populations were obtained for each cross: Fi, SSD (unselected control), ... The present study was undertaken to investigate the response of two harley popula-.
Plam Breeding 97, 345—351 (1986) © 1986 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0179-9541
Institute of Agronomy and Field Crops, University of Bologna (Italy)
Divergent Selection for Heading Date in Barley R. TuBERoSA, M. C. SANGUIKFT] and S. CONTI With 3 tables Received January 6, 1986 I Accepted April 27, 1986
Abstract Divergent selection for heading time was performed in two F^ barley populations. Eive populations were obtained for each cross: Fi, SSD (unselected control), 3E and 3L (from three cycles of selection for earliness or lateness), 2E1L and 2L1E (from two cycles of direct and one of reverse selection). These populations, together witb corresponding parents and Fi generarions, were evaluated over two years. The response to selection was 5.6 and 6.5 days in one direction (earlier heading) and 7.7 and 6.7 days in the other direction (later heading) in ihe two crosses, respectively. 3E and 3L populations were highly transgressive as compared to their parents. A sizeable amount of genetic variability was still present after two cycles of selection. Heading was probably controlled by a polygenic system with prevailing additive effects and alleles tor earliness and lateness somewhat equally distributed in the parents. Selection for heading time led to significant changes in plant height, yield and kernel weight. Early progenies were higher yielding than late ones. Key words: Hordeum vulgare— heading date — divergent selection -— correlated response
Divergent selection applied to a base population can be useful in investigating the genetic control of quantitative traits (Hii.t 1972, EAI.CONER 19SI), the correlated response of other charaeters (MATHER and JINKS 1971, CECCARELLI and FALCINT.LLI 1978)., and m developing genotypes for physiological studies (DUDLEY 1977). In many breeding programs, heading time is one of the mam selection criteria especially when earliness or lateness allows plants ro escape from unfavourable environmental conditions. Heading time in cereals is the end result of many hiochemical and physiological processes (YASUDA 1981) and has been reported to be under the control of simple or complex genetie systems (MUREET 1977). Researches conducted on harley {Hordcum vuigare L.) have shown that a simple genetic basis was inadequate to explain the quantitative variation of heading time, and that the relative importance of the components of genetic variability changed greatly according to the population involved (JANA 1975, VEGA and FREY 1980, THOM.\S and TAPSELL 1983). The present study was undertaken to investigate the response of two harley populations after three consecutive cycles of divergent selection for heading time carried out on a single-plant basis. U.S. Copynght CWr.n« enter Code Si.^m.n.^ 01 79-9541/S6/9704-0345$02.50/0
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TUBEROSA, SANGUINETI and GONTi
Materials and Methods The starting materials were two F, populations derived from the crosses 'Onice X Thibaut' and 'Opaie X Astri.x'. 'Onice' and 'Opaie' are short-strawed Italian cultivars, while 'Thibaut' and 'Astrix' arc French cultivars commonly grown in Italy. Among tke 900 widely spaced plants grown tor each F2, the 5-0 earliest and the 50 latest plants were selected. A plant was scored as headed when half the ear of the main shoot had emerged from the flag leaf sheath. The Fi and Fj early and late populations, respectively, were obtained for both crosses hy bulking 18 seeds for each of the 50 plants selected in the Fn and F3. A third cycle of direct selection and the first cycle of reverse selection were performed in the F4 by choosing 50 plants in each direction per population. Thus the following four F^ selected populations were obtained: 3E and 3L (from three cycles of selection for earliness and lateness, respectively), 2E1L and 2LlE (from two cycles ot direct and one of reverse selection). Unselected F, populations were obtained in both crosses by using the single seed descent (SSD) method. Trials were conducted in the Po valley near Bologna in 1983/84 and 1984/85. Each of the selected F.^ populations was represented by 40 progenies derived from 40 plants randomly chosen from the 50 selected in Fj, while F^ SSD populations were represented by 40 progenies derived from F4 plants chosen at random. The 40 progenies of each F5 population were randomly assigned to four groups of ten progenies each. The eight entries of each cross (five Fs populations, the corresponding parents and F;. population) were evaluated according to a randomized block design with four rephcations. Plots consisted often rows of 15 plants spaced 10 cm in the row and 40 em between rows. Every progeny of the F5 populations was assigned to one row. Each group was then assigned to one block together with 10 rows of the parental hnes and of the F^ population. The following traits were recorded on a single row basis considering only competitive plants: 1) heading time (days from May 1); 2) plant height (cm) measured from the crown to the base of the ear; 3) ear length (cm) excluding the awns; 4) grain yield/plant (g); 5) kernel weight (mg); 6) fertile shoots/plant (no.) at har\'est; 7) sterile shoots/plant (no.) at harvest; 8) grains/ear (no.); 9) leaf area (%) covered by powdery mildew, leaf rust or leaf blotch. An analysis of variance was computed for each year, 1) on the means of the ten rows included in each plot and 2) on the logarithms of the variances among rows within plots. Since experimental errors were homogeneous (Bartlett's test}, a combined analysis over the two years was performed. A mixed model was utilized considering years and populations as random and fixed factors, respectively. Phenotypic and genotypic correlations between heading time and other traits were calculated on the data of the F^ unselected progenies. Estimates of the environmental variance and covariance were computed as mean of the non-segregating generations (Po\aEA[TiS 1965).
