Transgenic sorghum plants have been obtained after microprojectile bombardment of immature zygotic embryos of a drought-resistant sorghum cultivar, P898012. DNA delivery parameters were optimized based on transient expression of R and Cl maize anthocyanin regulatory elements in scuteflar cells. The protocol for obtaining transgenic plants consists of the delivery of the bar gene to immature zygotic embryos and the imposition of bialaphos selection pressure at various stages during culture, from induction of somatic embryogenesis to rooting of regenerated plantlets. One in about every 350 embryos produced embryogenic tissues that survived bialaphos treatment; six transformed callus lines were obtained from three of the eight sorghum cultivars used in this research.Transgenic (To) plants were obtained from cultivar P898012(two independent transformation events). (1). It is a primary staple in the semiarid tropics of Africa and Asia for over 300 million people. These are evidentiary statistics of the significance of this crop in these regions, which are predominated by subsistence agriculture. In the western hemisphere sorghum is used primarily as livestock feed (2). The development of hybrid varieties of sorghum in the 1950s contributed substantially to the increase in production in the United States. Presently, sorghum is third amongst cereals in U.S. production and is the preferred crop in areas oflow water availability because of its yield stability under drought conditions. Advances in biotechnology are now beginning to be used to augment traditional approaches for crop improvement. Restriction fragment length polymorphism (RFLP) linkage maps are being constructed that should greatly facilitate plant breeding efforts for marker-assisted backcross programs (3,4) and, in the near future, may be used to clone agriculturally important genes through the use of map-based cloning strategies (5). To this date, however, there are no programs in sorghum to access the pool of genes that are available as the result of genetic engineering research, because of the lack of a transformation system. Transformation of protoplasts byThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. electroporation (6) or cell suspensions by microprojectile bombardment (7) has resulted in stable expression of transferred genes; however, transgenic plants were not obtained.Microprojectile bombardment as a method to introduce DNA into cells circumvents two major constraints of cereal transformation. These are the lack of an available natural vector such as Agrobacterium tumefaciens and the difficulty to regenerate plants when protoplasts are used for transformation. Particle bombardment can target cells within tissues or organs that have high morphogenic potential. Immature or mature zygotic embryos (8-10), immature inflorescences (11,12), and shoot tips (13) of sorghum exhibit emb...

Perceived by Charles Darwin in many vegetable plants and rediscovered by George H Shull and Edward M East in maize, heterosis or hybrid vigour is one of the most widely utilized phenomena, not only in agriculture but also in animal breeding. Although, numerous studies have been carried out to understand its genetic and/or molecular basis in the past 100 years, our knowledge of the underlying molecular processes that results in hybrid vigour can best be defined as superficial. Even after century long deliberations, there is no consensus on the relative/individual contribution of the genetic/epigenetic factors in the manifestation of heterosis. However, with the recent advancements in functional genomics, transcriptomics, proteomics, and metabolomics-related technologies, the riddle of heterosis is being reinvestigated by adopting systems-level approaches to understand the underlying molecular mechanisms. A number of intriguing hypotheses are converging towards the idea of a cumulative positive effect of the differential expression of a variety of genes, on one or several yield-affecting metabolic pathways or overall energy-use efficiency, as the underlying mechanism for the manifestation of heterosis. Presented here is a brief account of clues gathered from various investigative approaches targeted towards better scientific understanding of this process.

The results presented in this work support the hypothesis that Agrobacterium-mediated transformation of sorghum is feasible, analogous to what has been demonstrated for other cereals such as rice, maize, barley and wheat. The four factors that we found most influenced transformation were: the sensitivity of immature sorghum embryos to Agrobacterium infection, the growth conditions of the donor plant, type of explant and co-cultivation medium. A major problem during the development of our protocol was a necrotic response which developed in explants after co-cultivation. Immature sorghum embryos proved to be very sensitive to Agrobacterium infection and we found that the level of embryo death after co-cultivation was the limiting step in improving transformation efficiency. The addition of coconut water to the co-cultivation medium, the use of vigorous and actively growing immature embryos and the removal of excess bacteria significantly improved the survival rate of sorghum embryos and was critical for successful transformation. Hygromycin phosphotransferase (hpt) proved to be a good selectable marker for sorghum. We also found that β-glucuronidase (GUS) activity was low in most of the transgenic plant tissues tested, although it was very high in immature inflorescences. Although promising, the overall transformation efficiency of the protocol is still low and further optimization will require particular attention to be given to the number of Agrobacterium in the inoculum and the selection of sorghum genotypes and explants less sensitive to Agrobacterium infection.

A survey for Peanut bud necrosis virus (PBNV), Watermelon bud necrosis virus (WBNV), Capsicum chlorosis virus (CaCV), and Iris yellow spot virus (IYSV) was conducted between 2002 and 2009 in the major vegetable-growing areas in India. PBNV was documented widely in tomato and chili peppers in 14 states representing southern, north-western, north-eastern, and central regions and WBNV was predominantly detected in watermelons and cucurbits in all except north-eastern regions. In addition, the expanded host range of PBNV to watermelons and other cucurbits and WBNV to tomato and chili peppers was observed leading to natural mixed infection of the two viruses. IYSV was found in onion in southern, central, and north-eastern regions and CaCV in tomato and chili peppers in northern and southern regions, respectively. Phylogenetic analysis of the nucleocapsid gene revealed segregation of field isolates of PBNV and WBNV into two distinct subclades, whereas isolates of CaCV and IYSV each clustered into a single clade. A proposal for establishing WBNV as a distinct tospovirus species is made based on the molecular characterization of small- (S) and medium- (M) RNA segments.

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