Euphytica 40 : 1-14 (1989)© Kluwer Academic Publishers, Dordrecht - Printed in the Netherlands

The development of Raparadish (x Brassicoraphanus, 2n = 38), a new cropin agriculture

W. Lange, H . Toxopeus, J .H. Lubberts, O. Dolstra and J .L. HarrewijnFoundation for Agricultural Plant Breeding (SVP), Wageningen, The Netherlands

Received 13 August 1987 ; accepted in revised form 10 September 1987

Key words : Raparadish, X Brassicoraphanus, Brassica rapa, Raphanus sativus, amphidiploid, intergenerichybrid, fertility, resistance, beet cyst nematode, Heterodera schachtii

Summary

Raparadish, X Brassicoraphanus, the amphidiploid hybrid between Brassica rapa (syn . B.campestris) andRaphanus sativus (fodder radish) was made by Dolstra (1982) . Primary hybrid plants grew vigorously,suggesting that the amphidiploid AARR might be useful as a fodder crop. Three populations of this newmaterial were studied, with special attention to improvement of fertility and resistance to beet cyst nematode(Heterodera schachtii), whilst preserving genetic variability . For lack of progress one of the populations wasabandoned after the fourth generation . The other two populations were observed through nine or tengenerations. Apart from the last two generations mass selection for seed set was carried out on the basis ofsingle plants . This led to a considerable increase in average seed production, without losing a wide variationfor this trait . Thus more progress is being expected . Five cycles of mass selection for resistance to beet cystnematodes led to a considerable increase of the level of resistance of both populations . The prospects of thisnew agricultural crop are discussed .

Introduction

New crops may be developed either by domes-ticating natural species or by making new combina-tions between related cultivated species, mostly inthe form of amphiploid hybrids . The genus Brassi-ca (Cruciferae) is a good example of the latter case,containing three diploid species B. nigra (Braun),B. rapa L. (AA) and B. oleracea L. (CC) and thethree possible amphidiploid hybrids, B. napes L.(AACC) amongst them (U, 1935 ; Toxopeus,1974a; McNaughton 1976a & b; Thompson, 1976) .Since the late 1920s (Karpechenko, 1928) the

genus Raphanus was introduced extensively intoresearch programmes regarding interspecific hy-bridization in Brassica. Amphidiploids were madebetween R . sativus L. (RR) and both B. rapa and

B. oleracea (Dolstra, 1982; Prakash & Tsunoda,1983). Hybrids involving three genomes (A, C andR) were also reported (Clauss, 1978 ; Heyn, 1978 ;Dolstra, 1982) .

Oost (1984) showed that, following the Interna-tional Code of Botanical Nomenclature (1983), thename for all hybrids between Brassica and Rapha-nus should be x Brassicoraphanus Sageret. Oost(1984) also suggested the use of common names forthe various amphidiploid combinations . Radicolewas already coined by McNaughton (1979) as acrop name for the RRCC amphidiploid . Toxopeus(1985) proposed Raparadish, as a cultivar group,for the AARR genome combination .

In 1974 a research programme was initiated atthe SVP, aiming primarily at the transfer of gene(s)for resistance to the beet cyst nematode (Hetero-

2

dera schachtii Schm.) from R. sativus to B. rapa andB. napus . The first part of this research has exten-sively been published by Dolstra (1982) . The pro-gramme concentrated on the cross B. rapa x R .sativus because crossability in this combination wasfairly promising and the amphidiploid hybrid mightbe used as a bridge between R. sativus and B.nap us . Most primary hybrid plants grew vigorouslyand suggested that the amphidiploid AARR mightbe useful as a fodder crop, combining rapid growth,resistance to beet cyst nematode and to club-root(Plasmodiophora brassicae Woron .) and palata-bility .

With this prospect in mind research efforts weredirected towards developing the plant material intothis new fodder crop. One of the main problemswas the poor fertility in early generations of thematerial. Furthermore it appeared that the earlypopulations of the new amphidiploid had a lowlevel of resistance to the nematode and neededdrastic improvement in this respect .

