Root Regrowth Research Articles

Malate enhances recovery from aluminum-caused inhibition of root elongation in wheat

Toxic aluminum (Al) ion is a major constraint to plant growth in acid soils. Aluminum tolerance in wheat (Triticum aestivum L.) is strongly related to the Al-triggered efflux of malate from root apices. A role of the secreted malate has been postulated to be in chelating Al and thus excluding it from root apices (malate hypothesis), but the actual process has yet to be fully elucidated. We measured Al content and root growth during and after Al exposure using seedlings of near-isogenic lines [ET8 (Al tolerant) and ES8 (Al sensitive)] differing in the capacity to induce Al-triggered malate efflux. Aluminum doses that caused 50% root growth inhibition during 24-h exposure to Al in calcium (Ca) solution (0.5 mM CaCl2, pH 4.5) were 50 µM in ET8 and 5 µM in ES8. Under such conditions, the amount of Al accumulated in root apices was approximately 2-fold higher in ET8 than ES8. Al-treated seedlings were then transferred to the Al-free Ca solution for 24 h. Compared to control roots (no Al pretreatment), root regrowth of Al-treated roots was about 100% in ET8 and about 25% in ES8. The impaired regrowth in ES8 was observed even after 24-h exposure to 2.5 µM Al which had caused only 20% root growth inhibition. The addition of malate (100 µM) during exposure to 50 µM Al in ES8 enhanced root growth 1.6 times and regrowth in Al-free solution 7 times, resulting in similar root growth and regrowth as in ET8. Short-term Al treatments of ES8 for up to 5 h indicated that the Al-caused inhibition of root regrowth started after 1-h exposure to Al. The stimulating effect of malate on root regrowth was observed when malate was present during Al exposure, but not when roots previously exposed to Al were rinsed with malate, although Al accumulation in root apices was similar under these malate treatments. We conclude that the malate secreted from root apices under Al exposure is essential for the apices to commence regrowth in Al-free medium, the trait that is not related to the exclusion of Al from the apices.

Evaluation of corn hybrids for tolerance to corn rootworm (Diabrotica virgifera virgiferaLeConte) larval feeding

The western corn rootworm ( Diabrotica virgifera virgifera LeConte (WCR)) is a major pest of corn in USA. The pest arrived in Croatia in 1995, and today over 250.000 ha are infested. Insecticides are regularly used to control WCR, but the cost is high, can pose environmental risks, and may become ineffective due to resistance. Growing corn that is resistant to corn rootworms would be a valuable alternative to insecticides. Nine Croatian (Institute of Agriculture, Osijek) and two Pioneer Hi-Bred Int. Inc. (Johnston, Iowa, USA) commercial corn hybrids were evaluated for WCR resistance at two locations using complete randomized block design with four replications. One location was in east Croatia (Osijek) and one was in the USA (Iowa). The hybrids’ tolerance to larval feeding was rated using root injury, root regrowth and root size. Root injury was rated using the Node-Injury Scale 0–3 and evaluation of root size and root regrowth were done by scale 1–6. In an analysis of variance combined across locations, ...

Inheritance of Aluminum Tolerance and its Effects on Grain Yield and Grain Quality in Oats (Avena Sativa L.)

Aluminum toxicity due to the cation Al+3 is a major factor limiting yields in acid soils. Wide genetic variability to aluminum tolerance is found in oat genotypes. The objectives of this study were to determine the number of genes controlling aluminum tolerance in oats and to verify if any detrimental effects were present of the aluminum tolerance genes on grain yield and grain quality in Al+3free soils. Aluminum tolerance was estimated as the average regrowth of the main root after exposure to toxic levels of Al+3 in a hydroponic solution under controlled conditions. The number of genes controlling that trait was estimated from the distribution of the average root regrowth frequencies in a population of 333 recombinant inbred lines (RIL's) in generations F5:6 and F5:7. The effects on grain yield and grain quality were assessed in a subpopulation of 162 RIL's chosen based on their aluminum tolerance response. Aluminum tolerance in the evaluated population was controlled by one dominant major gene with the tolerant genotypes carying AlaAla and the sensitive ones alaala alleles. No detrimental effects of the Ala allele on grain yield or grain quality were detected.

