Grain yield analysis of a triticale (×Triticosecale Wittmack) collection grown in a Mediterranean environment

Field Crops Research 63 (1999) 199±210

Grain yield analysis of a triticale (Triticosecale Wittmack) collection grown in a Mediterranean environment F. Giunta*, R. Motzo, M. Deidda Dipartimento di Scienze Agronomiche e Genetica vegetale agraria, FacoltaÁ di Agraria, Via E.De Nicola, 07100 Sassari, Italy Received 4 February 1999; received in revised form 28 June 1999; accepted 30 June 1999

Abstract The breeding of triticale (Triticosecale Wittmack) is of great importance in those Mediterranean environments where low winter temperature and soil acidity interact with drought, increasing the adaptability of this species in comparison with other temperate cereals. In order to identify the way in which the various yield components contribute to the realisation of high yields in a Mediterranean environment, and the effect of a different phenology on these patterns, a two-year trial was carried out in Sardinia (Italy) with 271 pure lines grown under rainfed conditions. The relationships between characters were assessed by phenotypic correlation analysis after grouping the lines into phenological classes. In both years total biomass explained more of the variation in yield than harvest index and was little affected by earliness. Both total biomass and HI were strongly correlated with kernels mÿ2. More kernels mÿ2 are therefore essential to obtain high grain yields in triticale, regardless of earliness, highlighting the importance of the pre-anthesis period, even in conditions of increasing drought stress during spring. Grain yield showed a closer correlation with HI in the less favourable year, but became independent of HI above values of 20± 25,000 kernels mÿ2 and HI values of 0.35. The winter types were taller, with less spikes mÿ2, and a longer and more fertile spike than the spring types. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Yield components; Mediterranean environment; Triticale

1. Introduction Triticale (Triticosecale Wittmack) is an interesting species for fodder production in those Mediterranean environments where low winter temperature and soil acidity can exacerbate the effects of drought, limiting the productivity of wheat and barley (Arangino et al., 1987; Spanu et al., 1987). *

Corresponding author. Tel.: +39-79-229353; fax: +39-79229222 E-mail address: [email protected] (F. Giunta)

Like other temperate cereals, triticale can be used for the dual purpose of livestock forage and grain (Poysa, 1985). In this case the best cultivars are those with the maximum forage + grain yields. As a strong relationship exists between grain yield obtained after forage removal and grain yield realised without any forage removal, breeding for dual purpose could be done selecting, among the cultivars with high grain yields without clipping, those with the greatest forage production (Royo and TriboÂ, 1997). Dissecting the grain yield of a set of cultivars into its major functional components and proceeding to more

0378-4290/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 4 2 9 0 ( 9 9 ) 0 0 0 3 6 - 2

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F. Giunta et al. / Field Crops Research 63 (1999) 199±210

detailed level of organisation as the need arises, provides an excellent framework within which to set physiological work on yield improvement (Passioura, 1981). For grain yield, two useful conceptual frameworks are: grain yield = biomass  harvest index and grain yield = number of kernels mÿ2  kernel weight. These approaches are basically the same, as any increase in canopy development and duration will also stimulate tiller production, tiller fertility and spikelet and ¯oret numbers (Hay and Walker, 1989). Yield can be analysed according to these frameworks only if strong negative interactions between the factors are rare or can be avoided. Passioura (1977) pointed out the independence of biomass and harvest index and the value of this framework, particularly when grain yield in waterlimited environments is analysed. On the other hand, McNeal et al. (1978) have demonstrated that spike fertility (number of kernels per spike) and kernel weight are not negatively correlated genetically. Hence a simultaneous selection for these two characters is not hampered by compensation and allows for an increasing grain yield. Indeed breeding programs are very seldom aimed at selecting for single traits, rather their objective is the improvement of the aggregate of individual characters (Simmonds, 1979). This type of analysis can lead to a better understanding of the patterns to high yields in order to better choose parents for the creation of segregating populations from which superior lines can be extracted, and/or to begin introgression programs for the introduction of useful genes into already existing lines or cultivars (Richards, 1996). Whereas much data are available for wheat in this regard, this type of analysis has seldom been done for triticale. Environment modulates the expression of yield components, altering yield and their relative contribution to it (Wallace and Zobel, 1994). Daylength and