The present paper describes the improvement ofthree populations of Raparadish on both fertility

Table 1. Nomenclature and origin of parental material of Brassica rapa (syn . B. campestris) and Raphanus sativus used to make threepopulations of Raparadish (x Brassicoraphanus, PH, CH and MH)

Use inpopulation

Name according to

Olsson (1954) :

B. campestrisPH/MH ssp . pervirid&MH ssp . chinensisCH ssp . chinensisMH ssp . rapiferaMH ssp . rapiferaMH

ssp, nipposinica

Name according toHelm (1957) :

R. sativusPH/MH

var. oleiformisPH/CH/MH var. oleiformisPH/MH

var. oleiformis

MH

var. mougri

and nematode resistance whilst preserving geneticvariability. Data regarding performance of thecrop in the field will be reported, although no selec-tion was carried out on the possible improvementof agronomic characters .

Material and methods

The Raparadish material consisted of three pop-ulations coded PH, CH and MH . All primary cross-es between B. rapa and R. sativus were carried outby Dolstra (1982) who also described the first threegenerations of populations PH and CH. Details ofthe nomenclature and origin of the parental materi-al are summarized in Table 1 . The first generationof population PH consisted of 48 primary hybridplants . However, its genetic base for the formationof the next generation is narrower, because abouthalf of the plants had no or little stainable pollenand only 18 of them produced seeds . PopulationCH had an even more narrow parental base . Itconsisted of 14 primary hybrid plants, of which only

' this name was not mentioned by Olsson (1954), but would fit his nomenclatural system2 leafy plant types, with no or very little bulb formation

Accessionnumber

Ploidy andgenomes

Origin

Toxopeus and Oost (1985) :

B. rapa cultivar groupKomatsuna 2240 4x AAAA S. Ellerstrom, SvalovPak Choi 2x AA H. Toxopeus, WageningenPak Choi 2242 4x AAAA S. Ellerstrom, SvalovFodder turnip 2x AA H. Toxopeus, WageningenFodder turnip cv . Tigra 4x AAAA Sluis & Groot, EnkhuizenMizuna 2245 4x AAAA S. Ellerstrom, Svalov

Common name

fodder radish2 cv . Siletta 2x RR Van der Have, Kappellefodder radish2 cv . Palet 4x RRRR Van der Have, Kappellefodder radish2 RS 14 4x RRRR I.H. McNaughton, Pentland-

fieldrat-tailed radish RS 4.01 2x RR H. Toxopeus, Wageningen

7 produced seeds and two had little or no stainablepollen. Population MH had a more complex paren-tal background, involving many accessions (Table1) . The first generation consisted of 34 primaryhybrid plants, of which about half produced no orlittle stainable pollen and 14 produced seeds .

Three types of populations were studied, theso-called `base', `top' and `bulk' populations . In the`base' populations all half-sib families of the previ-ous generation were represented by at least onenew, half-sib family . The families were representedin equal numbers so as to avoid genetic drift . Theseed of the best individual plant(s) from each fam-ily was used for the next generation . The `top'populations (PH and MH) were composed of seedof the best plants from the best families, in an effortto accelerate progress . Finally `bulk' populationswere created by mixing equal amounts of seed fromthe best plants from the better families from both`base' and `top' populations, since performance ofthe last had not improved over a series of at leastthree generations compared to the former . For lackof progress population CH was abandoned afterthe fourth generation .

In the early generations, when plant numberswere limited, the plants were grown in pots in thegreenhouse or transplanted into the field, isolatedin mosquito gauze cages with a honeybee pop-ulation in each cage for intensive interpollination .Subsequent generations were sown in `jiffy' potsduring late winter and transplanted in spatial isola-tions of about 300 plants each, at a spacing of 10 x30 cm. Plants were observed and harvested individ-ually. Finally the `bulk' seed was sown at a rate of8 kg/ha, in spring, all material being annual . Atharvesting the field was cut in a swath and machinethreshed .

Three fertility components were recorded :number of seeds per plant, of all plants in the`base' and `top' populations ;percentage stainable pollen, staining pollenwith lactophenol acid fuchsine (Sass, 1964), ex-amining normally '200 pollen grains from 3-5flowers. In generations 1-3 two observations ineach flowering season were carried out, and ingenerations 4 and 5 only one observation ;number of siliquas per plant, in generations 1-4

3

for PH and CH, and in generations 1-2 for MH .In later generations the 1000-grain weight was re-corded .

