Effect of Shading on the Regrowth of Lolium perenne Swards in the Field

Simulated swards of Lolium perenne cv. S.23 growing in the fieldwere shaded at various stages of regrowth during August andSeptember, when insolation was most likely to be limiting. Reductionof ambient illumination to 50 per cent for periods up to 24days had little effect on the current production of herbage(mainly leaf blade), which progressed at the expense of rootand stubble growth. After defoliation, however, previously shadedswards transferred to full light regrew relatively slowly. Leafarea and leaf extension were increased by shading, but leafappearance rates were only slightly affected. Shading decreasedtiller densi ties, and hence stubble yields, but did not affectmean tiller weights. The dangers of relating herbage yield tocurrent rates of insolation and photosynthesis, and the relevanceof these findings to other grass varieties are discussed.     

Wise flies: a pre‐dispersal seed predator prefers hermaphrodites over females in the gynodioecious Polemonium foliosissimum

1. Oviposition choices can profoundly affect offspring performance. Oviposition decisions of the dipteran pre‐dispersal seed predator, Hylemya sp. (Diptera: Anthomyiidae), when choosing among sex morphs of their host‐plant—Polemonium foliosissimum Hook—were evaluated. Polemonium foliosissimum is gynodioecious, with female and hermaphrodite sex morphs that differ in flower size. 2. It was asked: Do female flies preferentially oviposit on hermaphrodite plants and, if so, are oviposition choices correlated with flower size? Is larval survivorship higher on hermaphrodite plants and, if so, is larval success correlated with flower size? Can the differences in oviposition and/or larval success be explained by slight differences in flowering phenology between the sexes? 3. Hermaphrodite flowers received 45% more Hylemya eggs than females. Although hermaphrodites had larger petals and sepals than females, egg loads were not correlated with petal or sepal size. Larval survival was 30% greater on hermaphrodites than females and higher on plants with larger sepals. However, the difference in sepal area between genders did not fully explain larval survival differences. Egg numbers declined over weeks, but differences in egg loads between the sex morphs were not attributable to a slight phenological delay of females. Larval survival declined over the season; however, larval survival differences between sex morphs were consistent. 4. Hylemya preferentially oviposited on hermaphrodites where their larvae had a significantly greater survival rate compared with females. The present results add to the knowledge that intra‐specific choices have consequences for phytophagous insects and that the relationship between antagonists and their gynodioecious host plants is complex.     

Can we bring Madagascar's critically endangered palms back from the brink? Genetics,ecology and conservation of the critically endangered palm Beccariophoenix madagascariensis

Madagascar has a highly distinctive flora and is one of the world biodiversity hot spots. There are more than 170 species of palms, the majority of which are vulnerable, endangered or critically endangered endemics. Palms are utilized for many human uses, many of which lead to plant death or seed harvesting. Combined with reduced populations resulting from extensive forest clearing, those species which are harvested from the wild are under additional threat of extinction. Species recovery programmes have the potential to save some of the most iconic species before it is too late. This study documented the current known populations of the critically endangered palm Beccariophoenix madagascariensis, a species utilized for both local and international purposes. The study specifically investigated the genetic diversity and inbreeding within populations and the potential differentiation between populations and with the newly described species B. alfredii . We found that despite critically small population sizes there was considerable genetic diversity within populations. We also found that ecologically and or geographically distinct populations were genetically distinct. Populations within 3 km of each other exhibited considerable gene flow, probably owing to seed dispersal. The populations were inbred but reproductive viability had been maintained. Conservation and recovery options are discussed. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 589–608.     

A metabolomic study in oats (Avena sativa) highlights a drought tolerance mechanism based upon salicylate signalling pathways and the modulation of carbon,antioxidant and photo‐oxidative metabolism

Although a wealth of information is available on the induction of one or several drought‐related responses in different species, little is known of how their timing, modulation and crucially integration influence drought tolerance. Based upon metabolomic changes in oat (Avena sativa L.), we have defined key processes involved in drought tolerance. During a time course of increasing water deficit, metabolites from leaf samples were profiled using direct infusion–electrospray mass spectroscopy (DI‐ESI‐MS) and high‐performance liquid chromatography (HPLC) ESI‐MS/MS and analysed using principal component analysis (PCA) and discriminant function analysis (DFA). The involvement of metabolite pathways was confirmed through targeted assays of key metabolites and physiological experiments. We demonstrate an early accumulation of salicylic acid (SA) influencing stomatal opening, photorespiration and antioxidant defences before any change in the relative water content. These changes are likely to maintain plant water status, with any photoinhibitory effect being counteracted by an efficient antioxidant capacity, thereby representing an integrated mechanism of drought tolerance in oats. We also discuss these changes in relation to those engaged at later points, consequence of the different water status in susceptible and resistant genotypes.     

Aphid density and community composition differentially affect apterous aphid movement and plant virus transmission

1. Although many vector‐borne pathogens are transmitted by an array of vector species, most studies do not account for the potential effects of species interactions. 2. By manipulating conspecific and heterospecific vector density in small experimental mesocosms, this study disentangled the impact of vector density and community composition on vector movement and plant virus transmission in the potato virus Y system. 3. The following predictions were tested: (i) increasing aphid density will increase aphid movement and virus transmission; (ii) adding low‐efficiency vectors and thereby decreasing the average transmission efficiency of the vector assemblage will decrease virus transmission; and (iii) aphid movement and the average vector transmission efficiency will mediate the effect of aphid density and community composition on virus transmission. 4. It was found that initial density positively affected aphid movement, but had no effect on virus transmission, and that conspecific density was more important than heterospecific density. Conversely, community composition affected both aphid movement and virus transmission. These effects were driven by species identity, rather than species richness per se. 5. The results of this study emphasise the importance of accounting for vector behaviour, and analysing it within the context of the wider vector assemblage.