Downy mildew resistance evaluation in 28 grapevine hybrids promising for breeding programs in Trentino region (Italy)

Downy mildew is a major grapevine disease caused by the biotrophic oomycete, Plasmopara viticola. Numerous disease resistance studies of diverse Vitis germplasm have been previously carried out to identify downy mildew resistance sources; however, ratings were mainly reported using leaf disc in vitro testing and foliage field assessment, or upon leaf and cluster field evaluations. In the current study, 28 grapevine hybrid cultivars were screened using leaf disc bioassay, for disease resistance characterization of both existing and wild-collected materials. 16 hybrids were identified as highly resistant or resistant, and will serve as relevant resistance donors in future pre-breeding and breeding programs. All grapevine hybrids were evaluated for foliar and cluster downy mildew resistance in an untreated field trial over three successive years. This study showed that the leaf disc bioassay provided some information on the resistance level of the genotypes under scrutiny, but it was a weak predictor of their resistance level under field conditions on leaves and even more on bunches. These findings are relevant to future applications in both traditional and marker-assisted breeding programs which promote sustainable viticulture.     

Synergy between grapevine vitiviruses and grapevine leafroll viruses

An interactive relationship between vitiviruses and grapevine leafroll viruses was characterized in grapevine. Grapevine viruses A and B (GVA and GVB) were found more frequently in the presence of co-infecting Grapevine leafroll associated viruses (GLRaV-1, ?2 or ?3) than in their absence. The titers of the vitiviruses in co-infection with leafroll viruses were found to be higher than were their titers in the absence of leafroll virus infection. The occurrence of vitivirus-associated stem-pitting symptoms was correlated with leafroll virus co-infection. Specific pairing associations on the species level were found between different viti- and leafroll virus species: GVB was associated preferentially with GLRaV-2; GVA was associated preferentially with GLRaV-1 and GLRaV-3. In contrast to the increase in vitivirus titer seen with leafroll virus co-infection, the incidence and titer of grapevine leafroll virus appeared to be unaltered by vitivirus co-infection. The potential for a synergistic enhancement of grapevine disease in co-infected vines is discussed.     

Effects of light quality on conidiophore formation of the melon powdery mildew pathogen <Emphasis Type="Italic">Podosphaera xanthii</Emphasis>

The lengths of conidiophores in fungal colonies of the melon powdery mildew pathogen Podosphaera xanthii Pollacci KMP-6 N cultured under greenhouse (natural) conditions differed markedly from those cultured in a growth chamber. We hypothesized that light wavelength was responsible for the differences in conidiophore length. In this study, we examined the effects of light-emitting diode (LED) irradiation (purple, blue, green, orange, and red light) and white light on colony development and conidiophore formation in KMP-6 N using a stereomicroscope and a high-fidelity digital microscope. Colonies on leaves were flat under greenhouse conditions and under red LED light irradiation but were stacked under growth chamber conditions and under purple, blue, green, and orange LED light irradiation. In addition, KMP-6 N formed catenated conidia comprising six conidia per conidiophore under greenhouse conditions and red light but more than seven conidia per conidiophore under growth chamber conditions and purple, blue, green, and orange light. Furthermore, almost none of the conidia on top of the conidiophores grown under blue light were fully constricted. Therefore, these fungi could not scatter their conidia and spread infection. This is the first report of the effects of LED lights on conidiophore formation in the melon powdery mildew fungus P. xanthii. The results provide insight into the mechanisms underlying the responses of conidiophores to light of specific wavelengths and conidial scatter from conidiophores of melon powdery mildew fungi.     

Effect of <Emphasis Type="Italic">Metarhizium guizhouense</Emphasis> infection on mating competition and mate choice of <Emphasis Type="Italic">Bactrocera latifrons</Emphasis> (Diptera: Tephritidae)

