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Developing high glucosinolate cultivars suitable for bio-fumigation from intergeneric hybrids

Angela P. Brown, Jack Brown & Jim B. Davis

Department of Plant, Soil & Entomological Sciences, University of Idaho,
Moscow, Idaho, USA 83844-2339. Email: abrown@uidaho.edu

Abstract

Four Brassicaceae species – Brassica rapa, B. nigra, B. napus and Sinapis alba were used in these hybridization studies. Spring planted hybrid progeny have shown a wide variation for yield, oil content, fatty acid profile and glucosinolate content. Hybrids between S. alba x winter B. napus have also been produced. B. juncea has been re-synthesized (winter B. rapa x B. nigra) as a winter type increasing the range of glucosinolate types available as a winter hardy plant. Plants showing high glucosinolate content and winter hardiness could be planted in the fall and would simultaneously prevent soil erosion and bio-fumigate the soil. ‘Humus’, a winter B. napus released in 1992 as a plow-down cultivar has 8.6 Ámolg-1, resynthesized B. juncea has 36 Ámolg-1, and S. alba x B. napus has 25.3 Ámolg-1 total glucosinolate in green leaf tissue. In addition to 4-pentenyl and 2-hydroxy-3-butenyl glucosinolate found in ‘Humus’ and all the hybrids, large quantities of allyl and butenyl glucosinolates are found in the re-synthesized B. juncea. These have been found to be effective in controlling a large range of soil pests. The predominant glucosinolates 3-indolylmethyl and p-hydroxybenzyl found in the S. alba x B. napus hybrid have been found effective in suppressing weed seed germination. The volatile isothiocyanates produced as breakdown products of the allyl and butenyl glucosinolates provide tremendous potential for biological soil fumigation without synthetic fumigants.

Keywords: Brassica rapa, B. nigra, B. napus, Sinapis alba, isothiocyanates

Introduction

Canola (Brassica napus) has high oil content and good quality meal suitable for animal feed; however, it has little tolerance to high temperatures, no drought tolerance, tends to shatter seeds at maturity and is very susceptible to a wide range of insect pests. Polish canola (B. rapa) has some drought tolerance and has less shatter at maturity. Yellow mustard (Sinapis alba), currently grown for condiment use, has many desirable agronomic traits including tolerance to high temperatures and drought, resistance to shattering, and shows tolerance to many of the early and late season pests that affect canola. Oriental mustard (B. juncea) is susceptible to late season pests. The oil content of mustard seed is lower than canola and the meal is high in glucosinolates.

Environmental concerns have caused restrictions on registration and use of synthetic fumigants in the U.S.A.. This has resulted in increased interest in biological control of soil-borne pests and diseases. Brassicaceae plants contain glucosinolates, which break down in the soil to produce toxic substances similar to methylisothiocyanate found in commercial soil fumigants - ‘Vorlex’ and ‘Vapam’. They have been shown to have insecticidal, herbicidal, fungicidal and nematicidal properties. Cultivars specifically designed as plow-down crops with allelopathic effects suitable to replace synthetic fumigants are now being developed. Erosion is a problem in the Pacific Northwest during winter, therefore priority has been given to a fall planted, winterhardy cover crop. This produces more biomass before plow-down than a spring planted crop, provides wind and water erosion control during winter and early spring, and recycles nutrients that might otherwise leach into groundwater or streams.

Materials and method

Four Brassicaceae species – B.rapa, B. nigra, B. napus and S. alba were used in these hybridization studies. The diploid species – B. rapa (AA), B. nigra (BB) and S. alba (DD) all have different glucosinolate profiles, the amphidiploids – B. napus (AACC) and B.juncea (AABB) contain glucosinolates from both diploid progenators. Parents for hybridization were raised in the greenhouse where bud pollinations were made. Details of hybrid production, fatty acid methyl ester determination and glucosinolate analysis can be found in Brown et al, 1997. Spring and fall planted hybrid types were produced between S. alba x B. napus. B. juncea (oriental mustard) has a different glucosinolate profile from yellow mustard and normally only exists as a spring planted type. A fall planted type of B. juncea was resynthesized by crossing fall planted B. rapa x B. nigra.

