Hereditas 124: 21 7-222 (1996)

Pre- and post-anthesis duration of two-rowed barleys in relation to stability of grain yield at high latitudes J. PELTONEN' and E. NISSILA2

University of Helsinki, Department of Plant Production, Helsinki, Finland Boreal Plant Breeding, Jokioinen, Finland

PELTONEN, J. and NISSILP;, E. 1996. Pre- and post-anthesis duration of two-rowed barleys in relation to stability of grain yield at high latitudes.- Hereditas 124: 217-222. Lund, Sweden. ISSN 0018-0661. Received December 22, 1995. Accepted June 3, 1996

A short growing season and consequent demand for early maturing cultivars are the main factors limiting yield potential of two-rowed barley in Finland. This study was undertaken to compare spikelet production of ten two-rowed barleys which differed in duration of pre-anthesis and grain filling, and to clarify how reduced duration of these phases contributes to stability of yield formation under long-day conditions. Spikelet set declined hut number of fertile spikelets increased with decrease in the length of the pre-anthesis phase. Breeding for a short pre-anthesis phase may not necessarily reduce grain yield, but could lead to instability in yield formation. In selecting breeding lines with a short pre-anthesis phase, a pre-anthesis phase to maturity class ratio ( P M ratio) of 0.58 was found to be suitable under Finnish conditions, resulting in higher spikelet fertility, higher number of grains spike-' and higher grain yield than either lower or higher ratios.

J. Peltonen. Plant Production Inspection Centre, Seed testing Department, P.O. Box 1 11, FIN-32201 Loimau, Finland

In Finlan barley (Hordeum vulgare L.) is grown at the northern limit of plant production, up to the 67th parallel, further north than in any other coun- try in the world. Two-rowed varieties predominate today in Finland because of their larger, plumper and uniform-sized kernels, being thereby more ac- ceptable to industry.

A short growing season and the consequent de- mand for early maturing varieties are the main factors limiting productivity of small-grain cereals in Finland. The long days enable cereals to develop rapidly, especially at pre-anthesis ( PELTONEN- SAINIO 1994). In Finland high temperatures and post-sowing drought may also shorten the duration of the pre-anthesis phase in cereals, and thus shoot apical development, decreasing the yield potential (PELTONEN-SAINIO 1991).

One strategy for improving productivity instead of prolonging maturity could be to increase the duration of grain-filling and shorten the pre-anthe- sis phase. It has been shown that a shorter pre-an- thesis phase in oats and spring wheat may result in decreased spikelet and floret set, but not necessar- ily in reduced grain yield (PELTONEN-SAINIO and PELTONEN 1995). Therefore, the present study was undertaken to compare spikelet production of ten two-rowed barleys which differed in duration of pre-anthesis and grain-filling phases and to clarify

how reduced duration of these phases could con- tribute to stability of yield formation under long- day conditions.

Materials and methods

Field trials were conducted in 1992 and 1993 at the Viikki (6Oo13'N), Rehtijiirvi (60"49'N), Mietoinen (60"38'N), and Kokemaki (60"58'N). The two- rowed barley varieties Inari, Kymppi, Kustaa, and seven two-rowed breeding lines were included in the trials. Due to their higher potential for produc- ing fertile spikelets, six-rowed barley cultivars Kilta and Loviisa were selected as controls. Standard nitrogen-phosphorus-potash (NPK) fertilisation, at 80 kg N, 20 kg P, and 40 kg K ha-', was used to correspond with current usage for Finnish spring barley production. Fertiliser was applied 7 cm deep at the time of sowing. Seeds were sown at the recommended rate for Finland of 500 viable seeds. A randomised complete block design with three replicates was employed. The row spacing was 12.5 cm and plot size was 10 mz. Weeds were con- trolled once at the three-leaf stage with MCPA [4-chloro-2-methyl-phenoxy) acetic acid] at 700 g ha-'.

