A glasshouse test to assess the sensitivity of potato cultivars to tobacco rattle virus

The sensitivity to tobacco rattle virus of nine potato cultivars and 24 potato clones from the potato breeding programme at SCRI was assessed in a glasshouse pot test and in field trials for two consecutive years. The results and analyses presented indicate that the pot test gives an accurate and reliable estimate of sensitivity to tobacco rattle virus. Methods of assessing severity of expression of disease symptoms were examined. The advantages of such a glasshouse pot test and its application are discussed.     

SOME EFFECTS OF FEEDING BY LYGUS VOSSELERI POPP. (HETEROPTERA, MIRIDAE) ON THE STEM APEX OF THE COTTON PLANT

The effects of damage to the main stem apex of the cotton plant caused by feeding of Lygus vosseleri Popp. have been investigated using a cell counting technique. It was found that mechanical damage of the tip due either to feeding of Lygus or to pricking with a glass needle caused an increase in cell division and maturation rates in the stem apex. The significance of this in relation to the possible effects of Lygus damage on plant height is discussed.     

The elimination of clover diseases by shoot tip culture

Shoot tip culture was used to eliminate white clover mosaic virus (WCMV) and red clover necrotic mosaic virus (RCNMV) from red clover, and clover phyllody disease (CP) and clover red leaf disease (CRL) from white clover. Shoot tips up to 2.4 mm (in some cases 3 mm) could regenerate plants free from the pathogens, but the efficiency of elimination, at least for WCMV and CRL, tended to decrease with increasing shoot tip size. The efficiency of plant regeneration from shoot tips generally improved with increasing tip size.     

Growth-Regulating Substances and the Growth of Tiller Buds in Barley; Effects of Cytokinins

An hypothesis was set up from which it was predicted that applicationof cytokinin to barley seedlings grown without mineral nutrientswould lead to rapid growth of the coleoptile and first leaftiller buds. Application of cytokinins to the leaves was ineffective,but supplying a number of known cytokinins by steeping the rootsof 4 d old seedlings in solution for 4 h led to significantgrowth of the coleoptile bud. Adenine and cytokinin analogueshad no effect. Supplying cytokinins through the roots also furtherenhanced the growth of buds of plants given mineral nutrients.Cytokinin treatment reduced root dry matter, with small reductionsin mean axis length and number of lateral roots. For plantsnot given mineral nutrients reduction in root weight was compensatedby an increase in weight of the aerial parts; however, for plantssupplied with mineral nutrients this was not so and the lowerroot weight resulted in a smaller total plant dry weight. An interpretation of tiller bud growth in terms of control byinteracting effects of mineral nutrition, assimilate supply,and cytokinin availability is proposed.     

Effect of Exposure Period and Algal Concentration on the Frequency of Infection of Aposymbiotic Ciliates by Symbiotic Algae from Paramecium bursaria

The effect of exposure period and concentration of algae on the frequency of infection of aposymbiotic ciliates by algae obtained from the same clone of Paramecium bursaria syngen 2, was studied. The frequency of infection was roughly proportional to the algal concentration and to the exposure time of ciliates to algae. The relationship of algal concentration to infection frequency closely fitted the Poisson distribution curve for N = 1, suggesting that the minimum number of algae required to infect a single ciliate is 1. However, the data also strongly suggested that the average number of algae required to initiate infection of an average ciliate was ? 1,000. Three possible resolutions of this situation are: (a) the selection by the ciliate of a rare infective variant from a heterogeneous population: (b) the rare escape of an alga from digestion by the ciliate; and (c) the requirement for a large number of algae-ciliate contacts to induce susceptibility in the ciliate. Splitting the exposure of ciliates to algae into 2 periods of 0.5 h, separated by 5 h in the absence of algae, produced a much higher frequency of infection than a single l-h exposure, supporting the suggestion that the large number of algae is required to induce susceptibility in the ciliate which can then be infected by as few as a single algal cell.     

Molluscan Metamorphosis: A Study in Tissue Transformation

Metamorphosis of the pelagic larvae of benthic marine invertebratesis often a cataclysmic event in which a rapid loss of organsspecialized for larval life occurs simultaneously with the renewalor increased rate of development of potential adult organs.In the nudibranch gastropod Phestilla sibogae this change involvesloss of the velum, shell, operculum, larval kidney, some retractormuscles, and some of the pedal mucous glands. Exit from thelarval shell at metamorphosis is rapid and is correlated withthe spread of epidermis from the larval foot over the visceralmass as the visceral mass emerges from the shell aperature.This spreading of epipodial epidermis to cover the entire bodyhas not been previously reported for other nudibranchs. Neithercell proliferation nor active cell motility are responsiblefor this epidermal migration. Rather it appears that the actionof larval muscles pulls the visceral organs out of the shelland simultaneously causes the epipodial epidermis to cover thevisceral mass. This epidermis becomes the definitive adult epidermis.     