Screening for resistance to beet cyst nematodewas carried out according to Toxopeus & Lubberts(1979). Seedlings were grown in 36 ml PVC tubesfilled with quarz sand (so-called silver sand), as isused in building industry . About 10 days after sow-ing plants were inoculated with a suspension of200-300 pre-hatched larvae by means of a veter-inary inoculation gun . The pathosystem was grownin a climate chamber at a constant temperature of21© C. Four weeks after inoculation the females hadreached their maximum size and showed up on theroots as small white globules of about 1 mm dia-meter, the so-called `white cyst' stage . In the fol-lowing such females will be referred to as cysts .Usually two figures were assessed :- average number of females per plant (estimated

on the basis of counting the cysts on the roots ofa random sample of plants ; the size of the sam-ples being mentioned in the text) ;

- proportion of plants with ten or fewer cysts onthe root system .

Tests for nematode resistance included the follow-ing parental types and controls : B. rapa (2x) culti-var groups Komatsuna and Pak Choi (both fromSVP collection), R. sativus cv . Siletta (2x), cv. Sile-tina (2x), cv. Palet (4x) and RS 14 .(4x) (for originsee Table 1), as well as oilseed rape (B. napes) cv .Jet Neuf (susceptible) and a susceptible selection ofSinapis alba (Sa 6.02.01) .

Agricultural performance was tested in fieldtrials in four successive years (1982-1985). Eachtrial had a randomised block design with threereplications . Size of the plots was 24 m2 . Seeds weredrilled, applying 25 cm between the rows and aim-ing at a plant density of about 200 plants/m 2. Thetrials were sown on 23, 21, 21 and 20 August, andharvested on 2, 3, 5 and 13 November, respec-tively. In the first two years each block consisted of30 items, later this number was raised to 50 . Ex-periments comprised Raparadish, radicole, fodderradish, fodder rape, white mustard and turnip, andwere set up to compare various sources of experi-mental material with known varieties . Three com-ponents were measured : fresh weight, dry weight,

4

and percentage crude protein as established with acolorimetric analysis, using the salicylate methodin a continuous-flow system (Krechting & Van Gel-der, 1983). For the present paper only the relevantpart of the results of these experiments will bereported. In 1984 information was acquired regard-ing the energy value of the dry matter for milk(VEM) and meat production (VEVI), according tothe system used in the Netherlands (van der Ho-ning et al ., 1977) .

Results

General plant morphology

In the vegetative stage plants of x Brassicorapha-nus develop a leaf-rosette . The shape of the leavesis intermediate between the parents, and is veryvariable. Leaves and petioles are pubescent, butnot as much as in R. sativus .

The majority of the plants does not require coldtreatment for flower induction, however, amongstthe remainder there will likely be plants that doneed a cold spell for flower induction, but this wasnot put to the test. Flowering plants have an erectmain stem with a terminal indeterminate inflores-cence. On the main stem many lateral brancheswith similar inflorescences are formed, often re-sulting in dense bushy plants with a height of about1 .5-2.0 m. The flowers are larger than those of B.rapa, and are white, purple or intermediate, rarelyyellow or cream, mostly with strikingly dark veins .

The early generations showed much variation forthe extent of flowering, ranging from abundantflowering to plants with a few flowers or no flower-ing at all . Some plants showed a typical abnormalbud development: the buds dried out and droppedprematurely .

The siliquas of x Brassicoraphanus are interme-diate between the parents, consisting of a dehiscentbivalved part with a septum, and a rather largeindehiscent part, the beak or rostrum, also contain-ing ovules (Fig . 1) . The size and shape of the seedare like B. rapa .

Fig . 1 . Siliquas of Raparadish (x Brassicoraphanus) .

Plant fertility

Three fertility traits were observed and recorded :number of seeds produced per plant, percentagestainable pollen, and number of siliquas per plant .Table 2 shows the average values and Figs . 2 and 3show frequency distributions for seed productionand pollen stainability .