21 8 J. PELTONEN AND R. NISSILA Hcrcdilas 124 (1996)

Table 1. Variation in morphological traits of six-rowed and two-rowed barley cultivars and breeding lines grouped into three categories according to maturity class (plot means of eight trials)

Genotype Group' Pre-anthesis, Grain-filling Maturity P M ratiod Grain Number of Number of Spikelet' days phase, days phase, days class yield, spikelet spikelets fertility

kgha-' primordia spike-' % spike I

Six-rowed Kikd Loviisa Two -rii wed Jo 1676 I Jo 1754 I Jo 1687 I Kustaa I 1 Jo 1752 I 1 Jo 1680 I1 Kymppi 111 Inari 111 Jo 1682 111 Jo 1760 111

Mean SE" Significanceb G x E interaction

51 48

50 50 51 50 50 51 53 54 55 55

52 f 0.7 *** ***

34 38

39 39 38 40 40 40 39 39 39 39

39 50.5 $** ***

85 86

89 89 89 90 90 91 92 93 94 94

90 k0.8

NS ***

0.60 0.56

0.56 0.56 0.57 0.56 0.56 0.56 0.58 0.58

0.59 0.59

39 10 4180

4330 4215 4515 4290 4455 4220 4690 4690 4505 4480

4370 * 121 *** ***

68 62

26 29 34 27 27 29 29 31 32 36

36 k 1.6 *** **

42 41

18 19 19 18 19 17 21 20 20 21

23 k0.9

NS ***

62 66

69 66 56 67 70 59 72 65 63 58

64 +_ 1.4 NS *

Standard error

Grouped according to maturity Calculated from duration of pre-anthesis phase: maturity class

I' Significance of difference between cultivars: ***P 5 0.001; **P 2 0.01; *P I 0.05; NS non-significant

' Calculated from grains/spike: maximum spikeletsispike

The following morpho-physiological traits were evaluated in each plot:

VELOPMENT TEAM 1989). The phenotypic stability of morpho-physiological traits indicating a signifi-

( 3 )

Maximum number of spikelet primordia per apex was recorded on ten shoots before flag leaf stage, using the dissection technique of KIRBY and APPLEYARD (1984). Pre-anthesis phase days, determined from sow- ing to date of pollination (DVS 10, WADDING- TON et al. 1983). Grain-filling period days, determined from pollination (DVS I0)to yellow ripeness (GS 85, ZADOKS et al. 1974). Number of tillers plant-'. Grain yield at 15% moisture content (kg ha-') Number of spikelets spike-', recorded on ten soots per plot. Spikelet abortion (%I), calculated as (6):( 1)

cant G x E interaction (P < 0.05) was computed on the basis of results from eight field experiments using the FINLAY-WTLKINSON ( 1963) regression method and EBERHARD-RUSSELL ( 1966) stability analysis. The phenotypic stability of grain yield was also calculated by relative yield as a ratio of genotype yield at each site and year to the site mean using the YAU and HAMBLIN (1994) method, where the yield of genotype at any site was expressed as RY,J = 100 x Y,/YJ where RY denotes relative yield; Y, is yield of genotype i at Site j ; Y denotes mean yield of Site j. At each site, genotypes having RY value < 100 yield less than the site average while genotypes having RY values > 100 yield more.

' 100%. (8) Kernel weight (mg). (9) Pre-anthesis phase to maturity class ratio (P:M Results

There was a rainy period of three weeks after The statistical significance of the differences in the sowing in 1992, but between May and June it was examined traits and genotype x environment about 2°C warmer than the mean temperature for (G x E) interactions were evaluated by factorial 1961-1990 and plants suffered drought through- analysis of variance and correlations (MSTAT DE- out the season. Therefore, crops matured at the

ratio), calculated as (2):[(2) + ( 3 ) ] .

