The objective of this experiment was to evaluate the male sterilizing activity induced by the chemical hybridizing agent (CHA) clofencet, on four wheat varieties: two Triticum aestivum cultivars, 'Pia' and 'Claudia', and two Triticum turgidum var. durum cultivars, 'Capri' and 'Ambra'. The CHA was sprayed at two stages of the Feekes scale, 7.5 and 8.5, using four rates of active ingredients (0, 3.5, 5.0 and 6.5 kgּha -1 ) in a split block design with fi ve replicates. The effi ciency of the treatments was determined by measuring developed seeds and calculating male sterility (MS). Results showed that MS increased with increasing dosage and was more pronounced at the latest stage of development. The MS average for the highest dosage was 47.3% in the fi rst stage of application and reached 84% at the second stage of application. Cultivars responded differently to the CHA, but no differences clearly attributable to species could be detected. T. aestivum cultivar 'Pia' reached 96% MS, a value that justifi es the use of clofencet as a CHA for hybrid wheat production. The insuffi cient levels of MS detected in the other cultivars were due to causes not determined in this study.
The F1 generation of a diallel cross among the soft red winter wheat genotypes ‘Vermillion,’ ‘Seneca,’ ‘Knox 62,’ ‘Benhur,’ ‘Arthur,’ and Purdue 5215 showed a significant expression of heterosis and heterobeltiosis in coleoptile elongation; all F1 progenies surpassed midparent and higher parent coleoptile lengths. However, this superiority was probably due in part to the larger seed size of the hand‐crossed seed, because the F2 progenies essentially equalled the midparental values. Genetic variation in coleoptile elongation appeared to be controlled largely by additive gene action. Regression coefficients of F1 on midparent and F2 on F1 were .957 to .783, respectively, indicating high heritability of the character. Study of small and large size seed fractions of the parents revealed a significant influence of seed size upon coleoptile elongation and seedling fresh weight.
Six soft red winter wheat (Triticum aestivum L. era. Thell.) genotypes were crossed in a diallel system to estimate gene action and heterosis as expressed for cold resistance. Following cold hardening in the seedling stage, parental and F1 genotypes were exposed to 2, −7, and −10 C for 4 hours and allowed to recover for 10 days. Both the traditional partitioning of genotypes and that by Gardner and Eberhart were performed. The F1 hybrids exceeded the better parents by 26% for regrowth tissue weight and by 30% for crown weight after freezing, averaged over all temperatures. These two characters were significantly correlated. The major portion of the genetic variability was associated with specific combining ability or specific heterosis effects due to dominance or addltive‐by‐additive gene action.
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