EFFECTS OF DESICCATION AND TEMPERATURE ON SURVIVAL OF CYPERUS ESCULENTUS TUBERS AND CYNODON DACTYLON RHIZOMES

Summary. The effects of all combinations of five desiccation treatments, two temperatures and three durations of desiccation on the survival of Cyperus esculentus tubers and two-node Cynodon dactylon rhizome fragments were examined in laboratory and glasshouse experiments.
Cyperus esculentus tuber survival was greater at 22°C than at 4°C. Duration of desiccation did not influence tuber survival, except at the lower temperature.
Survival of Cynodon dactylon rhizome fragments was greatly influenced by desiccation treatment, duration of desiccation and the interaction of these two factors. No buds survived when rhizomes reached 50% of their original weight, indicating good tolerance of desiccation since the original dry-matter content of rhizomes in this experiment was 41·2%.     

GRASSLAND RESEARCH ON BLANKET PEAT IN IRELAND

The results from 10 years of grassland research at the Peatland Experimental Station, Glenamoy, are summarized.
Grass and legume species were introduced by surface seeding, without cultivation or by direct seeding after rotavation, depending on the specific situation. The rate of establishment was dependent on pretreatment and the management of grazing animals before and after sowing.
The most suitable species were Trifolium repens, Lolium perenne, Festuca arumlinacea, Festuca rubra and Holcus lanatus .
A level of fertility suited to the introduced species must be reached initially and subsequently maintained. The requirements (per/ac) for Ca, P, K, N, Cu and Co were: 2240 lb (1016 kg) ground limestone, 36 lb (16 kg) P, 112 lb (51 kg) K, 20 lb (9 kg) N, 20 lb (9 kg) CuSO₄ and 2 lb (0–91 kg) CoSO₄ at sowing, with 27 lb (12–25 kg) P and 56 lb (254 kg) K annually.
Dry–matter yields of 6000 lb/ac (6720 kg/ha) were obtained from grass–clover swards without fertilizer N, and approximately twice this quantity where 400 lb N/ac (448 kg/ha) had been applied annually. A liveweight gain of 526 lb/ac (589–12 kg/ha) and a starch equivalent output of 2946 lb (3299–5 kg) were obtained with sheep. The relationship between these results and those on peat soils abroad are discussed.     

SOME SELECTIVE EFFECTS OPERATING ON WHITE- AND RED-CLOVER IN SWARDS

Populations of white- and red-clover were examined after they had been grown for several years in grass/clover swards. The method of sowing, nitrogen application, management and season affected the ratio of very similar clover cultivars differing specifically in the leaf mark when sown in the same mixture. The companion grass also infiuenced the proportion of legume cultivars in the sward. In addition, the mean date of emergence of a single cultivar of broad-red clover was affected by management.     

Some Aspects of the Growth and Spread of Fire in the Open

This paper describes some recent experimental and theoreticalwork on the growth and spread of fire in the open and discussessome examples of field data in terms of the theoretical calculationspresented. The lengths of flames from laboratory fires have been relatedto the size and rate of burning of the fuel by formulae derivedfrom a simplified dimensional analysis. The effects of a windblowing across a long fuel bed on the length and orientationof flames are also described. The scaling laws for flame heightsuggest that in the horizontal spread of fire, heat transferfrom the flames above the fuel bed is important primarily withshallow fuel beds. It is suggested that the main effect of a wind on crib firesis aerodynamic. The wind deflects the advancing fire front fromthe vertical, but perpendicular to this deflected front therate of spread of fire, at least for cribs, is roughly the sameas in still air. However, a theory of spread allowing for heattransfer through the fuel bed and radiation from the flamespredicts that there can be a stable ‘fast‘ spreadas well as a ‘slow’ spread. In ‘fast’spread the flames are thick and control the spread. In ‘slow’ spread radiant heat transfer from theburning zone is usually responsible for the spread. The flamesare thin and of low emissivity. The most important factors determiningthe rate of ‘slow’ spread R are ^pb the bulk densityof the fuel bed and ø the deflection from the verticalof the front of burning fuel which varies with wind speed. Rpb cos ø is approximately constant over a wide rangeof conditions with an order of magnitude of 5–10 mg cm^–2s^–1.     

Nachteilige Wirkungen eines Herbizids auf Gesundheit und Wuchsleistung von Pappeljungpflanzen

Ohne Zusammenfassung     

Prüfung vonSaco undSaco-Kreuzungen auf Resistenz Gegen das S-virus der Kartoffel

Zusammenfassung Die SorteSaco blieb bei allen Versuchen. das S-Virus mit Safteinreibungen zu übertragen, virusfrei. Nach 6 Wochen dauernden Pfropfungen mit S-haltigen Reisern war das Virus jedoch in zwei von 42 Pflanzen zur Vermehrung gelangt und wurde im Nachbau festgestellt. DieSaco-Resistenz wird als hohe Infektionsresistenz gegen das S-Virus bezeichnet. 204 S?mlinge und Klone der KombinationSaco selbst liessen sich ausnahmslos nicht mit dem S-Virus infizieren, gleichgültig, ob Pfropfungen oder Pressafteinreibungen selbst im jüngsten S?mlingsstadium durchgeführt wurden. Der Nachbau war ebenfalls S-frei. Nach den bisherigen Erfahrungen scheint sich die hohe Infektionsresistenz derSaco auf 100% ihrer Selbstungsnachkommenschaft zu vererben. Nur 10% von 704 pfropfinfizierten Klonen aus zwei verschiedenen Kombinationen derSaco mit S-anf?lligem Material brachten einen ganz oder teilweise S-freien Nachbau. Ihr Resistenzgrad war von dem derSaco nicht zu unterscheiden. 86–88% der Klone hatten ausschliesslich S-haltige Nachbaupflanzen. Bei Einreibung von S-haltigem Pressaft auf 6 Wochen alte Pflanzen der gleichen Kombinationen blieb der Nachbau von 34% der Klone ganz oder teilweise S-frei.

