Enhancement of Tuberization of Axillary Shoot Buds of Potato (Solarium tuberosum L.) Cultivars Cultured In Vitro

Factors controlling growth and tuberization of axillary budsin shoots of plantlets of potato (Solarium tuberosum L.) culturedin vitro were investigated. Correlative inhibition restrainedgrowth and tuberization of the axillary buds. Exposure of intactplantlets for various periods (4 to 48 h) to low (2 or 12C)or high (30 C) temperatures as comparedto 18C, did not alleviatecorrelative inhibition. Removal of the apical part of the shoot,the roots or both was generally ineffective Elevating sucroseconcentration from 30 to 80 g dm^–3 promoted tuberizationon axillary buds, and the cytokinin 6-(-dimethylallylamino)purine (2iP), alleviated correlative inhibition and enhancedtuberization in intact plantlets. In the whole plantlet mostof the tubers were formed on the basal nodes, however, oncecorrelative inhibition was eliminated by the dissection of theshoot to single node sections, tubers were formed on every axillarybud. The single most effective factor inducing tuberizationin single node sections was the growth retardant ancymidol,an inhibitor of giberellin biosynthesis. Key words: Potato, Solanum tuberosum L., in vitro tuberization, correlative inhibition     

Variation in the development of stem nematodes, Ditylenchus dipsaci, in susceptible and resistant crop plants

Dicotyledonous plants were reliably inoculated with stem nematodes by placing drops of 1.3% carboxymethylcellulose containing the surface sterilised worms between the cotyledons or in the leaf axils of recently emerged seedlings raised in pots of cool, moist soil. Inoculating onion leaves, bean stems and potato tubers or potato leaves gave variable results and inoculating onion, tulip and narcissus bulbs and lucerne and red clover stems was usually unsuccessful. An attempt to characterise 67 stem nematode populations by the reactions of a number of different plants failed for lack of useful differential hosts. Lucerne was, however, resistant to all but lucerne populations. Multiplication of stem nematode populations varied greatly between cultivars of lucerne or red clover. Some cultivars were resistant to some populations of lucerne or red clover stem nematodes and susceptible to others. These differences could not be ascribed to differences in viability of the nematodes or to differences in success of the inoculations. They indicate the presence of different pathotypes or biotypes in different populations of a so-called ‘host race’ and indicate the need for new resistant cultivars to be tested against a range of populations before they are released for general use. Amongst lucerne cultivars tested, Vertus was resistant to some lucerne stem nematode populations and susceptible to others. The supposedly resistant lucerne cultivars Euver and Lifeuil were as susceptible as was Europe. Amongst red clover cultivars tested, Redhead, Kühn, Changins and Mt Calme were susceptible, Britta, Lucrum and Temara were the least resistant, Renova, Rittinova and Quin were intermediate and susceptible to one or more of the populations tested but Norseman and especially Sabtoron were very resistant.     

Genetic Control of Early Embryogenesis in the Red Flour Beetle, Tribolium castaneum

SYNOPSIS. The power of genetic analysis possible with the fruitfly, Drosophila melanogaster, has yielded a detailed understandingof pattern formation controlled by homeotic and segmentationgenes in early embryogenesis. We are studying the genetic regulationof embryogenesis in the red flour beetle, Tribolium castaneum.The dynamic process of germ rudiment formation and sequentialsegmentation exhibited by Tribolium provides a context differentthan Drosophila within which to assess the function of homeoticand segmentation gene homologs. Our analyses of the genes inthe HOM-C suggest many similarities in structure and functionwith the well-characterized Drosophila genes. Abdominal resemblesits Drosophila homolog abdominal-A in functioning to establishsegmental identities in the abdomen, such that in each casemutations result in homeotic transformations to PS6. Althoughthe anterior functional boundary of abdominal-A homologs isprecisely conserved, the domain within which Abdominal is importantextends more posterior than that of abdominal-A. The final expression pattern of the segmentation gene engrailedin Tribolium is identical to Drosophila, suggesting that thesehomologs are involved in a conserved developmental process.However, as expected the development of that pattern is different;engrailed stripes anticipate the formation of each new segmentas they appear sequentially in the elongating germ band. Althoughthe grasshopper even-skipped and fushi tarazu homologs are notapparently important in segmentation, the expression patternsof the Tribolium homologs strongly suggest that they have gaineda role in segmentation in the lineage leading to beetles andflies. Nevertheless, differences between Tribolium and Drosophilain the dynamics of even-skipped expression and the fushi tarazumutant phenotype indicate divergence in the regulation and rolesof these genes.     

