DRYING AND CONDITIONING OF DIRECT–HARVESTED TIMOTHY SEED

An experiment is described in which S48 timothy seed, direct harvested at 3 stages of ripeness, was dried in layers 6 in. deep, at air temperatures from 75–135° F, immediately after harvest and after periods of from 1 to 3 days conditioning with cold air. Germination results for non-conditioned seed showed good agreement with those obtained in the previous year. The quality of seed hulled during threshing was inferior to that remaining unhulled after threshing, but the latter was more susceptible to high air temperature during drying. The relationship of the seed obtained in this experiment to commercial seed is discussed and a scheme for the practical application of the results will be presented in a subsequent paper.     

Genetic male sterility in wheat

The occurrence of genetic male sterility and development of highly sterile lines have been reported. The male sterility was not accompanied by any visible chromosomal aberration. It behaved as recessive and was governed by multiple factors. It was hypothesised that three major genes with additive effect were operating to produce highly sterile forms while less sterile forms would be dependent on one or two genes. The expression of male sterility was also influenced by modifying factors and environments.     

Non-random segregation of gene I for Fusarium resistance in the tomato

Significant deviations from the ratios expected, according to the single dominant gene hypothesis for resistance to Fusarium wilt, were found in crosses involving several susceptible and resistant tomato lines. The susceptible class was the deficient one in F₂ and F₃ populations, as well as in backcrosses in which the heterozygotic resistant F₁ served as the male parent. The reciprocal backcross, with the F₁ as the female and the homozygous susceptible as the male, gave segregations better approximating or consistent with the single gene hypothesis. Reciprocal F₁ and F₂ generations did not give any evidence of cytoplasmic effects.The results were interpreted assuming preferential fertilization of ovules by pollen grains carrying the dominant I allele for resistance.The practical implications of the phenomenon of preferential fertilization in breeding for Fusarium resistance are discussed.     

The breeding systems and some interspecific relations of a number of African Trifolium spp.

The breeding systems of 12 species and varieties of Trifolium from Africa were investigated. One annual and the three perennial species were allogamous and self-incompatible, the other annuals were autogamous.The effect of temperature on pollen germination and growth was variable. In some species high temperatures (30°C) adversely affected pollen germination and low temperatures (20°C) in others. A high humidity (93–98% R.H.) was essential for good pollen germination and growth.Approach grafts indicated that these species were closely related, however, this method of grafting may not be as reliable as the cleft graft for assessing species relations. From hybridization attempts between seven species, it appears that some interspecific hybrids may be possible within this group.     

The characteristics of European,Mediterranean and other populations of white clover (Trifolium repens L.)

Indigenous populations of white clover (Trifolium repens L) collected from Europe, the Mediterranean area, as well as other parts of the world have been grown as spaced plants at Aberystwyth. Data were collected on various morphological characters, green weight and leaf marks.Leaflet length, width, area, plant height and green weight were all strongly correlated, but not the flowering date or leaflet shape (= ratio length/width).The mean leaflet size of Mediterranean populations (the supposed centre of origin) was very variable, and decreased northwards. All British populations were uniformly small leaved.Most of the populations were much less vigorous than the bred control varieties and only a few equalled them. Nevertheless some of the introductions exhibited seasonal growth patterns, especially growth into the autumn, and large leaves that could be usefully incorporated in improved varieties. Populations originating one step back towards the centre of origin will probably be the most useful when immediate adaptation is the aim.     

The measurement of stem toughness in marrow-stem kale using a simple laboratory penetrometer

The construction and use of a variable force penetrometer for measuring the woodiness of kale stems is described.The force required to cause penetration of the probe through the xylem tissue was found to bear a close relationship to estimates of quality based on in vitro digestibility determinations, crude fibre content and visual assessment of lignification in stained transverse sections of stems.     

III. Buchbesprechungen

Ohne Zusammenfassung     

THE EFFECT OF THE BIPYRIDYL HERBICIDES ON HILL COMMUNITIES AND THEIR ROLE IN THE IMPROVEMENT OF HILL GRAZING

The improvement of hill land is important to the national economy of the United Kingdom. An increase in the amount of enclosed productive land results in a greater stock-carrying capacity of a hill farm. Improvement is not always possible by conventional implements, and herbicides are being used to kill the old sward. The bipyridyl herbicides offer a means of destroying or modifying the indigenous vegetation. The application of low doses of paraquat or diquat to an association containing Molinia caerulea, Nardus sfricta and Festuca avina resulted in a change in equilibrium in favour of the fescues. The application of 2 lb paraquat per acre practically eliminates all grass species in a sward and it is then possible to establish desirable pasture species after lightly cultivating the dead surface litter.     

