Agricultural and Food Science in Finland, Vol.10 (2001):165 –174 165 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 165–174. © Agricultural and Food Science in Finland Manuscript received April 2001 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 165–174. Chlormequat chloride and ethephon affect growth and yield formation of conventional, naked and dwarf oat Pirjo Peltonen-Sainio and Ari Rajala Department of Plant Production, PO Box 27, FIN-00014 University of Helsinki, Finland. Current address: MTT Agrifood Research Finland, Plant Production Research, FIN-31600 Jokioinen, Finland, e-mail: pirjo.peltonen-sainio@mtt.fi Plant growth regulators (PGRs) are not usually applied to oat (Avena sativa L.) crops. This study was designed to test whether the antigibberellin chlormequat chloride (CCC) and ethylene-releasing ethe- phon sprayed on to oat foliage represent potential agents for manipulation of yield formation under northern growing conditions. Effects of these PGRs on yield components and tiller growth and pro- ductivity were examined in detail. This study included a long-strawed landrace, a modern standard height cultivar, two naked (A. sativa ssp. nuda L.) and two dwarf oats. Field experiments were con- ducted at Viikki Experimental Farm, University of Helsinki, in 1995 and 1996. Chlormequat chloride was sprayed at the two-node stage and ethephon when the flag leaf ligule was just visible on the main shoot. Various traits characterizing growth and yield formation were assessed. Chlormequat chloride increased grain yield by 0% to 13% depending on cultivar and year, while ethephon most often de- creased it by up to 17%. No lodging occurred and the recorded increase in grain yield of CCC treated plants was not therefore due to prevention of lodging. However, CCC treatment resulted in more panicles per square meter and in 1995 tillers contributed more to grain yield. Ethephon treated plants had less grains per main shoot panicle, lower panicle filling rate (PFR) and parallel decreased harvest index (HI). Stem elongation of dwarf oat was enhanced by CCC, in contrast to that of conventional and naked cultivars. Key words: Antigibberellins, Avena sativa, cultivars, ethylene, crop yield, harvest index, tillering, yield components Introduction Plant growth regulators (PGRs) are not common- ly used to shorten straw and manipulate yield formation in oat (Rajala and Peltonen-Sainio 2000) as they are for barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.). Oat is of- ten regarded as a secondary crop that does not require inputs additional to those for basic crop management. Not only do PGRs reduce straw length and lodging sensitivity, but they may also directly enhance grain yield production through im- mailto:pirjo.peltonen-sainio@mtt.fi 166 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. & Rajala, A. Plant growth regulators affect yield formation of oat proved yield components built up from excess photosynthate not used for stem elongation. For example, in several studies with barley and wheat, PGR treatments resulted in more grains per ear (Humbries et al. 1965, Naylor 1989, Ma and Smith 1992a, Börnel and Meinel 1993). Fur- thermore, in studies of Ma and Smith (1991) both chlormequat chloride (CCC) and ethephon treat- ment, reduced abortion of spikelet primordia in barley. Oat might, however, represent even great- er potential for such manipulation, because the inflorescence rather than an ear is likely to be more responsive to environmental factors and crop management that favour yield formation (Peltonen-Sainio 1999). There have been few experiments with PGR-treated oat (Peltonen- Sainio and Peltonen 1997, Pietola et al. 1999, Rajala and Peltonen-Sainio 2000, Rajala et al., unpublished results), but some tentative evidence exists for oat responding to PGR treatments. For example, oat treated with CCC at two to three tiller stage (growth stage, GS22-23, Zadoks et