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Crop Science Abstract -

Indices of Plant Damage and Heritability of Tolerance to the Spotted Alfalfa Aphid in Alfalfa


This article in CS

  1. Vol. 29 No. 6, p. 1337-1340
    Received: July 13, 1988

    * Corresponding author(s):
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  1. H. O. Jimenez,
  2. J. L. Caddel,
  3. R. C. Berberet  and
  4. R. W. McNew
  1. D ep. of Entomology
    D ep. of Statistics,Oklahoma State Univ., Stillwater, OK 74078



Alfalfa, Medicago sativa L., cultivars expressing antibiosis or antixenosis resistance to the spotted alfalfa aphid (SAA), Therioaphis maculata (Buckton), impose selection pressure for more-virulent insect biotypes. Tolerant plants could be useful in reducing pressure for rapid development of new biotypes. Our studies were conducted to quantify tolerance to the SAA by assessing damage to plants that supported infestations with less damage than was typically observed in susceptible plants and to study the inheritance of tolerance. Vegetative propagation was used to provide replicates of tolerant plants for use in estimating the extent of genetic variability in the Oklahoma common cultivar OK08. Heritability of tolerance was estimated by parent-offspring regression of selfed and polycross progeny. Numbers of SAA were similar on tolerant and susceptible plants after 10 d of infestation and by Day 19, tolerant plants had much higher numbers. A tolerance index that considers stunted growth and percentage of leaves that exhibit no chlorosis was developed based on correlation of these variables with dry-matter production. After a 19-d infestation period, variation in expression of tolerance by 39 candidate plants was high and 35% of the variability was estimated to be genetic. Heritability of the tolerance characteristics was estimated at 25% in selfed progeny of these plants and 20% in polycross progeny. Reduction in heritability of tolerance in these progeny suggests that dominant effects may control expression of this trait in alfalfa.

Journal article no. J-5343 of the Oklahoma Agric. Exp. Stn., Stillwater.

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