Introduction

Blum et al. (1983b) suggested that chemical desiccation could be used to screen for post-anthesis stress tolerance, as destruction of the plant's photosynthetic system by desiccation would reveal those genotypes that were able to sustain translocation-based kernel growth. The chemical desiccants most commonly used for cereals are magnesium chlorate (Blum et al. 1983a,b, Cattivelli et al. 1990), potassium iodide (Nicolas and Turner 1993, Regan et al. 1993), and sodium chlorate (Hossain et al. 1990, Sabry and Taylor 1992, Haley and Quick 1993). The objective of this work was to evaluate the use of the chemical desiccant, Sodium Chlorate (NaClO₃), for screening barley for post-anthesis stress tolerance.

Materials and Methods

This test was conducted at the Field Crop Development Centre, Lacombe, AB (Chernozemic soil, Navarre loam) from 1990 to 1993. Precipitation during the growing season (May to September) was 362 mm in 1990, 348 mm in 1991, 209 mm in 1992 and 239 mm in 1993.

Three two-rowed barley cultivars were studied: Abee (feed), Hector (malt), and Klages (malt). Hill plots, 73 cm on-centre were used, with approximately 30 seeds sown per plot. Three times and four rates of sodium chlorate were evaluated. The times of spraying were 7, 14 and 21 days after anthesis. Concentration of spray was 0.0 (control), 1.5, 3.0 and 4.5% a.i. NaClO₃. One-half L of solution (rate on a w/v basis) was applied using a hand-held sprayer with 227 L nozzle. Application time was 10 seconds using 1.76 kg cm^-2 (25 lb in^-2) pressure. The experimental design was a split-split plot with rate within time within cultivar.

Measurements on a plot basis were days to anthesis, harvest index, test weight, kernel weight and grain protein (NIR analysis). Measurements on 10 selected heads per plot were kernel number and spikelet number per spike, and spike weight. Kernel and spikelet numbers reflect floret fertility.

Results and Discussion

These cultivars differed significantly in their days to anthesis so desiccation treatments were applied on a cultivar by cultivar basis. Harvest index was the only trait where cultivar interaction with rate of desiccation was significant. Hector maintained its HI at all desiccant rates while Abee and Klages had reduced HIs (Table 1). With increased desiccant rate test weights were reduced (Table 1).

Table 1. Effects of rate of desiccant on three barley cultivars grown in Lacombe, AB.

Desiccation	Harvest index			Test
rate	Abee	Klages	Hector	weight
%	----------------------------%----------------------------			kg m3
0	37	34	37	607
1.5	32	29	36	561
3.0	31	29	34	550
4.5	29	27	33	527
LSD (0.05)	---------------------------1.6----------------------------			11

The interaction effect of days after anthesis with rate of desiccant on kernel weights, kernel number per spike, spike weight and protein content was significant. As the rate of desiccant increased, kernel and spike weights were reduced with the effect most pronounced with the early treatment (Table 2). The desiccation caused a slight but significant reduction in kernel numbers per spike when applied at 7 and 14 days, but by 21 days there was no effect (Table 2). As the desiccant rate increased the protein levels of the grain increased, with the effect being muted with lateness of the treatment (Table 2). Post-anthesis desiccation was without effect on spikelet number per spike.

Spraying sodium chlorate from 7 to 21 days after anthesis at rates from 1.5 to 4.5% was effective in simulating post-anthesis stress conditions. Generally, as rates increased and applications were closer to anthesis, the effects of desiccation were more pronounced. A rate of 1.5 or 3% sodium chlorate at 7 to 14 d after anthesis, would be an effective post-anthesis stress screening technique for barley.

In these cultivars of barley, the only cultivar difference detected was for harvest index, with Hector being more resistant to desiccation than the other cultivars. All of these two-rowed cultivars have been grown in Alberta, so there may not have been a great deal of difference in adaptation to post-anthesis stress. Desiccation did cause loss of seed set and kernel weights, so this technique should be effective in screening out types that do not have post-anthesis stress tolerance.
 

Table 2. Effects of rate and timing of desiccation treatments of barley grown at Lacombe,

AB from 1990 to 1993.

Days
after	Rate of	Kernel	Kernels	Spike
anthesis	NaClO3	weight	per spike	weight	Protein
	%	mg	no.	g	%
7	0	43	25	1.44	13.5
	1.5	35	24	1.19	13.8
	3.0	33	23	1.06	13.9
	4.5	30	23	0.99	14.7
14	0	43	25	1.45	13.7
	1.5	35	23	1.13	13.8
	3.0	33	23	1.08	14.2
	4.5	32	23	1.05	14.4
21	0	42	24	1.38	13.9
	1.5	36	24	1.22	13.9
	3.0	34	25	1.23	13.8
	4.5	32	24	1.13	13.9
LSD (0.05)		1.6	0.9	0.7	0.4

References

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