Research Note Growth duration and above-ground dry-matter partitioning in oats Pirjo Peltonen-Sainio Peltonen-Sainio, P. 1994. Growth duration and above-ground dry-matter par- titioning in oats. Agricultural Science in Finland 3: 195-198. (Department of Plant Production, P.0.80x 27, FIN-00014 University of Helsinki, Finland.) Duration of vegetative, generative, and grain-filling phases contribute to dry-mat- ter accumulation and partitioning. Fourteen oat (Avena saliva L.) cultivars and six breeding lines were evaluated at the Viikki Experimental Farm, University of Hel- sinki, in 1988-1990. The following observations were made: (1) a short vegetative period accumulated less dry-matter into vegetative plant organs and resulted in higher grain yield and harvest index (HI), (2) a long period for maximum floret initiation yielded more grains per panicle and high panicle weight and (3) a short grain-filling period yielded high rates of panicle and grain filling associated with high HI. Hence, oat breeding and crop management should aim at improving the synchronization of the growth phases as shown in this study. Key words: Avena saliva L., development, grain yield, phytomass, harvest index Introduction A short growing season and the consequent de- mand for early maturing cultivars are the main factors limiting productivity of annual small grains grown in Finland. Long days enable cereals to rapidly reach and pass several developmental stages (DVS), especially at pre-anthesis (Pelto- nen-Sainio 1994). The growth period of cereals is divided into three phases: 1) the vegetative period from germination to double-ridge stage, 2) the generative period from initiation of double ridges to pollination and 3) the grain-filling peri- od. The vegetative period of oats is completed by 140 dd °C (base temperature 5°C) and hence, generative growth begins already at the two-leaf stage, and grain filling starts at <5OO dd °C in Finland (Peltonen-Sainio and Pekkala 1993). The duration of growth phases is likely to con- tribute to both source and sink capacities, i.e. expansion, persistence and assimilate production of green area, set and assimilate demands of flo- rets and grains, and the reciprocal feed-back ef- fects between sources and sinks. The HI indi- cates the success of the synchronization between sources and economic sinks. Hence, this study evaluated the contribution of duration of vegeta- tive, generative and grain-filling phases to dry- matter accumulation and partitioning in oats. Material and methods The plant material included 14 oat cultivars (Esa, Jalostettu maatiainen. Hankkijan Vouti, Karhu, Kyrö, Osmo, Pellervo, Pol, Puhti, Ryhti, Sisu, Svea, Veli, Virma) and six breeding lines from the Hankkija Plant Breeding Institute. Field stud- ies were conducted at the Viikki Experimental Farm, University of Helsinki (60° 13' N), in 1988- 1990. A completely randomized block design with four replications in 1988-1989 and three in 1990 was used. Plot size was 10 m 2, and 500 viable seeds nr 2 were sown. Sowing date was 9 May in 195 Agricultural Science in Finland 3 (1994) Agricultural Science in Finland 3 (1994) 1988 and 27 April in 1989 and 1990. Soil type was sandy clay, and 80 kg N ha 1 as NH4 N0 3 was applied at sowing (N:P:K; 18-5-10). Weeds were controlled with MCPA [(4-chloro-2-methylphen- oxy)acetic acid] at a rate of 700 g ha” 1 after the double-ridge stage, and bird cherry-oat aphids (Rhopalosiphum padi L.) twice in 1988 by alter- nating dimethoate and deltametrin at a rate of 400 g ha' 1 and 15 g ha 1 , respectively. Early double-ridge stage (DVS 3.4) (Pelto- nen-Sainio and Pekkala 1993), the developmen- tal stage when floret abortion begins (DVS 14.9) and pollination (DVS 25.3) were recorded from 10 randomly sampled main shoots, and were con- sidered to be reached when >60% of the plants were at that stage. Cumulated degree days (CDD, dd °C, base temperature 5°C) were calculated for: (1) the vegetative period (from sowing to DVS 3.4), (2) the period for production of maxi- mum floret number (from DVS 3.4 to DVS 14.9), and (3) the generative phase (from DVS 3.4 to DVS 25.3). The following traits were recorded: (1) grain yield (g nr2 at 15% moisture), (2) number of days from sowing to heading, (3) length of grain- filling period (d), (4) phytomass (g plant” 1 ), (5) vegetative phytomass (g plant 1 ), (6) panicle weight (g), (7) number of grains panicle 1 , (8) average grain weight (mg), (9) harvest index (HI, %), (10) average vegetative growth rate (VGR, mg plant' 1 d 1), (11) average phytomass growth rate (PGR, mg plant' 1 d 1); (12) average panicle-filling rate (PFR, mg panicle' 1 d 1), and (13) average grain-filling rate (GFR, mg grain' 1 d' 1 ). Traits (4)-(13) were measured from 40 ma- ture, randomly sampled plants. Linear regressions and second-degree polynomials between duration of growth period and morpho-physiological traits were calculated for different genotypes over years. Results and discussion The longer the growth period before heading, the higher was the grain yield, which resulted from increased weight of total phytomass and panicle (Table 1) associated with higher PGR. However, more dry-matter accumulated into above-ground vegetative plant organs in cultivars that were char- acterized by longer vegetative period (Fig. 1). Correlation between the length of the vegetative period and VGR (r=o.s2*) supported this finding. Table 1. Relationship between duration of pre-heading and grain-filling phases and morpho-physiolog- ical traits of oats in 1988-1990. Trait Days to heading Length of grain filling «probability U ..probability U Grain yield 0.47* 12.3 -0.32"" -8.66 Phytomass 0.60" 0.08 0.04"" 0.01 Vegetative phytomass 0.42 ns 0.03 0.25"" 0.02 Panicle weight 0.67'" 0.05 -0.20ns -0.02 No of grains 0.43" 0.99 -0.34ns -0.82 Grain weight 0.20 ns 0.25 0.28ns 0.37 HI 0.14"" 0.23 -0.57" -0.98 VGR -0.04"" -0.00 0.38ns 0.02 PGR 0.56" 0.80 -0.06"" -0.09 PFR 0.72'" 1.78 -0.64" -1.66 GFR 0.50' 0.02 -0.46' -0.02 r correlation coefficient b regression coefficient ***P