New Phytologist

BRETAGNOLLE, F.; THOMPSON, J. D.

doi: 10.1111/j.1469-8137.1995.tb03005.xpmid: 33874422

The production of 2n gametes in plants, i.e. gametes with a somatic chromosome number, is considered to be the dominant process involved in the origin of polyploid plants. In this review, we provide a synthesis of current knowledge concerning the production of 2n gametes. Firstly, we describe the different methods used to detect and quantify the production of 2n gametes in plants, which include morphological and flow cytometry screening of the occurrence of 2n pollen, the analysis of crosses among diploid and tetraploid parents and the instigation of micro‐and mega‐sporogenesis. Secondly, the high level of inter‐ and infra‐specific variation in 2n gametes production is described. Thirdly, the various cytological anomalies responsible for the production of 2n gametes are reviewed, with particular reference to the relative genetic consequences of the first and second restitution divisions that give rise to 2n gametes. Fourthly, the significance of 2n gametes in crop plant improvement is discussed, in relation to somatic chromosome doubling to obtain new polyploid varieties. In particular, we compare the genetic and yield consequences of methods based on unilateral and bilateral sexual polyploidization. Finally, we outline how knowledge of the variety of mechanisms involved in 2n gamete production have increased our understanding of the evolutionary significance of polyploidy and the population biology of polyploid plants.

NOOIJ, MARIANNE P.; PAUL, NIGEL D.; AYRES, PETER G.

doi: 10.1111/j.1469-8137.1995.tb03015.xpmid: 33874426

Quantitative variation in susceptibility to infection by the rust Coleosporium tussilaginis, and in reduction in growth owing to the infection, were determined in 30 clonally propagated genotypes of Tussilago farfara sampled from three geographically isolated sites, Arnhem (The Netherlands), Lancaster and Sheffield (both UK). Populations, and genotypes within populations showed no significant variation in intensity of disease after artificial inoculation under ideal conditions with a fungal isolate collected from the Lancaster population. By contrast, significant differences between and within populations were observed after natural secondary infection by spores produced from the artificially inoculated plants. Genotypes differed considerably in the reduction in growth caused by the infection, but this was not correlated with the extent of symptoms shown by the plants. Low resistance was associated with high tolerance, as in the Lancaster and Sheffield populations, while high resistance was associated with low tolerance, as in the Arnhem population. The evolutionary significance of these associations is discussed.

LEMOINE, M. C.; GOLLOTTE, A.; GIANINAZZI‐PEARSON, V.

doi: 10.1111/j.1469-8137.1995.tb03013.xpmid: 33874412

Previous studies showed that cell walls of endomycorrhizal fungi belonging to the Acaulosporaceae and Glomaceae contain β (1–3) glucan polymers as well as chitin. Indirect immunolabelling with monoclonal and polyclonal antibodies has been used to investigate the distribution of these structural polysaccharides in cell walls of Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe and Acaulospora laevis Gerd. & Trappe as they interact with pea and tobacco roots, respectively. The (l‐3) glucans were detected in the walls of external hyphae, and of hyphal coils and intercellular hyphae developing in outer root tissues. The glucan component was alkali‐insoluble but treatment with chitinase resulted in solubilization of most of the β(1–3) glucans from the fungal wall. A decrease in immunolabelling was associated with thinning out of the hyphal wall as the fungi colonized deeper in the host root, and β(1–3) glucans could not be detected in walls of intercellular hyphae or arbuscules in the parenchyma cortical tissue. The molecular configuration of cell walls of G. mosseae and A. laevis is discussed in relation to fungal morphogenesis and the symbiotic state in endomycorrhiza.

PETANIDOU, T.; NIJS, J. C. M.; OOSTERMEIJER, J. G. B.; ELLIS‐ADAM, A. C.

doi: 10.1111/j.1469-8137.1995.tb03019.xpmid: 33874419

The reproductive behaviour of Gentiana pneumonanthe L., a rare plant species in The Netherlands, was studied in a relatively large wet heathland population during summer 1989. The species co‐occurred with the grass Molinia caerulea and co‐flowered with Erica tetralix and Calluna vulgaris. The flowering period lasted from July to October, peaking in late August to late September. Flowers are protandrous. The species appeared to be self‐compatible, but spontaneous self‐pollination was strongly limited. Hand‐crossing and hand‐selfing resulted in the same amount of seed set as in natural pollination. Reproductive success was dramatically reduced late in the season. Pollination was achieved sternotribically by the species Bombus pascuorum, which visited the flowers for nectar. In the study area, three patch types were distinguished: co‐dominated by Erica, by Calluna and Erica, and by Molinia, respectively. Frequency of visits to Gentiana was highest in the Erica‐patch. However, this did not result in a higher seed set. In the Molinia‐patch seed set was reduced. However, in the Molinia‐patch the mean number of ovules was greater than in the others (as high as in plants raised indoors and in cross‐pollinated plants). Fruits from the Calluna‐patch had less ovules than those from the Erica‐patch. We conclude that, in this remnant population, Gentiana is not pollination‐limited. However, it is likely that in the Molinia‐patch geitonogamy is frequent, which may lead to inbreeding depression. The greater number of ovules observed in Molinia‐patches may reflect an excess of nutrients available there, relative to the Calluna‐patch where there may be reduced water availability.

