Subsoils with above normal levels of boron (B) occur commonly in dry areas. This may hinder root growth into the subsoil to take up stored moisture and adversely affect yield, especially in years of drought, besides directly causing B toxicity to crops not tolerant to B toxicity.

(1) Between collection sites

This study investigated the pattern of variation in B-toxicity tolerance among pureline barley selections between collection sites. This information may help to locate sites or areas where high B soils may occur, and where B-toxicity tolerant varieties may be needed.

Ten random pure-line selections from 24 sites (7 from Jordan, 17 from Syria) were screened for B-toxicity tolerance. The sites were chosen to give a representative samples of the two countries. Screening was conducted in a plastic house in big trays containing soil mixed evenly with boric acid at the rate of 50 mg B/kg soil (giving a hot water extract of around 26 ppm B). Hill plots of 5 seeds from each entry were sown, and there were two replicates. Foliar B-toxicity symptom scores were taken 4 weeks after sowing.

There were highly significant (P<0.001) differences in mean B-toxicity symptom scores between the collection sites. On average, Jordan selections had a significantly (P<0.001) lower symptom score than Syrian selections, suggesting that high B soils may be more of a problem in Jordan than in Syria. Purelines selected from a site in central Jordan had the lowest mean symptom score. Except for a wet collection site in north-western Jordan, selections from the other six Jordan sites had the best mean symptom scores.

Considering only Syrian selections, those from the wetter western part of the country had a slightly lower tolerance (P<0.10) than those collected in the drier east. However, when the two regions were further divided into four subregions, no significant differences were detected. As expected, when the sites were grouped based on annual rainfall, those from the low rainfall areas had better scores than (P<0.10) those from the moderate or high rainfall areas (Table 1).

Table 1. Mean B-toxicity scores of pureline selections from 24 collection sites in Jordan and Syria.

		Codes of sites	Symptom scores	Mean
Country	Grouping	included	of sites	score
Jordan		6, 7, 8, 36, 37, 38, 68	2.8, 2.9, 2.6, 2.7, 2.1, 2.5, 3.5	2.7
Syria	Low-rainfall	3, 5, 10, 22, 34, 40	3.5, 4.0, 2.9, 3.2, 3.0, 4.0	3.4
	Moderate-rainfall	9, 12, 19, 39, 42, 45	4.1, 4.0, 3.4, 3.8, 3.7, 3.9	3.8
	High-rainfall	30, 32, 58, 66, 67	4.0, 3.8, 3.8, 4.0, 4.0	3.9

Significant differences in B-toxicity symptom scores also existed between the selections within sites. Six selections had symptom scores comparable to the moderately tolerant check, Galleon. These six selections all came from dry sites. None of the 240 selections was as sensitive as the very sensitive check, Pirate.

(2) Within sites

In order to learn more about the within site variability in B-toxicity tolerance, 141 pureline selections from two collection sites were screened. One of the sites gave black-seeded lines (n = 78) and the other gave white-seeded lines (n = 63). The study was conducted under similar conditions as stated above.

There were highly significant differences (P<0.001) in B-toxicity symptom scores between the selections. Although the two populations had the same mean scores, the black-seeded populations had a slightly wider variation (Fig. 1). Besides, the best four selections having symptom scores comparable to the moderately tolerant check, Galleon, were black-seeded. None of the 141 selections was as sensitive as the sensitive check, Pirate.