Breeding of a New Tussah Variety "Gaoyou 1"

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Jilin Research Institute of Sericulture, Jilin 132012, China

Abstract The new tussah variety "Gaoyou 1" adopted "Kangda" as the basic material, used the method of systematic breeding, and adopted the method of regional feeding, systematic separation and directional cultivation. At the same time, taking into account the comprehensive balance of various economic indicators, through 8 years and 16 generations of systematic breeding, a new tussah variety with high fat content was bred. The breeding results showed that the whole cocoon weight was 12.3 g, the thousand-cocoon weight was 11.8 kg, the cocoon filament length was 1 222 m, the hundred-cocoon fiber weight was 125.6 g, the cocoon filament size was 6.21 D, the raw silk percentage of fresh cocoon was 8.48%, the unified viability of pupae was 93.2%, the oil content of single moth was 0.55 g and the oil content was 56.17%.

Key words Tussah, Breeding, High oil content

1 Introduction

Tussah (Antheraeapernyi) is the dominant silk-secreting insect resource in China. It contains 20 kinds of amino acids and 8 kinds of amino acids necessary for human body. The content of unsaturated fatty acids in male tussah moth is as high as 78.6%[1-3], of which 43% are essential fatty acids for human body, which has never been paralleled by other animals. The animals listed in theFoodCompositionTabledo not contain more essential amino acids than tussah moths, human essential fatty acids are essential precursors for the synthesis of human prostate, and essential amino acids are needed for the normal functioning of all biological membrane tissues. It also lowers blood cholesterol and prevents atherosclerosis.

In recent years, due to the improvement of people’s living standards and the need of deep processing and utilization of tussah silkworm, the breeding direction of tussah silkworm has changed, from the traditional disease resistance, high yield, high silk content to the breeding of tussah silkworm varieties with emphasis on pupa weight. We began the breeding preparation of high oil varieties in 2004, and officially launched the implementation of the program in 2008. By 2015, we had bred high oil varieties with oil content of 0.55 g and oil content rate of 56.17%. And identified by the experts of Jilin Provincial Department of Science and Technology, it was named "Gaoyou 1".

2 Breeding materials and methods

2.1BreedingmaterialsIn the spring of 2008, five moth eggs of "Kangda" varieties for autumn breeding were introduced from Yongji County, and the eggs were raised in a single moth area. Taking the green and yellow silkworm as the symbol, six generations were selected and sorted out. In the autumn of 2010, two generations were selected from the cocoons bred by farmers in Yongji County again and raised in large mixed cocoon production single moth area. In the spring of 2011, the individuals of the previous generation with the whole cocoon weight ♀>15 g, ♂>12 g, and cocoon fiber weight>1.7 g, mated in pairs and were subcultured according to procedures, and four generations were selected for breeding. In 2013, mating began in single moth area and between different batches. After 2014, attention was paid to the selection of male parent moths for subculture in high oil areas, and it was bred in 2015.

2.2BreedingmethodsBreeding in single moth area, systematic separation, pure line breeding. At the same time, the comprehensive balance of various economic indicators was taken into account.

2.2.1Selection of adults and egg stages. Improving the purity and oviposition performance of moths.

2.2.2Selection of larval stage. Purification of lineage, domestication, cultivation and selection of larval resistance. Timely and early picking cocoon, choosing fast-growing, complete cocoon moth area as the subculture retention area.

2.2.3Selection of pupal (cocoon) stage. The moth area with excellent biological comprehensive economic characters (vitality, cocoon yield, thousand-cocoon weight, whole cocoon weight, cocoon shell rate, purity) was selected for breed retention and subculture.

2.2.4Selection of adults. After the conventional breeding indexes were stable, the selection of oil content of male moths was emphasized (instrument and equipment: SOX500 automatic fat analyzer).