temperature are the most important such environmental factors, as they control development and determine whether the plant life cycle is matched to the resources and constraints of the environment (Shorter et al., 1991). The aim of this study was to identify, in a large set of triticale lines, the way in which the various yield components contribute to the realisation of high yields in a Mediterranean environment, and the effect of a different phenology on these patterns. 2. Material and methods The data were collected from a two-year trial in which a total of 271 pure lines of triticale were grown (239 of them over both years) under rainfed conditions in Sardinia, Italy (418N latitude; 48E longitude; 80 m elevation). The lines were winter, spring and facultative types with different growth habits (Table 1), mostly from CIMMYT nurseries (24th ITSN), and partly from the Italian National Register of cultivars. The environment has rainy winters and increasing drought during spring (Table 2). In addition to rainfall amount and distribution, low temperature may reduce growth during winter and/or may reduce spike fertility during early spring. The soil was a sandy clay loam with a depth of about 0.8 m in 1993 and 0.6 m in 1994, due to underlying layers of limestone (typic Xerochrepts). The mean water contents at ®eld capacity (ÿ0.02 MPa) and at permanent wilting point (ÿ1.5 MPa) were 22.4% and 11.9% by weight, respectively. The trials were sown at a rate of 350 viable seeds mÿ2 with a 6-row planter on 23 November, in both 1992 and in 1993. The unreplicated plots were 1.2 m long in 1992 and 2.0 m long in 1993, with rows 0.18 m apart. Before sowing a broadcast application was

Table 1 Origin and growth habit of the lines included in the experiment Lines

Origin

Growth habit

No. of lines

International spring triticale Screening nursery Facultative triticales Winter triticales Italian cultivars

CIMMYTÐMexico CIMMYTÐMexico CIMMYTÐMexico Italy

Erect Erect Prostrate Erect

200 27 29 15

Table 2 Rainfall, temperature and photothermal quotient over 10-day periods for the growing seasons 1992/93 and 1993/94 and long term averages Rainfall (mm) 1992/93

December January February March April May June

Total

1993/94

32-year average

22 34 0 86 0 7 0 0 0 29 1 14 38 0 2 27 15 29 12 54 0 4 1 9

55 14 3 24 16 25 34 23 0 8 14 0 0 0 0 10 28 30 1 17 0 0 19 0

28 35 35 25 25 23 14 20 18 13 24 12 15 15 21 14 16 15 14 16 8 10 3 3

386

321

420

Maximum temperature (8C)

Photothermal quotient (MJ mÿ2 dayÿ1 8Cÿ1)

1992/93

1993/94

32-year average

1992/93

1993/94

32-year average

1992/93

1993/94

9.1 9.1 8.8 7.0 4.9 4.5 3.3 6.2 5.0 5.0 2.1 1.5 1.5 4.5 3.8 6.6 7.0 9.1 9.5 11.3 12.0 13.6 14.0 15.3

12.4 6.6 8.4 8.5 7.2 4.9 7.2 3.8 4.0 3.4 1.6 4.2 3.8 5.0 5.4 7.8 7.0 7.8 10.5 12.2 14.0 13.0 13.5 14.6

10.7 9.5 8.0 7.2 6.9 6.5 5.9 5.8 6.2 6.3 5.7 5.8 6.0 6.6 7.7 8.3 8.3 9.0 10.3 11.4 12.6 13.6 14.6 15.9

18.7 16.0 15.8 14.0 13.8 11.4 9.6 13.0 12.6 13.4 12.1 9.4 10.1 15.6 13.4 15.3 16.0 18.8 20.4 20.1 23.7 25.6 23.3 27.2

19.6 15.1 14.9 15.2 13.7 11.2 12.7 10.3 11.5 10.7 9.6 14.2 14.3 13.6 18.6 13.4 13.9 18.0 22.1 22.3 26.7 25.4 24.3 26.9

19.4 17.4 15.4 14.4 14.1 13.6 13.1 13.0 13.3 13.6 13.1 13.9 14.1 15.1 16.3 17.1 17.3 18.5 20.4 22.0 23.4 24.7 26.0 27.9

0.5 0.4 0.5 0.4 0.7 0.7 1.4 0.7 1.1 1.4 3.5 5.0 5.7 2.7 3.2 2.3 2.2 1.4 1.8 1.4 1.6 1.3 1.4 1.4

0.5 0.9 0.6 0.7 0.6 1.0 0.5 1.1 1.2 1.7 3.7 2.3 2.8 2.4 2.4 2.1 1.7 1.8 1.9 1.0 1.4 1.6 1.5 1.5

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

November

Minimum temperature (8C)