Metarhizium guizhouense PSUM02 treated males of Bactrocera latifrons were investigated for the mating competition among males and mating choice by female flies to develop an auto-dissemination for the control of B. latifrons. In the present study, on day 1–4 of experiment, M. guizhouense–treated male flies were equally competitive with the normal male flies as we did not observe any differences in mating by treated and normal male flies of B. latifrons. Further, mating competitiveness were found low in treated adult male B. latifrons than normal male B. latifrons from 5th days of treatment until death. Kaplan-Meier survival analysis of treated male flies gave average survival times (AST) of 4.3?±?0.1 days, while the healthy female and male flies in the same cage showed AST of 9.3?±?0.3 and 8.3?±?0.4 days, respectively. The AST of untreated flies in control experiment ranged from 14.2–14.5 days. In mating preference experiment, M. guizhouense–treated male flies were chosen by virgin female than gravid female flies for mating. The treated male flies caused mortality in both virgin and gravid female flies in the same cage with AST of 4.4?±?0.1, 5.6?±?0.1 and 7.4?±?0.2 days, respectively, while untreated flies showed AST ranged from 13.9–14.3 days in control. The treated male flies could transmit the fungus infection to both untreated female and male flies as well as in virgin and gravid female flies by mating and contact. Our experiments showed the potentiality of M. guizhouense PSUM02 in management of B. latifrons by auto-dissemination with treated male flies, which transmit the fungus to a healthy population to reduce insect pest infestations.     

Alien species of aphids (Hemiptera: Aphididae) found in Serbia,new to the Balkan Peninsula

New alien species of aphids (Illinoia liriodendri (Monell), Wahlgreniella nervata (Gillete), Takecallis arundicolens (Clarke) and Tinocallis takachihoensis Higuchi) have been found for the first time in Serbia. These records are new for the Balkan Peninsula. Data of Ericaphis scammelli (Mason), species recently mentioned in Serbia, are also presented in the text. The species have been found during the last five years at four sites (Belgrade, Zemun, Mladenovac and Bojnik) on five cultivated plants. Ericaphis scammelli is a pest of blueberry and a vector of Blueberry scorch virus. The other four develop colonies on decorative plants: I. liriodendri has been found on Liriodendron tulipifera, W. nervata on Rosa sp., T. arundicolens on Pseudosasa japonica and T. takachihoensis on Ulmus x hollandica. The origin of three of the species (E. scammelli, I. liriodendri and W. nervata) is North America and two (T. arundicolens and T. takachihoensis) have come from East Asia. Their morphology, biology and the damage they inflict are discussed here, as well as their potential economic and environmental threat. Only parthenogenetic viviparous females of all 5 species have been collected. Their biology has not been studied enough in Europe and needs further examination. Original drawings of all species are presented.     

Susceptibility of eight Algerian olive cultivars to <Emphasis Type="Italic">Bactrocera oleae</Emphasis> infestation – a pomological and nutritional quality perspective

The olive fruit fly, Bactrocera oleae (Rossi), is the major olive pest in the Mediterranean Basin, being responsible for high losses in olive production. The objective of this work was to study the influence of B. oleae infestation on the pomological parameters and nutritive value (lipids, proteins, carbohydrates and ash) of eight olive cultivars (Abani, Aellah, Blanquette de Guelma, Chemlal, Ferkani, Limli, Rougette de Mitidja and Souidi) from Algeria. The results displayed different degrees of susceptibility of the studied cultivars to this pest. Fruit size (weight) and the Fruit weight / stone weight ratio are significantly correlated with the attack. The statistical treatment of the results (PCA and HAC) highlighted different behaviors from the cultivars, concerning the attack. There are some cultivars more susceptible, being the nutritional value also affected. The lipid and protein contents were positively correlated with the attack and the carbohydrates negatively, suggesting a careful choice by the B. oleae. Ovipositional preference of olive fruit fly females and the success of larval development in different olive cultivars are crucial to establishing new approaches in Integrated Pest Management (IPM) against this pest.     

Feeding potential of <Emphasis Type="Italic">Cryptolaemus montrouzieri</Emphasis> against the mealybug <Emphasis Type="Italic">Phenacoccus solenopsis</Emphasis>

Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) is an exotic species native to the USA, damaging cotton and other plant families. The feeding potential of different development stages of Cryptolaemus montrouzieri Mulsant, a biological control agent against mealybugs, was investigated on different development stages of P. solenopsis. Fourth instar grubs and adults of C. montrouzieri were the most voracious feeders on different instars of mealybug. The number of 1^st instar nymphs of mealybug consumed by 1^st, 2^nd, 3^rd and 4^th instar larvae and adult beetles of C. montrouzieri was 15.56, 41.01, 125.38, 162.69 and 1613.81, respectively. The respective numbers of 2^nd and 3^rd instar nymphs of mealybug consumed were 11.15 and 1.80, 26.35 and 6.36, 73.66 and 13.32, 76.04 and 21.16, 787.95 and 114.66. The corresponding figures for adult female mealybugs were 0.94, 3.23, 8.47, 12.71 and 73.40, respectively. The results indicate that C. montrouzieri has the potential to be exploited as a biocontrol agent in North India; inoculative releases of 4^th instar larvae and adults may provide instant control of P. solenopsis. Field experiments should be conducted to determine the efficiency of the ladybird on this mealybug.     

Advanced lentil lines screened for resistance to <Emphasis Type="BoldItalic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="BoldItalic">lentis</Emphasis> under greenhouse and field conditions

Fusarium oxysporum f. sp. lentis is the most important pathogen of lentil plants, and most areas under lentil cultivation are reported to have a fusarium wilt disease background. The plants are infected in the seedling stage and later stages of their development. Fusarium wilt disease, which has appeared at high incidence rates during recent years, has caused sharp drops in the yield, especially in Moghan, in the northwest of Iran. Forty-five isolates of the pathogen were collected from different regions of the country with two isolates from ICARDA in the summer of 2008 and identified using Nelson’s key. The pathogenicity of the collected isolates was studied on a sensitive line (ILL 4605) under greenhouse conditions and significant differences in pathogenicity were found among them. The most pathogenic isolates from three provinces, East Azerbaijan (EA 30), Ardebil (Ar 3) and Khorasan (Kh 45), were selected and used in screening of 55 developed lines under greenhouse and field conditions. In the greenhouse, test plants were inoculated by immersing root tips in spore suspension and sowing seeds in pre-infested pot soil. Field tests were carried out in a naturally highly infested farm. At all stages, the plant response to the disease was based on the percentage of dead plants. Cluster analyses of the greenhouse and field data led to the selection of three lines (81S15, FLIP2007-42 L and FLIP2009-18 L) that were resistant under greenhouse and field conditions.     

Black nightshade (<Emphasis Type="Italic">Solanum nigrum</Emphasis>) emergence and development is affected by seed density and burial depth

Black nightshade (Solanum nigrum L.) is a troublesome weed worldwide, affecting a large number of crops. As weed development is affected by a variety of factors, advanced knowledge on the plant’s biological and ecological qualities can support favorable management strategies. Seed density is an ecological factor affecting emergence and early growth of many weed species. For that reason, the current study characterizes and quantifies the seed density impact on black nightshade seedling-emergence and early growth, and the interaction between seed density and burial depth on these growth parameters. Greenhouse studies conducted in 2005, 2006 and 2010 examined black nightshade seed densities of 1, 5, 10, 25 and 50 seeds per pot, buried at, 1, 2, 3, 4 and 5 cm. Impact of seed density on weed emergence and growth was characterized by number of emerged plants and leaves, followed by biomass measurements. Seed density had no impact on emergence at the tested burial depths. There was a strong logistic relationship (P < 0.001, and R ²  > 0.97) between time and emergence, and a strong linear relationship (P < 0.002 and R ²  > 0.86) between time and number of leaves produced in all depths and seed densities. A negative relationship was observed between seed density and plant development and growth rate. Results of this study extend the knowledge on black nightshade biology and support decision-making concerning rational weed management.     

Biological control of postharvest diseases of fruit

Postharvest decay in harvested fruit causes considerable economical losses. Fungicides are the primary means to control these losses. Public concern in food safety and environmental issues and the increase of pathogen resistant populations have enhanced the interest in developing alternative methods to fungicides to control postharvest fruit decay. During the last two decades a huge information and advances concerning the selection of antagonists, mode of action, different approaches to enhance biocontrol activity, formulation and production have been achieved, and some biofungicides are already in the market. It is likely that several more products will enter the market in the near future, as the result of the biological control research programs worldwide. Nonetheless, it is necessary to continue finding new potential microorganisms, better understanding the mode of action, and pathogen, antagonist and host interactions, to increase the potential of biocontrol helping to become a real alternative to synthetic postharvest fungicides. This article presents an overview of postharvest biological control approaches and explores new research possibilities to improve biocontrol activity.