al. 1974) had more grains per panicle than con- trol plants (Peltonen and Peltonen-Sainio 1997). In addition to increasing grain number per ear in cereals, PGRs, CCC in particular, have en- hanced tillering – especially production of head- bearing tillers (Naylor et al. 1989, Ramos et al. 1989, Khan and Spilde 1992, Peltonen-Sainio and Peltonen 1997). This may also have a posi- tive impact on yield formation. The effect of PGRs on yield formation may range from yield enhancement to yield reduc- tion depending on growing conditions (Simmons et al. 1988, Ma and Smith 1992a, 1992b, Pelto- nen and Peltonen-Sainio 1997, Rajala and Pel- tonen-Sainio 2000). Genotypic differences in response to PGRs have also been reported. These are principally due to differences in straw length, but also due to genotypic differences in yield components and source to sink interaction. For this reason different oat types were included in this study. The landrace is a long-strawed, lodg- ing-sensitive cultivar with a relatively low grain to straw ratio (i.e., harvest index, HI) compared with other husked cultivars (Peltonen-Sainio 1990). Naked oat lines are often characterised by a low number of spikelets per panicle, asso- ciated with a high number of grains per spikelet and hence, reduced yielding ability (Peltonen- Sainio 1994). Furthermore, dwarf lines with the Dw6 gene have increased tillering ability, but not necessarily increased grain yield as tillers are not able to compensate for the lower main shoot panicle weight recorded under northern grow- ing condition (Mäkelä et al. 1996). As this dwarf- ing gene is likely to express reduced ability to produce gibberellic acid, the response of such lines to antigibberellins, such as CCC, and to ethephon may differ from that of the lines lack- ing Dw6. This study was designed to test whether foli- ar application of CCC and ethephon result in yield increases for reasons other than solely pre- venting lodging, including better combination of yield components and increased tiller formation and productivity. Furthermore, we tested whether there is genotype x PGR interaction for various morpho-physiological traits. Material and methods Field experiments were carried out at Viikki Experimental Farm, University of Helsinki, Fin- land (60°N13’N) in 1995 and 1996. The trials were sown on 9 May in 1995 and 22 May in 1996. Net plot size was 10 m2 (1.25 × 8 m, 12.5 cm between rows) and sowing rate 500 vi- able seeds m–2. Soil type was tentatively classi- fied as sandy clay. 80 kg of N ha–1 as NH 4 NO 3 was applied. Weeds were controlled with MCPA [(4-chloro-2-methylphenoxy) acetic acid] at 600 g a.i. ha–1 and dichlorprop at 600 g a.i. ha–1 after double ridge stage to avoid herbicide inju- ries on developing apices (Andersen 1954, Loub- ser and Cairns 1989). A split-plot design with four replicates was used, in which PGR treat- ments were applied to main plots and oat lines were split across them. Two PGR treatments, CCC and ethephon, in addition to a control were included in the de- 167 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 165–174. sign. CCC [(2-chloroethyl)-trimethylammonium chloride] was sprayed on to the plant foliage at 1.5 kg a.i. ha–1 (at 300 l ha–1) when the second main shoot node was evident (GS32), 35 and 40 days after sowing in 1995 and 1996, respec- tively. Ethephon (2-chloroethylphosphonic acid) at 240 g a.i. ha–1 (at 300 l ha–1) was applied when the flag leaf ligule was just visible on the main shoot (GS39), 42 and 45 days after sowing in 1995 and 1996, respectively. Six oat lines were included in the experi- ments: two were Finnish conventional lines (Ja- lostettu maatiainen, a long-strawed landrace re- leased in 1921, and Virma, a cultivar released in 1988), two were naked lines (Å 89106 from Norway and Rhiannon from UK), and two were dwarf lines with the Dw6 dwarfing gene (Grane from Norway and Pal from Minnesota, USA). The following