Intraspecific variation within Orosius argentatus Evans (Hemiptera: Cicadellidae): colour polymorphisms, morphometric analyses and host associations

Orosius argentatus shows extreme colour variation and is reputedly highly polyphagous, circumstances that both warrant confirmation that the taxon comprises only one species. Because the species transmits phytoplasma pathogens between plants, information on species status is relevant to epidemiological studies. Replicated field samples, taken in Mareeba, North Queensland, over 2 years indicated that O. argentatus is the most abundant leaf-hopper in stylo (Stylosanthes scabra) and is relatively host-specific on cultivated stylo, at least locally. A priori groupings of colour types were established for morphometric analyses of head, prothorax, tibia, wing and genitalia characters. No consistent morphological differences were detected across the colour types, and results from colour heritability trials, although limited, revealed that females could produce progeny that belong to multiple colour types. The results from this study suggest individuals that key out to the species O. argentatus, despite being polymorphic in colour, cannot be clearly separated on any morphological basis and therefore are likely to belong to a single, interbreeding population. The colour variation in adults is therefore a polymorphism

Two dicot-infecting mastreviruses (family Geminiviridae) occur in Pakistan

Most mastreviruses (family Geminiviridae) infect monocotyledonous hosts and are transmitted by leafhopper vectors. Only two mastrevirus species, Tobacco yellow dwarf virus from Australia and Bean yellow dwarf virus (BeYDV) from South Africa, have been identified whose members infect dicotyledonous plants. We have identified two distinct mastreviruses in chickpea stunt disease (CSD)-affected chickpea originating from Pakistan. The first is an isolate of BeYDV, previously only known to occur in South Africa. The second is a member of a new species with the BeYDV isolates as its closest relatives. A PCR-based diagnostic test was developed to differentiate these two virus species. Our results show that BeYDV plays no role in the etiology of CSD in Pakistan, while the second virus occurs widely in chickpea across Pakistan. A genomic clone of the new virus was infectious to chickpea (Cicer arietinum L.) and induced symptoms typical of CSD. We propose the use of the name Chickpea chlorotic dwarf Pakistan virus for the new species. The significance of these findings with respect to our understanding of the evolution, origin and geographic spread of dicot-infecting mastreviruses is discussed. © 2008 Springer-Verlag

Grapevine phytoplasmas

The diseases associated with phytoplasmas in grapevine are collectively called yellows and occur in the majority of grapevine-growing regions over the world. At first, a short overview of symptoms and damage associated with the presence of grapevine phytoplasmas is reported. Then, vectors, alternative host plants, and epidemiological cycles, where known, are discussed for the main grapevine yellows in the different continents. Moreover, potential insect vectors and host plants, together with molecular characterization of the associated phytoplasmas, are reported