Genetic diversity in Atlantic Forest trees: fragmentation effects on Astronium graveolens (Anacardiaceae) and Metrodorea nigra (Rutaceae), species with distinct seed dispersal strategies

We explore the genetic structure and variability in autochorous Metrodorea nigra (Rutaceae) and anemochorous Astronium graveolens (Anacardiaceae), two species affected by deforestation in the Atlantic Forest of Brazil. The effects of deforestation and the depletion of the habitat within the remaining patches of forest are evaluated by comparing the variability between saplings and adults of each of these two species. The results indicate that the depletion of forest land and the deteriorating condition of the remaining fragments of forest may reduce the level of endogamous breeding in wind‐dispersed species. In autochorous species, the fragmentation of forest land has less notable effects on genetic attributes, but pollen flow could be decreased as a result of the reduced number of insects flying between the forest remnants. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 326–336.     

Ranking Alaska Moose Nutrition: Signals to Begin Liberal Antlerless Harvests

Abstract: We focused on describing low nutritional status in an increasing moose (Alces alces gigas) population with reduced predation in Game Management Unit (GMU) 20A near Fairbanks, Alaska, USA. A skeptical public disallowed liberal antlerless harvests of this moose population until we provided convincing data on low nutritional status. We ranked nutritional status in 15 Alaska moose populations (in boreal forests and coastal tundra) based on multiyear twinning rates. Data on age-of-first-reproduction and parturition rates provided a ranking consistent with twinning rates in the 6 areas where comparative data were available. Also, short-yearling mass provided a ranking consistent with twinning rates in 5 of the 6 areas where data were available. Data from 5 areas implied an inverse relationship between twinning rate and browse removal rate. Only in GMU 20A did nutritional indices reach low levels where justification for halting population growth was apparent, which supports prior findings that nutrition is a minor factor limiting most Alaska moose populations compared to predation. With predator reductions, the GMU 20A moose population increased from 1976 until liberal antlerless harvests in 2004. During 1997-2005, GMU 20A moose exhibited the lowest nutritional status reported to date for wild, noninsular, North American populations, including 1) delayed reproduction until moose reached 36 months of age and the lowest parturition rate among 36-month-old moose (29%, n = 147); 2) the lowest average multiyear twinning rates from late-May aerial surveys (x = 7%, SE = 0.9%, n = 9 yr, range = 3-10%) and delayed twinning until moose reached 60 months of age; 3) the lowest average mass of female short-yearlings in Alaska (x̄ = 155 ± 1.6 [SE] kg in the Tanana Flats subpopulation, up to 58 kg below average masses found elsewhere); and 4) high removal (42%) of current annual browse biomass compared to 9-26% elsewhere in boreal forests. When average multiyear twinning rates in GMU 20A (sampled during 1960-2005) declined to <10% in the mid- to late 1990s, we began encouraging liberal antlerless harvests, but only conservative annual harvests of 61-76 antlerless moose were achieved during 1996-2001. Using data in the context of our broader ranking system, we convinced skeptical citizen advisory committees to allow liberal antlerless harvests of 600-690 moose in 2004 and 2005, with the objective of halting population growth of the 16,000-17,000 moose; total harvests were 7-8% of total prehunt numbers. The resulting liberal antlerless harvests served to protect the moose population's health and habitat and to fulfill a mandate for elevated yield. Liberal antlerless harvests appear justified to halt population growth when multiyear twinning rates average ≤10% and ≥1 of the following signals substantiate low nutritional status: <50% of 36-month-old moose are parturient, average multiyear short-yearling mass is <175 kg, or >35% of annual browse biomass is removed by moose.     

Winter Survival of Wild Turkey Females in Central Minnesota

Abstract: There is interest in expanding eastern wild turkey (Meleagris gallopavo silvestris) populations north of their current range. We hypothesized that winter survival and food availability are primary determinants in setting the northern extent of wild turkey distribution. To test our hypothesis, we translocated wild turkey females north of their present range into central Minnesota, USA, and compared survival in areas with supplemental food in the form of corn food plots versus areas with no supplemental food. During 2 winters with below-average snow, winter survival was higher for females with supplemental food. In one winter with above-average snow depths, survival was extremely low even with supplemental food. Supplemental food could augment survival during mild winters if wildlife managers arrange with farmers to, annually, retain standing corn near roosting habitat, but food plots may only partially offset effects of deep snow. Managers should critically evaluate northern habitats, long-term costs of sustained feeding, and potential outcomes of concentrating animals and introducing wild animals into new ecosystems. Winter survival may delimit the northern range of wild turkeys, though annual survival rates may also be important and need further research.