Hereditus 124 (1996) PRE- AND POST-ANTHESIS PHASES I N TWO-ROWED RARL.EYS 219

Tuble 2. Differences between barley cultivars and breeding lines in pre-anthesis and grain-filling phases and grain yield level analyzed with Finlay-Wilkinson and Eberhard-Russell analyses

Genotype Groupa Pre-anthesis phase, days (d) Grain-filling phase, days (d) Grain yield (kg ha-')

b, sZd R2 b, s2', R2 b, SZd R2

Six -rowed Kilta Loviisa Two -rowed Jo 1676 Jo 1754 Jo 1687 Kustaa Jo 1752 Jo 1680

Inari Jo 1682 Jo 1760

KYmPPi

I I I

I1 I1 II

I11 111 111 111

0.86 0.87

0.94 0.91 1.06 I .04 0.99 0.97 0.97 0.96 0.97 0.98

0.10 0.06

0.06 0.07 0.09 0.09 0.07 0.14 0.03 0.06 0.08 0.08

0.92*** 0.98***

0.98*** 0.96*** 0.96*** 0.96*** 0.96**' 0.88*** 0.98*** 0.98*** 0.96*** 0.96***

0.79 0.19 0.98 0.15

0.93 0.17 0.88 0.11 0.80 0.08 0.97 0.10 1.02 0.13 0.90 0.28 0.94 0.06 0.84 0.08 0.78 0.10 0.74 0.12

0.74** 0.86***

0.85*** 0.92*** 0.94*** 0.94*** 0.90*** 0.62* 0.98*** 0.96*** 0.92*** 0.86***

1.03 0.23 0.84 0.13

0.85 0.10 0.88 0.15 0.94 0.06 1.02 0.13 0.95 0.11 0.94 0.09 0.91 0.05 0.99 0.14 0.84 0.12 0.80 0.07

0.77** 0.86***

0.92*** 0.85*** 0.9 8 * * * 0.92*** 0.92*** 0.94*** 0.98*** 0.88*** O X * * * 0.96***

cf. Table 1 b, regression coefficient; sZd stability parameter; R2 coefficient of determination *** P < 0.001; **P 5 0.01; *P 5 0.05

beginning of August and the yields were low. The temperature during crop growth in 1993 coincided with the mean for 1961- 1990, but approximately 60-80 mm more rain fell prior to heading in 1993 than during 1961 -90. These conditions promoted very high grain yields, and ripening was delayed until late September.

There were significant differences between geno- types for all the morpho-physiological traits, ex- cept spikelet fertility (Table 1). In addition, the G x E interaction was significant during the pre- anthesis phase, and for grain-filling phase, grain yield, maximum number of spikelets spike-', and spikelet fertility. This enabled study of the interac- tion of these traits through stability analyses. The results of Finlay-Wilkinson analyses indicated, however, that only two genotypes responded with significant coefficients of determination for maxi- mum number of spikelet primordia spike-', and four genotypes for spikelet fertility. This did not permit clear conclusions regarding the stability of these traits to be made. However, significant coeffi- cients of determination for Finlay-Wilkinson analyses for all genotypes were established for the pre-anthesis phase, grain-filling phase and for grain yield (Table 2).

There was one fertile tiller per plant in six-rowed and, on average, two in two-rowed barleys, and the mean kernel weight was 41 mg for six-rowed and 45 mg for two-rowed barleys, but the differences were not statistically significant (data not shown). Six-rowed barleys matured earlier than two-rowed

barleys (Table 1). The pre-anthesis phase of the six-rowed variety Loviisa was shorter than that of two-rowed barleys, and the grain-filling phase of Kilta was shorter than that of two-rowed barleys (Table 1). The pre-anthesis phase to maturity class ratios (P:M ratio) were 0.60 for Kilta and 0.56 for Loviisa. Kilta and Loviisa both yielded below the average, expression of grain yield being somewhat unstable in Kilta (b, = 1.03) but stable in Loviisa (b, = 0.84). These results were further supported by the results from Eberhart-Russell analysis, which indicated the deviation from the regression line to be quite large for Kilta but small for Loviisa (Table 2). The abortion of spikelets in Kilta was below the average, and the short grain-filling phase of Kilfa was associated with stability (b, = 0.79). The pre- anthesis phase of Loviisa was the shortest and most stable (b, = 0.87) when compared with two-rowed barleys (Tables 1 and 2).

