Graduate Thesis Or Dissertation
 

Influence of aluminum toxicity in intergeneric crosses of wheat and rye

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  • A technique previously designed to screen wheat cultivars and segregating populations for tolerance to Aluminum utilizing nutrient solutions in growth chambers was found to be efficient in differentiating among cultivars of wheat, rye, and triticale for tolerance to Al under greenhouse conditions. A 5°C increase in temperature, from 25°C to 30°C of the nutrient solutions increased the toxicity of a given Al concentration. Screening of 263 entries including diploid, tetraploid and hexaploid wheat species and diploid rye provided evidence that adequate tolerance levels to Al in triticale can only be derived from some hexaploid wheats and some diploid ryes. The level of tolerance present in both wheat and rye was expressed in the F₁ hybrids but did not interact to produce hybrids that were more tolerant than the more tolerant parent. When the rye was more tolerant than the wheat and the Al concentration exceeded the level of tolerance provided by the wheat, the heterogencity of rye for Al tolerance was expressed in the resulting F₁ hybrids. When a tolerant wheat was crossed to a sensitive rye and the Al concentration exceeded the tolerance level of the rye, the F₁'s were uniformly tolerant indicating the parent wheat was homozygous for tolerance of Al. Chromosome doubling of F₁ hybrids did not cause any dosage effects in the reaction of amphiploids to Al. The F₁ progeny from the Penjamo 62 x Rye 1003 cross was tolerant to 1 ppm while sensitive plants to this Al concentration were observed in the amphidiploids derived from this F₁ possibly resulting from chromosome(s) loss or aneuploidy. The level of tolerance in tolerant wheats was somewhat reduced in the F₁ hybrids when crossed to sensitive ryes, but was fully recovered in the amphidiploids derived from these Fi's. The opposite was true when a tolerant rye was crossed to a sensitive wheat. The F₁ hybrid was almost as tolerant as the rye parent but this level of tolerance was not recovered in the amphidiploid. If aneuploidy was present it did not involve rye chromosomes because rye was the only tolerant parent and the amphidiploid was uniformly as tolerant as Atlas 66. Although the amphidiploid derived from the cross involving tolerant wheat x tolerant rye showed the highest level of tolerance, this was not as tolerant as the rye parent. It was believed that modifier genes from the wheat genotype influenced the expression of the full level of tolerance contributed by the rye parent in the amphidiploids. Nevertheless, it provided the resulting amphidiploids with a level of tolerance approximately twice that of Atlas 66. When tolerant rye was crossed to a sensitive wheat, the amphidiploid obtained had a level of tolerance similar to the tolerant wheat cultivar, Atlas 66. Aluminum affected mitotic activity of wheat, rye and triticale within the first three hours of Al treatment. Cell division decreased as exposure to Al increased; however, the mitotic activity of tolerant plants never reached zero. It appeared that a protective mechanism was induced and allowed mitotic activity to continue progressively causing roots to continue to elongate in the Al solution. It appears that Al affects some processes at interphase. Binucleated cells were observed in both Al treatments and controls. Therefore, Al alone cannot be responsible for inducing this type of cell.
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