J. Agronomy & Crop Science 169, 122-127 (1992) 0 1992 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0931-2250

Institut f u r Pflanzenwissenschaften der Eidgenossischen Technischen Hochschule Zurich, Switzerland

Root Development in Seedlings of Oilradish, White Mustard and Pea:*

B. ILGEN and P. STAMP

Authors' addresses: Dr. B. ILGEN, Institut fur Bodenkultur und Pflanzenbau e. V. Sunderuphof, Postfach 23 46, D-2390 Flensburg, Germany; Prof. Dr. P. STAMP, Institut fur Pflanzenwissenschaften, Eidgenossische Technische Hochschule Zurich, ETH-Zentrum, Universitatstr. 2, CH-8092 Zurich, Switzerland.

With 2 figures and one table

Received August 26, 1991; accepted December 5, 1991

Abstract Crucifers such as oilradish and white mustard and the legume pea are used as late season catch crops in cool temperate climates. Adequate establishment of the crop and soil improvement depend mainly on fast and efficient root development. Exact observations are still difficult under field conditions. For these reasons, plants of the above mentioned species were grown in tubes filled with a solid soil substrate for 36 days. Pea, with large seeds, had higher shoot and root dry weights and a larger leaf area and root surface area during the first three to four weeks. In spite of generally similar patterns of development of the two crucifers, shoot and root development increased at a much faster rate in oilradish than in white mustard. For this reason, the most vigorous plants were found in oilradish after 36 days. This species had a higher shoot : root dry weight ratio than white mustard. At the same time oilradish utilized root dry weight much more efficiently for root surface area than white mustard, giving it a very high root surface area. A highly synchronized leaf : root area existed between the crucifers. In pea, allocation of dry matter to roots was slow at later stages; a fast development of root surface area depended on an increasingly efficient utilization of high dry matter reserves, deposited at early stages. In this species, expansion of root surface area could still compete with white mustard, although the strategy of root development was very different with comparatively few long and thick first and second order laterals in pea.

Key words: Catch crop, Raphanus sativus, Sinapis alba, Pisum sativum, Root morphology.

Introduction indicate sufficiently root uptake efficiency and Catch crops are grown in order to avoid nitrate leaching and soil erosion (EHLERS and HART- MANN 1986, WOLFGARTEN et al. 1989). Al- though these expectations are based on root properties, few investigations have been car- ried out on root growth of catch crops (VETTER and SCHARAFAT 1964, SCHULTE 1980, OBENAUF 1984). No information exists about root mor- phology, but root dry matter alone does not

* Dedicated to Professor Dr. G. GEISLER.

rooting intensivity (DE WILLIGEN and VAN NOORDWIJK 1987). These latter parameters are partly correlated (GRIMME 1978, KOPKE 1979). Uptake efficiency largely depends on total number, length and surface area of roots (BOHM 1979). Catch crops are normally sown at the end of the growing season, and a fast establishment of these crops is a prerequisite for achieving the above mentioned goals. These investigations were concerned with the seedling root development of two small seed

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Root Development in Seedlings of Oilradish, White Mustard and Pea 123

600

crucifers and one large seed legume in a green- house.

A

-

Material and Methods The crucifers oilradish (Raphanus sativus var. oleif. Pers. cv. Nemex), white mustard (Sinapsis alba cv. Maxi) and the legume pea (Pisum sativum cv. Lisa) were grown in a greenhouse during the winter, under the following conditions: Additional light (120pmol x m-' s-' PAR) with a photoperiod of 1618 h, day/night temperatures 20 "/15 "C (+2 "C).

Average sized seeds had been imbibed at 5 "C for 16 h and pregerminated at 25 "C for 18 h. Vigourous seedlings were selected and planted in PVC tubes (length: 800 mm, inner diameter: 98 mm). The dry substrate consisted of 81 % sand, 12 YO silt and 7 % clay and was mixed with 15 weight % of a nutrient solution containing 136 mg KH2P04, 87 mg K2S04, 492 mg MgS04 X 7 H 2 0 , 332 mg CaCI, X 2 H 2 0 , 1.52 mg MnSOl X H20, 0.22 mg ZnS04 x 7H20, 0.07 mg CuSOl, 1 ml FeEDTA per liter. The plants were harvested 14,21, 29 and 36 days after gerrnina- tion. Leaf area was measured with a Delta-T Area

ahoot dry matter (ma)

r

k OILRADISH &

400 - --- MUSTARD

-8 PEA

I

80(

80C

40C

200

0

leaf area (cm * )

260 r

100 -

60 -

14 21 2s 38 d 1

14 21 2s 38 d

)ot dry matter (ma)

C

14 21 2s 38 d

iootlroot ratio

D I P

14 21 2s 38 d

Fig. 1 . Shoot dry matter (A), leaf area (B), root dry matter (C) and shoot : root ratio (D) of oilradish, white mustard and pea 14, 21, 29 and 36 days after germination (Vertical bars: LSD 0.05)

124

B

Meter. Roots were washed carefully and the length of the main root and number and length of lateral roots were determined. A microscope was used to measure root diameters of the different root types. Root surface area was calculated from these data based on the assumption that the roots were cylin- drical.