3 Breeding results and analysis

3.1AnalysisoftheresultsofsystematicplotbreedingAfter 8 years and 16 generations of systematic selection and cultivation, "Gaoyou 1" has met the requirements of the breeding index in an all-round way. The autumn results of this variety since its basic breeding (2009-2015) are analyzed as follows (Table 1)

Table1Comparisonofautumnbreedingresultsin"Gaoyou1"plot

YearOvipositionquantityEggyield∥%Number ofcocoons collectedThousand-cocoonweight∥kgCocooningrate∥%Whole cocoonweight∥gCocoon fiberweight∥gCocoon shellrate∥%Viability ofpupae∥%Aged/h200927895.786812.4227.4212.641.5612.3791.11-201024199.2510413.0545.2213.391.7012.6890.7753∶2201129799.9412210.2343.6411.001.2511.3295.00-201230599.1710711.6136.0312.101.4512.0082.87-201324799.907012.8727.9613.021.6412.5696.01-201429297.168611.7633.7112.321.5812.8098.6055∶1201530199.9515010.9251.7611.651.3611.6798.2753∶1Average28098.7010111.8038.012.301.5112.2093.2054∶7Qing 6 (CK)27498.609211.8038.512.001.4712.2196.0052∶4

According to the results of the above table, the average oviposition of "Gaoyou 1" was 280 eggs, which was six more than that of the control Qing 6 (274 eggs). The average egg yield (98.7%) was slightly higher than that of the control Qing 6 (98.6%). The average number of cocoons collected by single moth (101 eggs) was 9 more than that of the control Qing 6 (92 eggs), which was 9.78% higher than that of the control Qing 6. The average thousand-cocoon weight (12.3 g) was 0.3 g higher than that of the control Qing 6 (12.0 g). The average cocoon shell rate (12.20%) was basically the same as that of the control Qing 6 (12.21%). The average unified viability of pupae (93.2%) was 2.8 percentage points lower than that of the control Qing 6 (96.0%).

3.2DeterminationofdiseaseresistanceIn order to detect the disease resistance of new varieties, a study group on silkworm disease was commissioned in the autumn of 2015 and 2016 in accordance with the technical regulations for the preservation and identification of tussah germplasm resources oftheMinistryofAgricultureofthePeople’sRepublicofChina(NY/T2331-2013). The resistance of new varieties to NPV was determined by LC50(Table 2).

It can be seen from Table 2 that the resistance level of the new variety "Gaoyou 1" for two years was moderate resistance. When converted into disease resistance multiple, the resistance of the new variety to NPV was 2.1 times and 2.0 times higher than that of the control Qing 6, respectively.

Table2ComparisonofNPVresistancebetweenanewtussahvariety"Gaoyou1"and"Qing6"

YearVarietyMedial lethal concentration ∥LC50Anti-logMultiple comparison with Q6Disease resistance multiple∥XDisease resistance grade2015Gaoyou 11×10-3.5483 5322.11 ≤ X <3Moderate resistanceQing 61×10-3.8717 43011 ≤ X <3Moderate resistance2016Gaoyou 11×10-3.5443 4992.01 ≤ X <3Moderate resistanceQing 61×10-4.6854 84211 ≤ X <3Moderate resistance

3.3DeterminationofcocoonsilkqualityIn 2015, Liaoning Research Institute of Sericulture was commissioned to analyze and investigate the characteristics of hundred-cocoon filaments of new varieties according to the technical regulations for the preservation and identification of tussah germplasm resources oftheMinistryofAgricultureofthePeople’sRepublicofChina(NY/T2331-2013). It was found that Gaoyou 1 cocoon had filament length of 1 222 m, raw silk weight of 79.1 g, recovery rate of 72.4%, hundred-cocoon fiber weight of 125.6 g, cocoon filament size of 6.21 D, and fresh cocoon silk yield of 8.48% (Table 3).

