The influence of genotype and environment on yield, protein and related characters in hexaploid triticale (X. triticosecale Wittmack)

Abstract

To investigate the relationship between grain yield (GY) and grain protein content (GPC) in hexaploid triticale, eight lines were grown in 12 environments, viz Mid-August and October sowing, 0,40 and 300 kg N ha⁻¹ at sowing and anthesis, 0 kg N ha⁻¹ plots at 45 and 180 plants m⁻², other plots at 45 plants m⁻². The influence of several agronomic practices on GY, GPC, plant height (PHT) and 1000 seed weight (THSWT) was studied. Statistical analysis was used to evaluate stability and adaptation in 16 characters. Genetic parameter estimates for the variability of and correlations among characters were calculated. Plant N relationships with yield and dry matter distribution were investigated.

On average, there were no significant differences in GY, biological yield (BY), harvest index (HI) or THSWT between the two sowing dates. However, there were three significant (p≤0.05) interactions involving sowing date for HI and a significant (p≤0.05) date x line interaction for THSWT. Plant PHT was reduced by 3cm and GPC by 0.7 percentage points with late sowing. However there were four significant (p≤0.05) interactions involving sowing date that affected PHT and five significant interactions affecting GPC implying that these reductions were not general. GY, BY and HI were 33, 27 and 6% higher at 180 than at 45 plants m⁻², whereas THSWT and GPC were 5% and 6% lower. Although mean PHT was 1.1m for both sowing dates, a highly significant (p≤0.01) date x density x line interaction indicated that most lines had reduced PHT when early sown, but increased PHT when late sown, with increased plant density. Only BY, 5% higher with early than late applied N, was significantly (p≤0.05) affected by the simple effect for time of N application. The response of GPC to all factors was complex (a total of six two-factor, two three-factor and one four-factor interaction were significant, p≤0.05). Mean GY and GPC at 0, 40 and 300 kg N ha⁻¹ were 0.39, 0.42, 0.44 kg m⁻² , and 14.1, 14.8, 16.2 % respectively, indicating simultaneous increases in GY and GPC could be readily achieved with N application. None of the factors examined had appreciable negative effects on THSWT or PHT.

There were significant (p≤0.05) genotype x environment interactions for all characters except BY and THSWT. Due to a strong association between variation over environments and 2 other stability parameters, viz joint regression slope and ecovalence, variation over environments was the most suitable measure of phenotypic stability for all important characters. Spike lets per spike (SPLSPK), THSWT and HI were less sensitive to environmental variation than GY or the other yield components. The association between stability and mean performance was weak for both GY and GPC (r=0.41ns and r=-0.19ns respectively) indicating that it should be possible to breed for genotypes with both high mean performance and stability in these two characters.

Broad sense heritability (Hb), genetic coefficient of variation (GCV%) and genetic advance at 5% selection intensity (GA%) were all high for both GY and GPC (0.78, 23.9%, 43.1% and 0.91, 16.9%, 33.2% respectively) indicating simple breeding procedures would be suitable for their improvement. High estimates were also obtained for number of grains per spike (NORSPK), grain weight per spike (GWSPK), spike fertility (SPKFT), HI and grain protein yield (GPY).

GY was most strongly related to NGRSPK, GWSPK, SPKFT, and HI at the genetic level (rg=0.98**,0.98**, 0.96** and 0.98** respectively). GPC was negatively associated with GY (rg=-0.88**) and most other characters. Of these, HI had the strongest association at phenotypic, genotypic and random levels (rp=-0.86**, rg= 0.91**, rₑ=-0.46**). GPC had significant (p≤0.05) positive associations with PHT and straw yield (rg=0.71* and 0.81* respectively).

The mean inter-line regression (b=-2.1**) indicated a 1.5 percentage point reduction in GPC for every 1t ha⁻¹ increase in GY. This relationship was consistent with a relatively invariant GPY being diluted by more carbohydrate in higher yielding lines but did not accord with the extra energy cost of protein versus carbohydrate production. Adjustment of GPC values to a common HI using analysis of covariance was not statistically valid and did not give a meaningful assessment of 'true' genetic variation for GPC. Instead, high 'true' GPC was assigned to lines with a significant (p≤0.05) deviation from the theoretical relationship between GPC and HI based upon dilution of the mean GPY by more or less carbohydrate. A high 'true' GPC was associated with high nitrogen harvest index and plant nitrogen yield (PNY). In turn, high PNY resulted from high BY and/or high plant nitrogen concentration. The prospects of observing transgressive segregation for 'true' GPC in lines derived from crosses involving parents with a high 'true' OPC are encouraging. This, in tum, may lead to simultaneous genetic improvement in GY and GPC.

KEYWORDS: Triticale, Yield, Yield components, Harvest index, Protein, Sowing date, Plant density, Nitrogen, Stability, Heritability, Correlation.