morpho-physiological traits were measured on plants from each plot: 1) grain yield (g m–2, calculated at 15% moisture), 2) days from sowing to heading, 3) days from sowing to yellow ripeness, 4) length of grain-filling peri- od (d) from heading to yellow ripeness, 5) length of visible peduncle (cm) at maturity, 6) panicle length (cm) at maturity, 7) plant height (cm) from soil surface to panicle tips at maturity, 8) lodg- ing (%) at harvest, 9) number of panicles m–2 measured from 3 rows plot–1, each 0.5 m long, 10) tillers main shoot–1 (no.), 11) panicle-bear- ing tillers on main shoot (no.), 12) main shoot phytomass (g), 13) phytomass of tillers (g main shoot–1), 14) main shoot vegetative phytomass (g), 15) vegetative phytomass on tillers (g main shoot–1), 16) main shoot panicle weight (g) as a total weight of grains per panicle, 17) total weight of grains on tillers (g main shoot–1), 18) contribution of tillers to grain yield (%) as proportion of grain yield per plant produced by panicle-bearing tillers, 19) HI (%) as a pro- portion of total grain weight of grains per plant over total phytomass per plant, 20) single grain weight (mg), 21) number of grains per main shoot panicle, 22) panicle-filling rate (PFR, mg panicle–1 d–1), 23) grain-filling rate (GFR, mg grain–1 d–1), and 24) phytomass growth rate (PHGR, g m–2 d–1) as an average over the whole growth period from seedling emergence to yel- low ripeness. Traits 10 to 21 were measured from 40 randomly sampled mature plants in each plot. Statistical significance of differences be- tween years (random factor), PGR treatments, and oat lines (fixed factors) for grain yield and morpho-physiological traits were established with ANOVA. Least Significant Difference (LSD) or Student-Neuman-Keuls pairwise com- parison (SNK) at P = 0.05 was used for separat- ing significantly different means (SAS Institute Inc. NC, USA). Results Treatments with plant growth regulators, CCC and ethephon, affected grain yield, days to head- ing and maturity, plant height characteristics, HI, and number of grains and filling rate of main shoot panicle (P < 0.045). Year x PGR treatment interaction was statistically significant for grain yield, length of grain-filling period, days to ma- turity, number of tillers per main shoot and pani- cles per square meter, HI, plant height (P < 0.034) and contribution of tillers to grain yield (P = 0.063). Treatment with CCC resulted in in- creased grain yield by 0% to 13% depending on cultivar and year, and with ethephon in most cases decreased grain yield by up to 17% com- pared with the control (Table 1). There was no lodging and PGR induced changes in grain yield did not therefore result from differences in lodg- ing sensitivity. Both CCC and ethephon in- creased contribution of tillers to grain yield in 1995, and treatment with CCC also resulted in more panicles per square meter (Table 2). Number of grains per panicle, PFR and HI (in 1995) were, however, reduced through ethephon treatment. Oat line x PGR interaction was statistically significant for grain yield, the length of differ- ent growth phases and plant height characteris- tics (P < 0.029). Treatments with CCC, in par- ticular, tended to slightly delay heading and ma- 168 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. & Rajala, A. Plant growth regulators affect yield formation of oat T ab le 1 . P la nt g ro w th r eg ul at or e ff ec ts o n gr ai n yi el d, g ro w th d ur at io n, a nd p la nt h ei gh t ch ar ac te ri st ic s of c on ve nt io na l, n ak ed , a nd d w ar f oa t in 1 99 5 an d 19 96 . L in e an d G ra in y ie ld D ay s to D ay s to G ra in -f il li ng L en gt h of v is ib le P an ic le l en gt h P la nt h ei gh t T re at m en t (g m –2 ) he ad in g m at ur it y pe ri od ( d) pe du nc le ( cm ) (c m ) (c m ) 19 95 19 96 19 95 19 96 19 95 19 96 19 95 19 96 19 95 19 96 19 95 19 96 19 95 19 96 L a n d ra ce : C on tr ol 42 5 56 2 57 53 89 95 32 42 19 