A comparison of life history traits of sexual and asexual strains of the parasitoid wasp,Lysiphlebus fabarum (Braconidae: Aphidiinae)

1. This study examined biological characteristics of sexual and asexual strains of the parasitoid wasp, Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae). 2. Strains were reared in different instar hosts (the black bean aphid, Aphis fabae Scopoli) under identical environmental conditions (21 °C, 65–75% RH, and LD 16:8 h). 3. Results showed that the second instar of the aphid is the most suitable growth stage for both strains, as the wasps that emerged from the second instar hosts were larger, more fecund, and had larger egg size. Trade‐offs between the fitness components of the parasitoid were clearer when the parasitoids were reared in suboptimal instars. 4. According to the results, sexual females emerged around 1 day earlier and lived around 0.5 day less than asexual females. Also, sexual females emerged with a lower initial egg load, although these wasps tend to have larger eggs than asexual females. Asexual females may enjoy greater longevity and higher developmental plasticity which suggests a higher degree of synchronization with pest population dynamism. 5. The results suggest that sexual wasps, in contrast to asexual wasps, invest more in egg size than in egg load. This study suggests strain‐specific adaptations of L. fabarum to different instars of the black bean aphid by which the allocation of nutritional resources to various functions differs between strains. 6. Furthermore, differences in life history traits between strains can greatly influence the population dynamics of each strain, and hence their effectiveness in suppressing pest populations.     

Latency of Botrytis cinerea Pers.: Fr. and Biochemical Studies During Growth and Ripening of Two Grape Berry Cultivars, Respectively Susceptible and Resistant to Grey Mould

Latency and development of Botrytis cinerea were assessed under field conditions and after artificial inoculation of two grape varieties, Gamay (susceptible) and Gamaret (resistant). When the percentage of latent Botrytis was the same for both varieties, severity of visible grey mould remained very low in Gamaret berries, while Gamay clusters were destroyed by the disease to a high percentage. Some biochemical parameters were measured in berries, such as constitutive and induced anti‐fungal compounds, polymeric proanthocyanidins and lipid peroxidation products as markers of senescence. Differences were observed in polymeric proanthocyanidins (PPRA) of Gamaret compared with those of Gamay. Concentration and mean degree of polymerization (mDP) of PPRA were always higher in the berries of the resistant variety. The inhibitory effect of Gamaret PPRA on enzyme activity remained until harvest whereas Gamay PPRA lost their inhibitory activity at the beginning of véraison. Based on these results, resistance to B. cinerea seems to be linked to the maintainance of the fungus in its latent form in berries, mainly due to the ability of Gamaret PPRA to inhibit macerating fungal enzyme activities.     

Isolation and identification of the principal siderophore of the plant pathogenic fungusBotrytis cinerea

Summary The plant pathogenic hyphomyceteBotrytis cinerea has been shown to produce several trihydroxamate siderophores under conditions of low-iron stress. The total siderophores amounted to approximately 30 mg/l culture filtrate after 5 days of incubation in an asparagine/salt/glucose medium. Thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) on a reversed phase indicated that ferrirhodin is the predominant siderophore of this fungus. Chemical characterization of the principal siderophore by fast-atom-bombardment (FAB) mass spectrometry, nuclear magnetic resonance (¹H-NMR,¹³C-NMR) and comparison with a reference revealed the identity with ferrirhodin. NMR studies performed on desferrirhodin (desferrirhodin) in dimethylsulfoxide and water revealed the existence of two conformers in D₂O resulting from acis-trans isomerization of the hydroxamic acid groups. Comparative iron-uptake studies showed the following order of uptake inB. cinerea: ferrichrysin (100%), ferrirubin (57%), ferrirhodin (45%), hexahydroferrirhodin (45%), coprogen 6%. Concentration-dependent uptake of ferrirhodin resulted in saturation kinetics only in the low concentration range of 0–30 M (K _m = 2.5 M,V _max = 80 pmol min^–1 mg(^–1). A non-saturable, linear uptake was observed in the high concentration range of 30–80 M. The low concentration range appears to be the physiologically significant range, where siderophore-mediated iron transport inB. cinerea occurs.     

Characterization of two class II chitinase genes from peanut and expression studies in transgenic tobacco plants

Two different genes encoding class II chitinases from peanut (Arachis hypogaea L. cv. NC4), A.h.Chi2;1 and A.h.Chi2;2, have been cloned. In peanut cell suspension cultures, mRNA levels of A.h.Chi2;2 increased after ethylene or salicylate treatment and in the presence of conidia from Botrytis cinerea. The second gene, A.h.Chi2;1, was only expressed after treatment with the fungal spores. Transgenic tobacco plants containing the complete peanut A.h.Chi2;1 gene exhibited essentially the same expression pattern in leaves as observed in peanut cell cultures. Expression characteristics of transgenic tobacco carrying a promoter-GUS fusion of A.h.Chi2;1 are described.     

