Euphytica 69: 219-229,1993 .©1993 Kluwer Academic Publishers. Printed in the Netherlands .

Heterosis breeding in Indian mustard (Brassica juncea L. Czern & Coss) :Analysis of component characters contributing to heterosis for yield

Akshay K. Pradhan, Yaspal S . Sodhi, Arundhati Mukhopadhyay & Deepak PentalTata Energy Research Institute, 90 Jor Bagh, New Delhi 110 003, India

Received 13 January 1993; accepted 30 July 1993

Key words: Brassica juncea, Indian mustard, heterosis breeding, component characters

Summary

Divergence of 25 accessions of Brassica juncea of Indian, CIS (Commonwealth of Independent States, formerUSSR) and synthetic origin was studied by D 2 analysis. On the basis of divergence, ten accessions were select-ed and crossed in a diallel fashion without reciprocals to study the combining ability and heterosis . None of theaccessions was found to be a good general combiner for all the nine quantitative characters that were studied .Significant heterosis over better parent for single plant yield was recorded in CIS x Indian and synthetic x CIScrosses (5 each) followed by Indian x synthetic types (3) . The analysis of component characters showed thatthe mean performance of the majority of hybrids was intermediate for five out of six yield attributing traits,thus exhibiting dominance or partial dominance effect . To estimate the contribution of such yield attributingtraits towards heterosis for yield, a comparison was made among three parameters viz . heterosis over midparent (MP), better parent (BP) and better yielding parent (BYP) of the concerned hybrid . It was observedthat estimation of heterosis from BYP was a more accurate method to determine the contribution of compo-nent characters towards yield heterosis than the analysis based on MP and BR From the component characteranalysis, it was concluded that characters like number of primary and secondary branches, number of siliquaper plant and siliqua density contributed significantly towards heterosis in yield . Plot level yield trials of twoselected hybrids (Skorospieka II x RH30 and Donskaja IV x Varuna) over two growing seasons revealed 29 .4to 91.8% heterosis over BYP.

Introduction

Brassica juncea (Indian mustard) is a major oilseedcrop of the Indian subcontinent covering more thanfive million hectares during the winter growing sea-son. It is also grown in Australia, China, CIS andCanada. Due to its ability to grow well under lowmoisture conditions, B. juncea is being developed asa replacement crop for B. napus in the WesternCanadian prairies (Woods et al ., 1991). B. juncea is apredominantly self-fertilized crop with 5-15cross-fertilization (Asthana & Singh, 1973) . Culti-

var improvement in B. juncea has been mostly doneby breeding methodologies for self-fertilized graincrops. Heterosis breeding could be a potential al-ternative for substantially increasing the produc-tion of Indian mustard. Successful exploitation ofheterosis would depend upon the identification ofhybrids that are more productive than either of theparents and standard check cultivars and on theavailability of suitable male sterility, fertility re-storer systems. A number of cytoplasmic male ster-ility (CMS) systems have been described in B. jun-cea (Rawat & Anand, 1979 ; Prakash & Chopra,

220

1990; Pradhan et al ., 1991) . The barnase-barstar sys-tem for hybrid seed production has been reportedto work efficiently in B. napus (Mariani et al., 1990,1991) and therefore, could also be used in B. junceafor the production of hybrid seed .

Combining ability and Fl heterosis have beenused as guides for the selection of parent lines inheterosis breeding for yield in rapeseed and mus-tard (Brandle & McVetty, 1989; Campbell & Kon-dra, 1978 ; Lefert-Buson & Duttee, 1982 ; Grant &Beversdorf, 1985; Sernyk & Stefansson, 1983 ; Singh,1973). In rapeseed, Sernyk & Stefansson (1983)showed that Fl hybrids of Marnoo x Karat and Kar-at x Regent gave significant heterosis for yield .Brandle & McVetty (1989) showed that some of theinbred lines derived from Marnoo, Regent and Kar-at gave significantly higher heterosis than cultivarcrosses. However, in both the studies it is not clearwhat component characters contributed to hetero-sis in Fl, how the parents differed from each otherfor component characters and what componentcharacters were selected for high expression in theinbred lines for significant increase in the extent ofheterosis over the cultivar crosses. Similarly, Banga& Labana (1984) and Kumar et al. (1990) providedinformation that crosses like RLM 514 x EJ2 andRLM 198 x RH30 give high heterosis in B. junceabut offered no clues about the components thatcontributed to high heterosis . Consequently, thesestudies do not provide criteria for the selection ofgermplasm to advance the heterosis breeding pro-grammes further .