28 14 13 10 4 12 0 C C C 45 4 57 2 59 54 90 96 31 42 14 23 14 12 96 11 3 E th ep ho n 36 9 52 1 58 54 89 95 32 41 22 27 13 12 10 0 11 8 V ir m a : C on tr ol 50 1 58 8 57 53 89 96 32 43 14 20 14 13 92 10 3 C C C 54 1 58 9 59 55 90 96 31 41 9 17 15 13 84 96 E th ep ho n 41 6 55 3 58 54 90 95 33 41 13 18 12 13 82 98 Å 8 9 1 0 6 : C on tr ol 39 3 32 1 55 50 85 93 30 44 18 22 15 12 92 10 6 C C C 40 1 31 7 55 52 85 94 30 42 13 19 11 13 81 10 1 E th ep ho n 34 4 30 2 55 51 85 94 31 43 17 24 13 12 86 10 6 R h ia n n o n : C on tr ol 38 9 32 9 61 56 91 97 30 41 13 18 10 11 80 95 C C C 43 9 32 3 62 56 92 98 31 42 9 15 13 11 76 89 E th ep ho n 34 5 32 7 61 56 91 97 30 41 15 20 11 11 77 92 G ra n e: C on tr ol 54 9 45 9 62 56 90 95 28 39 6 10 13 12 71 81 C C C 56 3 58 5 61 56 90 96 29 40 8 10 11 12 75 85 E th ep ho n 52 0 53 8 62 57 90 96 29 39 8 9 13 11 72 81 P a l: C on tr ol 37 8 50 1 53 50 86 97 33 48 12 15 11 9 70 77 C C C 41 9 50 5 53 50 87 97 33 47 13 16 11 10 74 79 E th ep ho n 37 3 51 7 53 51 86 96 33 46 11 15 10 10 66 76 C V ( % ) 8. 7 7. 5 1. 1 1. 2 0. 7 0. 6 2. 7 2. 2 7. 1 9. 9 11 .3 6. 4 4. 0 2. 0 S N K 5% 18 .9 17 .4 0. 3 0. 3 0. 3 0. 3 0. 4 0. 5 0. 5 0. 9 0. 9 0. 4 1. 7 1. 0 C C C , c hl or m eq ua t ch lo ri de C V , c oe ff ic ie nt o f va ri at io n S N K , S tu de nt -N eu m an -K eu ls m ul ti pl e ra ng e te st a t th e 0. 05 p ro ba bi li ty l ev el 169 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 165–174. Table 2. Plant growth regulator (PGR) effects on total weight of grains from tillers, tiller contribution to grain yield, harvest index, number of grains per panicle, and panicle filling rate (PFR). Data for years are shown separately when year x PGR interaction was statistically significant for the trait. Trait and year Control CCC Ethephon LSD5% Panicles m–2: 1995 58233 63533 60933 51.4 1996 68233 66933 72033 67.6 Tiller contribution to grain yield (%): 1995 34.7 36.7 36.9 331.56 1996 21.7 21.4 19.4 332.44 Harvest index (%): 1995 46.4 47.2 43.2 332.46 1996 41.4 40.1 40.1 331.77 Grains panicle–1 (no): 323 333 293 332.03 PFR (mg panicle–1 d–1): 28.0 28.7 25.8 332.24 CCC, chlormequat chloride LSD, least significant difference at the 0.05 probability level turity in some oat lines, whereas effects of ethe- phon on duration of main growth phases were more inconsistent (Table 1). Elongation of the visible part of the peduncle tended to slow clearly more following CCC application than following ethephon when compared with the control, but only in conventional and naked lines. Similar effects were recorded on plant height, whereas no consistent effect on panicle length was es- tablished. Furthermore, dwarf cultivars, Grane and Pal, differed from other cultivars in their response to PGRs. Application of CCC resulted in increased plant height and increased elonga- tion of the visible part of the peduncle. No PGR effect, PGR x cultivar or PGR x year interaction were registered for number of tillers and panicle-bearing tillers per square meter, pro- duction of vegetative phytomass, total weight of grains on main shoot and tiller panicles, single grain weight and filling rate nor for PHGR. All of the measured traits (P < 0.001) except total weight of grains per tillers (P = 0.114) differed significantly among oat lines. Year x oat line interaction was recorded for traits (P < 0.037) other than number of tillers (P = 0.096) and pani- cle-bearing tillers per main shoot (P = 0.165) and panicle length at maturity (P = 0.300). Large gen- otypic variation in morpho-physiological traits was recorded (Table 3). Discussion Spraying CCC at the two-node stage of oat in- creased grain yield by 0% to 13% depending on cultivar and year. This was not due to reduced lodging. CCC induced enhancement of yielding ability was recorded especially in 1995, when high temperature and low precipitation occurred at pre-anthesis (Table 4), and resulted in produc- tion of less vegetative phytomass and