R. R. Duncan

Tissue Culture-Induced Variation and Crop Improvement

Publisher Summary The selection of regenerants with good agronomic performance depends on the relative effects of induced and introduced variation during the in vitro process. This variation can arise from any number of processes, but the key to successful selection of desirable regenerants with improved traits is the expression of a wide diversity for the traits, trait stability over generations, adequate population density to have a reasonable chance of visually selecting the desirable variants in the field, and the proper field environment that will foster trait expression. These criteria are identical to those required for all conventional and mutation breeding programs. The application of tissue culture regeneration in selection strategies must be advantageous to the breeder before it will be adopted. Only a synergistic and concerted effort by traditional breeders and plant biotechnologists can bring this technology to the potential level of efficiency and application that will result in enhanced breeding efforts and cultivars with improved value-added traits that can be grown profitably by producers. Finally, as with any breeding program, the variants must be evaluated in multiple environments to ensure that all desirable traits are stable over generations. Useful variants have been released, but compared to conventional breeding methodologies, the results thus far have been limited and disappointing. The reasons for the limited success are discussed in this chapter.

Turfgrass Molecular Genetic Improvement for Abiotic/Edaphic Stress Resistance

Publisher Summary Turfgrasses are subject to many climatic, soil, pest, and use-related stresses. The frequency, duration, and intensity of stresses are increasing in response to factors such as reduced water availability, frequent use of effluent water and irrigation water of lower quality, installation of turfgrass facilities on sites with marginal soil quality, and increasing usage of recreational sites. These factors, when coupled with steady environmental pressure toward reduced water, nutrient, and pesticide inputs, mandate the development of more stress-resistant grasses. This chapter reviews some of the biotechnology methods that lead turf enhancement programs into the 21st century. The scientific methodology must fit within a system or framework with other components in order to significantly improve turfgrasses. The chapter also presents a strategic framework for turfgrass improvement that incorporates gene technology. Enhanced abiotic or edaphic stress tolerance in turf can provide improvements in performance under environmental extremes, functional root systems that perform equally well in stressed and non-stressed environments, improved water use efficiency, and improved nutrient uptake or utilization efficiency.

Sorghum seedling root growth as influenced by H+, CA++, and MN++ concentrations 1

Abstract Root response mechanisms for acid soil tolerance adaptability are generally unknown. Sorghum [Sorghum bicolor (L.) Moench] cultivars (Funk G522DR, GP140, SC599, TAM428, SC283, and SC574) were grown in white quartz flintshot sand and watered with 0.01M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, or 6.0 and Ca++ (0, 10, 100 mgl‐1 as CaCl2) or Mn++ (0, 1.4, or 140.0 mgl‐1 as HnCl2). At the acid soil tolerance impact response phase (< 10 days old), Ca++ did not influence initial root growth. Increased H+ concentration inhibited juvenile root growth equivalently in all six cultivars. This inhibition was reversed by exogenous GA3 in Funks G522DR but not in SC283 or SC574. Excess Mn++ (140 mgl‐1) further decreased root growth. Induction of an auxinase inhibitor by GA3 would support a hypothesis of H+ concentration influence on IAA transport and/or availability. Root growth matched IAA water partitioning and exogenous IAA (10‐10 and 10‐9 M) reversed the H+ concentration influence on root growth of SC...

Tolerance of sorghum genotypes to an acid, aluminum toxic Tatum subsoil

Abstract Aluminum (Al) tolerant sorghum (Sorghum bicolor L. Moench) genotypes are needed for use on strongly acidic, infertile soils of the tropics and subtropics, where the crop is often grown in a low input, subsistence type of agriculture. Eleven genotypes were first screened for Al tolerance in greenhouse pots of acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic, Typic Hapludult) at pH 4.3 and 5.3. In two subseguent experiments, four genotypes showing wide differences in acid soil tolerance in the first test were grown over pH ranges of 4.3 to 6.4 and 4.7 to 7.0. Acid soil tolerance was determined by absolute dry shoot and root weights at low pH and relative (low pH/high pH %) shoot and root weights. Genotypes differed by as much as 10 fold in relative shoot weight and 8 fold in relative root weight. Genotypic tolerances to acid, Al toxic Tatum subsoil were in good agreement with those obtained on acid field sites in Georgia and Brazil. Hence, results indicated that Al toxicity is a major selection...