In this paper we present the results of four yearsof experiments on B. juncea designed to study -1) the extent of diversity amongst some selected In-

dian, exotic and synthetic types,2) heterosis for yield with a major emphasis on dis-

cerning the contribution of different componentcharacters that are contributing towards yield,

3) performance of some of the selected hybrids atthe field level .

The component analysis data has been used to sug-gest criteria for the future selection of lines for het-erosis breeding in Indian mustard .

Materials and methods

Experiment I (1988-89): Divergence

Twenty five accessions of Indian (Pusa bold, RH 30,Varuna, RLM514, Kranti, RH819, Krishna,RLM619, RLC1359, Pusa barani, RLM 198 and RC781), CIS (Volgogdraskaja, Donskaja IV, Skoros-pieka II, VNIIMK II, Malopoloska and Niesopay-coszi-zagaja) and synthetic (Narinosa-nigra, Chi-nensis-nigra, Rapa-nigra, Japonica-nigra and threeindependent selections from a cross B. campestrisssp. pekinensis x B. nigra, designated as PNMB,PNBPL and PNBL68) (Prakash,1973) origin weregrown during 1988-89 winter in a randomised com-plete block design with three replications at FieldResearch Station, Tata Energy Research Institute,Gwal Pahari, Haryana, India . Each genotype wasgrown in 10 rows of 4 m length . Observations wererecorded on ten competitive plants from middlerows for nine quantitative characters i .e. plantheight, days to 50% flowering, number of primaryand secondary branches, number of siliqua perplant, siliqua length, number of seeds per siliqua,1000 grain weight and single plant yield . For diver-gence studies, the data were subjected to Mahala-nobis D 2-statistic and the accessions were groupedinto different clusters following Tocher's method(Rao, 1952) .

Experiment II (1989-90) : Heterosis and combiningability

Ten selected parents were crossed in a diallel fash-ion without reciprocals . Parents and 45 FI hybridswere grown during winter 1989-90 at Gwal PahariField Research Station in a randomised completeblock design as mentioned in Experiment I with anexception that each accession was grown in threerows. Observations on previously mentioned ninequantitative characters were recorded for five com-petitive plants from the middle row . The divergenceand combining ability estimates were calculatedfollowing Rao (1952) and Griffing (1956) MethodII, Model I, respectively. Heterosis for all the com-ponent characters was estimated by using three par-

ameters i .e. percent increase over mid parent (MP),better parent (BP) and better yielding parent(BYP). Parent exhibiting higher single plant yieldwas chosen as the BYP in any hybrid combination .For plant height and days to 50% flowering hetero-sis over BP was calculated over shorter height andearly flowering parents, respectively.

Experiment III (1990-91 and 1991-92) : Hybrid yieldtrials

Yield trials of two selected hybrids alongwith BYPand standard checks (Kranti, Pusa bold and Pusabarani) were conducted for two consecutive years(1990-91, 1991-92) during winter at Gwal Pahari.Sufficient amount of hybrid seeds were producedby hand pollination . Plots were arranged in the fieldin a randomised complete block design with threereplications . Size of each plot was 12 .5 m x 4 m(50 m 2 ) . Observations on quantitative characterswere recorded as mentioned in experiment II. Yieldobtained from each plot (excluding the borderrows) was converted to quintals per hectare and da-ta were analysed following standard statistical pro-cedures (analysis of variance and test of signifi-cance) .

In all the three experiments, the seeds were sown

Resultsat commercial sowing density of 30 cm (row to row)and 10 cm (plant to plant) distance . Fertilizer was

Divergence, combining ability and heterosisapplied at 60-40-40 (N-P-K) kg ha-' . Standard cul-

The significant treatment mean squares indicated

Table 1 . Intra (diagonal values) and intercluster D values among 25 genotypes of Brassica juncea

221

tural practices were followed throughout the grow-ing season.

Estimation of correlation coefficient

Parental divergence data (D value) from Experi-ment I and II were used to determine correlationcoefficients between parental divergence and per-cent heterosis for single plant yield. The range ofpercent heterosis for single plant yield was dividedinto five classes numbering 1 to 5 in ascending order .Based on percent heterosis, different crosses wereranked from 1 to 5 depending on the class to whichthey belonged. Correlation coefficient betweenranks of different crosses and their parental diver-gence was estimated. Similar ranking procedurewas followed for other characters and differentranks were assigned depending on their percentheterosis calculated by three different methods de-scribed in experiment II . Rank total was estimatedby adding the ranks assigned to all the characters(excluding single plant yield) . Correlation coeffi-cients between rank total of different crosses andtheir parental divergence was estimated .