grains (Ta- ble 3). Ethephon applications at flag leaf emer- gence had a contrary effect to CCC, and yield reduction was most often recorded (Table 1). Our findings are thereby consistent with those record- ed for other cereals, for which CCC increased grain yield by 0% to 20% (De et al. 1982, Ma and Smith 1992a, Börnel and Meinel 1993) and ethephon effect ranged from a 64% yield reduc- tion up to 13% yield increase depending on growing conditions (Simmons et al. 1988, Tay- lor et al. 1991, Ma and Smith 1992a). Slight yield 170 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. & Rajala, A. Plant growth regulators affect yield formation of oat T ab le 3 . D if fe re nc es a m on g oa t li ne s in y ie ld c om po ne nt s th at w er e un af fe ct ed b y pl an t gr ow th r eg ul at or a pp li ca ti on i n 19 95 a nd 1 99 6. M ea ns f ol lo w ed b y a di ff er en t le tt er i n ea ch r ow w it hi n a ye ar a re s ig ni fi ca nt ly d if fe re nt ( S N K 5% ). T ra it # 19 95 19 96 L an dr ac e V ir m a Å 8 91 06 R hi an no n G ra ne P al L an dr ac e V ir m a Å 8 91 06 R hi an no n G ra ne P al T il le rs ( no . m ai n sh oo t– 1 ) 0. 31 a 0. 27 a 0. 28 a 0. 36 a 0. 27 a 0. 58 b 0. 77 ab 0. 65 a 1. 00 bc 0. 93 bc 0. 87 bc 1. 08 c P an ic le -b ea ri ng t il le rs (n o. m ai n sh oo t– 1 ) 0. 10 a 0. 04 a 0. 07 a 0. 19 b 0. 08 a 0. 37 c 0. 48 b 0. 34 a 0. 55 b 0. 58 b 0. 51 b 0. 75 c M ai n sh oo t ph yt om as s( g) 2. 11 cd 2. 26 d 1. 65 b 1. 98 c 2. 13 cd 1. 25 a 2. 46 c 2. 51 c 2. 41 c 2. 12 b 2. 01 b 1. 05 a P hy to m as s on t il le rs (g m ai n sh oo t– 1 ) 0. 12 a 0. 07 a 0. 09 a 0. 24 b 0. 09 a 0. 24 b 0. 80 b 0. 63 ab 0. 75 b 0. 83 b 0. 65 ab 0. 43 a M ai n sh oo t ve ge ta ti ve ph yt om as s (g ) 1. 22 c 1. 18 c 0. 97 b 1. 17 c 1. 00 b 0. 63 a 1. 34 c 1. 35 c 1. 54 c 1. 42 c 1. 12 b 0. 53 a V eg et at iv e ph yt om as s on t il le rs ( g m ai n sh oo t– 1 ) 0. 08 a 0. 04 a 0. 06 a 0. 15 b 0. 05 a 0. 13 b 0. 49 bc 0. 39 b 0. 54 bc 0. 61 c 0. 43 b 0. 26 a M ai n sh oo t pa ni cl e w ei gh t (g ) 0. 89 b 1. 08 c 0. 67 a 0. 81 b 1. 13 c 0. 62 a 1. 12 d 1. 16 d 0. 86 c 0. 71 b 0. 90 c 0. 52 a T ot al w ei gh t of g ra in s pe r ti ll er s (g m ai n sh oo t– 1 ) 0. 04 a 0. 02 a 0. 03 a 0. 09 b 0. 04 a 0. 11 b 0. 32 c 0. 24 b 0. 21 a 0. 22 ab 0. 23 ab 0. 17 a S in gl e gr ai n w ei gh t (m g) 31 .8 b 31 .5 b 23 .5 a 24 .4 a 31 .7 b 32 .0 b 33 .3 d 29 .4 c 21 .7 b 19 .1 a 34 .8 e 40 .4 f G F R ( m g gr ai n– 1 d– 1 ) 1. 01 c 0. 99 c 0. 78 a 0. 82 b 1. 12 d 0. 97 c 0. 80 d 0. 71 c 0. 51 b 0. 46 a 0. 89 e 0. 87 e P H G R ( g m –2 d –1 ) 14 .8 ab 16 .5 ab 14 .0 a 17 .4 b 15 .7 ab 14 .6 ab 25 .5 b 23 .4 b 23 .2 b 23 .0 b 21 .5 b 15 .3 a G F R , g ra in -f il li ng r at e P H G R , p hy to m as s gr ow th r at e S N K , S tu de nt -N eu m an -K eu ls m ul ti pl e ra ng e te st a t th e 0. 05 p ro ba bi li ty l ev el 171 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 10 (2001): 165–174. increases following CCC application were due to alterations in yield components, as differences between PGR treatments in length of the main growth phases were modest and inconsistent (i.e., most often one day delay if any). Traits contributing to CCC induced yield increase Although PGR applications enhanced tillering in barley and wheat (Naylor et al. 1986, 1987, Woodward and Marshall 1988, Craufurd and Cartwright 1989, Taylor et al. 1991, Khan and Spilde 1992, Ma and Smith 1992a), the response is likely to be limited under northern growing conditions. This is because tillering, especially production of head bearing tillers, is inhibited by long-day-induced hormonal signals that main- tain apical dominance (Peltonen-Sainio and Järvinen 1995). In this study, the number of pani- cle-bearing tillers was frequently far less than one per main shoot and was highest in the dwarf line Pal (Table 3). However, CCC tended to in- crease the total weight of grains per tiller pani- cle (P = 0.056) and in 1995, when