№429) it was sufficient to wind only 6-7 cocoons jointly, and correspondingly its cocoon thread length, thinness and other indices were rather low. In the following years, biotechnological characteristics of selective breeds were improved and the AGRICULTURE № 11(39), November 2018 cocoon thread length of the breed "Dighmuri" that was selected in 1985-1989 years reached 1800-200 meter, but this breed is characterized by low viability. Because of it, selection was continued for heighten worm viability and its resistance to diseases.
Material and methodology. As starting material we gave preference to local origin breeds (Dighmuri and Iveria) [4,5]. For the study and evaluation of initial breeds and starting populations obtained from those breeds we used a method of preliminary prognosis -by determination of form elements in hemolymph [6,7]. In some cases a method of injection of blood was also used.
To improve viability and to elevate resistance of a disease "nuclear polyhedrosis" in silkworm, we used method of artificial infestation (induction) of mulberry sulkworm. Besides, method of feeding on the provocative background (high temperature, 28-32°C, humidity more than 90%, rough feed) was also used.
To achieve 100% infestation of mulberry silkworm by polyhedrosis is factually impossible, only relatively weak worms are infected. This is why hemolymph was collected from diseased worms, as much as possible. Purification of polyhedrons was made by centrifugation at 3000 rev./min, at 4 o C, in 60, 40 and 29 saccharose linear gradient.
When the 4 th skin was changed, silkworm was counted in 100-100 pcs in 7 variants and 5 variants were given leaf that was sprayed with polyhedron suspensions; the 6 th variant was used as a dry control and the 7 th variantas a wet control.
Polyhedron suspensions were tested by carrying out annual reiterated feeding, till the concentration was established, at which a worm would be infested to the level, when it would be able to undergo metamorphosis into a moth and to lay grain.
According to the above given table, the greatest number of worms died in the version with 50000mm 3 polyhedron suspension, the smaller number died in 500 mm 3 variant.
The rescued worms span cocoon and from those cocoons the grain was prepared, which was tested for disease at the next feeding.
The concentrations of polyhedron suspensions when the biggest number of mulberry silkworm died as a result of experiments (50000mm 3 , 10000mm 3 , 5000 mm 3 and 1000 mm 3 ) were discarded from the test. Finally only one concentration of polyhedron suspension was prepared (500 mm 3 ), when small number of worms were infected, and the rescued silkworm reached the moth stage and as a result of pappillonage grain was obtained. Experimental results are given in Table 2.  Dry control  Wet control  1  ---2  ---3  ---4  1  -1  5  --1  6  1  -1  7  1  1  1  8  1  1  1  total q-ty % q-ty % q-ty % 4 4 2 2 5 5 Table 2 offers number of individuals who died at infestation by various concentration polyhedron suspensions and the percentage of lethal end according to days.
According to this table, 4% of worms was diseased in the first variant, while in the 7 th variant (wet control) 5 worms were diseased; in the process of metamorphosis 7% of worms died while the remaining worms span cocoon and from those cocoons grain was prepared.
From the worms rescued after every experiment the F1.... F7 generation was obtained by the method of sampling, and from that generation by long-term selection and sampling the improved lines were obtained [8,9,10]. After each feeding moth microanalysis was carried out and grain laid by diseased moth was discarded.
Simultaneously works were carried out by analytical and synthetic selection methods and sampling from generations [11,12]. Works which aimed to preserve significant technological indices and to improve worm viability in those lines were continued, in particular, by strict rejection and on the basis of non inbred crossing by propagation in generations; sampling of families and individuals with high indices was performed and on its base breed "V-1" was obtained from "Dighmuri" and "V-2" from "Iveria". The obtained breeds are distinguished by high biotechnological indices, especiallyby high viability.
The main goal of our research, that is elevation of mulberry silkworm viability in starting breeds from 88,7-91.5 %-to 95.6-97.3% was achieved, which is a great achievement in mulberry silkworm selection breeding work.