201

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F. Giunta et al. / Field Crops Research 63 (1999) 199±210

made of 10 g mÿ2 of N and 4.4 g mÿ2 of P as urea and ammonium phosphate. Weeds were chemically controlled before the beginning of stem elongation of the earliest lines. Crops were hand harvested in the ®rst half of June. Dates of anthesis (appearance of anthers on more than 50% of the spikes) and ripening (loss of green colour from more than 75% of the peduncles) were determined by regular inspections of the plots. Total plant height and spike length were measured at three locations per plot. At harvest, total biomass and total grain weight were determined from the whole plot. A sub-sample of 30 spikes was used to determine number of kernels per spike, kernel and chaff weight. The number of kernels mÿ2 was calculated dividing grain yield by kernel weight, and spikes mÿ2 as the ratio between this number and the number of kernels per spike. Minimum and maximum air temperatures, daily incident solar radiation and rainfall were recorded at the site. The photothermal quotient (MJ mÿ2 dayÿ1 8Cÿ1), an index of growth per unit of developmental time, was calculated according to Fischer (1985). Thermal time was computed as X …daily average temperatureÿTbase †: When the daily average temperature was below the Tbase (base temperature), it was set equal to the Tbase. A Tbase of 08C was assumed for the period from sowing to anthesis (Ritchie, 1991) and 98C for the period anthesis-ripening (Angus et al., 1981; Motzo et al., 1996). Given the key role of phenology in adaptation, the creation of phenological groups was considered more meaningful than any genetic classi®cation, allowing discrimination, not only between winter and spring pure lines, but also within these genetic groups. Four classes of pure lines of different earliness (thermal time to anthesis, base temperature 08C) were then created on the basis of the highest value recorded by each pure line in the two years. A class width of 508C d was arbitrarily chosen for the spring types so that differences between groups could not be entirely attributed to noise or interaction with the environment. Three classes of spring types were obtained, whose average anthesis date is reported in the results and discussion section, Table 4. Winter pure lines were all

included in the 4th class, with anthesis date from 14908C d onwards. Facultative types and Italian cultivars were included in one of these four classes. The differences in earliness between classes were statistically signi®cant by the F-test, utilising the withingroup mean square as the error term. Mean and standard deviation of the measured characters were calculated for each phenological class and for each year, including only the lines in common. An analysis of variance of the measured characters was carried out based on these phenological classes to calculate genotypic, environmental and interaction effects. The error term was estimated considering the lines within each class as pseudo replications. The analysis of grain yield was carried out following the framework yield = biomass  harvest index and yield = kernels mÿ2  kernel weight and the pattern to yield was assessed by phenotypic correlation analysis by both years and phenological classes. 3. Results and discussion In 1993 the amount of rainfall during the growing season (sowing to end of May) (316 mm) was close to the 32-year average (322 mm), whereas the distribution was distinct due to particularly high rainfall during April and May (137 mm). In this environment this coincides with the post-anthesis period. In the 1994 growing season the lower rainfall (233 mm) was associated with a prolonged dry spell during 40 days to the end of March, when most pure lines were in the stem-elongation phase. Post-anthesis rainfall was similar to the 32-year average, with 86 mm in April and May. The 32-year averages reveal mean temperatures around 108C in winter, increasing at the end of March and reaching 228C by the end of June. In 1994 maximum temperatures during May were about 28C higher than in 1993. Thermal time (20688C d, base 08C) was longer in growing season 1994 than in 1993 (19568C d), but was below the long-term average of 23668C d in both years. These climatic differences between years lead to a signi®cant effect of year (Table 3) and contributed to the signi®cant genotype  year interaction found for almost all measured characters, suggesting that separate analysis should be performed for the two years.

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

203

Table 3 Mean square and significance of the principal characters discussed, with classes of earliness (G), years (Y) and G  Y interaction as sources of variation

Anthesis (days from 1 January) (8C d) Ripening (days from 1 January) (8C d) Anthesis-ripening (days) (8C d) Plant height (cm) Spike length (cm) Kernels mÿ2 (no) Spikes mÿ2 (no) Kernel weight (mg) Kernels per spike (no) Chaff weight (g) Total biomass (g mÿ2) Harvest index Yield (g mÿ2)

G

Y

GY

13327** 2399214**

15262** 383312**

468** 53279**

2703** 2538068**

5870** 457871**

713** 201146**

4045** 1999a 10920** 56** 1.064E + 08** 85431** 960** 724** 1.33** 972355** 0.13153** 1057476**

2207** 3311a 1196** 246** 6.722E + 09** 814224** 3008** 12040** 18.79** 52415846** 0.26713** 18433476**

127** 69826** 3114** 4a 9.643E + 07** 20487* 15a 44a 0.13* 599065** 0.00111a 100270*

*

Significant at the F-test at the 0.05 and 0.01 level of probability, respectively. Significant at the F-test at the 0.05 and 0.01 level of probability, respectively. a Not significant. **