Note: Cluster I = Pusa bold, RLM619, Krishna, Varuna; II = Kranti, RH819 ; III = Pusa barani, RH30, RLC1359 ; IV = Narinosa nigra,Japonica nigra, PNMB, PNBPL; V = RLM198, PNBL68, Chinensis nigra ; V I = RLM514, Rapa nigra ; VII = Volgogdraskaja, Donskaja IV,Skorospieka II, VNIIMK II, Niesopaycoszi-zagaja; VIII = RC781 and IX = Malopoloska .

Cluster I II III IV V VI VII VIII IX

I 3 .16II 4 .54 2.92III 5 .59 8.88 2 .47IV 13 .85 10.89 17 .81 3 .57V 14 .17 10.69 18 .46 7 .00 3 .59V I 8 .18 5 .20 12 .67 8 .28 7 .87 3 .82VII 26 .91 24.16 29 .95 21 .02 16 .37 22.22 3 .11VIII 23 .22 20.04 26 .81 15 .49 11 .15 17.45 6 .59 0 .00IX 31 .76 29 .23 34 .81 25 .43 21 .34 26 .71 8 .96 12 .42 0 .00

222

Table 2 . Mean of parents and 12 selected Fl hybrids (upper row), heterosis over better parent (middle row) and heterosis over betteryielding parent (lower row) for yield and other component characters

* Significant at p = 0.05 ; ** significant at p = 0 .01 ; CD = Critical difference of parental means determined from 10 parents used in diallel ;better yielding parent .

Parents/crosses No. ofprimarybranches

No. ofsecondarybranches

No. of

Siliquasiliqua/plant length

No . of Single plant 1000 gr wt Plant height Days to 50%floweringseeds/siliqua yield

A. Parental MeanPusa bold 5 .20 13 .00 345 .07 4 .79 12 .09 20 .91 5 .48 174 .27 60.67RH30 4 .47 10 .13 275 .40 4 .76 11 .77 18 .45 7 .08 168 .73 58.00Varuna 5 .80 15 .07 390.93 5 .01 13.96 21 .80 5.23 186.67 63 .67RC781 11 .87 28.13 548.80 3 .19 12.33 13.18 2.55 286.13 111 .33Narinosa nigra 8.93 22.00 1036.13 3.79 10 .60 13 .06 2.74 266.27 75 .67Chinensis nigra 10.67 29.73 1010.67 3.42 9.35 15.81 2.28 287.00 80.67PNMB 11 .00 40.60 1420.93 3 .56 9.57 20.89 2 .91 282 .67 80 .00Donskaja IV 12 .80 26 .27 400.13 3 .03 10.83 9 .29 2 .41 290 .53 107 .00Skorospieka II 14 .47 26 .60 478 .33 3 .47 11 .37 10.52 3 .16 306 .73 114 .00CD (p= 0.05) 2 .00 10.00 299 .53 0.29 1 .46 9 .19 1 .28 17 .11 2 .38

B. CrossesDonskaja IV x Pusa bold' 10 .33 23 .80 1305 .25 4 .33 11 .61 42 .45 3 .96 234 .20 69.00

-11 .94 -9.39 226.20** -9.74** -4.02 103.00** -27.74** 34.39** 13.74**98.72** 83 .08* 278 .26** - 9.74** -4.02 103 .00** - 27.74** 34 .39** 13.74**

PNMB' x RH30 7.87 24.93 933 .53 4.44 11 .95 34 .27 4.30 225.40 64.67-28.48** -38.58** -34.30* -6.73* 1 .44 64 .02* -39.77** 33.58** 11 .49**-28 .48** -38 .58** -34 .30* 24.63** 24.91** 64.02* 47.77** -20 .26** - 19 .17**

RC781 x RH30' 7.87 24.73 920.00 4.33 13 .37 41 .97 4.42 226.20 71 .00- 33 .71** -12 .09 69.10 - 9.04** 8.49 127.46** - 37 .52** 34.06** 22 .41**76.12** 144.08** 236.96** - 9 .04** 13.53* 127.46** - 37 .52** 34.06** 22 .41**

