Effects of Plant Growth Retardants on Growth of Vetiver Grass

Xia Hanping (South China Institute of Botany, The Chinese Academy of Sciences, Guangzhou 510650)

Abstract Three kinds of plant growth retardants, B9, PP333, and CCC, all had influences on growing, tillering and flowering of vetiver grass (Vetiveria zizanioides); but different kinds or concentrations of retardants produced distinctly different effects in these respects. The three medicaments all promoted tiller formation, up to 11%_53% or so in a growing season. 8 g.L-1 B9 also retarded the growth of vetiver by 6%, delayed flowering for nearly 10 days, and reduced the number of inflorescence significantly by 80% at the same time, as compared to the control; but 4 g.L-1 B9 hardly retarded the growth and flowering except that it, too, reduced the number of ears, up to 50%. However, PP333 with concentrations of 0.6 and 1.2 g.L-1, and CCC with 1.0 and 2.5 ml.L-1 all promoted the height growth of vetiver, up to 5%_22%; and furthermore, the treatment of 1.2 g.L-1 PP333 also enhanced number of heads by 31%, and 0.6 g.L-1 PP333 promoted flowering 4 days earlier than CK did. The results above-mentioned indicate that B9, as the retardant of vetiver, had better effects than PP333 and CCC. The trial shows that impacts of the plant growth retardants on vetiver are obviously different from on most crops, which is most likely that vetiver had strong resistance and accordingly the retardants with conventional concentrations do not produce clear influence on it.

INTRODUCTION

Vetiver grass (Vetiveria zizanioides Nash), a perennial, has been spread rapidly throughout 160 countries and regions due to its miraculous effectiveness in erosion and sediment control since it was used for the above purpose 15 years ago (National Research Council, 1993; Adams et al, 1998). So far the Vetiver Eco-engineering in China has been broadly utilized to mitigate polluted environments, stabilize steep slopes and dykes, ameliorate micro-climates of farmlands as well as reduce erosion (Xu Liyu, 1998; Xia Hanping et al, 1998). The plant is by no means impeccable however; for example, it grows too high, and is of no beauty. This disadvantage makes it difficult to be applied around golf courses, tour resorts and the like that have a higher requirement to appearance. Although tail-cutting at intervals can curtail its ugliness, vetiver grows rapidly, up to 1 m or so in one month. Obviously it is unrealistic and impossible to shear vetiver once each month. Too frequent cutting to vetiver not only costs too much, but is unfavorable to its growth as well (Xia Hanping et al, 1994). So this is new topic to be settled urgently how to make vetiver become shorter.

We all know that vetiver does not produce seeds in common conditions, and it is multiplied by division of roots, much slower than those crops multiplied by seeds, which objectively inhibits its application on an extensive scale in a short time. Therefore how to accelerate the tillering formation of vetiver is another research topic demanding prompt solution.

It has been well documented that plant growth retardants (PGR) not only retard the growth of plants, but also increase the number of twigs or tillers, and make them become short, sturdy, and luxuriant. Thereby it would probably enhance vetiver's beauty and effectiveness in soil conservation if we could seek out a retardant that is capable of dwarfing it and promoting its tillering production.

Materials and Methods

3 kinds of cheap, widely-used retardants were adopted in this trial, which are B9 (daminozide), PP333 (paclobutrazol), and CCC (chlorocholine chloride). Each kind was diluted into 2 concentrations: 4 and 8 g.L-1 for B9 (T1 and T2 respectively), 0.6 and 1.2 g.L-1 for PP333 (T3 and T4 respectively), and 1.0 and 2.5 ml.L-1 for CCC (T5 and T6 respectively); 6 treatments altogether. In addition, a control (CK) was set up, which was sprayed clean water instead of retardants. The experiment was undertaken with a field plot, and was put in the vetiver nursery of South China Institute of Botany. Vetiver had grown for approximately 2 months before the trial was conducted. Each treatment was fixed 12 clumps of vetiver, and the 12 clumps were divided into 2 groups for the minimum experimental error. Thus there are 14 groups altogether and they were arrayed randomly. All tested vetivers were topped at 30 cm and then reckoned the tillers number of per clump prior to spraying. PGR were sprayed on the entire aerial part of vetiver until there are drips dropping along stems and leaves. The first spray was done on June 12, and did the second time after 10 days and no longer did afterwards.

After the first spray, 5 times of observation, once each month, were conducted, including plant height and number of tillers, but only the number of tillers was investigated at the last time. During the period of observation, recorded the date of growing out the first ear of vetiver in per treatment, and counted the total number of eras of each treatment from October 4, once a week until all treatments hardly produced new ears anymore.