With the exception of the duration of the period from anthesis to ripening (8C d), genotypic effects were signi®cant for all the characters, meaning that the calculated phenotypic correlations rely partly on genotypic variation. In the second year the crop ¯owered on 13 of April, i.e. 12 days earlier than in 1993 (Table 4) consistent with the calculated thermal time (578C d). It can be attributed therefore to the hastening effect on development of the 40 days of drought in this year, which could have raised canopy temperature. Angus and Moncur (1977) reported that the duration of the period from ¯oral initiation to anthesis was shortened for wheat subjected to various levels of drought stress. When phenological classes are considered, differences between years in time to anthesis were minimal in the 4th class (4 days), which included all the winter lines. The cold requirements of these lines reduced the effect of the higher temperatures of 1994 on the rate of development of the crop, given that thermal time to anthesis for this class was even higher in this year. As differences in anthesis date derive mostly from differences in duration of the vegetative stage

(Jamieson et al., 1998), the later anthesis of 1993 could be due to a longer vegetative stage, i.e. to a greater number of leaf primordia produced until collar differentiation. In addition to this longer vegetative stage, the greater availability of water due to the deeper soil, the higher rainfall during February and March, and a more favourable photothermal quotient (Table 2) resulted in the taller plants and larger sink capacity (spike fertility and number of spikes mÿ2) of 1993 (Table 4). In both years the 4th class was the tallest, probably because its longer vegetative period leads to more leaves and more elongated internodes (Kirby et al., 1985). Spike fertility increased progressively from the 1st to the 4th class. In the latter a longer spike with fewer kernels per g of chaff was recorded, indicating that its greater spike fertility was due to more spikelets per spike rather than to more kernels per spikelet. Royo et al. (1995) also found winter triticale to be taller, with longer growth cycles, and longer spikes with more spikelets per spike than spring types. Rawson (1970), working on wheat, found that in cultivars with a pronounced response to vernalisation, the length of

204

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

Table 4 Mean values and standard error of the mean for the principal characters discussed for the two years and each phenological class Year span

Classes and number of lines per class

1992/1993

Class 1 (38)

Class 2 (51)

Class 3 (111)

Class 4 (39)

Average (239)

106  0.2 1263  2.3

110  0.04 1311  0.5

114  0.1 1372  1.0

131  0.9 1613  14.4

115  0.5 1381  7.5

150  0.3 1537  3.4

150  0.3 1577  5.6

151  0.1 1628  3.5

156  0.6 1831  4.0

151  0.2 1636  6.5

44  0.3 274  2.6 113  1.7 11.7  0.4 20925  851 415  142 46  0.8 61  3.2 51  1.7 14  0.4 16  0.5 0.34  0.02 2431  78.3 0.36  0.01 945  35.2

40  0.3 267  2.8 116  1.6 11.7  0.3 20955  627 399  10.1 46  0.5 65  2.7 53  1.5 15  0.3 16  0.4 0.32  0.02 2349  59.5 0.37  0.003 954  27.9

37  0.1 256  1.3 124  1.0 12.7  0.2 23474433 426  8.4 45  0.4 59  1.7 56  1.0 15  0.2 18  0.3 0.37  0.01 2647  41.0 0.36  0.004 1047  17.5

25  0.7 218  6.5 136  5.0 13.8  0.3 19925  1000 330  13.1 38  0.6 50  2.2 60  1.6 13  0.5 15  0.6 0.38  0.02 2326  83.8 0.29  0.01 760  40.1

37  2.4 255  1.8 122  1.1 12  0.8 21952  333 403  5.8 44  0.3 59  1.2 56  0.7 14  0.2 17  0.2 0.36  0.37 2506  30.4 0.35  0.003 964  14.6

95  0.4 1227  4.3

97  0.2 1247  2.6

101  0.4 1286  4.0

127  1.3 1630  19.9

103  0.7 1324  9.6

139  0.5 1449  7.2

141  0.6 1482  6.2

143  0.5 1534  4.0

158  0.5 1931  5.0

144  0.5 1574  11.4

44  0.6 222  4.7 116  1.3 10.0  0.2 14318  388 336  7.6 40  0.6 83  3.9 43  1.0 11  0.3 13  0.3 0.17  0.01 1889  44.3 0.32  0.01 610  20.2

44  0.6 235  6.0 118  1.1 10.8  0.2 14163  397 321  8.5 40  0.7 81 3.2 44  0.9 11  0.2 13  0.3 0.18  0.01 1857  41.9 0.31  0.01 595  20.1