Donskaja IV x RH30' 8 .60 23 .00 1150.23 4 .29 12 .83 38.74 3 .95 212 .27 68 .00-32 .81** -12 .44 187 .46** -9.74** 8 .89 109.92** -44 .21** 25 .80** 17 .24**

92 .54** 126 .97* 317 .66** -9.74** 8 .89 109 .92** -44 .21** 25 .80** 17 .24**Skorospieka It x RH30' 7 .73 25 .80 1104 .73 4 .48 11 .61 46 .79 4 .90 243 .47 68 .00

-46.54** -3.01 130 .95** - 5 .89* -1 .42 153 .54** -30 .79** 44 .29** 17 .24**73 .13** 154 .61** 301 .14** - 5 .89* -1 .42 153 .54** -30.79** 44 .29** 17 .24**

RC781 x Varuna' 9 .00 26 .47 863 .40 4 .24 12 .99 38 .33 3 .92 244.40 77.67- 24 .16** -5 .92 57 .33* - 15 .36** -6.97 75 .81** -25 .05** 30.93** 21 .99**55 .17** 75 .66* 120 .86* -15 .36** -6.97 75 .81** -25 .05** 30 .93** 21 .99**

Donskaja IV x Varuna' 8 .07 23 .40 1340 .93 4 .34 11 .59 40 .09 3 .74 239.00 70.00-36.98** -10.91 235.12** - 13 .50** - 17 .04** 83.86** -28 .55** 28 .04** 9 .95**39.08** 55 .31* 243 .01** -13 .50** - 17 .04** 83.86** -28 .55** 28 .04** 9 .95**

Skorospieka II x 11 .27 35.33 1732 .25 3.73 11 .50 36.56 2.40 325 .47 83 .67Narinosanigra' -22 .12** 32.83 67.18** -1.50 1 .20 179.94** -24 .05** 22.26** 10.57**

26.12* 60.61* 67 .18** -1 .50 8 .52 179.94** -12 .30 22 .26** 10 .57**RC781 x Chinensis nigra' 12 .00 37 .27 2008 .40 2 .65 7 .17 31 .70 2 .70 295 .33 84 .67

1 .12 25 .34 98 .72** - 22 .42** - 41 .81** 100.55** 5 .74 2 .90 4 .96**12 .50 25 .34 98.72** -22 .42** - 23 .25** 100.55** 18.42 2 .90 4 .96**

Donskaja IV x 10 .87 24 .92 1579 .93 3 .56 10 .81 30 .74 2 .12 310 .73 94 .00Chinensis nigra' -15.10 -16.19 56 .33** 4 .09 -0 .18 94 .47** -8 .16 8 .27** 16 .53**

1 .87 -16.19 56 .33** 4 .09 15 .62* 94 .47** -2.92 8 .27** 16 .53**Donskaja IV x PNMB' 12.33 39 .40 2169 .80 3 .89 12 .25 38 .16 2 .61 287.27 83 .67

-3.65 -2.96 52 .70** 9 .26* 13 .12* 82 .68** -10.42 1 .63 4 .58**12 .12 -2.69 52 .70** 9 .26* 28 .01** 82 .68** -10.42 1 .63 4.50**

Skorospieka II x RC781' 13 .63 38 .80 1029 .33 3 .17 10 .07 38 .09 2 .77 351 .67 110.67-5 .76 37.91* 87.56** -8.56* - 18 .28* 113.04** -12 .34 22 .90** -0.6014.89 37.91* 87.56** -0.63 - 18 .28* 113.04** 8.49 22 .90** -0.60

variability amongst the accessions for all the ninecharacters that were studied . After computing D 2values, 25 accessions were grouped into 9 clusters(Table 1) . Maximum divergence was observed be-tween Indian and CIS types . On the basis of the di-vergence, ten genotypes, three from cluster I (Pusabold, RLM619, Varuna) two each from cluster IV(Narinosa-nigra and PNMB) and VII (Donskaja IVand Skorospieka II) and one each from cluster III(RH 30), V (Chinensis-nigra) and VIII (RC781)were selected and crossed in a 10 x 10 diallel fashionwithout reciprocals for studying heterosis and com-bining ability. The analysis of variance revealed sig-nificant differences among the accessions (parentsand F1s), for all the traits indicating the presence ofconsiderable amount of variation. Variances due togeneral (GCA) and specific combining ability(SCA) were highly significant for all characters ex-cept single plant yield where only SCA was found tobe significant (data on combining ability could beprovided on request) .

