Perennial grains hold promise, especially for marginal landscapes or with limited resources where annual versions struggle.
Using mycorrhizal fungi known to colonize wheat, the mycorrhizal dependence of various small grains including modem wheat varieties, primitive wheat lines, and wheat ancestors was studied. With the exception of the United States cultivar Newton and the German cultivars Apollo, Kanzler, and Sperber, dry weight of eight other modern wheats from the United States and Great Britain were increased by 29–100% following inoculation with mycorrhizal fungi. All landraces from Asian collections or early introduced American cultivars were also dependent on the symbiosis, with dry weight increases averaging 169 and 55%, respectively. All wheat ancestors of the AA and BB genomes (except Aegilops speltoides) benefitted significantly from the symbiosis, whereas no benefit was observed for ancestors of the DD genome, tetraploid wheats of the AABB or AAGG genomes, or in the hexaploid ancestor Triticum zhukovskyi (AAAAGG genome). These differences in mycorrhizal response of the ancestors, lines, and cultivars were highly correlated with root fibrousness ratings. When the fungi used as a combined inoculum in the previous experiment were inoculated individually onto selected plant species or cultivars, 6 of the 10 isolates stimulated growth of Andropogon gerardii, a highly dependent grass species, and 8 of the 10 stimulated the growth of 'Turkey' wheat. In contrast, none of the isolates positively affected growth of 'Newton' or 'Kanzler' wheat cultivars, and in fact several fungi decreased the biomass produced by these two cultivars. These studies have demonstrated a strong genetic basis for differences in mycorrhizal dependence among cultivars. A trend for greater reliance on the symbiosis in older cultivated wheats than iin wheat ancestors or modern wheats was also observed. The depression in growth associated with certain mycorrhizal fungi and wheat cultivars demonstrates that colonization of roots does not guarantee benefit from the symbiosis. Key words: root fibrousness, growth response, vesicular–arbuscular mycorrhizae.
Periodic evaluation of genetic improvement of crop cultivars is useful, both as a demonstration of the importance of plant breeding to the public and as a way of identifying traits or target environments that may require increased efforts by breeders. Evaluation of cultivars from different eras in a common environment is the most direct of the several methods that have been used to estimate breeding progress. Thirty‐five hard red winter wheat (Triticum aestivum L. em. Thell.) cultivars introduced or released between ca. 1874 and 1987 were evaluated in experiments at three locations in Kansas during 1986 and 1987 (three other cultivars were evaluated only in 1987) to estimate genetic progress achieved by hard red winter wheat breeding programs. Linear regression of cultivar means on years of release showed increases of 16.2 kg ha−1 yr−1 in grain yield, 0.4 kg m−3 yr−1 in volume weight, and 0.04 g yr−1 in thousand‐kernel weight. Days to heading and plant height decreased at rates of −0.1 d yr−1 and −0.5 cm yr−1, respectively. There were also significant increases over time in lodging resistance. There was no significant change in biomass yield over time. Rates of genetic improvement varied significantly across evaluation environments, with the greatest gain in grain yield (1.4% of the experiment mean per year) estimated in an epidemic of stem and leaf rust (caused by Puccinia graminis Pers. f. sp. tritici Eriks. & Henn., and P. recondita Rob. ex. Desm. f. sp. tritici, respectively). Moderate gain per year (0.6%) was estimated in the most highly productive environment, lower gain (0.4%) was found under drought stress, and there was no gain when evaluation was conducted under an epidemic of tan spot (caused by Helminthosporium tritici‐ repentis Died.), a foliar disease. High levels of resistance to H. tritici‐repentis had not been incorporated into hard red winter wheat cultivars. No evidence of a yield plateau was found for hard red winter wheat cultivars evaluated under a range of environmental conditions in Kansas.
The genomic in situ hybridization (GISH) technique was used to discriminate between chromosomes of the C genome and those of the A and A/D genomes in allopolyploid oat species (genus Avena). Total biotinylated DNA from A. strigosa (2n = 2x = 14, AsAs genome) was mixed with sheared, unlabelled total DNA from A. eriantha (2n = 2x = 14, CpCp) at a ratio of 1:200 (labelled to unlabelled). The resulting hybridization pattern consisted of 28 mostly labelled and 14 mostly unlabelled chromosomes in the hexaploids. Attempts to discriminate between chromosomes of the A and D genomes in A. sativa (2n = 6x = 42, AACCDD) were unsuccessful using GISH. At least eight intergenomic translocation segments were detected in A. sativa 'Ogle', several of which were not observed in A. byzantina 'Kanota' (2n = 6x = 42, AACCDD) or in A. sterilis CW 439-2 (2n = 6x = 42, AACCDD). At least five intergenomic translocation segments were observed in A. maroccana CI 8330 'Magna' (2n = 4x = 28, AACC). In both 'Ogle' and 'Magna', positions of most of these translocations matched with C-banding patterns.
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