THE EFFECT OF FERTILIZER NITROGEN AND FREQUENCY OF DEFOLIATION ON YIELD OF GRASSLAND HERBAGE

The effects of 4 levels of applied nitrogen, ranging from nil to a maximum of 417 lb N/ acre/annum, in all combinations with 3 frequencies of defoliation, ranging from 2 to a maximum of 10 cuts per annum, on herbage production from a perennial ryegrass/ timothy/meadow fescue/white clover sward were measured. These treatments were operative for 2J years, and in a subsequent year the residual effect of cutting frequency was tested. Dry-matter yields of total herbage and of the clover fraction are quoted, together with N yields of total herbage. Yield response to N was higher than in some other experiments in the U. K. Cutting frequency had a very large effect and, in general, the longer the interval between cuts, the higher was the dry-matter (though not the N) yield. There was a marked interaction between cutting frequency and level of N: at the high cutting frequency, dry-matter yield increased linearly with increasing level of N; at the medium frequency, response tended to fall off at the highest level of N; at the low frequency, yield declined with increasing level of N beyond 139 lb N per acre per anum.     

Experiments on the germination of potato seeds. II

Summary The experiments reported fall into three groups: experiments on techniques of extraction and testing that reveal the maximal germination of which seed is capable; experiments on dormancy; and experiments on longevity. Dormancy is present in various degrees in most fresh potato seeds; it is preserved by dry or cool storage and broken by the application of gibberellic acid. Estimates of longevity vary widely from a few to many years, depending on plant material and storage conditions. A general review of the biology of potato seeds is presented in 4.Discussion.

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Zusammenfassung Einige Kartoffelbeeren (warscheinlich die meisten) sind im Alter von sechs Wochen reif. Samen von jüngeren Beeren zeigen eine herabgesetzte Lebensf?higkeit und eine kürzere Keimruhe-periode (Tab. 1). Mit Hilfe einer Mischmachine k?nnen die Samen auf sichere Art gewonnen werden, wenn auch dabei einige Samenschalen zerbrochen werden. Für Keimversuche eignen sich Petrischalen, die mit feuchtem Filterpapier ausgelegt und unter Licht bei ungef?hr 20 C gehalten werden; Schaumgummi kann ebenfalls verwendet werden, nicht aber Fliesspapier. Kleine Samenk?rner haben eine verminderte Lebensf?higkeit. Bei Samen, die sich nicht mehr im Stadium der Keimruhe befinden, wird die Keimung durch Dunkelheit etwas gehemmt (Abb. 1). Die meisten Kartoffelsamen sind noch im Zustand der Keimruhe, wenn sie aus den Beeren gewonnen werden. Die Keimung von Proben nach vier Wochen ergibt ein umgekehrtes Mass für die Keimruhe, vorausgesetzt dass die Muster wie oben erw?hnt behandelt werden. Die Keimruhe in heterogenen Samenmustern von diploiden und tetraploiden Gew?chsen nahm in 6 Monaten merklich ab, doch verschwand sie auch nach 18 monatiger luftiger Lagerung nicht vollst?ndig (Abb. 2) Bei Versuchen, die Keimruhe zu unterbrechen, blieben verschiedene physikalische Vorbehandlungen wirkungslos; Sch?len war teilweise. Gibberellins?ure sogar sehr wirksam. Gibberellins?ure, in suboptimaler Menge angewendet, erzeugte mit Cystein synergistische Wechselwirkung (Tab. 2, 3 und 6). Licht begünstigt das Heraustreten aus dem Zustand der Keimruhe und hat, zusammen mit chemischen Behandlungen, komplexe Wechsel-wirkungen zur Folge (Tab. 3). Die Aufbewahrung von Samen w?hrend 8 Monate unter kalten oder trockenen Lagerungsbedingungen verz?gert das Erwachen aus dem Ruhezustand, und trockene Lagerung scheint die Keimruhe sogar zu verst?rken (Tab. 4). Das Auswechseln des als Keimmedium gebrauchten Filterpapiers f?rdert die Keimung ruhender Samen (Abb. 3); dies deutet auf das Vorhandensein eines wasserl?slichen Hemmstoffes, aber die Anstrengungen zu Identifizierung endigten nur in der Feststellung, dass in allen geprüften Samen unspezifische Hemmstoffe vorhanden waren (Tab. 5). Es gibt keinen Beweis dafür, dass phenolische Stoffe für den Zustand der Keimruhe ausschlaggebend sind. Die Keimf?higkeit von luftig aufbewahrten Samenmustern von Wildarten dauerte 6–8 Jahre, nach 11–12 Jahren war sie nur noch gering (Tab. 7). Einige alte Samenmuster zeigten eine h?chst unregelm?ssige “sekund?re Keimruhe” unbekannter Natur. Eine übersicht bezüglich der Korngr?sse von Wildkartoffelsamen ergab eine Schwankung zwischen 22 und 96 mg pro 100 Samen. Die Unterschiede sind nicht fest an die Zahl der Erbs?tze oder die Artzugeh?rigkeit gebunden. Ein allgemeiner überblick über die Biologie der Kartoffelsamen wird in der Diskussion geboten.