Table3Analysisandinvestigationofcocoonsilkcharacteristicsofhundred-cocoonfilaments(Gaoyou1)

YearReelability investigationGropedend%Droppingendtime/eggsReelingthread troubletime/eggsCocoonfilamentlength∥mReelabilityrate%Reelabilityfilamentlength∥mFiber distributionRaw silkweightgRecoveryrate∥%Largetussah wasterate∥%Secondarytussah wasterate∥%Waddingrate ofpupa∥%Hundred-cocoonfiberweight∥gCocoonfilamentsize∥DRaw silkpercentageof freshcocoon∥%201585.062.050.71 222.0032.8400.8279.0972.399.187.311.14125.586.708.48Qing 6 (CK)84.871.770.41 196.8936.12433.2383.7967.549.5812.0010.89124.636.347.39

3.4DeterminationofoilcontentinmalemothsFrom 2014 to 2016, Jilin Silkworm Product Quality Inspection and Testing Center was commissioned according to theNationalStandardofChinesePeople’sRepublicofChinaand (GB5009.6-2016)—DeterminationofFatinNationalFoodSafetyStandards, to determine the oil content of male silkworm moth in tussah germplasm resources. The results showed that the oil content of "Gaoyou 1" male silkworm moth in 3 years was the highest among the 23 samples tested, which indicated that the fat content of tussah had a certain correlation with the variety. The average oil content of every single moth for "Gaoyou 1" was 0.55 g, and the average oil content was 56.17% (Table 4).

Table4StatisticsofoilcontentofmaletussahmothinJilintussahgermplasmresourcesfrom2014to2016

VarietyNumber of mothstestedSingle moth dryweight∥gSingle moth oilcontent∥gOilcontent∥%Number of generations(spring + autumn)Percentage of male mothwith oil content≥61%Gaoyou 1450.970.5556.173+117.78Jiqing1000.860.4855.053+117.00Yongqing1330.860.4954.893+112.78Liao 882390.890.5154.823+120.51Qing 61220.820.4654.733+114.75Xuanda 41020.860.4854.563+114.718891000.880.4954.385+217.00Chao 64470.820.4654.332+121.28Fangshanhuang380.810.4453.493+110.53Jizuo 88-2490.810.4453.492+114.29L7698H430.780.4353.402+16.98802750.760.4253.352+120.00Zaoer680.780.4353.322+114.71Heida540.770.4253.182+112.96Xuanda 1220.810.4453.002+14.55Xiaohuangpi450.740.4052.702+111.11Xinghuang630.700.3752.032+16.35Xuanda 2470.800.4351.902+16.38Long 1470.750.4050.432+16.38Xuanda 3280.710.3750.162+10.00Heie560.630.3249.583+18.93Qingyihua610.510.2547.622+04.92Jihuangyihua340.510.2547.992+011.76Total1 4180.770.4252.81-11.98

4 Discussions

After eight years and 16 generations of systematic selection and cultivation, the indexes of the variety have reached the requirements of breeding index in an all-round way, and have passed the identification. This variety belongs to the green and yellow silkworm system, and is a bivoltine variety of middle-late maturity. The number of eggs laid by single moth was 359 in spring and 280 in autumn. The whole cocoon weight was 12.3 g and the thousand-cocoon weight was 11.8 kg. The cocoon shell rate was 12.20%, the cocoon formation rate was 38.0%, and the unified viability of pupae was 93.2%. The length of cocoon filament is 1 222 m, the weight of hundred-cocoon fiber is 125.6 g, the size of cocoon filament is 6.21 D, and the raw silk percentage of fresh cocoon is 8.48%. The dry weight, oil content and oil percentage of male moths for breeding were 0.97 g, 0.55 g and 56.17%, respectively.

In silkworm breeding, He Xiulingetal[4]. selected two pairs of male silkworm varieties "Huajing×Pinghao" and "Huajing × Ping 28" with high moth oil content by comparing the oil contents of different varieties of male silkworm moth. The content of moth oil is more than 50%[4]. The oil content of tussah male moth was 56.17%, which was higher than that of other silkworm varieties.

The results of oil content test of tussah pupae showed that there was no positive correlation between oil content of male moth and oil content of male pupae, and the relationship between the inheritance of oil content of tussah silkworm and the changes of metamorphosis needs to be further studied.