Euphytica 28 (1979) 219-225

C O N T R I B U T I O N O F G R O W T H R A T E A N D H A R V E S T I N D E X TO G R A I N Y I E L D O F O A T S

(AVENA SATIVA L.) F O L L O W I N G S E L F I N G A N D O U T C R O S S I N G OF M 1 P L A N T S 1

B. S. J A L A N I 2, K. J. F R E Y , and T. B. B A I L E Y , Jr.

Department of Agronomy, Iowa State University, Ames, Iowa 50011, USA

Received 25 September 1978

INDEX WORDS

Avena sativa, oats, growth rate, harvest index, grain yield, mutation breeding, mutagenesis, induced variation.

SUMMARY

Three populations of oats, each with 790 lines, were derived from CI 7555: (a) one (M population) consisted of Mz-derived lines obtained from EMS treatment of naked seeds, (b) one (0 population) consisted of F 2- derived lines from crosses of M 1 with check plants, and (c) one (C population) consisted of check lines.

About 9 8 ~ of the grain yield (GYD) variation in each population was due to variation in growth rate (GR) and harvest index (HI).

There was greater variation for both GR and HI in M and 0 than in the C population, showing that mutat ions were induced for both traits. Generally, mutat ions for these two traits were for reduced ex- pression: high HI and GR are desired in a practical oat breeding program, so most induced mutations were deleterious.

Mutat ion breeding, either with direct selection or outcrossing to release the induced mutations, does not appear to be a desirable method for improving GR or HI of oats.

INTRODUCTION

Grain yield in cereal crops is the product of biological yield times harvest index. For cereals, biological yield is the total dry matter produced per unit area by a crop during one life cycle, and it is the product of growth rate (expressed on a per-day basis) times the growth duration. Harvest index is the ratio of grain to biological yield. All of these traits are important factors to the grain yielding capacity of oat (Arena sativa L.) cultivars. ROSlELLE & FREY (1975) showed that the genotypic correlations between grain and biological yields and grain yield and harvest index were 0.88 and 0.42, respectively. When they used a restricted selection index for grain yield, which held heading date and plant height means of selected lines equivalent to the population means, the gain in yield was only 57~ as great as when unrestricted selection was used. However, when harvest index was added as a secondary trait in the restricted selection

Journal Paper No. J-9308 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011. Project No. 1752. This work was supported in part by the International Atomic Energy Agency, Vienna, Austria, in the form of a fellowship for the senior author. 2 National University of Malaysia, Kuala Lumpur, Malaysia (formerly Visiting assistant Professor in Agronomy, Iowa State University).

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B. S. JALANI, K. J. FREY AND T. B. BAILEY, JR.

index, the gain was increased to 70~o of that from unrestricted selection. TAKEDA FREY (1976, 1977) found that more than 90~o of the variation in grain yield among oat lines from A. sativa × A. sterilis crosses was due to growth rate and harvest index, and the contribution of growth rate was 1.27 times greater than that of harvest index.

In areas where oats have short growth duration, such as the Corn Belt of the United States, biological yield tends to be medium to low, and even with a high harvest index, average grain yields seldom exceed 3.5 t/ha. Lengthening the growing period for oats to increase yields is not desirable because of the presence of midsummer stresses due to diseases, high temperature, and water deficiency. FREV (1976) reported grain-yield improvement of up to 30~o for oat lines from crosses ofA. sativa x A. sterilis, and these high-yielding lines had growth durations and harvest indexes identical to the A. sativa

parents. TAKEDA & FREV (1976) showed that harvest index seemed to be optimal at ca. 4 5 ~ o for Iowa, USA.

Our objectives were (a) to investigate the contributions of growth rate and harvest index to grain yield in mutagen-derived oat populations, (b) to evaluate the release of induced genetic variation for growth rate and harvest index from crossing mutagen- derived plants with untreated materials, and (c) to interpret predicted responses from selection in relation to an oat breeding program.