The induction of normal and teratoid viviparae by a juvenile hormone and kinoprene in two species of aphids

ABSTRACT. Topical application of a juvenile hormone (JH1) and the JH mimic, kinoprene, to short-day, ovipara-producers of Megoura viciae usually leads to the production of oviparous/viviparous intermediate forms in the progeny sequence, in place of the expected sexual females (oviparae). The ovaries of these abnormal forms may contain embryos rather than the haploid yolky eggs of oviparae; 'mixed' ovaries containing both haploid eggs and embryos are also observed. The intermediates range in form from winged (alate) to wingless (apterous). The fully alate individuals usually contain only parthenogenetic ovaries but differ from the naturally occurring alate viviparae in that they are invariably infertile, have fewer antennal sense organs and often bear pheromone releasing glands on the metathoracic tibiae. The hormonally induced production of normal viviparae is difficult in this species but has been achieved by rearing short-day aphids on kinoprene-treated bean plants.
In Aphis fabae similar oviparous/viviparous teratomorphs have been reported and, in addition, single JH1 treatments were shown to induce normal viviparae at the end of the progeny sequence. Multiple applications, beginning prenatally and continuing through the postnatal development of the gynopara (winged ovipara-producer), showed that the numbers of viviparae born were related to the earliness of the treatment and to the dosage. The results are compared with the effect of a switch in photoperiod and discussed in relation to the endocrine control of aphid polymorphism.     

Tomato T2 ribonuclease LE is involved in the response to pathogens

T2 ribonucleases (RNases) are RNA-degrading enzymes that function in various cellular processes, mostly via RNA metabolism. T2 RNase-encoding genes have been identified in various organisms, from bacteria to mammals, and are most diverse in plants. The existence of T2 RNase genes in almost every organism suggests an important biological function that has been conserved through evolution. In plants, T2 RNases are suggested to be involved in phosphate scavenging and recycling, and are implicated in defence responses to pathogens. We investigated the function of the tomato T2 RNase LE, known to be induced by phosphate deficiency and wounding. The possible involvement of LE in pathogen responses was examined. Expression analysis showed LE induction during fungal infection and by stimuli known to be associated with pathogen inoculation, including oxalic acid and hydrogen peroxide. Analysis of LE-suppressed transgenic tomato lines revealed higher susceptibility to oxalic acid, a cell death-inducing factor, compared to the wild type. This elevated sensitivity of LE-suppressed lines was evidenced by visual signs of necrosis, and increased ion leakage and reactive oxygen species levels, indicating acceleration of cell death. Challenge of the LE-suppressed lines with the necrotrophic pathogen Botrytis cinerea resulted in accelerated development of disease symptoms compared to the wild type, associated with suppressed expression of pathogenesis-related marker genes. The results suggest a role for plant endogenous T2 RNases in antifungal activity.     

Yield loss of faba bean (Vicia faba) due to chocolate spot (Botrytis fabae) in sole and mixed cropping systems in Ethiopia

Two field experiments were conducted during 2004 and 2005 cropping seasons at Adet Agricultural Research Center, Ethiopia to assess yield losses caused by chocolate spot(Botrytis fabae) of faba bean in sole and mixed cropping systems using two cultivars. Cropping systems were sole faba bean (FB), faba bean mixed with field pea (FB: FP), barley (FB: BA) and maize (FB: MA). Mancozeb was sprayed at the rate of 2.5 kg a.i/ha at 7-, 14- and 21-day interval to generate different levels of chocolate spot disease in all the four cropping systems, and unsprayed control was also included. The treatments were arranged in a randomised complete block design (RCBD) with four replications. FB: MA mixed cropping significantly reduced disease severity and the area under disease progress curve (AUDPC) and increased faba bean grain yield. The highest faba bean grain yield among the three mixed croppings under different spray schedules was obtained from FB: MA mixed cropping in both 2004 and 2005 (2.56 and 3.74 t/ha, respectively) cropping seasons. There were highly significant yield differences (P < 0.05) among the spray intervals of mancozeb in both seasons. The highest grain yield (4.9 t/h) was recorded from the 7-day spray interval in 2005. The unsprayed faba bean had a lower grain yield (1.9 t/ha in 2004 and 2.3 t/ha in 2005) compared to the sprayed plots. The highest relative yield loss (67.5%) was calculated in 2005 from FB: FP mixed cropping in unsprayed plots. The relative yield losses in the unsprayed plots were in the range of 35.8–41.5% in 2004 and 52.6–67.5% in the 2005 cropping season. Severity and AUDPC were inversely correlated with faba bean grain yield. Significant differences were recorded in the 100-seed weight and days to maturity (DM). The unsprayed plots had shorter DM ranging from 126 to 128.5 day (except FB: MA mixed cropping) in 2004 and 122–123.9 days in 2005. In the sprayed plots DM was relatively longer than the unsprayed plots. A higher seed weight was recorded in the sole FB (56 g) and FB: MA (55 g) mixed cropping, and the lowest value of 100-seed weight was recorded from FB: FP (53 g) mixed cropping. The productivity of the mixed cropping evaluated by land equivalent ratio (LER) exceeded that of sole cropping. Faba bean grain yield was highly influenced by the severity of chocolate spot. The disease affects the DM, forcing early maturing of the plants.