Field evaluation of resistance to black bean aphid, Aphis fabae, in close relatives of the Faba bean, Vicia faba

A field assessment of 26 accessions of Vicia narbonensis and three of V. johannis confirmed previous laboratory studies demonstrating higher levels of resistance to Aphis fabae in these two wild species compared to the closely related crop, Vicia faba. Accessions of V. johannis were significantly more resistant than most accessions of V. narbonensis for all resistance indices measured except survival of aphid nymphs. Plant growth stage significantly affected levels of resistance in both Vicia species, resistance being moderate at pre-bud stage, decreasing on flowering and rising again at pod fill and onset of leaf senescence. Significant intraspecific variability in aphid resistance was found only within the 26 accessions of V. narbonensis, var. serratifolia being more resistant than var. narbonensis. Possible resistance factors and the agronomic potential of these two wild relatives of Faba bean are considered.     

A New Generalized Logistic Sigmoid Growth Equation Compared with the Richards Growth Equation

A new sigmoid growth equation is presented for curve-fitting,analysis and simulation of growth curves. Like the logisticgrowth equation, it increases monotonically, with both upperand lower asymptotes. Like the Richards growth equation, itcan have its maximum slope at any value between its minimumand maximum. The new sigmoid equation is unique because it alwaystends towards exponential growth at small sizes or low densities,unlike the Richards equation, which only has this characteristicin part of its range. The new sigmoid equation is thereforeuniquely suitable for circumstances in which growth at smallsizes or low densities is expected to be approximately exponential,and the maximum slope of the growth curve can be at any value.Eleven widely different sigmoid curves were constructed withan exponential form at low values, using an independent algorithm.Sets of 100 variations of sequences of 20 points along eachcurve were created by adding random errors. In general, thenew sigmoid equation fitted the sequences of points as closelyas the original curves that they were generated from. The newsigmoid equation always gave closer fits and more accurate estimatesof the characteristics of the 11 original sigmoid curves thanthe Richards equation. The Richards equation could not estimatethe maximum intrinsic rate of increase (relative growth rate)of several of the curves. Both equations tended to estimatethat points of inflexion were closer to half the maximum sizethan was actually the case; the Richards equation underestimatedasymmetry by more than the new sigmoid equation. When the twoequations were compared by fitting to the example dataset thatwas used in the original presentation of the Richards growthequation, both equations gave good fits. The Richards equationis sometimes suitable for growth processes that may or may notbe close to exponential during initial growth. The new sigmoidis more suitable when initial growth is believed to be generallyclose to exponential, when estimates of maximum relative growthrate are required, or for generic growth simulations.Copyright1999 Annals of Botany Company Asymptote,Cucumis melo,curve-fitting, exponential growth, intrinsic rate of increase, logistic equation, maximum growth rate, model, non-linear least-squares regression, numerical algorithm, point of inflexion, relative growth rate, Richards growth equation, sigmoid growth curve.     

Legume Seeds: the Defences of Wild and Cultivated Species of Phaseolus Against Attack by Bruchid Beetles

A range of accessions (182) of wild, semi-cultivated and cultivatedPhaseolus were subjected to attack by two Old World bruchids,Callosobruchus maculatus and Caliosobruchus chinensis and twoNew World bruchids Zabrotes subfasciatus and Acanthoscelidesobtectus. Six different stages in the progression of the brochid-legumeinteraction, at which resistance may occur, are described andassessed. Resistance is shown by: no oviposition; disruptedembryo development; failure of larvae to penetrate the testa;death of larvae within the cotyledon; failure of pupation oradult emergence; reduced fitness of adults. The occurrence ofresistance at each of these stages is discussed in the contextof possible causal mechanisms. The patterns of resistance tothe two pairs of bruchids of different geographical origin isconsidered in relation to co-evolutionary processes Phaseolus, wild species, resistance, bruchids, Callosobruchus maculatus, Callosobruchus chinensis, Zabrotes subfaciatus, Acanthoscelides obtectus     