Results The analysis of variance showed a different response of genotypes to year variations for most of the investigated traits. This can be related to the very different weather conditions which occurred in the two years durmg the heading and grain filling phases: cool-wet in 1984 and hot-dry in 1985. However, the interactions were mainly due to differences in magnitude and not in direction or rank. Heading time Means and variances combmed over two years for heading time are reported in Table 1. Parental lmes of both crosses showed differences of approximately one day. Mean heading date was significantly transgressive for earliness in both the F2 populations. The F^ SSD mean value of the cross 'Onice X Thibaut' was within the range of the parental lines, whereas that of 'Opaie X Astrix' was transgressive (1.4 days earlier than 'Astrix') and equal to the value of the Fi. The differences between the unselected populations (F3 SSD) andF5 progenies selected for earliness (3E) and lateness (3L) were, respectively, 7.7 and 5.6 days in 'Onice X Thibaut', and 6.7 and 7.5 days in 'Opaie X Astrix'. No overlap was detected among the single values of the 3E and 3L progenies. In both crosses the differences
Divergent Selection for Heading Date in Barley Tah. }
347
Means and variances over two years for heading time and plant height in the two crosses
Population
Heading time (d) X') S-
Thibaut Onice F; F, SSD 3E 2E1L 2L1E 3L
16.4 b 17.1 h 14.7 e 16.9 b 9.2 d 12.7 c 18.1 b 22.5 a
0.26 c 0.34 c
Astrix Opaie F, F.SSD 3E 2E1L 2L1E 3L
16.8 b 17.6 h 15.4 c 15.4 c 8.7 d 13.8 c 18.8 b 22.9 a
Plant height (cm) X') S-
7.98 a 2.31 h 4.52 a 1.89b 2.64 b
89.0 a 68.3 d 86.1 a 79.2 b 84.6 a 72.9 c 85.6 a 67.4 d
7.9 c 6.7 c — 128.0 a 25.4 b 126.0 a 145.5 a 29.6 b
0.37 c 0.19 c — 8.33 a 3.82 b 10.21 a 2.81 b 2.30 b
93.1 a 63.1 e 83.5 c 83.4 c 87.0 b 79.0 d 78.7 d 66.5 e
14.6 b 5.9 c — 112.2 a 18.3 b 144.0 a 141.0 a 30.8 b
•
—
') Expressed in days from May 1 Values followed by different letters are significantly different at P 0.05 (test of ScOTT and KNOTT 1974)
between 3E and 2E1L, as well a.s between 3L and 2LlE, were significant and similar in extent. As compared to the F5 SSD, a sizeable reduction of the phenotypic variahility was observed within the 3E and 3L populations, whose variances were greater than those of the parental Unes. The variability amonj; 2E1L progenies was significantly greater than that among 3E progenies, whereas no difference was detected between variances of 2E1E and 3E populations. Plant height Selection for heading date brought about noticeable changes in plant height [Table I), for which trait the parental hnes of both crosses where highly differentiated. Compared to the unselected populations (F=^ SSD), the 3E progenies showed a significant reduction m plant height in both crosses while the 3E progenies showed a significant increase. Reverse selection for days to heading was very effective in changing plant height, as is particularly evident in the 2ElE progenies of 'Oniee x Thibaut' which were as tali as the 3E progenies. A strong, reduction in height variability was detected within early and late populations as compared to the unselected ones. The variance.s among families obtained after one cycle of reverse selection (2E1E and 2E1E) were not significantly different from those among the E5 SSD lines. Phenotypic correlation coefficients between heading time and plant height, calculated on the unsclected control, were negative and highly significant in hoth crosses (Table 3). Their values ( — 0.48 and —0.41} were of intermediate magnitude and similar to those of the genotypic coefficients. Yield and its components Although mean values of these traits were affected by selection, the corresponding variances did not show noticeable changes and therefore are not reported.
348 Tab. 2
TuBEROSA, SANCUINF.TI and CONTI Means over two years for vield and its components in the rwo crosses
Populatjon
Grain yield/plant
Kernel weight
Grains/ear (no.)
fertile (no.)
sterile (no.)