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Summary The American varietySaco is commonly assumed to be S-immune. Several attempts to induce infection by sap inoculation failed. Two out of 42 plants on which S-infected scions had been grafted for 6 weeks each yielded one S-infected tuber out of a total of 3. This indicates thatSaco is highly resistant but not immune to infection. Attempts to infect 202Saco selfs by grafting or sap inoculation failed (Table 1); no virus was detected in the tuber progeny. The high level of resistance inSaco seems, therefore, to be transmitted to 100% of the selfed progeny. Tests were made on two families ofSaco pollinated with S-susceptible Max-Planck-Institute clones (49.540/2 and44.1004/5), which possess other resistance and quality characters rendering them particularly suitable for use in European breeding programmes involvingSaco. The method of testing mainly used is shown in Fig. 1: serological tests were done on mature leaves from shoots which had been subjected for 6 weeks to the effects of S-infected scions below them. In addition, tubers from these plants were grown on and the resulting plants tested serologically. 704 clones of 2 families were grafted but only 564 and 75, respectively, formed tubers. The results of S-tests on the tuber progenies, given in Table 2, show that 86–88% of the clones were readily infected but about 10% produced few or no infected tubers and did not behave significantly differently fromSaco. No results were obtained from about 3% of the clones on account of secondary virus infection, early death etc. Sap inoculation of 110 six-week-old F₁ plants produced 36 plants with S-free or partially S-free tuber progenies (Table 3). Sap inoculation of very young seedlings produced only 7.9% healthy plants. We can conclude from the relatively poor transmission of S-resistance to F₁ progenies thatSaco is not an ideal source. The 34% of resistant or partially resistant plants selected by sap inoculation may, however, allow the production of a reasonable amount of breeding material with adequate resistance under field conditions. Howeyer, the faults, agronomic and otherwise, of the F₁ clones suggest that a second breeding step is necessary, i.e.Saco F₁.

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Résumé La variété américaineSaco est réputée être immune au virus S. Nous aussi n’avons trouvé aucune infection par virus S dans différents essais par inoculation de jus, mais à la suite de greffe de scions malades de S durant 6 semaines, deux plantesSaco récoltées étaient infectées de S sur un total de 42 plantes testées. Chacune de ces deux plantes produisaient trois tubercules dont un était infecté, les deux autres étaient libres de S. II résulte de cette expérience que le type de résistance deSaco est la plus haute résistance à l’infection. Les essais d’infection d’autofécondations deSaco par greffes ou transmission de jus ne donnaient aucune multiplication du virus dans 202 plantes (Tableau 1). De même les descendances des tubercules ne montraient pas de virus S. Par conséquent, la haute résistance à l’infection deSaco semble se transmettre à 100% à la descendance autofécondée. Deux familles deSaco pollinisée par des clonesgéniteurs du Max-Planck-Institut (49.540/2 et44.1004/5) furent testées pour la présence du virus S. Ces clones-géniteurs étaient susceptibles au virus S mais possédaient d’autres résistances et des caractères de bonne qualité qui les destinaient à des programmes prometteurs d’amélioration européenne basée surSaco. La technique de test la plus utilisée est montrée dans Fig. 1: des tests sérologiques sont effectués sur des feuilles m?res de branches qui ont poussé durant 6 semaines sous l’influence d’un scion infecté de S placé en-dessous En outre, les tubercules de telles plantes furent plantés et les plantes de la descendance furent également testées sérologiquement. 704 clones des deux familles furent greffés. mais seulement 564 et 75 donnèrent des tubercules. Les résultats de tests S sur les descendances par tubercules sont donnés dans Tableau 2. Coneluant sur la base des descendances par tubercules totalement infectées, 86–88% des clones étaient susceptibles. Environ 10% seulement des clones donnaient des tubercules sains ou quelques tubercules sains. Ces clones étaient catalogués comme hautement ou faiblement résistants et ne montraient aucune diffétence significative avecSaco dans les conditions des essais. Environ 3% des clones ne donnaient aucun résultat à la suite d’infection virologique secondaire, mort précòce, etc. A la suite de la transmission par jus à 110 plantes F₁ à l’age d’environ 6 semaines, 36 plantes donnaient des tubercules totalement ou partiellement libres de virus (Tableau 3). Cependant à la suite de la transmission par jus à de très jeunes plantules, on rècoltait seulement 7,9% de plantes saines. Des résultats relativement pauvres de la transmission de la résistance deSaco à sa descendace F₁ dans des tests de greffe, nous concluons queSaco n’est pas la source idéale de résistance au S dans des programmes d’amélioration. Le taux de quelque 34% de plantes saines à la suite d’inoculation par jus permet néanmoins la production d’une quantité raisonnable de matériel d’amélioration avec résistance suffisante dans les conditions du champ. La faible qualité des clones F₁ semble toutefois exiger une seconde étape d’amélioration, par ex.Saco-F₂.