S alba x B. napus hybrids, resulting from crosses of S. alba with low erucic acid (LEA) or high erucic acid (HEA) B. napus parents, were evaluated in small field plots, 2 feet x 18 feet. Two replicates of thirty hybrids were planted at the Parker Farm outside Moscow, Idaho in 1997. ‘IdaGold’ (yellow mustard), ‘Cyclone’ (canola) and ‘Sterling’ (rapeseed) were used as controls. Characters reported here are seed yield, oil content, fatty acid profile and glucosinolate content.

Results and discussion

A wide range of variation existed in the field grown spring hybrids. The results are shown in Tables 1 and 2. The mean yield of LEA hybrids was 398 kg/ha, the lowest yield was 58 kg/ha and the highest yield was 817 kg/ha. The mean yield of HEA lines was 1321 kg/ha, the lowest yield was 328 kg/ha and the highest yield was 2345 kg/ha. IdaGold yielded 1692 kg/ha, the two B. napus varieties average yield is 1800kg/ha.

Table 1. Average seed yield (kg/ha), oil content (%) and range of these traits from S.alba x B. napus (low erucic acid, LEA) and from S.alba x B. napus (high erucic acid, HEA) hybrids. Also shown are data from traditional yellow mustard (IdaGold), spring canola (Cyclone) and spring rapeseed (Sterling).

Genotype

Seed Yield

Oil Content

IdaGold

1692

26

Cyclone

-

40

Sterling

-

41

LEA – Mean
- Range

398
58 – 817

29
22 – 34

HEA – Mean
- Range

1321
328 – 2345

36
30 – 41

The oil content of the seed also showed a wide range of variation. IdaGold had 26%, Cyclone 40% and Sterling 41%. The LEA mean was 29% from the range 22 to34%. The HEA mean was 36% from a range of 30 to 41%.

Similarly the seed fatty acid content of the different lines varied. LEA crosses showed a mean of 46% oleic acid, the lowest showed 31% and the highest 62% oleic acid. HEA crosses had a mean of 29% oleic acid, the lowest at 14% and the highest 62% oleic acid. The standards have varied levels of oleic acid: IdaGold 28%, Cyclone 63% and Sterling 15%. It is interesting to note that some of the progeny generated from both LEA and HEA crosses were producing 62% oleic acid, levels comparable to those found in commercial canola cultivars. The level of erucic acid in the standards was IdaGold 35%, Cyclone 0% and Sterling 50%. Progeny originating from LEA combinations showed a mean erucic acid content of 15% from the range 3 to 15%, whereas those originating from HEA crosses showed a mean of 30% from the range 4 to 49%. Again the higher value in the range is similar to cultivars grown to produce industrial oil.

Table 2. Average oleic acid content (%), erucic acid content (%) and total glucosinolate content (Ámol g-1 defatted seed meal) and range of these traits from S.alba x B. napus (low erucic acid, LEA) and from S. alba x B. napus (high erucic acid, HEA) hybrids. Also shown are data from traditional yellow mustard (IdaGold), spring canola (Cyclone) and spring rapeseed (Sterling).

Genotype

Oleic acid

Erucic acid

Total Glucosinolate

IdaGold

28

35

129

Cyclone

63

0

2

Sterling

15

50

7

LEA – Mean
- Range

46
31 – 62

15
3 – 28

62
27 – 129

HEA – Mean
- Range

29
14 – 62

30
4 – 49

37
9 – 104

The total glucosinolate content of defatted seed meal also showed much variation. Cyclone and Sterling, the B. napus cultivars have 2 Ámol g-1 and 7 Ámol g-1 respectively. IdaGold has 129 Ámol g-1 total glucosinolate. Progeny from LEA combinations showed a mean of 62 Ámol g -1 from the range 27 to 129 Ámol g-1 total glucosinolate, while progeny from HEA combinations showed a mean of 37 Ámol g -1 from the range 9 to 104 Ámol g-1.

Wide variation for yield, oil content, fatty acid profile and glucosinolate content existed in these spring hybrids, with the possibility of developing canola and rapeseed quality cultivars. Some of the lines have glucosinolate levels in the de-fatted seed meal which would be suitable for animal feed while others have much higher levels more suited as a bio-fumigant.