Within the 89 day maturity class (Group I) of two-rowed barleys, breeding lines Jo 1676 and Jo 1754 had similar length phases of pre-anthesis (50 days) and grain-filling (39 days) and the P:M ratios were 0.56. Prolonging the pre-anthesis phase by one day and decreasing grain-filling by one day, within same maturity class, changed the P:M ratio of Jo 1687 to 0.57, increasing maximum spikelet number by 5-8 spikelets spike-', and decreasing spikelet survival by 10-13%. Jo 1687 and Jo 1676 had equal numbers of grains spike- ' but one grain more than Jo 1754. The significantly higher, and relatively stable, grain yield of Jo 1687, in compari-

220 J. PELTONEN AND E. NISSILA Hereditas 124 (1996)

Table 3. Relative yield (genotype yield as a percentage of mean site yield) of two six-rowed and three two-rowed barley cultivars and seven breeding lines at four sites in 1992 and 1993 grouped according to mean yield of the sites

Genotype Group" Site

Mietoinen-92 Viikki-92 RehtIJarvi-92 Kokemaki-92 Kokemaki-93 RehtijBrvi-93 Mietoinen-93 Viikki-93 ~

Six-rowed Kilta Lo v i i s a Two -rowed Jo 1676 I Jo 1754 I Jo 1687 I Kustaa II Jo 1752 11 Jo 1680 11 Kymppi 111 Inari Ill Jo 1682 III Jo 1760 III

Mean grain yield (kg ha-')

-~

105 87

92 98

105 101 106 82

104 114 104 I00

2240

~

99 92

91 99

107 I10 115 90

104 111 93 89

3400

~

86 87

93 92

100 90

101 I09 114 I15 1 I7 97

3655

~~

94 98

96 97 98

109 90

103 101 120 98 94

4590

81 110

114 99

102 94 95 95

112 110 89

100

4730

90 85

93 100 103 93

107 93

109 108 101 112

i360

71 90

109 102 101 102 99

100 105 97

116 108

5420

100 109

96 77

110 90

107 94

107 94

106 108

5590

" cf. Table I

son with Jo 1676and Jo 1754, was associated with instability of the pre-anthesis phase (Table 2). Jo 1676 and Jo 1754 had below average yield in low yielding sites at Mietoinen-92, Viikki-92, and Rehtijarvi-92, and Jo 1687 was more specifically adapted to low-yielding environments within early maturing class than Jo 1676 and Jo 1754 (Table 3).

The most stable duration of pre-anthesis phase and superior stability of grain yield were found in the later maturing breeding lines Jo 1682 and Jo 1760 (Table 1, Group III), for which the P:M ratio was 0.59. Jo 1760 had a maximum of 36 spikelet primordia spike - I , of which only 58% were fertile. This was significantly less compared with Jo 1682, which had a maximum of 32 spikelets per apex, of

which 63% survived. However, higher spikelet fer- tility did not have a significant impact on grain yield of Jo 1682. When comparing the lines with a long pre-anthesis phase (Jo 1682 and Jo 1760) with those having a short pre-anthesis phase (Jo 1676 and Jo 1754, all with a similar duration of grain- filling phase, the later maturing lines produced 3-10 more spikelets spike-', and 1-2 more grains per spike than early maturing ones. In late matur- ing lines differences in spikelet number led to 290 kg ha-' more grain than in early maturing lines.