Contribution of GCA was higher than SCA forcharacters like plant height, number of primarybranches and 1000 grain weight thus indicating apredominance of additive gene action . Maximumcontribution of SCA was observed in single plantyield followed by number of seeds per siliqua andnumber of siliqua per plant suggesting that the non-additive gene effects are predominantly influencingthe expression of these characters . For other char-acters (number of secondary branches, siliqualength and days to 50% flowering), the contributionof SCA was relatively higher than GCA .

None of the accessions was found to be good gen-eral combiner for all the characters . AccessionsRH30 and RLM619 were relatively good generalcombiners because of their significant general com-bining effects for single plant yield and other char-acters like siliqua length, number of seeds per sili-qua and 1000 grain weight . Accessions RC781, Don-skaja IV and Skorospieka II were good generalcombiners for number of primary and secondarybranches. All the three synthetic types were goodgeneral combiners for the number of siliqua perplant.

In general, all the crosses except three showedheterosis over BP for single plant yield . Significant

223

heterosis was recorded in 15 crosses. Both Indian xCIS and synthetic x CIS recorded a maximum num-ber (five each) of significant heterotic combina-tions, followed by three combinations in Indian xsynthetic cross . In case of Indian x Indian crosses,only two combinations were heterotic for singleplant yield . In both these crosses RC781, a genotypedivergent from other Indian types, was used as oneof the parents .

Analysis of components contributing to yield

Heterosis and mean performance of 12 top highyielding F1 hybrids alongwith corresponding paren-tal mean for single plant yield and component char-acters are given in Table 2 . It was observed that themean performance of most of the hybrids was with-in the range of parental means for all the compo-nent characters except number of siliqua per plantbut the single plant yield exceeded the yield of thebetter parents (Table 2, upper row of section B) . Forexample, the F1 hybrid, PNMB x RH30 (Table 2,middle row of section B) exhibited 64 .02% yieldheterosis over BP despite the fact that five of the sixyield contributing traits i .e. number of primary andsecondary branches, number of siliqua per plant, si-liqua length and 1000 grain weight showed signif-icant negative heterosis and the sixth trait, numberof seeds per siliqua, showed only marginal increase(1.44%) over the BP. Even the MP-heterosis data(not shown) did not explain the yield increase in thishybrid. We, therefore, estimated the contribution ofdifferent characters towards yield heterosis by com-paring the values of different component charactersof hybrids with the respective component charac-ters of the BYP. In this analysis BYP would notchange from one character to another in a partic-ular cross in contrast to usual method of estimatingheterosis over BP in which BP could change foreach component character. The parameter usedhere should not be confused with the parameterused for estimating standard heterosis (comparisonof F1 with the standard check) . Table 2 (lower rowof section B) shows the percent heterosis over BYPfor different component characters in 12 selectedhybrids revealing heterotic effects for number of

Tabl

e 3.

Mean

and

ran

ge o

f pe

rcen

t he

tero

sis

of a

ll t

he c

ross

es i

n 10

x 1

0 di

alle

l

Perc

ent

heterosis

* Significant at p =

0.05 ;

**

Sign

ific

ant

at p

= 0

.01.

MP

= Mi

d pa

rent

;BP

= Be

tter

par

ent ;

BYP = Better yielding parent.

Over MP

Over BP

Over BYP

Mean

Minimum

Maximum

Mean

Minimum

Maximum

Mean

Minimum

Maxi

mum

-5.63

-26

.05*

29.4

1-22

.12*

-46

.34**

27.5

424

.00*

-28

.48**

98.72**

8.30

-29

.10*

45.4

0*-1

2.1

6-5

2.05**

37.9

1*33

.65*

-38

.59**

54.61**

62.1

7**

-32.2

525

0.31**

29.8

5*-

54.84**

235.

12**

84.79**

-34

.30*

317.

66**

5.65

*-1

9.72**

24.32**

-4.0

5-

22.42**

12.24**

-1.9

2-22

.42**

24.6

3**

4.10

-33.80**

29.91**

-2.9

2-4

1.81**

16.5

9*1.

87-2

6.77**

28.8

9**

76.8

5**

-9.2

722

2.93**

49.4

9*-2

6.2

817

9.94**

49.4

9*-2

6.2

817

9.94

**0.

05-

18.6

0*30

.30**

-16

.73**

-44.21**

24.09**

-9.5

7*-4

4.2

1**

47.7

7**

1.67

-12

.50**

18.63**

17.96**

-7.59**

44.29**

15.22**

-20

.26*

*44

.29*

*-9.

