Numeric codes for developmental stages of oat apex in the growing conditions of Southern Finland Pirjo Peltonen-Sainio and Tiina Pekkala Peltonen-Sainio, P. & Pekkala, T. 1993.Numeric codes for developmental stages of oat apex in the growing conditions of Southern Finland. Agric. Sci. Finl. 2: 329-336. (Dept. Plant Production, FIN-00014 University of Helsinki, Finland.) Scales that categorize the development of cereal apex have been introduced by several authors. Daylength markedly affects the rate of apex organogenesis and, hence, numeric codes for developmental stages of apices introduced for lower latitudes cannot be used in Finland without modifying them into a ratio scale. The present study introduces numeric codes that categorize the 22 developmental stages ofoat (Avena saliva L.) apex in the growing conditions of Southern Finland. Field experiments, including 14 oat cultivars and six breeding lines that differ in the duration of the period from initiation of double ridges to pollination, were carried out at the Viikki Experimental Farm of the University ofHelsinki (60°13’N) for two years. The numeric codes were established by relating them to cumulated degree days (CDD). This study showed that when estimating the developmental stages of oat apex by calculating CDD from sowing, the error of estimation was ±1 stage unit at the most. Key words: oats, apex, developmental stage, degree day, numeric code Introduction Temperature, daylength, and precipitation affect crop growth and development. In cereals, the higher the temperature and the longer the photope- riod, the higher the rate ofdevelopment and the less leaf, spikelet, and floret primordia per head (Rashid et al. 1984, Kirby et al. 1985, Cao and Moss 1989, Craufurd and Cartwright 1989, Miglietta 1989,Peltonen-Sainio 1993). The ef- fects of water deficit on apical development are, however, equivocal. In oats, moderate and severe water stress considerably reduced floret and grain set, but did not affect the duration of pre-anthesis phase (Peltonen-Sainio 1991). Several scales describing the development of ce- real apex from initiationofdoubleridges to pollina- tion have been introduced for use in crop manage- ment (Table I). Precise timing of inputs - e.g., application of supplemental nitrogen according to developmental stages ofapices (Darwinkel 1983, Peltonen and Peltonen 1990, Peltonen 1992) - is an important strategy particularly in integrated crop production. Moreover, phenoxy acetic acid herbicides, such as MCPA and 2,4-D, whenapplied close to the double ridge stage, may cause apex abnormalities including twisted rachis, unilateral spikelet set, fusion of spikelets, branched spikes, and retarded differentiation (Andersen 1954, Loubser and Cairns 1989). In addition, certain developmental stages of apex may be particularly sensitive to injuries caused by insect pests and pathogens. Markedly reduced grain set, following infection caused by barley yellow dwarf virus at the 329 Agric. Sei. Finl. 2 (1993) https://www.c-info.fi/en/info/?token=NGo09Ui987IygLIv.c93a4AbDZPbS31wyRlbK_w.gZv5sB4b8NnoujQt3Ch_DTdlGruppA8qzwPmS4XZNg3CM2N-ugUAQVOSa6XW4xP5V97KDBpHsE62dc1ZbSMGTmLJmxsU0-5AR62ni6X7YPmkLRd8LyK0VKo3d_CaFHNaugjdhvZEtdmn8ssC0qxsCxcmXtjl7-VfSooTvjgwDxheJWXy7zoDMWTVOUPkX38i0UZKbTyeFHprMlIsVRtV4eI7EEzd0JK-nOiRiNl837Q6ubp3FOmVKGNzvGxXbLQa6e2iU3MxzUIWROW-IVpfpMz2tHRFtadRNhf2-IE7 330 Table 1. Comparison of numeric and letter codes that describe development of apices. Description* Andersen Banerjee Williams Waddington Åfors (1952) 1,2 & Wienhues (1966)3 etal. et. al. (1965)2,3,4 (1983) 2'3 (1988) 1,2,3 Vegetative cupola stage 0-1 1-2 - 1 A Transition apex - 3 16 1.5 B Early double ridge stage - 4 22 2 C Double ridge stage 2 5-6 24 2.5 D Triple mound stage 3 7 26 - E Glume primordium present - 28 3 F Lemma and floret primordium present 4 8 28 3.25-3.5 G Stamen primordium present 5 9 30-32 4 H Pistil