Inheritance in oat (Avena sativa L.) of tolerance to soil aluminum toxicity

Aluminum toxicity is a limiting factor for the expression of the yield potential in oat. The development of aluminum toxicity-tolerant genotypes is the cheapest and most feasible alternative for cultivation of soils with acid subsoil. Objectives of this study were to determine the gene action, number of genes and heritability of tolerance of oat genotypes to toxic aluminum concentrations. Parent genotypes and the F1 and F2 generations of some crossings plus the F3, F4, F5, BC1F1, and BC2F1 generations were discriminated by the analysis of root regrowth in plantlets exposed to aluminum. Additive gene action predominated among the genetic effects. Only one segregating gene was found which has multiple alleles, two for tolerance (Al1 and Al2) and one for sensitivity (al). The heritability of the trait was high, indicating that tolerant genotypes can be selected in early generations of improvement programs.

(114) Effects of Planting Depth on Landscape Tree Survival and Girdling Root Formation

Landscape trees are frequently planted with their root collars below grade, and it has been suggested that such deep planting predisposes trees to transplant failure and girdling root formation. The objective of the present research was to examine the effect of planting depth on the health, survival, and root development of two popular landscape trees, red maple (Acer rubrum) and `Yoshino' cherry (Prunus ×yedoensis). Trees were transplanted with their root flares at grade, 15 cm below grade or 31 cm below grade. Deep planting had a strong negative effect on the short-term survival of `Yoshino' cherries. Two years posttransplant, 50% of the 15-cm- and 31-cm-deep planted cherries had died, whereas all the control cherries had survived (P< 0.001; 2). Short-term survival of maples was not affected by planting depth. Deep-planted trees of both species exhibited little fine root regrowth into the upper soil layers during the first year after transplant. Four years posttransplant, control maples had 14% ± 19% of their trunk circumference encircled by girdling or potentially-girdling roots; this number rose to 48% ± 29% and 71% ± 21% for 15-cm- and 31-cm-deep planted maples, respectively (P< 0.01; ANOVA main effect). There were no treatment-related differences in girdling root development in the cherries.

A reliable screening system for aluminium tolerance in barley cultivars

Aluminium (Al) toxicity in the soil is an important factor that limits the production of barley in areas with acid soil. Selection and breeding of barley cultivars tolerant to Al toxicity is one of the most useful approaches to increase productivity. A reliable screening system is very important for selecting Al-tolerant plants in a breeding program. Using a hydroponic culture technique in which all the treatments were isolated in order to minimise complex interaction between genotypes, experiments were conducted to distinguish between susceptible and tolerant cultivars. Three different methods were investigated. Two previously reported methods could not provide consistent results or detect the difference between tolerant and susceptible cultivars. A new method was developed as follows: pre-germinated seedlings (2 days at 22°C) were cultured for 3 days in nutrient solution (Al free) followed by 24 h growing in a solution with 50 or 100 µm Al, and then 48 h regrowth in Al free nutrient solution. Following this method, seminal root regrowth length (SRRL) and relative seminal root regrowth length (RSRRL) showed significant differences between tolerant and sensitive cultivars. The SRRL of the most tolerant cultivar, Dayton, was 4–8 times greater than of the sensitive cultivars and about twice as long as of the other tolerant cultivars, FM404 and Brindabella. All the sensitive cultivars showed significantly shorter SRRL or RSRRL. Both SRRL and RSRRL were found to be closely correlated with plant height, plant dry weight, and grain weight in a soil-based experiment. This method was also used to evaluate F2 populations from crosses between tolerant and susceptible cultivars. Both SRRL and RSRRL gave results consistent with the hypothesis that the tolerance was controlled by a single dominant gene.

Growing Pinus nigra Seedlings in Spinout™-Treated Containers Reduces Root Malformation and Increases Growth After Transplanting

