Complete genome sequences of two novel begomoviruses infecting common bean in Venezuela.

The complete genome sequences of isolates of two new bipartite begomoviruses (genus Begomovirus, family Geminiviridae) found infecting common bean in Venezuela are provided. The names proposed for each of these viruses are "bean yellow chlorosis virus" (BYCV) and "bean white chlorosis mosaic virus" (BWCMV). Phylogenetic analysis showed that they segregated in two distinct clades of New World begomoviruses. This is the first report of begomoviruses infecting common bean in Venezuela.

Diverse population of a new bipartite begomovirus infecting tomato crops in Uruguay.

Several isolates of a novel begomovirus were characterized from tomato samples collected in northern Uruguay exhibiting disease symptoms associated with Bemisia tabaci infestations. Analysis of full-length sequences of DNA-A and DNA-B components revealed the presence of a new begomovirus with the typical genome organization of a New World begomovirus, for which the name tomato rugose yellow leaf curl virus (ToRYLCV) is proposed. A high degree of nucleotide sequence diversity was found for both components, suggesting the presence of a diverse virus population. Recombination analysis suggested relationships of ToRYLCV to begomoviruses reported from the New World. Although common regions from DNA-As and DNA-Bs were surprisingly divergent for a cognate pair, a DNA-A and DNA-B pair cloned from one sample were infectious in Nicotiana benthamiana and tomato and reproduced symptoms observed in field-infected tomato plants, suggesting that ToRYLCV is the causal agent of the disease observed. This is the first report of a begomovirus infecting tomato crops in Uruguay and of the presence of begomovirus in this country.

Sweepoviruses cause disease in sweet potato and related Ipomoea spp.: fulfilling Koch's postulates for a divergent group in the genus begomovirus.

Sweet potato (Ipomoea batatas) and related Ipomoea species are frequently infected by monopartite begomoviruses (genus Begomovirus, family Geminiviridae), known as sweepoviruses. Unlike other geminiviruses, the genomes of sweepoviruses have been recalcitrant to rendering infectious clones to date. Thus, Koch's postulates have not been fullfilled for any of the viruses in this group. Three novel species of sweepoviruses have recently been described in Spain: Sweet potato leaf curl Lanzarote virus (SPLCLaV), Sweet potato leaf curl Spain virus (SPLCSV) and Sweet potato leaf curl Canary virus (SPLCCaV). Here we describe the generation of the first infectious clone of an isolate (ES:MAL:BG30:06) of SPLCLaV. The clone consisted of a complete tandem dimeric viral genome in a binary vector. Successful infection by agroinoculation of several species of Ipomoea (including sweet potato) and Nicotiana benthamiana was confirmed by PCR, dot blot and Southern blot hybridization. Symptoms observed in infected plants consisted of leaf curl, yellowing, growth reduction and vein yellowing. Two varieties of sweet potato, 'Beauregard' and 'Promesa', were infected by agroinoculation, and symptoms of leaf curl and interveinal loss of purple colouration were observed, respectively. The virus present in agroinfected plants was readily transmitted by the whitefly Bemisia tabaci to I. setosa plants. The progeny virus population present in agroinfected I. setosa and sweet potato plants was isolated and identity to the original isolate was confirmed by sequencing. Therefore, Koch's postulates were fulfilled for the first time for a sweepovirus.

Water relations in culture media influence maturation of avocado somatic embryos.

Application of transformation and other biotechnological tools in avocado (Persea americana Mill.) is hampered by difficulties in obtaining mature somatic embryos capable of germination at an acceptable rate. In this work, we evaluated the effect of different compounds affecting medium water relations on maturation of avocado somatic embryos. Culture media were characterized with respect to gel strength, water potential and osmotic potential. Improved production of mature somatic embryos was achieved with gelling agent concentrations higher than those considered standard. The osmotic agents such as sorbitol and PEG did not have positive effects on embryo maturation. The number of w-o mature somatic embryos per culture was positively correlated with medium gel strength. Gel strength was significantly affected by gelling agent type as well as by gelling agent and PEG concentration. Medium water potential was influenced by sorbitol concentration; incorporation of PEG to a culture medium did not affect medium water potential. The highest maturation results were achieved on a medium gelled with 10 gl(-1) agar. Moreover, these somatic embryos had improved germination rates. These results corroborate the role of water restriction as a key factor controlling maturation of somatic embryos.