Kymppi and Inari (Group 111) had the highest (4690 kg ha-'), and Jo 1676 and Jo 1754 (Group I) the lowest grain yield (4330 and 4215 kg ha-',

Table 4. Variation in two-rowed growth phases and grain yield of four barley breeding lines in comparison with Kustau (plot means of eight trials)

Cultivar Crosses Pre-anthesis Grain-filling Maturity Grain phase, days phase, days class, days yield

(kg ha-')

Kustaa Mari*S/Monte Cristo//Impala/Kristina 50 Jo 1754 Kustaa/Eero 80 50

Jo 1752 Kustaa/Jo 1359 50 Jo 1680 Kustaa/Jo 1359 51

Jo 1682 Kustaa/Eero 80 55

Mean SEA Significanceb G x E interaction

51 *1

NS ***

40 39 39 40 40

40

NS NS

.O i 0 .77

90 4290 89 4215 94 4505 90 4455 91 4220

91 4337 * 1.2 i 173.7

NS NS *** *

Standard error Significance of difference between cultivars: ***P I 0.001; *P 2 0.05; NS non-significant.

Hereditus 124 (1996) PRE- AND POST-ANTHESIS PHASES IN TWO-ROWED BARLEYS 221

respectively). The P:M ratios for Kymppi and Inari were 0.58. The instability of grain yield among these varieties seemed to slightly increase (Jo 1676 b, = 0.85; Jo 1754 b, = 0.88; Kymppi b, = 0.91; Inari b, = 0.99) when the duration of the pre-anthesis phase increased from 50 days (Jo 1676 and Jo 1754) to 53-54 days (Kymppi and Inari), but the length of the grain-filling phase remained un- changed (39 days). The maximum number of spikelets per apex in Kymppi and Inari was clearly below the average, and spikelet survival above average. The one day shorter pre-anthesis phase of Kymppi, compared with that of Inari, resulted in a decreased maximum number of spikelet primordia per spike, but a significantly higher number of spikelets survived. Closer examination of the data shows that Kymppi and Inari had above average yields across most sites, supporting the use of the variance of relative yield as stability measure. Kymppi was specifically adapted to both low- and high-yielding sites. In contrast, Inari had below average yield in high-yielding sites at Mietoinen-93 and Viikki-93 (Table 3).

For further work, Kustaa and breeding lines derived from crosses between Kustaa and Eero 80 and Kustaa and Jo 1359, were selected on the basis of the differences in the duration of their pre-an- thesis phases (Table 4). A major difference was that a five day increase in pre-anthesis phase for Kustaa x Eero 80 crosses increased grain yield of Jo 1682 significantly by 215-290 kg ha-', when compared with Jo 1754 and Kustaa. In contrast, for Kustaa x Jo 1359, a one day shorter pre-anthe- sis phase significantly increased grain yield of Jo 1752 compared with Jo 1680.

Discussion Six-rowed barleys had more grains per spike, they matured earlier (Table 1), and kernel weight and tillering capacity seemed to be lower than for two-rowed barleys. This indicates that earliness of six-rowed barley was associated with low and sta- ble grain yield, with low kernel weight and low tillering capacity.

Spikelet set of two-rowed barley declined with decrease in duration of the pre-anthesis phase within each of the Groups (1-111) (Table 1); spikelet fertility and number of grains spike-' in- creased. The stability of grain yield improved only within Group I when the duration of the pre- anthesis phase shortened, but decreased within

Groups I1 and I11 (Table 2). The superior stability of grain yield in late maturing Jo 1760 and Jo I682 was associated with stability of the grain-filling phase and a long-lasting pre-anthesis phase. In regions where the growing is short, as in Finland ( PELTONEN-SAINIO 1991) and the mid-western and western USA (GUPTA et al. 1987), later matu- rity cannot be used, however, as a selection crite- rion because of the risk of considerable crop losses from delayed harvesting. Improved productivity would be possible in such marginal areas through development of varieties with increased numbers of fertile spikelets and grains spike-'. This hypothesis supports results from previous studies indicating that breeding spring wheat ( PELTONEN-SAINIO and PELTONEN 1994) and oats (PELTONEN-SAINIO 1990), respectively, during the past 50 and 70 years in Finland has increased grain numbers in modern cultivars by five to ten grains per spike, while kernel weight has been the most stable trait of spring wheat and oats during intensive breeding ( PELTONEN-SAINIO 1990; PELTONEN-SAINIO and PELTONEN 1994).