Abstract Root malformation originating during container production causes mechanical instability and plant mortality when those seedlings are transplanted. We investigated the effects of chemical (interior container surfaces treated with Spinout™ or not) or mechanical container modifications (vertical slits or no vertical slits), and the effects of substrate bulk density on the growth of Pinus nigra (Arnold) seedlings during plug production and after transplanting. Seedlings grown in compacted substrate had the greatest shoot, root and total plant dry weights five months after seeding in plug trays. However the incidence of root malformation was also greatest when seedlings were grown in compacted substrate. Unless root pruned, root malformations were retained after transplanting. Seedlings with unpruned roots grown in Spinout™-treated containers had higher regenerated root dry weight than those grown in untreated containers four months after transplanting. Root pruning before transplanting reduced growth of the seedlings regardless of container configuration and of substrate bulk density. Root regrowth and seedling quality after transplanting were greatest for seedlings grown in the treatment combination of no Spinout™, compacted substrate and no slits. Seedlings produced under natural photoperiods formed a resting bud when the seedlings were approximately 2.5 cm (1 in) tall in spring season. Within two weeks shoot elongation resumed, which resulted in branched seedlings. Root malformation can be induced during plug production and is retained after transplanting unless corrected by root pruning.

THE EFFECTS OF PROGRESSIVE ROOT REMOVAL PRIOR TO PLANTING ON SHOOT AND ROOT GROWTH OF BETULA PENDULA Roth

Summary Root loss during transplanting of bare rooted nursery stock is thought to limit water uptake during establishment. An initial investigation into the effects on growth under well watered conditions of progressive removal of root material from dormant trees of Betula pendula Roth, was set up in spring 1994. Trees with roots ≤1 mm removed (40% removal by mass) and with roots ≤ 5 mm removed (84% removal by mass) were compared to controls. Some limited measurements of water relations were also made. Shoot and root growth were increasingly limited by progressive root removal. Root regrowth was apparently proportional to the amount of old root material left behind after transplanting. In addition, the most severe treatment (roots ≤ 5 mm were removed) limited root growth in favour of shoot growth. Direct measurements of water relations proved to be difficult and inconclusive, however, increases in stem diameter, an indirect measurement of changes in water relations, indicated that progressive root removal subtly increased water stress in the trees. Alternative hypotheses for the observed of changes in growth based on limitations in sugar physiology and hormone imbalance are also discussed.

Identification of Aluminum Resistant Genotypes Among Madeiran Regional Wheats

Forty‐eight genotypes representing wheat diversity from the Island of Madeira were screened for resistance to aluminum (Al) in nutrient solution. Seeds of wheat used in the experiments were obtained from local farmers. The soil pH and content of ionic Al of plots cultivated with wheat were analyzed. The pH of topsoils varied between 3.83 and 6.59. The amount of ionic Al in soil samples varied between 0.38 and 1.36 cmol Al3 + per kg of soil and was positively correlated with the altitude of a plot. Eriochrome cyanine staining was used to evaluate the effect of Al ions on the root elongation. Seventy‐two hour exposure of 3‐day‐old seedlings to 100 and 200 µM Al in nutrient solution revealed a high number of Al resistant genotypes among wheat germplasm. After withdrawal of Al stress, survival and root regrowth was observed in 28 and 23 genotypes screened at 100 and 200 µM Al in nutrient solution, respectively. Enhanced resistance to Al among Madeiran genotypes was associated with the amount of ionic Al in the soils. Complexity and various patterns of responses of tested cultivars to Al stress may suggest that Madeiran germplasm could be a valuable source of genes controlling Al resistance for conventional breeding programs and for studies of molecular bases of mechanisms of Al resistance.

Organic acid exudation associated with aluminium stress tolerance in triticale and wheat

Three triticale cultivars differing in aluminium (Al) stress response, together with 1 Al-tolerant wheat cultivar (Carazinho) and 1 Al-tolerant wheat line (ET3), were used to investigate the root exudation of organic acids during Al stress. The likely relationship of organic acid exudation with Al tolerance, as assessed by root regrowth in nutrient solutions, was also examined. An enzymatic assay was used to detect malate release from both root tips and the whole root system; high performance liquid chromatography (HPLC) was also used to measure the exudation of organic acids from Al-stressed root tips. The enzymatic assay revealed some associations between Al tolerance and malate efflux from Al-stressed wheat or triticale roots, although Al-tolerant triticale cvv. Tahara and 19th ITSN 70-4 released less malate than the Al-tolerant wheat. HPLC analysis indicated that malate and citrate were not the main exudates related to the different levels of Al tolerance in these triticale cultivars. A yet to be identified organic acid in 19th ITSN 70-4 showed significant concentration differences from 2 other cultivars tested. This study highlighted the importance and necessity of elucidating the biochemical mechanisms involved in Al stress tolerance in triticale and other crops.

