Dormancy in Rice Seed: IV. VARIETAL RESPONSES TO STORAGE AND GERMINATION TEMPERATURES

Serial germination tests were carried out on dormant seeds ofsix rice varieties (four varieties of Oryza sativa L. and twovarieties of O. glaberrima Steud.) stored at several differentconstant temperatures within the range 27° C to 57°C. Probit analyses of the results were carried out to determmethe mean dormancy period for each variety at each temperature.Regression lines fitted to these data showed that there is adirect negative relationship between storage temperature andlog mean dormancy period over the range 27° C to 47°C, thus confirming a previous result obtained on a single variety.At 7° C there were indications of a slight departure fromthis relationship in that the mean dormancy periods at thistemperature were slightly longer than would have been predictedby extrapolation of the regressions calculated from the resultsobtained at lower temperatures. In all cases where the resultswere unambiguous (i.e. in all the sativa varieties and one ofthe glaberrima varieties) a constant Q₁₀ of 3.13 was shown forthe rate of loss of dormancy over the range of storage temperaturesfrom 27° C to 47° C. In the remaining glaberrima variety,where the results were less reliable, a Q₁₀ of 2.54 was found. Germination tests on all varieties were carried out at 32°C, but in the case of one sativa variety germination tests forall storage treatments were also duplicated at 27° C. Thisinvestigation showed that, in contrast to the effect of storagetemperature, the higher temperature during the germination testconsistently resulted in a lower percentage germination. Inaddition the results demonstrated that there is no interactionbetween storage temperature and germination temperature: consequentlythe storage-temperature coefficient has the same value irrespectiveof germination temperature. Some theoretical implications ofthe results are discussed.     

VALSA EUGENIAE IN RELATION TO THE SUDDEN-DEATH DISEASE OF THE CLOVE TREE (EUGENIA AROMATICA)

The sudden-death disease of the clove tree is invariably associated with the fungus Valsa eugeniae. The pathogenicity of this fungus has been investigated experimentally, and it has been shown that it is a primary parasite on mature clove trees, that saplings are resistant to it, and that seedlings are immune. It has been experimentally demonstrated that water-borne spores of the fungus can invade the absorbing and the fibrous roots of the clove tree. The slow-decline disease, which affects clove saplings only, is associated with a slow and progressive root-rot over a period of many years. Valsa is also invariably associated with this disease, which occurs only in areas which have been replanted after the previous stand has been killed by sudden death. It is thought that slow decline is the symptom-expression of Valsa attack on young trees when these still retain some measure of juvenile resistance to it.     

Anatomical and Biochemical Changes Associated with the Induction of Oilseed Rape (Brassica napus) Pod Dehiscence by Dasineura brassicae (Winn.)

Dehiscence of pods at an early stage of development is a characteristicof oilseed rape pods damaged by Dasineura brassicae (pod midge).Anatomical examination of pods exhibiting symptoms of infestationrevealed a loss of cohesion between intact cells of the dehiscencezone, a narrow tissue of thin-walled cells present between thevalve margins. Determination of hydrolytic enzyme activity inpericarp tissues of damaged siliquae showed localized enhancementof both polygalacturonase (EC 3.2.1.15 [EC] ) and cellulase (ß1,4 glucanase, EC 3.1.2.4 [EC] ) activity, positionally consistent withthese factors being responsible for the observed cell wall degradation.Mechanistic similarities of midge-induced and maturation-associatedpod dehiscence are discussed. Oilseed rape, Brassica napus L. cv., Bienvenu, pod shatter, pod midge, Dasineura brassicae (Winn.), cellulase, polygalacturonase     

The Development of Desiccation-tolerance and Maximum Seed Quality During Seed Maturation in Six Grain Legumes