RESULTS AND DISCUSSION

1 Effects PGR on Growing of Vetiver

Except T2, which stunted vetiver with respect to height by 6% compared with CK, the other 5 treatments made vetiver become higher than CK (Fig. 1). Variance analysis indicates that the plant heights presented significant differences among all treatments and CK (indicated with letters in Fig. 1). For example, no matter which investigation, the plant heights of T3 and T4 from PP333 were all higher than those of CK(P<0.05) and than those of T2 (P<0.01); Values with different letters in same observations have statistical differences at P<0.05 (LSD test) and the 2 treatments of CCC presented the similar phenomenon. It seems to indicate that the two retardants, PP333 and CCC, became “promoters” to vetiver, which was probably due to the too low applied concentrations of the two retardants to the plant. As a matter of fact, the concentrations of PP333 and CCC used in this trial are all the recommended concentrations in agricultural production. For example, the low concentration of 0.1~0.5 mg.L-1 PP333 was enough high to make the seedlings of squash become short and thick (Zhao Jianping et al, 1998). Since vetiver has a very strong resistance to environmental factors, as a result the concentration of medicaments that can produce an inhibitory influence on common crops seemed too low to influence it effectively and therefore, could not dwarf it and even enhance its growth. But the 2 concentrations of P9 used in this study were far higher than those that are recommended in farming production (1~2 g.L-1), as a result the relatively high concentrations of B9 (T2) produced a distinctly retardant impact on the growth of vetiver. It can be inferred that enhancing the sprayed concentration of PP333 and CCC would probably decelerate vetiver's growth, too; conversely, abating the sprayed concentration of P9 would probably accelerate its growth. In fact, as compared to 8 g.L-1 B9, 4 g.L-1 B9 assumed a slight promotion to vetiver's growth, namely the vetivers of T2 were a bit higher than those of CK. There has been a study indicating that over 6 g.L-1 B9 could damage chrysanthemum and even kill it (Cui Jiuman et al, 1990). However, vetiver, even treated by 8 g.L-1 B9, was not found to be hurt yet, further indicating its strong resistance to drug.

Fig. 1 Effects of different concentrations of plant growth retardants

on the growth of vetiver

Values with different letters in same observations have statistical differences at P<0.05 (LSD test)

If we make an inspection to the effect of PGR on the net height increment of vetiver per month, then we can find that the significant differences among plant heights of different treatments and CK emerged in the first two months, especially in the first month (P=0.002, Table 1). Afterwards, the differences became smaller and smaller, and had no longer significances from the third month on, in spite of the fact that the two treatments of PP333 still presented relatively high growth in the fourth month. This is mainly because PP333 made vetiver grow out heads earlier and more than B9 and CCC, and therefore their whole heights surpassed other treatments. This can be seen in Fig. 2.

Table 1 Effects of different plant growth regulators on monthly net height growth of vetiver (Mean║└SD cm)

Treatments First month

(12/6~11/7)

Second month

(12/7~11/8)

Third month

(12/8~11/9)

Fourth month

(12/9~11/10)

CK 95.7║└19.8* 17.0║└6.9 10.8║└6.7 10.9║└6.4
4g.L-1 B9 98.4║└15.5 16.3║└7.7 11.7║└7.7 11.1║└6.0
8g.L-1 B9 84.2║└17.6 20.9║└8.0 10.2║└6.7 9.3║└8.3
0.6g.L-1 PP333 114.7║└13.0 19.8║└6.8 16.0║└5.8 20.4║└12.3
1.2g.L-1 PP333 111.2║└7.9 15.3║└5.0 18.5║└10.2 15.3║└13.6
1ml.L-1 CCC 107.3║└17.4 13.8║└4.4 16.8║└6.9 12.7║└4.0
2.5ml.L-1 CCC 105.3║└13.6 14.2║└6.6 12.6║└6.7 10.8║└5.2
Significant level (P) 0.0002 0.021 0.056 0.061
LSD (0.05) 13.0 5.6 / /

2 Effect of PGR on Tillering of Vetiver

Obviously, 3 PGR all had somewhat or strong promotion to the tillering production of vetiver (Table 2). At the fifth time of observation, the net tiller increments of 6 treatments with medicaments were all more than that of CK, increased by 11%~53%. Among them T1 increased most, over 50%; PP333 and CCC all presented that the higher concentrations had bigger promotion than the lower concentrations, whereas B9 did on the contrary. This suggests that the concentration of 8 g.L-1 B9 was perhaps too high to promote tillering as effectively as that of 4 g.L-1; but its effect in this aspect still was not inferior to the 4 treatments of PP333 and CCC. On the whole, the abilities of 3 PGR to promote tillering formation of vetiver are ranked as B9 > PP333 > CCC.

Table 2 Effects of different treatments of PRG on tillering of vetiver

Treatments Observing date (Day/Month)
  12/7 12/8 12/9 12/10 12/11
CK 30 (100)* 80 (100) 142 (100) 167 (100) 192 (100)
4g.L-1 B9 45 (150) 133 (166) 216 (152) 256 (153) 293 (153)
8g.L-1 B9 24 (80) 85 (106) 164 (115) 208 (125) 236 (123)
0.6g.L-1 PP333 27 (90) 95 (119) 177 (125) 207 (124) 228 (119)
1.2g.L-1 PP333 34 (113) 117 (146) 195 (137) 219 (131) 245 (128)
1ml.L-1 CCC 23 (77) 84 (105) 155 (109) 193 (116) 214 (111)
2.5ml.L-1 CCC 30 (100) 93 (116) 162 (114) 207 (124) 240 (125)

* Increment of total tillers per treatment compared with that prior to application of retardants; values in parentheses are percentage relative to the control

Unlike their influence on the growth of height, the influence of PGR on production of tillers lasted longer time. The net increments of tillers of almost all treatments greatly rised 2 and 3 months after spraying medicaments with compared to CK; there were still somewhat or big increases 4 months later; and even 5 months later treatment T1 was still higher 50% than CK (Table 3).