primordium present - 9 32 4.25 I Carpel primordium present - 9 32 4.5 K Carpel surrounded by enlarged stamens - 10-11 34 5 L Stylar canal closing, ovarian cavity still open above 6 11-12 34-36 5.5 M Stylar canal remaining as a narrow opening and two short style primordia present 6 12 36 6 N Styles begin elongating, still projecting 7 - - - O Styles strongly elongating 7 13 38 6.5 P Stigmatic branches differentiating as swollen cells on styles 7 14 38-42 7 Q Stigmatic branches elongating 8 14 - - R Unicellular hairs differentiating on ovary walls, stigmatic branches still elongating 8 14 42 7.5 S Hairs on ovary wall strongly elongating, stigmatic branches as well 8 14 42-46 8 T Stigmatic branches form a tangles mass (wheat and barley) and are erect (oats) 9 15 46 8.5 U Style and stigmatic branches erect, stigmatic hairs differentiating 10 16-17 50 9 V Stigmatic hairs well-developed, branches spreading outward 10 17 50 9.5 X Styles curved outward and stigmatic branches spread wide, pollen grains on well-developed stigmatic hairs 10 17 55 10 Y * According to Waddington et al. (1983) and Åfors et al. (1988) 1 Codes described for oats, 2 barley, 3 wheat, and 4 rye early reproductive phase of oats, indicates such sensitivity (Peltonen-Sainio and Karjalainen 1990). When evaluating the effects of management practices and abiotic and biotic stresses on apex organogenesis, numeric codes are needed to cat- egorize the development of apex in a ratio scale. However, numeric codes earlier introduced for bar- ley and wheat are not linearly related to any factor. Furthermore, the applicability ofnumeric codes for different genotypes has to be tested because, for example, in the studies ofKirby and Appleyard (1980), barley cultivars responded differently to daylength. The present study was carried out to simulate the uniform numeric codes for developmental stages of oat apices. The codes established can be used in the photoperiodic conditions of Southern Finland. Evaluation of performance of different oat lines was based on testing of 20 oat cultivars and breed- ing lines that differ in duration of the period from initiation ofdouble ridges to pollination. Material and methods Plant material consisted of 14 oat cultivars (Table 2) and six breeding lines bred at the Hank- kija Plant Breeding Institute, Finland. The oat lines were tested in experiments at the Viikki Ex- perimental Farm of the University of Helsinki (60° 13’ N) in 1989-1990. A completely random- ized block design with four replications in 1989and three in 1990 was used. Plot size was 10 m, and 500 viable seeds were sown per m . Planting date was 27 April in both years, and soil type was sandy clay. 80 kg N ha" 1 (NH4NO3) was applied at sowing together with P, K, etc. fertilizers. Weeds were controlled with MCPA [(4-chloro-2methylphe- noxyl)acetic acid] at a rate of 700 g ha 1 after the double ridge stage. The developmental stages of the oat apices were recorded from 10 randomly sampled main stems per plot according to the scale introduced by Åfors et al. (1988). The stage of development was deter- mined on the terminal spikelet, which is the most advanced spikelet in oats. The interval of plant samplings was between two and seven days de- pending on the rate of differentiation. Cumulated daily growing degree days (CDD) to reach different developmental stages were calculated using +5°C as the base temperature. Numeric codes, at ratio scale, for each develop- mental stage ofapex were established to replace the letter codes ofÅfors et al. (1988). The letter code A was changed to 1, B to 2, C to 3 and so on. Correlations between these integers that correspond to the letter codes A-Y and the weighted means of CDD required to reach the developmental stages were calculated over years and cultivars (MSTAT Development Team 1989). Regression coefficients Table 2. Oat cult! vars tested in the study, year of release, and