Effects of row spacing and plant density on corn rootworm (Coleoptera: Chrysomelidae) emergence and damage potential to corn.

Planting corn, Zea mays L., in row spacings less than the conventional width of 76 cm has been shown to increase grain yields. This study was conducted to determine if row spacing and plant density affected corn rootworm, Diabrotica virgifera virgifera LeConte and D. barberi Smith & Lawrence, adult emergence, larval injury to the roots, and plant tolerance to injury. Field experiments were conducted at Ames and Nashua, IA, in 1998, 1999, and 2000. Treatments were row spacings of 38 and 76 cm, and plant populations of 64,500 and 79,600 plants per hectare. Adult emergence was 31% greater in 38 cm compared with 76-cm rows. However, root injury was not significantly different between row spacings or plant populations. Row spacing alone did not significantly influence tolerance to injury, measured as root size and the amount of root regrowth. However, at one environment where precipitation was low, plants in 38-cm rows produced 25% more regrowth compared with plants in 76-cm rows. Root dry weight and regrowth were suppressed by 16 and 32%, respectively, at the high plant population. Although lodging was 51% lower in the 38-cm rows compared with the 76-cm rows, grain yields were not significantly different between row spacings. Reducing the row spacing of field corn from 76-38 cm should not increase the potential for injury from corn rootworm larvae.

Aluminum tolerance in barley: methods for screening and genetic analysis

Aluminum (Al) tolerance in roots of two cultivars of barley was studied using hematoxylin staining and root re-growth procedures. This study was performed in two F2 segregating populations originated from crosses between the tolerant FM-404 and sensitive Harrington cultivars. The F2 progeny analysed with hematoxylin staining revealed a segregation ratio of 3 tolerant: 1 sensitive, showing that the Al tolerance is controlled by a single gene with complete dominance for tolerance. The root re-growth measures do not confirm the 3:1 ratio. This last result can be explained due to the occurrence of genes that affect root growth rate or to the difficulties found in the evaluation of root re-growth. Barley has a complex root system, which makes it difficult to measure root re-growth after an extended period in nutrient solution. Due to the simplicity, reliability and better precision, the hematoxylin staining is the best procedure to determine the Al tolerance and its inheritance in barley.

Differential responses to selection for aluminium stress tolerance in triticale

A directional selection program was initiated to select triticale genotypes with improved aluminium (Al) tolerance and presumably acid-stress tolerance. Two consecutive cycles of 2-way selection for either high or low apparent Al tolerances from a base population, Tahara, resulted in the production of 6 selected lines, whose progenies were tested for Al tolerance response in terms of root regrowth characteristics in nutrient solutions to assess selection effectiveness. In addition, 1 cycle of 2-way selection from 2 other base populations, Empat and 19th ITSN 70-4, resulted in 4 selected lines.Selective responses differed among selected lines, depending largely on the direction of the selection made and, to a lesser extent, on the genetic background of the original population. Upward selection for longer root regrowth produced progeny with more highly Al-tolerant plants. Although varying estimates of realised heritability were generated, the 2 cycles of upward selection resulted in an enhanced Al tolerance of 14.5% in the progeny A9701 derived from the base population Tahara. These results suggest that directional selection based on longer root regrowth in nutrient solutions was effective in improving Al tolerance. A pot-culture experiment showed that the second selection generation (S2) Al-tolerant lines were more productive than their moderately Al-tolerant counterparts, further implicating the effectiveness of directional selection in enhancing Al stress tolerance and plant productivity.