42  0.5 248  4.8 119  0.8 11.1  0.1 13966  306 307  6.6 40  0.5 78  2.0 46  0.7 11  0.2 130.2 0.18  0.01 1853  34.2 0.32  0.003 601  15.6

31  1.0 301  5.0 124  3.5 11.9  0.2 12319  861

41  6.6 250  3.2 119  0.8 11  0.7 13743  233 316  4.5 39  0.3 80  1.6 45  0.5 11  0.1 130.1 0.18  0.003 1844  22.7 0.30  0.004 571  11.2

Anthesis (days from 1 January) (8C d) Ripening (days from 1 January) (8C d) Anthesis-ripening (days) (8C d) Plant height (cm) Spike length (cm) Kernels mÿ2 (no) Spikes mÿ2 (no) Kernel weight (mg) Kernels per g of chaff (no) Kernels per spike (no) Kernels per g of biomass (no) Productivity per day (g mÿ2 dÿ1) Ear : stem ratio Total biomass (g mÿ2) Harvest index Yield (g mÿ2) 1993/1994 Anthesis (days from 1 January) (8C d) Ripening (days from 1 January) (8C d) Anthesis-ripening (days) (8C d) Plant height (cm) Spike length (cm) Kernels mÿ2 (no) Spikes mÿ2 (no) Kernel weight (mg) Kernels per g of chaff (no) Kernels per spike (no) Kernels per g of biomass (no) Productivity per day (g mÿ2 dÿ1) Ear : stem ratio Total biomass (g mÿ2) Harvest index Yield (g mÿ2) a

Not recorded.

a

34  0.9

a a a

11  0.6 a

1756  71.5 0.24  0.01 420  32.4

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

the period to ¯oral initiation was of prime importance in determining the potential number of spikelets per spike. While a greater number of spikes mÿ2 was expected due to the longer vegetative period of this class, in fact it was the smallest among the classes (330). Madry et al. (1995) also identi®ed the number of spikes mÿ2 as the more limiting yield component in winter triticales. A negative association between number of spikes per plant and number of spikelets per spike was found by Rawson (1970) in vernalised and non vernalised wheat plants The earliest anthesis of 1994 determined ripening to be earlier by 7 days than in 1993, notwithstanding the longer period from anthesis to ripening (41 days against 37 in 1993 on average). Differences between years in the length of this period changed with phenological class, being minimum in the 1st (0 days) and maximum in the 4th (6 days). The longer period from anthesis to ripening of 1994 was a response to the less stressful environmental conditions encountered by the crop due to the earlier anthesis. In this year the 4th class ¯owered on 17 April, whereas in the preceding year it ¯owered on 11 May. Kernel weight results from the product of rate and duration of grain ®lling. If the period from anthesis to ripening is considered as roughly representative of the duration of grain ®lling, then the greater kernel weight of 1993 (44 mg against 39 mg in 1994) resulted from a higher rate, favoured by the greater source capacity under the more favourable conditions in the preanthesis period. Indeed Trethowan et al. (1990) found a close correlation between biomass at anthesis, i.e. source capacity, and rate of grain ®lling under drought conditions in triticale. Within each year the decrease in the duration of grain ®lling from the 1st to the 3rd class was compensated by an increase in rate, resulting in almost identical kernel weights among these classes. In the 4th class, compensation was ineffective because, due to lateness, grain ®lling occurred in more stressful conditions, resulting in the smallest kernels (38 mg in 1993 and 34 mg in 1994). The grain yield in 1993 exceeded the 571 g mÿ2 harvested in 1994 by 69%, with 3rd class the greatest in 1993, and 4th the smallest in both years (Table 4). In both years and in each phenological class, grain yield was strongly correlated with total biomass and HI (Table 5) and total biomass explained more of the