Ornithine Decarboxylase and Trypanothione Reductase Genes in Leishmania braziliensis guyanensis

. Ornithine decarboxylase and trypanothione reductase are the key enzymes in polyamine and trypanothione metabolism in kinetoplastids. Using a heterologous Trypanosoma brucei brucei probe for ornithine decarboxylase and a mixed synthetic probe of 29 oligonucleotides for trypanothione reductase, we have detected the putative genes for these enzymes by Southern blot hybridization using genomic DNA of Leishmania braziliensis guyanensis MHOM/SR/80/CUMC I. The trypanothione reductase probe was constructed both from the conserved codon usage of the redox active site for other flavin oxidoreductases over a wide evolutionary scale, and the preferred codon usage for other genes in species of Leishmania .     

Disturbance and the community structure of stream invertebrates: patch-specific effects and the role of refugia

1. We have previously shown that the impact of spates on stream invertebrates may differ among patches separated by distances of metres or less. Here we analyse the species-specific flood responses of larval chironomids and adult and near mature copepods living in different patch types. Four patch types (with eight replicates of each) were compared: the sandy mid-channel, fine sediments around dams, coarse sediments around dams, and dam debris. Additionally, since some fine sediment patches had been shown previously to act as flow refugia while others did not, we also examined species-specific responses in refugium vs. non-refugium fine sediment patches. Detrended correspondence analysis was used to test for changes in assemblage structure (species composition and relative abundance). 2. Species richness was not altered in a predictable manner by floods; the least stable patch types (mid-channel and coarse patches) did not necessarily show reduced species richness during the spate. 3. As indicated by the spread of DCA ordination scores, there was generally a high degree of overlap in the species composition among the four patch types. Nevertheless, copepod species composition and relative abundance were more similar among patch types during the spate than pre-spate. Spates may induce a re-distribution of copepod species among the patch types. Chironomid species composition and relative abundance were no more similar among patch types during the spate than pre- or post-spate. 4. For both chironomids and copepods, species composition and relative abundance (as assessed by DCA ordination scores) in refugium patches changed more in response to the spate than in the non-refugium patches. An influx of individuals from just a few species for each group was responsible for the change in assemblage structure. Thus, despite the fact that our past work has shown that refugia may confer enhanced resistance and resilience of copepod and chironomid assemblages in terms of total faunal abundances, the present work suggests that resistance and resilience of the species composition of the community apparently are no greater in refugium patches than in non-refugium patches.     

Evaluation of assisted colonization strategies under global change for a rare,fire‐dependent plant

As a clear consensus is emerging that habitat for many species will dramatically reduce or shift with climate change, attention is turning to adaptation strategies to address these impacts. Assisted colonization is one such strategy that has been predominantly discussed in terms of the costs of introducing potential competitors into new communities and the benefits of reducing extinction risk. However, the success or failure of assisted colonization will depend on a range of population‐level factors that have not yet been quantitatively evaluated – the quality of the recipient habitat, the number and life stages of translocated individuals, the establishment of translocated individuals in their new habitat and whether the recipient habitat is subject to ongoing threats all will play an important role in population persistence. In this article, we do not take one side or the other in the debate over whether assisted colonization is worthwhile. Rather, we focus on the likelihood that assisted colonization will promote population persistence in the face of climate‐induced distribution changes and altered fire regimes for a rare endemic species. We link a population model with species distribution models to investigate expected changes in populations with climate change, the impact of altered fire regimes on population persistence and how much assisted colonization is necessary to minimize risk of decline in populations of Tecate cypress, a rare endemic tree in the California Floristic Province, a biodiversity hotspot. We show that assisted colonization may be a risk‐minimizing adaptation strategy when there are large source populations that are declining dramatically due to habitat contractions, multiple nearby sites predicted to contain suitable habitat, minimal natural dispersal, high rates of establishment of translocated populations and the absence of nonclimatic threats such as altered disturbance regimes. However, when serious ongoing threats exist, assisted colonization is ineffective.     