An exceptional combination of climatologicalconditions in the spring of 1983 was responsible forvery poor growth conditions, resulting in very smallplants producing few seeds . This is most apparentin Table 2. The seasons of the other years werereasonably conducive to growth. Since fields andgenerations could not be replicated, possible envi-ronmental effects or interactions with genotypecould not be determined . Therefore the figuresshould be considered to reflect trends .As to seed production, the populations PH and

MH showed a more or less gradual increase, whichin the early generations largely could be attributedto an increase in number of siliquas per plant .Population CH remained rather poor, which is notunderstood . Despite the similarity in increase offertility of PH and MH, Fig . 2 shows important

differences . Population PH showed considerablyless variation and a quicker decrease of the numberof plants giving no or very few seeds . The potentialof seed production can be characterised by theobservation in 1984 that both populations PH andMH contained several plants with more than 5,000seed, the highest number being 7,914 seed perplant .

In both populations PH and MH the differencesbetween the `base' and `top' populations weresmall and variable . It therefore was concluded thatthe efforts to speed up progress had been ineffec-tive and the populations were merged after the1984 harvest . They were carried on as bulk pop-ulations, without further selection on a single plantbasis . Seed yield was established in two consecutivegenerations, in 1985 and 1986. For population PH

Table 2 . Results of assessment of three fertility traits (seedset, percentage pollen stainability, and number of siliquas ; average values perplant) in three populations of Raparadish (x Brassicoraphanus, PH: `base' and `top' ; CH : `base' ; MH : `base' and `top')

seed yields were 40 and 80 kg/ha, respectively andfor population MH these figures were 98 and100 kg/ha .

The stainability of pollen was assessed in theearly generation of all three populations (Table 2and Fig. 3), the increase being slow or absent .Apparently the availability of pollen was not alimiting factor in seed set .

Finally Table 3 shows average values of the 1000-grain weight of populations PH and MH and someparental material. Both populations showed a widevariation between plants . Taking into acount thatRaparadish is tetraploid, the seed weight is near tothat of the Brassica parental material and much lessthan the seed weight of some of the R . sativusparents .

5

Year Genera-tion

Number of Seedset Pollenstainabil-ity (%)

Siliquas Number of Seedset Pollenstainabil-ity (%)

Siliquas

families plants families plants

PH `base' PH `top'1977 1 - 48 7 24 1011978 2 18 64 14 37 1641979 3 37 180 72 49 449 8 59 92 49 6141980 4 100 618 109 41 679 40 357 87 49 9391981 5 61 583 107 50 52 302 151 521982 6 60 289 502 57 277 5191983 7 61 276 180 62 301 1731984 8 62 303 401 62 306 974

1977 1CH `base'- 14 6 47 146

1978 2 7 21 3 35 541979 3 6 25 23 47 1611980 4 16 93 33 30 5981981 5 12 117 25

1977 1MH `base'- 34 8 39 98

MH `top'

1979 2 12 92 21 19 1561980 3 51 215 581981 4 28 249 163 331982 5 31 294 326 31 287 1781983 6 50 252 32 50 285 1431984 7 50 276 812 51 280 703

Plan

ts 'l.

70 60 50 40 30 20 10 0 70 60 50 40 30 20 10 0n

PH 1

CH 1

R-

2

nn

3

11 n

4

5

2

3

4

5

n

70 60

M H 1

2

3

4

50 40 30 20-

10 0

n

n

12 3 4 5

1 2 3 4 5

1 2 3 4 5

1 2 3 4

5

12

3 4

5

Year

:

1977

1978

1979

1980

1981

1 2 3 4 5

5

7 6

7

MA

1 2 3 4 5

12 3 4 5

1982

1983

1984

Fig.

2.F

requ

ency

dis

trib

utio

ns o

f pl

ants

of three populations of

x Br

assi

cora

phan

us(PH: `base' and `top'; CH

: `b

ase'; MH

: `b

ase'

and

`top')

reg

ardi

ng n

umbe

r of

see

ds p

er p

lant

. Fo

r av

erag

e va

lues

see

Tab

le 2

. Cl

asse

s of

see

dset

: 1

= 0-

2, 2

= 3

-16, 3 = 17-125, 4 =

126-1000, and 5 = >1000 seeds per plant.

Open

col

omns

: `base' populations

; hatched columns:

`top' populations

.

Plants 'l.