49.1 a 52.2 a 50.4 a 47.2 a 47.8 a 53.3 a 48.1 a
14.2 a 13.6 a 13.2 a 14.3 a 13.7 a 12.4 a 13.2 a
0.8 a O.S a 0.7 a 1.0a 0.6 a 0.5 a 0.9 a
50.3 b 48.3 b 49.2 b 57.4 a 48.6 b 49.4 b 45.4 b
13.8 a 13.4 a 13.6 a 12.8 a 13.2 a 13.2 a 12.4 a
0.7 d 1.3 c 1.2 c 0.8 d 1.0 c !.5b 2.1 a
(g) Thibaut Onice* >. SSD 3E 2E1L 2L1E 3L
37.1 a 28.3 c 30.8 b 33.9 a 31.2 b 31.2 b 26.0 c
53.1 a 40.2 b 46.1 a 51.3 a 48.6 a 47.5 a
Astrix Opaie
34.2 a 26.1 c 3C.9b 34.7 a 29.3 b 27.9 c 21.1 d
50.C a 40.9 b 46.0 a 47.6 a
3E 2E1L 2L1E 3L
42.] b
46.C 3
43.2 b 39.8 b
Shoois/plant
Values followed by differeni letters are significantly different at P 0.05 (test of ScOTT and KNOTT 1974)
In each cross, selectton for heading time caused siiinificant changes of grain yield (Table 2) in both directions. As compared to tke unselected control, the 3L population ol 'Opaie X Astrtx' showed a decrease of 32 % and the 3E population an increase of 12 %. The response to reverse selection confirmed the effects of heading date on plant yield. In both crosses progenies selected for earliness were not significantly different from the corresponding high yielding parents. Among yield components, kernel weight was the most affected. The 3L lines showed a reduction of lC % in 'Onice x Thibaut' and of 16 % in 'Opaie X Astrix' with respect to the F5 SSD. The other yield C(jmponents were affected by selection to a lesser extent and in different ways, depending on the cross involved. In 'Onice x Thibaut' no significant changes were detected, while in 'Opaie X Astrix' grains/ear and sterile shoots/plant were Tab. J Phenotypic (r^) and genotypic (r^) correlation coefficients between heading time and other traits calculated on the P\ SSD progenies of the two crosses Gross
Plant height
Grain yield/plant
Kernel weight
Grains/car
Shoots'plant fertile
sterile
'C)nice X Thibaut'
-0.39""-"
-0.5C
0.29-' 0.35
-0.41
-0.07 -0.11
-0.20 -0.28
0.08 0.00
-0,43'^^'-0.51
-0.31-0.49
-Q.27-"
-0.43
0.43-^ 0.56
0.35 0.46
'Opaie X Astrix' -0.41
'•", '•''•' indicate significance at the 0.05 and 0.01 levels of probability, respectively
Divergent Selection tor Heading Date m Barley
349
significantly affected by selection. In the latter cross the 3E as compared to the 3L population averaged 12.0 more grams/ear and 1.3 less sterile shoots/plant. The 3L progenies showed a higher number of sterile culms than the late pareni. The correlation between heading time and grain yield/plant, or each ot its components, were ali significant in 'Opalc x Astrix', whereas in 'Onicc x Thibaut' significant associations were detected only with grain yield/plant and kernel weight (Table 3). Selection for heading time caused no significant change in car length and in the extent of the main barley diseases, although infection levels were high in both years. These data, therefore, arc not reported.
Discussion The results of this experiment show that three cycles ot individual selection tor heading time were highly effective in modifying the trait's mean value in both directions, although ncghgiblc differences were present between the parental lines of the base populations. The response to reverse selection suggests the presence ol a sizeable amount of genetic variabihty within the F4 populations obtained after two cycles of selection for earhncss or lateness. These findmgs would indicate that in the investigated populations heading date is under the control of a polygenic system with a somewhat symmetrical distribution in the parents of the alleles for earliness and lateness. Moreovei, in considering the pattern of response to direct and reverse selection, it can be assumed that the genes involved were to some extent independent and had pre\'ailing additive effects. Other studies conducted on heading time of different barley genotypes have also sbown a prevalence of additivity (CoNTi and FERRARLSI 1972, Cj:CC.=LRt;n.i et al. 1974, SHAKAAN et al. 1982). As expected, direct selection greatly reduced phenotypic variability among families within 3E and 3L populations. By contrast, it is quite difficult to interpret the high variability among families of the 2E1L populations. Such a result cannot be ascribed to the heterozygosit)' of the F4 plants for genes controlling heading time, since the trait was scored in the Fs generation on a mean progeny basis. This variability is more likely to be related to the interference of environmental factors on the selection of the late Fj plants within 2E populations. An unfavourable environment generally delays plant development and flowering. Divergent selection for heading time produced a significant correlated response in some of the investigated traits. Selfing, the typical reproduction system of strictly autogamous species such as barley, leads to a quick fixation of gene associations present in the E: generation. Therefore, it is not possible to distinguish if the observed correlated responses are a consequence of pleiotropic rather than linkage effects. Nevertheless, from a practical standpoint, it is interesting to evaluate the indirect effects brought about by direct selection for one trait. The analysis of means and varianees of plant height would indicate a conspicuous association of the gene systems controlling plant height and heading date. However, the genotypic correlation coefficients calculated on the unselected progenies did noi support this hypothesis. The correlated response observed in our study could thus be explained in relation to the scoring of heading, which can be biased by the pattern of neck elongation during ear emergence as pointed out by THOMAS and TAPSFLL(19^3). An association between these two traits could otherwise be postulated on an ontogenetic basis, since the expression of both plant height and ear emergence is influenced by common physiological processes, i.e. mitotic rate of the meristems and cell enlargement. Consequently, plants might have been unintentionally selected according to their height and not just according to heading date.