PATIÑO, SANDRA; TYREE, MELVIN T.; HERRE, E. ALLEN

doi: 10.1111/j.1469-8137.1995.tb03016.xpmid: 33874424

Hydraulic parameters were measured in seven species of Fiats (three free‐standing and four hemi‐epiphytic) on stem segments of 3–35 mm in wood diameter. Parameters measured included Kh (water flux per unit pressure gradient), Kh (leaf specific conductivity =Kh per unit leaf area), Ks (specific conductivity =Hh per unit wood cross section), and Hv (Huber value = wood cross section per unit leaf area).

WEST, H. M.

doi: 10.1111/j.1469-8137.1995.tb03014.xpmid: 33874427

The impact of rust infection (Puccinia lagenophorae Cooke) on growth of mycorrhizal and non‐mycorrhizal Senecio vulgaris L. was examined under three levels of phosphorus fertilization. Seeds were then collected from infected and control plants and germination, seed chemistry and offspring vigour were examined. Rust infection did not become established on plants which were phosphorus limited, but on hosts fed with medium or high levels of P, the proportion of total leaf number exhibiting infection was a function of leaf production. Capitula production was decreased by rust infection and increased by mycorrhizal colonization in plants fed with a medium concentration of P. In plants fed with a high P concentration, leaf number was reduced by rust infection of mycorrhizal plants, whilst rust was deleterious to both mycorrhizal and non‐mycorrhizal plants grown with a medium P supply. However, the effects of the rust were less marked in the mycorrhizal plants. Seed production and weight were unaffected by fungal treatments, although percentage germination of the resultant seeds was reduced by maternal mycorrhizal colonization and enhanced in seed from rusted, mycorrhizal plants grown at high soil P. The amount of total C, N and P was also reduced by maternal mycorrhizal infection at high soil P and increased in seeds from rusted, mycorrhizal mothers. Vigour of offspring produced from treated mother plants was influenced by mycorrhizal × phosphorus and rust × phosphorus interactions with respect to bud and leaf numbers. Mycorrhizal infection of mother plants grown with a medium P supply benefited the offspring as increased leaf and bud production was observed, but rusted mothers at the same P level produced offspring with reduced leaf number and potential fecundity.

GLOVER, BEVERLEY J.; ABBOTT, RICHARD J.

doi: 10.1111/j.1469-8137.1995.tb03018.xpmid: 33874421

Primula scotica Hook., a rare Scottish endemic, is threatened with extinction due to habitat destruction. A survey of genetic variability within the species was conducted on five populations from the Orkney islands and nine from the Scottish mainland. Isozyme analysis revealed variation between individuals at only one of 15 enzyme encoding loci examined, while a survey of DNA sequence variation via RAPD analysis revealed no genetic diversity either within or between a subsample of four populations surveyed. Individuals exhibited a ‘fixed’ heterozygous genotype at seven of the enzyme encoding loci, indicating that P. scotica is of allopolyploid origin. Despite the high level of heterozygosity per individual and the biochemical diversity that may stem from it, the species remains restricted to a very specific habitat. Implications for the conservation of the species are considered, including the need for habitat protection.

ARROYO, JUAN; DAFNI, AMOTS

doi: 10.1111/j.1469-8137.1995.tb03017.xpmid: 33874423

Narcissus tazetta shows a genetically‐based discrete polymorphism for style length similar to that well known in heterostylous plants. Plants are either short‐ (S) or long‐styled (1). In Israel, marsh populations are dominated by S plants and hill populations by L plants. Populations differ in size, flowering time and duration, flower orientation, inflorescence display, vegetative reproduction, and pollinators. The main visitors to flowers in marshes are hawkmoths, whereas in the hills they are visited by short‐tongued insects: solitary bees and hoverflies. The pollination efficiency of these insects was investigated by studying foraging behaviour, visit rate, and pollen deposition on stigmas. Our findings are consistent with the hypothesis of lower efficiency of pollination of S flowers by short‐tongued insects, resulting in the exclusion of this morph from the hills. Additionally, we considered the possibility that there might be pollination ecotypes corresponding to the two habitats (marsh and hill) and examined variation in a set of continuous flower traits related to pollination biology. Flower tube length was the only trait showing a distinct difference between the two habitat types. Although the concentration of nectar was not different between habitats, L flowers presented more concentrated nectar than S flowers. Such a difference in nectar concentration may he of adaptive value for the pollination of the L flowers by short‐tongued pollinators in the hills.

SMEULDERS, S. M.; GORISSEN, A.; JOOSTEN, N. N.; VEEN, J. A.

doi: 10.1111/j.1469-8137.1995.tb03008.xpmid: 33874420

Effects of short‐term ozone exposure of mature trees were compared with those of seedlings. Both 25‐yr‐old Douglas firs [Pseudotsuga menziesii (Mirb.) Franco] and 3‐yr‐old Douglas fir seedlings were exposed to 0, 200 and 400 μgm−1ozone for about 1.5 wk and then labelled with 14CO2 to study the effect on net photosynthesis, translocation and partitioning of assimilates.

HELLER, L. I.; SHAW, A. J.; JACOBSON, J. S.

doi: 10.1111/j.1469-8137.1995.tb03009.xpmid: 33874417

Two‐year‐old red spruce (Picea rubens Sarg.), raised from seed collected at five locations from Maine to North Carolina, were exposed in a greenhouse to either sulphuric or nitric acid mist (median pH 2–85). Exposures were performed three times a day, four days a week over an eleven‐week period during the growing season. Each exposure consisted of 4 h of misting followed by a 3.75 h drying period. Immediately before each drying period, acidic droplets were either left to dry directly on the foliage or were removed by a 15 min deionized water (diw) rinse.