205

variation in yield than HI. As HI and total biomass were not negatively correlated, grain yield was analysed according to the framework proposed by Passioura (1977): grain yield = total biomass  HI. 3.1. Total biomass On average, the total biomass in 1994 was 73.6 % of that of 1993 (Table 4). The phenological classes only differed signi®cantly in 1993, with the 3rd class showing the greatest total biomass (2647 g mÿ2). In the 4th class, biomass was similar to that of the ®rst two classes and corresponded with the lowest number of spikes mÿ2, indicating in this class the greater importance of height in determining total biomass. Indeed this class included lines which reached heights of 2 m. When double utilisation of triticale is sought, it is important to know if biomass production depends more on height or on stem density. A large biomass due mainly to tall plants cannot be useful for grazing as it is mainly realised after stem elongation. In both years the variation in total biomass was highly correlated with kernels mÿ2 (Table 5) and less with plant height. In the latter case the proportion of biomass variation explained was very small (R2 = 0.21 in 1993 and 0.16 in 1994) and similar correlation values were found for each phenological class. Only in 1994 was total biomass also correlated with kernel weight. The fewer kernels mÿ2 made the differences in kernel weight more relevant to total biomass production, and avoided the compensation between kernel weight and kernels mÿ2. Total biomass was little affected by earliness (Table 5), as the negative correlation between the duration of the pre- and post-anthesis periods (r = ÿ0.95** in 1993 and r = ÿ0.78** in 1994) determines that gains from a longer pre-anthesis period are lost by a shorter grain-®lling period. The best compromise was achieved by the 3rd class which, in the more favourable 1993 conditions, realised the greatest biomass ¯owering in the second half of April. On the other hand, the small total biomass of the 4th class was the result, not only of its shorter grain-®lling period, but also of at its longer pre-anthesis period, associated with taller but fewer tillers, and hence with less kernels mÿ2. More kernels mÿ2 could therefore be the driving force behind the increase in total biomass, both

206

Table 5 Simple phenotypic correlation coefficients between yield and yield components and their significance for the different classes and for the two years. 1992/93 class 1

class 2

class 3

class 4

0.78 0.75** 0.77**

0.93 0.84** 0.88**

0.96 0.82** 0.93**

0.85 0.71** 0.91**

0.87** 0.80** 0.90**

Total biomass

- HI

0.29 ns

0.35**

0.13 ns

0.44**

0.32**

0.18 ns

0.61**

0.63**

0.43**

0.47**

Total biomass

-

anthesis (8Cd)a anthesis -ripening (8Cd) height spikes mÿ2 kernels mÿ2 kernel weight spike fertility

0.60** 0.69** 0.85** 0.18 ns 0.61**

ÿ0.15* 0.08 ns 0.46** 0.60** 0.84** 0.18* 0.30**

-

anthesis (8Cd) anthesis -ripening (8Cd) height spikes mÿ2 kernels mÿ2 kernel weight spike fertility

0.22* ÿ0.03 ns 0.41** 0.05 ns 0.46**

ÿ0.40** 0.58** 0.62**

ÿ0.22 ns 0.48** 0.58**

ÿ0.40** 0.55** 0.36**

0.32* 0.51** 0.82** 0.47** 0.48**

0.52** 0.68** 0.83** 0.62** 0.26**

0.50** nab 0.85** 0.30 ns ±

ÿ0.24** 0.45** 0.40** 0.63** 0.82** 0.49** 0.30** ÿ0.63** 0.04 ns 0.09 0.50** 0.70** 0.51** 0.36**

ÿ0.25 ns 0.70** 0.76** 0.41** 0.30 ns

0.14 ns 0.19 ns 0.67** 0.51** 0.62**

0.05 ns 0.67** 0.78** 0.48** 0.15 ns

0.32** 0.54** 0.81** 0.39** 0.39**

ÿ0.18 ns na 0.69** 0.28 ns ±

0.06 ns 0.87** 0.56**

ÿ0.16* 0.62** 0.45**

0.52** 0.60** 0.64**

0.23 ns 0.74** 0.40**

0.32** 0.74** 0.42**

0.16 ns na na

0.33** 0.72** 0.43**

0.42** 0.55**

0.44**

0.15 ns

0.13 ns

0.85**

0.45** 0.56**

0.63** ÿ0.37** ÿ0.40**

0.60**

0.51**

0.70**

na

ÿ0.26**

na

- kernel weight - spikes mÿ2 - spike fertility

Kernel weight

- rate of grain filling (mg dÿ1) - anthesis-ripening (days)

0.85**

0.49**

0.85**

0.34*

Spikes mÿ2

- productivity per day - anthesis (8Cd) - spike fertility

0.59**

0.66**

0.55**

0.70**

ÿ0.42**

ÿ0.55**

*

**

ÿ0.67** 0.50** ÿ0.22** 0.36** 0.55** 0.38** 0.23**

Kernels mÿ2

ÿ0.26 ns

**

0.08 ns

ÿ0.22 ns

ÿ0.29*

significant respectively at the 0.05 and 0.01 level of probability; ns, not significant. ** significant respectively at the 0.05 and 0.01 level of probability; ns, not significant. a the correlations with anthesis and anthesis-ripening were not calculated for each phenological class given the uniformity in phenology within each class. b na, data not available.