350
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and GRANDO (1981}, performing a divergent .selection for culm length in barley, concluded that this tran and heading time were largely independent. In our study negative phenotypic and genotypic correlations were observed between heading time and plant yield. From a breeding point of view, it is interesting to note that earh- progenies were characterized by high yield levels. This was particularly the case with the population selected for earliness in 'Opale X Astrix', which was as productive as the best parent although significantly shorter and earlier. Therefore, it was possible to select for earliness while otherwise maintaining high yields. An analogous finding was reported by VEGA-ORTEGA (1979), who suggested the possibility of improving grain yield in barley by selecting for earliness. Our results showed that kernel weight was the yield component most influenced by selection for heading time. The low kernel weight of late progenies (3L) could be related to genetic factors limiting the physiological processes occurring during kernel development and/or to a reduction of the actual grain filling period. In .small grain cereals the influence of the gram filling period on yield is not very clear, probably owing to the different environmental conditions during the ripening phase. In barley, METZGER et al. (1984) found no significant correlation between the two traits, while a positive association was detected by GEBi-YEiiou et al. (1982J in durum wheat and by SHERTZ et al. (1971) in spring wheat. Selection for heading time significantly affected other yield components only in 'Opale X Astrix'. In this cress earliness was associated with an increase in seeds/ear and a decrease in sterile shoots/plant but did not affeet fertile shoots/plant. SIMMONS et al. (1982) pointed out that sterile shoots/plant may be important when considering ways to increase barley yields. This trait might be considered an indicator of the efficiency of the plant in allocating available photosynthates to the developing kernels (Ric^Gs et al 1981). Our research indicates the usefulness of selection for early heading date. However, a point will be reached at which the potential advantages of earliness will be outweighed by losses due to low temperatures occurring during anthesis or by morpho-physiological limits to the yield components differentiated before anthesis. CECCAREI.LI
Zusammenfassung Gegensinnige Auslese auf den Schofitermin bei Gerste In zwei E^-Nachkommenschaften wurde bei Gerste auf den Schofizeitpunkt in beide Richtungen ausgelesen. Aus jeder Kreuzung gingen fiinf Populationen hervor: F5 SSD (nicht selektierte KontroUe), 3E und 3L (nach drei Selektionszyklen auf friihen bzw. spaten Schofitermin), 2E1L und 2E1E (naeh zw^-i Zyklcn in die eine Richtung und einer Seiektion in die entgegengesetzte Richtung). Diese Populationen wurden zusammen mit den zugehorigen Eltern und Fi-Nachkommenschaften zwei Jahrc lang bewertet. Der Selektionsgewinn betrug bei den beiden Kreuzungen 5,6 und 6,5 Tage in der einen Richtung (friiher Schofitermin) und 1,7 und 6,7 Tage in der anderen Richtung (spater SchofStermin). Im Vergleich zu ihren Eltern wiesen die 3E- und 3L-Populationen in beachtlichem MafJe Transgrcssionen auf. Nach zwei Selektionszyklen gab es noch einen betrachtUchcn Anteil an genetischer Variabilitat. Der Schofitermin wird wahrschcinlich von einem polygenischen System gesteuert, wobei additive Effekte und Allele fur friihes und spates Schossen vorherrschen, die ziemlich gleichmaliig auf die Eltern verteilt sind. Die Auslese auf den Schofitermin hat signifikante Anderungen der Pflanzenhohe, des Ertrages und des Korngewichts zur Folge. Eriihschossende Nachkommenschaftcn waren ertragreichcr als spatschossendc. Research partially supported by "Ministero Agricoltura e Foreste" as part of the "Protgetto Cereali".
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Authors' address: R, TUBEROSA, M- C. SANGUINETI, and S. GONTl, Istkuto di Agronomia generale e coltivazioni erbacee, Universita degli Studi di Bologna, Via Eilippo Re 6, 40126 Bologna (Italy),