12**

-20.93**

9.93**

6.09**

-14

.58**

33.75**

3.62

*-26

.35**

33.75**

Char

acte

rParental mean

No.

of p

rima

ry b

ranc

hes

8.98

± 3.

71No

. of

sec

onda

ry b

ranc

hes

22.60

± 9.

46No

. of siliqua/plant

639.

84±

380.

06Siliqua length (cm)

3.96

± 0.

75No

. of

see

ds/s

iliq

ua11

.34 ±

1.35

Single plant yield (

gm)

16.79±

5.14

1000

gra

in w

eigh

t (gm)

3.93

± 1.

71Plant height (cm)

243.

30± 56

.89

Days

to

50%

flow

ering

80.20±

19.

86

primary and secondary branches which otherwiseshowed negative heterosis over BP (Table 2, middlerow of section B) .

A comparison of the three methods of estimatingheterosis (heterosis over MP, BP and BYP) confirmthe above results (Table 3) . For characters like num-ber of primary and secondary branches, mean ofpercent heterosis was significant when heterosiswas estimated over BYP but was not significantwhen heterosis was estimated over MP and BPThese two characters were low expression yieldcontributing traits of BYP in majority of hybridcombinations (Table 2) . Increase in these charac-ters in the hybrids remained undetected when esti-mates were made over MP or BP values but couldbe detected when estimates were made over the val-ues of BYP. For characters like siliqua length andnumber of seeds per siliqua the mean of percentheterosis over MP was higher than mean of percentheterosis over BYP (Table 3) . In majority of cross-es, both siliqua length and number of seeds per sili-qua were high expression characters of BYP As aconsequence, most of the hybrids exhibited hetero-sis over MP but not over BYP. This indicated thatboth these characters have not contributed signif-icantly towards yield heterosis in hybrids but havemaintained the potential of high expression byshowing significant level of MP-heterosis . From thedata given in Table 2 and 3 it could be concludedthat the number of siliqua per plant, number of pri-mary and secondary branches contributed signifi-cantly towards heterosis in yield .

Correlation ofparental divergence with heterosis foryield and yield components

The relationship between the parental divergenceand heterosis for yield was assessed by estimatingthe correlation coefficients . The results indicatedthat the divergence had significant positive correla-tion with single plant yield of hybrids (r = 0.740 and0.738) and also with MP- (r = 0.711 and 0.695) andBP/BYP-heterosis (r = 0.599 and 0.600) for singleplant yield (Table 4) . The rationale followed herewas that if yield and heterosis for single plant yieldshows significant positive correlation with parental

225

divergence then the sum total of component char-acters contributing to yield-heterosis should alsoshow significant correlation with parental diver-gence. To test this hypothesis correlation coeffi-cients were estimated between parental divergenceand rank total of percent heterosis based on comm-ponent characters calculated over MP, BP and BYPvalues. Ranking was done to take into account thenegative values of the heterotic effects in somecharacters. Rank total was determined (see Materi-als and methods) in order to pool together the rela-tive contribution of individual characters towardsyield heterosis. Number of classes (5) was initiallystandardized on the basis of single plant yield insuch a way that the correlation between divergenceand rank of single plant yield was almost similarwith correlation between parental divergence andabsolute values (Table 4) .

When correlation coefficients between parentaldivergence and rank total of percent heterosisbased on component characters were calculated(Table 4), it was observed that the divergenceshowed significant positive correlation with ranktotal of percent heterosis over BYP (r = 0 .722 and0.702) . Very low correlations were obtained withother two parameters (r = 0 .142 and 0.142 with MPand r = 0.175 and 0.192 with BP) . Correlation withsingle plant yield confirm the above results byshowing higher correlation with BYP (r = 0 .695) ascompared to other two methods of estimating het-erosis (r = 0 .351 with MP ; r = 0.363 with BP) . Thisindicated that estimation of heterosis from BYP is amore accurate parameter to determine the contri-bution of component characters towards yield het-erosis .