‘Physiological maturity’, i.e. the time when seedsreach their maximum dry weight during development, occurredwhen maturation drying on the parent plant in the field hadreduced seed moisture content to approximately 60 per cent infaba bean (Vicia faba L.), lentil (Lens culinaris Medic.), chickpea(Cicer arietinum L.), white lupin (Lupinus albus L.), soya bean(Glycine max [L.] Merr.) and pea (Pisum sativum L.) The onsetof desiccation-tolerance, i.e. the ability of seeds to germinatefollowing harvest and rapid artificial drying, coincided withphysiological maturity, except in pea where it occurred a littleearlier at about 70 per cent moisture content. Maximum seedquality as determined by maximum viability, minimum seedlingabnormalities and maximum seedling size occurred in pea, chickpeaand lupin when seeds were harvested for rapid drying at physiologicalmaturity; but for maximum seed quality in the other speciesmaturation drying had to proceed further - to about 45 per centmoisture content in soya bean and to about 30 per cent moisturecontent in lentil and faba bean seed crops. Much of this variationamongst the six species, however, was due to differences inthe variation in maturity within each seed crop. Results forindividual pods showed that peak maturity, i.e. maximum seedquality following harvest and rapid artificial drying, was achievedin all six species once maturation drying had reduced the moisturecontent of the seeds to 45–50 per cent. In pea, faba beanand soya bean there was a substantial decline in viability andan increase in seedling abnormalities when harvest was delayedbeyond the optimal moisture content for harvest.     

Local adaptation of Ruellia nudiflora (Acanthaceae) to biotic counterparts: complex scenarios revealed when two herbivore guilds are considered

This study evaluated whether the herb Ruellia nudiflora is locally adapted to a specialist insect seed predator (SP) and insect folivores, and if plant local adaptation (LA) to the former is more likely. A reciprocal transplant experiment was conducted using three sites in Yucatan (Mexico) (n = 864 plants). A third of the plants of each origin were placed at each site, and we recorded the following during a 9‐month period: fruit number, leaf damage, and fruits attacked by SP. Results indicated lack of plant LA for all the variables measured. Instead, seed predation was c. 100% greater for native plants at one study site, suggesting insect LA or plant maladaptation; folivory was homogeneous across sites/origins. Based on these results, we discuss differences in the potential each herbivore guild has to promote plant LA, as well as divergent evolutionary outcomes of plant–herbivore interactions across sites.     

Studies on the Effect of Sulphur Dioxide on Perennial Ryegrass (Lolium perenneL.): I. CHARACTERISTICS OF FUMIGATION SYSTEM AND PRELIMINARY EXPERIMENTS

The characteristics of a wind tunnel fumigation system in whichplants can be exposed to air pollutants under controlled conditionsover prolonged time periods and at near ambient wind speedsare described. Preliminary experiments exposing perennial ryegrass(Lolium perenne L.) to 650, 700, and 2600 µg SO₂ m^–3showed (i) the consistency of performance of the system and(ii) the lack of correlation in relative response of individualclones to acute and chronic fumigation. The results obtainedare compared with those of other research groups.     

Auxin and the Control of Ethylene Production during the Development and Senescence of Leaves and Fruits

The levels of endogenous IAA and the production of ethylenehave been followed during maturation and senescence in herbaceous(Phaseolus vulgaris, Ecballium elaterium) and deciduous (Prunusserrulata) leaves. Comparisons have been made with similar estimationsduring ripening of a herbaceous fruit. Ecballium elaterium.Whereas a correlation can be made between auxin content andethylene production in immature tissues, no such relationshipexists in senescing or ripening tissues where ethylene productionappears to be independent of the total endogenous auxin content.Both IAA and fusicoccin enhance ethylene production in developingleaves but fail to do so in senescent tissues. A mechanism forthe regulation of the rate of ethylene biosynthesis is described.This involves modifications in the release from a membrane-boundor membrane-enclosed compartment of cofactor(s) essential toone or more steps in the pathway. The mechanism accommodatesobserved normal and senescence-related rates of ethylene production.