50

40

30

20

10

0

50

40

30

20

10

0

50

40

30

20

10

0 J

nnn

MH 1

n1 2 3 4 5

1 2 3 4 5

1

Year :

1977

1978

Resistance to the beet cyst nematode, Heteroderaschachtii

In 1980 to 1982 three tests were carried out toscreen approximately 7,000 plants for resistance tothe beet cyst nematode . The plants were raisedfrom seeds of the populations PH and MH, pro-duced in preceding years, whereby the number of

PH 1

2

CH 1

2

nn

3 4 5

H n

n

3

2

4

nn

4

2 3 4 5

1 2 3 4 5

1 2 3 4 5

1979

1980

1981

7

Fig. 3 . Frequency distributions of plants of three populations of x Brassicoraphanus (PH: `base' and `top' ; CH: `base' ; MH : `base')regarding stainability of pollen . For average values see Table 2 . Classes of pollen stainability : 1 = 0-20%, 2 = 21-40%, 3 = 41-60%,4 = 61-80% and 5 = 81-100% . Open columns: `base' populations ; hatched columns : `top' populations .

tested plants per family differed because of limitedavailability of seed . In general population MHshowed a higher proportion of plants with ten orfewer cysts . In total about three hundred plantswith ten or fewer cysts were selected and grown inisolation cages for seed production . Plants of thetwo original populations were grown in mixedstand. However, seed production of the selected

n

Table 3 . Average thousand-grain weights (in g) of two populations of Raparadish (x Brassicoraphanus, PH and MH), as well asparental material

x Brassicoraphanuspopulation PH

B. rapacultivargroup Komatsuna (2x) 4 .2

`base' 4 .3 cultivargroup Komatsuna (4x) 3 .8`top' 4 .6 cultivargroup Pak Choi (2x) 3 .0`bulk' 4 .6 cultivargroup Pak Choi (4x) 3 .9

cultivargroup Fodder turnip (2x) 2 .1population MH cultivargroup Mizuna (2x) 2 .0`base' 4 .1`top'`bulk'

4 .24 .9

R. sativusfodder radish cv. Siletta (2x) 10.0fodder radish cv. Palet (4x) 15 .5fodder radish RS 14 (4x) 12 .8

8

plants was too low to support a continuing cycle ofmass selection .

Early in 1984 a second selection cycle was start-ed, using a mixture of varying numbers of seed ofall previously selected plants. Nearly 3,000 plantswere raised and screened for resistance. In a ran-dom sample of about one-third of the plants thecysts on the roots were counted . Nearly 200 plantswith ten or fewer cysts were selected and growntogether in spatial isolation to produce the nextgeneration . In 1985 a screening test was carried outto compare resistance in this generation with thatof the original populations PH `bulk' and MH`bulk' . Three groups of approximately 1,000 plantseach were screened. Per group, the number of cystsper plant was determined in a random sample ofabout ten per cent of the plants . The remainingplants were selected without counting cysts. Oncemore the selected plants were planted out in isola-tion to produce the next generation . Table 4 sum-marises the results of the screening tests of 1984 and1985 . Selection resulted in a shift in the level ofresistance of the population : the proportion of verysusceptible plants decreased and the proportion ofplants with ten or fewer cysts on the roots in-creased, although the level of resistance of R . sati-vus was not yet reached .

Table 4 . Results of two tests for resistance to the beet cyst nematode (Heterodera schachtii) in two populations of Raparadish(x Brassicoraphanus, PH and MH, as well as their combined progenies) . Attack expressed as percentage of plants in three classesaccording to number of cysts on the roots

Plant

Selectionmaterial

cycle

x Brassicoraphanuspop. PH `bulk'

1pop. MH `bulk'

1pop. PH + MH

2pop. PH + MH

3

ControlsB. rapa'R. sativus2

-S. alba3

-

1 cultivar groups Komatsuna and Pak Choi2 cv . Siletta, cv . Palet and RS 143 selection 6 .02 .01

In 1986 two more screening tests were carriedout, both to show the response to mass selection forresistance, and to continue such selection . Thetests consisted of replicated trials (Exp . 1 : threereplications of 24 plants; Exp. 2 : four replicationsof 20 plants) . Experiment 2 included three pop-ulations consisting of two progenies (a and b),which derived from parental plants out of Experi-ment 1, that were selected for having (a) no cysts,and (b) 1-5 cysts on the roots .