The trial was arranged in twelve blocks and each tube with one plant was counted as one replication. The SAS package was used for statistical analysis.

2.0

1.6

1.0

0.5

root surface area (cm * r I

-

-

-

-

14 21 29 38 d

total number of root tips (x 1000) 7r

ILGEN and STAMP

Results During the first three weeks after germination, the shoot growth of peas was much faster than that of the two crucifers (Fig. 1 A). The latter showed a very similar pattern of growth for the first four weeks with oilradish having persis- tently higher shoot dry weights. From 29 to 36 days after germination, the picture changed considerably with growth rates accelerating

4 o t

0 ' I 14 21 28 38 d

surface arealdry matter (cm2/mg)

2'51

.o ' 14 21 20 36 d

Fig. 2. Root surface area (A), total root length (B), number of roots (C) and the ratio root surface area : root dry matter (D) of oilradish, white mustard and pea 14, 21, 29 and 36 days after germination (Vertical bars: LSD 0.05)

Root Development in Seedlings of Oilradish, White Mustard and Pea 125

more in crucifers than in pea. Even in absolute terms, the shoot dry weight of oilradish ex- ceeded that of pea during this period. Leaf area development followed a similar pattern of de- velopment as that of the shoots throughout the experimental period (Fig. 1 B).

A slower start and a faster late development of the small seeded crucifers as compared with pea was even more obvious when leaf area expansion was considered . Root growth was very similar in both crucifers during the whole observation period (Fig. 1 C). Because root dry matter accumulated very slowly in pea from 14 to 36 days after germination, its initial advantage over the crucifers was lost during the fifth week after germination. A relatively high partition of organic matter to the roots was observed for white mustard during the whole period, while in pea the shoot : root ratio increased from 1 to 3 (Fig. 1 D). In oil- radish, the ratio widened similarly for four weeks and then stabilized at a value slightly below 2.

After three weeks of slow development, the expansion of root surface area increased rapid- ly in both crucifers (Fig. 2A). Mustard at-

tained the same value as pea after four weeks, and the root surface area of oilradish was twice as high as that of the other species after two or more weeks. During the first weeks, the higher values found for pea were not due to the total root length (Fig. 2B) but rather to the large diameters of the roots (Table 1). While differ- ences in total length and number of roots were small during the first three weeks, develop- ment was much faster in oilradish thereafter, and the values for mustard tended to exceed those of pea (Fig. 2 B, 2 C). The low number of laterals in pea was compensated for by longer first order laterals during the first three weeks and by longer second order laterals dur- ing the whole observation period (Table 1). The utilization of root dry matter for root surface area increased steadily in pea during the whole period while in crucifers it stopped after four weeks (Fig. 2D). Final values were the same for pea and oilradish and much lower in mustard.

The ratio between the assimilating areas, leaf area and root surface area slowly decreased in pea from moderately high values two weeks after germination (Table 1). In crucifers, the

Table 1. Length of the main root [A] and first [B] and second [C] order laterals, root diameter of first [D] and second [El order laterals, and the ratio leaf area : root surface area [F] of oilradish, white mustard and pea 14, 21, 29 and 36 days after germination

Species Plant age Root length Root diameter Ratio ( 4 (mm) (mm)

A B C D E F

Oilradish

Mustard

Pea

LSD 0.05

14 355 21 448 29 514 36 692

14 356 21 383 29 423 36 533

14 384 21 455 29 503 36 492

14 20 21 35 29 57 36 189

53.6 68.8 87.4

107.5

43.0 58.0 88.3 98.3

62.6 78.5 80.6 98.0

4.0 4.3

25.6 33.0

5.0 0.22 0.08 0.99 5.0 0.29 0.10 0.56 9.5 0.44 0.17 0.25

12.6 0.44 0.23 0.28

3.0 0.18 0.05 0.97 4.0 0.26 0.09 0.58

12.9 0.41 0.24 0.23 15.3 0.44 0.25 0.32

3.0 0.42 0.11 0.79 3.0 0.43 0.12 0.57

18.7 0.58 0.40 0.48 22.5 0.60 0.41 0.35

0.1 0.04 0.03 - 0.2 0.04 0.04 - 7.0 0.08 0.12 - 6.3 0.08 0.35 -

126 ILGEN and STAMP

development of this ratio was almost identical; it declined sharply two to four weeks after germination and increased slightly thereafter.