M A T E R I A L S A N D M E T H O D S

Our materials consisted of three populations of oat lines derived from the pure-line genotype C.I. 7555 (FREv et al., 1971): (a) Check population (C): The check population consisted of 790 lines, each derived as the bulk progeny from a plant of C.I. 7555. (b) Mutagen-derived population (M): Dehulled primary seeds of C.1. 7555 were soaked in 0.12 M ethyl methanesulfonate (EMS) solution for four hours, rinsed in tap water, and planted immediately in pots in the greenhouse. M 1 plants produced from these EMS-treated seeds were allowed to self. M 2 seeds from the top five spikelets of a plant were space sown in a progeny row in the field, and the bulked seed from each of two M 2 plants in each of 395 M 1 progeny rows was harvested to establish the 790 M z- derived lines in this population. (c) Outcross-derived population (0): Primary seeds of C.I. 7555 were treated with EMS and sown as described for the M population. The primary florets in the top five spikelets of each of 440 M 1 plants in this population were emasculated prior to anthesis, and the emasculated florets on each M1 plant were pollinated with pollen from one untreated plant of C.I. 7555. One F~ seed from each M 1 plant crossed to C.I. 7555 was sown in the greenhouse to produce F 2 seeds. F 2 seeds from each F 1 plant were space down in a progeny row in the field, and the bulked seed from each of t w o F 2

plants in 395 F~ progeny rows was harvested to establish the 790 F2-derived lines in this population.

For the M and O populations, we used seeds and florets, respectively, from only the top five spikelets on the M 1 plants. By limiting our experimental materials to this panicle section, it was assumed that EMS-treated tissues would be more-or-less in the same stage of development for all plants when the treatment was applied.

The 2370 oat lines (i.e., 790 from each of the C, M, and O populations) were

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evaluated in a field-grown experiment with a randomized complete block design and four replicates, two at Ames (central), and one each at Kanawha (north central) and Sutherland (nortwhest), Iowa. The soil at each test site was highly fertile, and 40 kg/ha of N was broadcast before planting. A plot was a hill sown with 30 seeds, and the hills were spaced 30.5 cm apart in perpendicular directions. Plots were hand weeded, and plants were sprayed with a fungicide at weekly intervals from anthesis to maturity to preclude damage from foliar disease.

Heading date (HD) was recorded on a per-plot basis (on the two replicates at Ames) when 50~o of the panicles in a plot were completely emerged. Plant height (PH) was measured on a per-plot basis as cm from the ground surface to panicle tips on all plots at Kanawha and Sutherland. When mature at Kanawha and Sutherland, plants in a plot were harvested at ground level, dried, and weighed to give biological yield (BYD), after which the ptants were threshed and a grain yield (GYD) was taken. Straw yield (SYD) was computed as BYD ~ GYD, and harvest index (HI) was computed as the ratio (GYD/BYD) x 100. Growth rate (GR) was calculated as SYD divided by number of days for vegetative growth (days from sowing to HD (TAKEDA & FREY, 1976). HD and GYD were measured on different plots so the replicates of HD data from Ames were assigned at random to be used with SYD data at Kanawha and Sutherland to permit the computation of GR's. The correlation for heading dates of oats between environments (on a plot basis) is high (FREY & HORNER, 1957), SO we were justified in combining HD and SYD from different sites.

We analyzed the contribution of GR and HI to GYD via multiple regression techniques. Mean squares and cross products were calculated on a population basis for use in computing variances, covariances, correlations, heritabilities, and predicted responses.

RESULTS

Means for GR, HI, and GYD were significantly lower for the M and O than for the C population (Table 1), and standard deviations were larger in the M and O than in the C population for all three traits. These results show that the mutagen treatment induced mutations for GR, HI, and GYD, but generally, the mutations caused reductions in trait expression.