tiller contri- bution to grain yield was much lower than in 1996, tillers of CCC treated plants contributed more to grain yield than did those of the con- trols (Table 2). Also more panicles per square meter was recorded in CCC treated plants. Yield- ing ability of tillers was not enhanced at the ex- pense of the main shoot, even though it occurred under growing conditions that did not favour till- er growth in general (Table 4), as CCC did not alter the number of grains per panicle, PFR, GFR or single grain weight on main shoot (Tables 1 and 2). We estimated that the recorded 2% unit increase in tiller contribution to grain yield in 1995 averaged 90 kg more grain ha–1. When com- paring the PGR effects on panicle yield in na- ked and husked oats, our results did not suggest that PGRs have potential for modifying yield formation of naked oat through enhancing spike- let and grain set. High number of grains per spikelet and low numbers of spikelets per pani- cle are associated with lower productivity in naked oat compared with conventional oat (Pel- tonen-Sainio1994). The slight effects of CCC on growth and pro- ductivity may result from decreased intra-plant competition for photoassimilates, as spraying with CCC resulted in shorter stems. Peltonen- Sainio and Peltonen (1995) showed that numer- ous sinks, such as tiller growth, stem elongation and floret set, simultaneously demand assimi- lates at late pre-anthesis. The finding of Knapp et al. (1987) further supports a decrease in intra- plant competition. They found that both CCC and ethephon increased the total amount of water- soluble carbohydrates in wheat culm, which may indicate enhanced accumulation of reserved as- similates in stems. In this study, the length of the visible part of the peduncle was reduced by 14% to 36% with CCC in conventional and na- ked oat cultivars depending on year, whereas the corresponding decrease in plant height from soil surface to panicle tip was 5% to 12% (Table 1). Table 4. Monthly mean temperature and precipitation for growing seasons 1995 and 1996 and the long- term means (1961–1990) at Kaisaniemi Meteorological Station, Helsinki. Month Mean temperature (°C) Precipitation 1995 1996 Long-term 1995 1996 Long-term May 8.8 8.6 9.7 66 68 31 June 17.3 13.3 15.0 31 58 41 July 15.8 15 17.0 28 122 60 August 16.3 18.1 15.7 51 1 74 September 11.9 9.8 11.1 67 28 73 172 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. & Rajala, A. Plant growth regulators affect yield formation of oat Thus, our results indicate that the CCC effect was predominantly on the uppermost internode and no statistically significant PGR effect on panicle length (P = 0.105) was recorded in this study. By enhancing rather than inhibiting stem elongation the response of dwarf cultivars to CCC differed from that of conventional and na- ked oat (Table 1). For example, the visible pe- duncle was up to 33% longer and plants were 3– 6% higher at maturity when compared with the untreated control. Rajala and Peltonen-Sainio (2001) also reported this phenomenon. The au- thors hypothesise that CCC resulted in abundant accumulation of gibberellin (GA) biosynthesis precursors in addition to those resulting from the expression of the dominant Dw6 gene. This over- dose of GA precursors possibly served subse- quently as an abundant source for GA synthesis in CCC treated plants. As a consequence of this stem elongation of CCC treated plants exceeded that of the control plants. Enhanced stem elon- gation in dwarf cultivars following CCC treat- ment was already recorded at late pre-anthesis (data not shown). This finding, however, con- tradicts that of Burrows (1986) who found that treatment with GA 3 , enhanced peduncle elonga- tion in dwarf oat. Furthermore, contrary to our results concerning the Dw6 gene of oat, Behar- av et al. (1994) reported Rht alleles in wheat to reduce sensitivity to endogenous and exogenous GA, and also to inhibitors of