Resistance to boron toxicity amongst several barley and wheat cultivars: A preliminary examination of the resistance mechanism

The mechanism of resistance toB toxicity in barley and wheat was studied in a solution culture experiment using several cultivars displaying a large range of sensitivity to excessB supply. Plants were cultured for 35 d atB concentrations ranging from normal to excessive (15 to 5000 M, respectively) then examined for dry matter production and theB distribution between roots and shoots.In both species, increasedB supply was accompanied by increased tissueB concentrations, development ofB toxicity symptoms and depressed growth. At each level ofB supply, however, resistant cultivars accumulated considerably lessB than did sensitive cultivars, in both roots and shoots. Even at the lowestB supply, at which noB toxicity symptoms developed and growth was not affected, resistant cultivars maintained relatively low tissueB concentrations. No cultivar displayed an ability to tolerate high tissueB concentrations.These results indicate that sensitivity toB toxicity in barley and wheat is governed by the ability of cultivars to excludeB. If theB concentrations of tissues is used to indicate resistance toB toxicity, then cultivars have the same ranking whether cultured at a normal or excessB supply.     

Effects of root pruning of wheat at different nitrogen levels

In two experiments, wheat plants growing in solutions of different nitrogen concentration were subjected to root pruning. In higher concentrations of nitrogen the growth rate was higher, and the proportional allocation of growth to shoot higher, but pruning did not affect the allocation of growth at either level of nitrogen. This result gives no support to Thornley's source-sink model of the control of shoot: root ratio.     

Use of a root assessment tray for the detection of take-all on lateral roots of wheat seedlings

A root assessment tray was designed for the meticulous assessment of take-all on wheat seedling roots from soil bioassays. Subsequently, the detection of lateral root infections (in addition to the more obvious infections on main axes of seminal roots) resulted in increased estimates of propagule numbers of the take-all fungus (Gaeumannomyces graminis var.tritici) for 196 of the 368 soil samples bioassayed in a field study conducted in Western Australia between 1984 and 1986.     

Natural selection of allozyme polymorphisms: a microgeographic climatic differentiation in wild emmer wheat (Triticum dicoccoides)

Summary Allozymic variation in proteins encoded by 48 loci was analyzed electrophoretically in 1984 and 1985 in 137 individual plants of wild emmer wheat, Triticum dicoccoides, from a microsite in Yehudiyya, northeast of the Lake of Galilee, Israel. The test involved two climatic microniches in the open Tabor oak forest (1) sunny between trees and (2) shady under trees' canopies. Significant genetic differentiation at single-, two- and multilocus structures was found between neighboring climatic niches, which were only separated by a few meters. Our results suggest that allozyme polymorphisms in wild emmer wheat are partly adaptive, and differentiate primarily at the multilocus level by climatic factors presumably related to aridity stress.     

The 5S DNA units of bread wheat (Triticum aestivum)

A collection of 44 cloned 5S DNA units fromTriticum aestivum cv. Chinese Spring were grouped into 12 sequence-types based on sequence similarity and the respective consensus sequences were then produced. The relationship between these 12 consensus sequences (T. aestivum S 1-S 8 andT. aestivum L 1-L 4), together with two clones sequenced byGerlach andDyer, and the 5S DNA consensus sequences from diploidTriticum spp. were then determined by numerical methods. Both phenetic and cladistic analyses were carried out. The following wheat 5S DNA sequences were found to group with respective sequences from diploidTriticum spp.:T. aestivum S 4, S 6 withT. tauschii S;T. aestivum S 3 withT. monococcum S andT. monococcum S-Rus 7;T. aestivum L 1 andT. aestivum L-G&D withT. speltoides L;T. aestivum L 2, L 3 withT. tauschii L;T. aestivum L 4 withT. monococcum L andT. monococcum L-Rus 12. The analyses suggested that 5 out of the 65S Dna loci present in wheat were identified at the sequence level. The locus that could not be identified in this analysis was the5S Dna-B 1 locus. A group ofT. aestivum sequences (T. aestivum S 1, S 7, S 8, S-G&D) were found to be distinct from the other 5S DNA sequences in the data base. The existence of the distinct group of 5S DNA sequences suggests that there is a gap in our current understanding of wheat evolution with respect to the5S Dna loci.     

Tolerance to high concentrations of boron for the amphiploid of Triticum aestivum × Agropyron elongatum

The response to high concentrations of B in soil was compared for Triticum aestivum L. (vars. Chinese Spring and Halberd) and the amphiploid of Chinese Spring × Agropyron elongatum (Host). The tolerance of the three genotypes, with respect to yield at the high B treatments, was amphipolid>Halberd>Chinese Spring. The concentration of B in whole shoots was similar for the amphiploid and Halberd and significantly higher for Chinese Spring. The mechanism for tolerance to B appears to be the same for the amphiploid and wheat and is related to reduced accumulation of B in shoots.     

Identification of ‘Amigo’ and ‘Kavkaz’ translocations in Ohio soft red winter wheats (Triticum aestivum L.)