Table 3 The net increment of tillers of vetiver per month under different treatments of medicaments

Treatment First month Second month
Third month
Fourth month Fifth month
CK 30 (100)* 50 (100) 62 (100) 25 (100) 25 (100)
4g.L-1 B9 45 (150) 88 (176) 83 (134) 40 (160) 37 (148)
8g.L-1 B9 24 (80) 61 (122) 79 (127) 44 (176) 28 (112)
0.6g.L-1 PP333 27 (90) 68 (136) 82 (132) 30 (120) 21 (84)
1.2g.L-1 PP333 34 (113) 83 (166) 78 (126) 24 (96) 26 (104)
1ml.L-1 CCC 23 (77 ) 61 (122) 71 (115) 38 (152) 21 (84)
2.5ml.L-1 CCC 30 (100) 63 (126) 69 (111) 45 (180) 33 (132)

*Values in parentheses are percentage relative to the control

  1. Effect of PRG on Earing of Vetiver

Vetiver usually comes into ears in fall. In this study, the treatment growing out eras first was T3, and then, in order of time, T4, CK, T5, T1, T6, and T2; their first ear appeared on September 29th, October 2nd, 3rd, 5th, 5th, 9th, and 12th, respectively, apart 14 days. In over one month after that, their earing speeds greatly varied, too. T3, the treatment producing heads earliest, did not produce the largest number of heads in the end; but T2, the treatment producing heads latest, produced the fewest heads from beginning to end and further, far fewer than the other treatments. That means T2 had a considerably inhibitory impact on vetiver's earing and flowering. Vetiver had an earing peak in the middle and end of October, afterwards the earing speeds became slow clearly, but T4 and T3 (both from PP333) recreated a conspicuous earing peak in the first half of November, resulting in the outcome that the numbers of their ears were much more than those of the other treatments (Fig. 2). The reason producing the phenomenon is probably because the efficacy of PP333 to vetiver recurred at that time, promoting the its heading and flowering again. At the last time of counting on November 29, the ratios of the 6 treatments to CK with special reference to the number of ears were T4 : T3 : T6 : T1 : T5 : T2 : CK = 1.52 : 1.23 : 0.71 : 0.68 : 0.61 : 0.19 : 1, namely T4 had the largest number of ears, more 52% than CK, whereas T2 had the smallest, only 19% of CK; the rate of T4 to T2 in regard to the number of ears was up to 7.8 : 1.

Fig. 2 Changes of ears number of vetiver under different treatments of PGR

Here, we can define the concept of “ Earing rate ” with the following formula:

Number of ears

Earing rate = ——————— ║┴100

Number of tillers

Undoubtedly, it is more accurate to use the earing rate than to use the number of ears for comparison of the situation of earing between these treatments and CK. It is easy to calculate their earing rates of the last time of counting, from which the ratios of them to CK can be obtained, they were T4 : T3 : T6 : T5 : T1 : T2 : CK = 1.31 : 1.15 : 0.61 : 0.60 : 0.50 : 0.17 : 1. In comparison with the ratios of number of ears above-mentioned, the ratios of earing rate all decreased, and furthermore T1 became smaller than T5. The reasons producing the two changes are obviously owing to the facts: 1) the 3 kinds of PGR all promoted the tillering of vetiver, and the final numbers of tillers of the 6 treatments were all more than that of CK; and 2) the tillers number of T1 in the end was far more than that of T5 (Table 2).

It is thus clear that the influence of 3 PGR on earing of vetiver was quite tangible no matter what approach to reflect the situation of its earing; their inhibitory effects presented distinctly in order of B9 > CCC > PP333. Among them, PP333 made vetiver flower earlier and promoted it to produce more heads, and moreover this promotion did not occur perhaps until the late stage of its growth, as a result it made the vetivers sprayed with PP333 still presented relatively high growing speeds in this stage (Table 1); but B9 and CCC did by contraries, in particular B9, which assumed a greatly inhibitory and retardant impact in this aspect.

Conclusion

The Plant Growth Retardants, B9, CCC, PP333, all affected vetiver in all its aspects of growing, tillering, and earing, etc. But different retardants produced different influences, and some were positive and some negative. In this study, B9 produced the strongest inhibition to the height growth, the best promotion to the tillering formation, and the most effective retardation to earing production. However, B9 was used the highest concentration among the 3 kinds of PGR, which would perhaps be pernicious to the environment. On the whole, the effectiveness of PGR in dwarfing vetiver were not so ideal, therefore the research work that how to made vetiver become short remains to be undertaken further; maybe gene mutation would be an orientation.

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