Genotypic correlations between Gr and GYD were 0.97, 0.90, and 0.92, and between HI and GYD, they were 0.99, 0.77, and 0.77 for populations C, M, and O, respectively (Table 2), indicating that both Gr and HI were important factors in GYD variation. Genotypic correlations for GYD with SYD ranged from 0.90 to 0.99. H1 was highly correlated with SYD in the C population (i.e., r = 0.99), whereas in the M and O populations, comparable correlations were 0.42 to 0.48, respectively. Genotypic cor- relations of l iD with GR, HI, and GYD were generally negative, but low in magnitude, whereas those for PH with these traits generally were positive but low to medium in magnitude.

Genotypic correlations between GR and H1 ranged from 0.44 to 0.72 for the three populations (Table 2), whereas the comparable environmental correlations ranged from -0.03 to -0.18 (Table 3): The resulting phenotypic correlations between GR and HI ranged from 0.12 to 0.22. Environmental correlations of Gr and H1 with GYD were

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B. S. JALANI, K. J. FREY AND T. B. BAILEY, JR.

Table 1. Means, standard deviations, and ranges for grain yield (in g/plot), growth rate (g/day/plot) and harvest index (in percent) in the C, M, and O populations of oats.

Population Mean + SE Standard Range deviation

Growth Rate ( GR) C 0.54 +_ 0.003 0.063 0.13-0.77 M 0.48 + 0.003 0.093 0.23-0.73 O 0.50 _+ 0.003 0.091 0.10-0.80

Harvest Index (HI) C 43.3 + 0.09 2.57 34.0-51.6 M 41.4 +__ 0.13 3.50 23.8-49.5 O 42.3 + 0.11 3.17 28.6-49.1

Grain Yield (GYD) C 34.2 + 0.21 5.99 5.5-54.5 M 28.9 _+ 0.25 7.14 9 .0-49.5 O 30.8 +_ 0.25 6.50 4 .0-52.0

Table 2. Genotypic correlations of growth rate (GR), harvest index (HI), and grain yield (GYD) with heading date (HD), plant height (PH), and straw yield (SYD) in the C, M, and O populations of oat lines.

Trait Population Trait

GR

HI

GYD

HI GYD HD PH SYD

C 0.72 0.97 4).29 0.68 0.99 M 0.44 0.90 0.37 0.74 0.99 O 0.48 0.92 4).23 0.67 0.99

C 0.99 0.29 0.04 0.99 M 0.77 0.31 0.24 0.42 O 0.77 4).20 0.27 0.47

C 4).02 0.36 0.99 M -0.34 0.63 0.90 O 0.21 0.59 0.91

Table 3. Phenotypic and environmental correlations among growth rate (GR), grain yield (GYD) and harvest index (HI) for the C, M, and O populations of oats.

Population Phenotypic Environmental correlations correlation

GR/HI GR/GYD HR/GYD GR/HI GR/GYD HI/GYD

C 0.12 0.82** 0.65** -0.18 0.75 0.49 M 0.21" 0.85** 0.68** -0.04 0.78 0.57 O 0.22* 0.85** 0.67** -0.03 0.77 0.58

* and ** significant at 5~o and 1 ~oo levels of probability, respectively.

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positive, but they were much lower than their genotypic counterparts. The coefficients of determination for GR and HI with GYD were either 0.97 or 0.98 in

all three populations; thus, practically all variation in GYD was due to variation in these two traits (Table 4). Standard partial regression coefficients for GR with GYD ranged from 0.74 to 0.76 for the three populations, whereas comparable values for HI with GYD ranged from 0.51 to 0.56. The ratios of b'GR to b'nl were 1.36, 1.42, and 1.45 for C, M, and O, respectively, which shows that GR was more important than HI in determining GYD.

We computed the relative predicted GYD's for the three populations with varying GR's and HI's (Table 5). Reference values used were H1 = 4 0 ~ and GR -= 0.5 g/day/plot, which are approximately equivalent to the means for our oat populations. For a given combination of GR and HI values, GYD were higher in the C than in the M and O populations. In all populations, the gains in GYD were approximately equal from increasing either GR by 0.1 g/day/plot or HI by 5 .0~ .