GA synthesis, in- cluding CCC. Evidently, further experiments are needed to test our hypothesis. Meanwhile, anti- gibberellins cannot be recommended for manip- ulation of yield formation in dwarf oat as they may stimulate rather than inhibit stem elonga- tion. Traits modified with ethephon In contrast with CCC, ethephon most often re- duced grain yield of oat (Table 1). This was ev- ident as fewer grains per panicle was set. PFR was reduced by 8%, and in 1995 HI lowered by 3 percentage units. Reduction of grain number by three per main shoot panicles is likely to be the predominant factor contributing to yield re- duction following ethephon application. It is also possible that in 1995 especially, recorded ten- dency of enhanced tiller productivity through ethephon treatment was biologically inefficient for the plant, resulting in reduced HI. The risk of ethylene stimulated yield reduction in oat is hence similar to that reported for barley and wheat (Simmons et al. 1988, Taylor et al. 1991, Ma and Smith 1992b). Yield losses often occur in unfavourable growing conditions and are therefore suggested to result from an overdose of ethylene in plant tissues. In addition to exog- enously applied ethylene released from ethe- phon, endogenous ethylene production is stimu- lated by stresses. In conclusion, the results from our studies showed that yield formation of oat was respon- sive to PGR treatments. The antigibberellin CCC enhanced growth, whereas application of ethyl- ene-releasing ethephon resulted in yield losses in oat. Increased grain yield attributable to CCC application resulted from more panicles per square meter and higher contribution of tillers to grain yield. 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Myös tutkimus on keskitty- nyt näihin ensin mainittuihin viljalajeihin. Kaura saattaa kuitenkin reagoida tähkällisiä viljoja herkem- min kasvuoloissa tapahtuviin muutoksiin, myös kas- vunsäädekäsittelyihin. Siksi tutkimme kasvunsäätei- den vaikutuksia kauran sadonmuodostukseen Suomen kasvuoloissa mittaamalla jyväsadon lisäksi 24 kas- vuston rakennetta ja sadonmuodostusta kuvaavaa ominaisuutta. Peltokokeet järjestettiin Helsingin yli- opiston Viikin koetilalla vuosina 1995 ja 1996. Ta- vanomaisen kauran lisäksi tutkimme kasvunsääteiden vaikutuksia paljasjyväisen ja kääpiökauran sadontuot- toon. Tutkittujen kasvunsääteiden vaikutus perustuu kasvien hormonitoiminnan muutoksiin. Klormekvat- tikloridi (CCC) ehkäisee gibberelliinihapon biosyn- teesiä ja etefoni lisää etyleenin tuotantoa. Kaurakasvustojen käsittely CCC:lla kaksisolmu- asteella lisäsi satoa parhaimmillaan 13 %, kun ete- foni-käsittely lippulehden kielekkeen tultua esille yleensä vähensi satoa. Koska kaurakasvustot eivät lakoontuneet, kasvunsääteet vaikuttivat sadonmuo- dostukseen muuttamalla kasvustorakennetta. Kumpi- kin kasvunsääde lyhensi tavanomaisten ja paljasjy- väisten kauralajikkeiden kortta, erityisesti näkyvää osaa ylimmästä nivelvälistä. Kääpiölajikkeiden kor- si kuitenkin piteni CCC-käsittelyn seurauksena. CCC lisäsi röyhyjen määrää neliöllä ja versojen tuottamaa osuutta sadosta. Myös etefoni-käsittely lisäsi verso- jen merkitystä sadontuottajina, mutta tämä oli seu- rausta lähinnä pääverson heikentyneestä sadontuot- tokyvystä. Etefoni-käsiteltyjen kaurojen pääversois- sa oli vähemmän jyviä ja röyhyn täyttymisteho sekä satoindeksi jäivät kontrollikasveja alhaisemmiksi. Tutkimustemme mukaan tilanteissa, joissa kas- vunsääteillä ei ensisijaisesti lakoa ehkäisemällä py- ritä turvaamaan sadontuottoa, antigibberelliinikäsit- telyin (CCC) voitaneen vähissä määrin parantaa kau- ran sadonmuodostusta. Etefonia käytettäessä riski satotappioille on ilmeinen. Edullisetkaan vaikutukset sadontuottokykyyn eivät olleet riittäviä, jotta käsit- telyiden voisi arvioida olleen taloudellisesti kannat- tavia tilanteessa, jossa lakoa ei esiinny. Title Introduction Material and methods Results Discussion References SELOSTUS