It is evident from the results of this study that it is difficult to improve number of spikelets spike - ' in two-rowed barley by selecting genotypes with higher numbers of spikelet primordia spike - ' (Table I). The higher the number of spikelet pri- mordia spike-', the lower the spikelet fertility. It can be hypothesized that aborted florets are always a waste of photoassimilates which also decrease grain yield formation. In this study, about 30-40% of the spikelets were lost. The processes which lead to the death of spikelets are not well understood. It was proposed that it is due to competition for limited resources between apex and stem (BROOK- ING and KIRBY 1981), or alternatively, spikelet death may be due to hormonal changes at a partic- ular stage of plant development (COTTERELL et al. 1985). The results of this study showed that selec- tion for a shorter pre-anthesis phase within differ- ent cross progenies could be an important strategy for improving yielding ability of two-rowed barley, resulting in improved spikelet fertility and grain yield (Table 4).

However, due to absence of statistically signifi- cant coefficients of determination for number of spikelets spike - ' and spikelet fertility, following Finlay-Wilkinson analyses, no conclusion concern- ing these traits could be reached. In the regression, ecologically different environments are juxtaposed with similar phenotypic means, but the different responses of genotypes to such different ecological

222 I. PELTONEN AND E. NISSILA Hereditas 124 (1996)

conditions with the same mean cannot be detected, and-especially if only a few environments are included in the data-the effect of very low or very high potential environments, far from the overall mean, can alone exert the major influence. For these reasons, knowledge concerning the envi- ronmental factors promoting G x E interactions is essential for application of Finlay-Wilkinson and Eberhart-Russell methods.

The highest grain yields were obtained when the P:M ratio was 0.58 (Kymppi, l m r i ) . No further increase in grain yield was achieved if P:M ratio remained below or exceeded 0.58 (Table I). One may speculate that extreme shortening or prolong- ing the pre-anthesis phase, in reIation to grain filling, results either i n faster development of the spike primordia, which possibly leads to a de- creased number of fertile spikelets in early matur- ing breeding lines, or that the grain-filling phase of later ripening lines passes too fast in relation to the pre-anthesis phase, thus restricting the transloca- tion of assimilates from leaves and stems to devel- oping grains.

The two-rowed barleys Kymppi and Inari were closest to the desired barley cultivar with respect to stability of yield formation. Although the maxi- mum number of spikelet primordia of Kymppi and lnari was clearly below the average, spikelet sur- vival was above avcrage, following relatively stable grain yield formation. Kymppi was specifically adapted to both low-and-high-yielding sites (Table 3). Thc results from this study support the idea that two-rowed barley genotypes, in which the relative stable length of the growth phases are synchronised as a relatively long period for appear- ance of maximum spikelet numbcr, of which the greater part ( >65%) develop into grains during a moderate duration of grain-filling, are likely to be advantageous in the growing conditions prevailing in Finland.

In conclusion, based on the discussion above, the use of stability indices (e.g., b, and sZd and rclative yield as a percentage of mean site yield), and the duration of pre-anthesis and grain-filling phases with average P:M ratios and grain-yields - the characteristics of a crop which are routinely measured in breeding - are recommended for im- proving the productivity of two-rowed barley. Breeding for a short pre-anthesis phase in two-

rowed barley does not necessarily reduce grain yield in the growing conditions prevailing in Fin- land. Selection for a shorter pre-anthesis phase with a P:M ratio of 0.58, results in a large number of grains spike-' and improves yielding ability of two-rowed barley within a maturity class. These traits would provide further information about the sensitivity of different genotypes in response to various environments.

Acknowtedgements. - The authors acknowledge the excellent technical assistance by Mr. Veikko Kenippi and Mr. Ari Rajala.

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