Next, we estimated the genetic advances to be obtained by selecting for each trait ( 1 0 ~ selection intensity) and recombining the selected lines to produce a new popu- lation (Table 6). Generally, expected advances were from two to three times greater in the M and O than in the C population. However, these results are somewhat mislead- ing, because generally, means of the M and O populations were lower than those of the

Table 4. Standard partial regression coefficients and coefficients of determination for grain yield (GYD) on grown rate (GR) and harvest index (HI) for the C, M, and O populations of oat lines.

Population R 2 ? b'GRy ° b'Hl b'GR/b'HI

C 0.98 0.76 0.56 1.36 M 0.98 0.74 0.52 1.42 O 0.97 0.74 0.51 1.45 Mean 0.98 0.75 0.53 1.41

t R 2 = coefficient of determination. °b'c, R and b',~ = standard partial regression coefficients for GYD yield on GR and HI. respectively.

Table 5. Predicted grain yields (GYD) for oat lines with varying combinations of growth rate (GR) and harvest index (HI).

Population HI (%) GR (g/day/plot)

0.5 0.6 0.7 0.8

P* 40 27.7 (100) 33.8 (122) 39.9 (144) 46.1 (166) 45 34.2 (123) 40.3 (145) 46.4 (167) 52.6 (190)

M 1 40 29.9 (100) 35.6 (119) 41.3 (138) 46.9 (159) 45 35.4 (118) 41.1 (137) 46.8 (157) 52.4 (175)

0 2 40 28.0 (100) 33.7 (120) 39.3 (140) 45.0 (161) 45 33.7 (120) 39.2 (140) 44.8 (160) 50.5 (180)

*GYD = 1.3 HI + ZGYD = 1.1HI + 2GYD = l. l HI +

61.2 GR 54.9 56,8 GR 42.5 56.6 GR = 44.3

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Table 6. Expected responses for grain yield (GYD), growth rate (GR), harvest index (HI), heading date (HD), plant height (PH), and straw yield (SYD) from recombining the highest 10~o of oat lines to form the next generation, and the expected relative responses (i.e., relative to when selection is direct) when selection is for GR and HI.

Expected response Population Trait and trait selected

GYD GR HI HD PH SYD (g) (g/day) (~o) (day) (cm) (g)

Advance from C 4.9 0.04 1. l 0.5 1.7 3.0 direct selection M 11.1 0.13 3.2 2.2 5.2 10.5

O 10.7 0.14 3.6 1.7 6.0 11.1

Relative correlated C 77 100 115 31 74 101 response with GR M 86 100 64 -36 81 101 selection O 90 100 36 25 71 100

Relative correlated C 71 81 100 27 -35 93 response with HI M 71 42 100 -29 25 41 selection O 66 42 100 -20 25 41

C population; therefore, the expected means of the next generation from selecting in the M or O population were little or no greater than the comparable value from selecting in the C population. For example, the expected gains from selecting for GYD were 4.9, 11.1, and 10.7 g per plot, respectively, in the C,M, and O populations, but the expected means for the new populations after recombination would be 39.1,40.0, and 41.5 g, respectively, and maximum difference would be only 6~o.

The relative correlated responses for the other five traits when selection was applied for GR or HI were obtained by dividing the correlated response by the response from direct selection for each trait. Selection for GR resulted in GYD advances that were 77 to 90~o as large as when GYD was selected directly, and selection for HI increased YD from 66 to 71 ~o as much as direct selection (Table 6). GR was as effective for increasing SYD as selecting for this trait itself. Generally, selection for G R or HI caused positive correlated responses in all traits except HD for which five of six responses were negative; thus, selection for high GR or HI resulted in early HD. This is an interesting result with respect to oat breeding for the Corn Belt, USA, because selecting for high GR and/or HI would result in the saving of early lines with improved GYD. This is the exact goal of our breeding program and is counter to the retention of late lines that occurs when selection is practiced for GYD only.