Stem canker (Rhizoctonia solani) on five early and seven maincrop potato cultivars. II Effects on growth and yield

In 1983 and 1984, potato seed tubers of five early and seven maincrop cultivars were inoculated with cultures of Rhizoctonia solani during planting in field experiments to simulate severe seed infection. The size of foliage was assessed during June-August and tuber yields recorded during growth and at harvest in October. Stem canker delayed shoot emergence, decreased the number and length of stems and caused increased variation in stem length; these effects were greatest with Maris Peer and Arran Comet (early cultivars) and King Edward and Pentland Squire (maincrop cultivars). Total weight of foliage was decreased, especially with earlies, dry matter of stems increased and the proportion of foliage on lateral stems increased. With the early cultivars, tuber yield from sprouted Maris Peer seed 11 wk after planting in 1983 was decreased by 24%, and 13 wk after planting in 1984 yields were decreased by 42% (Maris Peer), 40% (Ulster Sceptre), 34% (Estima), 30% (Arran Comet) and 17% (Ulster Prince) with sprouted seed and by 20, 29, 53, 39 and 28% respectively with non-sprouted seed. Decrease in total yield at harvest in October averaged 13% with sprouted seed and 10% with non-sprouted seed. In all cultivars the weight of small tubers was decreased and with Estima the weight of large tubers was increased. Tuber bulking was also delayed with all maincrop cultivars and at harvest yields from sprouted King Edward seed were decreased by 13% in 1983 and by 16% (sprouted seed) and 23% (non-sprouted seed) in 1984; yields of Pentland Squire were decreased by 5, 16 and 21% respectively. Yield losses with other cultivars ranged from 5–13% with sprouted seed and 0–16% with non-sprouted seed. The yields of small tubers were decreased with all cultivars and yields of large tubers were increased with Pentland Squire, Pentland Crown and Cara.     

Hippuric acid and benzoic acid inhibition of urine derived N2O emissions from soil

Atmospheric concentrations of the greenhouse gas nitrous oxide (N₂O) have continued to rise since the advent of the industrial era, largely because of the increase in agricultural land use. The urine deposited by grazing ruminant animals is a major global source of agricultural N₂O. With the first commitment period for reducing greenhouse gas emissions under the Kyoto Protocol now underway, mitigation options for ruminant urine N₂O emissions are urgently needed. Recent studies showed that increasing the urinary concentration of the minor urine constituent hippuric acid resulted in reduced emissions of N₂O from a sandy soil treated with synthetic bovine urine, due to a reduction in denitrification. A similar effect was seen when benzoic acid, a product of hippuric acid hydrolysis, was used. This current laboratory experiment aimed to investigate these effects using real cow urine for the first time. Increased concentrations of hippuric acid or benzoic acid in the urine led to reduction of N₂O emissions by 65% (from 17% to <6% N applied), with no difference between the two acid treatments. Ammonia volatilization did not increase significantly with increased hippuric acid or benzoic acid concentrations in the urine applied. Therefore, there was a net reduction in gaseous N loss from the soil with higher urinary concentrations of both hippuric acid and benzoic acid. The results show that elevating hippuric acid in the urine had a marked negative effect on both nitrification and denitrification rates and on subsequent N₂O fluxes. This study indicates the potential for developing a novel mitigation strategy based on manipulation of urine composition through ruminant diet.     

Effects of Nutrient Factors, Water-Supply, and Growth-Regulating Substances on the Vegetative Growth Pattern of Peas and their Relationship to the Node of First Flower

Peas were grown at two levels each of nutrient- and water-supply:some were pretreated with gibberellic acid (GA), N-dimethylaminosuccinamicacid (B995), or N-formylhydroxyaminoacetic acid (NFHAA). Alltreatments had some effect on internode extension and leaf growth.B995 and NFHAA acted as general inhibitors of growth, ratherthan suppressing growth of particular organs: their effect inlowering the number of the first flowering node (F) might berelated to this inhibition. Water-supply had a greater effecton the rate of node formation than had nutrient-supply, B995,or NFHAA, but had no effect on F: in this case there is no clearrelationship between vegetative growth and flowering. Theseresults are briefly discussed in relation to earlier work.