The results of both tests are summarised in Table5 . An ANOVA was carried out for the averagenumber of cysts per plant and for the relative num-ber of cysts per plant (relative to B . napus cv . JetNeuf). For both parameters a significant effect ofpopulation was observed, so LSD-values could becalculated (Table 5) . The proportion of plants withten or fewer cysts was analysed by means of aStudent's t-test (P<0 .05); it was tested whether theproportion significantly differed : from zero .

These tests clearly show that mass selection forresistance to the beet cyst nematode in x Brassi-coraphanus was substantially successful . The pro-portion of resistant plants gradually increased froma few per cent in the unselected populations' (Ta-bles 4 and 5) to about eighty per cent after fivecycles of selection . Thus the level of resistance in

Exp.year

Numberof plants

Number of cysts/plant

0-10 11-46 >47

1985 121 4 53 431985 90 3 73 241984 1040 22 35 431985 90 21 77 2

1984 90 2 6 921984 105 48 43 91985 153 1 45 54

the best material of x Brassicoraphanus surpassedthe original level of the resistant parent (R . sativus)considerably .

The tests carried out in 1985 and 1986 did notconfirm the earlier indications as that the originallevels of resistance in populations PH and MHwould be different from each other. The compari-son, in Experiment 2, between the three pairs ofpopulations (a vs b) indicated that both ways ofselection were at least equally effective . In only onecase (pop . PH + MH, selection cycle 4) there was aconsiderable difference between a and b, but theresponse was opposite to expectation .

Table5. Response to mass selection for resistance to the beet cyst nematode (Heterodera schachtii) in two populations of Raparadish(x Brassicoraphanus, PH and MH, as well as their combined progenies), in a series of selection cycles

x Brassicoraphanuspop. PH `bulk'pop . PH `bulk'pop. PH `bulk'pop. MH `bulk'pop. MH `bulk'pop. MH `bulk'pop. MH `bulk'pop. MH `bulk'pop . PH + MHpop. PH + MHpop. PH + MHpop. PH + MHpop. PH + MHpop. PH + MH

ControlsB. rapa KomatsunaR. sativus cv . SiletinaB. napus cv . Jet Neuf

LSD (5%)

Agricultural performance

Raparadish as a crop should be used as a foddercrop with important green manure effects. Whensown around the 20th of August, into the stubble ofwheat or barley, the crop is quick to grow andrapidly covers the ground, suppressing the growthof weeds. The plants develop a leaf-rosette, remainvegetative, have an abundant development of leav-es, and grow a strong taproot . The foliage, how-ever, starts to deteriorate rather early, so that theharvest for fodder should not be later than by theend of October. By then the crop has reached aheight of about 65 cm (Fig . 4) . Field experience hasshown that cattle likes to eat Raparadish . Theplants are susceptible to frost and will be killed,

' (a) from preceding generation through plants without cysts, (b) from preceding generation through plants with 1-5 cysts2 based on a random sample of five plants per replication3 proportion of plants with ten or fewer cysts* significantly different from zero, at P --0 .05

9

Plant Selection Experiment No 1 Experiment No 2material cycle'

Cysts per plant Resistant Cysts per plant2 Resistantplants (%)3 plants (%)3

average relative average relative

1 46 135 32 37 108 18*3 (b) 14 43 46*1 27 78 132 27 78 252 (b) 8 25 63*3 (a) 15 46 34*3 (b) 11 32 42*3 25 75 25*4 19 55 44*4 (a) 22 67 33*4 (b) 3 8 81*5 (a) 3 8 88*5 (b) 9 27 75*

35 102 024 72 2634 100 8 33 100 12

8 24 13 40

10

The results of the present as well as earlier studies(for references see Tsunoda et al ., 1980) allow toextend the Brassica triangle of U (1935) to the

Fig. 4. Raparadish, a new crop in agriculture .

Brassica-Raphanus diamond (Fig . 5), representing

Table 6. Fresh weight, dry weight and percentage crude protein (on dry weight basis) of two populations of Raparadish (x Brassi-coraphanus, PH and MH), compared with some cultivars of fodder radish (Raphanus sativus) and fodder rape (Brassica napus)

Plant material

RaparadishPH `bulk' 1981PH `bulk' 1984MH `bulk' 1984

Fodder radishcv . Siletinacv . Peglettacv . Resal

Fodder rapecv . Akelacv. Emeraldcv. Ramoncv. Valuas

LSD (5%)

even in mild winters, making the crop suited to beused as green manure .

