Plants were regenerated from cultured excised leaf segments of monohaploid (2n = x = 12) and diphaloid (2n = 2x = 24) potato (Solanum tuberosum L.) and a sample has been studied cytologically. In the case of monohaploids, a single leaf regeneration cycle resulted in almost total recovery of doubled monohaploid plants (2n = 2x = 24), whilst 50% of the plants regenerated from doubled monohaploid leaves had doubled again to the doubled double monohaploid (or homozygous tetraploid, 2n = 4x --48) level. Regeneration from dihaploid leaf pieces also gave a good proportion (60%) of doubled genotypes. Very few mixoploids and very few aneuploids were found. These results, together with the general applicability of the method to a large number of potato eultivars, suggest that it can be used as a simple and reliable method of obtaining homozygous tetraploid potatoes.
The response of four spring-sown combinable arable crops [Pisum sativum (peas), Hordeum vulgare (barley), Vicia faba (beans). Brassica napus (oilseed rape)] to competition from cultivated oats {Avena sativa), mimicking wild-oats (Avena fatua), was studied in three field experiments (1989-91). Reductions in crop growth and yield per oat plant m~^ were calculated from regressions of weight (yield) against oat numbers. Competitive effects from the oats were greatest in 1991, the year with the highest rainfall. The oats had least effect on the barley and rape (yield loss per oat plant m"''^=0-2-3%), and most effect on the peas and beans (0 34-718%). Samples harvested during the summer showed how the crops' responses to competition from oats changed as they matured. Data was also col lected on the effects of the crops on the oats. The results are discussed in relation to the development of threshold-based systems of weed management. La reponse de quatre cultures de printemps d la competition des mauvaises herbesLa reponse de quatre cultures de printemps {Pisum sativum (pois), Hordeum vulgare (orge), Vicia faba (feveroUe), Brassica napus (colza)] a la competition de Tavoine cultivee {Avenasativa) prise comme modele de folie avoine {Avena fatua) a ete etudiee lors de trois experimentations au champ (1989-91). Les reductions de croissance et de rendement des plantes cultivees en fonction de la densite de I'avoine ont €t€ calculees par des regressions entre le poids (rendement) et le nombre de pieds d'avoine m"^. L'effet competitif de I'avoine fut le plus important en 1991, pedode ou les precipitations furent les plus elevees. L'effet de I'avoine 6tait le moins important sur I'orge et le colza (la perte de rendement par pied d'avoine m"'^ etait comprise entre 0 et 2,3%) et le plus important sur le pois et la feveroUe (034-7,18%). Des echantillons recoltes pendant l'ete ont montre comment les reponses des plantes cultivees a la competition de 1 'avoine se sont modif iees au cours de la maturation. Des donnees sur les effets des plantes cultivees sur les avoines ont aussi ete recueillies.Les resultats sont discutes en relation avec le developpement de systemes de lutte contre les mauvaises herbes bases sur les seuils de nuisi-bUite. Unkrautkonkurrenz in vier SommerkulturenDie Konkurrenz von Saat-Hafer {Avena sativa) als Modell fur Flag-Hafer {Avena fatua) wurde in 4 Sommerkulturen [Erbse {Pisum sativum), Gerste {Hordeum vulgare), Acker-Bohne {Vicia faba) und Raps {Brassica napus)\ in 3 Freilandversuchen (1989-91) untersucht. Die Wachtumsund Ertragsreduktion je nach der Hafer-Dichte wurde nach der Gewichts-bzw. ErtragseinbuBe berechnet. Die Konkurrenz durch den Hafer war 1991, dem Jahr mit dem hochsten Niederschlag, am groBten; auf Gerste und Raps war sie am geringsten (0 bis 2,3 % Ertragsverlust pro Hafer-Pflanze m"-^), auf Erbse und Acker-Bohne (0,34 bis 7,18 %) am starksten. Durch Messungen der Biomasse wahrend der Vegetationsperiode 138 P. J. W. Lutman et al. kotinte gezeigt werden, wie sich die Konkurrenz durch den Hafe...
The promoter region of the Agrobacterium tumefaciens T-cyt gene was linked in a translational fusion to the coding DNA of the reporter gene uidA (for beta-glucuronidase or GUS protein; EC 3.2.1.31) and to nos 3' flanking DNA. The chimaeric gene was introduced by Agrobacterium transformation into potato (Solanum tuberosum L. cv. Désirée). In nine transgenic lines, the average GUS levels were highest in extracts from stems and roots of in vitro grown plants (ca. 11,000 GUS activity units per pmol MU per mg protein per min) but lower in leaves of the in vitro grown plants (ca. 7000 units). GUS activity was intermediate in stems and roots of plants grown in soil as well as in in vitro crown galls (ca. 3000 units). Activity was low in tubers, irrespective of whether these developed in vitro or in soil (both ca. 100 units), and lowest of all in leaves of soil-grown plants (ca. 10-15 units). However, in shoot cultures reestablished from soil-grown plants, GUS activity in the leaves increased to that determined in the original shoot cultures. Hence, plant culture conditions strongly influenced the expression of the T-cyt-uidA-nos gene. In particular, it was silenced in leaves of soil-grown plants. The results are compared with previous analyses of the promoter region of the wild-type T-cyt gene and with the growth properties of a large number of crown gall cell lines and crown-gall-derived plants, including over forty S. tuberosum cv. Désirée cell lines isolated in the present study that were transformed with the wild-type T-cyt gene and six promoter-mutated derivatives. A number of implications are discussed for crown gall formation and for control of expression of plant genes which contain Activator or G-box type 5' expression control sequences.
Sixteen experiments have investigated alternative methods of predicting the competitive effects of a simulated weed (oats) on the yields of spring barley, spring oilseed rape (canola), peas, spring field (faba) beans and flax. The experiments were designed to discover whether early postemergence assessments of crop and weed vigor would achieve more reliable prediction of yield loss than weed density. Weed density (plants m−2) was a very variable predictor of yield loss. The standardized ranges (range/mean) of values over 3 to 4 years of data for the five crops, in the densities causing 5% yield loss, were between 1.14 and 2.59. Predictions based on the relative dry weight of crop and oats (oat dwt/(oat dwt + crop dwt)), assessed while the plants were still small, achieved more reliable predictions, as the standardized ranges were between 0.10 and 1.86. In three of the experiments, predictions based on relative dry weights were compared to similarly timed predictions based on measurements of relative leaf area and of ground cover, assessed subjectively (by eye) and photographically. Subjective and objective (photographic) assessments of cover achieved similar predictions of yield loss, indicating that visual assessments could be a viable tool to assess the potential competitive effects of weeds.
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