country of origin. Cultivar Year of release Country of origin Jalostettu maatiainen 1921 Finland Osmo 1921 Finland Esa 1922 Finland Pellervo 1935 Finland Sisu 1948 Finland Kyrö 1959 Finland Ryhti 1970 Finland Pol 1974 Norway Svea 1976 Sweden Puhti 1978 Finland Veli 1981 Finland Hankkijan Vouti 1982 Finland Karhu 1985 Sweden Virma 1988 Finland were tested with Student’s t-test (SAS Institute 1989) and the codes for the different developmental stages adjusted until correlation was absolute (R"=1.00 ). Numeric codes (CODE) over geno- types were established using the formula: [1 ] CODE = -6.08 + 0.067 * CDD where CDD is cumulated degree days required to reach different developmental stages of apex from transitionapex to pollination. Results and discussion When evaluating the effects of management prac- tices and abiotic and biotic stresses on apex organo- genesis, numeric codes are needed to categorize the development of apex in a ratio scale. In this study, numeric codes were established over 20 genotypes (Table 3). The developmental stage, when carpel primordium is initiated, was not recorded in this study. This stage of apex is rapidly transient and hard to distinguish from the preceding one. When testing the validity of theregression equa- tion [ 1] for different years and genotypes, our res- ults showed that CDD from sowing explained 88- 99% of the variation in the developmental stage of 331 Agric. Sei. Fint. 2 (1993) Table 3. CDD from sowing to reach different developmental stages of apex and estimated numeric codes (CODE) for growing conditions of Southern Finland. Letter code for Number of CDD (°C) CODE developmental stage observation Mean S.E. S.D. (Åfors et al. 1988) A 165 136 1.6 16.3 B 215 137 1.4 19.6 3.12 C 151 141 1.7 8.9 3.40 D 84 151 2.2 14.1 4.04 E 197 168 1.5 6.9 5.20 F 218 173 1.4 8.7 5.51 G 296 191 1.2 17.8 6.70 H 186 205 1.5 17.7 7.68 I 189 216 1.5 10.8 8.39 K 0 - - - 9.20* L 472 240 0.9 18.8 10.00 M 88 276 2.2 26.6 12.39 N 133 291 1.8 21.2 13.41 O 151 303 1.7 14.7 14.51 P 142 310 1.7 19.6 14.70 Q 150 314 1.7 20.5 14.95 R 102 333 2.0 30.7 16.24 S 121 341 1.9 30.3 16.79 T 144 357 1.7 29.8 17.81 U 266 378 1.3 24.7 19.28 V 159 410 1.6 33.8 21.42 X 156 438 1.6 27.8 23.42 Y 315 469 1.2 19.7 25.34 * interpolated apices in 1989 and 95-98% in 1990. The median was 98% in 1989 and 97% in 1990. Precipitation was higher at pre-anthesis in 1989 than in 1990 (Fig. 1). In 1990, degree days cumulated faster at early growth stages, and double ridges initiated about one week earlier than in 1989. Since then, degree days cumulated more slowly in 1990, and oats pollinated five days later than in 1989. Comparison ofregression coefficients for differ- ent oat genotypes by F-test showed that apical de- velopment of 11 genotypes did not differ signific- antly between years. The 11 genotypes are all bred in Finland, whereas the nine genotypes that were excluded from further analyses included, for in- stance, the foreign cultivars. Data on both years for the 11 genotypes were combined and new regres- sion equations were established. Then, CDD from sowing explained 96-98% of the variation in the development of apices (Table 4). The more ad- vanced the developmental stage, the higher was the deviation from the uniform trend (Fig. 2). Further grouping of oats, e.g., into old and modem cultivars and breeding lines, was not statistically justified. In general, differences in intercepts and regression co- efficients between the eleven oat genotypes were modest (Table 4). The relatively homogeneous re- sponse of lines to CDD, recorded in this study, can be attributed to resemblance of genetic background 332 Agric. Sei. Finl. 2 (1993) of oats bred in Finland (REKUNEN 1988, JUSSILA et al. 1992). Regarding estimation of the developmental stage of apex by calculating CDD from sowing, our res- ults showed that root mean square errors (Root MSB) for different