Table 6 summarises the relevant part (only Rap-aradish, fodder radish, and fodder rape) of fieldtrials that were carried out to test agricultural per-formance. The production of fresh matter is nearlyas high as for fodder radish, the dry matter produc-tion is more like fodder rape, whereas the produc-tion of crude protein is intermediate . For the har-vest in 1984 data regarding the energy value of thedry matter for milk and meat production were ac-quired. The average value for Raparadish wasabout ten per cent higher than for fodder radishand about five per cent lower than the value forfodder rape . However, it should be born in mindthat no selection for agricultural traits has yet beencarried out .

Discussion

Fresh weight (ton/ha) Dry weight (ton/ha) Crude protein (%)

1982 1983 1984 1985 1982 1983 1984 1985 1982 1983 1984 1985

44 .8 16 .7 23 .7 - 3 .1 1 .1 1 .9 - 23 .7 18 .7 19 .9 -- - 31 .0 - - - 2 .3 - - 23 .7

- 30 .2 - - 2.4 - 20.7

47 .8 18 .9 35 .4 - 3 .5 2 .0 3 .1 - 23 .1 18 .8 20 .3 -23 .9 32 .0 30 .9 - 2.6 3 .0 3 .0 18 .0 17 .3 17 .3

- - 28.0 36.6 - - 2 .2 2 .9 - 20 .6 22 .0

34 .1 18 .7 16 .4 - 3 .3 2 .2 2 .0 - 24 .7 16 .9 19 .3 -35 .5 18.4 25 .3 - 3 .2 2 .0 2 .7 - 22 .5 18 .9 17 .2

- - 21 .8 - 2 .3 - 20 .2- - 24 .9 - - - 2.8 - - - 18 .2

5 .9 3 .0 8.8 5 .8 0 .6 0 .4 0.6 2 .4 - 2 .9 2 .0

11

Fig. 5 . The Brassica-Raphanus diamond, showing the species relationships of the majority of the cruciferous crops . Common or cropnames : B. nigra : black mustard ; B. juncea: Indian or brown mustard ; B. rapa (syn: B. campestris) : turnip, turnip-rape seed, orientalvegetables ; B. carinata : Ethiopian mustard; B. oleracea : various types of cole crops ; B. napus: oil-seed rape, fodder rape, swede ;x Brassicoraphanus: AARR = cultivar group Raparadish, CCRR = radicole ; R. sativus: radish, fodder radish, oil-seed radish .

12

the species relationships of the majority of the cru-ciferous crops. The introduction of R. sativus ininterspecific hybridisation in Brassica until nowgave rise to two new hybrid crops . In the 1970s thecrop radicole was created from hybrids between R.sativus (?) and B. oleracea (d') . At Pentlandfield(Scotland, UK), McNaughton (1979) developedmaterial from amphidiploids between fodder rad-ish and thousand-headed kale as well as curly kale .Similarly, Ellerstrom & co-workers produced hy-brid material between fodder radish and marrow-stem kale (for references see Olsson, 1986), whichhybrids show potential as a fodder crop . The pre-sent study adds another type of x Brassicorapha-nus, Raparadish, to the list of potential new crops .

Raparadish and radicole have much in common .As a crop they resemble fodder rape, althoughRaparadish grows a leaf-rosette and both fodderrape and radicole grow a vegetative stem . The fo-liage of the three crops is palatable . In Raparadishand radicole the production of fresh matter mostlyis considerably higher than in fodder rape, but alower dry matter content leads to a more or lessequal dry matter production (Table 6 ; McNaugh-ton, 1979) .

A major advantage of both Raparadish and rad-icole over fodder rape is resistance to the beet cystnematode. The present study has shown that forRaparadish continuing mass selection led to veryhigh levels of resistance, comparable with those ofthe best material of fodder radish . Toxopeus &Lubberts (unpubl . results) obtained the same re-sponse by applying this selection procedure onboth types of radicole . It is worth noting that resist-ance of the intergeneric hybrids undoubtedly isderived from R. sativus, in which as such no selec-tion for resistance was carried out . It also should bekept in mind that most material ofR. sativus usedto make Raparadish is different from the materialin radicole .