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Résumé Certaines baies de pomme de terre (la plupart, probablement) sont m?res à l'age de six semaines, et les graines provenant de baies plus jeunes présentent une certaine réduction de la viabilité et de la dormance (Tableau 1). Les graines peuvent être extraites sans risque au moyen d'un malaxeur, bien qu'une certaine proportion ait le tégument endommagé par l'opération. Pour les tests de germination, des bo?tes de Pétri contenant du papier-filtre humide, conservées à la lumière à 20 C environ donnent satisfaction. Le plastiquemousse convient également comme milieu de germination, mais le papier buvard n'est pas approprié. Les graines de petite dimension se révèlent moins viables. La germination de graines non dormantes est légèrement inhibée par l'obscurité (fig. 1). La plupart des graines de pomme de terre sont en état de dormance au moment où elle sont récoltées, et la germination d'échantillons à quatre semaines suivant le procédé décrit ci-dessus fournit une mesure inverse de la dormance. La dormance de lots hétérogènes de graines de variétés cultivées diplo?des et tétraplo?des diminuait nettement en 6 mois, mais il en restait encore des traces jusque après 18 mois de conservation en plein air (fig. 2). Dans les essais de suppression de l'état de dormance, différents traitements physiques restèrent sans effet, l'enlèvement du tégument avait un effet partiel et l'administration d'acide gibérellique se révéla très efficace; ce dernier, administré à une dose inférieure à la dose optimale, produisait un effet synergique avec la cystéinc (Tableaux 2, 3 et 6). La lumière hate la fin de la dormance et présente des interactions complexes avec les traitements chimiques (Tableau 3). Le stockage des semences pendant huit mois dans un milieu froid ou sec retarde la fin de la dormance, et la sécheresse semble même rendre la dormance plus profonde pendant cette période (Tableau 4). Le renouvellement du papier-filtre servant de milieu de germination stimule la germination des graines en dormance (Fig. 3); cela implique la présence d'un substance inhibitrice hydrosoluble, mais les efforts tendant à l'identification de cette substance ont uniquement permis de démontrer la précence d'une ou de plusieurs, substances inhibitrices non specifiques dans toutes les semences étudiées (Tableau 5). Rien ne porte à croire que des corps phénoliques soient responsables de la dormance. La durée de vie des échantillons d'espèces sauvages conservées en plein air se trouva être de 6 à 8 ans, et on ne trouva que peu de faculté germinative après 11 à 12 ans (Tableau 7). Il existe très irrégulièrement une “seconde dormance” de nature inconnue dans certains lots de semences anciens. Un aper?u des grosseurs des graines de pommes de terre sauvages présente une variation de 22 à 96 mg les 100 graines, cette variabilité n'étant pas liée systématiquement à la plo?die ni à la taxonomie. La Discussion donne un aper?u général de la biologie des graines de pomme de terre.

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Continuation of —Fortserzung von —contiuation de: Europ. Potato J., Vol. 6 (1963) No. 1 (March) 45–60.