Protein Kinase C and Melanocyte Transformation

Melanoma cells which have been isolated from metastatic melanoma tissue are able to survive and proliferate in serum supplemented media. In contrast, normal human melanocytes require the presence of growth stimulators if they are to survive in culture. A tumor promotor, 12–0-tetradecanoyl-phorbol-13-acetate (TPA) and substances that increase intracellular levels of cyclic-adenosine-monophosphate (cAMP), such as cholera toxin or isobutylmethyl xanthine, have been widely used for this purpose. The phorbol diester receptor was shown in 1982 to be the phospholipid- and calcium-dependent enzyme protein kinase C (PKC). We therefore directed our studies to the role of PKC regulation in the growth of normal human melanocytes and their transformation. Our studies show that while melanoma cells are inhibited by TPA, the growth of normal melanocytes is stimulated in a dose-dependent manner. The inhibitor, 1-(5-isoquinolinesulfonyl)-2-methyl-piperizine dihydrochloride (H7), which has been found to be the most specific for PKC, had no effect on the growth of normal melanocytes, but inhibited the growth of melanoma cells in a dose-dependent manner. PKC was isolated from the membrane and cytosol of normal melanocytes and melanoma cells. The basal (resting) levels of PKC activity in normal melanocytes was low compared to that measured in melanoma cells, and after short-term (1 hour) treatment with TPA the PKC activity was greatest at the membrane, with the activity decreasing the cytosol. Upon prolonged (48 hours) treatment with TPA, this redistribution of activity continued in normal melanocytes and the total activity increased. In melanoma cells, however, the total PKC activity decreased, particularly in the membrane fraction. A difference in activity and distribution of the enzyme was also seen after short-term (1 hour) treatment with H7. There was very little effect seen on PKC in normal melanocytes; however, the effect on melanoma cells was similar to that seen after 48 hours of exposure to TPA with a decrease in total activity, particularly in the membrane fraction. These results indicate that the regulation of PKC, in particular its activation by TPA, is altered during the transformation of normal human melanocytes     

Taxonomy, evolution and domestication of Vicia in relation to aphid resistance

Thirty Vicia species and 28 V. faba cultivars were evaluated for Aphis fabae resistance by measuring rates of aphid population increase (r_m) on the host plants. A subset of these species (22) and cultivars (five) were evaluated for resistance to Acyrthosiphon pisum and Megoura viciae. For the same subset of 22 Vicia species and all three aphid species, positive correlations were observed between the concentration and numbers of leaf and stem non-protein amino acids and the level of aphid resistance. Correlations were also observed between trichome density, on some organs of the host, and both nymphal survival and development time. Aphid resistance, together with these possible physical and chemical resistance mechanisms, showed a pattern which was described in relation to the taxonomy of the genus Vicia and the degree of domestication of the host. The least advanced Vicia species were most resistant whilst the more specialised species and those most closely related to V. faba and V. faba itself were most susceptible. Within each taxonomic group (subgenus or section), the most domesticated species were least resistant. The merits of utilising the resistance found in some V. faba cultivars and in other wild Vicia species were considered.     

The Uptake of Growth Substances: I. FACTORS CONTROLLING THE UPTAKE OF PHENOXYACETIC ACIEDS BY LEMNA MINOR

An analysis has been made of the factors controlling the uptakeof 2:4-dichloro-phenoxyacetic acid (2:4-D) and related compoundsby Lemna minor, grown under controlled conditions. All compoundswere labelled with ¹⁴C in the carboxyl group and the ¹⁴C inthe plants, after liquid combustion, assayed as barium carbonate. With 2:4-D the rate of entry from concentrations of 8 to 32mg./l. is maximal in the first 20 minutes, then falls progressivelyuntil the rate is zero between 1 and 2 hours and in the thirdphase (up to 24 hours) there is a net loss from the plants dueto an outward movement of the compound back into the externalsolution. When the chlorine substitutions are in the 2:6-positionthe course of uptake is similar, save that loss to the solutiontakes place later. For the 2-chloro-substitution, after theinitial phase of uptake there is some loss but this is followedby a period of recovery and uptake again proceeds, but slowly.In contrast, the course of uptake over 24 hours of phenoxyaceticacid is normal, i.e. there is a steady accumulation. When plants are pretreated with labelled 2:4-D for 30–60minutes and transferred to water or culture solution then over90 per cent. of the ¹⁴C is found in the external medium after4:5 hours and this release cannot be accounted for in termsof exchange processes since the addition of unlabelled compoundto the medium retards the rate of loss. This loss is slowedbut not stopped at 1.25°C. and up to 22.5°C. the rangeof the Q₁₀ is 1.6–1.9. Uptake in the first 30 minutes is temperature sensitive between7.5 and 30°C. (Q₁₀ 2.3–2.6) and in general is positivelyand curvilinearly related to the external concentration. Pretreatmentwith unlabelled compound up to 2 hours progressively depressesthe subsequent initial uptake of labeled growth regulator. Itis concluded that initially the rate of entry greatly exceedsthe rate of loss but that with time the ratio steadily diminishesto less than unity. Initial uptake of 2:4-D is markedly dependent on the pH of thesolution and closely but not completely correlated with theexternal concentration of undissociated molecules. On the otherhand, the outward movement is relatively unaffected by the externalpH. Combinations of concentration and time of exposure which bringabout loss to the solution need not cause any permanent retardationof growth. In fact, exposure for 1 hour to 8 mg./l. significantlyaccelerated growth in the next 8 days. These results are discussed in relation to previous findingsand it is concluded that the pattern of uptake is determinedon the one hand by the chemical structure of the growth substanceand on the other by specific physiological differences at celllevel.