Agro Inform reproductive and viability characteristics of

2/ 2021
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Agro Inform
and the Russian Academy of Sciences jointly 
researched unique and sex-regulated silkworm 
lines with balanced lethal genes created based on 
complex genetic schemes [6], [7]. In recent years, 
some Japanese scientists have conducted research 
to improve methods of obtaining the lines sex-
limited larval markings, balanced on embryonic 
lethal [8], [9].
Today, the Uzbek Silk Research Institute 
is researching the preservation and monitoring 
of translocation in the genotype of the breeds 
balanced on Z-lethal genes, as well as on the 
creation of new hybrid combinations. In particular, 
Nasirillaev B.U., Umarov Sh. R., Jumaniyozov M.Sh., 
Khalilova M.F. [10], Achilov Sh. I., Umarov Sh.R. [11], 
Nasirillaev B.U. and Abdikodirov M.A. [12], [13], 
[14] are conducting genetic research to increase 
the technological indicators of the lines sex-limited 
on the color of the eggs by backcross breeding, to 
maintain a high level of cocoon productivity and to 
create new hybrid combinations and to recommend 
them in production.
The main goal of our study is to improve 
the background of the main economic traits of 
the unique C-8 ngl breed of mulberry silkworm 
balanced on embryonic Z-lethal by transferring to 
its genotype technological traits of fine fiber L-28 
line by maintaining the lethal balance.
Materials and methods
The experiments were conducted by 
scientists from the Uzbek Silk Research Institute 
under the Committee for the Development of 
Sericulture and Wool Industry of the Republic 
of Uzbekistan and the Department of Genetics 
of the National University of Uzbekistan. In the 
experiment, the mulberry silkworm Bombyx 
mori L. sex-limited at the egg stage, C-8 ngl breed 
balanced on embryonic Z-lethal, sex-limited trw
2
w
2
× L-67, as well as simple non sex-limited L-28 line 
were used. The genetic scheme of improvement 
of this C-8 ngl breed with the L-28 line with high 
genetic characteristics is shown in Figure 2.
The worms of breed and lines selected for 
the experiment were reared at a young instar at 
a temperature of 26-27 °C and 70-75% relative 
humidity, and adult worms at a temperature of 24-
25 °C and relative humidity of 65-70% in a special 
cocoonery of the Uzbek Silk Research Institute. 
1000 kg of mulberry leaves were used for 1 box of 
worms. The worms were fed with mulberry leaves 
of Uzbek breeding varieties Jarariq 4, Jarariq 5, 
and Jarariq 6. The sequence of determination of 
reproductive indicators in the study was carried 
out in the following order:
The prepared egg-layings – the breeds 
(lines) used as parents and the egg-layings with 
their participation were analyzed individually.
During the analysis, the eggs in each egg-laying were 
taken and their number was determined using the 
individual counting method. From these analyzed 
eggs, asexual and dried-up eggs were isolated, and 
physiological defect indicators were determined. 
Eggs in the egg-laying were individually weighed 
on a torsion scale.
To determine egg hatchability in the 
experimental material, the eggs of each breed (line) 
and hybrid were incubated during the spring worm 
feeding season. During the incubation period, the 
egg samples were taken by 100 eggs from egg-
layings of each breed and F
1
hybrid in 4 replications. 
Only in the whitening stage of the embryonic period 
of the C-8 ngl breed, 200 pieces were obtained due 
to the death of more than 50% of males and females 
under the influence of lethal genes.
The number of unhatched eggs was 
determined on the third day after mass hatching 
of the eggs. The hatchability rate was calculated by 
taking the ratio of the number of hatched worms 
and 100 total number of worms in the sample.