Heterosis at the plot level

Heterosis at single plant level revealed that onlyfour crosses (Skorospieka II x RH30, DonskajaIV x Pusabold, Donskaja IV x Varuna and RC781 xRH30) had high SCA coupled with highper se per-formance and heterosis for single plant yield . Twohybrids, Skorospieka II x RH30 and Donskaja IV xVaruna, were tested for two years (1990-91 and1991-92) in plot level yield trials . Two other hybrids

226

Table 4. Simple correlation between parental divergence and heterosis involving all the crosses in 10 x 10 diallel

* Significant at p = 0 .05 ; ** Significant at p = 0 .01 . ' Correlation coefficient between parental divergence and rank of yield and yield-heterosis . MP = Mid parent; BP = Better parent ; BYP = Better yielding parent .

were not considered because of their weak stemsresulting in lodging at the grain filling stage .

The mean performance of the plot yield of thehybrids were significantly higher than the BYP andstandard checks (Table 5) . The performance of theparents was poor during 1991-92 growing season asthe trial was conducted on a marginal land . How-

Table 5. Field performance of two hybrids alongwith better yielding parents and standards for yield and yield contributing traits during

* Siliqua density was calculated as number of siliqua per unit centimeter length of main shoot .A = 1991 ; B = 1992 .

ever, the hybrids were more stable as compared toBYP and standard checks . Analysis of componentcharacters in the hybrids revealed that characterslike number of primary and secondary branches,number of siliqua per plant and siliqua densityshowed significant increase over their correspond-

1991 and 1992

Parent/Cross Year Plot Yield(Q/ha)

No. ofprimarybranches

No. ofsecondarybranches

No. of

Siliquasiliqua/plant density*

1000 grain Siliquaweight (gm) length (cm)

No. ofseeds/siliqua

Skorospieka II A 28.69 8 .1 15 .5 449 .3

0.90 4.4

4.5 12 .1x RH30 B 28 .11 5 .8 653 .0 5 .1

4.2 11 .1Donskaja IV A 29.47 6 .8 14.9 510 .8

0.84 3.6

4.5 11 .9x Varuna B 25.40 5 .3 570 .3

- 4.0

4.3 11 .1RH30 A 21 .26 4 .7 9.9 231 .3

0.55 6.4

4.6 12.5B 16 .28 4 .2 331 .7

- 5.6

4.1 11.0Varuna A 22.77 4 .9 9 .4 224.3

0.56 4.8

5.1 14.4B 13 .24 4 .0 196.9

- 5.3

5.4 12.1Pusa bold A 23.53 3 .7 7 .7 170.2

0.52 7.6

4.9 12.5B 16.84 3 .5 - 179.7

- 7.6

5.0 10.6Pusa barani A 22.99 5.0 9 .9 255 .8

0.56 6.3

4.8 13.5B 17.31 4.0 188.7 5 .8

4.9 12.7Kranti A 23 .19 4.5 8 .6 221 .3

0.61 4 .1

4.4 12.6B 17 .26 4.7 307 .5

- 5.2

4.5 11.9CD (p = 0 .05) A 3 .13 1.41 5 .97 197 .4

0.14 1 .11

0.28 0.77B 8.08 1 .11 324 .9

- 0.79

0.55 1.48

Heterosis Parameters Parental divergence (D value) Single plant yield ofhybrids

1988 1989

% heterosis for single plant yield MP 0.711** 0.695**0.708**' 0.661**'

BP/ 0.599** 0.600**BYP 0.615**' 0.606**'

Single plant yield of hybrids 0 .740** 0.738**0 .709**' 0 .715**'

Rank total of percent heterosis based on MP 0.142 0.142 0.351component characters BYP 0.722** 0.702** 0.695**

BP 0.175 0.192 0.363*

ing BYP thus corroborating the earlier findingsfrom diallel analysis (Table 2, 5) .

Discussion

Methodology to study the contribution ofcomponent characters

In the present study, it was observed that Fl hybridsin general remained within the range of values re-corded for their parents for majority of yield com-ponents but single plant yield exceeded the yield ofthe better parents (Table 2) . Similar intermediateperformance of the hybrids for yield attributingtraits have earlier been reported in other crops(Williams, 1959; Pawlisch & Dijk, 1965). Sinha &Khanna (1975) have highlighted these problemswhile reviewing the genetic basis of yield compo-nents in relation to yield heterosis in sorghum,maize and wheat. Williams (1959) observed no het-erosis or overdominance for five component char-acters while all the hybrids exceeded their parentsin fruit yield in tomatoes . He concluded that thesecharacters behaved as independent units and theirdominance or partial dominance was responsiblefor heterosis in yield because of multiplicative in-teraction . The heterotic effect for yield in B. junceahybrids could be due to favourable combination ofthe yield components of the parental cultivars . Inthe present study, the Indian genotypes have fa-vourable yield components like siliqua length, num-ber of seeds per siliqua and 1000 grain weightwhereas the synthetic and CIS types have high pri-mary and secondary branches and number of sili-qua per plant (Table 2) . Favourable combination ofthese traits of both parents has resulted in dom-inance or partial dominance for majority of yield at-tributing traits in Fl hybrids.

