A. L. Fleming

Development of alfalfa strains with differential tolerance to aluminum toxicity

SummaryAluminum toxicity limits root growth in acid subsoils that are difficult to lime. An alternative to subsoil liming is the development of plants having greater tolerance to Al. Alfalfa (Medicago sativa L.) is considered an Al-susceptible species. Preliminary studies indicated that alfalfa cultivars differ in Al tolerance, but the extreme plant-to-plant variation within cultivars prevented the establishment of clearcut cultivar differences.Tolerant and susceptible plants were selected from each of six cultivars (‘DuPuits’, ‘Atlantic’, ‘Team’, ‘Buffalo’, ‘Grimm’, and ‘Sirsa 9’) grown on an Al-toxic Bladen soil at pH 4.1 to 4.3. The tolerant selections were repotted and interpollinated to form one population of polycross seed. Susceptible selections were treated similarly to form a second population. These two populations, tolerant and susceptible, were subjected to an additional cycle of recurrent phenotypic selection for tolerance and susceptibility, respectively, to Al-toxic Bladen soil at pH 4.6.Plants from the population selected for tolerance to the acid Bladen soil were significantly higher in both root and top vigor on Al-toxic Tatum soil than plants from the population selected for susceptibility. The results indicated that Al tolerance is a heritable trait in these alfalfa populations and that recurrent selection can be used effectively to develop strains having differential tolerance to Al-toxic soils. The observation that only 2% of the plants from the tolerant population were in the most tolerant class suggests a good opportunity for more progress in selecting toward Al tolerance.

Differential response of barley varieties to Fe stress

Abstract Previous studies indicated that plant genotypes which tolerate acid soils may be susceptible to Fe stress when grown at high pH. Evidence of this relationship was obtained through comparisons of species adapted to strongly acid or alkaline soil environments and of plant populations within species which differ widely in acid or alkaline soil tolerance. Such a correlation between Fe inefficiency and tolerance to excess Al has not been shown for barley (Hordeum vulgare L.). The purpose of the present investigation was to determine whether barley varieties, representing a range of Al tolerance, also respond differently to Fe stress. Al‐tolerant ‘Dayton’ and Al‐sensitive ‘Kearney’ barley were grown in nutrient solutions containing Fe concentrations ranging from 0.025 to 2.0 ppm, as FeEDDHA, at an initial pH of 6.5. Kearney was more resistant to Fe deficiency than Dayton and maintained more normal growth at the lower Fe levels. In addition, this variety established a lower pH in the root zone and a hig...

Differential resistance of weeping lovegrass genotypes to iron‐related chlorosis

Abstract Genotypes of weeping lovegraes (Eragrostis curvula (Schrad.) Nees) differ widely in resistance to an Fe‐related chlorosis on certain calcareous soils. To explore the physiology of this relationship in greater detail, chlorosis‐resistant FQ 22 and chlorosis‐susceptible FQ 71 genotypes were grown in nutrient solutions containing 1 ppm Fe (half as NaFeEDTA and half as FeSO4.7H20) at initial pH 4.0. When the solution pH was left unadjusted, the FQ 71 quickly increased the pH of the medium from 4.0 to the range of 6.5 to 7.0; iron was visibly precipitated within the solutions and on plant root surfaces; and plant tops became chlorotic. Under the same conditions, the FQ 22 maintained the solution pH within the range of 4.0 to 4.9; nutrient solutions remained clear; roots were white; and plant tops were green. FQ 22 absorbed 5 times as much NH+ 4 as FQ 71. When nutrient solutions were adjusted to pH 4.0 daily, both genotypes grew well and remained green; nutrient solutions were clear; and all roots were...

Effect of manganese on concentrations of Zn, K, Ca and Mg in two bush bean cultivars grown in solution culture

Abstract Two bush bean cultivars [Phaseolus vulgaris L. cv. ‘Wonder Crop 2’ (WC‐2) and ‘Green Lord’ (GL)], differing in Mn toxicity, were grown in a growth chamber for 12 days in Hoagland No. 2 nutrient solution containing 0.05 to 1 ppm Mn as MnCl24H2O with 1 ppm Fe as Fe‐EDTA, at an initial pH 5.00. Concentrations of Zn, K, Ca and Mg in the tissues of two bush bean cultivars were examined in relation to Mn toxicity. The concentration of Zn in the leaves of Mn‐sensitive WC‐2 increased significantly with increasing Mn concentration in the solution, but such levels were not toxic to the plants. The percent distribution of Zn and K in Mn‐sensitive WC‐2 plants (% of total uptake) significantly increased in the tops and decreased in the roots with increasing Mn concentration in the nutrient solution; however, Mn treatment had no effect on distribution of either Ca or Mg in WC‐2. External Mn concentration had little or no effect on the K, Ca, or Mg concentration in the tops of Mn‐tolerant GL.