genotypes ranged from 0.94 to 1.39. It means that estimation of developmental stages of apices by calculating CDD from sowing resulted in error of ±1 developmental stage unit at the most. The residual scatter plot of cultivar Veli, shown in Figure 3, is similar to that of other culti- vars examined. The three developmental stages that may be incorrectly estimated, i.e., they mixed with each other, are when styles began to elongate until stigmatic branches elongated (Fig. 3). Because these stages of apex are particularly rapidly tran- sient, they may mix with each other. Logarithmic modifications of the variables did not improve the Fig. I. CDD and precipitation in 1989 and 1990 at Kaisaniemi, Helsinki (* = emergence, C = double ridge stage, Y = pollination). Fig. 2. Regressions between development of apex and CDD in 11 oat lines. Broken lines indicate confidence interval at 95% level. 333 Agric. Sei. Fin!. 2 (1993) Table 4. Intercepts and regression coefficients between established numeric codes for developmental stages of apex and CDD in 11 oat cultivars. Cultivar Intercept Regression coefficient R 2 Estimate Ratio* Estimate Ratio* Confidence intervals* Jalostettu maatiainen -5.29 4.2 0.064 0.011 [0.065,0.063] 0.97 Pellervo -5.53 4.0 0.062 0.012 [0.063,0.061] 0.97 Sisu -5.863.2 0.0660.010 [0.067,0.065] 0.98 Ryhti -5.283.8 0.0620.011 [0.063,0.061] 0.98 Puhti -5.454.0 0.0630.012 [0.064,0.062] 0.97 Veli -6.003.3 0.0650.010 [0.066,0.064] 0.98 Hankkijan Vouti -4.904.3 0.0610.011 [0.062,0.060] 0.97 Hja 76416 -5.145.4 0.0650.015 [0.067,0.063] 0.96 Hja 76420 -5,48 4.60.066 0.013 [0.068,0.064] 0.97 Hja 78033 -5.264.0 0.0630.011 [0.064,0.062] 0.97 Hja 80090 -5.043.6 0.0640.009 [0.065,0.063] 0.98 * S.E. divided by estimate (%) validity of estimation of the three developmental stages of apex. However, CDD estimates accur- ately the double ridge stage and, hence, phenoxy acetic acid herbicides should not be sprayed until CDD >l7O °C in oats to avoid apex abnormalities and possible crop losses. In conclusion, the numeric codes for 22 develop- mental stages ofoat apices were simulated by relat- ing them to CDD. These codes can be used for oats when cultivated in Southern Finland. Our results indicate that estimation of apical development by calculating CDD when timing management prac- tices may result in an error of ±1 developmental stage unit at the most. References Åfors, M, Ohlander, L. & Stendahl, F. 1988. Stråsädens utveckling I. En litteraturstudie och beskrivning av en skala förbestämning av stråsädens ax- respektive vippan- lag. Sveriges Lantbruksuniversitet. Institutionen för växtodlingslära. 75 p. Uppsala. Andersen, S. 1952. Methods for determining stages of devel- opment in barley and oats. Physiol. Plantarum 5: 199- 210. 1954. Effects of 2,4-D on ear development in barley. Physiol. Plantarum 7; 517-522. Banerjee, S. & Wienhues, F. 1965. Comparative studies on the development of the spike in wheat, barley and rye. Z. Pflanzenziichtg. 54: 130-142. Cao, W. & Moss, D.N. 1989. Temperature effect on leaf emergence and phyllochron in wheat and barley. Crop Sci. 29; 1018-1021. Craufurd, P.Q. & Cartwright, P.M. 1989. Effect of pho- toperiod and chlormequat on apical development and growth in a spring wheat (Triticum aestivum ) cultivar. Ann. Bot. 63:515-525. Fig. 3. Residual scatter plot in Veli. Residual was calculated by subtracting the simulated developmental stage from the observed one. 334 Agric. Sei. Fint. 2 (1993) Darwinkel, A. 1983. Ear formation and grain yield of winter wheat as affected by time of nitrogen supply. Neth. J. Agric. Sci. 31: 211-225. Jussila, M., Sontaq-Strohm, T. & Ulvinen, O. 1992. The identification of Finnish oat cultivars (Avena sotiva L.) by the use of SDS-PAGE of the avenins in homogeneous and gradient gels. Acta Agric. Scand., Sect. B, Soil and Plant Sci. 42: 106-110. Kirby, E.J.M. & Appleyard, M. 1980. Effects of photope- riod on the relation between development and yield per plant of a range of spring barley varieties. Z. Pflanzen- ziichtg. 