RESUMO
Foliar diseases of maize cause severe economic losses in India and around the world. The increasing severity of maize leaf blight (MLB) over the past ten years necessitates rigorous identification and characterization of MLB-causing pathogens from different maize production zones to ensure the success of resistance breeding programs and the selection of appropriate disease management strategies. Although Bipolaris maydis is the primary pathogen causing MLB in India, other related genera such as Curvularia, Drechslera, and Exserohilum, and a taxonomically distant genus, Alternaria, are known to infect maize in other countries. To investigate the diversity of pathogens associated with MLB in India, 350 symptomatic leaf samples were collected between 2016 and 2018, from 20 MLB hotspots in nine states representing six ecological zones where maize is grown in India. Twenty representative fungal isolates causing MLB symptoms were characterized based on cultural, pathogenic, and molecular variability. Internal Transcribed Spacer (ITS) and glyceraldehyde-3-phosphate dehydrogenase (GADPH) gene sequence-based phylogenies showed that the majority of isolates (13/20) were Bipolaris maydis. There were also two Curvularia papendorfii isolates, and one isolate each of Bipolaris zeicola, Curvularia siddiquii, Curvularia sporobolicola, an unknown Curvularia sp. isolate phylogenetically close to C. graminicola, and an Alternaria sp. isolate. The B. zeicola, the aforesaid four Curvularia species, and the Alternaria sp. are the first reports of these fungi causing MLB in India. Pathogenicity tests on maize plants showed that isolates identified as Curvularia spp. and Alternaria sp. generally caused more severe MLB symptoms than those identified as Bipolaris spp. The diversity of fungi causing MLB, types of lesions, and variation in disease severity by different isolates described in this study provide baseline information for further investigations on MLB disease distribution, diagnosis, and management in India.
RESUMO
Maize is the principal grain crop of the world. It is also the crop where genetic engineering has been employed to a great extent to improve its various traits. The ability to transform maize is a crucial step for application of gene technology in maize improvement. There have been constant improvements in the maize transformation technologies over past several years. The choice of genotype and the explant material to initiate transformation and the different types of media to be used in various stages of tissue culture can have significant impact on the outcomes of the transformation efforts. Various methods of gene transfer, like the particle bombardment, protoplast transformation, Agrobacterium-mediated, in planta transformation, etc., have been tried and improved over years. Similarly, various selection systems for retrieval of the transformants have been attempted. The commercial success of maize transformation and transgenic development is unmatched by any other crop so far. Maize transformation with newer gene editing technologies is opening up a fresh dimension in transformation protocols and work-flows. This review captures the various past and recent facets in improvement in maize transformation technologies and attempts to present a comprehensive updated picture of the current state of the art in this area.