DISCUSSION

We found that GR and HI were responsible for about 9 8 ~ of the GYD variation in the C, M, and O populations. Similarly, TAKEDA & FREY (1977) found 9 0 ~ or more of GYD variation among segregates from interspecific crosses (A. sativa x A. sterilis) was due to Gr and HI. These results were expected because GR and duration of vegetative growth determine the magnitude of the vegetative plant parts, and HI

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determines what proportion of BYD is partitioned in GYD. Commercial oat cultivars have HI's between 40 and 46 ~ , and TAKEDA & FREY (1976)estimated the optimum HI to be 45~. Any deviation from this optimum range seems to lead to reduced GYD. The means of our populations fell within the optimal range for HI, and 92, 74, and 83~ of the lines in populations C, M, and O, respectively, had HI's between 40 and 500/o .

Because HI's of commercial oat cultivars are optimum, we suggest that the magni- tude of vegetative growth must be the major factor that limits grain-yielding capacity of Corn Belt oat cultivars. The magnitude of vegetative growth can be increased by having a longer vegetative growth duration and/or a greater GR. Elongation of growth duration for the midwestern USA would be undesirable because high temperature, low water availability, and disease infection are common stressing factors on oat plants after midsummer. Thus, the obvious way to obtain greater magnitude of vegetative growth is by increasing GR. The variation induced by EMS treatment was sizable for both GR and HI. For example, genetic variances for GR in the M and O populations were 2.5 larger than in the C population (JALAN1 • FREY, 1979), but most induced mutations were for reduced GR. Indeed, our C, M, and O populations had only 3; 2, and 2~ , respectively, of lines with GR equal to or greater than 0.7 g/day/plot, the rate that TAKEDA & FREV (1976) considered necessary for optimum GYD. One line in population O had a GR greater than the best line in population C.

Most GYD variation among oat lines in mutagen-derived populations can be attributed to variation in GR and/or HI. High proportions of the lines from direct mutagen treatment or from outcrossing M 1 plant to the untreated check were in the optimal range (i.e., 40-50~) for H1 ; thus, the generally low GYD's for lines from M and O populations must have been due to most mutations for GR being deleterious. BRocK (1965) conducted induced mutation studies with subterranean clover( Trifolium subterraneum), and he did not find a single mutation for improved GR. Therefore, the evidence indicates that induced mutations for GR are overwhelmingly deleterious.

REFERENCES

BROCK, R .D. . 1965. Induced mutat ions affecting quantitative characters. Radiat Bot. 5 (Suppl.): 451 4 6 4 .

FREY, K. J. & T. HORNER, 1957. Heritability in standard units. Agron. J. 49 : 59 62. FREV, K. J., 1976. Plant breeding in the seventies: Useful genes from wild plant species. Egypt. J.

Genet. Cytol. 5: 462482 . FREY, K, J., J. A. BROWNING & R. L. GRINDLAND, 1971. Registration of Multiline M68. Multiline

M 69, and M ultiline M 70 oat cultivars. Crop Sci. l I : 940. JALANI, B. S. ~; K. J, FREY, 1979. Variation in growth rate and harvest index of oats (Arena sativa L.)

following selfing and outcrossing o fM ~ plants. In preparation. ROSlH,LE, A. A. & K. J. FREV, 1975. Application of restricted selection indices for grain yield im-

provement in oats. Crop Sci. 15 : 544-547. TAKEDA, K. & K. J. FREY, 1976. Contributions of vegetative growth rate and harvest index to grain

yield in progenies from A vena sativa × A. sterilis crosses. Crop Sci. 16 : 817 821. TAKEDA, K. & K. J. FREY, 1977. Growth rate inheritance and associations with other traits in back-

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