Freezing Tolerance of Six Cultivars of Buffalograss

Freezing tolerance is an important trait that determines geographical adaptation of a turfgrass. This study was conducted to assess the relative freezing tolerance, seasonal changes in freezing tolerance (LT50), and winter survival of six cultivars of buffalograss [Buchloë dactyloides (Nutt.) Engelm.]. The cultivars 91‐118, Tatanka, Texoka, Stampede, UCR‐95, and 609 were grown in the field at Fort Collins, CO. From September 1998 to April 1999 and from October 1999 to May 2000, stolons were sampled monthly from each plot and subjected to laboratory freezing tests. Survival and recovery following the freezing test indicated that all cultivars had similar LT50 in September and gradually increased in winter hardiness during fall. However, the capacity to acclimate and the maximum freezing tolerance were significantly different among the cultivars. Ranking of grasses for mean LT50 (°C) was Tatanka (−18.1) = 91‐118 (−18.0) ≤ Texoka (−17.1) < 609 (−14.4) < Stampede (−12.4) < UCR‐95 (−9.2) during midwinter in 1998‐1999 and Texoka (−21.7) = 91‐118 (−21.6) = Tatanka (−21.0) < 609 (−15.8) = Stampede (−15.1) < UCR‐95 (−14.0) during midwinter in 1999‐2000. Following freezing treatments, Tatanka and 91‐118 maintained a higher relative shoot and root regrowth than other cultivars. Root regrowth was reduced by freezing to a greater extent than shoot regrowth for all cultivars. Field winter survival, a measure of winter hardiness, in 1998, 1999, and 2000 was generally in agreement with laboratory test results, showing that Stampede, 609, and UCR‐95 were more susceptible to winterkill than 91‐118 and Tatanka. The differences in freezing tolerance among the cultivars tested indicates substantial intraspecific variation that may be used for breeding improvement.

Fine root dynamics of shaded cacao plantations in Costa Rica

Root turnover may contribute a significant proportion of recycled nutrients in agroforestry systems and competition between trees and crops for nutrients and water may depend on temporal fine root regrowth patterns. Fine root biomass (≤ 2 mm) and fine root productivity were measured during one year in plantations of cacao (Theobroma cacao) shaded by Erythrina poeppigiana or Cordia alliodora planted on a deep alluvial soil in Turrialba, Costa Rica. Fine root biomass of approximately 1.0 Mg ha−1 varied little during the year with maximum values at the beginning of the rainy season of 1.85 Mg ha−1 in the cacao-C. alliodora system compared to 1.20 Mg ha−1 for cacao-E. poeppigiana. Fine root productivity of C. alliodora and E. poeppigiana (maximum of 205 and 120 kg ha−1 4 week−1, respectively) was greatest at the end of the rainy season, while for cacao it was greatest at the beginning of the rainy season (34–68 kg ha−1 4 week−1), which suggests that if nutrient competition occurs between the shade trees and the cacao, it could be minimized by early fertilization during the beginning of the rains immediately after pruning the shade trees. Annual fine root turnover was close to 1.0 in both systems. Assuming that fine root biomass in these mature plantations was constant on an annual basis, nutrient inputs from fine root turnover were estimated as 23–24 (N), 2 (P), 14–16 (K), 7–11 (Ca) and 3–10 (Mg) kg ha−1 year−1, representing 6–13% and 3–6% of total nutrient input in organic matter in the C. alliodora and E. poeppigiana systems, respectively.

Variabilidade genética e herança da tolerância à toxicidade do alumínio em aveia

Vinte e um genótipos de aveia (Avena sativa L.) do programa de melhoramento da Universidade Federal do Rio Grande do Sul foram avaliados quanto à reação ao alumínio (Al) tóxico em solução nutritiva. Os níveis de Al testados foram 5, 10, 15, 20 e 30 g kJ-1, e o recrescimento da raiz foi medido depois de 48 horas sob a ação do metal. A variabilidade fenotípica foi observada a partir de 10 g kJ-1; em 20 g kJ-1 foram discriminados genótipos tolerantes e sensíveis. As bases genéticas da tolerância ao Al foram estudadas nas gerações P1, P2, F1 e F2, em nove cruzamentos entre genótipos tolerantes x sensíveis. Foi observado nas populações segregantes que a tolerância foi condicionada por um gene, de efeito dominante. A herdabilidade no sentido amplo foi moderada a elevada, permitindo que a seleção de indivíduos homozigotos tolerantes possa ser realizada em gerações precoces, acompanhada de teste de progênie. Por ser um método de relativa facilidade e rapidez, a seleção de germoplasma tolerante ao Al pode ser parte integrante da rotina dos programas de melhoramento de aveia.

