High-resolution spectral information enables phenotyping of leaf epicuticular wax in wheat

Table 3 Coefficients of determination (R²) and root mean square error (RMSE in mg·dm⁻²) of the indices developed for phenotyping EW in leaves

Index	Model parameters
Index	a	B	R²	RMSE	95% CI	p-value
Broad indices / RGB and NIR spectral bands
EWI-1 _Blue/Red	0.213	0.04	0.44	1.19	1.037–2.17	< 0.0001
EWI-2 _Blue/NIR	0.07	0.13	0.39	1.18	0.98–1.98	< 0.0001
EWI-3 _{(NIR-Red)/Blue}	− 0.93	− 0.01	0.31	1.19	1.04–1.97	< 0.0001
EWI-4 _(Red²_{-Blue)/(Red-Blue}²₎	− 0.09	− 0.03	0.32	1.19	1.09–2.55	< 0.0001
Narrow indices / two narrow spectral bands
EWI-5 ₆₇₆	0.019	0.005	0.45	0.97	0.75–1.21	< 0.0001
EWI-6 _658/712	0.12	0.03	0.52	1.02	0.70–1.36	< 0.0001
EWI-7 _625/706	0.22	0.05	0.50	0.96	0.67–1.28	< 0.0001
EWI-8 _694/625	− 0.006	− 0.002	0.42	1.08	0.96–1.55	< 0.0001
EWI-9 _{(670–718) / (670+718)}	− 0.85	0.03	0.51	1.04	0.61–1.54	< 0.0001
EWI-10 _{(691–661) / (691+661)}²	4.92	− 1.03	0.48	0.99	0.74–1.27	< 0.0001
EWI-11 _{(1/661)—(1/694)}	29.13	− 5.73	0.48	1.01	0.71–1.35	< 0.0001
EWI-12 _(622/718)-1	0.62	0.12	0.51	0.99	0.74–1.28	< 0.0001
Narrow indices / three narrow spectral bands
EWI-13 _{625 (1/736 – 1/832)}	0.008	0.004	0.65	1.01	0.622–1.426	< 0.0001
EWI-14 _{(625–736) / 832}	0.02	0.007	0.62	0.98	0.65–1.35	< 0.0001

R² was calculated in the training set by a leaving one out cross validation analysis (LOOCV) and the RMSE was estimated in the validation set. B is the slope of the line and a is the intercept of the dependent variable

ISSN: 1746-4811