Discussion Although root studies under optimized condi- tions cannot replace field studies, they d o offer the opportunity to compare the developmental patterns of different species. Large seed re- serves enable pea to grow faster initially than the crucifers but this advantage begins to dis- appear after four weeks. This holds generally true for the four major parameters shoot and root dry weight, and leaf and root surface area. A fast root growth of oilradish has been de- scribed previously (LEHFELDT 1986). Although general patterns of shoot and root develop- ment were remarkably similar for both cruci- fers, a more vigourous development of oilrad- ish at the later stages was found. A deeper rooting system of this species has been de- scribed by DEBRUCK (1971 a, 1971 b). Accord- ing to field observations of VETTER and SCHARAFAT (1964), white mustard develops a deeper rooting system than peas. A thorough investigation of root parameters has always been impeded by methodological difficulties and many studies have concentrated on an assessment of root dry weight. It was shown for maize that root dry weight is an unreliable indicator of root surface area (STAMP 1984). In this study, this seems to be true for pea which showed a time lag between allocation of dry matter to roots and its utilization for root surface area (Fig. 1 A, 2A). The high storage capacity of pea roots for carbohydrate reserves may be due in part to the large diameters of single roots. Similar differences between pea and the crucifers have been observed before ( V E ~ E R and SCHARAFAT 1964), FILIMONOVA (1974) reported high numbers of laterals in white mustard. O u r results show an even high- er capacity of oilradish to develop lateral roots. GEISLER (1967) found slightly greater numbers of laterals in pea but this species partly com- pensated for a small number of roots by longer and thicker roots. For this reason, the root surface area of pea could still compete with that of white mustard after five weeks of growth. Root surface area is the integrative sum of all single root parameters and, under optimum homogenous soil conditions, it can

indicate root efficiency (GLIEMEROTH 1954, BOHM 1979). For this reason, it is of interest to observe that different strategies of root system development can result in the same root sur- face area for white mustard and pea. Further investigations are necessary to determine whether these differences in strategy are im- portant for adaption to adverse conditions. It was shown for maize that the ratio of leaf area to root surface area can be a very stable charac- ter of different genotypes at a specific on- togenetic stage (STAMP 1984). O u r results show a similarly parallel development of this ratio for the two crucifers, while in pea less root surface area is available per unit leaf area at late growth stages. Pea, on the whole, is better able to establish an early seedling root system at a fast rate, whereas the crucifers can compete well at later growth stages due to the develop- ment of many thin, comparatively short la- terals.

Zusammenfassung

Wurzelentwicklung von Jungpflanzen der Arten Olrettich, WeiBer Senf und Erbse

In kuhl-gemaBigten Klimaten werden Kruzife- ren wie Olrettich und Senf sowie die Legumi- nose Erbse als spat gesate Zwischenfruchte eingesetzt.

Eine befriedigende Bestandesentwicklung und eine gute Bodenverbesserung hangen von einer raschen und ausreichenden Wurzelent- wicklung ab. Unter Feldbedingungen sind ex- akte Beobachtungen dieses Vorgangs immer noch schwierig. Daher wurden Pflanzen der oben genannten Arten fur maximal 36 Tage in mit festem Substrat befullten Rohren angezo- gen. Wahrend der ersten drei bis vier Wachs- tumswochen bildete die groflsamige Erbse die hochsten SproB- und Wurzeltrockenmassen sowie die grogten Blatt- und Wurzeloberfla- chen aus. Das Entwicklungsmuster war fur die beiden Kruziferen prinzipiell ahnlich, jedoch wies Olrettich raschere Wachstumsraten als Senf im SproB- und Wurzelbereich auf. Nach 36 Tagen hatte Olrettich die groBte Biomasse ausgebildet. Auch das SproB/Wurzelverhaltnis war bei dieser Art groi3er als bei Senf. Durch eine effiziente Umsetzung von Wurzeltrocken- masse in Wurzeloberflache bildete Olrettich auch die groi3te Wurzeloberflache aus. Die Entwicklung des Blatt/Wurzeloberflachenver-

Root Develooment in Seedlings of Oilradish. White Mustard and Pea 127

haltnisses verlief bei beiden Kruziferen voll- kommen identisch. Bei der Erbse nahm die Wurzeltrockenmasse nach der zweiten Wachs- tumswoche nur langsam zu. Der dennoch ra- sche Aufbau von Wurzeloberflache stiitzte sich auf die Ausniitzung der friih angelegten Reser- ven. Die Strategie der Wurzelentwicklung der Erbse war durch vergleichsweise wenige, dafiir aber sehr lange und dicke Seitenwurzeln erster und zweiter Ordnung gekennzeichnet.

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FILIMONOVA, L. N., 1974: Root development of pea and its productivity in mixed stands. Izvestija Timirjazevskoi Sel’skochozjajstvennoj Akademii 3, 4 1 4 8 .

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