Herança da tolerância ao alumínio em populações híbridas de trigo

Plântulas originárias de populações híbridas, em geração F2, de 26 cruzamentos entre cultivares de trigo tolerantes (BH-1146, IAC-227, IAC-24, IAC-60, C-3, IAC-5, IAC-18 e IAC-21) e sensíveis (Anahuac 75, IAC-287, IAC-289, Siete Cerros e Veery "S") à toxicidade de alumínio e de 18 cruzamentos entre cultivares tolerantes (BH-1146, IAC-227, IAC-24, IAC-60, C-3, IAC-5, IAC-21, C-17, IAC-74 e IAC-18) foram avaliadas em relação à tolerância a 3 mg/L de Al3+, empregando soluções nutritivas. A tolerância à toxicidade de alumínio foi medida pela capacidade de crescimento da raiz primária central em solução nutritiva completa, após um tratamento de 48 horas em solução contendo 3 mg/L de Al3+. Avaliando-se as plântulas das populações F2 provindas de cruzamentos entre cultivares tolerantes e sensíveis, verificou-se que a tolerância à toxicidade de Al3+ foi dominante, e que em 24 dos cruzamentos, as cultivares tolerantes diferiram das sensíveis por um par de genes. Não foi detectada diferença entre as cultivares tolerantes em relação ao par de genes dominantes em relação à tolerância. Qualquer uma dessas cultivares poderá ser utilizada como fonte de tolerância num programa de cruzamentos em que essa característica for desejada.

Combining ability for aluminium tolerance in triticale

Root re-growth, following aluminium (Al) stress, has been used as an indicator of Al stress tolerance. Genetic variation in root re-growth characteristics among eight triticale genotypes was investigated by a diallel analysis. Highly significant variation due to both general combining ability (GCA) effects and specific combining ability (SCA) effects indicated that both additive effects and non-additive effects were important in explaining the genetic variation for Al tolerance. The high estimates of heritability and the predictability ratio for root re-growth revealed the preponderance of additive genetic variance in the inheritance of Al tolerance. Differences in patterns of GCA effects and SCA effects among the parents provided strong evidence that the genetic control of variation for Al tolerance as assessed by root re-growth was a complex polygenic system. Three Al-tolerant genotypes, Tahara, Abacus, and 19th ITSN 70–4, were found to be the best general combiners for larger root re-growth, and they could be used in hybridization programmes to improve Al stress tolerance by following a simple pedigree method of selective breeding.

Inheritance of root regrowth as an indicator of apparent aluminum tolerance in triticale

Aluminum (Al) toxicity is a predominant growth-limiting factor in acid soils. Better understanding of the genetic mechanisms by which plants tolerate toxic Al expedites the development of tolerant plant genotypes. The genetic behavior of apparent Al tolerance in two triticale crosses as measured by root regrowth of seedlings at a level of 10 μg · g−1 Al stress in nutrient solutions was analyzed by following a bi-parental (BIP) mating design. The validity of the additive-dominance genetic model was tested with relevant gene effects estimated. The continuous variation of regrown root length showed that apparent Al tolerance was a metrical character in nature. Both the additive and dominance effects were responsible while the additive effects played a major role in the expression of Al tolerance. Non-allelic interaction (or epistasis) was indicated from the inadequacy of the model and different types of epistatic gene effects were detected in the two crosses. These results suggest that Al tolerance was of polygenic system rather than simply inherited. One to three pairs of genes were involved in apparent Al tolerance for the parental difference. The moderately high value of estimates of heritability together with the estimates of genetic advance (GA) could be used in planning a selective breeding program aimed at greater Al tolerance.

HERANÇA DA TOLERÂNCIA AO ALUMÍNIO EM TRIGO

Cruzamentos e retrocruzamentos foram efetuados entre os cultivares de porte semi-anão IAC-24 e Anahuac, tolerante e sensível à toxicidade de alumínio, respectivamente. Plântulas dos parentais e da geração F1 do cruzamento entre eles bem como dos retrocruzamentos para ambos os parentais foram avaliadas em soluções nutritivas de tratamento contendo 2 mg/litro de Al3+. Progênies de gerações F2 e F3 do cruzamento e progênies F2 dos retrocruzamentos foram também avaliadas . A tolerância à toxicidade de alumínio foi medida pela capacidade de crescimento da raiz primária central em solução nutritiva completa, após um tratamento de 48 horas em solução contendo 2 mg/litro de Al3+. O cultivar IAC-24 diferiu do Anahuac por um par de genes dominantes para tolerância à presença dessa concentração de alumínio nas soluções nutritivas.