The estimate of heterosis over BP could not as-sess the contribution of different yield attributingtraits that showed dominance or partial dominancein the hybrids. It was observed that when estimatesof heterosis were made over BYP the contributionof the component characters were more effectivelyassessed compared to the estimation of heterosisover MP and BP (Tables 2 and 4). The premise was

227

that if the BYP is fixed on the basis of yield then anyimprovement in constituent characters in the hy-brid over the constitutent characters of the BYPwill certainly contribute towards higher yield in thehybrids. A BYP may not show high level of expres-sion for all the constitutent characters as comparedto the other parent . When heterosis is estimatedfrom low expression yield contributing traits ofBYP, it is possible to detect partial dominance anddominance that otherwise cannot be detected whenheterosis is estimated over BP Thus the componentcharacters showing dominance or partial dom-inance in the hybrids could be estimated more ef-fectively by comparing the performance of Fl hy-brid with BYP of the concerned hybrid .

Identification of component character contributingto yield in mustard

Our results from diallel and plot level experimentsshowed that four component traits, number of pri-mary and secondary branches, number of siliquaper plant and siliqua density contributed signifi-cantly towards yield heterosis . Two of these (num-ber of secondary branches and number of siliquaper plant) showed higher SCA effects that are desir-able in heterosis breeding. Siliqua length and num-ber of seeds per siliqua are associated characterswhereas number of seeds per siliqua shows negativecorrelation with 1000 grain weight (Paul et al .,1974). In such cases, a compromise has to be madein selecting the parents for these characters . But theparents should be contrasting for the number of pri-mary and secondary branches and number of sili-qua per plant . At least one of the parents should bea high yielding parent and such ideal situation hasbeen found in CIS x Indian crosses in the presentstudy. However, care should be taken for charactersof low heritability e.g. branch number (Singh, 1973) .Branch number is a character that is highly affectedby population density. Therefore, emphasis shouldbe given to increasing the number of siliqua on pri-mary branches. This could be best achieved by se-lecting a high siliqua density type as one of the par-ents. It was observed that Fl hybrids between CIS xIndian types had a siliqua density of 0 .84 to 0.90 as

228

against better yielding Indian parents that had sili-qua density of 0 .52 to 0 .61 (Table 5) . The high siliquadensity in the hybrids was inherited from CIS types .Although, the siliqua density was not studied thor-oughly in our initial experiments, we feel that thischaracter should be emphasized in any future selec-tion of genotypes for heterosis breeding in both ra-peseed and mustard .

Plot level heterosis

Sinha & Khanna (1975) pointed out that the extentof yield heterosis obtained at single plant basis ishigher than that obtained at the field level . In caseof B. juncea, depending upon the type of crosses,heterosis upto 262.67% (Banga & Labana, 1984),182.09% (Kumar et al., 1990) and 179 .94% (thisstudy) over BP have been observed at single plantlevel. None of the earlier studies have reportedyield heterosis in plot level trials . Our results indi-cate that heterosis at the population level is lowerthan that observed at the single plant level . Thus thereal potential of the hybrids could only be evaluatedfrom plot level yield trials and not from single plantdata. However, the analysis of the component char-acters of the hybrids in plot level trials exhibitedtrends that were observed in diallel analysis .

In conclusion, our results demonstrate that con-siderable potential exists in B. juncea for heterosisbreeding using single cross hybrids . The pro-gramme on heterosis breeding can be advanced fur-ther by selecting lines, from the extensive germ-plasm collections, that could compensate low ex-pression component characters of high yielding cul-tivars that are extensively grown on the Indiansub-continent . Similar strategy could be adopted inother parts of the world for enhancing yield of B .juncea .

Acknowledgements

We thank Dr S. Prakash of Indian Agricultural Re-search Institute, New Delhi and Project Coordina-tor, Oilseeds (Rapeseed and mustard) of IndianCouncil of Agricultural Research, Govt of India for

germplasm. Technical assistance was provided byMr J.K. Verma and B.S. Yadav. This research wassupported by a CEC grant number ECII-0193-IND(BA) .

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