0.65** ÿ0.19** ÿ0.29**

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

0.90 0.69** 0.90**

0.17 ns 0.62** 0.74** 0.45** 0.30 ns

**

overall

0.86 0.83** 0.86**

0.32* ÿ0.12 ns 0.59** 0.08 ns 0.74**

**

class 2

0.92 0.47** 0.92**

0.22 ns 0.21 ns 0.63** ÿ0.29 ns 0.59**

**

class 1

0.94 0.65** 0.92**

0.49** 0.53** 0.79** 0.10 ns 0.19*

**

overall

0.95 0.57** 0.94**

0.75** 0.63** 0.86** 0.18 ns 0.30*

**

class 4

- total biomass - HI - productivity per day

0.61** 0.58** 0.81** 0.14 ns 0.39*

**

class 3

Yield

HI

**

1993/94

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

through their relationship with the number of spikes mÿ2, and through a sink control of leaf photosynthesis (Blum et al., 1988). Stapper and Fischer (1990) reported that when a large biomass at anthesis is due to genotypic variation, it is associated with an increased spike density. In 1993, the year in which the largest variation among classes in spikes mÿ2 was observed, a low negative correlation was found with anthesis date. This result reveals that growth rate during the pre-anthesis period is more important than duration to determine the number of spikes mÿ2. Whan et al. (1991), in a survey on wheat cultivars, showed that more tillers can be responsible for a larger LAI and, ultimately, for early vigour, resulting in a greater yield and biomass in environments where rain events are frequent immediately after sowing. Working on triticale, Sandha et al. (1990) found a close correlation between productivity per day, calculated as kg haÿ1 dÿ1 of grain yield from sowing to maturity, yield and spikes mÿ2. When the same parameter is calculated from our experiment, similar conclusions can be drawn, both within years and within each phenological class (Table 5). 3.2. Harvest index Harvest index (HI) of the phenological classes ranged from 0.24 to 0.37, similar to those reported for triticale by other authors (Aggarwal et al., 1986b; Lopez-CastanÄeda and Richards, 1994). HI was smaller in 1994 than in 1993 and did not change among the ®rst three classes, whereas in both years it was smaller in the 4th (Table 4). The relationship between yield and HI (Fig. 1) reveals that yield becomes independent of HI above HI  0.35, when yield increase becomes mostly dependent on increase in total biomass. This is consistent with the greater dependence of yield on HI in the less favourable 1994 conditions (R2 = 0.62, average HI = 0.30), than in 1993 (R2 = 0.48, average HI = 0.35). Abdalla and Trethowan (1990) found that grain yield of triticale exhibited a strong correlation with HI under severe drought stress. In wheat, HI values below 0.35 were associated by Sadras and Connor (1991) to conditions, such as drought stress, in which pre-anthesis assimilates make a greater contribution to yield.

207

Fig. 1. Relationship between yield and harvest index (HI) (1993, empty symbols; 1994, solid symbols).

In both years and in each class HI was correlated with kernels mÿ2, indicating the importance of sink capacity in determining the ef®ciency in biomass partitioning. This relationship was best ®tted by a second order polynomial, for both single classes over the two years and when all data were considered. In this case a signi®cant (P<0.01) quadratic component was calculated (Fig. 2), showing a limit to the increase in HI above 20,000±25,000 kernels mÿ2. This limit highlights the source limitation due to the greater number of kernels mÿ2 produced in the more favourable pre-anthesis period of 1993. Although the source limitation caused a negative correlation between kernels mÿ2 and kernel weight in this year, yield was positively and linearly correlated with kernels mÿ2

Fig. 2. Relationship between harvest index (HI) and kernels mÿ2. Data from both years (1993, empty symbols; 1994, solid symbols) are fitted by the quadratic function y = ÿ3ÿ10x2 + 2ÿ5x + 0.1373 (R2 = 0.51). Data from 1994 are fitted by the linear function y = 9ÿ6x + 0.1859 (R2 = 0.58).