McNaughton (1979) also reports high levels ofresistance to club-root (Plasmodiophora brassicae)to occur in radicole . Raparadish was not tested forclub-root resistance, but fodder radish has veryhigh levels of resistance to a range of isolates of thedisease (Toxopeus, 1974b) . Therefore, it can beexpected that Raparadish will have relevant levelsof resistance, too .

The major disadvantage of Raparadish and rad-icole is their poor seed production . The presentstudy shows that for Raparadish repeated selectionfor high seed production has been successful . Atpresent an average seed yield of 100 kg/ha has beenreached. This figure is still too low as compared towhat would be necessary for economic seed pro-duction, but the material still shows a wide varia-tion and thus potential for further selection . Alsothe material obtained by McNaughton (1979) andby Ellerstrom & co-workers (Olsson, 1986) respon-ded well to selection in the early generations . Theauthors mentioned to be at about one-half andone-third, respectively, of the level of seed produc-tion which would be enough for a commercial crop .Toxopeus & Lubberts (unpubl . results) applied amild system of mass selection for good seed pro-duction in the materials of McNaughton & Eller-strom, starting in the late 1970s . At present, thebest of these materials yields approximately 700 kg/ha of seed, which is nearly twice as much as report-ed by McNaughton (1979), and would be enoughfor commercial seed production .

Another problem of both Raparadish and rad-icole is seed extraction. The siliquas have a de-hiscent part containing the major part of theovules . The remaining ovules (for radicole up to20% ; McNaughton, 1979) develop on the inde-hiscent apical part of the siliqua, the beak or ros-trum. This means that special attention should begiven to the threshing equipment and threshingprocedures. It even might be worthwhile to lookfor material with a dehiscent beak, or to selecttypes in which seed development is restricted to thedehiscent basal part of the siliqua .

Ellerstrom & co-workers studied sterility andembryo development in their materials of radicole(Olsson, 1986), and concluded that the main causefor sterility is a disturbance of a more general na-ture in interaction between the parental genomes .Dolstra (1982) observed a complex of sterility fac-tors operating in the early generations of Raparad-ish, viz . incompatibility reactions between pollenand pistil, disorientation of growth of the pollentubes in the ovary, poor setting and growth ofsiliquas, and poor growth and arrested develop-ment of embryos. In general, poor seed setting was

considered to be under genetic control . As thesterility factors were similar to elements of thecrossing barrier in the original cross, Dolstra (1982)interpreted sterility in x Brassicoraphanus interms of the incongruity theory of Hogenboom(1973 ; 1975) . Residual factors of incongruityamong B. rapa and R. sativus were considered tooperate in the newly established hybrids and tocause sterility . The present study has shown a con-siderable improvement in fertility in a limited num-ber of generations, under circumstances that highlyfacilitated recombination as well as natural selec-tion for seed setting . It seems plausible to suggestthat the major changes in fertility were due toadjustments in the penetration capacity of pollen .This led to an increasing number of plants with highseed yields. It remains surprising, however, thatthe effect of a stronger selection intensity, as ap-plied in the so-called `top' populations, was rela-tively small . The strategy to avoid inbreeding mayhave reduced the selective advantage of plus-al-leles of barrier genes, and consequently also thechances to fix them . Another more likely explana-tion could be linkage between genes of the barrierand the penetration capacities, as well as a lowinitial frequency of the favourable alleles . Thesealleles most probably are recessive, suggesting thatimprovement of fertility might be accelerated by asystem of recurrent selection based on the perform-ance of S t progenies. It might even be worthwhileto select in Raparadish for a self-fertile matingsystem, as happened in nature with several allo-tetraploid cruciferous species, e .g . in B. napus .

The present results indicate that a broad geneticbase of the material has been favourable to theimprovement of fertility . The population CH hadto be abandoned because progress was extremelyslow; this population had a very narrow geneticbase. In contrast, the most diverse population, i .e .MH, gave the best response to selection . Thus,further progress may be achieved by broadeningthe genetic base of Raparadish, first by combiningpopulations PH and MH, and second by makingnew crosses. In this respect hybrids from crosseswith R. sativus as a female parent may be a usefulextension .

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