Plants showing winter hardiness and high total glucosinolate content could be planted in the fall and would simultaneously prevent soil erosion and fumigate the soil, therefore winter B. napus x S. alba hybrids have now been produced. B. juncea has also been resynthesized (B. rapa x B. nigra) as a winter type increasing the range of glucosinolate types available in a winter hardy plant. Table 3 shows the total glucosinolate content of these two hybrids compared to ‘Humus’, a winter B. napus released in 1992 as a plow-down crop. To be fully effective as a bio-fumigant, the glucosinolate content of Humus is too low. The hybrid between B. rapa x B nigra has 36 Ámol g-1, more than four times that found in Humus. The hybrid between S. alba x B. napus had 25.3 Ámol g –1, over three times the levels found in Humus.

Table 3. Glucosinolate profile and total glucosinolate content (Ámol g-1 green leaf tissue) of Humus winter rapeseed, winter form of S. alba x B. napus and winter form of B. rapa x B. nigra (re-synthesized B. juncea).

Glucosinolate type

B. napus (Humus)

B. rapa x B. nigra

S. alba x B. napus

Allyl

0.0

14.3

0.0

3-butenyl

1.0

13.8

0.0

4-pentenyl

3.3

3.4

0.1

2-OH-3-butenyl

2.3

4.3

1.1

OH-benzyl

0.0

0.0

16.3

Phenylethyl

0.4

0.1

0.1

3-indolylmethyl

0.5

Trace

6.8

4-OH-3-indolylmethyl

Trace

0.1

0.9

Total

8.6

36.0

25.3

The type of glucosinolate is as important as the levels of glucosinolate. Table 3 shows the different types of glucosinolates found in leaf tissue samples taken from the two Fall planted hybrids and Humus. The most common glucosinolates present in Humus are 4-pentenyl and 2-hydroxy-3-butenyl glucosinolate. These compounds are also present in the resynthesized B. juncea as well as large quantities of allyl and butenyl glucosinolates. These glucosinolates have been found to be effective against a large range of soil pests (Brown et al, 1995, Jimenez-Osbornio et al, 1987). The predominant glucosinolates in S. alba x B. napus were p-hydroxybenzyl and 3-indolylmethyl glucosinolates, which have been found to be very effective at suppressing the germination of weed seeds (Brown et al, 1996, Boydston et al, 1995).

The volatile isothiocyanates produced from glucosinolate breakdown are key compounds inhibiting weed seeds and other plant pests, providing tremendous potential for these hybrids as allelopathic plow-down crops that could provide biological soil fumigation without synthetic fumigants.

References

1. Auld, D.L., Mahler, K.A., Erickson, D.A. & Raymer, P.L. 1992. Registration of Humus Rapeseed. Crop Sci. 32:1068

2. Boydston, R.A., and A. Hang. 1995. Rapeseed (Brassica napus) green manure crop suppresses weeds in potato (Solanum tuberosum). Weed Technol. 9.

3. Brown, J., Brown, A.P., Davis, J.B. & Erickson, D. 1997. Intergeneric hybridization between Sinapis alba x Brassica napus. Euphytica 93:163-168

4. Brown, P.D., and M.J. Morra. 1995. Glucosinolate-containing plant tissues as bioherbicides. J. Agric. Food Chem. 43:3070-3074.

5. Brown, P.D., and M.J. Morra. 1996. Hydrolysis products of glucosinolates in Brassica napus tissues as inhibitors of seed germination. Plant Soil 181:307-316.

6. Jimenez-Osborino, J.J. and S.R. Gliessman. 1987. Allel interference in a wild mustard (Brassica campestris L.) and broccoli (Brassica oleracea L. var italica) intercrop agroecosystem. In G.R. Waller (Ed), Allelochemicals: Role in Agriculture and Forestry. American Chemical Society, pp 262-288.

7. U. N., 1935. Genome analysis in Brassica with special reference to the experimental formation of B.napus and peculiar mode of fertilization. Jap. J. Bot. 7:389-452.

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