One cultivar (GR876) and two advanced Ohio soft red winter wheat lines (OH413 and OH414), with Kavkaz in their pedigrees, were examined for the presence of the Kavkaz, 1RS/1BL rye/wheat chromosome translocation. Another advanced line (OH416), with Amigo in its pedigree, was examined for the presence of the Amigo, 1RS/1AL translocation. Only two satellited chromosomes were observed in most mitotic root-tip cells from GR876, OH413, and OH414, compared to four in most cells from OH416. Heteromorphic bivalents were observed in most PMCs from hybrids produced by crossing GR876, OH413, and OH414 as females to Chinese Spring. No heteromorphic bivalents were observed in PMCs from OH416 x Chinese Spring hybrids. When GR876 and the Ohio lines were hybridized with Chinese Spring dimonotelosomic-1B, telosomic trivalents, consisting of the short- and longarm telosomes paired with chromosome 1B, were only observed in PMCs from 43-chromosome hybrids involving OH416. The long-arm telosome paired with the translocation chromosome, while the short-arm telosome remained unpaired in all other 43-chromosome hybrids. Separation of gliadin proteins from GR876 and the Ohio lines by PAGE revealed that secalin bands for GR876, OH413, and OH414, migrated similarly to the secalins for Kavkaz. Bands for OH416, identified as possible secalins, migrated similarly to those for Amigo. Cultivar GR876 and advanced Ohio soft red winter wheat lines OH413 and OH414 carry the Kavkaz translocation, while OH416 carries the Amigo translocation.Communicated by K. Tsunewaki     

What limits nitrate uptake from soil?

Abstract. An accepted view, that unless nitrate concentrations in the soil solution are very low (e.g. below 0.1–0.2 mol m^?3) the growth of high-yielding crops is not limited by the availability of nitrogen, is challenged. Conventional analyses of nutrient supply and demand, based on calculations of apparent inflow rates (uptake rates per unit total root length) are invalid. Apparent inflow rates are inversely proportional to root length. The convention of using total root length grossly overestimates the fraction of the root system active in nutrient uptake. Consequently, inflow rates based on total root lengths underestimate the true values, indicating unrealistically low nutrient concentration differentials between bulk soil and root surfaces required to drive uptake. An alternative method of analysis is suggested. This is based on total nutrient uptake rather than on inflow rate. Measurements of the former do not depend on estimates of active root length and can be made directly and reliably. The method was applied to data obtained from a pot experiment using spring wheat (Triticum aestivum L., cv. Wembley) grown in soil without nitrogen fertilizer (N₀) or with nitrogen fertilizer equivalent to 200kg N ha^?1 (N⁺). Soil nitrate concentrations calculated using the conventional method based on total root length, suggested that any increases in concentration above those measured in the N⁰ treatment should not have resulted in increased uptake and growth. However, the N⁺ plants were always bigger than those in the No treatment, refuting this suggestion. Theoretical uptakes of nitrogen (calculated initially on the basis of a fully active root system) were adjusted, by reducing the effective root length incrementally, until the theoretical uptake matched the measured net uptake of nitrogen. The mean fractions of the root systems likely to have been involved in nitrate uptake were 11% and 3.5% of the total lengths of root in the N⁰ and N⁺ treatments, respectively.     

Epidermal conductance in different parts of durum wheat grown under Mediterranean conditions: the role of epicuticular waxes and stomata

Abstract. Epidermal (non-stomatally-controlled) conductance from the fourth leaf, first node leaf, flag leaf and ear of durum wheat (Triticum turgidum var durum L.) grown under Mediterranean field conditions has been measured, along with leaf stomatal frequency and the amount and distribution of epicuticular waxes. Measurements were carried out on varieties and land-races from the Middle East, North Africa, ‘Institut National de la Recherche Agricole’ (INRA) and ‘Centra Internacional de Mejora de Maiz y Trigo’ (CIMMYT). Significant differences were observed among genotypes in the epidermal conductances (g_e) of the four organs. For each of the four organs tested, genotypes from the Middle East and CIMMYT showed higher g_e. values than those from North Africa and INRA. Ears showed epidermal conductances that were more than four times higher than those of leaves when g_e. values were expressed per unit dry weight. The amount of epicuticular waxes was higher in the fourth leaves, intermediate in the first node and flag leaves and lower in the ears. For each organ, g_e differences among genotypes were unrelated with the amount of epicuticular waxes. Removal of epicuticular waxes by dipping the organs into chloroform significantly increased the epidermal conductance for the fourth and first node leaves and the ear. However, this did not occur for the flag leaf. For the fourth leaf, g_e of intact leaves and g_e of leaves in which epicuticular waxes were removed were unrelated (r = -0.265). The regression coefficient of this relation for the first node and flag leaves showed values of 0.666 and 0.650 (P > 0.05), respectively, and values were even higher in the ear (r > m 0.892, P > 0.01). Scanning electron microscope analysis showed that wax bloom decreased from the fourth leaf to the flag leaf, whereas the extent of amorphous wax increased. Wax bloom in leaves consisted mainly of deposits of thin wax plates. In the ears and the adaxial surface of flag leaves, fibrillar waxes predominated. In the first node and flag leaves, the wax deposits on the adaxial side cover the surface of the leaf more densely and uniformly than those on the abaxial side. There was no significant correlation between g_e and total stomatal density, or between g_e and either adaxial or abaxial stomatal density for any sample of the three different leaves. The contribution of epicuticular waxes plus total stomatal frequency only explained 42.4, 11.8, 28.3 and 16% of g_e (per unit leaf area) variations for the fourth leaf, first node leaf, flag leaf and the combined variation of the three leaves together, respectively. From these results, it is concluded that complex interrelationship between different morphophysiological characteristics probably control g_e differences among genotypes and that these interrelationships differ for each different plant part.