85: 226-239. —, Appleyard,M. & Fellowes, G. 1985. Effect of sowing date on main shoot leaf emergence and number of leaves of barley and wheat. Agronomie 5: 117-126. Loubser, J.M. & Cairns, A.L.P. 1989. Abnormalities of the growth point and ear of barley caused by 2,4-dichloro- phenoxy acetic acid. South African J. Plant Soil 6: 103- 107. Miglietta, F. 1989. Effect of photoperiod and temperature on leaf initiation rates in wheat (Triticum spp.). Field Crops Res. 21: 121-130. MSTAT Development Team 1989. User’s Guide to MSTAT-C: A Microcomputer program for the design, management, and analysis of agronomic research experi- ments. Michigan State Univ., East Lansing. Peltonen, J. 1992. Ear developmental stage used for timing supplemental nitrogen application to spring wheat. Crop Sci. 32; 1029-1033. & Peltonen, P, 1990.Effect of apical timed urea spraying on yield components and quality properties of spring wheat (Triticum aestivum L.) in greenhouse experiments. Acta Agric. Scand. 40: 33-43. Peltonen-Sainio, P. 1991. Effect of moderate and severe drought stress on the pre-anthesis development and yield formation of oats. J. Agric. Sci. Finl. 63: 379-389. 1993. Response to daylength in oats: Pre-anthesis devel- opment and set of spikelets and florets. J. Agron. Crop Sci. (in press.) & Karjalainen, R. 1990. Yield reduction of oat cultivars in relation to disease development caused by barley yel- low dwarf virus. J, Agric. Sci. Finl, 62: 265-273. Rashid, A.H., Flalloran, G.M. & Hamaßashid, A. 1984. Influence of photoperiod on culm elongation and apical development in semi-dwarf and standard-height wheats. Ann. Bot. 54: 375-382. Rekunen, M. 1988. Advances in the breeding of oats. Com- parative trials with historical varieties in 1977-1987. J. Agric. Sci. Finl. 60: 307-321. SAS Institute 1989. User’s Guide. Vol. I. Anova-Freq. and Vol. 2. GLM-VARCOMP. Version 6. SAS Institute Inc., Cary N.C., USA. Waddington, S.R., Cartwright, P.M. & Wall, P.C. 1983. A quantitative scale of spike initiation and pistil develop- ment in barley and wheat. Ann. Bot. 51: 119-130. Williams, R.F. 1966. The physiology ofgrowth in the wheat plant. 111. Growth of the primary inflorescence. Aust. J. Biol. Sci. 19: 949-966. Manuscript received April 1993 Pirjo Peltonen-Sainio Tiina Pekkala Department of Plant Production Section of Crop Husbandry Box 27, Viikki FIN-00014 University of Helsinki, Finland 335 Agnc. Sei. Fint. 2 (1993) SELOSTUS Kauran kukinnon kehitysvaiheiden lukuarvot Etelä-Suomen kasvuoloissa Pirjo Peltonen-Sainio jaTiina Pekkala Helsingin yliopisto Viikinkoetilalla tutkittiin vuosina 1989 ja 1990 tehoisan läm- pötilasumman ja kauran kukinnon kehittymisen välistä yh- teyttä. Tutkimusaineistona oli 20 kauralajiketta ja -linjaa, joi- den tiedettiin aikaisempien kokeiden perusteella eroavan pö- lyttymisajankohdaltaan. Aineiston perusteella luotiin 22 ku- kinnon kehitysvaiheelle (siirtymävaiheesta pölyttymiseen) suhdeasteikolla olevat numerokoodit, joita voidaan käyttää kaikille kauralajikkeille Etelä-Suomen kasvuoloissa. Tutkimuksessa selvitettiin myös voidaanko kauran kukin- non kehitysvaiheita arvioida epäsuorasti laskemalla tehoisa lämpötilasumma. Tutkimus osoitti, että tämä menetelmä saat- toi aiheuttaa enimmillään yhden kehitysvaiheen virheen. Tosin esimerkiksi kaksoiskehävaihe, joka on herkkä fenoksi- herbisidien (esim. MCPA) aiheuttamille vioituksille, voitiin arvioida luotettavasti. Rikkakasveja ei tulisi torjua fenoksi- herbisideillä ennenkuin tehoisaa lämpötilasummaa on kerty- nyt vähintään 170 °C. Tällöin pääverson neljäs kasvulehti on työntymässä ulos lehtitupesta. Lisätutkimuksia tarvitaan pa- rantamaan kehitysvaiheiden epäsuoraa arviointia - erityisesti helposti tutkittavien, ulkoisten morfologisten ominaisuuksien avulla. 336 Agric. Sd. Fin!. 2 (1993)