INFLUENCE OF SILICA ON GROWTH, QUALITY, AND WEAR TOLERANCE OF SEASHORE PASPALUM

Wear is a predominant stress affecting growth of turfgrass. Silica, which is deposited in epidermal cells of leaf blades, may potentially increase rigidity of a turfgrass stand. This research was undertaken to determine if application of silicon (Si) would enhance turfgrass wear tolerance, growth, and quality. This research was conducted during two consecutive field trials in 1998 on two greens-quality ecotypes established on a native Applying (Typic Kanhapludult) soil at the University of Georgia Experiment Station in Griffin, GA. Silica was applied to two ecotypes of seashore paspalum (Paspalum vaginatum Swartz.) as potassium (K) silicate at two foliar rates (1.1 and 2.2 kg Si ha−1) and as a soil drench rate of 22.4 kg Si ha−1. Potassium chloride, which added K at the amount in the drench treatment (15.6 kg K ha−1), was also applied as a K check. Best turf quality responses on nonwear plots resulted from highest rates of Si application as well as from the K only treatment. A positive association was found between leaf tissue K concentration and turf quality scores, while increasing Si concentration reduced quality scores. Wear tolerance was enhanced either by K alone or by the high rate of Si and K. Turf growth was not affected by fertility treatments. Enhanced wear tolerance, due to application of either K alone or Si and K, reduced wear injury from 35% to 14% (K) or 20% (Si and K) averaged across both studies. This may be attributed to increased leaf turgor pressure or reduced total cell wall (TCW).

H+, Ca++, and Mn++ influence on sorghum seedling shoot growth

Plant response mechanisms for acid soil tolerance adaptability are generally unknown. Sorghum [Sorghum bicolor (L.) Moench] cultivars (Funk G522DR, GP 140, SC 599, TAM 428, SC 283, and SC 574) were grown in white quartz flintshot sand and watered with 0.01 M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, or 6.0 with concurrent treatments of Ca++ (0, 10, 100 mgl‐1 as CaCl2) or Mn++ (0, 1.4, 140.0 mgl‐1 as MnCl2). At the acid soil tolerance impact response phase (<10 days old), Ca++ or Mn++ did not influence seed germination (i.e., radicle exsertion). Ca++ did not influence initial shoot growth. Increased H+ concentration greatly inhibited juvenile shoot growth equivalently in all six cultivars. This inhibition was explicable as an influence of gibberellic acid (GA) availability to the aleurone layer and was explained as an accumulation (partitioning) of GA into lipid cellular constituents. Excess Mn++ further exacerbates this condition by limiting GA biosynthesis.

Breeding and Improvement of Forage Sorghums for the Tropics

Publisher Summary Sorghum belongs to the tribe Andropogoneae of the Gramineae family Poaceae. It is a coarse, perennial grass that is treated as an annual in temperate or subtropical climes where cold temperature limits growth and development. In tropical regions, however, it can be harvested many times. All types, except the Sudan grasses, produce some grain that adds to the feeding quality and enhances subsequent utilization. Forage sorghums in the tropics are used predominately as a temporary alternative to perennial forages when the latter are in a low-biomass production cycle or their quality is not adequate to sustain animals. In general, temperate grasses are more digestible than tropical ones. High temperatures, low nutrient inputs, pathogen pressure, acid soil infertility and stresses, and genetic variability all contribute to this low digestibility problem in the tropics. This chapter concentrates on the genetic improvement of forage sorghums.

Sorghum genotype comparisons under variable acid soil stress

Abstract Sorghum [Sorghum bicolor (L.) Moench] is quite sensitive to acid soil stress, but differentially responsive genotypes have been found. To learn more about the overall acid soil tolerance mechanism(s), four genotypes differing in acid soil tolerance/susceptibility were evaluated for nutrient content and grain yield at three locations during 1983 to 1985. Plants were grown on soil pH >6.0 and 6.0 x 100) were 96% for SC283, 40% for SC599 (moderately susceptible), and 19 and 14% for RTx430 and TAM 428 (susceptible genotypes), respectively. Mechanisms involving Ca, Mg, and K may be important links in the overall acid soil tolerance mechanism of sorghum.

Sorghum cultivar variation in Ca2+ and aluminum influence on root curvature

Abstract Calcium (Ca2+) and aluminum induced unilateral root growth inhibitions (i.e. root curvature) when applied in agar to one side of sorghum [Sorghum bicolor (L.) Moench] roots. PCMBS (p‐chloromercuribenzenesulfonic acid) (10 mM) stopped the root growth inhibition (i.e. curvature) by aluminum in SC574 and SC283 (acid‐soil‐stress tolerant cultivars) but not in Funk G522DR (acid‐soil‐stress sensitive). PCMBS influenced Ca2+‐induced root growth inhibition (i.e. curvature) in Funk G522DR and SC283, but not in SC574.

Nifedipine influence on calcium and aluminum absorption in roots of three sorghum cultivars

Abstract A 1,4‐dihydroxypyridine type of ion channel blocker, nifedipine [1,4‐dihydro‐2,6‐dimethyl‐4‐(2‐nitrophenyl)‐3,5‐pyridinedicarboxylate dimethyl ester], was tested on the root absorption of Al3+ and Ca2+ by sorghum [Sorghum bicolor (L.) Moench] cultivars with varying acid stress tolerance. In an acid stress sensitive cultivar, Funk G522DR, nifedipine (1 μM) influenced Ca2+ but not Al3+ absorption. In one acid stress tolerant cultivar, SC574, nifedipine (1 μM) influenced both Ca2+ and Al3+ absorption. In a second acid stress tolerant cultivar, SC283, nifedipine (1 μM) did not influence Ca2+ but did influence Al3+ absorption. Considerable genetic diversity is present in Ca2+ and Al3+ absorption between sorghum cultivars.