208

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

(r = 0.88**). Below the limit of 20±25,000 kernels mÿ2, i.e. when only the most stressful year is considered, the relationship between HI and kernels mÿ2 is linear, con®rming the importance, in stress conditions, of the sink capacity developed in the preanthesis period (Aggarwal and Sinha, 1987). In these conditions there is no compensation between kernel weight and kernel number, marked by their positive correlation coef®cients calculated both as a whole, and for the 1st and 3rd classes (Table 5). The positive relationship between HI and kernel weight found in the ®rst three classes derives from this lack of compensation. Similar results were reported by Aggarwal et al. (1986a) working on wheat and triticale, but contrast with those of Fischer et al. (1977), who used a single cultivar and established different sink capacities only by means of environmental conditions prior to anthesis. Notwithstanding the negative correlation between spikes mÿ2 and spike fertility, kernels mÿ2 can be increased acting both on either components (Table 5), explaining that compensation within the limits of population density imposed by the environment and the management practices is incomplete. Passioura (1977) and Fischer (1979) have suggested that a higher HI is essential for obtaining high wateruse ef®ciency in the post-anthesis period in waterlimited conditions. On the other hand, given the close relationship between kernels mÿ2 and biomass, an increase in the sink capacity could be detrimental because a greater total biomass at anthesis can be responsible for a faster depletion of soil water during grain ®lling (Giunta et al., 1995). On the other hand, kernel number could also be increased per unit biomass at anthesis (KNBA). Siddique et al. (1989a) found that modern cultivars convert biomass at anthesis into kernel number more ef®ciently than old cultivars, reaching average values of 16 kernels gÿ1. In our experiment straw yield, obtained by the difference between total biomass and grain yield, could roughly represent biomass at anthesis. The KNBA calculated in this way was of the same order as the values reported by Siddique et al. (1989a), ranging from 7 to 22 kernels gÿ1, with an average of 14 in 1993 and 11 in 1994. As KNBA was not correlated with total biomass, for either years or single classes, an increase in KNBA via genotype could increase kernel number without negative effects of

a greater total biomass. Fischer (1985) showed that KNBA is constant within the same genotype over different agronomic conditions, i.e. management is a less ef®cient way to increase kernels mÿ2. The increase in HI has often been related to the increase in yield of modern cultivars (Siddique et al., 1989a). But while HI is affected by post-anthesis stress, the ratio of the weight of the ear to stem at anthesis (ear : stem ratio) is determined early in the life cycle and may therefore give a better indication of potential yield (Siddique et al., 1989b). Straw yield and chaff weight were therefore also utilised to estimate ear : stem ratio from our data. Ear : stem ratio was not correlated with yield, or with HI in either year or phenological classes. This result contrasts that of Siddique and Whan (1994) although, as in this study, ear : stem was explained more by the variation in spike (r > 0.82** in both years) than in stem weight (r = ÿ0.40** in both years). The absence of a positive relation between ear : stem ratio and kernels mÿ2, i.e. yield, is explained by the negative correlation between spike weight mÿ2 at anthesis and the number of kernels per unit of spike weight (Fig. 3). This suggests that the variation in spike fertility of triticale is more dependent on the number of spikelets per spike than on spikelet fertility. Positive phenotypic and genotypic correlations were found in this species by Kumar and Singh (1993) between spike fertility, number of spikelets per spike and spike length. Moreover, the contribution of additional spikelets to spike weight at anthesis could be more relevant than its contribution

Fig. 3. Relationship between number of kernels per unit of spike weight at anthesis and spike weight at anthesis. Data from both years are fitted by the logarithmic function y = ÿ34.264 ln(x) + 260.23 (R2 = 0.56).

F. Giunta et al. / Field Crops Research 63 (1999) 199±210

to spike fertility, due to the lower grain set of distal spikelets. 4. Conclusions In the Mediterranean environment studied, large kernel numbers mÿ2 are essential to obtain high grain yields in triticale, as already reported for other small grain cereals (Evans, 1993). This highlights the importance of the pre-anthesis period in achieving high yields, even in conditions of increasing drought stress during spring, not only for its effect on the sink formation (kernels mÿ2), but also because it affects the source capacity allowing high rates of grain ®lling in the post-anthesis period. In 1994, the year characterised by a pre-anthesis drought and the longer post-anthesis period, the lowest rate of grain ®lling and the smallest kernel weights were observed. Kernels mÿ2also affect partitioning, as shown by the close correlation between HI and kernels mÿ2. The linear relationship between HI and kernels mÿ2 up to 20±25,000 kernels mÿ2, and the positive relationship between number and weight of kernels within this range, indicates a sink limitation to yield. On the other hand, when kernels mÿ2 exceed 20±25,000 (HI  0.35), total biomass increases mostly due to the increase in grain, with a negligible effect on HI. In these conditions the increase in grain yield depends mostly on an increased assimilation after anthesis and therefore becomes source-limited, as evidenced by the negative correlation between number and weight of kernels. The number of kernels mÿ2 could be increased through both spike number and spike fertility. In the ®rst case a limit is set to the potential increase in biomass at anthesis by drought, whereas it is possible to increase the number of kernels per g of biomass at anthesis, without the risk of a more rapid soil water depletion. As far as the effect of earliness on grain yield is concerned, no differences were found, within the range of earliness explored. Differences were only detected at yield levels between non-winter and winter types (4th phenological class), with the latter showing the smaller yields in both years because of a low number of spikes mÿ2. Within the range of anthesis explored by the spring and facultative lines (1st±3rd

209

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